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A single platform with van der Pauw geometry for measurement of Seebeck coefficient, resistivity, and Hall effect of thin films
Authors:
Niraj Kumar Singh,
Martin Falk,
Per-Anton Schön Wallander,
Per Sandström,
Per Eklund,
Arnaud le Febvrier
Abstract:
A modular thermoelectric properties measurement setup in van der Pauw configuration was developed for a straightforward and simultaneous measurement of electrical resistivity and Seebeck coefficient in an extensive temperature range of 25°C - 600°C and can also perform Hall measurements at room temperature. The setup is optimized for accurate measurement of voltages and temperatures gradients by m…
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A modular thermoelectric properties measurement setup in van der Pauw configuration was developed for a straightforward and simultaneous measurement of electrical resistivity and Seebeck coefficient in an extensive temperature range of 25°C - 600°C and can also perform Hall measurements at room temperature. The setup is optimized for accurate measurement of voltages and temperatures gradients by minimizing possible errors from offset voltages, wire contributions and thermal contact resistances which helps getting reliable data. The setup is user friendly, and the measurements are fully automated and controlled using a LabVIEW program. The detachable modules make this setup quite versatile and provide an all-in-one (except thermal conductivity) solution for thermoelectric measurements.
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Submitted 26 June, 2026;
originally announced June 2026.
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Cold Pools Reduce the Impacts of Deforestation on Convection Initiation
Authors:
Nicholas M. Falk,
Gabrielle R. Leung,
Leah D. Grant,
Susan C. van den Heever
Abstract:
The individual and synergistic impacts of cold pools and land surface heterogeneity on convection initiation are investigated. Idealized large eddy simulations of deep convection over the Amazon rainforest are conducted. Simulations test realistic and homogenized vegetation, along with realistic and suppressed low-level evaporation which eliminates cold pools. Updrafts are tracked to determine con…
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The individual and synergistic impacts of cold pools and land surface heterogeneity on convection initiation are investigated. Idealized large eddy simulations of deep convection over the Amazon rainforest are conducted. Simulations test realistic and homogenized vegetation, along with realistic and suppressed low-level evaporation which eliminates cold pools. Updrafts are tracked to determine convection initiation locations. The aggregation of initiation locations is quantified with an organization index. Initiation locations are randomly distributed over homogeneous vegetation, with or without cold pools, demonstrating that cold pools have minimal impacts on initiation locations over homogeneous vegetation. With realistic vegetation, convection initiation is more frequent over forested than deforested areas due to favorable thermodynamics. Heterogeneous vegetation effectively aggregates initiation locations and precipitation compared to homogeneous vegetation, whereas cold pools disaggregate initiation locations and precipitation by propagating into deforested regions and initiating convection. Thus, cold pools partially counteract the effects of anthropogenically driven land surface heterogeneity.
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Submitted 21 November, 2025;
originally announced November 2025.
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Suppression of errors in collectively coded information
Authors:
Martin J. Falk,
Leon Zhou,
Yoshiya J. Matsubara,
Kabir Husain,
Jack W. Szostak,
Arvind Murugan
Abstract:
Modern life largely transmits genetic information from mother to daughter through the duplication of single physically intact molecules that encode information. However, copying an extended molecule requires complex copying machinery and high fidelity that scales with the genome size to avoid the error catastrophe. Here, we explore these fidelity requirements in an alternative architecture, the vi…
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Modern life largely transmits genetic information from mother to daughter through the duplication of single physically intact molecules that encode information. However, copying an extended molecule requires complex copying machinery and high fidelity that scales with the genome size to avoid the error catastrophe. Here, we explore these fidelity requirements in an alternative architecture, the virtual circular genome, in which no one physical molecule encodes the full genetic information. Instead, information is encoded and transmitted in a collective of overlapping and interacting segments. Using a model experimental system of a complex mixture of DNA oligomers that can partly anneal and extend off each other, we find that mutant oligomers are suppressed relative to a model without collective encoding. Through simulations and theory, we show that this suppression of mutants can be explained by competition for productive binding partners. As a consequence, information can be propagated robustly in a virtual circular genome even at mutation rates expected under prebiotic conditions.
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Submitted 24 September, 2025; v1 submitted 29 August, 2025;
originally announced August 2025.
