Showing 1–50 of 56 results for author: Allen, M

VORA: Rapid Association of Earthquake Phases from Local to Global

Authors: Junhao Song, Weiqiang Zhu, Haoyu Wang, Utpal Kumar, Taka'aki Taira, Richard M Allen

Abstract: Earthquake phase association, which groups seismic phase arrivals into common origins, is a key step towards more complete and reliable seismicity catalogs. It has become a challenging task because of the massive phase datasets produced from dense seismic networks and advanced phase picking methods. Here we present VORA (Voronoi tessellation- and Origin-time-based Rapid Associator), an efficient a… ▽ More Earthquake phase association, which groups seismic phase arrivals into common origins, is a key step towards more complete and reliable seismicity catalogs. It has become a challenging task because of the massive phase datasets produced from dense seismic networks and advanced phase picking methods. Here we present VORA (Voronoi tessellation- and Origin-time-based Rapid Associator), an efficient and scalable earthquake phase associator that treats association as an unsupervised spatio-temporal clustering problem. Specifically, VORA depends on two primary constraints: the estimated earthquake origin time (temporal) and seismic station adjacency (spatial). Recent advances in deep learning models have enabled detection of S- and P-phases with similar effectiveness, making it straightforward to estimate corresponding earthquake origin times from candidate phase pairs given a prescribed range of velocity ratios or directly from raw waveforms. We then leverage the Voronoi diagram to define each station's neighbors, cluster the origin times across neighboring stations, and apply an optional sub-clustering step to separate overlapping events. Benchmarks on synthetic and real datasets show that VORA achieves the fastest runtime and maintains robust performance (high recall and precision) even under intense seismicity. Applying it to a two-week global-scale pick dataset covering the 2019 Ridgecrest earthquake sequence further demonstrates that the same framework scales from local networks to a global station set. VORA requires no training and generalizes across local-to-global regions, varying velocity models, and evolving network geometries, helping to meet the growing demands of expanding seismic networks and the increasing volume of automated phase picks. △ Less

Submitted 11 July, 2026; originally announced July 2026.

Performance and User Response of Android's Smartphone-Based Alerts in the 2025 Marmara Ereglisi Earthquake

Authors: S. Mostafa Mousavi, Patrick Robertson, Richard M. Allen, Alexei Barski, Robert Bosch, Nivetha Thiruverahan, Youngmin Cho, Tajinder Gadh, Steve Malkos, Boone Spooner, Greg Wimpey, Edward Shi, Marc Stogaitis

Abstract: This study presents a comprehensive evaluation of Googles Android Earthquake Alert (AEA) system during the Mw 6.2 Marmara Ereglisi, Turkiye earthquake. AEA detected the event 5.31 seconds after its initiation, alerting over 16 million users. Warning times for weak shaking (MMI III) reached up to 150 seconds, with a median of 56 seconds. While near-source warning windows were shorter, the system ac… ▽ More This study presents a comprehensive evaluation of Googles Android Earthquake Alert (AEA) system during the Mw 6.2 Marmara Ereglisi, Turkiye earthquake. AEA detected the event 5.31 seconds after its initiation, alerting over 16 million users. Warning times for weak shaking (MMI III) reached up to 150 seconds, with a median of 56 seconds. While near-source warning windows were shorter, the system achieved 90% true positives and 99% precision overall. The high density of the phone network enabled faster detection than traditional stations, even for this offshore epicenter. Feedback data shows AEA recipients were highly likely to take protective actions, such as drop, cover, and hold on, or warn others. Timely alerts substantially increased user engagement, perceived usefulness, and future trust. These results highlight how crowd-sourced technology and behavioral insights can effectively enhance seismic resilience on a massive scale. △ Less

Submitted 9 July, 2026; originally announced July 2026.

The performance of the TA$\times$4 surface detector array: 4.3 years of the first-half expansion

Authors: Telescope Array Collaboration, R. U. Abbasi, T. Abu-Zayyad, M. Allen, J. W. Belz, D. R. Bergman, F. Bradfield, I. Buckland, W. Campbell, B. G. Cheon, K. Endo, A. Fedynitch, T. Fujii, K. Fujisue, K. Fujita, M. Fukushima, G. Furlich, A. Gálvez Ureña, Z. Gerber, N. Globus, T. Hanaoka, W. Hanlon, N. Hayashida, H. He, K. Hibino , et al. (105 additional authors not shown)

Abstract: The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arriva… ▽ More The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$\times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$\times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90\% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$~sr~yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array. △ Less

Submitted 26 June, 2026; originally announced June 2026.

Comments: 24 pages, 9 figures, submitted to Nuclear Inst. and Methods in Physics Research, A

Leveraging LLMs and Social Media to Understand User Perception of Smartphone-Based Earthquake Early Warnings

Authors: Hanjing Wang, S. Mostafa Mousavi, Patrick Robertson, Richard M. Allen, Alexie Barski, Robert Bosch, Nivetha Thiruverahan, Youngmin Cho, Tajinder Gadh, Steve Malkos, Boone Spooner, Greg Wimpey, Marc Stogaitis

Abstract: Android's Earthquake Alert (AEA) system provided timely early warnings to millions during the Mw 6.2 Marmara Ereglisi, Türkiye earthquake on April 23, 2025. This event, the largest in the region in 25 years, served as a critical real-world test for smartphone-based Earthquake Early Warning (EEW) systems. The AEA system successfully delivered alerts to users with high precision, offering over a min… ▽ More Android's Earthquake Alert (AEA) system provided timely early warnings to millions during the Mw 6.2 Marmara Ereglisi, Türkiye earthquake on April 23, 2025. This event, the largest in the region in 25 years, served as a critical real-world test for smartphone-based Earthquake Early Warning (EEW) systems. The AEA system successfully delivered alerts to users with high precision, offering over a minute of warning before the strongest shaking reached urban areas. This study leveraged Large Language Models (LLMs) to analyze more than 500 public social media posts from the X platform, extracting 42 distinct attributes related to user experience and behavior. Statistical analyses revealed significant relationships, notably a strong correlation between user trust and alert timeliness. Our results indicate a distinction between engineering and the user-centric definition of system accuracy. We found that timeliness is accuracy in the user's mind. Overall, this study provides actionable insights for optimizing alert design, public education campaigns, and future behavioral research to improve the effectiveness of such systems in seismically active regions. △ Less

Submitted 24 March, 2026; originally announced March 2026.

Freeform Spectrally Stable Topological Photonic Vortex Resonators

Authors: Yuma Kawaguchi, Daria Smirnova, Filipp Komissarenko, Daria Kafeeva, Svetlana Kiriushechkina, Jeffery Allen, Monica Allen, Andrea Alù, Alexander Khanikaev

Abstract: Topological concepts have been at the forefront of materials research in recent years, driving a revolution in our understanding of the response of quantum materials and enabling new ways to manipulate light and sound in topological metamaterials. Topological defects and topological boundaries of different dimensions have driven a paradigm shift in photonics, where topological photonic crystals an… ▽ More Topological concepts have been at the forefront of materials research in recent years, driving a revolution in our understanding of the response of quantum materials and enabling new ways to manipulate light and sound in topological metamaterials. Topological defects and topological boundaries of different dimensions have driven a paradigm shift in photonics, where topological photonic crystals and metamaterials can be engineered to create one-way flow of energy robust to defects or to control such flows with synthetic degrees of freedom along topological domain walls. More recently, topological point singularities encoded into photonic structures have been shown to enable confinement of optical modes with the topologically nontrivial nature of the cavity imprinted into the vorticity of optical far fields. Here we demonstrate that the two latter concepts - domain wall and point singularities - can be unified into an even more powerful tool to enable arbitrarily shaped resonant cavities of any dimension supporting spectrally stable zero-energy modes. We experimentally confirm that such modes, whose existence is guaranteed by topological principles, allow an unprecedented degree of control over the optical field, which appears to have no phase modulation across space, can have any desirable radiation pattern, and enables spectral stability regardless of shape or length. △ Less

Submitted 22 March, 2026; originally announced March 2026.

Comments: 13 pages, 5 figures

Long-term marine acoustic and seismic monitoring using distributed acoustic sensing and deep learning

Authors: Chun Zhang, Weiqiang Zhu, Barbara A. Romanowicz, Richard M Allen, Kenichi Soga, Yuxin Wu

Abstract: The ocean remains one of the least instrumented parts of Earth, and many geophysical, biological, and anthropogenic signals go undetected for lack of instrumentation. Distributed acoustic sensing (DAS) can transform submarine fiber-optic cables into dense seafloor sensor arrays, but extracting diverse signals from massive DAS recordings remains challenging. Here we present DASNet, a deep learning… ▽ More The ocean remains one of the least instrumented parts of Earth, and many geophysical, biological, and anthropogenic signals go undetected for lack of instrumentation. Distributed acoustic sensing (DAS) can transform submarine fiber-optic cables into dense seafloor sensor arrays, but extracting diverse signals from massive DAS recordings remains challenging. Here we present DASNet, a deep learning framework that detects, classifies, and picks arrival times of diverse marine signals in continuous DAS data. Applied to nearly four years of Seafloor Fiber-Optic Array in Monterey Bay recordings, DASNet identifies more than 620,000 events. These detections reveal local earthquakes; distant earthquake- and volcanic-eruption-generated T-waves from the southwestern Pacific and mid-ocean ridge systems; more than 510,000 blue and fin whale calls with seasonal and interannual variability consistent with hydrophone records; and vessel traffic near the cable. Together, these results show that submarine fiber-optic cables combined with deep learning enable scalable, high-resolution ocean monitoring. △ Less

Submitted 3 July, 2026; v1 submitted 16 March, 2026; originally announced March 2026.

