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The development for equations of state both for polyimide and its reaction products is presented along with hydrody- namic simulations linking the two EOS through an Arrhenius rate law. The equations of state compare favorably to available data, and the hydrodynamic simulations are able to qualitatively reproduce many of the features seen in both legacy shock data and more modern embedded gauge data. However, quantitative agreement is not achieved, suggesting that new rate laws are needed to fully capture the effect of the reaction over a wide range of conditions.

A synchrotron beamline requires a set of reference values for calibration of photon beam energy, which are generally obtained from the absorption edges of different materials. However, due to oxidation and other chemical effects, these values are often different from the values of a pristine material. This makes the task of energy calibration difficult. In the present study, we have used a W/B4C multilayer for wavelength calibration for Soft x-ray reflectivity beamline (BL-03) at Indus-2. The structural parameters of the multilayer were obtained from Grazing Incidence X-ray Reflectivity (GIXRR) measurements. For energy calibration of soft x-ray beam, the reflectivity data at three different wavelengths were collected and analyzed to find correct wavelength values. The values so obtained were linearly interpolated to generate a curve for photon beam energy for 400-1500eV energy range.

Temperature dependent studies of optical transmission profiles of CaF2 crystals in the range 12–300 K are performed using vacuum ultraviolet (VUV) synchrotron radiation. The observed spectral profiles near the transmission edgeare fitted using the universal Urbach tail expression modified appropriately to incorporate the effects of residual gases present in high vacuum (10-6 mbar) systems. Satisfactory fit of the experimental data is obtained by including fitting parameters representing scattering and absorption by deposited layers, predominantly due to water. Details of the experimental setup, results and analysis of the data are discussed.

Nowadays, radiation has been utilized and importance in our daily life. Importantly, the radiation to achieve most effective goal and prevent radiation hazards for safe and accuracy. The principle of radiation protection are called "As Low As Reasonably Achievable" make sure staff follow these 3 major safety principles consisting of distance, time, and shielding. The radiation shielding material are common used as lead in manufacturing process lead are high toxicity. Therefore, the researcher is interested in using other elements to replace lead. This study used by glass structure formula (60-x) P2O5: 10Al2O3: 20Na2O: 10Gd2O3: xHo2O3 where x = 0.00, 0.05, 0.10, 0.50, 1.00 and 3.00 mol%. The result shows that the linear attenuation coefficient (µm) was increased when Ho2O3 concentration were increased. The mass attenuation coefficient (µ) was increased when Ho2O3 concentration were increased. The half value layer (HVL) was decreased when Ho2O3 concentration were increased. The results in this study in glass formula 57P2O5: 10Al2O3: 20Na2O: 10Gd2O3: 3Ho2O3 has high quality in the X-ray shielding range of 50-120 kVp compared to the concentration of 0.00, .0.0, .0.., 0.50 and 1.00 mol% respectively. The HVL of glass samples doped with Holmium compared with commercial windows, red brick, concrete, X-ray windows, and the results show that 0.50, 1.00 and 3.00 % mole the HVL less than X-ray glass. This study shows the properties of Ho2O3 in X-ray shielding and highly practical potentials in the environmental friendly radiation shielding materials without an additional of lead.

Extended-magnetohydrodynamics (MHD) transports magnetic flux and electron energy in high-energy-density experiments, but individual transport effects remain unobserved experimentally. Two factors are responsible in defining the transport: electron temperature and electron current. Each electron energy transport term has a direct analog in magnetic flux transport. To measure the thermally driven transport of magnetic flux and electron energy, a simple experimental configuration is explored computationally using a laser-heated pre-magnetized under-dense plasma. Changes to the laser heating profile precipitate clear diagnostic signatures from the Nernst, cross-gradient-Nernst, anisotropic conduction, and Righi-Leduc heat-flow. With a wide operating parameter range, this configuration can be used in both small and large scale facilities to benchmark MHD and kinetic transport in collisional/semi-collisional, local/non-local, and magnetized/unmagnetized regimes.

MgO is used as an optical element in multilayer mirror for synchrotron beamlines applications. However, it is highly hygroscopic in nature leading to deterioration of its optical properties. In this study we have shown how the optical properties of MgO thin film modifies on its exposure to ambient condition in the energy range of 45-70 eV covering the Mg L-edge region. We have carried out energy dependent soft X-ray reflectivity measurements on freshly prepared and aged MgO thin film for determination of optical constants. It is observed that the optical constants values of the aged sample deviate from the freshly prepared sample owing to water adsorption and increasing surface roughness as confirmed from atomic force microscopy (AFM) images.

The prediction of gas-phase ignition characteristics of a coal dust layer by a hot metal particle located on its surface was performed by numerical simulation. The theoretical study results can be used in practice to develop the provisions of fire safety management aimed at preventing large fires and man-made disasters. In this paper we consider coal dust, the particle dispersion of which varies in the range of 0.1–1 mm. As local sources of heating steel disk-shaped and parallelepiped-shaped particles with the same specific size of 10 mm are used. The nonideality factor influence of the thermal contact of a local heat source and a dispersed brown coal layer on its gas-phase ignition delay-times when the parameters in the considered system vary over a wide range, including the initial temperatures of metal particles from 1100 to 1600 K.

