bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotary trigger double spark gap switch for repetitive pulse generator and production of silver nanocolloid
Authors: Cho Chuhyun , Jin Yun-Sik
Published: August 2018

High-voltage, repetitive pulse generation technology plays a key role in underwater discharge applications such as water treatment and metal nanocolloid production. For these applications, a high-voltage, high-speed switching technology was crucial to swiftly transfer the energy stored in the capacitor to the electrodes in water. A rotary-triggered double spark gap switch was developed for this purpose in this study. Two spark gaps dedicated for charge and discharge were arranged in this switch, and they eliminated the irregular and unstable pulse generation due to the simultaneous charging and discharging in the pulse-generating circuits. Using this technique, pulses with 12 kV and 100 ns rise time were generated at a repetition rate of 150 pulses per second and applied to underwater discharge to produce silver nanocolloids.
First-principles study on vibrationally resolved fluorescence of fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin molecule
Authors: Qiu Feifei , Song Ce , Li Li , Wei Yong , Tian Guangjun
Published: August 2018

The vibrationally resolved fluorescence spectrum of a narrow-line single-molecule transducer, fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin (fused-H2P) molecule, has been calculated by time-dependent density functional theory with the inclusion of both Franck-Condon and Herzberg-Teller contributions. Analytical transition dipole derivatives are used for the calculations of Herzberg-Teller terms to eliminate the possible errors caused by numerical differentials. The performance of different exchange-correlation functionals including B3LYP, ωB97X-D, and M06-2X has been examined. The comparison with the high-resolution experimental emission spectrum indicates that all three functionals can satisfactorily describe the fluorescence spectral profile, while ωB97X-D and M06-2X give slightly better excitation energy than B3LYP. Detailed analysis shows that the fluorescence spectrum is dominated by the Franck-Condon contribution, while the Herzberg-Teller term contributes mostly to its low energy tail. It is found that the size of the basis set has limited influence on the fluorescence spectrum, and a standard 6-31G(d, p) basis set is adequate for the purpose. The substitution of terthiophene side chains is found to have minor effects on the fluorescence spectrum. Our study provides unambitious assignments for all the vibronic structures in the experimental spectrum.
Understanding the effects of symmetric salt on the structure of a planar dipolar polymer brush
Authors: Mahalik Jyoti P. , Sumpter Bobby G. , Kumar Rajeev
Published: August 2018

The effects of added salt on a planar dipolar polymer brush immersed in a polar solvent are studied using a field theoretic approach. The field theory developed in this work provides a unified framework for capturing effects of the inhomogeneous dielectric function, translational entropy of ions, crowding due to finite sized ions, ionic size asymmetry, and ion solvation. In this paper, we use the theory to study the effects of ion sizes, their concentration, and ion-solvation on the polymer segment density profiles of a dipolar brush immersed in a solution containing symmetric salt ions. The interplay of crowding effects, translational entropy, and ion solvation is shown to exhibit either an increase or decrease in the brush height. Translational entropy and crowding effects due to finite sizes of the ions tend to cause expansion of the brush as well as uniform distribution of the ions. By contrast, ion-solvation effects, which tend to be stronger for smaller ions, are shown to cause shrinkage of the brush and inhomogeneous distribution of the ions.
Effect of temporally modified ultra-short laser pulses on ion acceleration from thin foil targets
Authors: Tayyab M. , Bagchi S. , Chakera J. A. , Khan R. A. , Naik P. A.
Published: August 2018

We demonstrate the significant enhancement of ion energy from the interaction of intense, chirped pulse amplification based ultrashort laser pulse with thin foil targets by adjusting the laser temporal characteristics with a simple adjustment of grating pair separation inside the pulse compressor. The laser pulse was focused to a maximum intensity of 3.2 × 1019 W/cm2 on to thin metallic foil targets of submicron thickness. The pulse duration was varied from 25 to 500 fs by adjusting the laser pulse compressor grating separation for fixed laser pulse energy (2.1 J). Contrary to the conventional belief, we found that the ion acceleration is not optimum at the shortest laser pulse duration and, thus, at highest intensity as predicted by the previous intensity scaling data. Instead, stretched pulses are better suited for efficient ion acceleration. In addition to this, we found a contrasting effect with respect to the sign of the laser chirp for almost the same laser pulse duration. In particular, we show 70% enhancement in maximum ion energy (from 6 MeV to 10 MeV) with positively chirped 250–350 fs stretched pulses. On the contrary, negatively chirped pulses show gradual monotonic reduction in ion energy and flux. Independent electron energy spectra measurement along the laser forward direction exhibits a strong correlation with proton data. The temporal pulse skewness arising due to displaced grating separation is believed to be responsible for this asymmetric proton acceleration behaviour. Efficient absorption of positively modified skewed pulses (shallow rise time and sharp fall) along with the characteristic ion acceleration time can qualitatively explain the experimental result. The present study can be very much important for efficient ion acceleration based on modern day compact, ultra-short pulse 100 TW to PW class lasers.
Characteristics of an electron beam extracted from a microwave electron cyclotron resonance plasma cathode
Authors: Li Liang , Liu Yifei , Chen Longwei , Wang Gong , Liu Ming , Ren Zhaoxing , Zhao Ying , Liu Bingshan , Zhao Guangheng
Published: August 2018