Electrically driven plasmon-polaritonic bistability in Dirac electron tunneling transistors

Authors: Shuai Zhang, Yang Xu, Junhe Zhang, Dihao Sun, Yinan Dong, Matthew Fu, Takashi Taniguchi, Kenji Watanabe, Cory R. Dean, Monica Allen, Jeffery Allen, F. Javier Garcia de Abajo, Antti J. Moilanen, Lukas Novotny, D. N. Basov

Abstract: Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at… ▽ More Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in graphene/hexagonal-boron-nitride/graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical memory, sensing, and optoelectronic switching. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Comments: 48 pages, 17 figues

Journal ref: hys. Rev. Lett. 136, 136904 (2026)

AI4X Roadmap: Artificial Intelligence for the advancement of scientific pursuit and its future directions

Authors: Stephen G. Dale, Nikita Kazeev, Alastair J. A. Price, Victor Posligua, Stephan Roche, O. Anatole von Lilienfeld, Konstantin S. Novoselov, Xavier Bresson, Gianmarco Mengaldo, Xudong Chen, Terence J. O'Kane, Emily R. Lines, Matthew J. Allen, Amandine E. Debus, Clayton Miller, Jiayu Zhou, Hiroko H. Dodge, David Rousseau, Andrey Ustyuzhanin, Ziyun Yan, Mario Lanza, Fabio Sciarrino, Ryo Yoshida, Zhidong Leong, Teck Leong Tan , et al. (43 additional authors not shown)

Abstract: Artificial intelligence and machine learning are reshaping how we approach scientific discovery, not by replacing established methods but by extending what researchers can probe, predict, and design. In this roadmap we provide a forward-looking view of AI-enabled science across biology, chemistry, climate science, mathematics, materials science, physics, self-driving laboratories and unconventiona… ▽ More Artificial intelligence and machine learning are reshaping how we approach scientific discovery, not by replacing established methods but by extending what researchers can probe, predict, and design. In this roadmap we provide a forward-looking view of AI-enabled science across biology, chemistry, climate science, mathematics, materials science, physics, self-driving laboratories and unconventional computing. Several shared themes emerge: the need for diverse and trustworthy data, transferable electronic-structure and interatomic models, AI systems integrated into end-to-end scientific workflows that connect simulations to experiments and generative systems grounded in synthesisability rather than purely idealised phases. Across domains, we highlight how large foundation models, active learning and self-driving laboratories can close loops between prediction and validation while maintaining reproducibility and physical interpretability. Taken together, these perspectives outline where AI-enabled science stands today, identify bottlenecks in data, methods and infrastructure, and chart concrete directions for building AI systems that are not only more powerful but also more transparent and capable of accelerating discovery in complex real-world environments. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Many-Eyes and Sentinels in Selfish and Cooperative Groups

Authors: Charlie Pilgrim, Andrew M Bate, Anna Sigalou, Mélisande Aellen, Joe Morford, Elizabeth Warren, Christopher Krupenye, Dora Biro, Richard P Mann

Abstract: Collective vigilance describes how animals in groups benefit from the predator detection efforts of others. Empirical observations typically find either a many-eyes strategy with all (or many) group members maintaining a low level of individual vigilance, or a sentinel strategy with one (or a few) individuals maintaining a high level of individual vigilance while others do not. With a general anal… ▽ More Collective vigilance describes how animals in groups benefit from the predator detection efforts of others. Empirical observations typically find either a many-eyes strategy with all (or many) group members maintaining a low level of individual vigilance, or a sentinel strategy with one (or a few) individuals maintaining a high level of individual vigilance while others do not. With a general analytical treatment that makes minimal assumptions, we show that these two strategies are alternate solutions to the same adaptive problem of balancing the costs of predation and vigilance. Which strategy is preferred depends on how costs scale with the level of individual vigilance: many-eyes strategies are preferred where costs of vigilance rise gently at low levels but become steeper at higher levels (convex; e.g. an open field); sentinel strategies are preferred where costs of vigilance rise steeply at low levels and then flatten out (concave; e.g. environments with vantage points). This same dichotomy emerges whether individuals act selfishly to optimise their own fitness or cooperatively to optimise group fitness. The model is extended to explain discrete behavioural switching between strategies and differential levels of vigilance such as edge effects. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Universality of Shallow Global Quenches in Critical Spin Chains

Authors: Julia Wei, Méabh Allen, Jack Kemp, Chenbing Wang, Zixia Wei, Joel E. Moore, Norman Y. Yao

Abstract: Measuring universal data in the strongly correlated regime of quantum critical points remains a fundamental objective for quantum simulators. In foundational work, Calabrese and Cardy demonstrated how this data governs the dynamics of certain global quenches to 1+1-dimensional conformal field theories. While the quasiparticle picture they introduce has been widely successful in both theory and exp… ▽ More Measuring universal data in the strongly correlated regime of quantum critical points remains a fundamental objective for quantum simulators. In foundational work, Calabrese and Cardy demonstrated how this data governs the dynamics of certain global quenches to 1+1-dimensional conformal field theories. While the quasiparticle picture they introduce has been widely successful in both theory and experiment, their seminal prediction that the critical exponents are simply encoded in the relaxation rates of local observables is more challenging to investigate experimentally; in particular, the specific initial state required for their analysis is generated via imaginary time evolution. In this work, we examine the critical quench dynamics of local observables from two types of readily-accessible initial conditions: ground states and finite-temperature ensembles. We identify universal scaling collapses and scaling functions in both cases, utilizing a combination of conformal perturbation theory and tensor network numerics. For the finite-temperature quenches, we determine a regime in which the conformal field theory results are recovered, thereby allowing universal quantum critical data to be extracted from realistic quenches. △ Less

Submitted 26 September, 2025; originally announced September 2025.

Comments: 12+14 pages, 4+7 figures

The Computational Foundations of Collective Intelligence

Authors: Charlie Pilgrim, Joe Morford, Elizabeth Warren, Mélisande Aellen, Christopher Krupenye, Richard P Mann, Dora Biro

Abstract: Why do collectives outperform individuals when solving some problems? Fundamentally, collectives have greater computational resources with more sensory information, more memory, more processing capacity, and more ways to act. While greater resources present opportunities, there are also challenges in coordination and cooperation inherent in collectives with distributed, modular structures. Despite… ▽ More Why do collectives outperform individuals when solving some problems? Fundamentally, collectives have greater computational resources with more sensory information, more memory, more processing capacity, and more ways to act. While greater resources present opportunities, there are also challenges in coordination and cooperation inherent in collectives with distributed, modular structures. Despite these challenges, we show how collective resource advantages lead directly to well-known forms of collective intelligence including the wisdom of the crowd, collective sensing, division of labour, and cultural learning. Our framework also generates testable predictions about collective capabilities in distributed reasoning and context-dependent behavioural switching. Through case studies of animal navigation and decision-making, we demonstrate how collectives leverage their computational resources to solve problems not only more effectively than individuals, but by using qualitatively different problem-solving strategies. △ Less

Submitted 6 September, 2025; originally announced September 2025.

A Wideband Tunable, Nonreciprocal Bandpass Filter Using Magnetostatic Surface Waves with Zero Static Power Consumption

Authors: Xingyu Du, Yixiao Ding, Shun Yao, Yijie Ding, Dengyang Lu, Shuxian Wu, Chin-Yu Chang, Xuan Wang, Mark Allen, Roy H. Olsson III

Abstract: Modern wireless systems demand compact, power-efficient RF front-end components that support wideband tunability and nonreciprocity. We present a new class of miniature bandpass filter that achieves both continuously tunable frequency operation (4-17.7 GHz) and high nonreciprocity (>25 dB), all within a compact size of 1.07 cm3. The filter employs a microfabricated 18 micrometer thick Yttrium Iron… ▽ More Modern wireless systems demand compact, power-efficient RF front-end components that support wideband tunability and nonreciprocity. We present a new class of miniature bandpass filter that achieves both continuously tunable frequency operation (4-17.7 GHz) and high nonreciprocity (>25 dB), all within a compact size of 1.07 cm3. The filter employs a microfabricated 18 micrometer thick Yttrium Iron Garnet waveguide with meander-line aluminum transducers, enabling low-loss unidirectional propagation via magnetostatic surface waves. Leveraging a benzocyclobutene planarization fabrication process, this study enables a dispersion profile unique to thick YIG films, resulting in enhanced filter skirt performance with minimal spurious modes. Frequency tuning is enabled by a zero-static-power magnetic bias circuit using transient current pulses, eliminating continuous power consumption. The filter demonstrates low insertion loss (3-5 dB), high out-of-band rejection (>30 dB), narrow bandwidth (100-200 MHz), robust power handling (>10.4 dBm), and high linearity (IIP3 > 26 dBm). △ Less

Submitted 22 October, 2025; v1 submitted 14 May, 2025; originally announced May 2025.

Self-consistent GW via conservation of spectral moments

Authors: Oliver J. Backhouse, Marcus K. Allen, Charles C. J. Scott, George H. Booth

Abstract: We expand on a recently introduced alternate framework for $GW$ simulation of charged excitations [Scott et. al., J. Chem. Phys., 158, 124102 (2023)], based around the conservation of directly computed spectral moments of the GW self-energy. Featuring a number of desirable formal properties over other implementations, we also detail efficiency improvements and a parallelism strategy, resulting in… ▽ More We expand on a recently introduced alternate framework for $GW$ simulation of charged excitations [Scott et. al., J. Chem. Phys., 158, 124102 (2023)], based around the conservation of directly computed spectral moments of the GW self-energy. Featuring a number of desirable formal properties over other implementations, we also detail efficiency improvements and a parallelism strategy, resulting in an implementation with a demonstrable similar scaling to an established Hartree--Fock code, with only an order of magnitude increase in cost. We also detail the applicability of a range of self-consistent $GW$ variants within this framework, including a scheme for full self-consistency of all dynamical variables, whilst avoiding the Matsubara axis or analytic continuation, allowing formal convergence at zero temperature. By investigating a range of self-consistency protocols over the GW100 molecular test set, we find that a little-explored self-consistent variant based around a simpler coupled chemical potential and Fock matrix optimization to be the most accurate self-consistent $GW$ approach. Additionally, we validate recently observed evidence that Tamm--Dancoff based screening approximations within $GW$ lead to higher accuracy than traditional random phase approximation screening over these molecular test cases. Finally, we consider the Chlorophyll A molecule, finding agreement with experiment within the experimental uncertainty, and a description of the full-frequency spectrum of charged excitations. △ Less

Submitted 7 August, 2025; v1 submitted 24 April, 2025; originally announced April 2025.

