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Interfacial chirality-induced magnetic-field-free switching with high energy efficiency in all-vdW heterostructures
Authors:
Kai-Xuan Zhang,
Suik Cheon,
Seungbok Lee,
Joonyoung Choi,
Jihoon Keum,
Hyuncheol Kim,
Yeochan An,
Woonghee Cho,
Suhan Son,
Jingyuan Cui,
Pyeongjae Park,
Younjung Jo,
Jun Sung Kim,
Hyun-Woo Lee,
Je-Geun Park
Abstract:
Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral…
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Chirality, a central concept across many scientific disciplines, continues to inspire the discovery of novel physical phenomena. In condensed matter physics, structural chirality - defined by the absence of mirror plane symmetries - has primarily been explored in bulk materials. However, new chiral phenomena can emerge uniquely at the interface, distinct from their bulk counterparts, when a chiral material forms a heterostructure. Here, we demonstrate that all van-der-Waals (vdW) heterostructure composed of the chiral Co1/3TaS2 and the achiral vdW ferromagnet Fe3GeTe2 exhibits two distinct and unconventional spin-orbit torques originating from the interfacial chirality. These torques enable magnetic-field-free switching of perpendicular magnetization with ultralow current density ~ 10^6 A/cm^2 and minimal power dissipation < 10^15 W/m^3. Moreover, by replacing Fe3GeTe2 with a similar vdW ferromagnet, Fe3GaTe2, but of higher Curie temperature, we achieved the magnetic-field-free switching at room temperature in the Fe3GaTe2/Co1/3TaS2 vdW heterostructure. Our findings establish interfacial chirality as a powerful new handle for spintronic control, opening a new pathway to explore chirality-induced phenomena beyond the bulk symmetry constraints - and paving the way toward highly efficient, low-power spintronic devices based on all-vdW heterostructures.
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Submitted 8 July, 2026;
originally announced July 2026.
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Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface
Authors:
S. Hadi Badri,
Sanam Saeidnahaei,
Jong Su Kim
Abstract:
A thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of the VO2. For y-polarized incident f…
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A thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of the VO2. For y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO2. For x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO2, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch.
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Submitted 11 May, 2026;
originally announced May 2026.
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High-Q Fano resonance in all-dielectric metasurfaces for molecular fingerprint detection
Authors:
S. Hadi Badri,
M. M. Gilarlue,
Sanam Saeidnahaei,
Jong Su Kim
Abstract:
We present and numerically investigate a high-quality factor (high-Q) meta-atom with Fano resonance. Numerical simulations indicate that the designed meta-atom has a single sharp Fano resonance in the 1350-1750 1/cm range. Moreover, the frequency of the single resonance can be tuned in this frequency range by scaling the meta-atom. We exploit these properties to design a pixelated metasurface for…
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We present and numerically investigate a high-quality factor (high-Q) meta-atom with Fano resonance. Numerical simulations indicate that the designed meta-atom has a single sharp Fano resonance in the 1350-1750 1/cm range. Moreover, the frequency of the single resonance can be tuned in this frequency range by scaling the meta-atom. We exploit these properties to design a pixelated metasurface for spectrometer-less molecular fingerprint retrieval. The proposed meta-atom with an average quality factor of 2000 makes it possible to decrease the scaling step of metapixels without introducing any resonance overlap between the metapixels leading to higher precision in label-free and non-destructive identification of the molecular fingerprints.
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Submitted 8 May, 2026;
originally announced May 2026.
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Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material
Authors:
S. Hadi Badri,
M. M. Gilarlue,
Sanam SaeidNahaei,
Jong Su Kim
Abstract:
A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a reso…
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A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground-plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the insulator phase of VO2, the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon insulator-to-metal transition of VO2, the metasurface achieves a broadband absorption with the FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase-transition of VO2, we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to symmetry and works well for a very wide range of incident angles. In the metallic state of VO2, the absorber has an absorption exceeding 0.5 in the 3.57-8.45 THz frequency range with incident angles up to 65°.
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Submitted 7 May, 2026;
originally announced May 2026.
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Parallel-plate chambers as radiation-hard detectors for time-based beam diagnostics in carbon-ion radiotherapy
Authors:
Na Hye Kwon,
Sung Woon Choi,
Soo Rim Han,
Yongdo Yun,
Min Cheol Han,
Chae-Seon Hong,
Ho Jin Kim,
Ho Lee,
Changhwan Kim,
Do Won Kim,
Woong Sub Koom,
Jin Sung Kim,
N. Carolino,
L. Lopes,
Dong Wook Kim,
Paulo J. R. Fonte
Abstract:
Accurate range verification of carbon ion beams is critical for the precision and safety of charged particle radiotherapy. In this study, we evaluated the feasibility of using a parallel-plate ionization chamber for real-time, time-based diagnostic monitoring of carbon ion beams. The chamber featured a 0.4 mm gas gap defined by metallic electrodes and was filled with carbon dioxide (CO$_2$), a non…
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Accurate range verification of carbon ion beams is critical for the precision and safety of charged particle radiotherapy. In this study, we evaluated the feasibility of using a parallel-plate ionization chamber for real-time, time-based diagnostic monitoring of carbon ion beams. The chamber featured a 0.4 mm gas gap defined by metallic electrodes and was filled with carbon dioxide (CO$_2$), a non-polymerizing gas suitable for high-rate applications. Timing precision was assessed via self-correlation analysis, yielding a precision approaching one picosecond for one-second acquisitions under clinically relevant beam conditions. This level of timing accuracy translates to a water-equivalent range uncertainty of approximately 1 mm, which meets the recommended clinical tolerance for carbon ion therapy. Furthermore, the kinetic energy of the beam at the synchrotron extraction point was determined from the measured orbital period, with results consistently within 1 MeV/nucleon of the nominal energy. These findings demonstrate the potential of parallel-plate chambers for precise, real-time energy and range verification in clinical carbon ion beam quality assurance.