Under ultra-low pressure, an electron beam is generated by the microwave electron cyclotron resonance plasma with a permanent magnet. By means of the Hall coil and Miller ampere meter, two electron current signals at the end of the extraction anode (Ia) and the sample holder (Is) were measured. The influences of discharge power, gas pressure, and accelerating voltage on the electron beam current Is were analyzed. The experimental results indicated that the extracted electron current can reach 75.1 mA at a gas pressure of 1.4 × 10−3 Pa, an accelerating voltage of 8 kV, and an orifice size of 3 mm in diameter. In order to estimate the focusing properties of the electron beam by the beam-focusing coil, the influence of the coil current on the size of the electron beam spot on the sample holder was presented and discussed. The intrinsic mechanism of electron beam extraction and propagation is revealed by numerical simulation.
Calorimetric investigations in a gas aggregation source
Authors: Gauter Sven , Haase Fabian , Solař Pavel , Kylián Ondřej , Kúš Peter , Choukourov Andrei , Biederman Hynek , Kersten Holger
Published: August 2018

A gas aggregation source based on DC magnetron sputtering was investigated using a passive thermal probe and supplementary diagnostics (Langmuir probe and quartz crystal microbalance). Parameter variations of pressure, axial distance, and magnetron current have been performed for three different targets (pure Cu, pure W, composite Cu/W) in argon discharge. The measurements showed the energy flux to be significantly higher for the case of the pure tungsten and the composite target compared to the copper target, which is likely a result of the strongly increased amount of neutrals being reflected from the heavier targets. Furthermore, gas rarefaction by the sputtered atoms was found to be essential for the understanding of the observed energy flux and that the dominant contributors to the energy flux in the higher pressure regime are comparable to those observed in the conventional lower pressure regime. Selected deposited films have been investigated ex-situ by scanning electron microscopy, which allowed us to gain insight into the nanoparticle formation in relation to the observed energy conversion.
Direct hydroxylation of benzene to phenol mediated by nanosized vanadium oxide cluster ions at room temperature
Authors: Cui Jia-Tong , Zhao Yue , Hu Ji-Chuang , Ma Jia-Bi
Published: August 2018

Gas-phase vanadium oxide cluster cations and anions are prepared by laser ablation. The small cluster ions (<1000 amu) are mass-selected using a quadrupole mass filter and reacted with benzene in a linear ion trap reactor; large clusters (>1000 amu) with no mass selection are reacted with C6H6 in a fast flow reactor. Rich product variety is encountered in these reactions, and the reaction channels for small cationic and anionic systems are different. For large clusters, the reactivity patterns of (V2O5)n+ (n = 6-25) and (V2O5)nO− (n = 6-24) cluster series are very similar to each other, indicating that the charge state has little influence on the oxidation of benzene. In sharp contrast to the dramatic changes of reactivity of small clusters, a weakly size dependent reaction behavior of large (V2O5)6-25+ and (V2O5)6-24O− clusters is observed. Therefore, the charge state and the size are not the major factors influencing the reactivity of nanosized vanadium oxide cluster ions toward C6H6, which is not common in cluster science. In the reactions with benzene, the small and large reactive vanadium oxide cations show similar reactivity of hydroxyl radicals (OH•) toward C6H6 at higher and lower temperatures, respectively; different numbers of vibrational degrees of freedom and the released energy during the formation of adduct complexes can explain this intriguing correlation. The reactions investigated herein might be used as the models of how to realize the partial oxidation of benzene to phenol in a single step, and the observed mechanisms are helpful to understand the corresponding heterogeneous reactions, such as those over vanadium oxide aerosols and vanadium oxide catalysts.
Effective potential between negatively charged patches on acidic proteins immersed in various electrolyte solutions
Authors: Suematsu Ayumi , Sawayama Takuto , Akiyama Ryo
Published: August 2018