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Learning via mechanosensitivity and activity in cytoskeletal networks
Authors:
Deb S. Banerjee,
Martin J. Falk,
Margaret L Gardel,
Aleksandra M. Walczak,
Thierry Mora,
Suriyanarayanan Vaikuntanathan
Abstract:
In this work we show how a network inspired by a coarse-grained description of actomyosin cytoskeleton can learn - in a contrastive learning framework - from environmental perturbations if it is endowed with mechanosensitive proteins and motors. Our work is a proof of principle for how force-sensitive proteins and molecular motors can form the basis of a general strategy to learn in biological sys…
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In this work we show how a network inspired by a coarse-grained description of actomyosin cytoskeleton can learn - in a contrastive learning framework - from environmental perturbations if it is endowed with mechanosensitive proteins and motors. Our work is a proof of principle for how force-sensitive proteins and molecular motors can form the basis of a general strategy to learn in biological systems. Our work identifies a minimal biologically plausible learning mechanism and also explores its implications for commonly occuring phenomenolgy such as adaptation and homeostatis.
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Submitted 21 April, 2025;
originally announced April 2025.
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Stochastic evolution elasto-plastic modeling of a metallic glass
Authors:
Bin Xu,
Zhao Wu,
Jiayin Lu,
Michael D. Shields,
Chris H. Rycroft,
Franz Bamer,
Michael L. Falk
Abstract:
This paper develops a general data-driven approach to stochastic elastoplastic modelling that leverages atomistic simulation data directly rather than by fitting parameters. The approach is developed in the context of metallic glasses, which present inherent complexities due to their disordered structure. By harvesting statistics from simulated metallic glass shear response histories, the material…
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This paper develops a general data-driven approach to stochastic elastoplastic modelling that leverages atomistic simulation data directly rather than by fitting parameters. The approach is developed in the context of metallic glasses, which present inherent complexities due to their disordered structure. By harvesting statistics from simulated metallic glass shear response histories, the material state is mapped onto a two-dimensional state space consisting of the shear stress and the inelastic contribution to the potential energy. The resulting elastoplastic model is intrinsically stochastic and represented as a non-deterministic dynamical map. The state space statistics provide insights into the deformation physics of metallic glasses, revealing that two state variables are sufficient to describe the main features of the elastoplastic response. In this two-dimensional state space, the gradually quenched metallic glass rejuvenates during the initial quasi-elastic shearing, ultimately reaching a steady state that fluctuates about a fixed point in the state space as rejuvenation and aging balance.
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Submitted 1 October, 2024;
originally announced October 2024.
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Condensed Matter Systems Exposed to Radiation: Multiscale Theory, Simulations, and Experiment
Authors:
Andrey V. Solov'yov,
Alexey V. Verkhovtsev,
Nigel J. Mason,
Richard A. Amos,
Ilko Bald,
Gérard Baldacchino,
Brendan Dromey,
Martin Falk,
Juraj Fedor,
Luca Gerhards,
Michael Hausmann,
Georg Hildenbrand,
Miloš Hrabovský,
Stanislav Kadlec,
Jaroslav Kočišek,
Franck Lépine,
Siyi Ming,
Andrew Nisbet,
Kate Ricketts,
Leo Sala,
Thomas Schlathölter,
Andrew Wheatley,
Ilia A. Solov'yov
Abstract:
This paper reviews the new highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The paper highlights several relevant examples of recent advances in the field and provides a roadmap for the development of the field in the next decade. Condensed matter systems exposed to radiation may have very different natures, being inorganic, organic or…
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This paper reviews the new highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The paper highlights several relevant examples of recent advances in the field and provides a roadmap for the development of the field in the next decade. Condensed matter systems exposed to radiation may have very different natures, being inorganic, organic or biological, finite or infinite, be composed of many different molecular species or materials, existing in different phases (solid, liquid, gaseous or plasma) and operating under different thermodynamic conditions. The essential and novel element of this research is that, despite the vast diversity of such systems, many of the key phenomena related to the behavior of irradiated systems (such as radiation-induced damage, mechanisms of damage repair and control, radiation protection, etc.) are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. One of the essential features of the aforementioned phenomena concerns their multiscale nature as the manifestation of the radiation-induced effects occurring at different spatial and temporal scales ranging from the atomic to the macroscopic. The multiscale nature of the effects and similarity of their manifestation in systems of different origins necessarily brings together different disciplines, such as physics, chemistry, biology, materials and nano-science, and biomedical research, demonstrating numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.
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Submitted 4 December, 2023; v1 submitted 22 November, 2023;
originally announced November 2023.