California Earthquake Dataset for Machine Learning and Cloud Computing

Authors: Weiqiang Zhu, Haoyu Wang, Bo Rong, Ellen Yu, Stephane Zuzlewski, Gabrielle Tepp, Taka'aki Taira, Julien Marty, Allen Husker, Richard M Allen

Abstract: The San Andreas Fault system, known for its frequent seismic activity, provides an extensive dataset for earthquake studies. The region's well-instrumented seismic networks have been crucial in advancing research on earthquake statistics, physics, and subsurface Earth structures. In recent years, earthquake data from California has become increasingly valuable for deep learning applications, such… ▽ More The San Andreas Fault system, known for its frequent seismic activity, provides an extensive dataset for earthquake studies. The region's well-instrumented seismic networks have been crucial in advancing research on earthquake statistics, physics, and subsurface Earth structures. In recent years, earthquake data from California has become increasingly valuable for deep learning applications, such as Generalized Phase Detection (GPD) for phase detection and polarity determination, and PhaseNet for phase arrival-time picking. The continuous accumulation of data, particularly those manually labeled by human analysts, serves as an essential resource for advancing both regional and global deep learning models. To support the continued development of machine learning and data mining studies, we have compiled a unified California Earthquake Event Dataset (CEED) that integrates seismic records from the Northern California Earthquake Data Center (NCEDC) and the Southern California Earthquake Data Center (SCEDC). The dataset includes both automatically and manually determined parameters such as earthquake origin time, source location, P/S phase arrivals, first-motion polarities, and ground motion intensity measurements. The dataset is organized in an event-based format organized by year spanning from 2000 to 2024, facilitating cross-referencing with event catalogs and enabling continuous updates in future years. This comprehensive open-access dataset is designed to support diverse applications including developing deep learning models, creating enhanced catalog products, and research into earthquake processes, fault zone structures, and seismic risks. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Co-existing topological and Volkov-Pankratov plasmonic edge states in magnetized graphene

Authors: Samyobrata Mukherjee, Viktoriia Savchuk, Jeffery W. Allen, Monica S. Allen, Gennady Shvets

Abstract: Graphene placed in a perpendicular magnetic field supports optical modes known as magnetoplasmons which are transversally confined to the graphene layer. Unlike ordinary graphene plasmons, these magnetoplasmonic surface waves are characterized by a band gap corresponding to the cyclotron frequency. In addition, these magnetoplasmon bands are topological, characterized by a non-zero Chern number. T… ▽ More Graphene placed in a perpendicular magnetic field supports optical modes known as magnetoplasmons which are transversally confined to the graphene layer. Unlike ordinary graphene plasmons, these magnetoplasmonic surface waves are characterized by a band gap corresponding to the cyclotron frequency. In addition, these magnetoplasmon bands are topological, characterized by a non-zero Chern number. This leads to the existence of topologically protected edge states at domain edges where the Chern number changes. Since the Chern number is dependent on the direction of the magnetic field, edge states exist at domain edges across which the magnetic field flips direction. Physically, the magnetic field can only flip direction at gradual domain edges with finite width creating topological heterojunctions. These topological heterojunctions support extra edge states known as Volkov-Pankratov edge states which can enter the band gap and support propagation in both directions. The number of Volkov-Pankratov states at a heterojunction varies as a function of the width of the gradual domain edge. △ Less

Submitted 5 February, 2025; originally announced February 2025.

Gemini & Physical World: Large Language Models Can Estimate the Intensity of Earthquake Shaking from Multi-Modal Social Media Posts

Authors: S. Mostafa Mousavi, Marc Stogaitis, Tajinder Gadh, Richard M Allen, Alexei Barski, Robert Bosch, Patrick Robertson, Nivetha Thiruverahan, Youngmin Cho, Aman Raj

Abstract: This paper presents a novel approach to extract scientifically valuable information about Earth's physical phenomena from unconventional sources, such as multi-modal social media posts. Employing a state-of-the-art large language model (LLM), Gemini 1.5 Pro (Reid et al. 2024), we estimate earthquake ground shaking intensity from these unstructured posts. The model's output, in the form of Modified… ▽ More This paper presents a novel approach to extract scientifically valuable information about Earth's physical phenomena from unconventional sources, such as multi-modal social media posts. Employing a state-of-the-art large language model (LLM), Gemini 1.5 Pro (Reid et al. 2024), we estimate earthquake ground shaking intensity from these unstructured posts. The model's output, in the form of Modified Mercalli Intensity (MMI) values, aligns well with independent observational data. Furthermore, our results suggest that LLMs, trained on vast internet data, may have developed a unique understanding of physical phenomena. Specifically, Google's Gemini models demonstrate a simplified understanding of the general relationship between earthquake magnitude, distance, and MMI intensity, accurately describing observational data even though it's not identical to established models. These findings raise intriguing questions about the extent to which Gemini's training has led to a broader understanding of the physical world and its phenomena. The ability of Generative AI models like Gemini to generate results consistent with established scientific knowledge highlights their potential to augment our understanding of complex physical phenomena like earthquakes. The flexible and effective approach proposed in this study holds immense potential for enriching our understanding of the impact of physical phenomena and improving resilience during natural disasters. This research is a significant step toward harnessing the power of social media and AI for natural disaster mitigation, opening new avenues for understanding the emerging capabilities of Generative AI and LLMs for scientific applications. △ Less

Submitted 14 June, 2024; v1 submitted 28 May, 2024; originally announced May 2024.

Global Data in Astronomy: Challenges and Opportunities

Authors: Renee Hložek, Chenzhou Cui, Mark Allen, Patricia Whitelock, Jess McIver, Giuseppe Longo, Christopher Fluke, Ajit Kembhavi, Pranav Sharma, Ashish Mahabal

Abstract: Policy Brief on "Global Data in Astronomy: Challenges and Opportunities", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Astronomy is increasingly becoming a data-driven science. Advances in our understanding of the physical mechanisms at work in the Universe require building… ▽ More Policy Brief on "Global Data in Astronomy: Challenges and Opportunities", distilled from the corresponding panel that was part of the discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. Astronomy is increasingly becoming a data-driven science. Advances in our understanding of the physical mechanisms at work in the Universe require building ever-more sensitive telescopes to gather observations of the cosmos to test and advance our theoretical models of how the universe works. To confront the observed data with our theoretical models we require data hosting, archiving and storage and high-performance computing resources to run the theoretical calculations and compare our simulated and observed universe. We also require the sophisticated development of highly skilled human resources. Newer large projects are often run through international collaborations and partnerships, driving a need for 'open science' and collaborative structure across national boundaries. While astronomical data are useful scientifically, the data do not come with the same ethical/privacy-related restrictions as medical/biological data. Moreover, the ability to use data for new scientific analysis extends and expands the impact and reach of scientific surveys -- this is a strength that national funding agencies should capitalize on. We discuss the management and analysis of such large volumes of data and the corresponding significant challenges that require policy-level preparations. The policy webinar took place during the G20 presidency in India (2023). A summary based on the seven panels can be found here: arxiv:2401.04623. △ Less

Submitted 19 February, 2024; originally announced February 2024.

Comments: 5 pages. The panel videos including keynotes and the white papers are available on the S20 site at: https://s20india.org/science-policy-webinar-astroinformatics-for-sustainable-development/

AstroInformatics: Recommendations for Global Cooperation

Authors: Ashish Mahabal, Pranav Sharma, Rana Adhikari, Mark Allen, Stefano Andreon, Varun Bhalerao, Federica Bianco, Anthony Brown, S. Bradley Cenko, Paula Coehlo, Jeffery Cooke, Daniel Crichton, Chenzhou Cui, Reinaldo de Carvalho, Richard Doyle, Laurent Eyer, Bernard Fanaroff, Christopher Fluke, Francisco Forster, Kevin Govender, Matthew J. Graham, Renée Hložek, Puji Irawati, Ajit Kembhavi, Juna Kollmeier , et al. (23 additional authors not shown)

Abstract: Policy Brief on "AstroInformatics, Recommendations for Global Collaboration", distilled from panel discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. The deliberations encompassed a wide array of topics, including broad astroinformatics, sky surveys, large-scale international initiatives, global data repositories, space-related data, regi… ▽ More Policy Brief on "AstroInformatics, Recommendations for Global Collaboration", distilled from panel discussions during S20 Policy Webinar on Astroinformatics for Sustainable Development held on 6-7 July 2023. The deliberations encompassed a wide array of topics, including broad astroinformatics, sky surveys, large-scale international initiatives, global data repositories, space-related data, regional and international collaborative efforts, as well as workforce development within the field. These discussions comprehensively addressed the current status, notable achievements, and the manifold challenges that the field of astroinformatics currently confronts. The G20 nations present a unique opportunity due to their abundant human and technological capabilities, coupled with their widespread geographical representation. Leveraging these strengths, significant strides can be made in various domains. These include, but are not limited to, the advancement of STEM education and workforce development, the promotion of equitable resource utilization, and contributions to fields such as Earth Science and Climate Science. We present a concise overview, followed by specific recommendations that pertain to both ground-based and space data initiatives. Our team remains readily available to furnish further elaboration on any of these proposals as required. Furthermore, we anticipate further engagement during the upcoming G20 presidencies in Brazil (2024) and South Africa (2025) to ensure the continued discussion and realization of these objectives. The policy webinar took place during the G20 presidency in India (2023). Notes based on the seven panels will be separately published. △ Less

Submitted 9 January, 2024; originally announced January 2024.

Comments: 7 pages

Frequency Tunable Magnetostatic Wave Filters With Zero Static Power Magnetic Biasing Circuitry

Authors: Xingyu Du, Mohamad Hossein Idjadi, Yixiao Ding, Tao Zhang, Alexander J. Geers, Shun Yao, Jun Beom Pyo, Firooz Aflatouni, Mark Allen, Roy H. Olsson III

Abstract: A single tunable filter simplifies complexity, reduces insertion loss, and minimizes size compared to frequency switchable filter banks commonly used for radio frequency (RF) band selection. Magnetostatic wave (MSW) filters stand out for their wide, continuous frequency tuning and high-quality factor. However, MSW filters employing electromagnets for tuning consume excessive power and space, unsui… ▽ More A single tunable filter simplifies complexity, reduces insertion loss, and minimizes size compared to frequency switchable filter banks commonly used for radio frequency (RF) band selection. Magnetostatic wave (MSW) filters stand out for their wide, continuous frequency tuning and high-quality factor. However, MSW filters employing electromagnets for tuning consume excessive power and space, unsuitable for consumer wireless applications. Here, we demonstrate miniature and high selectivity MSW tunable filters with zero static power consumption, occupying less than 2 cc. The center frequency is continuously tunable from 3.4 GHz to 11.1 GHz via current pulses of sub-millisecond duration applied to a small and nonvolatile magnetic bias assembly. This assembly is limited in the area over which it can achieve a large and uniform magnetic field, necessitating filters realized from small resonant cavities micromachined in thin films of Yttrium Iron Garnet. Filter insertion loss of 3.2 dB to 5.1 dB and out-of-band third order input intercept point greater than 41 dBm are achieved. The filter's broad frequency range, compact size, low insertion loss, high out-of-band linearity, and zero static power consumption are essential for protecting RF transceivers and antennas from interference, thus facilitating their use in mobile applications like IoT and 6G networks. △ Less

Submitted 19 September, 2023; v1 submitted 1 August, 2023; originally announced August 2023.