Effective interactions between O-sized anions in various electrolyte solutions were calculated by using the integral equation theory with some simple models. The results indicated that only multivalent cations mediated a strong effective attraction between O-sized anions at a certain concentration. The effective interaction turned from repulsive to attractive as the electrolyte concentration increased, and the effective attraction decreased when more electrolyte was added. Moreover, the effective interactions between O-sized anions in the electrolyte solution did not present a long repulsive tail, although the effective attraction caused by the divalent cations appeared. By contrast, the effective attraction mediated by monovalent cations and the reentrant behavior did not appear and the effective interaction was basically repulsive. These behaviors agree with the experimental results for reentrant condensation of acidic proteins in various electrolyte solutions. The calculated results suggest that the dissociated carboxylic acidic groups on the proteins form attractive patches between proteins under certain concentration conditions.
A distributed electrical model for superconducting nanowire single photon detectors
Authors: Zhao Qing-Yuan , Santavicca Daniel F. , Zhu Di , Noble Brian , Berggren Karl K.
Published: August 2018

To analyze the switching dynamics and output performance of a superconducting nanowire single photon detector (SNSPD), the nanowire is usually modelled as an inductor in series with a time-varying resistor induced by the absorption of a photon. Our recent experimental results show that, due to the effect of kinetic inductance, for a SNSPD made of a nanowire of sufficient length, its geometrical length can be comparable to or even longer than the effective wavelength of frequencies contained in the output pulse. In other words, a superconducting nanowire can behave as a distributed transmission line so that the readout pulse depends on the photon detection location and the transmission line properties of the nanowire. Here, we develop a distributed model for a superconducting nanowire and apply it to simulate the output performance of a long nanowire designed into a coplanar waveguide. We compare this coplanar waveguide geometry to a conventional meander nanowire geometry. The simulation results agree well with our experimental observations. With this distributed model, we discuss the importance of microwave design of a nanowire and how impedance matching can affect the output pulse shape. We also discuss how the distributed model affects the growth and decay of the photon-triggered resistive hotspot.
Chromatic confocal microscopy to rapidly reveal nanoscale surface/interface topography by position-sensitive detection
Authors: Zhuo Guan-Yu , Hsu Chia-Huan , Wang Yen-Hsiang , Chan Ming-Che
Published: August 2018

This paper presents a confocal microscope for the rapid and noninvasive capture of three-dimensional (3D) images showing the surface/interface topography in a far-field configuration. The proposed microscope features a nanoscale optical ruler capable of performing fast depth measurements based on the chromatic aberration of microscope objectives. A diffraction grating and a position-sensitive detector were used to extract the spectral shift, which directly maps the height of the surface with a nanoscale resolution. Because neither the mechanical scanning nor the spectrometer, which limit the speed of 3D imaging, are needed in the axial direction, full 3D surface topography images with nanoscale depth resolution can be acquired rapidly using the nanoscale optical ruler in conjunction with 2D lateral beam scanning. The presented technique overcomes the limitation of the detection speed of conventional chromatic confocal microscopy. In experiments, the 3D static and dynamic nanoscale surface profiles of several representative optoelectronic and electronic devices were demonstrated. This fast and non-invasive approach with nanoscale depth resolution to the measurement of topography images has considerable promise in academic research and industrial applications.
Superconducting radio-frequency virtual cavity for control algorithms debugging
Authors: Echevarria Pablo , Aldekoa Eukeni , Jugo Josu , Neumann Axel , Ushakov Andriy , Knobloch Jens
Published: August 2018

Superconducting radio-frequency (SRF) cavities are one of the most important elements in modern particle accelerators as they are used for beam acceleration, bunch manipulation, bunch focusing and defocusing, etc. Nevertheless, the availability of these complex structures prior to their installation in the accelerator is limited, either due to a lack of a real cavity or due to the time needed for the experiment setup (vacuum, cryogenics, cabling, etc.), and thus it can block or delay the development of new algorithms such as low level RF control, quench detection, etc. In this paper, we present a hardware virtual cavity to be used in hardware-in-the-loop simulations. The system implements a cavity electrical model for the transmitted and reflected voltages and more advanced features such as mechanical vibration modes driven by Lorentz-force detuning or external microphonics, hard quenches, and the Q-slope. As viewed from the RF input and output, this virtual cavity acts like a real SRF cavity and can replace such a system in early-stage debugging and operation of ancillary control systems.
Increase in detection sensitivity of surface acoustic wave biosensor using triple transit echo wave
Authors: Choi Youn-Suk , Lee Joonhyung , Lee Yeolho , Kwak Jiwon , Suk Lee Soo
Published: August 2018