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Heart Valve Component Fatigue Demonstration Testing Attribute and Variables Demonstration Test Planning and Sample Size Determination
Authors:
Wayne M Falk,
William Q Meeker
Abstract:
The fatigue demonstration test program may be carried out using either the attribute or variables approach. For either approach, a robust test program fulfills the objective of unambiguously demonstrating reliability, as well as, demonstrating understanding of when and how the components could fracture. To this end, it is recommended that a robust test program should aim to produce data for both s…
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The fatigue demonstration test program may be carried out using either the attribute or variables approach. For either approach, a robust test program fulfills the objective of unambiguously demonstrating reliability, as well as, demonstrating understanding of when and how the components could fracture. To this end, it is recommended that a robust test program should aim to produce data for both surviving units and fractured units.
Test planning is needed to determine sample sizes and test levels of strain to prove that the component meets the target reliability. The two risks that must be addressed by the test plan are 1) the risk that an unreliable component will pass the test, i.e., Type 1 error, or 2) the risk of a test failing for a sufficiently reliable component, i.e., Type 2 error.
Test planning methods are described to design a test plan that efficiently meets these objectives for attribute and variable approaches. The attribute approach offers the advantage of straight forward planning and a simple output. Sample size is calculated using a well-known formula. Testing to fracture is recommended to complement the traditional attribute testing approach to identify the test failure modes. The variables approach is more complex to plan and analyze, however it enables a greater understanding of reliability. Sample sizes and test levels of strain are determined using a simulated data strategy to provide a clear picture of possible outcomes of the test.
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Submitted 8 August, 2023;
originally announced August 2023.
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Three-dimensional structure and stability of discontinuities between unmagnetized pair plasma and magnetized electron-proton plasma
Authors:
M E Dieckmann,
D Folini,
M Falk,
A Bock,
P Steneteg,
R Walder
Abstract:
We study with a 3D PIC simulation discontinuities between an electron-positron pair plasma and magnetized electrons and protons. A pair plasma is injected at one simulation boundary with a speed 0.6$c$ along its normal. It expands into an electron-proton plasma and a magnetic field that points orthogonally to the injection direction. Diamagnetic currents expel the magnetic field from within the pa…
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We study with a 3D PIC simulation discontinuities between an electron-positron pair plasma and magnetized electrons and protons. A pair plasma is injected at one simulation boundary with a speed 0.6$c$ along its normal. It expands into an electron-proton plasma and a magnetic field that points orthogonally to the injection direction. Diamagnetic currents expel the magnetic field from within the pair plasma and pile it up in front of it. It pushes electrons, which induces an electric field pulse ahead of the magnetic one. This initial electromagnetic pulse (EMP) confines the pair plasma magnetically and accelerates protons electrically. The fast flow of the injected pair plasma across the protons behind the initial EMP triggers the filamentation instability. Some electrons and positrons cross the injection boundary and build up a second EMP. Electron-cyclotron drift instabilities perturb the plasma ahead of both EMPs seeding a Rayleigh-Taylor-type instability. Despite equally strong perturbations ahead of both EMPs, the second EMP is much more stable than the initial one. We attribute the rapid collapse of the initial EMP to the filamentation instability, which perturbed the plasma behind it. The Rayleigh-Taylor-type instability transforms the planar EMPs into transition layers, in which magnetic flux ropes and electrostatic forces due to uneven numbers of electrons and positrons slow down and compress the pair plasma and accelerate protons. In our simulation, the expansion speed of the pair cloud decreased by about an order of magnitude and its density increased by the same factor. Its small thickness implies that it is capable of separating a relativistic pair outflow from an electron-proton plasma, which is essential for collimating relativistic jets of pair plasma in collisionless astrophysical plasma.
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Submitted 9 June, 2023;
originally announced June 2023.
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Manifold learning for coarse-graining atomistic simulations: Application to amorphous solids
Authors:
Katiana Kontolati,
Darius Alix-Williams,
Nicholas M. Boffi,
Michael L. Falk,
Chris H. Rycroft,
Michael D. Shields
Abstract:
We introduce a generalized machine learning framework to probabilistically parameterize upper-scale models in the form of nonlinear PDEs consistent with a continuum theory, based on coarse-grained atomistic simulation data of mechanical deformation and flow processes. The proposed framework utilizes a hypothesized coarse-graining methodology with manifold learning and surrogate-based optimization…
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We introduce a generalized machine learning framework to probabilistically parameterize upper-scale models in the form of nonlinear PDEs consistent with a continuum theory, based on coarse-grained atomistic simulation data of mechanical deformation and flow processes. The proposed framework utilizes a hypothesized coarse-graining methodology with manifold learning and surrogate-based optimization techniques. Coarse-grained high-dimensional data describing quantities of interest of the multiscale models are projected onto a nonlinear manifold whose geometric and topological structure is exploited for measuring behavioral discrepancies in the form of manifold distances. A surrogate model is constructed using Gaussian process regression to identify a mapping between stochastic parameters and distances. Derivative-free optimization is employed to adaptively identify a unique set of parameters of the upper-scale model capable of rapidly reproducing the system's behavior while maintaining consistency with coarse-grained atomic-level simulations. The proposed method is applied to learn the parameters of the shear transformation zone (STZ) theory of plasticity that describes plastic deformation in amorphous solids as well as coarse-graining parameters needed to translate between atomistic and continuum representations. We show that the methodology is able to successfully link coarse-grained microscale simulations to macroscale observables and achieve a high-level of parity between the models across scales.