Comments: 65 pages, PDF; one supplementary note added, Revised spelling error in acknowledgement, results unchanged

MilliKelvin microwave impedance microscopy in a dry dilution refrigerator

Authors: Leonard Weihao Cao, Chen Wu, Rajarshi Bhattacharyya, Ruolun Zhang, Monica T. Allen

Abstract: Microwave impedance microscopy (MIM) is a near-field imaging technique that has been used to visualize the local conductivity of materials with nanoscale resolution across the GHz regime. In recent years, MIM has shown great promise for the investigation of topological states of matter, correlated electronic states and emergent phenomena in quantum materials. To explore these low-energy phenomena,… ▽ More Microwave impedance microscopy (MIM) is a near-field imaging technique that has been used to visualize the local conductivity of materials with nanoscale resolution across the GHz regime. In recent years, MIM has shown great promise for the investigation of topological states of matter, correlated electronic states and emergent phenomena in quantum materials. To explore these low-energy phenomena, many of which are only detectable in the milliKelvin regime, we have developed a novel low-temperature MIM incorporated into a dilution refrigerator. This setup which consists of a tuning-fork-based atomic force microscope with microwave reflectometry capabilities, is capable of reaching temperatures down to 70 mK during imaging and magnetic fields up to 9 T. To test the performance of this microscope, we demonstrate microwave imaging of the conductivity contrast between graphite and silicon dioxide at cryogenic temperatures and discuss the resolution and noise observed in these results. We extend this methodology to visualize edge conduction in Dirac semimetal cadmium arsenide in the quantum Hall regime △ Less

Submitted 29 September, 2023; v1 submitted 5 May, 2023; originally announced May 2023.

Comments: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments and may be found at doi.org/10.1063/5.0159548

Journal ref: Volume 94, Issue 9, Year 2023

Acceleration of a Positron Bunch in a Hollow Channel Plasma

Authors: Spencer Gessner, Erik Adli, James M. Allen, Weiming An, Christine I. Clarke, Chris E. Clayton, Sebastien Corde, Antoine Doche, Joel Frederico, Selina Z. Green, Mark J. Hogan, Chan Joshi, Carl A. Lindstrom, Michael Litos, Kenneth A. Marsh, Warren B. Mori, Brendan O'Shea, Navid Vafaei-Najafabadi, Vitaly Yakimenko

Abstract: Plasmas are a compelling medium for particle acceleration owing to their natural ability to sustain electric fields that are orders of magnitude larger than those available in conventional radio-frequency accelerators. Plasmas are also unique amongst accelerator technologies in that they respond differently to beams of opposite charge. The asymmetric response of a plasma to highly-relativistic ele… ▽ More Plasmas are a compelling medium for particle acceleration owing to their natural ability to sustain electric fields that are orders of magnitude larger than those available in conventional radio-frequency accelerators. Plasmas are also unique amongst accelerator technologies in that they respond differently to beams of opposite charge. The asymmetric response of a plasma to highly-relativistic electron and positron beams arises from the fact that plasmas are composed of light, mobile electrons and heavy, stationary ions. Hollow channel plasma acceleration is a technique for symmetrizing the response of the plasma, such that it works equally well for high-energy electron and positron beams. In the experiment described here, we demonstrate the generation of a positron beam-driven wake in an extended, annular plasma channel, and acceleration of a second trailing witness positron bunch by the wake. The leading bunch excites the plasma wakefield and loses energy to the plasma, while the witness bunch experiences an accelerating field and gains energy, thus providing a proof-of-concept for hollow channel acceleration of positron beams. At a bunch separation of 330 um, the accelerating gradient is 70 MV/m, the transformer ratio is 0.55, and the energy transfer efficiency is 18% for a drive-to-witness beam charge ratio of 5:1. △ Less

Submitted 30 December, 2023; v1 submitted 4 April, 2023; originally announced April 2023.

Cell-format-dependent mechanical damage in silicon anodes

Authors: Marco-Tulio F. Rodrigues, Sathish Rajendran, Stephen E. Trask, Alison R. Dunlop, Avtar Singh, Jeffery M. Allen, Peter J. Weddle, Andrew M. Colclasure, Andrew N. Jansen

Abstract: It is generally believed that silicon-based anodes for Li-ion batteries would benefit from stronger binders, as cyclic volume changes would not disrupt the cohesion of the composite electrode. Here, we put this belief to the proof by testing electrodes containing SiOx particles and an aromatic polyimide binder. We observe that the electrodes can stretch laterally by as much as 6% during the first… ▽ More It is generally believed that silicon-based anodes for Li-ion batteries would benefit from stronger binders, as cyclic volume changes would not disrupt the cohesion of the composite electrode. Here, we put this belief to the proof by testing electrodes containing SiOx particles and an aromatic polyimide binder. We observe that the electrodes can stretch laterally by as much as 6% during the first cycle, indicating that internal stresses are high enough to induce plastic deformation on the copper current collector. Remarkably, no coating delamination is observed. Additional consequences were size-dependent: while pouch-cell-sized electrodes developed wrinkles, coin-cell-sized ones remained mostly smooth. We demonstrate that wrinkling of the current collector damages the electrode coating, inactivating SiOx domains and accelerating capacity fade. This size-dependent performance decay indicates that, in extreme cases, testing outcomes are highly dependent on scale. Novel battery materials may require testing at larger cell formats for complete validation. △ Less

Submitted 24 March, 2023; originally announced March 2023.

Graphene-Quantum Dot Hybrid Photodetectors from 200 mm Wafer Scale Processing

Authors: Sha Li, Zhenxing Wang, Bianca Robertz, Daniel Neumaier, Oihana Txoperena, Arantxa Maestre, Amaia Zurutuza, Chris Bower, Ashley Rushton, Yinglin Liu, Chris Harris, Alexander Bessonov, Surama Malik, Mark Allen, Ivonne Medina-Salazar, Tapani Ryhänen, Max C. Lemme

Abstract: A 200 mm processing platform for the large-scale production of graphene field-effect transistor-quantum dot (GFET-QD) hybrid photodetectors is demonstrated. Comprehensive statistical analysis of electric data shows a high yield (96%) and low variation of the 200 mm scale fabrication. The GFET-QD devices deliver responsivities of 10${^5}$ - 10${^6}$ V/W in a wavelength range from 400 to 1800 nm, at… ▽ More A 200 mm processing platform for the large-scale production of graphene field-effect transistor-quantum dot (GFET-QD) hybrid photodetectors is demonstrated. Comprehensive statistical analysis of electric data shows a high yield (96%) and low variation of the 200 mm scale fabrication. The GFET-QD devices deliver responsivities of 10${^5}$ - 10${^6}$ V/W in a wavelength range from 400 to 1800 nm, at up to 100 frames per second. Spectral sensitivity compares well to that obtained using similar GFET-QD photodetectors. The device concept enables gate-tunable suppression or enhancement of the photovoltage, which may be exploited for electric shutter operation by toggling between the signal capture and shutter states. The devices show good stability at a wide operation range and external quantum efficiency of 20% in the short-wavelength infrared range. Furthermore, an integration solution with complementary metal-oxide-semiconductor technology is presented to realize image-sensor-array chips and a proof-of-concept image system. This work demonstrates the potential for the volume manufacture of infrared photodetectors for a wide range of imaging applications. △ Less

Submitted 1 March, 2023; originally announced March 2023.

Comments: 29 pages

Journal ref: Sci Rep 15, 14706 (2025)

Energetic electron precipitation driven by electromagnetic ion cyclotron waves from ELFIN's low altitude perspective

Authors: V. Angelopoulos, X. -J. Zhang, A. V. Artemyev, D. Mourenas, E. Tsai, C. Wilkins, A. Runov, J. Liu, D. L. Turner, W. Li, K. Khurana, R. E. Wirz, V. A. Sergeev, X. Meng, J. Wu, M. D. Hartinger, T. Raita, Y. Shen, X. An, X. Shi, M. F. Bashir, X. Shen, L. Gan, M. Qin, L. Capannolo , et al. (61 additional authors not shown)

Abstract: We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data from the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibi… ▽ More We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data from the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at 0.5 MeV which are abrupt (bursty) with significant substructure (occasionally down to sub-second timescale). Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Using two years of ELFIN data, we assemble a statistical database of 50 events of strong EMIC wave-driven precipitation. Most reside at L=5-7 at dusk, while a smaller subset exists at L=8-12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an L-shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio's spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven 1MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to 200-300 keV by much less intense higher frequency EMIC waves. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation. △ Less

Submitted 28 November, 2022; originally announced November 2022.

Photonic Dirac Waveguides

Authors: Svetlana Kiriushechkina, Anton Vakulenko, Daria Smirnova, Sriram Guddala, Filipp Komissarenko, Monica Allen, Jeffery Allen, Alexander B. Khanikaev

Abstract: The Dirac equation is a paradigmatic model that describes a range of intriguing properties of relativistic spin-1/2 particles, from the existence of antiparticles to Klein tunneling. However, the Dirac-like equations have found application far beyond its original scope, and has been used to comprehend the properties of graphene and topological phases of matter. In the field of photonics, the oppor… ▽ More The Dirac equation is a paradigmatic model that describes a range of intriguing properties of relativistic spin-1/2 particles, from the existence of antiparticles to Klein tunneling. However, the Dirac-like equations have found application far beyond its original scope, and has been used to comprehend the properties of graphene and topological phases of matter. In the field of photonics, the opportunity to emulate Dirac physics has also enabled topological photonic insulators. In this paper, we demonstrate that judiciously engineered synthetic potentials in photonic Dirac systems can offer physical properties beyond both the elementary and quasi-particles, and topological realms. Specifically, we introduce a new class of optical Dirac waveguides, whose guided electromagnetic modes are endowed with pseudo-spin degree of freedom. Pseudo-spin coupled with the ability to engineer synthetic gauge potentials acting on it, enables control over the guided modes which is unattainable in conventional optical waveguides. In particular, we use a silicon nanophotonic metasurface that supports pseudo-spin degree of freedom as a testing platform to predict and experimentally confirm a spin-full nature of the Dirac waveguides. We also demonstrate that, for suitable trapping potentials, the guided modes exhibit spin-dependent field distributions, which gives rise to their distinct transport and radiative properties. Thereby, the Dirac waveguides manifest spin-dependent radiative lifetimes - the non-Hermitian spin-Hall effect - and open new avenues for spin-multiplexing, controlling characteristics of guided optical modes, and tuning light-matter interactions with photonic pseudo-spins. △ Less

Submitted 1 November, 2022; originally announced November 2022.

