bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimistic vs. pessimistic endings in climate change appeals
Authors: Morris Brandi S. , Chrysochou Polymeros , Karg Simon T. , Mitkidis Panagiotis
Published: September 2020

The use of emotion in climate change appeals is a hotly debated topic. Warning about the perils of imminent mass extinction, climate change communicators are often accused of being unnecessarily ‘doomsday’ in their attempts to foster a sense of urgency and action among the public. Pessimistic messaging, the thinking goes, undermines engagement efforts, straining credulity and fostering a sense of helplessness, rather than concern. Widespread calls for more optimistic climate change messaging punctuate public discourse. This research puts these claims to the test, investigating how affective endings (optimistic vs. pessimistic vs. fatalistic) of climate change appeals impact individual risk perception and outcome efficacy (i.e., the sense that one’s behavior matters). The findings of three online experiments presented in this paper suggest that climate change appeals with pessimistic affective endings increase risk perception (Studies 1 and 2) and outcome efficacy (Study 3), which is the result of heightened emotional arousal (Studies 1–3). Moreover, the results indicate that the mediating effect of emotional arousal is more prevalent among political moderates and conservatives, as well as those who hold either individualistic or hierarchical world views. Given that these audiences generally exhibit lower risk perception and outcome efficacy in relation to climate change, the results suggest that climate change appeals with pessimistic endings could trigger higher engagement with the issue than optimistic endings. These findings are interpreted in light of recent research findings, which suggest that differences in threat-reactivity and emotional arousal may be attributable to brain functions/anatomy mappable to basic motivations for safety and survival. Implications for scholars and practitioners are discussed.
Regularization of 1/X2 potential in general case of deformed space with minimal length
Authors: Samar M. I. , Tkachuk V. M.
Published: September 2020

In the general case of deformed Heisenberg algebra leading to the minimal length, we present a definition of the inverse square position operator. Our proposal is based on the functional analysis of the square of the position operator. Using this definition, a particle in the field of the inverse square potential is studied. We obtain analytical and numerical solutions for the energy spectrum of the considerable problem in different cases of deformation function. We conclude that the energy spectrum weakly depends on the choice of deformation function.
Paving the way to dislocation reduction in Ge/Si(001) heteroepitaxy using C-based strained layer superlattices
Authors: Barnscheidt Y. , Franck M. , Jörg Osten H.
Published: September 2020

Epitaxial Ge films were grown on Si(001) substrates by molecular beam epitaxy. During epitaxial growth, two carbon interlayers were deposited at varying substrate temperatures (140−620°C) and with varying C quantity (0−1.5monolayers). The influence of the second carbon interlayer on in-plane strain was investigated using high-resolution x-ray diffraction and transmission electron microscopy (TEM). All samples exhibited compressive strain, which was attributed to substitutional incorporation of carbon atoms. In-plane strain decreases with increasing substrate temperature during carbon deposition, indicating that enhanced surface mobility of carbon adatoms leads to formation of carbon clusters. This was confirmed by cross-sectional TEM investigations. Variation of C quantity at 180°C reveals maximum strain at an intermediate quantity of 0.8 monolayers. Omission of the second C interlayer results in much lower strain, indicating a mismatch between the two Ge layers separated by a C interlayer. This could be used to enforce dislocation filtering following the principle of strained layer superlattices. An upper estimate of 1×10−3 was found for the mismatch strain, resulting in a critical thickness for dislocation filtering of hc=153nm. A sample just exceeding hc exhibited a clear dislocation reduction effect as shown by TEM.
Modeling the electron collision frequency during solid-to-plasma transition of polystyrene ablator for direct-drive inertial confinement fusion applications
Authors: Pineau A. , Chimier B. , Hu S. X. , Duchateau G.
Published: September 2020

Within the inertial confinement fusion (ICF) framework, the solid-to-plasma transition of the ablator arouses increasing interest, in particular due to the laser-imprint issue. Phase evolution of the ablator is linked to the evolution of the electron collision frequency, which is of crucial importance since it drives electron heating by laser energy absorption and lattice-ion heating due to collisions between electrons and the lattice-ion system. Thus, an accurate description of electron collisions over the whole temperature range occurring in ICF, starting from a few tens of kelvins (solid state) up to tens of millions of kelvins (plasma state), is necessary. In this work, a polystyrene ablator is considered, and a model of chemical fragmentation is presented to describe the heated polystyrene evolution. Electron collisions are described by electron–phonon collisions in the solid state and by electron–ion and electron–neutral collisions in the plasma state. An effective electron collision frequency valid over the whole range of temperatures reached in ICF experiments is established and discussed. Thermal conductivity is also deduced from collisions in the plasma state and shows a good agreement with the one evaluated by ab initio calculations.
Pinhole quantum ghost imaging
Authors: Vega Andres , Saravi Sina , Pertsch Thomas , Setzpfandt Frank
Published: September 2020