Here, we present a surface acoustic wave (SAW) biosensor for the highly sensitive detection of cardiac troponin I, a gold standard biomarker for the diagnosis of myocardial infarction, using a triple transit echo (TTE) wave of a SAW rather than a conventional main wave. Compared with the main wave, the TTE wave is caused by reflections from output and input interdigitized transducers (IDTs) after traversing the propagation path three times between input and output IDTs. The SAW biosensor using a TTE wave signal showed enhanced sensitivity for measuring the viscosity of glycerol solution and the mass loading effect of immunoassay reaction due to much bigger modulation induced in the amplitude, phase, frequency, and time-delay of the TTE wave. Our results showed that the proposed SAW biosensor could quantitatively analyze cardiac troponin I. Detection limit values using the main wave and the TTE wave were 766 pg/ml and 24.3 pg/ml, respectively. Therefore, one can say that the sensitivity of the SAW biosensor substantially improved when the TTE wave is used.
Robust ferroelectricity in epitaxial Hf1/2Zr1/2O2 thin films
Authors: Lyu J. , Fina I. , Solanas R. , Fontcuberta J. , Sánchez F.
Published: August 2018

Ferroelectric orthorhombic Hf0.5Zr0.5O2 thin films have been stabilized epitaxially on La2/3Sr1/3MnO3/SrTiO3(001) by pulsed laser deposition. The epitaxial orthorhombic films, (111)-oriented and with a very flat surface, show robust ferroelectric properties at room temperature. They present a remnant polarization around 20 μC/cm2 without the need of a wake-up process, a large coercive electric field of around 3 MV/cm, an extremely long retention extending well beyond 10 years, and an endurance up to about 108 cycles. Such outstanding properties in the nascent research on epitaxial HfO2-based ferroelectric films can pave the way for a better understanding of the effects of orientation, interfaces, strain, and defects on ferroelectricity in HfO2.
Atomistic model of xenon gas bubble re-solution rate due to thermal spike in uranium oxide
Authors: Setyawan Wahyu , Cooper Michael W. D. , Roche Kenneth J. , Kurtz Richard J. , Uberuaga Blas P. , Andersson David A. , Wirth Brian D.
Published: August 2018

Atomistic simulations are performed to study the response of Xe gas bubbles in UO2 to ionizing fission products through the thermal spike approximation. A portion of the total electronic stopping power (Se) is taken as the thermal spike energy through a ratio variable ζ. The thermal spike energy causes extreme melting within the fission track cylindrical region. Molecular dynamics is employed to quantify the probability of a Xe gas atom to be re-solved (re-dissolved) back into the UO2 matrix. Subsequently, a re-solution model is developed and parametrized as a function of bubble radius (R), off-centered distance (r), and thermal spike energy (ζSe). The off-centered distance measures the shift of the thermal spike axis from the bubble center. To evaluate the re-solution model, independent fission product yield of U-235 fission due to thermal neutrons (0.0253 eV), taken from the JEFF-3.3 database, is used. The kinetic energy of the fission products is taken from the EXFOR database. Subsequently, the decay of Se over distance for each fission product is simulated. Finally, the evaluated re-solution rate (re-solution probability per second) is presented as a function of bubble radius for a range of ζ.
Enhanced Raman scattering of graphene using double resonance in silicon photonic crystal nanocavities
Authors: Gomulya W. , Machiya H. , Kashiwa K. , Inoue T. , Chiashi S. , Maruyama S. , Kato Y. K.
Published: August 2018

We demonstrate enhancements of Raman scattering from graphene on two-dimensional photonic crystals using double resonances, which originate from simultaneous enhancements by a localized guided mode and a cavity mode. By adjusting the photonic crystal cavity parameters, the double resonance can be tuned to the G′ Raman scattering. Excitation wavelength dependence measurements show a large Raman peak enhancement when the excitation and emission wavelengths meet the double resonance condition. Furthermore, spatial imaging measurements are performed to confirm that the enhancement is localized at the cavity, and we find that the enhanced Raman intensity is 60 times larger compared to the on-substrate Raman signal. The observed cavity enhancement of Raman scattering opens up new possibilities for the development of graphene-based light sources for silicon photonics.
Controlling topological electronic structure of multifunctional MXene layer
Authors: Balcı Erdem , Akkuş Ünal Özden , Berber Savas
Published: August 2018

The electric field- and charge transfer-induced topological properties of Sc2C(OH)2 MXene layers are reported. The system transforms from a trivial insulator to a topological insulator and to a metal. The s-pd orbitals are exchanged during the topological phase transition. The modification of the bandgap along with the transition to the topological phase reveals that Sc2C(OH)2 MXene is a multifunctional material. The nearly free states, which form ideal conduction channels, are responsible for the topological electronic band structures.
Application of agro-waste derived materials as heterogeneous base catalysts for biodiesel synthesis
Authors: Basumatary Sanjay , Nath Biswajit , Kalita Pranjal
Published: August 2018