Comments: 16 pages, 5 figures

ATHENA Detector Proposal -- A Totally Hermetic Electron Nucleus Apparatus proposed for IP6 at the Electron-Ion Collider

Authors: ATHENA Collaboration, J. Adam, L. Adamczyk, N. Agrawal, C. Aidala, W. Akers, M. Alekseev, M. M. Allen, F. Ameli, A. Angerami, P. Antonioli, N. J. Apadula, A. Aprahamian, W. Armstrong, M. Arratia, J. R. Arrington, A. Asaturyan, E. C. Aschenauer, K. Augsten, S. Aune, K. Bailey, C. Baldanza, M. Bansal, F. Barbosa, L. Barion , et al. (415 additional authors not shown)

Abstract: ATHENA has been designed as a general purpose detector capable of delivering the full scientific scope of the Electron-Ion Collider. Careful technology choices provide fine tracking and momentum resolution, high performance electromagnetic and hadronic calorimetry, hadron identification over a wide kinematic range, and near-complete hermeticity. This article describes the detector design and its e… ▽ More ATHENA has been designed as a general purpose detector capable of delivering the full scientific scope of the Electron-Ion Collider. Careful technology choices provide fine tracking and momentum resolution, high performance electromagnetic and hadronic calorimetry, hadron identification over a wide kinematic range, and near-complete hermeticity. This article describes the detector design and its expected performance in the most relevant physics channels. It includes an evaluation of detector technology choices, the technical challenges to realizing the detector and the R&D required to meet those challenges. △ Less

Submitted 13 October, 2022; originally announced October 2022.

Journal ref: JINST 17 (2022) 10, P10019

JWST/NIRCam Coronagraphy: Commissioning and First On-Sky Results

Authors: Julien H. Girard, Jarron Leisenring, Jens Kammerer, Mario Gennaro, Marcia Rieke, John Stansberry, Armin Rest, Eiichi Egami, Ben Sunnquist, Martha Boyer, Alicia Canipe, Matteo Correnti, Bryan Hilbert, Marshall D. Perrin, Laurent Pueyo, Remi Soummer, Marsha Allen, Howard Bushouse, Jonathan Aguilar, Brian Brooks, Dan Coe, Audrey DiFelice, David Golimowski, George Hartig, Dean C. Hines , et al. (31 additional authors not shown)

Abstract: In a cold and stable space environment, the James Webb Space Telescope (JWST or "Webb") reaches unprecedented sensitivities at wavelengths beyond 2 microns, serving most fields of astrophysics. It also extends the parameter space of high-contrast imaging in the near and mid-infrared. Launched in late 2021, JWST underwent a six month commissioning period. In this contribution we focus on the NIRCam… ▽ More In a cold and stable space environment, the James Webb Space Telescope (JWST or "Webb") reaches unprecedented sensitivities at wavelengths beyond 2 microns, serving most fields of astrophysics. It also extends the parameter space of high-contrast imaging in the near and mid-infrared. Launched in late 2021, JWST underwent a six month commissioning period. In this contribution we focus on the NIRCam Coronagraphy mode which was declared "science ready" on July 10 2022, the last of the 17 JWST observing modes. Essentially, this mode will allow to detect fainter/redder/colder (less massive for a given age) self-luminous exoplanets as well as other faint astrophysical signal in the vicinity of any bright object (stars or galaxies). Here we describe some of the steps and hurdles the commissioning team went through to achieve excellent performances. Specifically, we focus on the Coronagraphic Suppression Verification activity. We were able to produce firm detections at 3.35$μ$m of the white dwarf companion HD 114174 B which is at a separation of $\simeq$ 0.5" and a contrast of $\simeq$ 10 magnitudes ($10^{4}$ fainter than the K$\sim$5.3 mag host star). We compare these first on-sky images with our latest, most informed and realistic end-to-end simulations through the same pipeline. Additionally we provide information on how we succeeded with the target acquisition with all five NIRCam focal plane masks and their four corresponding wedged Lyot stops. △ Less

Submitted 31 August, 2022; v1 submitted 1 August, 2022; originally announced August 2022.

Comments: 23 pages, 18 figures, to appear in the Proceedings of the SPIE Astronomical Telescopes + Instrumentation (2022)

First High-speed Video Camera Observations of a Lightning Flash Associated with a Downward Terrestrial Gamma-ray Flash

Authors: R. U. Abbasi, M. M. F. Saba, J. W. Belz, P. R. Krehbiel, W. Rison, N. Kieu, D. R. da Silva, Dan Rodeheffer, M. A. Stanley, J. Remington, J. Mazich, R. LeVon, K. Smout, A. Petrizze, T. Abu-Zayyad, M. Allen, Y. Arai, R. Arimura, E. Barcikowski, D. R. Bergman, S. A. Blake, I. Buckland, B. G. Cheon, M. Chikawa, T. Fujii , et al. (127 additional authors not shown)

Abstract: In this paper, we present the first high-speed video observation of a cloud-to-ground lightning flash and its associated downward-directed Terrestrial Gamma-ray Flash (TGF). The optical emission of the event was observed by a high-speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric-field… ▽ More In this paper, we present the first high-speed video observation of a cloud-to-ground lightning flash and its associated downward-directed Terrestrial Gamma-ray Flash (TGF). The optical emission of the event was observed by a high-speed video camera running at 40,000 frames per second in conjunction with the Telescope Array Surface Detector, Lightning Mapping Array, interferometer, electric-field fast antenna, and the National Lightning Detection Network. The cloud-to-ground flash associated with the observed TGF was formed by a fast downward leader followed by a very intense return stroke peak current of -154 kA. The TGF occurred while the downward leader was below cloud base, and even when it was halfway in its propagation to ground. The suite of gamma-ray and lightning instruments, timing resolution, and source proximity offer us detailed information and therefore a unique look at the TGF phenomena. △ Less

Submitted 9 August, 2023; v1 submitted 10 May, 2022; originally announced May 2022.

Journal ref: Geophysical Research Letters, 50, e2023GL102958 (2023)

Crowdsourcing Felt Reports using the MyShake smartphone app

Authors: Qingkai Kong, Richard M. Allen, Steve Allen, Theron Bair, Akie Meja, Sarina Patel, Jennifer Strauss, Stephen Thompson

Abstract: MyShake is a free citizen science smartphone app that provides a range of features related to earthquakes. Features available globally include rapid post-earthquake notifications, live maps of earthquake damage as reported by MyShake users, safety tips and various educational features. The app also uses the accelerometer to detect earthquake shaking and to record and submit waveforms to a central… ▽ More MyShake is a free citizen science smartphone app that provides a range of features related to earthquakes. Features available globally include rapid post-earthquake notifications, live maps of earthquake damage as reported by MyShake users, safety tips and various educational features. The app also uses the accelerometer to detect earthquake shaking and to record and submit waveforms to a central archive. In addition, MyShake delivers earthquake early warning alerts in California, Oregon and Washington. In this study we compare the felt shaking reports provided by MyShake users in California with the US Geological Survey's "Did You Feel It?" intensity reports. The MyShake app simply asks "What strength of shaking did you feel" and users report on a five-level scale. When the reports are averaged in spatial bins, we find strong correlations with the Modified Mercalli Intensity scale values reported by the USGS based on the much more complex DYFI surveys. The MyShake felt reports can therefore also be used to generate shaking intensity maps. △ Less

Submitted 25 January, 2023; v1 submitted 26 April, 2022; originally announced April 2022.

Modeling the bounce of a gas-filled ball

Authors: Martin Allen, Bruce Allen

Abstract: The coefficient of restitution $ε$ characterizes the energy retained when a ball bounces, and can easily be measured in an ``at home'' experiment. For thin-walled gas-filled balls such as basketballs, we construct a simple two parameter model to describe how $ε$ changes as a function of the ball's internal pressure. A comparison with data shows good agreement. With additional assumptions, the mode… ▽ More The coefficient of restitution $ε$ characterizes the energy retained when a ball bounces, and can easily be measured in an ``at home'' experiment. For thin-walled gas-filled balls such as basketballs, we construct a simple two parameter model to describe how $ε$ changes as a function of the ball's internal pressure. A comparison with data shows good agreement. With additional assumptions, the model also predicts how $ε$ changes as a function of temperature. A comparison with tennis ball data shows surprisingly good agreement. △ Less

Submitted 26 December, 2024; v1 submitted 7 February, 2022; originally announced February 2022.

Comments: 9 pages, 7 figures, 2 tables, revised to include basketball data and comparison with other models in the literature

Observation of Variations in Cosmic Ray Single Count Rates During Thunderstorms and Implications for Large-Scale Electric Field Changes

Authors: R. U. Abbasi, T. Abu-Zayyad, M. Allen, Y. Arai, R. Arimura, E. Barcikowski, J. W. Belz, D. R. Bergman, S. A. Blake, I. Buckland, R. Cady, B. G. Cheon, J. Chiba, M. Chikawa, T. Fujii, K. Fujisue, K. Fujita, R. Fujiwara, M. Fukushima, R. Fukushima, G. Furlich, N. Globus, R. Gonzalez, W. Hanlon, M. Hayashi , et al. (140 additional authors not shown)

Abstract: We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km$^{2}$ area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of t… ▽ More We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km$^{2}$ area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of the 700 km$^{2}$ detector, without dealing with the limitation of narrow exposure in time and space using balloons and aircraft detectors. In this work, variations in the cosmic ray intensity (single count rate) using the TASD, were studied and found to be on average at the $\sim(0.5-1)\%$ and up to 2\% level. These observations were found to be both in excess and in deficit. They were also found to be correlated with lightning in addition to thunderstorms. These variations lasted for tens of minutes; their footprint on the ground ranged from 6 to 24 km in diameter and moved in the same direction as the thunderstorm. With the use of simple electric field models inside the cloud and between cloud to ground, the observed variations in the cosmic ray single count rate were recreated using CORSIKA simulations. Depending on the electric field model used and the direction of the electric field in that model, the electric field magnitude that reproduces the observed low-energy cosmic ray single count rate variations was found to be approximately between 0.2-0.4 GV. This in turn allows us to get a reasonable insight on the electric field and its effect on cosmic ray air showers inside thunderstorms. △ Less

Submitted 18 November, 2021; originally announced November 2021.