We propose a quantum ghost imaging scheme based on biphotons, which, by using a collimated pump beam of the right size for biphoton generation, obviates the need for lenses to achieve imaging. The scheme is found to be analogous to the classical pinhole camera, where we show that the equivalent to the classical pinhole size depends not only mainly on the width of the pump beam but also on the thickness of the nonlinear crystal and the wavelengths of the biphoton.
Omnithermal metamaterials switchable between transparency and cloaking
Authors: Yang Shuai , Xu Liujun , Dai Gaole , Huang Jiping
Published: September 2020

Transparency and cloaking are two typical functions of thermal metamaterials that have attracted intensive research interest. However, two restrictions remain to be solved. The first one is that existing studies considered only one or two modes of heat transfer, which may not be consistent with practical conditions because conduction, radiation, and convection often coexist. The second one is that transparency and cloaking cannot be switched between at will. To solve these problems, we propose an effective medium theory to handle conductive, radiative, and convective (herein called omnithermal) processes simultaneously, which is based on the Fourier law, the Rosseland diffusion approximation, and the Darcy law. With the present theory, we further design an omnithermal metamaterial switchable between transparency and cloaking, which results from the nonlinear properties of radiation and convection. Finite-element simulations indicate that our scheme is robust under different boundary conditions. These results have potential applications such as in thermal camouflage, nonlinear thermotics, and intelligent thermotics.
A numerical study of particle jetting in a dense particle bed driven by an air-blast
Authors: Koneru Rahul Babu , Rollin Bertrand , Durant Bradford , Ouellet Frederick , Balachandar S.
Published: September 2020

In this work, the particle jetting behavior in a blast-driven dense particle bed is studied at early times. Four-way coupled Euler–Lagrange simulations are performed using a high-order discontinuous Galerkin spectral element solver coupled with a high-order Lagrangian particle solver, wherein the inter-particle collisions are resolved using a discrete element method collision model. Following the experiments of Rodriguez et al. [“Formation of particle jetting in a cylindrical shock tube,” Shock Waves 23(6), 619–634 (2013)] and the simulations of Osnes et al. [“Numerical simulation of particle jet formation induced by shock wave acceleration in a Hele-Shaw cell,” Shock Waves 28(3), 451–461 (2018)], the simulations are performed in a quasi-two-dimensional cylindrical geometry (Hele-Shaw cell). Parametric studies are carried out to assess the impact of the coefficient of restitution and the strength of the incident shock on the particle jetting behavior. The deposition of vorticity through a multiphase (gas–particle) analog of Richtmyer–Meshkov instability is observed to play a crucial role in channeling the particles into well-defined jets at the outer edge of the particle bed. This is confirmed by the presence of vortex pairs around the outer jets. Furthermore, the effect of the relaxation of the relative velocity between the two phases on the vorticity generation is explored by analyzing the correlation between the radial velocity of particles and the radial velocity of the gas at the particle location.
Perspective on Kramers symmetry breaking and restoration in relativistic electronic structure methods for open-shell systems
Authors: Kasper Joseph M. , Jenkins Andrew J. , Sun Shichao , Li Xiaosong
Published: September 2020

Without rigorous symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of the relativistic electronic structure, if time-reversal symmetry is not enforced in calculations of molecules not subject to a magnetic field, it is possible to artificially break Kramers degeneracy in open shell systems. This leads to a description of excited states that may be qualitatively incorrect. Despite this, different electronic structure methods to incorporate correlation and excited states can partially restore Kramers degeneracy from a broken symmetry solution. For single-reference techniques, the inclusion of double and possibly triple excitations in the ground state provides much of the needed correction. Formally, however, this imbalanced treatment of the Kramers-paired spaces is a multi-reference problem, and so methods such as complete-active-space methods perform much better at recovering much of the correct symmetry by state averaging. Using multi-reference configuration interaction, any additional corrections can be obtained as the solution approaches the full configuration interaction limit. A recently proposed “Kramers contamination” value is also used to assess the magnitude of symmetry breaking.
Microwave absorption and optical emission spectrometry analyses of ambient air plasmas induced by pulsed electron beams
Authors: Ribière M. , Eichwald O. , Yousfi M.
Published: September 2020

This work is devoted to the characterization of plasmas produced by an intense pulsed relativistic electron beam propagating in air at atmospheric pressure. A large range of a time integrated dose is investigated [0.75 to 7.4] kGy(air) inducing electron densities from 2 × 1012 up to 1.6 × 1014 cm−3. The air plasmas are analyzed by two complementary diagnostics: microwave absorption and optical emission spectroscopy, to deduce plasma parameters during the creation and relaxation phases, respectively. A reduced air kinetics model is used to calculate transmission measurements during the electron beam pulse and to infer electric conductivities, which are compared to the results of three-dimensional Maxwell calculations. Optical emission spectra are measured and compared to calculated ones, giving rotational and vibrational temperatures during the relaxation phase of the plasma. These plasma characterizations may be used to model non-equilibrium atmospheric air plasma chemistry in the framework of, for instance, streamer dynamics as well as corona or dielectric barrier discharges.
Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon
Authors: Hamyeh S. , Tauk R. , Adam P.-M. , Kazan M.
Published: September 2020