Agro-wastes are the post-harvest products or agricultural residues generated through various agricultural activities which have diverse scopes for various applications. Reutilization of agro-waste is an environmentally safe and cost-effective process of waste management. Proper and optimal utilization of these waste by-products is one of the major challenges for the human society nowadays. The recent trend around the globe is to transform waste into different products useful for various applications. Agro-waste derived ashes have recently been extensively studied as the heterogeneous base catalysts in biodiesel synthesis which is attracting increasing attention worldwide. Agro-waste derived catalysts are easily available, simple to prepare, easy to handle, biodegradable, non-toxic, more environmentally benign, and more cost-effective. In this study, an attempt has been made to review the utilization of agro-waste derived ashes as heterogeneous catalysts and metal loaded ash catalysts in synthesis of biodiesel through transesterification reaction of various oil feedstocks. Several parameters like the calcination temperature, catalyst amount, ratio of methanol to oil, reaction times, and temperatures which affect the transesterification reaction were also briefly discussed herein. The agro-waste derived heterogeneous base catalysts are highly active for catalysing transesterification of oil to biodiesel with a shorter reaction time and higher conversion up to 100% as compared to commercial catalysts and other catalysts derived from other renewable biomasses such as egg shells, fish scales, and bones. Further, the performance of agro-waste derived heterogeneous base catalysts is better and more efficient than that of the metal source loaded ash catalysts. The high activities of these catalysts are due to the higher potassium content which is accrediting their high basicity. Moreover, efficient utilization of waste materials will help to reduce global warming and enhance the clean and clear environment in the society.
Limit cycle oscillations of a violin string
Authors: Shayak B.
Published: August 2018

In this work, we write and solve a first principles model for the motion of a bowed string. We find limit cycle oscillations driven by stick-slip friction. The shape of these oscillations is in accordance with the Helmholtz-Rayleigh motion. We observe that when bow force, bow speed, and other parameters are varied, the stable limit cycle occurs in a narrow region of parameter space. This explains why it is difficult for amateurs to produce musically acceptable sounds from the instrument.
Hydrodynamics of water-worked and screeded gravel beds: A comparative study
Authors: Padhi Ellora , Penna Nadia , Dey Subhasish , Gaudio Roberto
Published: August 2018

The turbulence characteristics within flows over water-worked gravel beds (WGBs) and screeded gravel beds (SGBs) were examined by measuring the instantaneous flow velocity field using a two-dimensional particle image velocimetry system. To compare the responses of a WGB and an SGB to velocity and various turbulence characteristics, the flow Froude number was kept identical for both the beds that remained immobile. The roughness structures of both the beds were measured using a laser scanner. The results showed that the bed surface roughness was higher in the WGB than in the SGB. However, the longest axis of the gravels of WGBs was oriented streamwise owing to the action of water work, but the gravels of SGBs were randomly poised. The distribution of bed roughness fluctuations was negatively skewed in the WGB and positively skewed in the SGB. Double averaging methodology was applied to analyze the flow parameters. In this paper, the vertical profiles of the double-averaged streamwise velocity and the turbulence parameters, specifically the spatially averaged (SA) Reynolds shear and normal stresses, form-induced shear and normal stresses, turbulent kinetic energy (TKE) and form-induced TKE fluxes, quadrant analysis of SA Reynolds shear stress, etc., are presented and analyzed critically by focusing on comparisons between a WGB and an SGB. A comparative study reveals that in the near-bed flow zone, the SGB underestimates the turbulence parameters compared to the WGB. Therefore, in order to represent the prototypical flow in laboratory, the experiments should be performed in a WGB.
Ferroelectric switching dynamics in 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 thin films
Authors: Silva J. P. B. , Kamakshi K. , Negrea R. F. , Ghica C. , Wang J. , Koster G. , Rijnders G. , Figueiras F. , Pereira M. , Gomes M. J. M.
Published: August 2018