Surface detectors of the TAx4 experiment

Authors: Telescope Array Collaboration, R. U. Abbasi, M. Abe, T. Abu-Zayyad, M. Allen, Y. Arai, E. Barcikowski, J. W. Belz, D. R. Bergman, S. A. Blake, R. Cady, B. G. Cheon, J. Chiba, M. Chikawa, T. Fujii, K. Fujisue, K. Fujita, R. Fujiwara, M. Fukushima, R. Fukushima, G. Furlich, W. Hanlon, M. Hayashi, N. Hayashida, K. Hibino , et al. (124 additional authors not shown)

Abstract: Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in the Northern Hemisphere. It explores the origin of UHECRs by measuring their energy spectrum, arrival-direction distribution, and mass composition using a surface detector (SD) array covering approximately 700 km$^2$ and fluorescence detector (FD) stations. TA has found evidence for a cluster of cosmic rays with… ▽ More Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in the Northern Hemisphere. It explores the origin of UHECRs by measuring their energy spectrum, arrival-direction distribution, and mass composition using a surface detector (SD) array covering approximately 700 km$^2$ and fluorescence detector (FD) stations. TA has found evidence for a cluster of cosmic rays with energies greater than 57 EeV. In order to confirm this evidence with more data, it is necessary to increase the data collection rate.We have begun building an expansion of TA that we call TAx4. In this paper, we explain the motivation, design, technical features, and expected performance of the TAx4 SD. We also present TAx4's current status and examples of the data that have already been collected. △ Less

Submitted 1 March, 2021; originally announced March 2021.

Comments: 26 pages, 17 figures, submitted to Nuclear Inst. and Methods in Physics Research, A

Reconsidering the design of planar plasmonic lasers: gain, gap layers, and mode competition

Authors: Marianne Aellen, Aurelio A. Rossinelli, Robert C. Keitel, Raphael Brechbühler, Felipe V. Antolinez, Jian Cui, David J. Norris

Abstract: Because surface plasmons can be confined below the diffraction limit, metallic lasers that support plasmonic modes can provide miniaturized sources of electromagnetic waves. Such devices often exploit a multilayer design, in which a semiconductor gain layer is placed near a metallic interface with a gap layer in between. However, despite many experimental demonstrations, key considerations for the… ▽ More Because surface plasmons can be confined below the diffraction limit, metallic lasers that support plasmonic modes can provide miniaturized sources of electromagnetic waves. Such devices often exploit a multilayer design, in which a semiconductor gain layer is placed near a metallic interface with a gap layer in between. However, despite many experimental demonstrations, key considerations for these planar metallic lasers remain understudied, leading to incorrect conclusions about the optimal design. Here, we pursue a detailed experimental and theoretical study of planar metallic lasers to explore the effect of design parameters on the lasing behavior. We print semiconductor nanoplatelets as a gain layer of controllable thickness onto alumina-coated silver films with integrated planar Fabry-Pérot cavities. Lasing behavior is then monitored with spectrally and polarization-resolved far-field imaging. The results are compared with a theoretical waveguide model and a detailed rate-equation model, which consider both plasmonic and photonic modes. We show that the nature of the lasing mode is dictated by the gain-layer thickness. Moreover, by explicitly treating gain in our waveguide model, we find that, contrary to conventional wisdom, a gap layer with high refractive index is advantageous for plasmonic lasing. Additionally, our rate-equation model reveals a regime where plasmonic and photonic modes compete within the same device, raising the possibility of facile, active mode switching. These findings provide guidance for future designs of metallic lasers and could lead to on-chip lasers with controlled photonic and plasmonic output, switchable at high speeds. △ Less

Submitted 14 January, 2021; originally announced January 2021.

Comments: 51 pages, 14 figures (main text and supporting information merged)

Observations of the Origin of Downward Terrestrial Gamma-Ray Flashes

Authors: J. W. Belz, P. R. Krehbiel, J. Remington, M. A. Stanley, R. U. Abbasi, R. LeVon, W. Rison, D. Rodeheffer, the Telescope Array Scientific Collaboration, :, T. Abu-Zayyad, M. Allen, E. Barcikowski, D. R. Bergman, S. A. Blake, M. Byrne, R. Cady, B. G. Cheon, M. Chikawa, A. di Matteo, T. Fujii, K. Fujita, R. Fujiwara, M. Fukushima, G. Furlich , et al. (116 additional authors not shown)

Abstract: In this paper we report the first close, high-resolution observations of downward-directed terrestrial gamma-ray flashes (TGFs) detected by the large-area Telescope Array cosmic ray observatory, obtained in conjunction with broadband VHF interferometer and fast electric field change measurements of the parent discharge. The results show that the TGFs occur during strong initial breakdown pulses (I… ▽ More In this paper we report the first close, high-resolution observations of downward-directed terrestrial gamma-ray flashes (TGFs) detected by the large-area Telescope Array cosmic ray observatory, obtained in conjunction with broadband VHF interferometer and fast electric field change measurements of the parent discharge. The results show that the TGFs occur during strong initial breakdown pulses (IBPs) in the first few milliseconds of negative cloud-to-ground and low-altitude intracloud flashes, and that the IBPs are produced by a newly-identified streamer-based discharge process called fast negative breakdown. The observations indicate the relativistic runaway electron avalanches (RREAs) responsible for producing the TGFs are initiated by embedded spark-like transient conducting events (TCEs) within the fast streamer system, and potentially also by individual fast streamers themselves. The TCEs are inferred to be the cause of impulsive sub-pulses that are characteristic features of classic IBP sferics. Additional development of the avalanches would be facilitated by the enhanced electric field ahead of the advancing front of the fast negative breakdown. In addition to showing the nature of IBPs and their enigmatic sub-pulses, the observations also provide a possible explanation for the unsolved question of how the streamer to leader transition occurs during the initial negative breakdown, namely as a result of strong currents flowing in the final stage of successive IBPs, extending backward through both the IBP itself and the negative streamer breakdown preceding the IBP. △ Less

Submitted 12 October, 2020; v1 submitted 29 September, 2020; originally announced September 2020.

Comments: Typo fixed and reference added. Manuscript is 36 pages. Supplemental Information is 42 pages. This paper is to be published in the Journal of Geophysical Research: Atmospheres. Online data repository: Open Science Framework DOI: 10.17605/OSF.IO/Z3XDA

Sustainable financing of permanent CO2 disposal through a Carbon Takeback Obligation

Authors: Stuart Jenkins, Eli Mitchell-Larson, Stuart Haszeldine, Myles Allen

Abstract: Unless there is immediate, unprecedented, reduction in global demand for carbon-intensive energy and products, then capture and permanent storage of billions of tonnes of carbon dioxide (CO2) annually will be needed before mid-century to meet Paris Agreement goals. Yet competition from cheaper, temporary, carbon storage means that permanent disposal remains starved of investment, currently represe… ▽ More Unless there is immediate, unprecedented, reduction in global demand for carbon-intensive energy and products, then capture and permanent storage of billions of tonnes of carbon dioxide (CO2) annually will be needed before mid-century to meet Paris Agreement goals. Yet competition from cheaper, temporary, carbon storage means that permanent disposal remains starved of investment, currently representing about 0.1% of Energy and Industrial Process (EIP) emissions. This stored fraction must reach 100% to stop EIPs causing global warming. Here we show that a cost-effective transition can occur by mandating an increasing stored fraction through a progressive Carbon Takeback Obligation (CTO) on fossil fuel producers and importers. Projected costs of storage to the consumer are lower than pricing carbon emissions in conventional 1.5°C scenarios until the 2040s, and comparable or lower thereafter. A CTO combined with measures to reduce CO2 production would deliver the lowest-risk pathway to achieving net zero. △ Less

Submitted 16 July, 2020; originally announced July 2020.

Comments: 10 pages, 1 figure, SI available on request

The ELFIN Mission

Authors: V. Angelopoulos, E. Tsai, L. Bingley, C. Shaffer, D. L. Turner, A. Runov, W. Li, J. Liu, A. V. Artemyev, X. -J. Zhang, R. J. Strangeway, R. E. Wirz, Y. Y. Shprits, V. A. Sergeev, R. P. Caron, M. Chung, P. Cruce, W. Greer, E. Grimes, K. Hector, M. J. Lawson, D. Leneman, E. V. Masongsong, C. L. Russell, C. Wilkins , et al. (57 additional authors not shown)

Abstract: The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (~93deg inclination), nearly circular, low-Earth (~450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism… ▽ More The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (~93deg inclination), nearly circular, low-Earth (~450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (~90min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50keV to 5MeV electrons with deltaE/E<40% and a fluxgate magnetometer (FGM) on a ~72cm boom that measures magnetic field waves (e.g., EMIC waves) in the range from DC to 5Hz Nyquist (nominally) with <0.3nT/sqrt(Hz) noise at 1Hz. The spinning satellites (T_spin~3s) are equipped with magnetorquers that permit spin-up/down and reorientation maneuvers. The spin axis is placed normal to the orbit plane, allowing full pitch-angle resolution twice per spin. An energetic particle detector for ions (EPDI) measures 250keV-5MeV ions, addressing secondary science. Funded initially by CalSpace and the University Nanosat Program, ELFIN was selected for flight with joint support from NSF and NASA between 2014 and 2018. △ Less

Submitted 16 June, 2020; v1 submitted 13 June, 2020; originally announced June 2020.

Comments: Submitted to Space Science Reviews April 2020. 51 pages, 7 tables, 21 figures

Towards Global Earthquake Early Warning with the MyShake Smartphone Seismic Network Part 2 -- Understanding MyShake performance around the world

Authors: Qingkai Kong, Robert Martin-Short, Richard M. Allen

Abstract: The MyShake project aims to build a global smartphone seismic network to facilitate large-scale earthquake early warning and other applications by leveraging the power of crowdsourcing. The MyShake mobile application first detects earthquake shaking on a single phone. The earthquake is then confirmed on the MyShake servers using a "network detection" algorithm that is activated by multiple single-… ▽ More The MyShake project aims to build a global smartphone seismic network to facilitate large-scale earthquake early warning and other applications by leveraging the power of crowdsourcing. The MyShake mobile application first detects earthquake shaking on a single phone. The earthquake is then confirmed on the MyShake servers using a "network detection" algorithm that is activated by multiple single-phone detections. In part two of this two paper series, we report the first order performance of MyShake's Earthquake Early Warning (EEW) capability in various selected locations around the world. Due to the present sparseness of the MyShake network in most parts of the world, we use our simulation platform to understand and evaluate the system's performance in various tectonic settings. We assume that 0.1% of the population has the MyShake mobile application installed on their smartphone, and use historical earthquakes from the last 20 years to simulate triggering scenarios with different network configurations in various regions. Then, we run the detection algorithm with these simulated triggers to understand the performance of the system. The system performs best in regions featuring high population densities and onshore, upper crustal earthquakes M<7.0. In these cases, alerts can be generated ~4-6 sec after the origin time, magnitude errors are within ~0.5 magnitude units, and epicenters are typically within 10 km of true locations. When the events are offshore or in sparsely populated regions, the alerts are slower and the uncertainties in magnitude and location increase. Furthermore, even with 0.01% of the population as the MyShake users, in regions of high population density, the system still performs well for earthquakes larger than M5.5. For details of the simulation platform and the network detection algorithm, please see part one of this two paper series. △ Less

Submitted 17 September, 2019; originally announced September 2019.