The Novosibirsk FEL facility includes three FELs operating in the terahertz, far-, and mid- infrared spectral ranges. It has rather long history, but its potential has not been fully revealed so far. The first FEL of this facility has been operating for users of terahertz radiation since 2004. It remains the world's most powerful sources of coherent narrow- band radiation in its wavelength range (90 – 340 µm). The second FEL was commissioned in 2009. Now it operates in the range of 35 – 80 µm, but we plan to replace its undulator soon with a new one, and its short wavelength boundary will be shifted down to 15 µm. The third FEL was commissioned in 2015 to cover the wavelength range of 5 – 20 µm. Its undulator comprises three separate sections. Such lattice is suited very well to demonstrate the new off-mirror way of radiation outcoupling in an FEL oscillator (so called electron outcoupling), which we also plan for near future. We also intend to improve the accelerator injection system. As a result, the average electron beam current and consequently the radiation power of all the three FELs will increase. In this paper, we present an overview of the facility and discuss our recent achievements and future plans.

The paper studies the effect of electric arc surfacing modes with T-590-N and EN-60M coated electrodes on the physical, mechanical and operational properties of coatings applied to low-alloy steel 09G2S. It is shown that the characteristics of heat and mass transfer are significantly influenced by the energy parameters of the mode, as well as the algorithm for changing them in the low-frequency range. To assess the degree of influence of energy parameters, thermal imaging was used as part of a research diagnostic complex for registering rapidly occurring heat and mass transfer processes. It is found that modifying the structure of surfaced coatings by electric arc pulsed action allows increasing its uniformity, dispersion, hardness and wear resistance. Changing the energy parameters of the modes reduces the structural inhomogeneity that occurs during surfacing along the coating cross-section by reducing the size of the structural components.

Single walled carbon nanotubes (SWNTs) films are prepared by dispersing SWNTs in DMF solution which is filtered over flexible polycarbonate membrane by vacuum filtration method. SWNTs film has been functionalized with different amounts (0.1 mg, 0.2 mg and 1 mg) of SnO2 nanoparticles of size 20-30 nm. Sensor is made by mounting a piece of CNT and different CNT/SnO2 films on PCB headers and contacts are taken by using Au wire. The sensing behavior of CNT/SnO2 towards NO2 and NH3 in the concentration range of 0.5 to 100 ppm has been studied. The sensing response has been compared to that obtained from pristine SWNTs. SWNTs with 0.1 mg of SnO2 has given the maximum improvement of 1.6-8.5% and 0.8-1.75 times in response for NH3 and NO2 respectively, as compared to pristine CNTs..

In this work, we synthesized the Dy doped BaF2 phosphor by co-precipitation method and studied its kinetic parameters. The synthesized BaF2:Dy was found to possess FCC structure and having an average crystallite size around 52 nmas obtained from XRD. BaF2:Dy was irradiated with 6MeV electron using Microtron Accelerator. The optimized TL result shows a single glow peak at 155 °C. Peak shape and Glow Curve Deconvolution (GCD) method has been usedto study the activation energy. Using the GCD method, we found better kinetics parameters than peak shape method when we compared it with experimental data. In GCD, we resolved TL glow curve into two peaks. The GCD results indicates that parameters for 1st peak and 2nd peak are E=0.9eV, b=1.8, s=6.27×1011 s−1 and E=1eV, b=1.09, s=3.4×1012s−1 respectively. BaF2:Dy shows a linear response over a wide range of radiation doses.

Structural changes in the Seymchan meteoritic substance after the experiments on loading with spherically converging shock waves have been studied by optical and electron microscopy. It was noted that shock pressure and temperature increases from the outer part to the center of the loaded balls. In one experiment with shock-wave loading, it was possible to obtain varieties of textures with different degrees of shock and thermal metamorphism. These results prove that the shock wave loading experiment can be successfully applied in modeling space shocks and can be used to experimentally model processes at the small bodies of the solar system. The cooling rates of the melted zone of the shocked octahedral sample was estimated for the crystallization range.

Exciton absorption spectra of thin films of complex compounds AgPbBr3, AgPb2Br5, and AgPb3Br7 were studied in the photon energy range 2–6 eV. It was established that the compounds belong to the direct band dielectrics; low-frequency excitons are localized in the structural layers (PbBr8)6– of the crystal lattice and have a quasi-two-dimensional nature.

The electronic structure and optical properties of GdNi2Mnx compounds (x = 0, 0.4, 0.6) were investigated. Spin-polarized electronic structure calculations were performed in the approximation of local electron spin density corrected for strong electron correlations using the LSDA+U method. The changes in the magnetic moments and exchange interactions in GdNi2Mnx (x = 0, 0.4, 0.6) governing the increase in the Curie temperature with manganese concentration were determined. The optical constants of the compounds were measured by the ellipsometric method in the wide spectral range of 0.22–15 μm. The peculiarities of the evolution of the frequency dependences of optical conductivity with a change in the manganese content were revealed. Based on the calculated densities of electron states, the behavior of these dispersion curves in the region of interband absorption of light was discussed. The concentration dependences of several electronic characteristics were determined.