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Submitted 23 July, 2021; v1 submitted 1 March, 2021;
originally announced March 2021.
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Preferential acceleration of positrons by a filamentation instability between an electron-proton beam and a pair plasma beam
Authors:
M E Dieckmann,
S J Spencer,
M Falk,
G Rowlands
Abstract:
Particle-in-cell (PIC) simulations of collisionless jets of electrons and positrons in an ambient electron-proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. The dominant instability within the jet was a filamentation instability between electrons, protons and positrons. In this work we show that a filamentation instability, between an initially unm…
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Particle-in-cell (PIC) simulations of collisionless jets of electrons and positrons in an ambient electron-proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. The dominant instability within the jet was a filamentation instability between electrons, protons and positrons. In this work we show that a filamentation instability, between an initially unmagnetized ambient electron-proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed.
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Submitted 1 November, 2020;
originally announced November 2020.
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Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling
Authors:
Paul Fassl,
Vincent Lami,
Felix J. Berger,
Lukas M. Falk,
Jana Zaumseil,
Bryce S. Richards,
Ian A. Howard,
Yana Vaynzof,
Ulrich W. Paetzold
Abstract:
The internal luminescence quantum efficiency ($Q_\mathrm{i}^\mathrm{lum}$) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine $Q_\mathrm{i}^\mathrm{lum}$ of perovskite films from the experimentally accessible external luminescence quantum efficiency ($Q_\mathrm{e}^\mathrm{lum}$) it is essential to account for photon recycling, and this requires knowledge…
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The internal luminescence quantum efficiency ($Q_\mathrm{i}^\mathrm{lum}$) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine $Q_\mathrm{i}^\mathrm{lum}$ of perovskite films from the experimentally accessible external luminescence quantum efficiency ($Q_\mathrm{e}^\mathrm{lum}$) it is essential to account for photon recycling, and this requires knowledge of the photon escape probability ($p_\mathrm{e}$). Here, we establish an analysis procedure based on a curve fitting model that accurately determines $p_\mathrm{e}$ of perovskite films from photoluminescence (PL) spectra measured with a confocal microscope and an integrating sphere setup. We show that scattering-induced outcoupling of initially-trapped PL explains commonly observed red-shifted and broadened PL spectral shapes and leads to $p_\mathrm{e}$ being more than 10% higher in absolute terms compared to earlier assumptions. Applying our model to CH$_3$NH$_3$PbI$_3$ films with exceptionally high $Q_\mathrm{e}^\mathrm{lum}$ up to 47.4% sets a real benchmark for $Q_\mathrm{i}^\mathrm{lum}$ at $78.0 \pm 0.5\%$, revealing there is beyond a factor of two more scope for reducing non-radiative recombination than previously thought.
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Submitted 24 October, 2020;
originally announced October 2020.
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Effect of Precursor Stoichiometry on the Performance and Stability of MAPbBr3 Photovoltaic Devices
Authors:
Lukas M. Falk,
Katelyn P. Goetz,
Vincent Lami,
Qingzhi An,
Paul Fassl,
Jonas Herkel,
Fabian Thome,
Alexander D. Taylor,
Fabian Paulus,
Yana Vaynzof
Abstract:
The wide band gap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light-emitting diodes. Despite its utility, there is only a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examine…
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The wide band gap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light-emitting diodes. Despite its utility, there is only a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examined in detail. Although photovoltaic cells based on these solution changes exhibit similar initial performance, the shelf-storage depends strongly on the precursor solution stoichiometry. While all devices exhibit some degree of healing, the bromide-deficient films show a remarkable improvement, more than doubling in their photoconversion efficiency. Photoluminescence spectroscopy experiments performed under different atmospheres suggest that this increase is due in part to a trap healing mechanism that occurs upon exposure to the environment. Our results highlight the importance of understanding and manipulating defects in lead halide perovskites to produce long-lasting, stable devices.