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.
Directional acoustic emission via topological insulators based on cavity-channel networks
Authors: Tong Shuaishuai , Ren Chunyu
Published: September 2020

In this paper, directional acoustic emission via topological insulators is investigated. For this purpose, a topological insulator based on a cavity-channel network is constructed, and the band structure of this topological insulator is studied theoretically and numerically. Topologically protected edge states between the topological insulators are numerically demonstrated. Directional emission with a half-power angular width as narrow as 5° can be achieved via the topological surface, which is composed of a few layers of topological insulators. This device, based on the topologically protected edge state, shows robustness to defects. This work shows the potential for making robust and tunable acoustic emission devices.
Experimental photoacoustic observation of the photogenerated excess carrier influence on the thermoelastic response of n-type silicon
Authors: Markushev D. K. , Markushev D. D. , Aleksić S. M. , Pantić D. S. , Galović S. P. , Todorović D. M. , Ordonez-Miranda J.
Published: September 2020

Based on the experimental and theoretical signals of an open photoacoustic cell operating with modulation frequencies from 20 Hz to 20 kHz, a significant contribution of photogenerated excess carriers on the thermal and thermoelastic responses of an n-type silicon plate is observed for the very first time. This is achieved by comparing the measured amplitude and phase of the photoacoustic signal with their corresponding theoretical thermoelastic counterparts, for high enough modulation frequencies mainly. It is shown that the amplitude of the thermoelastic component of plasma-thin samples varies about two orders of magnitude with respect to the corresponding one of plasma-thick samples. Furthermore, we find a maximal temperature difference ΔT = − 35 nK between the illuminated and non-illuminated sample surfaces, which shows that thin silicon plates with excess carriers could be used as heat sinks.
Isolator characteristics under steady and oscillatory back pressures
Authors: R. Saravanan , Desikan S. L. N. , T. M. Muruganandam
Published: September 2020

Experiments are carried out to characterize the un-start/re-start phenomena in an isolator with steady and low-frequency oscillatory back pressures (0.75 Hz–2.5 Hz) in Mach 1.7 flow. In the present study, the effect of shock train interaction with the intake shocks is focused to capture these phenomena. It is demonstrated that the un-start mechanism is a continuous process with steady back pressures, whereas it is a discontinuous process under oscillatory back pressures. The un-start mechanism is triggered once the oscillatory back pressure is above the maximum isolator pressure. As the frequency of back pressure oscillation is increased, the isolator experiences an early un-start and a delayed re-start. On the other hand, if the oscillatory back pressure is decreased, the re-start process is initiated. During the re-start process, the time lag is found to be increased, and the hysteresis loss is decreased with an increase in oscillatory frequencies. These phenomena are studied through both the steady and unsteady pressure measurements along with instantaneous schlieren images for different dynamic pressures. Furthermore, the un-start can be avoided or delayed by increasing the freestream dynamic pressure.
Opto-mechanically induced thermoplasmonic response of unclonable flexible tags with hotspot fingerprint
Authors: Emanuele Lio Giuseppe , De Luca Antonio , Umeton Cesare Paolo , Caputo Roberto
Published: September 2020

Gold nanoparticle arrangements are identified as plasmonic heaters due to the photo-thermal effects originating from the strong plasmonic confinement of light at the nanoscale. The specific design of the nanoparticle arrangement is crucial to optimize the generation of heat and control its flux. Accurate manipulation of the photo-thermal response of the system is possible by dynamically changing the plasmonic hotspots distribution. Indeed, a macroscopic deformation of the sample results in a nanoscale modification of the relative position of nanoparticles, thus realizing a specific control of the hotspots formation. In this contribution, an analysis of the thermal response of the system based on the interplay between exciting light polarization and sample deformation is reported. The absorption cross section and the production of heat at the nanoscale is considered with the system at rest and under applied mechanical stress. Finally, the implementation of a flexible tag for physical unclonable functions has been studied. The introduction of a defect, obtained by displacing a single nanoparticle of the previously ordered configuration, produces noteworthy variations in the absorption cross section. Indeed, the excitation of the novel arrangement at a proper exciting wavelength, different from the resonant one for the unmodified arrangement, produces a twofold temperature increase with respect to the case of the ordered array considered at the same excitation wavelength. Such a result paves the way for the realization of a novel device to be exploited as a thermal flexible fingerprint for unclonable tags with fast response and low production cost.
Reformulation of the self-guided molecular simulation method
Authors: Wu Xiongwu , Brooks Bernard R.
Published: September 2020