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Submitted 16 July, 2025;
originally announced July 2025.
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Operation of the Trigger System for the ICARUS Detector at Fermilab
Authors:
ICARUS collaboration,
F. Abd Alrahman,
P. Abratenko,
N. Abrego-Martinez,
A. Aduszkiewicz,
F. Akbar,
L. Aliaga Soplin,
M. Artero Pons,
J. Asaadi,
W. F. Badgett,
B. Baibussinov,
F. Battisti,
V. Bellini,
R. Benocci,
J. Berger,
S. Berkman,
S. Bertolucci,
M. Betancourt,
A. Blanchet,
F. Boffelli,
M. Bonesini,
T. Boone,
B. Bottino,
A. Braggiotti,
D. Brailsford
, et al. (164 additional authors not shown)
Abstract:
The ICARUS liquid argon TPC detector is taking data on the Booster (BNB) and Main Injector (NuMI) Neutrino beam lines at Fermilab with a trigger system based on the scintillation light produced by charged particles in coincidence with the proton beam extraction from the accelerators. The architecture and the deployment of the trigger system in the first two runs for physics are presented, as well…
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The ICARUS liquid argon TPC detector is taking data on the Booster (BNB) and Main Injector (NuMI) Neutrino beam lines at Fermilab with a trigger system based on the scintillation light produced by charged particles in coincidence with the proton beam extraction from the accelerators. The architecture and the deployment of the trigger system in the first two runs for physics are presented, as well as the triggered event rates. The event recognition efficiency has been evaluated as a function of the deposited energy and the position of cosmic muons stopping inside the detector.
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Submitted 5 August, 2025; v1 submitted 25 June, 2025;
originally announced June 2025.
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Electron Fourier ptychography for phase reconstruction
Authors:
Jingjing Zhao,
Chen Huang,
Ali Mostaed,
Amirafshar Moshtaghpour,
James M. Parkhurst,
Ivan Lobato,
Marcus Gallagher-Jones,
Judy S. Kim,
Mark Boyce,
David Stuart,
Elena A. Andreeva,
Jacques-Philippe Colletier,
Angus I. Kirkland
Abstract:
Phase reconstruction is important in transmission electron microscopy for structural studies. We describe electron Fourier ptychography and its application to phase reconstruction of both radiation-resistant and beam-sensitive materials. We demonstrate that the phase of the exit wave can be reconstructed to high resolution using a modified iterative phase retrieval algorithm using data collected i…
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Phase reconstruction is important in transmission electron microscopy for structural studies. We describe electron Fourier ptychography and its application to phase reconstruction of both radiation-resistant and beam-sensitive materials. We demonstrate that the phase of the exit wave can be reconstructed to high resolution using a modified iterative phase retrieval algorithm using data collected in an alternative optical geometry. This method achieves a spatial resolution of 0.63 nm at a fluence of $4.5 \times 10^2 \, e^-/\text{nm}^2$, as validated on Cry11Aa protein crystals under cryogenic conditions. Notably, this method requires no additional hardware modifications, is straightforward to implement, and can be seamlessly integrated with existing data collection software, providing a broadly accessible alternative approach to structural studies.
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Submitted 1 September, 2025; v1 submitted 12 February, 2025;
originally announced February 2025.
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Angular dependent measurement of electron-ion recombination in liquid argon for ionization calorimetry in the ICARUS liquid argon time projection chamber
Authors:
ICARUS collaboration,
P. Abratenko,
N. Abrego-Martinez,
A. Aduszkiewic,
F. Akbar,
L. Aliaga Soplin,
M. Artero Pons,
J. Asaadi,
W. F. Badgett,
B. Baibussinov,
B. Behera,
V. Bellini,
R. Benocci,
J. Berger,
S. Berkman,
S. Bertolucci,
M. Betancourt,
M. Bonesini,
T. Boone,
B. Bottino,
A. Braggiotti,
D. Brailsford,
S. J. Brice,
V. Brio,
C. Brizzolari
, et al. (156 additional authors not shown)
Abstract:
This paper reports on a measurement of electron-ion recombination in liquid argon in the ICARUS liquid argon time projection chamber (LArTPC). A clear dependence of recombination on the angle of the ionizing particle track relative to the drift electric field is observed. An ellipsoid modified box (EMB) model of recombination describes the data across all measured angles. These measurements are us…
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This paper reports on a measurement of electron-ion recombination in liquid argon in the ICARUS liquid argon time projection chamber (LArTPC). A clear dependence of recombination on the angle of the ionizing particle track relative to the drift electric field is observed. An ellipsoid modified box (EMB) model of recombination describes the data across all measured angles. These measurements are used for the calorimetric energy scale calibration of the ICARUS TPC, which is also presented. The impact of the EMB model is studied on calorimetric particle identification, as well as muon and proton energy measurements. Accounting for the angular dependence in EMB recombination improves the accuracy and precision of these measurements.
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Submitted 9 August, 2024; v1 submitted 17 July, 2024;
originally announced July 2024.