The self-assembly of binary colloidal mixtures provides a bottom-up approach to create novel functional materials. To elucidate the effect of composition, temperature and pressure on the self-assembly behavior of size-asymmetric mixtures, we performed extensive dynamics simulations of a simple model of polymer-grafted colloids. We have used a core-softened interaction potential and extended it to represent attractive interactions between unlike colloids and repulsion between like colloids. Our study focused on size-asymmetric mixtures, where the ratio between the sizes of the colloidal cores was fixed at $\frac{\sigma_{B}}{\sigma_{A}}=0.5$. We have performed extensive simulations in the NPT and NVT ensembles to elucidate the phase behavior and dynamics of mixtures with different stoichiometric ratios. Our simulation results uncovered a rich phase behavior, including the formation of hierarchical structures with many potential applications. For compositions where the small colloids are the majority, sublattice melting occurs for a wide range of densities. As the temperature is decreased, the small colloids localize, akin to a metal-insulator transition, with the small colloids playing a role similar to electrons. Under these conditions the large colloids form a well-defined lattice, whereas small colloids can diffuse through the system. Our results are summarized in terms of phase diagrams.

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility ( μe), electron transport time ( TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

Ge doping in AlGaN was studied over a wide dopant concentration range. For high Ge concentrations, the formation of VIII–nGeIII was determined to be the main point defect limiting the conductivity. It was shown that the complex formation could be suppressed by controlling chemical potentials during growth, leading to a higher maximum achievable carrier concentration and selective stabilization of a certain complex type. Chemical potential of the growth species was varied by changing the V/III ratio and growth temperature. Free carrier concentrations as high as 4 × 1019 cm−3 were achieved in Al0.4Ga0.6N:Ge grown on sapphire substrates under “metal-rich” conditions. The ability to control the onset of self-compensation and to stabilize a certain charge state of the compensating defect is of great technological importance for application of AlGaN in various devices.

The crystal structure of tungsten monocarbide (WC) is researched from 0 to 650 GPa through first principles calculations. The results verify that the experimental structure (hP2-WC) with the space group P 6¯m2 is the most stable phase in a wide range of pressure. Above 231 GPa, a new stable structure (space group P63/mmc, hP4-WC) is found to be the most stable phase, and it will transform to a CsCl-type phase (cF8-WC) around 582 GPa. Phonon calculations reveal that the hP4-WC phase is dynamically stable and may be a metastable structure at ambient conditions. The cF8-WC phase possesses dynamical stability above 20 GPa. The hP4-WC phase is a low compressible material with a large bulk modulus of 377 GPa at zero pressure. The hardness values of hP2-WC and hP4-WC at zero pressure are 32 and 21 GPa, respectively, while the cF8-WC phase possesses a hardness of 21 GPa at 20 GPa, implying that these phases are potential hard materials. The temperature–pressure phase boundary of WC is obtained by means of the quasi-harmonic approximation method. As the temperature increases, the transition pressure from hP2-WC to hP4-WC remained nearly unchanged. The transition pressure between hP4-WC and cF8-WC decreases with the increasing temperature.

We report on the results of an experimental campaign to measure time-varying velocity distributions in the near-field of a low power Hall thruster. We employ a sample-hold technique, enhanced by parallelizing the measurement hardware into several signal processing channels that vastly increases the data acquisition rate. The measurements are applied to study flow field dynamics in a commercial BHT-600 Hall thruster undergoing unforced breathing mode oscillations in the 44–49 kHz range. A very detailed experimental picture of the near-field emerges from these studies. The results indicate that velocity fluctuations lessen further downstream of the exit plane. Along the thruster axis where there is a general appearance of a central jet, there is evidence of a low velocity ion population in between the periodic bursts of high velocity ions, indicative of local ionization of neutrals outside of the thruster. One possible source of this residual ionization may be background chamber gas, which is not unexpected with the limited pumping capacity of ground test facilities.

A simple model describing the most significant impact of electromagnetic heating on pathogen-containing aerosols is presented. While the physics of ohmic heating are well understood, the connection between the unsteady temperature increase with net pathogen inactivation in an aerosolized electrolyte solution over a range of frequencies is not clear. The model is composed of two parts: a thermal model of electromagnetic heating of the droplets and a survival model describing the active pathogen population as a function of time. The droplets of saline solution, whose electrical conductivity depends on salt concentration and carrier frequency, are assumed to be small enough so that ambient air flows are sufficient to counter gravity, and the droplets are assumed to be equally spaced. As the droplets move with the ambient air, energy transport is limited to conduction, and within an adiabatic system, the mean spatial mode dominates the thermal transients of the air-droplet system. The kill rate of the pathogen depends on temperature, and the result of our thermal model informs the pathogen population through the Arrhenius kill rate. The model shows strong qualitative agreement with microwave inactivation of MS2 bacteriophages in aerosolized droplets. Inactivation is improved with larger electric field amplitudes, even for small duty cycles. We show that for a range of viruses with known activation energy, the thermal inactivation mechanism is more reliable for viruses with larger activation energy.

Optical trapping has become an important tool in a wide range of fields. While these traps are most commonly realized using optical tweezers, dual-beam optical traps offer specific advantages for certain experiments. It is commonly assumed that a particle will become trapped midway between the focal points of the two beams. However, this is not always the case. We perform a theoretical and experimental investigation of trapping positions of weakly absorbing, spherical particles in a dual-beam optical trap. We evaluate the effect of offsetting the beams in the direction of propagation and identify four regimes with distinct trapping behavior. The effect of an offset perpendicular to the propagation direction and an imbalance in power between the two beams is also considered. Experiments utilize an aqueous aerosol particle whose size can be readily controlled and monitored over hundreds of nanometers. As such, it serves as an excellent probe of the optical trap. We demonstrate that it is possible to fit the evolution of the particle trapping position in order to determine the position of the particle relative to the focal point of each beam. The results presented here provide key insights into the workings of dual-beam optical traps, elucidating more complex behaviors than previously known.