Self-guided molecular/Langevin dynamics (SGMD/SGLD) simulation methods were developed to enhance conformational sampling through promoting low frequency motion of molecular systems and have been successfully applied in many simulation studies. Quantitative understanding of conformational distribution in SGLD has been achieved by separating microscopic properties according to frequency. However, a missing link between the guiding factors and conformational distributions makes it highly empirical and system dependent when choosing the values of the guiding parameters. Based on the understanding that molecular interactions are the source of energy barriers and diffusion friction, this work reformulates the equation of the low frequency motion to resemble Langevin dynamics. This reformulation leads to new forms of guiding forces and establishes a relation between the guiding factors and conformational distributions. We call simulations with these new guiding forces the generalized self-guided molecular/Langevin dynamics (SGMDg/SGLDg). In addition, we present a new way to calculate low frequency properties and an efficient algorithm to implement SGMDg/SGLDg that minimizes memory usage and inter-processor communication. Through example simulations with a skewed double well system, an argon fluid, and a cryo-EM map flexible fitting case, we demonstrate the guiding effects on conformational distributions and conformational searching.
Fast rise breakdown in dielectric filled air gap for surge protection
Authors: Yang P. , Sorenson J. D. , Gomez C. A. , Blea-Kirby M. A. , Moffatt W. C.
Published: September 2020

Electric discharge across an air gap can be self-healing, providing a unique capability for repetitive, fast, high-voltage/current switching applications through arc conduction. Furthermore, incorporating dielectric granules in the air gap stimulates gas ionization, which lowers the breakdown voltage and narrows breakdown voltage distribution, thereby enabling engineered surge protection from multiple lightning strikes on aerospace vehicles and sensitive solid-state electronics in critical systems. This study investigates the effect of the permittivity of dielectric granules, gap filling, surface roughness, and metal work function on fast-rising, high-voltage breakdowns. In addition to the air gap width, these factors play important roles in gas ionization, field concentration, and initiation of electrical discharge and arcing. Therefore, they could potentially be used to control and narrow operational breakdown voltages for practical applications. Additionally, a modified Langevin–Debye model is developed to correlate the breakdown voltage and the permittivity of the dielectric filler. These investigations identify and highlight key underpinning mechanisms governing the gas discharge behavior across a dielectric filled air gap during voltage surge events.
Understanding omni-directional reflectors and nominating more dielectric materials for deep ultraviolet light-emitting diodes with inclined sidewalls
Authors: Zheng Yuxin , Zhang Ji , Chang Le , Chu Chunshuang , Tian Kangkai , Zheng Quan , Li Qing , Zhang Yonghui , Bi Wengang , Zhang Zi-Hui
Published: September 2020

In this work, unique properties and tremendous advantages for an omni-directional reflector (ODR) on an inclined sidewall for flip-chip AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) are systematically investigated via a three-dimensional finite-difference time-domain method. It is found that although the reflectivity of Ag is far lower than that of Al, the light extraction efficiency for the inclined sidewall DUV LED with the Ag-based ODR is not always lower than that with Al-based one within certain incident angles. The reason is that the total internal reflection (TIR) of the ODR on the inclined sidewall plays an important role in extracting light. We also find that the reflectivity for TIR can be strongly suppressed if surface plasmon polaritons (SPPs) resonance absorption occurs. To avoid SPP resonance absorption, our studies in this work propose the design strategy for ODR on the inclined sidewall as follows: if the ODR structure of the DUV LED with an inclined sidewall adopts thin dielectric layers, the high-index material should be selected as the dielectric layer; if a thick dielectric layer is adopted for the ODR structure, the low-index material should be selected as the dielectric layer.
Harvesting of surface plasmon polaritons: Role of the confinement factor
Authors: Gong Zu-Yong , Xie Zhen , Tian Guangjun , Duan Sai , Luo Yi
Published: September 2020

Surface plasmon polaritons (SPPs) are propagating waves generated at the interface of a metal (metamaterial) and a dielectric. The intensity of SPPs often exponentially decays away from the surface, while their wavelengths can be tuned by the confinement effect. We present here a computational method based on quantum-mechanical theory to fully describe the interaction between confined SPPs and adsorbed molecules at the interface. Special attention has been paid to the roles of the confinement factor. Taking a prototype dye sensitized solar cell as an example, calculated results reveal that with the increase in the confinement factor in metal/dielectric interfaces, the breakdown of the conventional dipole approximation emerges, which allows efficient harvesting of SPPs with low excitation energies and, thus, increases the efficiency of the solar energy conversion by dye molecules. Furthermore, at the metamaterial/dielectric interface, SPPs with large confinement factors could directly excite the dye molecule from its ground singlet state to the triplet state, opening an entirely new channel with long-living carriers for the photovoltaic conversion. Our results not only provide a rigorous theory for the SPP–molecule interaction but also highlight the important role played by the momentum of the light in plasmon related studies.
Kinetic energy flows in activated dynamics of biomolecules
Authors: Li Huiyu , Ma Ao
Published: September 2020