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Calibration and simulation of ionization signal and electronics noise in the ICARUS liquid argon time projection chamber
Authors:
ICARUS collaboration,
P. Abratenko,
N. Abrego-Martinez,
A. Aduszkiewic,
F. Akbar,
L. Aliaga Soplin,
M. Artero Pons,
J. Asaadi,
W. F. Badgett,
B. Baibussinov,
B. Behera,
V. Bellini,
R. Benocci,
J. Berger,
S. Berkman,
S. Bertolucci,
M. Betancourt,
M. Bonesini,
T. Boone,
B. Bottino,
A. Braggiotti,
D. Brailsford,
S. J. Brice,
V. Brio,
C. Brizzolari
, et al. (156 additional authors not shown)
Abstract:
The ICARUS liquid argon time projection chamber (LArTPC) neutrino detector has been taking physics data since 2022 as part of the Short-Baseline Neutrino (SBN) Program. This paper details the equalization of the response to charge in the ICARUS time projection chamber (TPC), as well as data-driven tuning of the simulation of ionization charge signals and electronics noise. The equalization procedu…
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The ICARUS liquid argon time projection chamber (LArTPC) neutrino detector has been taking physics data since 2022 as part of the Short-Baseline Neutrino (SBN) Program. This paper details the equalization of the response to charge in the ICARUS time projection chamber (TPC), as well as data-driven tuning of the simulation of ionization charge signals and electronics noise. The equalization procedure removes non-uniformities in the ICARUS TPC response to charge in space and time. This work leverages the copious number of cosmic ray muons available to ICARUS at the surface. The ionization signal shape simulation applies a novel procedure that tunes the simulation to match what is measured in data. The end result of the equalization procedure and simulation tuning allows for a comparison of charge measurements in ICARUS between Monte Carlo simulation and data, showing good performance with minimal residual bias between the two.
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Submitted 5 August, 2024; v1 submitted 16 July, 2024;
originally announced July 2024.
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Multi-Convergence-Angle Ptychography with Simultaneous Strong Contrast and High Resolution
Authors:
Wei Mao,
Weiyang Zhang,
Chen Huang,
Liqi Zhou,
Judy. S. Kim,
Si Gao,
Yu Lei,
Xiaopeng Wu,
Yiming Hu,
Xudong Pei,
Weina Fang,
Xiaoguo Liu,
Jingdong Song,
Chunhai Fan,
Yuefeng Nie,
Angus. I. Kirkland,
Peng Wang
Abstract:
Advances in bioimaging methods and hardware facilities have revolutionised the determination of numerous biological structures at atomic or near-atomic resolution. Among these developments, electron ptychography has recently attracted considerable attention because of its superior resolution, remarkable sensitivity to light elements, and high electron dose efficiency. Here, we introduce an innovat…
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Advances in bioimaging methods and hardware facilities have revolutionised the determination of numerous biological structures at atomic or near-atomic resolution. Among these developments, electron ptychography has recently attracted considerable attention because of its superior resolution, remarkable sensitivity to light elements, and high electron dose efficiency. Here, we introduce an innovative approach called multi-convergence-angle (MCA) ptychography, which can simultaneously enhance both contrast and resolution with continuous information transfer across a wide spectrum of spatial frequency. Our work provides feasibility of future applications of MCA-ptychography in providing high-quality two-dimensional images as input to three-dimensional reconstruction methods, thereby facilitating more accurate determination of biological structures.
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Submitted 25 March, 2024;
originally announced March 2024.
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Optical Fiber-Based Needle Shape Sensing in Real Tissue: Single Core vs. Multicore Approaches
Authors:
Dimitri A. Lezcano,
Yernar Zhetpissov,
Alexandra Cheng,
Jin Seob Kim,
Iulian I. Iordachita
Abstract:
Flexible needle insertion procedures are common for minimally-invasive surgeries for diagnosing and treating prostate cancer. Bevel-tip needles provide physicians the capability to steer the needle during long insertions to avoid vital anatomical structures in the patient and reduce post-operative patient discomfort. To provide needle placement feedback to the physician, sensors are embedded into…
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Flexible needle insertion procedures are common for minimally-invasive surgeries for diagnosing and treating prostate cancer. Bevel-tip needles provide physicians the capability to steer the needle during long insertions to avoid vital anatomical structures in the patient and reduce post-operative patient discomfort. To provide needle placement feedback to the physician, sensors are embedded into needles for determining the real-time 3D shape of the needle during operation without needing to visualize the needle intra-operatively. Through expansive research in fiber optics, a plethora of bio-compatible, MRI-compatible, optical shape-sensors have been developed to provide real-time shape feedback, such as single-core and multicore fiber Bragg gratings. In this paper, we directly compare single-core fiber-based and multicore fiber-based needle shape-sensing through identically constructed, four-active area sensorized bevel-tip needles inserted into phantom and \exvivo tissue on the same experimental platform. In this work, we found that for shape-sensing in phantom tissue, the two needles performed identically with a $p$-value of $0.164 > 0.05$, but in \exvivo real tissue, the single-core fiber sensorized needle significantly outperformed the multicore fiber configuration with a $p$-value of $0.0005 < 0.05$. This paper also presents the experimental platform and method for directly comparing these optical shape sensors for the needle shape-sensing task, as well as provides direction, insight and required considerations for future work in constructively optimizing sensorized needles.
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Submitted 8 September, 2023;
originally announced September 2023.