In this work, the ferroelectric characteristics of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) thin films grown on 0.7 wt. % Nb-doped (001)-SrTiO3 (Nb:STO) single-crystal have been investigated. High-resolution transmission electron microscopy and electron energy loss spectroscopy revealed a very sharp Nb:STO/BCZT interface, while selected area electron diffraction revealed the epitaxial growth of the BCZT layer on the Nb:STO substrate. The ferroelectric nature of the BCZT films have been investigated by piezoresponse force microscopy and hysteresis loops. The effect of electric field on polarization switching kinetics has been investigated and has been analyzed by the nucleation limited switching model with a Lorentzian distribution function. The local field variation was found to decrease with the increase in the electric field, and thus, the switching process becomes faster. The peak value of the polarization current and the logarithmic characteristic switching time exhibited an exponential dependence on the inverse of electric field. This model gave an excellent agreement with the experimental polarization reversal transients throughout the whole time range.
Ground and low-lying excited states of phenoxy, 1-naphthoxy, and 2-naphthoxy radicals via anion photoelectron spectroscopy
Authors: Kregel Steven J. , Garand Etienne
Published: August 2018

We present the slow electron velocity map imaging spectroscopy of cryogenically cooled phenoxide, 1-naphthoxide, and 2-naphthoxide anions. The results allow us to examine the ground state and the lowest energy excited state in the corresponding neutral radicals. Care was taken to minimize autodetachment signals in the photoelectron spectra, allowing for more straightforward comparisons with Franck-Condon analyses. The ground states of these three aromatic oxide radicals all have the unpaired electron residing in a π orbital delocalized throughout the molecule. The electron affinity of 1-naphthoxy is measured to be 2.290(2) eV, while that of 2-naphthoxy is measured to be 2.404(2) eV, both of which are higher than that of the smaller phenoxy molecule at 2.253(1) eV. The first excited states have the unpaired electron residing in a more localized σ orbital, yielding measured term energies for the Ã state of 1.237(2) eV in 1-naphthoxy and 1.068(1) eV in 2-naphthoxy, while that of phenoxy is lower at 0.952(1) eV. The calculated Franck-Condon spectra generally showed good agreement with the experimental spectra, yielding assignments of the more active vibrations in each electronic state. Significant autodetachment signals arising from dipole bound states near the ground states of all three radicals were observed in our efforts to avoid them, and comparably less autodetachment signals were observed near the excited states. Besides this type of non-Franck-Condon intensities in the photoelectron spectra, we also observed minor features arising due to vibronic coupling in the ground states of all three radicals.
Neutral collisions in affecting diffusion and collective oscillation of magnetized complex plasma
Authors: Kong Wei , Liu Songfen , Yang Fang , Shi Feng , Wang Yupei
Published: August 2018

By comparing with the Bohm-like diffusion 1/B of magnetized complex plasma, it is found that the neutral collisions, i.e., collisions between neutral gas and charged dust particles, nonlinearly damp the motion of the system at a rate much slower than 1/ν, where B is the external magnetic field and ν is the neutral collision frequency. The effects of neutral collisions on longitudinal and transverse waves are discussed based on the current-current correlation function. The non-damping feature of strong neutral collisions to shorter-wavelength modes is observed. The phonon energy of the system tends to be distributed into a broader k–ω space in the strong damping regime.
Conductive tail-to-tail domain walls in epitaxial BiFeO3 films
Authors: Jin Yaming , Xiao Shuyu , Yang Jan-Chi , Zhang Junting , Lu Xiaomei , Chu Ying-Hao , Cheong S.-W. , Li Jiangyu , Kan Yi , Yue Chen , Li Yang , Ju Changcheng , Huang Fengzhen , Zhu Jinsong
Published: August 2018

The complex conductive behavior of ferroelectric domain walls is attracting more and more attention for their potential application as an independent nanoelectronic component. For the (001) epitaxial BiFeO3 films, we find that the domain wall conductivity varies among 71° domain walls, with tail-to-tail (T-T) domain walls more conductive than head-to-head (H-H) and head-to-tail (H-T) ones. Furthermore, it is observed that most of the conductive areas are composed of two parallel lines around the T-T domain walls. These experimental results can be well simulated by our theoretical model based on the polarization configuration and a tunneling mechanism. Our work will help to understand the mechanism of domain wall conductance in ferroelectric materials and further promote the usage of domain walls in advanced nano-devices.
Plasma density and ion energy control via driving frequency and applied voltage in a collisionless capacitively coupled plasma discharge
Authors: Sharma Sarveshwar , Sen Abhijit , Sirse N. , Turner M. M. , Ellingboe A. R.
Published: August 2018