Protein conformational changes are activated processes essential for protein functions. Activation in a protein differs from activation in a small molecule in that it involves directed and systematic energy flows through preferred channels encoded in the protein structure. Understanding the nature of these energy flow channels and how energy flows through them during activation is critical for understanding protein conformational changes. We recently [W. Li and A. Ma, J. Chem. Phys. 144, 114103 (2016)] developed a rigorous statistical mechanical framework for understanding potential energy flows. Here, we complete this theoretical framework with a rigorous theory for kinetic energy flows: potential and kinetic energies interconvert when impressed forces oppose inertial forces, whereas kinetic energy transfers directly from one coordinate to another when inertial forces oppose each other. This theory is applied to analyzing a prototypic system for biomolecular conformational dynamics: the isomerization of an alanine dipeptide. Among the two essential energy flow channels for this process, dihedral ϕ confronts the activation barrier, whereas dihedral θ1 receives energy from potential energy flows. Intriguingly, θ1 helps ϕ to cross the activation barrier by transferring to ϕ via direct kinetic energy flow all the energy it received—an increase in θ̇1 caused by potential energy flow converts into an increase in ϕ̇. As a compensation, θ1 receives kinetic energy from bond angle α via a direct mechanism and bond angle β via an indirect mechanism.
Pyroelectric energy harvesting for dye decolorization using Ba0.9Ca0.1TiO3 ceramics
Authors: Sharma Moolchand , Patel Satyanarayan , Singh V. P. , Vaish Rahul
Published: September 2020

Ba0.9Ca0.1TiO3 (BCT) ceramic was prepared via a mixed-oxide route. Its microstructural characterization was done using x-ray diffraction, Raman spectrum, and scanning electron microscopy. Furthermore, its electrical properties were studied using dielectric measurement and impedance spectroscopy. BCT was also examined for the pyroelectric effect with the pyroelectric coefficient of ∼2.4 × 10−4 C/m2 K. An open circuit voltage was obtained during a temporal temperature change on BCT. Methylene blue dye degradation was recorded due to pyrocatalytic reactions in 120 heating/cooling cycles. The results show that pyrocatalysis could be an effective solution for the utilization of pyroelectric energy for water cleaning applications.
Reversible triplet energy hopping in photo-excited molecules: A two-site model for the spin polarization
Authors: Kandrashkin Yuri E. , Di Valentin Marilena , van der Est Art
Published: September 2020

The effect of reversible energy hopping between different local environments on the properties of spin-polarized excited states is investigated theoretically using a two-site model. The kinetic equations for the populations of the spin sublevels of the excited state are derived and then used to obtain analytical expressions for the evolution of the spin polarization of excited triplet states under specific conditions. The time dependence of the triplet state polarization patterns is also obtained by numerical solution of the kinetic equations. It is shown that the reversible energy hopping can lead to significant changes in the properties of the triplet state, including changes in the shape of the observed spectrum and, in some cases, the inversion of the sign of the polarization, the generation of the net polarization, and anisotropic spin-lattice relaxation. The relations between the parameters that can be observed experimentally by time-resolved electron paramagnetic resonance spectroscopy and the kinetic and dynamic parameters of the system are discussed.
Ultra-low magnetic damping in epitaxial Li0.5Fe2.5O4 thin films
Authors: Zheng Xin Yu , Riddiford Lauren J. , Wisser Jacob J. , Emori Satoru , Suzuki Yuri
Published: September 2020

The realization of more energy efficient nanomagnetic information devices relies on the existence of magnetic insulators capable of supporting pure spin currents in the absence of a dissipative charge current. Currently, there is a limited number of thin-film magnetic insulators with low magnetic damping. Li0.5Fe2.5O4 (LFO) is well known to possess the lowest damping among the bulk spinel structure oxides, but, thus far, LFO thin films have not lived up to these expectations. Here, we demonstrate low magnetic damping (even lower than typical bulk values) and bulk magnetization in 3 nm thick epitaxial LFO thin films. At room temperature, SQUID magnetometry shows a high saturation magnetization of 320 kA/m, and broadband ferromagnetic resonance measurements yield an effective Gilbert damping parameter of 1.3×10−3, which is among the lowest reported for ferro-/ferrimagnetic films of comparable thickness. Our results show the promise of LFO as a candidate material for spin current-based spintronics.
Cross-plane thermal conductivity in amorphous Si/SiO2 superlattices
Authors: Anufriev Roman , Tachikawa Saeko , Gluchko Sergei , Nakayama Yoshinori , Kawamura Tomoto , Jalabert Laurent , Nomura Masahiro
Published: September 2020