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Allying nanophotonic structures with two-dimensional van der Waals materials
Authors:
Yuan Meng,
Hongkun Zhong,
Zhihao Xu,
Tiantian He,
Justin S. Kim,
Sangmoon Han,
Yijie Shen,
Mali Gong,
Sang-Hoon Bae,
Qirong Xiao
Abstract:
The integration of two-dimensional (2D) materials with photonic structures has catalyzed a wide spectrum of optical and optoelectronic applications. Conventional nanophotonic structures generally lack efficient reconfigurability and multifunctionality. The atomically thin 2D van der Waals materials can thus infuse new functionality and reconfigurability to the well-established library of photonic…
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The integration of two-dimensional (2D) materials with photonic structures has catalyzed a wide spectrum of optical and optoelectronic applications. Conventional nanophotonic structures generally lack efficient reconfigurability and multifunctionality. The atomically thin 2D van der Waals materials can thus infuse new functionality and reconfigurability to the well-established library of photonic structures such as integrated waveguides, optical fibers, photonic crystals, micro-cavities, and metasurface, to name a few. Thanks to the handiness of van der Waals interfaces, the 2D materials can be easily transferred and mixed with other prefabricated photonic templates with high degrees of freedom, and can act as the optical gain, modulation, sensing, or plasmonic media for diverse applications. Here we review recent advents on combining 2D materials to nanophotonic structures for new functionality development or performance enhancements. Challenges and emerging opportunities in integrating van der Waals building blocks beyond 2D materials are also discussed.
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Submitted 12 May, 2023;
originally announced May 2023.
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COVIDHunter: COVID-19 pandemic wave prediction and mitigation via seasonality-aware modeling
Authors:
Mohammed Alser,
Jeremie S. Kim,
Nour Almadhoun Alserr,
Stefan W. Tell,
Onur Mutlu
Abstract:
Early detection and isolation of COVID-19 patients are essential for successful implementation of mitigation strategies and eventually curbing the disease spread. With a limited number of daily COVID-19 tests performed in every country, simulating the COVID-19 spread along with the potential effect of each mitigation strategy currently remains one of the most effective ways in managing the healthc…
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Early detection and isolation of COVID-19 patients are essential for successful implementation of mitigation strategies and eventually curbing the disease spread. With a limited number of daily COVID-19 tests performed in every country, simulating the COVID-19 spread along with the potential effect of each mitigation strategy currently remains one of the most effective ways in managing the healthcare system and guiding policy-makers. We introduce COVIDHunter, a flexible and accurate COVID-19 outbreak simulation model that evaluates the current mitigation measures that are applied to a region, predicts COVID-19 statistics (the daily number of cases, hospitalizations, and deaths), and provides suggestions on what strength the upcoming mitigation measure should be. The key idea of COVIDHunter is to quantify the spread of COVID-19 in a geographical region by simulating the average number of new infections caused by an infected person considering the effect of external factors, such as environmental conditions (e.g., climate, temperature, humidity), different variants of concern, vaccination rate, and mitigation measures. Using Switzerland as a case study, COVIDHunter estimates that we are experiencing a deadly new wave that will peak on 26 January 2022, which is very similar in numbers to the wave we had in February 2020. The policy-makers have only one choice that is to increase the strength of the currently applied mitigation measures for 30 days. Unlike existing models, the COVIDHunter model accurately monitors and predicts the daily number of cases, hospitalizations, and deaths due to COVID-19. Our model is flexible to configure and simple to modify for modeling different scenarios under different environmental conditions and mitigation measures. We release the source code of the COVIDHunter implementation at https://github.com/CMU-SAFARI/COVIDHunter.
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Submitted 14 June, 2022;
originally announced June 2022.
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Abdominal synthetic CT reconstruction with intensity projection prior for MRI-only adaptive radiotherapy
Authors:
Sven Olberg,
Jaehee Chun,
Byong Su Choi,
Inkyung Park,
Hyun Kim,
Taeho Kim,
Jin Sung Kim,
Olga Green,
Justin C. Park
Abstract:
An MRI-only adaptive radiotherapy (ART) workflow is desirable for managing interfractional changes in anatomy, but producing synthetic CT (sCT) data through paired data-driven deep learning (DL) for abdominal dose calculations remains a challenge due to the highly variable presence of intestinal gas. We present the preliminary dosimetric evaluation of our novel approach to sCT reconstruction that…
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An MRI-only adaptive radiotherapy (ART) workflow is desirable for managing interfractional changes in anatomy, but producing synthetic CT (sCT) data through paired data-driven deep learning (DL) for abdominal dose calculations remains a challenge due to the highly variable presence of intestinal gas. We present the preliminary dosimetric evaluation of our novel approach to sCT reconstruction that is well suited to handling intestinal gas in abdominal MRI-only ART.
We utilize a paired data DL approach enabled by the intensity projection prior, in which well-matching training pairs are created by propagating air from MRI to corresponding CT scans. Evaluations focus on two classes: patients with (1) little involvement of intestinal gas, and (2) notable differences in intestinal gas presence between corresponding scans. Comparisons between sCT-based plans and CT-based clinical plans for both classes are made at the first treatment fraction to highlight the dosimetric impact of the variable presence of intestinal gas.
Class 1 patients ($n=13$) demonstrate differences in prescribed dose coverage of the PTV of $1.3 \pm 2.1\%$ between clinical plans and sCT-based plans. Mean DVH differences in all structures for Class 1 patients are found to be statistically insignificant. In Class 2 ($n=20$), target coverage is $13.3 \pm 11.0\%$ higher in the clinical plans and mean DVH differences are found to be statistically significant.
Significant deviations in calculated doses arising from the variable presence of intestinal gas in corresponding CT and MRI scans may limit the effectiveness of adaptive dose escalation efforts. We have proposed a paired data-driven DL approach to sCT reconstruction for accurate dose calculations in abdominal ART enabled by the creation of a clinically unavailable training data set with well-matching representations of intestinal gas.
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Submitted 2 July, 2021;
originally announced July 2021.