Nanofluids-dispersions of nanometer-sized particles in a liquid medium-have been proposed for a wide variety of thermal management applications. It is known that a solid-like nanolayer of liquid of typical thicknesses of 0.5-1 nm surrounding the colloidal nanoparticles can act as a thermal bridge between the nanoparticle and the bulk liquid. Yet, its effect on the nanofluid viscosity has not been elucidated so far. In this article, we compute the local viscosity of the nanolayer using equilibrium molecular dynamics based on the Green-Kubo formula. We first assess the validity of the method to predict the viscosity locally. We apply this methodology to the calculation of the local viscosity in the immediate vicinity of a metallic nanoparticle for a wide range of solid-liquid interaction strength, where a nanolayer of thickness 1 nm is observed as a result of the interaction with the nanoparticle. The viscosity of the nanolayer, which is found to be higher than its corresponding bulk value, is directly dependent on the solid-liquid interaction strength. We discuss the origin of this viscosity enhancement and show that the liquid density increment alone cannot explain the values of the viscosity observed. Rather, we suggest that the solid-like structure of the distribution of the liquid atoms in the vicinity of the nanoparticle contributes to the nanolayer viscosity enhancement. Finally, we observe a failure of the Stokes-Einstein relation between viscosity and diffusion close to the wall, depending on the liquid-solid interaction strength, which we rationalize in terms of the hydrodynamic slip.

We present the results of calculations of the ion microfield distribution function of a two-component fully ionized classical Coulomb plasma having ion charge numbers from two to three, performed by the molecular dynamics method. The model of ultracold plasma is used, where particles interact according to the Coulomb law without any restrictions at large or small distances. The calculations are carried out in a wide range of the strong coupling parameter. A comparison with the results of calculations for other plasma models is given. The results obtained can be used for any classical non-degenerate strongly coupled plasma.

Harvesting multi-frequency sound energy from environmental noise is a meaningful topic to supply energy for potential devices. In this work, we constructed an array of Helmholtz resonators (HRs) with cross-linked polypropylene (IXPP) ferroelectret films on the inner walls of HR cavities, whose resonant frequencies range from 300 to 800 Hz and quasi-static piezoelectric coefficient d33 is 230 pC/N. The energy harvesting performance of IXPP films is investigated, both theoretically and experimentally, in a single HR with various sizes, showing the high energy conversion capability close to the resonant frequencies of HRs, e.g., 337, 375, 445, 522, 588, 661, 739, 782, and 795 Hz, in the experiment. By putting one, two, three, and four samples of nine different sized HRs in series connection in order, we measured the average output power of 3.16, 5.31, 7.36, and 8.66 nW at the resonant frequencies. It shows that the output power of IXPP films has been significantly improved at multiple frequencies by series connection of IXPP films. In parallel, the optimal electrical resistance increases in a quasilinear way compared to the number of HRs. These results are helpful for designing efficient sound energy harvesters in the broadband frequency range.

A graphite anode ablates in an arc system producing nanoparticles. Experiments show that the ablation rate increases sharply when the current density at the anode exceeds some critical value, which separates the low ablation and high ablation modes. According to the existing hypotheses, the high ablation mode takes place when the anode voltage drop, which is negative in the low ablation mode, turns positive. Based on the work of Nemchinsky [J. Appl. Phys. 130, 103304 (2021)], where the anode voltage drop was evaluated, in this paper, the thermal regime of the anode is considered. It is shown that the main heating mechanism is electron condensation on the anode. The main cooling mechanism is radiation in the low ablation mode and cooling by sublimation in the high ablation mode. In the last case, the energy necessary to compensate for the strong cooling effect of sublimation is delivered by electrons accelerated at the positive anode drop inside the anode sheath. The proposed model allows one to find the ablation rate for a wide range of arc currents and anode diameters. Comparison to the available experimental data shows reasonable agreement. Based on analysis of the experiments and calculations, it was hypothesized that the ablation rate is not sensitive to the presence of a catalyst.

We report the laser intensity dependence of multiply charged atomic ions (MCAIs) Arn+ with 2 ≤ n ≤ 8 from argon clusters in focused nanosecond laser fields at 532 nm. The laser field, in the range of 1011–1012 W/cm2, is insufficient for optical field ionization but is adequate for multiphoton ionization. The MCAI sections of the mass spectra for clusters containing 3700 and 26 000 atoms are dominated by Arn+ with 7 ≤ n ≤ 9, extending to Ar14+. While the distributions of the MCAIs remain largely constant throughout the intensity range of the laser, the abundance of Ar+ relative to the abundances of the MCAIs increases dramatically with increasing laser intensity. Consequently, exponential fittings of the yields result in a larger exponent for Ar+ than for MCAIs, and the exponents of MCAIs with 2 ≤ n ≤ 8 are similar, with only slight variations for different charge states. The width of the arrival time and, hence, the corresponding kinetic energy of Ar+ also increases with increasing laser intensities, while the width of the arrival time of MCAIs remains constant throughout the range of measurements. These results call for more detailed theoretical investigations in this regime of laser–matter interactions.