Heat conduction in superlattices demonstrates various atomic-scale effects, one of which is the ultra-low thermal conductivity. Remarkably, theoretical works even promise sub-amorphous thermal conductivity in superlattices made of amorphous materials. Yet, these predictions were not tested experimentally. Here, we experimentally study the cross-plane thermal transport in amorphous Si/SiO2 superlattices at room temperature. Using the micro time-domain thermoreflectance technique, we measured the thermal conductivity of superlattices with periods of 6.6, 11.8, and 25.7 nm. The thermal conductivity values are in the range of 1.1–1.5 W m−1 K−1 and generally agree with the values reported for amorphous Si and SiO2. However, the superlattice with the highest density of interfaces seems to have the thermal conductivity slightly below the amorphous limit. These data suggest that heat conduction below the amorphous limit might be possible in amorphous superlattices with a periodicity shorter than 6.6 nm.
BACKGROUND MATERIAL (with transparency masters)
Authors: Morse Robert A.
Published: September 2020

This section gives a brief review of some aspects of electrostatics. It is intended only as a reminder and does not attempt to fully develop the concepts mentioned. For a complete development of the physics, please see any of the standard textbooks on the subject. A recent short discussion of interest is given by W.R. Mellen (“Inexpensive Fun with Electrostatics”, The Physics Teacher, 27(2), 86, Feb 1989).
HOMEWORK ASSIGNMENTS
Authors: Morse Robert A.
Published: September 2020

A large variety of qualitative, semi-quantitative and quantitative homework problems on electrostatics can be found in various textbooks. Among the good sources are Conceptual Physics, by Paul Hewitt, both the college and high school versions, the Project Physics Text, various editions of PSSC Physics, and the questions sections of college and university texts such as those by Halliday and Resnick, Serway, Tipler, and others.
Used Math
Authors: Swartz Clifford E.
Published: September 2020

Here is a helpful reference work designed for the college science student needing a quick explanation of the mathematics found in the first two years of the college science curriculum. Rather than giving lengthy explanations of abstract mathematical theory, this useful handbook focuses on math as a scientist’s working tool.

Part reference and part reminder—the volume reinforces the student’s previous knowledge of math and guides the reader through the many unfamiliar mathematical computations that are part of his or her science requirements. Numerous examples throughout the book are drawn from actual situations encountered in science courses. The chapters may be used in any sequence and are extensively cross-indexed for user convenience.

Demonstrating how formal course work in chemistry, physics, astronomy, and the other sciences employ certain vital areas of mathematics, the book covers a broad range of important subjects, including reporting and analyzing uncertainty, units and dimensions, graphs, the simple functions of applied math, statistics, quadratic and high power equations, and simultaneous equations. Other chapters are devoted to determinants, vectors, complex numbers, calculus-differentiation, integration, series and approximations, common differential equations, and differential operators. The book contains many useful reference tables and summaries of formulas and techniques.

A valuable study aid for every science student and an auxiliary reference work certain to be used frequently, USED MATH gives solid explanations and examples of the "old and used" math fundamental to all science courses.
The Simple Functions of Applied Math
Authors: Swartz Clifford E.
Published: September 2020

Many physical phenomena can be described in terms of a very few simple math functions. Even when the description is not exact, the simple functions are often good approximations over a limited range. It is particularly gratifying to believe that nature is so constructed that these few functions describe essentially all the phenomena of interest in introductory science courses. Alternatively, one would have to believe that introductory science deals only with those topics that can be handled with simple math.

In this section we shall describe these simple functions—naming them, defining them algebraically, graphing them, illustrating their use, and demonstrating special properties, such as their slopes.
Some Common Differential Equations
Authors: Swartz Clifford E.
Published: September 2020

The problem of solving differential equations is very much like that of solving integrals. There are some common forms and techniques but no automatic method that always works. Simple differential equations can sometimes be reduced to integrals.
ELECTRICITY AND MAGNETISM
Authors: Frier G. D. , Anderson F. J.
Published: September 2020

Triboelectric effects are used to define the signs of charges. A glass rod rubbed with silk has a positive charge and an ebonite rod rubbed with cat’s fur is negatively charged. The components should be kept in a desiccator to keep them dry. There are many materials from which one can obtain charges due to triboelectric effects.
Physics Laboratory Activity #8a Force Distribution
Authors: Nelson Jim , Nelson Jane Bray
Published: September 2020

Obtain a beam, two bathroom scales, and two wood wedges. Place one wedge on each scale. Place the beam on the wedges, and adjust the position of the scales so that the wedges are near the ends of the beam.
Physics Laboratory Activity #9a Centripetal Force Àla PSSC
Authors: Nelson Jim , Nelson Jane Bray
Published: September 2020

An object moving with Uniform Circular Motion (UCM) is moving in a circular path with a constant speed. Remind yourself that such on object is accelerating because it is changing direction as it moves. The goal of this laboratory activity is to determine the relationship (i.e., the equation) among the variables for an object moving with uniform circular motion.
Physics Laboratory Activity #12a Hot Wheels Down the Track or Work & Kinetic Energy
Authors: Nelson Jim , Nelson Jane Bray
Published: September 2020