The dynamical characteristics of a single frequency low pressure capacitively coupled plasma (CCP) device under varying applied RF voltages and driving frequencies are studied using particle-in-cell/Monte Carlo collision simulations. An operational regime is identified where for a given voltage the plasma density is found to remain constant over a range of driving frequencies and to then increase rapidly as a function of the driving frequency. The threshold frequency for this mode transition as well as the value of the constant density is found to increase with an increase in the applied voltage. Over the constant density range, for a given voltage, the sheath width is seen to increase as a function of the increasing driving frequency, thereby changing the ion energy without affecting the ion density. Our parametric study thus indicates that the twin knobs of the applied voltage and driving frequency offer a means of independently controlling the density and the ion energy in a low pressure CCP device that may be usefully exploited for plasma processing applications.
An integral transform technique for kinetic systems with collisions
Authors: Heninger J. M. , Morrison P. J.
Published: August 2018

The linearized Vlasov-Poisson system can be exactly solved using the G-transform, an integral transform introduced in Morrison and Pfirsch [Phys. Fluids B 4, 3038–3057 (1992)] and Morrison [Phys. Plasmas 1, 1447 (1994); Transp. Theory Stat. Phys. 29, 397 (2000)] that removes the electric field term, leaving a simple advection equation. We investigate how this integral transform interacts with the Fokker-Planck collision operator. The commutator of this collision operator with the G-transform (the “shielding term”) is shown to be negligible. We exactly solve the advection-diffusion equation without the shielding term. This solution determines when collisions dominate and when advection (i.e., Landau damping) dominates. This integral transform can also be used to simplify gyro-/drift-kinetic equations. We present new gyrofluid equations formed by taking moments of the G-transformed equation. Since many gyro-/drift-kinetic codes use Hermite polynomials as base elements, we include an explicit calculation of their G-transform.
Demonstration of field emission driven microscale gas breakdown for pulsed voltages using in-situ optical imaging
Authors: Meng Guodong , Gao Xinyu , Loveless Amanda M. , Dong Chengye , Zhang Dujiao , Wang Kejing , Zhu Bowen , Cheng Yonghong , Garner Allen L.
Published: August 2018

While multiple studies have explored the mechanism for DC and AC microscale gas breakdown, few have assessed the mechanism for pulsed voltage gas breakdown at the microscale. This study experimentally and analytically investigates gas breakdown for gap widths from 1 μm to 25 μm. Using an electrical-optical measurement system with a spatial resolution of 1 μm and a temporal resolution of 2 ns, we measure the breakdown voltages and determine breakdown morphology as a function of the gap width. An empirical fit shows that the breakdown voltage varies linearly with the gap distance at smaller gaps, agreeing with an analytical theory for DC microscale gas breakdown coupling field emission and Townsend avalanche that shows that the slope is a function of field emission properties. Furthermore, the curved breakdown paths captured between 5 μm and 10 μm demonstrate a similar effective length (∼11.7 μm) independent of the gap width, which is consistent with a “plateau” in breakdown voltage. This indicates that Townsend avalanche alone is insufficient to drive breakdown for these gaps and that ion enhanced field emission must contribute, in agreement with theory. The overall agreement of measured breakdown voltage with theoretical predictions from 1 μm to 25 μm indicates the applicability of DC microscale gas breakdown theory to pulsed breakdown, demonstrating that pulsed voltages induce a similar transition from Townsend avalanche to field emission as DC and AC voltages at the microscale.
Transient response of magnetorheological elastomers to step magnetic field
Authors: Wen Qianqian , Wang Yu , Feng Jiabin , Gong Xinglong
Published: August 2018

The time-dependent performance of magnetorheological elastomers (MREs) under a magnetic field is important for the precise control of smart devices based on MREs. Here, the transient responses of anisotropic magnetorheological elastomers, including magnetic field-induced storage modulus (ΔG′) and loss modulus (ΔG″), were investigated under different step magnetic fields. The results indicated that ΔG′ increased over time while ΔG″ decreased after the initial jump in the loading stage of the step field. ΔG′ quickly dropped to 0, while ΔG″ continued to decrease gradually in the removal stage of the step field. A comprehensive model based on magnetic dipolar and viscoelastic parameter models was proposed to explain the transient responses.
Effect of Cold Plasma Treatment of Carbon Nanostructures on the Hydrogen Sorption
Authors: Dolbin A. V. , Vinnikov N. A. , Esel’son V. B. , Gavrilko V. G. , Basnukaeva R. M. , Khlistyuck M. V. , Prokhvatilov A. I. , Meleshko V. V. , Rezinkin O. L. , Rezinkina M. M.
Published: August 2018

Using X-ray diffraction and thermo-programmed desorption, the present study investigated the effect of treatment with pulsed high-frequency discharge in a hydrogen environment on the structure and sorption characteristics of the carbon synthetic nanoporous sorbent SCN (spherical carbonite saturated). Treatment with SCN by a pulsed gas discharge led to chemisorption of 0.4% hydrogen by weight, as well as 1.7 times greater physical sorption of hydrogen. We can assume this increase in sorption capacity is due to changes in the equivalent pore sizes that result from chemical interaction of the carbon atoms of SCN with hydrogen ionized during the discharge process.