Granular molecular crystals show a large variation in the orientation, length, shape, and cohesive interactions of interfaces when embedded in a polymer matrix. But the determination of the associated excess of free energy is not straightforward, especially due to the entropic contribution which is not negligible for molecular compounds. The surface free energy (SFE) is also important to predict crystal shapes and growth or to prove crucial insights into the mesoscale interfaces in the granular composites often with interfacial defects, voids, and pores. In this paper, we use Molecular Dynamics (MD) and assess and adapt two non-equilibrium methods, namely, non-equilibrium thermodynamic integration (NETI) and modified steered MD (SMD), to determine the SFE of various facets of a high-energy molecular crystal of interest: β-HMX. Starting with defect-free surfaces, both methods agree well with experiment concerning the most stable facets, whose energy is further lowered by a large entropic contribution. For some facets, surface creation (debonding process) and annihilation (bonding process) show fundamentally different paths, henceforth irreversible. Then, we discuss some sources of discrepancy between theoretical and experimental SFE, considering non-reversible dissipative events, surface roughness, and differences between various experimental techniques. These non-equilibrium methods can be applied to a wide range of molecular crystals and to study interface stability in polycrystals or with binding polymers, including the effects of various defects.

The dimer under study is a dielectric structure formed of two identical sub-units. Dimer interactions with electromagnetic waves are widely studied in connection with electromagnetic properties of complex systems. The dimer in the form of two closely spaced grapes is also a subject of high public interest because its gap region sparks curiously in a household microwave oven. A recent paper presented the first scientific interpretation of this long-standing puzzle. It attributed the sparking phenomenon to an electromagnetic hotspot in the gap created by electromagnetic resonances in the dimer. This study has opened up a fertile ground for further research as well as motivating the current study on an independent mechanism. Our simulation and experimental results consistently point to an electrical origin for the sparks. The triggering mechanism is a two to three orders-of-magnitude buildup of localized electric field in the narrow gap, which results from the mutual enhancement of polarization charges on opposite sides of the gap. Consequently, sparks are observed at the frequency of 27 MHz, at which no electromagnetic resonance in the dimer is possible. Results also indicate a broad frequency range of the electrical mechanism, which persists even when the dimer is in strong electromagnetic resonance with the first few higher-order modes. These quantitative characterizations of basic dimer properties, in particular the broad frequency range of the polarization-charge enhancement effect, may be helpful for the understanding of collective behavior of multi-particle systems under electromagnetic radiations.

A numerical tool for analysing spatially anisotropic electron populations in electron cyclotron resonance (ECR) plasmas has been developed, using a trial-and-error electron energy distribution function (EEDF) fitting method. The method has been tested on space-resolved warm electrons in the energy range $2-20\,\mathrm{keV}$, obtained from self-consistent simulations modelling only electron dynamics in ECR devices, but lacked real-world validation. For experimentally benchmarking the method, we attempted to numerically reproduce the experimental X-ray emission spectrum measured from an argon plasma. Results of this analysis have provided crucial information about density and temperature of warm electrons, and competing distributions of warm and hot electron components. This information can be fed back to simulation models to generate more realistic data. Subsequent application of the numerical tool as described to the improved simulation data can result in continuous EEDFs that reflect the nature of charge distributions in anisotropic ECR plasmas. These functions can be also applied to electron dependent reactions, in order to reproduce experimental results, like those concerning space-dependent K$\alpha$ emissions.

We study the motion of radially driven fluid-immersed particles in a novel Hele-Shaw cell with open boundaries. The initially uniform suspension forms a striped pattern within a specific range of horizontal oscillation frequencies and for sufficiently large amplitudes. We observe that the initial coarsening dynamics of the stripes gradually slows down and the pattern reaches a steady state after a few minutes. The distance between the stripes in the steady state exhibits an exponentially saturating increase with increased oscillation amplitude or frequency. The width of the stripes decreases as a power-law with the frequency while its amplitude dependence follows a logistic function. We propose a mechanism -- based on the interplay between shear stress, hydrodynamic interactions, and frictional forces -- to link the structural characteristics of the stripes to the properties of the oscillatory external drive., Comment: 7 pages, 4 figures

The equation of states, diffusions, and viscosities of strongly coupled Fe at 80 and 240 eV with densities from 1.6 to 40 g/cm3 are studied by orbital-free molecular dynamics, classical molecular dynamics with a corrected Yukawa potential and compared with the results from average atom model. A new local pseudopotential is generated for orbital free calculations. For low densities, the Yukawa model captures the correct ionic interaction behavior around the first peak of the radial distribution function (RDF), thus it gives correct RDFs and transport coefficients. For higher densities, the scaled transformation of the Yukawa potential or adding a short range repulsion part to the Yukawa potential can give correct RDFs and transport coefficients. The corrected potentials are further validated by the force matching method. Keywords: Transport properties, Orbital-free molecular dynamics, Yukawa model, Force matching, PACS codes: 34.20.Cf, 52.25.Fi, 52.27.Gr, 52.65.Yy

The absorption spectra of thin films of KPb2(Cl1-xBrx)5 (0 ≤ x ≤ 1) are studied in the spectral range of 2–6 eV (T = 90 K). Solid solutions with a mixed monoclinic structure are formed at all concentrations 0 ≤ x ≤ 1 and a tetragonal structure is found for 0.9 ≤ x ≤ 1. The temperature of the tetragonal to monoclinic phase transition in the solid solutions increases with the amount of Cl additive. The concentration dependences of the spectral location and half width of the long-wavelength exciton bands are the result of small-scale and large-scale fluctuations in the composition of the solid solution.