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Continuous body 3-D reconstruction of limbless animals
Authors:
Qiyuan Fu,
Thomas W. Mitchel,
Jin Seob Kim,
Gregory S. Chirikjian,
Chen Li
Abstract:
Limbless animals such as snakes, limbless lizards, worms, eels, and lampreys move their slender, long bodies in three dimensions to traverse diverse environments. Accurately quantifying their continuous body's 3-D shape and motion is important for understanding body-environment interactions in complex terrain, but this is difficult to achieve (especially for local orientation and rotation). Here,…
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Limbless animals such as snakes, limbless lizards, worms, eels, and lampreys move their slender, long bodies in three dimensions to traverse diverse environments. Accurately quantifying their continuous body's 3-D shape and motion is important for understanding body-environment interactions in complex terrain, but this is difficult to achieve (especially for local orientation and rotation). Here, we describe an interpolation method to quantify continuous body 3-D position and orientation. We simplify the body as an elastic rod and apply a backbone optimization method to interpolate continuous body shape between end constraints imposed by tracked markers. Despite over-simplifying the biomechanics, our method achieves a higher interpolation accuracy (~50% error) in both 3-D position and orientation compared with the widely-used cubic B-spline interpolation method. Beyond snakes traversing large obstacles as demonstrated, our method applies to other long, slender, limbless animals and continuum robots. We provide codes and demo files for easy application of our method.
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Submitted 11 October, 2025; v1 submitted 8 March, 2021;
originally announced March 2021.
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Carrier Multiplication via Photocurrent Measurements in Dual-Gated MoTe_2
Authors:
Jun Suk Kim,
Minh Dao Tran,
Sung-Tae Kim,
Daehan Yoo,
Sang-Hyun Oh,
Ji-Hee Kim,
Young Hee Lee
Abstract:
Although van der Waals layered transition metal dichalcogenides from transient absorption spectroscopy have successfully demonstrated an ideal carrier multiplication (CM) performance with an onset of nearly 2Eg,interpretation of the CM effect from the optical approach remains unresolved owing to the complexity of many-body electron-hole pairs. We demonstrate the CM effect through simple photocurre…
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Although van der Waals layered transition metal dichalcogenides from transient absorption spectroscopy have successfully demonstrated an ideal carrier multiplication (CM) performance with an onset of nearly 2Eg,interpretation of the CM effect from the optical approach remains unresolved owing to the complexity of many-body electron-hole pairs. We demonstrate the CM effect through simple photocurrent measurements by fabricating the dual-gate P-N junction of a MoTe2 film on a transparent substrate. Electrons and holes were efficiently extracted by eliminating the Schottky barriers in the metal contact and minimizing multiple reflections. The photocurrent was elevated proportionately to the excitation energy. The boosted quantum efficiency confirms the multiple electron-hole pair generation of >2Eg, consistent with CM results from an optical approach, pushing the solar cell efficiency beyond the Shockley-Queisser limit.
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Submitted 26 October, 2020;
originally announced October 2020.
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Band restructuring of ordered/disordered blue TiO2 for visible photocatalyst
Authors:
Simgeon Oh,
Ji-Hee Kim,
Hee Min Hwang,
Doyoung Kim,
Joosung Kim,
G. Hwan Park,
Joon Soo Kim,
Young Hee Lee,
Hyoyoung Lee
Abstract:
Black TiO2 with/without noble metal has been proposed for visible photocatalyst, still leaving poor catalyst efficiency. Alternatively, phase-mixed TiO2 such as anatase and rutile has been commonly used for visible catalysts with the inevitable inclusion of noble metal. Here, we perform a noble metal-free visible photocatalyst blue TiO2 with type-II band-aligned ordered anatase/disordered rutile s…
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Black TiO2 with/without noble metal has been proposed for visible photocatalyst, still leaving poor catalyst efficiency. Alternatively, phase-mixed TiO2 such as anatase and rutile has been commonly used for visible catalysts with the inevitable inclusion of noble metal. Here, we perform a noble metal-free visible photocatalyst blue TiO2 with type-II band-aligned ordered anatase/disordered rutile structure, via phase-selective reduction with alkali metals. The changed band alignment in this heterostructure was identified by absorption and ultraviolet photoemission spectroscopy, which was further confirmed by transient charge separation. The band alignment of type-I and type-II was clearly restructured by converting from ordered to disordered phase with a prolonged reduction period and as followed light absorbance enhancement also observed. Initiated type-I in a pristine sample, the type-II was organized from disordered rutile phase in 3-day Li-reduction. The type-II disordered rutile TiO2 heterostructure exhibits a remarkable photocatalytic performance by 55 times higher than conventional P25 TiO2 in solar-light driven hydrogen evolution reaction owing to an efficient electron and hole separation of type-II heterojunction. Furthermore, this restructured heterojunction type-II TiO2 demanded 10 times less Pt amount as a co-catalyst for the comparable photocatalytic performance, compared to Pt decorated type-I pristine anatase/rutile phase-mixed TiO2.
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Submitted 19 October, 2020;
originally announced October 2020.