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Submitted 29 July, 2020;
originally announced July 2020.
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Atomic nonaffinity as a predictor of plasticity in amorphous solids
Authors:
Bin Xu,
Michael L. Falk,
Sylvain Patinet,
Pengfei Guan
Abstract:
Structural heterogeneity of amorphous solids present difficult challenges that stymie the prediction of plastic events, which are intimately connected to their mechanical behavior. Based on a perturbation analysis of the potential energy landscape, we derive the atomic nonaffinity as an indicator with intrinsic orientation, which quantifies the contribution of an individual atom to the total nonaf…
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Structural heterogeneity of amorphous solids present difficult challenges that stymie the prediction of plastic events, which are intimately connected to their mechanical behavior. Based on a perturbation analysis of the potential energy landscape, we derive the atomic nonaffinity as an indicator with intrinsic orientation, which quantifies the contribution of an individual atom to the total nonaffine modulus of the system. We find that the atomic nonaffinity can efficiently characterize the locations of the shear transformation zones, with a predicative capacity comparable to the best indicators. More importantly, the atomic nonaffinity, combining the sign of third order derivative of energy with respect to coordinates, reveals an intrinsic softest shear orientation. By analyzing the angle between this orientation and the shear loading direction, it is possible to predict the protocol-dependent response of plastic events. Employing the new method, the distribution of orientations of shear transformation zones in a model two-dimensional amorphous solids can be measured. The resulting plastic events can be understood from a simple model of independent plastic events occurring at variously oriented shear transformation zones. These results shed light on the characterization and prediction of the mechanical response of amorphous solids.
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Submitted 4 February, 2021; v1 submitted 28 May, 2019;
originally announced May 2019.
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Gender and Sexual Diversity Issues in Physics: The Audience Speaks
Authors:
Nicole Ackerman,
Timothy J. Atherton,
Wouter Deconinck,
Michael L. Falk,
Savannah Garmon,
Edward Henry,
Elena Long
Abstract:
An account is presented of the special session on "Gender and Sexual Diversity Issues in Physics" which took place at the American Physical Society March Meeting 2012. The opinions of those who attended this session were solicited via an anonymous survey, the results of which are reported here. Drawing both upon ideas put forward by the speakers and audience from the meeting, a set of recommended…
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An account is presented of the special session on "Gender and Sexual Diversity Issues in Physics" which took place at the American Physical Society March Meeting 2012. The opinions of those who attended this session were solicited via an anonymous survey, the results of which are reported here. Drawing both upon ideas put forward by the speakers and audience from the meeting, a set of recommended actions is proposed for the Physics community to become more inclusive of LGBT+ people.
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Submitted 18 June, 2012;
originally announced June 2012.
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An elasticity theory for self-assembled protein lattices with application to the martensitic phase transition in bacteriophage T4 tail sheath
Authors:
Wayne M. Falk,
Richard D. James
Abstract:
We propose an elasticity theory for one and two dimensional arrays of globular proteins for which the free energy is affected by relative position and relative rotation between neighboring molecules. The kinematics of such assemblies is described, the conditions of compatibility are found, a form of the free energy is given, and formulas for applied forces and moments are developed. It is shown…
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We propose an elasticity theory for one and two dimensional arrays of globular proteins for which the free energy is affected by relative position and relative rotation between neighboring molecules. The kinematics of such assemblies is described, the conditions of compatibility are found, a form of the free energy is given, and formulas for applied forces and moments are developed. It is shown that fully relaxed states of sheets consist of helically deformed sheets which themselves are composed of helical chains of molecules in rational directions.
We apply the theory to the fascinating contractile deformation that occurs in the tail sheath of the virus bacteriophage T4, which aids its invasion of its bacterial host. Using electron density maps of extended and contracted sheath, we approximate the domains of each molecule by ellipsoids and then evaluate our formulas for the position and orientation of each molecule. We show that, with the resulting kinematic description, the configurations of extended and contracted tail sheath are generated by a simple formula. We proposed a constrained version of the theory based on measurements on extended and contracted sheath. Following a suggestion of Pauling [{\em Discussions of the Faraday Society} {\bf 13}, 170-6 (1953)], we develop a simple model of the molecular interaction. The resulting free energy is found to have a double-well structure. Certain simple deformations are studied (tension, torsion inflation); the theory predicts a first-order Poynting effect and some unexpected relations among moduli. Finally, the force of penetration is given, and a possibly interesting program of epitaxial growth and patterning of such sheets is suggested.
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Submitted 12 September, 2005;
originally announced September 2005.