The work is concerned with the modeling of low-current quasi-stationary discharges, including the Townsend and corona discharges. The aim is to develop an integrated approach suitable for the computation of the whole range of existence of a quasi-stationary discharge from its inception to a non-stationary transition to another discharge form, such as a transition from the Townsend discharge to a normal glow discharge or the corona-to-streamer transition. This task includes three steps: (i) modeling of the ignition of a self-sustaining discharge, (ii) modeling of the quasi-stationary evolution of the discharge with increasing current, and (iii) the determination of the current range where the quasi-stationary discharge becomes unstable and the non-stationary transition to another discharge form begins. Each of these three steps is considered in some detail with a number of examples, referring mostly to discharges in high-pressure air.

The generation of two-photon photocurrent plays an essential role in realizing intermediate-band solar cells (IBSCs) with high conversion efficiencies. This current generation process strongly depends on the photocarrier dynamics in the intermediate levels, which can sometimes give rise to a deficient output current unexpectedly. In this work, we investigated the two-photon photocurrent generation process in InAs quantum dot (QD)-in-well intermediate-band solar cells. The two-photon photocurrent is generated by an interband transition in the structure (for example, in the well or the QD) and a subsequent intraband transition in the QD, and we used two different light sources to separately control these transitions. We found that, in the case of QD interband excitation in a sample with multiple wells, the carrier collection efficiency does not simply increase with the intraband excitation intensity; in the range from about 0.08 to 0.5 W/cm2, the collection efficiency decreases with increasing intraband excitation density. A comparison between samples with different numbers of wells revealed that the repetition of carrier trapping and detrapping during the transport in a multi-well structure can effectively modulate the recombination rate. This modulation induces a reduction of the current yield under certain illumination conditions. We propose a model to explain this phenomenon and verify it by investigating the bias dependence of the two-photon photocurrent from the QD.

A conspicuous emission phenomenon of luminous particles from the liquid anode surface of an atmospheric pressure DC glow discharge is reported. The emission has been shown to occur when the plasma forms a pattern on the surface of the liquid electrolyte. The spatial-temporal evolutions of the trajectories of emitted particles were studied using a high-speed imaging system. Particles were sampled in flight using a witness plate for analysis. Critical particle characteristics were examined using electron microscope technologies. The morphology of the resulting splats and compositions suggest that they are molten droplets with a great deal of structure, including evidence of nanoprecipitation. A theoretical model was employed to estimate the particle size from the measured splats, which provides a radius range within a hundred micrometers. This experiment leads to the postulation of a mechanism in which particle emission at the plasma liquid interface is likely driven by the Taylor cone effect.

Temperature dependencies of optical reflectance and cathodoluminescence (CL) spectra were measured for the MgO single crystal using a custom-built vacuum ultraviolet (VUV) spectroscopic system. Simultaneous observation enabled us to identify free exciton (FE) and bound exciton (BE) emissions by comparing the CL emission with the exciton resonance structures. The results indicated that the BE emission dominates the near-band edge emission, and the FE emission was observed as a shoulder at 300 K. The results ensure strong excitonic nature and potential of a rock salt-structured MgO-based material system for an active element in the VUV light emitter.

In SiN/AlGaN/GaN heterostructures, the evaluation of interface charges at the SiN/AlGaN and AlGaN/GaN interfaces is crucial since they both rule the formation of the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. In this paper, we conducted a thorough analysis of the gate-to-channel capacitance CGC(VG) and of the drain current ID(VG) over a gate voltage VG range enabling the depletion of the 2DEG and the formation of the electron channel at the SiN/AlGaN interface. This work includes the establishment of analytical equations for VTH1 (formation of the 2DEG) and VTH2 (formation of the electron channel at the SiN/AlGaN interface) as a function of interface charges and of the p-doping below the 2DEG. The inclusion of the p-doped layer below the 2DEG and the use we made of VTH2 have not been reported in previous studies. Our analysis allows a reliable estimate of the interface charges at the AlxGa1−xN/GaN and SiN/AlxGa1−xN interfaces for various Al concentrations x as well as to demonstrate that the polarization charge at the SiN/AlxGa1−xN interface is compensated, which confirms previous findings. Moreover, this compensation is found to be induced by the AlGaN layer rather than the SiN layer.