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Antimony thin films demonstrate programmable optical non-linearity
Authors:
Zengguang Cheng,
Tara Milne,
Patrick Salter,
Judy S. Kim,
Samuel Humphrey,
Martin Booth,
Harish Bhaskaran
Abstract:
The use of metals of nanometer dimensions to enhance and manipulate light-matter interactions for a range of emerging plasmonics-enabled nanophotonic and optoelectronic applications is an interesting, yet not highly explored area of research outside of plasmonics1,2. Even more importantly, the concept of an active metal, i.e. a metal that can undergo an optical non-volatile transition has not been…
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The use of metals of nanometer dimensions to enhance and manipulate light-matter interactions for a range of emerging plasmonics-enabled nanophotonic and optoelectronic applications is an interesting, yet not highly explored area of research outside of plasmonics1,2. Even more importantly, the concept of an active metal, i.e. a metal that can undergo an optical non-volatile transition has not been explored. Nanostructure-based applications would have unprecedented impact on both the existing and future of optics with the development of active and nonlinear optical tunabilities in single elemental metals3-5. Compared to alloys, pure metals have the material simplicity and uniformity; however single elemental metals have not been viewed as tunable optical materials, although they have been explored as viable electrically switchable materials. In this paper we demonstrate for the first time that antimony (Sb), a pure metal, is optically distinguishable between two programmable states as nanoscale thin films. We then show that these states are stable at room temperature, and the states correspond to the crystalline and amorphous phases of the metal. Crucially from an application standpoint, we demonstrate both its optoelectronic modulation capabilities as well as speed of switching using single sub-picosecond (ps) pulses. The simplicity of depositing a single metal portends its potential for use in applications ranging from high speed active metamaterials to photonic neuromorphic computing, and opens up the possibility for its use in any optoelectronic application where metallic conductors with an actively tunable state is important.
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Submitted 20 August, 2020;
originally announced August 2020.
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Lateral oscillation and body compliance help snakes and snake robots stably traverse large, smooth obstacles
Authors:
Qiyuan Fu,
Sean W. Gart,
Thomas W. Mitchel,
Jin Seob Kim,
Gregory S. Chirikjian,
Chen Li
Abstract:
Snakes can move through almost any terrain. Similarly, snake robots hold the promise as a versatile platform to traverse complex environments like earthquake rubble. Unlike snake locomotion on flat surfaces which is inherently stable, when snakes traverse complex terrain by deforming their body out of plane, it becomes challenging to maintain stability. Here, we review our recent progress in under…
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Snakes can move through almost any terrain. Similarly, snake robots hold the promise as a versatile platform to traverse complex environments like earthquake rubble. Unlike snake locomotion on flat surfaces which is inherently stable, when snakes traverse complex terrain by deforming their body out of plane, it becomes challenging to maintain stability. Here, we review our recent progress in understanding how snakes and snake robots traverse large, smooth obstacles that lack anchor points for gripping or bracing. First, we discovered that the generalist variable kingsnake combines lateral oscillation and cantilevering. Regardless of step height and surface friction, the overall gait is preserved. Next, to quantify static stability of the snake, we developed a method to interpolate continuous body in three dimensions (both position and orientation) between discrete tracked markers. By analyzing the base of support using the interpolated continuous body 3-D kinematics, we discovered that the snake maintained perfect stability during traversal, even on the most challenging low friction, high step. Finally, we applied this gait to a snake robot and systematically tested its performance traversing large steps with variable heights to further understand stability principles. The robot rapidly and stably traversed steps nearly as high as a third of its body length. As step height increased, the robot rolled more frequently to the extent of flipping over, reducing traversal probability. The absence of such failure in the snake with a compliant body inspired us to add body compliance to the robot. With better surface contact, the compliant body robot suffered less roll instability and traversed high steps at higher probability, without sacrificing traversal speed. Our robot traversed large step-like obstacles more rapidly than most previous snake robots, approaching that of the animal.
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Submitted 18 September, 2025; v1 submitted 30 March, 2020;
originally announced March 2020.
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Pulsed-laser epitaxy of metallic delafossite PdCrO$_2$ films
Authors:
Jong Mok Ok,
Matthew Brahlek,
Woo Seok Choi,
Kevin M. Roccapriore,
Matthew F. Chisholm,
Soyeun Kim,
Changhee Sohn,
Elizabeth Skoropata,
Sangmoon Yoon,
Jun Sung Kim,
Ho Nyung Lee
Abstract:
Alternate stacking of a highly conducting metallic layer with a magnetic triangular layer found in delafossite PdCrO2 provides an excellent platform for discovering intriguing correlated quantum phenomena. Thin film growth of the material may enable not only tuning the basic physical properties beyond what bulk materials can exhibit, but also developing novel hybrid materials by interfacing with d…
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Alternate stacking of a highly conducting metallic layer with a magnetic triangular layer found in delafossite PdCrO2 provides an excellent platform for discovering intriguing correlated quantum phenomena. Thin film growth of the material may enable not only tuning the basic physical properties beyond what bulk materials can exhibit, but also developing novel hybrid materials by interfacing with dissimilar materials, yet this has proven to be extremely challenging. Here, we report the epitaxial growth of metallic delafossite PdCrO2 films by pulsed laser epitaxy (PLE). The fundamental role of the PLE growth conditions, epitaxial strain, and chemical and structural characteristics of the substrate is investigated by growing under various growth conditions and on various types of substrates. While strain plays a large role in improving the crystallinities, the direct growth of epitaxial PdCrO2 films without impurity phases was not successful. We attribute this difficulty to both the chemical and structural dissimilarities between the substrates and volatile nature of PdO layer, which make nucleation of the right phase difficult. This difficulty was overcome by growing CuCrO2 buffer layers before PdCrO2 were grown. Unlike PdCrO2, CuCrO2 films were rather readily grown with a relatively wide growth window. Only monolayer thick buffer layer was sufficient to grow the correct PdCrO2 phase. This result indicates that the epitaxy of Pd-based delafossites is extremely sensitive to the chemistry and structure of the interface, necessitating near perfect substrate materials. The resulting films are commensurately strained and show an antiferromagnetic transition at 40 K that persists down to as thin as 3.6 nm in thickness.
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Submitted 20 February, 2020; v1 submitted 19 February, 2020;
originally announced February 2020.