A. Allow a free wheeling toy car (e.g., a hot wheels car) to roll down a track for a total distance of about one meter. The track should be inclined at an angle of elevation of a few degrees.
Physics Laboratory Activity #26a Magnetic Field at the Center of a Square Loop
Authors: Nelson Jim , Nelson Jane Bray
Published: September 2020

Using one of the aluminum frames, wrap a long piece of wire around the frame. The number of turns wrapped around the frame should be between five and ten. Set the aluminum frame more than two feet from any ferromagnetic material. This includes metal parts of table, chair, your “power” supply and your ammeter. A small hand compass may be used to investigate the proposed site for the aluminum frame.
Background Information
Authors: Davids Mark , Rea R. Stephen , Zitzewitz Paul W.
Published: September 2020

At the conclusion of this unit, students will be able to :List the three major parts of a dynamic speaker.Describe the energy conversions that occur in a speaker, microphone, LED, and solar cell.Design, construct, and test a one-way telephone system.Construct, test, and explain the fundamentals of a reflection “photophone.”Construct and explain a circuit that can transmit a sound signal over a light beam produced by an LED.Define “attenuation” in a sentence. Use a mathematical example to show a calculation of attenuation.Define “bandwidth” and “carrier wave.”Apply Nyquist’s Theorem to a telephone system.Describe the fundamental differences between analog and digital signals.Identify several advantages of digital communications over analog communications.Convert an analog signal into a digital signal and visa versa.List several advantages of optical fiber over copper cable.Briefly describe the fundamentals of TDM (time domain multiplexing).
LABORATORY ACTIVITIES FOR TEACHING ABOUT MAGNETISM
Authors: Reiland Robert J.
Published: September 2020

Materials: Two bar magnets per group, a strong horseshoe magnet (optional), copper wire, fine iron filings or powder, paper clips, wood, plastic, nails, aluminum foil, water, sand, salt, glass, sheets of paper, coins and anything else that happens to be lying around.
MAGNETISM IN MODERN PHYSICS AND TECHNOLOGY
Authors: Reiland Robert J.
Published: September 2020

There are two major uses of magnets in modern particle accelerators. The first is to control the particle beams in circular accelerators with bending and focusing magnets, and the second is to determine the momenta of charged particles that are tracked in detectors. The second use usually involves very large solenoidal magnets.
Reproductive performance in goats and causes of perinatal mortality: a review
Authors: Robertson S. M. , Atkinson T. , Friend M. A. , Allworth M. B. , Refshauge G.
Published: September 2020

Goat meat production is an expanding industry in Australia. However, there is limited data quantifying the levels of reproductive performance, particularly under extensively grazed rangeland conditions, which would inform interventions to improve performance. This review aimed to quantify the levels of reproduction, time and causes of reproductive wastage in goats. It considers the levels of fertility, fecundity, embryonic loss, fetal loss and post-natal survival reported under Australian conditions, and comparisons are made with international reports. Key management factors that may contribute to reproductive performance include breed, seasonality, nutritional conditions, and weather conditions at kidding. While goats are potentially prolific breeders, in Australia, the variation in weaning rate (kids/doe joined) among properties is large (51–165%), although the causes of this variation are not well defined. Generally, conception and kidding rates are high, although fetal loss associated with undernutrition is more likely in goats than sheep. As with sheep, perinatal losses are generally the largest source of wastage, with an average 20% kid mortality, but this level is influenced by litter size and appears to be higher under extensive rangeland systems. The causes of perinatal kid loss under Australian conditions are similar to those in sheep, with starvation–mismothering–exposure and dystocia or stillbirth the key causes. Studies are needed to accurately quantify the level and causes of reproductive wastage in commercial herds, including a range of management situations, to enable effective interventions to be developed.
Stacking models for nearly optimal link prediction in complex networks
Authors: Ghasemian Amir , Hosseinmardi Homa , Galstyan Aram , Airoldi Edoardo M. , Clauset Aaron
Published: September 2020

Significance

Networks are a powerful tool for modeling complex biological and social systems. However, most networks are incomplete, and missing connections can negatively affect scientific analyses. Today, many algorithms can predict missing connections, but it is unknown how accuracy varies across algorithms and networks and whether link predictability varies across scientific domains. Analyzing 203 link prediction algorithms applied to 550 diverse real-world networks, we show that no predictor is best or worst overall. We then combine these many predictors into a single state-of-the-art algorithm that achieves nearly optimal performance on both synthetic networks with known optimality and real-world networks. Not all networks are equally predictable, however, and we find that social networks are easiest, while biological and technological networks are hardest.
Plasmacytoid dendritic cells cross-prime naive CD8 T cells by transferring antigen to conventional dendritic cells through exosomes
Authors: Fu Chunmei , Peng Peng , Loschko Jakob , Feng Li , Pham Phuong , Cui Weiguo , Lee Kelvin P. , Krug Anne B. , Jiang Aimin
Published: September 2020