Performance and lifetime analysis of electrospray thrusters requires accurate knowledge of the mass and charge distributions of the plume. Mass flux and current density distributions were measured for a single capillary electrospray emitter using EMI-Im and found to be substantially different across a wide range of flow rates and emission voltages. Mass flux measurements yield an n∼3 super-Gaussian profile across all flow rates and voltages, while current density measurements change shape from n∼1.5– 2.5 super-Gaussian profiles monotonically with decreasing flow rate, where n=1 is Gaussian and higher n values correspond to increasingly more flat-top “super-Gaussian” profiles with steeper drop-off toward higher angles. For increasing flow rate, the mass flux profile grows while maintaining its shape, whereas the current density profile exhibits higher kurtosis, i.e., plumes that distribute proportionately more charge to higher angles. Additionally, higher extraction voltages exhibited tilted emission that led to highly off-axis plumes, ∼10°, for both mass flux and current density. Lifetime and performance assessments of electrospray thrusters must consider that mass flux and current density in the plume display different distribution shapes and trends in shape across changes in extraction voltage and flow rate.

Creating strong materials at 325 degrees Celsius using particles in the nanometer range that arrange perfectly in supercrystals via self-assembly

Efficient carrier separation and suitable band edge position are necessary conditions for photocatalytic water splitting. Based on density functional theory, the electronic properties and optical performance of the GeC/ZnTe vdW heterostructure are systematically explored. The heterostructure with inherent type-II band arrangement is conducive to constantly separate the hole–electron pairs, thus improving the utilization of solar energy. Meanwhile, an excellent optical absorption coefficient has been proved in the heterostructure with large carrier mobility. Within the strain range of –4% to +3%, the heterostructure possesses appropriate band edges for photocatalytic water splitting and the light absorption performance is obviously improved. High solar-to-hydrogen efficiency (26.81%) means that the heterostructure can effectively convert photon energy into water splitting. These findings predict the possibility of GeC/ZnTe heterostructures as photocatalysts for water splitting and other optoelectronic devices.

Depletion interactions between colloids of discoidal shape can induce their self-assembly into columnar aggregates. This is an effect of entropic origin with important implications in a range of colloidal systems, particularly in the clustering of erythrocytes that determine the rheological properties of blood. Here, we investigate the equilibrium state reached by discoidal colloids in a solution of smaller depletant particles. We develop a thermodynamic model of depletion-induced aggregation based on self-assembly theory and solve it analytically. We test the validity of the model by using Langevin simulations of a system of discs and depletant particles in which the depletion interaction emerges naturally. In addition, we consider the effect of an attractive interaction between depletant and discoidal particles, which we show induces a re-entrant dependence of aggregation with temperature.

Ion implantation is performed in 4H-SiC with 11B, 27Al, 31P, 51V, 71Ga, and 75As ions using energies between 40 and 300 keV at various fluences along the [000-1] or the ⟨11-2-3⟩ axes. Secondary ion mass spectrometry is utilized to determine the depth distribution of the implanted elements. A Monte Carlo binary collision approximation (MC-BCA) code for crystalline targets is then applied to explain the influence of the electronic shell structure on electronic stopping and the obtained channeled ion depth distributions. The results show that, as the atomic number increases in a row of the periodic table, i.e., as the ionic radius decreases and the electron clouds densify, the interaction with the target electrons increases and the range is reduced. The decreased range is particularly pronounced going from 27Al to 31P. The reduction in channeling depth is discussed in terms of electronic shells and can be related to the ionic radii, as defined by Kohn–Sham. It is shown that these shell effects in channeled implantations can easily be included in MC-BCA simulations simply by modifying the screening length used in the local treatment of electronic stopping in channels. However, it is also shown that, for vanadium ions with an unfilled d-shell, this simple model is insufficient to predict the electronic stopping in the channels.

The high-absorption ultra-thin metasurface absorber has important applications in EM radiation prevention and stealth design. In this paper, the proposed metasurface absorber composed of one-dimensional phase gradient supercell and uniform resonant supercell can reach perfect absorption at 10 GHz by reducing the scattering of the surface wave. Furthermore, the two-dimensional phase gradient metasurface absorber has better absorption of waves with different polarization angles and a wider range of incident angles. Our work provides a promising method to achieve high absorption, which is simpler and more robust than adjusting the effective EM parameters of metasurface absorber.

Ratcheted multi-step hopping electron transfer systems can plausibly produce directional charge transport over very large distances without requiring a source–drain voltage bias. We examine molecular strategies to realize ratcheted charge transport based on multi-step charge hopping, and we illustrate two ratcheting mechanisms with examples based on DNA structures. The charge transport times and currents that may be generated in these assemblies are also estimated using kinetic simulations. The first ratcheting mechanism described for nanoscale systems requires local electric fields on the 109 V/m scale to realize nearly 100% population transport. The second ratcheting mechanism for even larger systems, based on electrochemical gating, is estimated to generate currents as large as 0.1 pA for DNA structures that are a few μm in length with a gate voltage of about 5 V, a magnitude comparable to currents measured in DNA wires at the nanoscale when a source–drain voltage bias of similar magnitude is applied, suggesting an approach to considerably extend the distance range over which DNA charge transport devices may operate.

Table-top neutron/x-ray sources are of great interest for uses in neutron activation analyses, in neutron/x-ray radiography, and also in medical applications. Inertial electrostatic confinement fusion (IECF) is a multiple neutron source that can emit neutrons, protons, x rays, etc., as basic products when operated in both continuous and pulsed modes. In this work, D-D neutrons are produced in the steady-state mode using a cylindrical IECF device. The neutron production rate has been optimized by using cathodes having different dimensions and geometrical transparencies. The maximum neutron production rate is found to be approaching 107n/s, using a cathode having eight grid wires and a diameter of 3 cm. The neutrons are successfully used for neutron activation analysis of materials containing explosive elements. X-ray spectrum having a wide range of photon energies (30–70 keV) has been detected from this device while operated in the continuous mode. X-ray radiography of high density objects has also been performed and reported for the first time using the cylindrical IECF source with negative polarity of the central grid in this paper.