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A Comprehensive Model of the Degradation of Organic Light-Emitting Diodes and Application for Efficient Stable Blue Phosphorescent Devices with Reduced Influence of Polarons
Authors:
Bomi Sim,
Jong Soo Kim,
Hyejin Bae,
Sungho Nam,
Eunsuk Kwon,
Ji Whan Kim,
Hwa-Young Cho,
Sunghan Kim,
Jang-Joo Kim
Abstract:
We present a comprehensive model to analyze, quantitatively, and predict the process of degradation of organic light-emitting diodes (OLEDs) considering all possible degradation mechanisms, i.e., polaron, exciton, exciton-polaron interactions, exciton-exciton interactions, and a newly proposed impurity effect. The loss of efficiency during degradation is presented as a function of quencher density…
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We present a comprehensive model to analyze, quantitatively, and predict the process of degradation of organic light-emitting diodes (OLEDs) considering all possible degradation mechanisms, i.e., polaron, exciton, exciton-polaron interactions, exciton-exciton interactions, and a newly proposed impurity effect. The loss of efficiency during degradation is presented as a function of quencher density, the density and generation mechanisms of which were extracted using a voltage rise model. The comprehensive model was applied to stable blue phosphorescent OLEDs (PhOLEDs), and the results showed that the model described the voltage rise and external quantum efficiency (EQE) loss very well, and that the quenchers in emitting layer (EML) were mainly generated by dopant polarons. Quencher formation was confirmed from a mass spectrometry. The polaron density per dopant molecule in EML was reduced by controlling the emitter doping ratio, resulting in the highest reported LT50 of 431 hours at an initial brightness of 500 cd/m2 with CIEy<0.25 and high external quantum efficiency (EQE) >18%.
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Submitted 10 December, 2019;
originally announced December 2019.
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Spin- and orbital-Hall effect in cyclic group symmetric metasurface
Authors:
Yeon Ui Lee,
Igor Ozerov,
Frederic Bedu,
Ji Su Kim,
Frederic Fages,
Jeong Weon Wu
Abstract:
Light possesses both spin and orbital angular momentum (AM). While spin AM is determined by helicity of circular-polarization, orbital AM is characterized by topological charge of vortex beam. Interaction of AM with optical beam orbit leads to optical spin Hall or orbital Hall effect, exhibited as spin-dependent or topological charge-dependent transverse shift of optical beam. Conservation of AM e…
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Light possesses both spin and orbital angular momentum (AM). While spin AM is determined by helicity of circular-polarization, orbital AM is characterized by topological charge of vortex beam. Interaction of AM with optical beam orbit leads to optical spin Hall or orbital Hall effect, exhibited as spin-dependent or topological charge-dependent transverse shift of optical beam. Conservation of AM enables spin-to-orbital AM conversion, where circular-polarized Gaussian beam is converted to opposite-helicity circular-polarized vortex beam with topological charge $\pm 2$, an example of controlling spatial beam profiling by spin flip. However, the resultant vortex beam has the beam center of gravity unchanged, the same as that of incident Gaussian beam, meaning a null transverse shift. Here we introduce a cyclic group symmetric metasurface to demonstrate generation of vortex beam exhibiting spin-dependent transverse shift, namely, spin- and orbital-Hall effect, attributed to an alteration of dynamical phase of scattered beam according to the order $n$ of cyclic group while keeping geometric phase constant. Capability of spin-controlled spatial beam profiling with a transverse shift via spin- and orbital-Hall effect has important implications for spatial demultiplexing in optical communication utilizing orbital AM mode division multiplexing as well as for optical vortex tweezer and signal processing involving vortex beams.
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Submitted 17 August, 2016; v1 submitted 16 July, 2016;
originally announced July 2016.
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Feasibility Study of Neutron Dose for Real Time Image Guided Proton Therapy: A Monte Carlo Study
Authors:
Jin Sung Kim,
Jung Suk Shin,
Daehyun Kim,
EunHyuk Shin,
Kwangzoo Chung,
Sungkoo Cho,
Sung Hwan Ahn,
Sanggyu Ju,
Yoonsun Chung,
Sang Hoon Jung,
Youngyih Han
Abstract:
Two full rotating gantry with different nozzles (Multipurpose nozzle with MLC, Scanning Dedicated nozzle) with conventional cyclotron system is installed and under commissioning for various proton treatment options at Samsung Medical Center in Korea. The purpose of this study is to investigate neutron dose equivalent per therapeutic dose, H/D, to x-ray imaging equipment under various treatment con…
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Two full rotating gantry with different nozzles (Multipurpose nozzle with MLC, Scanning Dedicated nozzle) with conventional cyclotron system is installed and under commissioning for various proton treatment options at Samsung Medical Center in Korea. The purpose of this study is to investigate neutron dose equivalent per therapeutic dose, H/D, to x-ray imaging equipment under various treatment conditions with monte carlo simulation. At first, we investigated H/D with the various modifications of the beam line devices (Scattering, Scanning, Multi-leaf collimator, Aperture, Compensator) at isocenter, 20, 40, 60 cm distance from isocenter and compared with other research groups. Next, we investigated the neutron dose at x-ray equipments used for real time imaging with various treatment conditions. Our investigation showed the 0.07 ~ 0.19 mSv/Gy at x-ray imaging equipments according to various treatment options and intestingly 50% neutron dose reduction effect of flat panel detector was observed due to multi- leaf collimator during proton scanning treatment with multipurpose nozzle. In future studies, we plan to investigate experimental measurement of neutron dose and validation of simulation data for x-ray imaging equipment with additional neutron dose reduction method.
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Submitted 11 March, 2015;
originally announced March 2015.