Significance

Whether and how pDCs cross-prime CD8 T cells in vivo remain controversial despite extensive studies. Using a vaccine model where antigens were only delivered to pDCs, this report demonstrated that pDCs induced cross-priming and durable CD8 T cell immunity in vivo. However, cross-presenting pDCs required cDCs to achieve cross-priming by transferring antigens to cDCs. cDC1s but not cDC2s played a critical role in pDC-mediated cross-priming, despite both subsets acquiring antigens from pDCs similarly. Antigen transfer from pDCs to bystander cDCs was mediated by pDC-derived exosomes (pDCexos), which were generated under various conditions. Importantly, these pDCexos required cDCs to prime CD8 T cells, similarly to cross-presenting pDCs, thus identifying the pDCexo/cDCs pathway as a mechanism for pDCs to achieve cross-priming.
Ataxin-1 regulates B cell function and the severity of autoimmune experimental encephalomyelitis
Authors: Didonna Alessandro , Canto Puig Ester , Ma Qin , Matsunaga Atsuko , Ho Brenda , Caillier Stacy J. , Shams Hengameh , Lee Nicholas , Hauser Stephen L. , Tan Qiumin , Zamvil Scott S. , Oksenberg Jorge R.
Published: September 2020

Significance

Over 200 genomic loci have been found associated with the risk of developing multiple sclerosis (MS). Despite this important body of data, limited information exists on the cellular pathways and molecular mechanisms underlying MS genetic complexity. In this study, we report the functional characterization of the ataxin-1 encoding
ATXN1
susceptibility locus. Ataxin-1 is a polyglutamine protein that is classically associated with the neurodegenerative disorder spinocerebellar ataxia type 1 (SCA1). Here, we show that ataxin-1 also exerts a protective activity against autoimmune demyelination in a preclinical model of MS. This function is associated with an immunomodulatory role mainly targeting the B cell compartment. Altogether, these findings expand our current knowledge on both MS pathogenesis and ataxin-1 biology.
Interplay between cell-adhesion molecules governs synaptic wiring of cone photoreceptors
Authors: Cao Yan , Wang Yuchen , Dunn Henry A. , Orlandi Cesare , Shultz Nicole , Kamasawa Naomi , Fitzpatrick David , Li Wei , Zeitz Christina , Hauswirth William , Martemyanov Kirill A.
Published: September 2020

Significance

Humans, like most diurnal species, utilize cone photoreceptors to enable daylight vision. They detect color, cover a wide range of light intensities, and sustain fast responsiveness to faithfully sample rapidly changing scenery. All of these features that allow us to accurately see the world depend on the ability of cones to transmit their light-evoked signals to the brain. For this, cones form functional contacts with their downstream neurons—a process known as “synaptic wiring.” The molecular mechanisms that mediate establishment of cone synaptic contacts are largely unknown. Our studies fill this gap by identifying a set of molecules involved in functional wiring of cones.
A kinetic rationale for functional redundancy in fatty acid biosynthesis
Authors: Ruppe Sophia , Mains Kathryn , Fox Jerome M.
Published: September 2020

Significance

Fatty acid synthesis is a centrally important metabolic process in which a subset of enzymes often share catalytic roles, a form of “functional redundancy.” We developed a detailed kinetic model of the fatty acid pathway of
Escherichia coli
and paired that model with an experimentally reconstituted pathway to determine how partially redundant enzymes work together to build fatty acids. Our results suggest that enzymes with overlapping activities afford tight control of competing biochemical objectives (i.e., the total production, unsaturated fraction, and average length of fatty acids). This work describes how functional redundancy enhances the versatility of fatty acid synthesis and provides a powerful toolset for studying pathway kinetics.
A network of immune and microbial modifications underlies viral persistence in the gastrointestinal tract
Authors: Macleod Bethany L. , Elsaesser Heidi J. , Snell Laura M. , Dickson Russell J. , Guo Mengdi , Hezaveh Kebria , Xu Wenxi , Kothari Akash , McGaha Tracy L. , Guidos Cynthia J. , Brooks David G.
Published: September 2020

Many pathogens subvert intestinal immunity to persist within the gastrointestinal tract (GIT); yet, the underlying mechanisms that enable sanctuary specifically in this reservoir are unclear. Using mass cytometry and network analysis, we demonstrate that chronic LCMV infection of the GIT leads to dysregulated microbial composition, a cascade of metabolic alterations, increased susceptibility to GI disease, and a system-wide recalibration of immune composition that defines viral persistence. Chronic infection led to outgrowth of activated Tbet–expressing T reg cell populations unique to the GIT and the rapid erosion of pathogen-specific CD8 tissue-resident memory T cells. Mechanistically, T reg cells and coinhibitory receptors maintained long-term viral sanctuary within the GIT, and their targeting reactivated T cells and eliminated this viral reservoir. Thus, our data provide a high-dimensional definition of the mechanisms of immune regulation that chronic viruses implement to exploit the unique microenvironment of the GIT and identify T reg cells as key modulators of viral persistence in the intestinal tract.