Crystal-orientation-dependent properties in low symmetric two-dimensional material ReS2 have inspired its novel applications in photonics, electronics, and optoelectronics. In this work, Ar+ ion bombardment is used to treat ReS2 with different thicknesses, and different amounts of defect densities are introduced in ReS2 flakes. Angular dependent polarized Raman spectra is used to probe the change in anisotropy. The intensities of mode V exhibit maximum and minimum intensities with incident polarization along the b-axis and perpendicular. The intensity ratio Imin/Imax is used as a quantity to detect the change in anisotropy. It is found that with the same defect density, the change in anisotropy in 1-layer (L) ReS2 is the highest among ReS2 flakes; thus, 1L ReS2 is susceptible to ion bombardment. With an increase in the defect density in 1L ReS2, an increase in the Imin/Imax value is observed. A phenomenological model is established to understand the quantitative relationship between defect density and anisotropy, and the isotropic scattering range associated with defects is obtained. The results here provide ways of quantitatively understanding anisotropy by angular polarized Raman spectroscopy as well as ways of tuning anisotropy in two-dimensional anisotropic materials by ion bombardments.

Elastic properties of amorphous solids remain a topic of intense interest due to their important roles in a wide range of applications. Prior works have focused on short-range, local structural features, such as number density and coordination number, to elucidate the underlying mechanism of elastic moduli in glasses. Here, we report strong correlations among the spatial extension of the interatomic potential, elastic moduli, and the coherence lengths of the medium-range structural order through molecular dynamics simulations for single element glasses. Our findings demonstrate an unconventional design principle to engineer elastic properties by extending the medium-range order and provide insights into the microscopic origin of elastic properties in amorphous solids.

Binary collision rates are calculated for the permeable particles undergoing (i) Brownian motion, (ii) gravity sedimentation, (iii) uniaxial straining flow, and (iv) shear flow. Darcy's law is used to describe the flow inside the permeable particles, and no-slip boundary conditions are applied at particle surfaces. A leading-order asymptotic solution of the problem is developed for the weak permeability regime K=k/a2≪1, where k=12(k1+k2) is the mean permeability and a=a1a2/(a1+a2) is the reduced radius; ai, ki (i = 1, 2), respectively, is the radius and permeability of each particle. The resulting collision rates are given by the quadrature of the pair mobility functions for permeable particles in the near-contact lubrication region and size-ratio-dependent parameters obtained from standard hard-sphere pair mobility functions. Collision rates in shear flow vanish below a critical value of the permeability parameter K* that increases with diminishing size ratio. The analogous problem of pair collision rates of particles with small-amplitude surface roughness δa is also analyzed. The formulas for the collision rates of rough particles provide accurate analytical approximations for the collision rates of permeable particles for all four aggregation mechanisms and a wide range of size ratios using an equivalent roughness δ=0.72K2/5.

Collision of two vortex rings (VR) initially arranged in axis-offset and orthogonal configurations at Reynolds numbers ( ReΓ) in the range of 5000–200 000 was simulated to investigate turbulent energy cascade associated with their reconnection. Two elliptical VRs are generated by joining each part of the first VR with another part of the second VR for the axis-offset collision, while two VRs associate to form a double U-shaped vortex, and this vortex reconnects itself at two points to form three elliptical VRs linked by the vortex filaments for the orthogonal collision. Many vortex structures in various scales and shapes, including small-scale VRs and horseshoe vortices, are observed in connection regions for both cases. As ReΓ increases, the energy of formed small vortices raises and their wavenumber (k) range enlarges. The flow energy spectrum approaches a k−5/3 slope of the Kolmogorov hypotheses at low wavenumbers. For the axis-offset collision, the energy spectrum at medium wavenumbers continuously changes from k−3.0 at ReΓ= 5000 to k−1.8 at ReΓ= 200 000, and the exponent (α) of the wavenumber is determined by a function as α=0.3304 ln(ReΓ)−5.6538. Meanwhile, the energy spectrum at two medium-wavenumber subranges for the orthogonal collision with ReΓ≥ 20 000 approaches the slopes of k−3.0 and k−2.6. Turbulent mixing performance due to the axis-offset collision of two vortex rings is better than that with the orthogonal one.

A new approach to estimate the pitch angle of highly energetic postdisruption runaway electrons is presented by imaging the polarized runaway electron synchrotron emission. The vertical to horizontal polarization ratio is found to range between 3 and 14 in image-average studies looking at repeated shots as well as the polarization in a single discharge. Numerical studies with guiding center and full orbit simulations performed with the SOFT and KORC codes are given and compared to the experiment. The pitch angle evolution analyzed using a 1D impurity diffusion model in combination with kinetic simulations is also presented. These studies find agreement in the magnitude of the pitch angle, but not in the temporal rate of change of pitch angle. The measured pitch angle evolution timescale of order 50 ms falls between a modeled timescale of 20 ms in an equilibrium model and ≫100 ms in a nonequilibrium model.