Comments: 13 figures, submitted to Seismological Research Letters

Journal ref: Seismological Research Letters (2020) 91(4): 2218-2233

Towards Global Earthquake Early Warning with the MyShake Smartphone Seismic Network Part 1 -- Detection algorithm and simulation platform

Authors: Qingkai Kong, Robert Martin-Short, Richard M. Allen

Abstract: The MyShake project aims to build a global smartphone seismic network to facilitate large-scale earthquake early warning and other applications by leveraging the power of crowdsourcing. The MyShake mobile application first detects earthquake shaking on a single phone. The earthquake is then confirmed on the MyShake servers using a "network detection" algorithm that is activated by multiple single-… ▽ More The MyShake project aims to build a global smartphone seismic network to facilitate large-scale earthquake early warning and other applications by leveraging the power of crowdsourcing. The MyShake mobile application first detects earthquake shaking on a single phone. The earthquake is then confirmed on the MyShake servers using a "network detection" algorithm that is activated by multiple single-phone detections. In this part one of the two paper series, we present a network detection algorithm and a simulation platform to test earthquake scenarios at various locations around the world. The proposed network detection algorithm is built on the DBSCAN classic spatial clustering algorithm, with modifications to take temporal characteristics into account and the association of new triggers. We test our network detection algorithm using real data recorded by MyShake users during the M4.4 January 4th, 2018, Berkeley and the M5.2 June 10th, 2016, Borrego Springs earthquakes to demonstrate the system's utility. In order to test the entire detection procedure and to understand the first order performance of MyShake in various locations around the world representing different population and tectonic characteristics, we then present a software platform which can simulate earthquake triggers in hypothetical MyShake networks. Part two of this paper series explores our MyShake early warning simulation performance in selected regions around the world. △ Less

Submitted 17 September, 2019; originally announced September 2019.

Comments: 7 figures, Submitted to Seismological Research Letters

Journal ref: Seismological Research Letters (2020) 91(4): 2206-2217

MyShake: Detecting and characterizing earthquakes with a global smartphone seismic network

Authors: Qingkai Kong, Sarina Patel, Asaf Inbal, Richard M Allen

Abstract: MyShake harnesses private/personal smartphones to build a global seismic network. It uses the accelerometers embedded in all smartphones to record ground motions induced by earthquakes, returning recorded waveforms to a central repository for analysis and research. A demonstration of the power of citizen science, MyShake expanded to 6 continents within days of being launched, and has recorded 757… ▽ More MyShake harnesses private/personal smartphones to build a global seismic network. It uses the accelerometers embedded in all smartphones to record ground motions induced by earthquakes, returning recorded waveforms to a central repository for analysis and research. A demonstration of the power of citizen science, MyShake expanded to 6 continents within days of being launched, and has recorded 757 earthquakes in the first 2 years of operation. The data recorded by MyShake phones has the potential to be used in scientific applications, thereby complementing current seismic networks. In this paper: (1) we report the capabilities of smartphone sensors to detect earthquakes by analyzing the earthquake waveforms collected by MyShake. (2) We determine the maximum epicentral distance at which MyShake phones can detect earthquakes as a function of magnitude. (3) We then determine the capabilities of the MyShake network to estimate the location, origin time, depth and magnitude of earthquakes. In the case of earthquakes for which MyShake has provided 4 or more phases (21 events), either P- or S-wave signals, and has an azimuthal gap less than 180 degrees, the median location, origin time and depth errors are 2.7 km, 0.2 s, and 0.1 km respectively relative to USGS global catalog locations. Magnitudes are also estimated and have a mean error of 0.0 and standard deviation 0.2. These preliminary results suggest that MyShake could provide basic earthquake catalog information in regions that currently have no traditional networks. With an expanding MyShake network, we expect the event detection capabilities to improve and provide useful data on seismicity and hazards. △ Less

Submitted 22 April, 2019; originally announced April 2019.

Comments: Submitted to Seismological Research Letters, 10 figures, 3 tables

Journal ref: Seismological Research Letters (2019) 90 (5): 1937-1949

Quantifying the Value of Real-time Geodetic Constraints for Earthquake Early Warning using a Global Seismic and Geodetic Dataset

Authors: C. J. Ruhl, D. Melgar, A. I. Chung, R. Grapenthin, R. M. Allen

Abstract: Geodetic earthquake early warning (EEW) algorithms complement point-source seismic systems by estimating fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because such earthquakes are rare, it has been difficult to demonstrate that geodetic warnings improve ground motion estimation significantly. Here, we quantify and compare timeliness and accuracy of m… ▽ More Geodetic earthquake early warning (EEW) algorithms complement point-source seismic systems by estimating fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because such earthquakes are rare, it has been difficult to demonstrate that geodetic warnings improve ground motion estimation significantly. Here, we quantify and compare timeliness and accuracy of magnitude and ground motion estimates in simulated real time from seismic and geodetic observations for a suite of globally-distributed, large earthquakes. Magnitude solutions saturate for the seismic EEW algorithm (we use ElarmS) while the ElarmS-triggered Geodetic Alarm System (G-larmS) reduces the error even for its first solutions. Shaking intensity (MMI) time series calculated for each station and each event are assessed based on MMI-threshold crossings, allowing us to accurately characterize warning times per-station. We classify alerts and find that MMI 4 thresholds result in only 12.3% true positive (TP) alerts with a median warning time of 16.3 +- 20.9 s for ElarmS, but 44.4% TP alerts with a longer median warning time of 50.2 +- 49.8 s for G-larmS. The geodetic EEW system reduces the number of missed alerts for thresholds of MMI 3 and 4 by over 30%. If G-larmS was triggered instantaneously at the earthquake origin time, the performance statistics are similar, with slightly longer warning times and slightly more accurate magnitudes. By quantifying increased accuracy in magnitude, ground motion estimation, and alert timeliness; we demonstrate that geodetic algorithms add significant value, including better cost savings performance, to EEW systems. △ Less

Submitted 30 January, 2019; originally announced January 2019.

Measurement of transverse wakefields induced by a misaligned positron bunch in a hollow channel plasma accelerator

Authors: C. A. Lindstrøm, E. Adli, J. M. Allen, W. An, C. Beekman, C. I. Clarke, C. E. Clayton, S. Corde, A. Doche, J. Frederico, S. J. Gessner, S. Z. Green, M. J. Hogan, C. Joshi, M. Litos, W. Lu, K. A. Marsh, W. B. Mori, B. D. O'Shea, N. Vafaei-Najafabadi, V. Yakimenko

Abstract: Hollow channel plasma wakefield acceleration is a proposed method to provide high acceleration gradients for electrons and positrons alike: a key to future lepton colliders. However, beams which are misaligned from the channel axis induce strong transverse wakefields, deflecting beams and reducing the collider luminosity. This undesirable consequence sets a tight constraint on the alignment accura… ▽ More Hollow channel plasma wakefield acceleration is a proposed method to provide high acceleration gradients for electrons and positrons alike: a key to future lepton colliders. However, beams which are misaligned from the channel axis induce strong transverse wakefields, deflecting beams and reducing the collider luminosity. This undesirable consequence sets a tight constraint on the alignment accuracy of the beam propagating through the channel. Direct measurements of beam misalignment-induced transverse wakefields are therefore essential for designing mitigation strategies. We present the first quantitative measurements of transverse wakefields in a hollow plasma channel, induced by an off-axis 20 GeV positron bunch, and measured with another 20 GeV lower charge trailing positron probe bunch. The measurements are largely consistent with theory. △ Less

Submitted 25 February, 2018; originally announced February 2018.

Comments: 5 pages, 4 figures. Submitted to Physical Review Letters

Journal ref: Phys. Rev. Lett. 120, 124802 (2018)

Perfect Diffraction with Bianisotropic Metagratings

Authors: Zhiyuan Fan, Maxim R. Shcherbakov, Monica Allen, Jeffery Allen, Gennady Shvets

Abstract: One highly desirable function of a diffraction grating is its ability to deflect incident light into a specific diffraction order with near-perfect efficiency. While such asymmetry can be achieved in a variety of ways, e.g., by using a sawtooth (blazed) geometry, a recently emerged approach is to use a planar metagrating comprised of designer multi-resonant periodic units (metamolecules). Here we… ▽ More One highly desirable function of a diffraction grating is its ability to deflect incident light into a specific diffraction order with near-perfect efficiency. While such asymmetry can be achieved in a variety of ways, e.g., by using a sawtooth (blazed) geometry, a recently emerged approach is to use a planar metagrating comprised of designer multi-resonant periodic units (metamolecules). Here we demonstrate that a bianisotropic unit cell supporting four resonances interfering in the far field can be used as a building block for achieving the prefect deflection. A coupled mode analysis shows that these modes provide a small number of orthogonal electromagnetic radiation patterns that are needed to suppress transmission/reflection into all but one diffraction order. Bianisotropy caused by a mirror symmetry breaking enables a normally incident wave to excite, through near-field couplings, two otherwise "dark" resonant modes. We design and experimentally realize bianisotropic metamolecules which are sub-wavelength in all three dimensions, and whose optical properties are desensitized to fabrication imperfections by their geometric simplicity. We show that optical beams tightly focused onto the metagratings with just a few unit cells can also be asymmetrically deflected with high efficiency, paving the way for compact broadband optical devices. △ Less

Submitted 5 February, 2018; originally announced February 2018.

Comments: 18 pages, 4 figures

Gamma-ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders

Authors: R. U. Abbasi, T. Abu-Zayyad, M. Allen, E. Barcikowski, J. W. Belz, D. R. Bergman, S. A. Blake, M. Byrne, R. Cady, B. G. Cheon, J. Chiba, M. Chikawa, T. Fujii, M. Fukushima, G. Furlich, T. Goto, W. Hanlon, Y. Hayashi, N. Hayashida, K. Hibino, K. Honda, D. Ikeda, N. Inoue, T. Ishii, H. Ito , et al. (99 additional authors not shown)

Abstract: Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700~square kilometer cosmic ray observatory located in southwestern Utah, U.S.A. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-pro… ▽ More Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700~square kilometer cosmic ray observatory located in southwestern Utah, U.S.A. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-producing flashes were obtained with a 3D lightning mapping array, and electric field change measurements were obtained for an additional seven flashes, in both cases co-located with the TASD. National Lightning Detection Network (NLDN) information was also used throughout. The showers arrived in a sequence of 2--5 short-duration ($\le$10~$μ$s) bursts over time intervals of several hundred microseconds, and originated at an altitude of $\simeq$3--5 kilometers above ground level during the first 1--2 ms of downward negative leader breakdown at the beginning of cloud-to-ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward-beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of $\simeq$$10^{12}$--$10^{14}$ photons for $16^{\circ}$ half-angle beams. We conclude that the showers are terrestrial gamma-ray flashes (TGFs), similar to those observed by satellites, but that the ground-based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful TGFs. △ Less

Submitted 18 May, 2018; v1 submitted 17 May, 2017; originally announced May 2017.