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Measurement Limits to 134Cs Concentration in Soil
Authors:
J. K. Ahn,
J. S. Kim,
H. M. Lee,
T. H. Kim,
J. N. Park,
Y. S. Kang,
H. S. Lee,
S. J. Kim,
J. Y. Park,
S. Y. Ryu,
H. Ch. Kim,
W. G. Kang,
S. K. Kim
Abstract:
We investigate the caesium concentrations in soils in mountain areas near Gori nuclear power plant in Korea, focusing on the measurement limits to the 134Cs. In order to lower the minimum detectable amount (MDA) of activity for the 134Cs, we have used the ammonium molybdophosphase (AMP) precipitation method to get rid of the 40K existing in natural radioactivity, which reduces the MDA activity abo…
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We investigate the caesium concentrations in soils in mountain areas near Gori nuclear power plant in Korea, focusing on the measurement limits to the 134Cs. In order to lower the minimum detectable amount (MDA) of activity for the 134Cs, we have used the ammonium molybdophosphase (AMP) precipitation method to get rid of the 40K existing in natural radioactivity, which reduces the MDA activity about ten times smaller than those without the AMP precipitation method. The MDA results for the 134Cs were found to be in the range between 0.015 and 0.044 Bq/kg-dry weight. In order to diminish the background, we also have measured a part of the soil samples in Yangyang, a small town in the east coast of Korea. However, it turns out that in order to detect the 134Cs in the samples the MDA should be reduced to the level of mBq/kg-dry weight.
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Submitted 22 December, 2011; v1 submitted 10 January, 2009;
originally announced January 2009.
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Priority queues with bursty arrivals of incoming tasks
Authors:
N. Masuda,
J. S. Kim,
B. Kahng
Abstract:
Recently increased accessibility of large-scale digital records enables one to monitor human activities such as the interevent time distributions between two consecutive visits to a web portal by a single user, two consecutive emails sent out by a user, two consecutive library loans made by a single individual, etc. Interestingly, those distributions exhibit a universal behavior,…
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Recently increased accessibility of large-scale digital records enables one to monitor human activities such as the interevent time distributions between two consecutive visits to a web portal by a single user, two consecutive emails sent out by a user, two consecutive library loans made by a single individual, etc. Interestingly, those distributions exhibit a universal behavior, $D(τ)\sim τ^{-δ}$, where $τ$ is the interevent time, and $δ\simeq 1$ or 3/2. The universal behaviors have been modeled via the waiting-time distribution of a task in the queue operating based on priority; the waiting time follows a power law distribution $P_{\rm w}(τ)\sim τ^{-α}$ with either $α=1$ or 3/2 depending on the detail of queuing dynamics. In these models, the number of incoming tasks in a unit time interval has been assumed to follow a Poisson-type distribution. For an email system, however, the number of emails delivered to a mail box in a unit time we measured follows a powerlaw distribution with general exponent $γ$. For this case, we obtain analytically the exponent $α$, which is not necessarily 1 or 3/2 and takes nonuniversal values depending on $γ$. We develop the generating function formalism to obtain the exponent $α$, which is distinct from the continuous time approximation used in the previous studies.
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Submitted 9 April, 2009; v1 submitted 7 May, 2008;
originally announced May 2008.
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Dynamics of Multi-Player Games
Authors:
E. Ben-Naim,
B. Kahng,
J. S. Kim
Abstract:
We analyze the dynamics of competitions with a large number of players. In our model, n players compete against each other and the winner is decided based on the standings: in each competition, the mth ranked player wins. We solve for the long time limit of the distribution of the number of wins for all n and m and find three different scenarios. When the best player wins, the standings are most…
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We analyze the dynamics of competitions with a large number of players. In our model, n players compete against each other and the winner is decided based on the standings: in each competition, the mth ranked player wins. We solve for the long time limit of the distribution of the number of wins for all n and m and find three different scenarios. When the best player wins, the standings are most competitive as there is one-tier with a clear differentiation between strong and weak players. When an intermediate player wins, the standings are two-tier with equally-strong players in the top tier and clearly-separated players in the lower tier. When the worst player wins, the standings are least competitive as there is one tier in which all of the players are equal. This behavior is understood via scaling analysis of the nonlinear evolution equations.
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Submitted 28 April, 2006;
originally announced April 2006.
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A Resonant Cavity for Single-Shot Emittance Measurement
Authors:
J. S. Kim,
C. D. Nantista,
D. H. Whittum,
R. H. Miller,
S. G. Tantawi,
A. W. Weidemann
Abstract:
We present a non-invasive, resonant cavity based approach to beam emittance measurement of a shot-to-shot non-circular beam pulse of multi-bunches. In a resonant cavity, desired field components can be enhanced up to Q_L_lambda/pi, where Q_L_lambda is the loaded Q of the resonance mode lambda, when the cavity resonant mode matches with the beam operating frequency. In particular, a Quad-cavity,…
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We present a non-invasive, resonant cavity based approach to beam emittance measurement of a shot-to-shot non-circular beam pulse of multi-bunches. In a resonant cavity, desired field components can be enhanced up to Q_L_lambda/pi, where Q_L_lambda is the loaded Q of the resonance mode lambda, when the cavity resonant mode matches with the beam operating frequency. In particular, a Quad-cavity, with its quadrupole mode at beam operating frequency, extracts the beam quad-moment exclusively, utilizing the symmetry of the cavity and some simple networks to suppress common modes. Six successive beam quadrupole moment measurements, performed at different betatron phases in a linear transport system, allow us to determine the beam emittance, i.e., the beam size and shape in the beam's phase space. One measurement alone provides the rms-beam size if the beam position is given, for instance, by nearby beam-position-monitors. This paper describes the basic design and analysis of a Quad-cavity beam monitoring system.
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Submitted 18 September, 2002;
originally announced September 2002.