Journal ref: J. Geophys. Res. Atmos., 123 (2018)

Molecular simulations of entangled defect structures around nanoparticles in nematic liquid crystals

Authors: Anja Humpert, Samuel F. Brown, Michael P. Allen

Abstract: We investigate the defect structures forming around two nanoparticles in a Gay-Berne nematic liquid crystal using molecular simulations. For small separations, disclinations entangle both particles forming the figure of eight, the figure of omega and the figure of theta. These defect structures are similar in shape and occur with a comparable frequency to micron-sized particles studied in experime… ▽ More We investigate the defect structures forming around two nanoparticles in a Gay-Berne nematic liquid crystal using molecular simulations. For small separations, disclinations entangle both particles forming the figure of eight, the figure of omega and the figure of theta. These defect structures are similar in shape and occur with a comparable frequency to micron-sized particles studied in experiments. The simulations reveal fast transitions from one defect structure to another suggesting that particles of nanometre size cannot be bound together effectively. We identify the 'three-ring' structure observed in previous molecular simulations as a superposition of the different entangled and non-entangled states over time and conclude that it is not itself a stable defect structure. △ Less

Submitted 9 February, 2017; originally announced February 2017.

Comments: keywords: molecular-simulation, defects, nematic, disclination, algorithmic classification ; 8 pages, 7 figures, 1 table

9 GeV Energy Gain in a Beam-Driven Plasma Wakefield Accelerator

Authors: M Litos, E Adli, J M Allen, W An, C I Clarke, S Corde, C E Clayton, J Frederico, S J Gessner, S Z Green, M J Hogan, C Joshi, W. Lu, K A Marsh, W B Mori, M Schmeltz, N Vafaei-Najafabadi, V Yakimenko

Abstract: An electron beam has gained a maximum energy of 9 GeV per particle in a 1.3 m-long electron beam-driven plasma wakefield accelerator. The amount of charge accelerated in the spectral peak was 28.3 pC, and the root-mean-square energy spread was 5.0%. The mean accelerated charge and energy gain per particle of the 215 shot data set was 115 pC and 5.3 GeV, respectively, corresponding to an accelerati… ▽ More An electron beam has gained a maximum energy of 9 GeV per particle in a 1.3 m-long electron beam-driven plasma wakefield accelerator. The amount of charge accelerated in the spectral peak was 28.3 pC, and the root-mean-square energy spread was 5.0%. The mean accelerated charge and energy gain per particle of the 215 shot data set was 115 pC and 5.3 GeV, respectively, corresponding to an acceleration gradient of 4.0 GeV/m at the spectral peak. The mean energy spread of the data set was 5.1%. These results are consistent with the extrapolation of the previously reported energy gain results using a shorter, 36 cm-long plasma source to within 10%, evincing a non-evolving wake structure that can propagate distances of over a meter in length. Wake-loading effects were evident in the data through strong dependencies observed between various spectral properties and the amount of accelerated charge. △ Less

Submitted 20 November, 2015; originally announced November 2015.

Comments: 11 pages, 3 figures, Laser and Plasma Accelerators Workshop (LPAW) 2015 Proceedings

Gyromagnetically Induced Transparency of Meta-Surfaces

Authors: S. Hossein Mousavi, Alexander B. Khanikaev, Jeffery Allen, Monica Allen, Gennady Shvets

Abstract: We demonstrate that the violation of the time-reversal (TR) symmetry in the presence of a gyromagnetic substrate can produce an analog of electromagnetically induced transparency in metallic meta-molecules. The simplest implementation of such gyromagnetically induced transparency (GIT) in a meta-surface comprised of an array of resonant antenna pairs placed on a gyromagnetic substrate and illumina… ▽ More We demonstrate that the violation of the time-reversal (TR) symmetry in the presence of a gyromagnetic substrate can produce an analog of electromagnetically induced transparency in metallic meta-molecules. The simplest implementation of such gyromagnetically induced transparency (GIT) in a meta-surface comprised of an array of resonant antenna pairs placed on a gyromagnetic substrate and illuminated by a normally incident electromagnetic wave is analyzed. TR symmetry breaking introduced by the magnetic field makes meta-molecules bi-anisotropic and causes spectrally-sharp Fano interference between the otherwise uncoupled electric and magnetic dipolar resonances of the meta-molecules. The applied magnetic field results in a sharp transmission peak through the otherwise reflective meta-surface. We show that, for oblique wave incidence, one-way GIT can be achieved by the combination of spatial dispersion and TR symmetry breaking. These theoretically predicted phenomena pave the way to non-reciprocal switches and isolators that can be dynamically controlled by electric currents. △ Less

Submitted 31 May, 2014; v1 submitted 15 November, 2013; originally announced November 2013.

Comments: 9 pages, 5 figures

Journal ref: Phys. Rev. Lett. 112, 117402 (2014)

Dynamics of ions in the selectivity filter of the KcsA channel: Towards a coupled Brownian particle description

Authors: Salvatore M. Cosseddu, Igor A. Khovanov, Michael P. Allen, P. M. Rodger, Dmitry G. Luchinsky, Peter V. E. McClintock

Abstract: The statistical and dynamical properties of ions in the selectivity filter of the KcsA ion channel are considered on the basis of molecular dynamics (MD) simulations of the KcsA protein embedded in a lipid membrane surrounded by an ionic solution. A new approach to the derivation of a Brownian dynamics (BD) model of ion permeation through the filter is discussed, based on unbiased MD simulations.… ▽ More The statistical and dynamical properties of ions in the selectivity filter of the KcsA ion channel are considered on the basis of molecular dynamics (MD) simulations of the KcsA protein embedded in a lipid membrane surrounded by an ionic solution. A new approach to the derivation of a Brownian dynamics (BD) model of ion permeation through the filter is discussed, based on unbiased MD simulations. It is shown that depending on additional assumptions, ion's dynamics can be described either by under-damped Langevin equation with constant damping and white noise or by Langevin equation with a fractional memory kernel. A comparison of the potential of the mean force derived from unbiased MD simulations with the potential produced by the umbrella sampling method demonstrates significant differences in these potentials. The origin of these differences is an open question that requires further clarifications. △ Less

Submitted 31 July, 2013; originally announced July 2013.

Comments: to appear in Eur. Phys. J. Spec. Top

Journal ref: Eur. Phys. J. Spec. Top 222, 2595-2605 (2013)

Surrogate Parenthood: Protected and Informative Graphs

Authors: Barbara Blaustein, Adriane Chapman, Len Seligman, M. David Allen, Arnon Rosenthal

Abstract: Many applications, including provenance and some analyses of social networks, require path-based queries over graph-structured data. When these graphs contain sensitive information, paths may be broken, resulting in uninformative query results. This paper presents innovative techniques that give users more informative graph query results; the techniques leverage a common industry practice of provi… ▽ More Many applications, including provenance and some analyses of social networks, require path-based queries over graph-structured data. When these graphs contain sensitive information, paths may be broken, resulting in uninformative query results. This paper presents innovative techniques that give users more informative graph query results; the techniques leverage a common industry practice of providing what we call surrogates: alternate, less sensitive versions of nodes and edges releasable to a broader community. We describe techniques for interposing surrogate nodes and edges to protect sensitive graph components, while maximizing graph connectivity and giving users as much information as possible. In this work, we formalize the problem of creating a protected account G' of a graph G. We provide a utility measure to compare the informativeness of alternate protected accounts and an opacity measure for protected accounts, which indicates the likelihood that an attacker can recreate the topology of the original graph from the protected account. We provide an algorithm to create a maximally useful protected account of a sensitive graph, and show through evaluation with the PLUS prototype that using surrogates and protected accounts adds value for the user, with no significant impact on the time required to generate results for graph queries. △ Less

Submitted 17 June, 2011; originally announced June 2011.

Comments: VLDB2011

The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

Authors: G0 Collaboration, D. Androic, D. S. Armstrong, J. Arvieux, R. Asaturyan, T. D. Averett, S. L. Bailey, G. Batigne, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, J. Birchall, A. Biselli, P. Bosted, H. Breuer, P. Brindza, C. L. Capuano, R. D. Carlini, R. Carr, N. Chant, Y. -C. Chao, R. Clark, A. Coppens , et al. (105 additional authors not shown)

Abstract: In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized bea… ▽ More In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed. △ Less

Submitted 3 March, 2011; originally announced March 2011.

Comments: Submitted to Nuclear Instruments and Methods

Journal ref: Nucl. Instrum. Methods A 646 (2011)59

Objective Climate Model Predictions Using Jeffreys' Prior: the General Multivariate Normal Case

Authors: Stephen Jewson, Dan Rowlands, Myles Allen

Abstract: Objective probabilistic forecasts of future climate that include parameter uncertainty can be made by using the Bayesian prediction integral with the prior set to Jeffreys' Prior. The calculations involved in determining the prior can then be simplified by making parametric assumptions about the distribution of the output from the climate model. The most obvious assumption to make is that the clim… ▽ More Objective probabilistic forecasts of future climate that include parameter uncertainty can be made by using the Bayesian prediction integral with the prior set to Jeffreys' Prior. The calculations involved in determining the prior can then be simplified by making parametric assumptions about the distribution of the output from the climate model. The most obvious assumption to make is that the climate model output is normally distributed, in which case evaluating the prior becomes a question of evaluating gradients in the parameters of the normal distribution. In previous work we have considered the special cases of diagonal (but not constant) covariance matrix, and constant (but not diagonal) covariance matrix. We now derive expressions for the general multivariate normal distribution, with non-constant non-diagonal covariance matrix. The algebraic manipulation required is more complex than for the special cases, and involves some slightly esoteric matrix operations including taking the expectation of a vector quadratic form and differentiating the determinants, traces and inverses of matrices. △ Less

Submitted 21 May, 2010; originally announced May 2010.