PACS: 61.43.Gt Powders; porous materials; 52.77.–j Plasma applications; 88.30.R– Hydrogen storage.
Recombination and long-term relaxation of photoconductivity in p+–p–p− structures of CdxHg1-xTe (0.24 ≤ x ≤ 0.29)
Authors: Ismayilov N. J. , Rajabli A. A. , Musayev M. A. , Abbasov I. I.
Published: August 2018

The paper presents the results of a study of the photoconductivity of p+−p−p− structures of CdxHg1–xTe (0.24 ≤ x ≤ 0.29) single crystals obtained by thermal diffusion of copper at T = 130°C. The long-term relaxation (LR) of photoconductivity with a duration of up to 10 ms in the presence of a thermal background of intensity Φ = 1016−1017 cm−2·s−1 is observed for the first time in narrow-gap materials in the T = 77–150 K range. Recombination, diffusion-drift processes in the sample are analyzed, which cause LR and spectral features of photoconductivity. The obtained structures are promising for the development of various highly sensitive IR detectors with an elevated operating temperature.
Isochoric thermal conductivity of solid 2-propanol
Authors: Konstantinov V. A. , Sagan V. V. , Karachevtseva A. V.
Published: August 2018

The isochoric thermal conductivity of solid 2-propanol (C3H7OH) was measured for samples of different densities, in the temperature range from 140 K up to melting. It was found that thermal expansion significantly affects the temperature dependence of thermal conductivity in monohydric alcohols studied at pre-melting temperatures. The isochoric thermal conductivity of all samples decreased with increasing temperature weaker than at a saturated vapor pressure, and deviates strongly from the k ∝ 1/T dependence. We describe the experimental results in the framework of a model involving thermal transfer by the propagons and diffusons; further, we discuss its principled difference from the simple Debye model, which does not take into account the dispersion and real density of phonon states. The contributions of propagons and diffusons in 1-and 2-propanol are calculated, and a comparison of thermal conductivities of isomers performed. It was found that the contribution of the diffusons is much higher than that of the propagons, and, in 2-propanol, both contributions are significantly smaller than in 1 - propanol. It was shown that the coefficients Ai responsible for the contribution of the propagons were essentially dependent on the density, while the coefficients Bi describing the contribution of the diffusons were practically constant.
Structures and infrared spectra of 5-chlorouracil molecules in the low-temperature inert Ar, Ne matrices and composite films with oxide graphene
Authors: Ivanov A. Yu. , Rubin Yu. V. , Belous L. F. , Karachevtsev V. A.
Published: August 2018

The structures and vibrational spectra of biologically active molecules of 5-chlorouracil (5CU) in various states were studied. The IR Fourier spectra of 5CU molecules isolated in the low-temperature Ar and Ne matrices were obtained in the infrared range of 3800–500 cm–1. The populations of 5CU tautomers were estimated, and vibrational spectra were calculated using the DFT/B3LYP method with a basis of 6-311++G(df,pd). In the Ar matrix, 7 Raman modes of 5CU amplified by Fermi resonance were detected in the spectral range of 1900–500 cm–1. In the region of fundamental vibrations νCO and in the vibration region of the ring, triple Fermi resonances were observed. Thin 5CU films on the surface of graphene oxide (GO) and composite films 5CU/GO obtained from an aqueous solution were grown and investigated at cryogenic temperatures. It was shown that, as the temperature rises from the helium temperature to room temperature, the 5CU film crystallizes on the GO surface. Comparison of the spectra of the 5CU films obtained enabled identification of vibrations whose absorption bands were most sensitive to changes in the crystal structure of the film. Most of these fundamental modes were associated with vibrations of the NH group. With an increase in the concentration of 5CU in the 5CU/GO composite films, a nonuniform distribution of the 5CU micro-crystals over the sample area was observed.
The exciton absorption spectrum of thin films of ternary compounds in the AgBr–PbBr2 system
Authors: Kovalenko E. N. , Yunakova O. N. , Yunakov N. N.
Published: August 2018

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.
Effect of electron irradiation on the scattering of carriers in YBa2Cu3O7−δ single crystals
Authors: Azarenkov N. A. , Voevodin V. N. , Vovk R. V. , Khadzhai G. Ya.
Published: August 2018

The effect of electron irradiation at T ≲ 10 K (energy 0.5–2.5 MeV, dose 1018 cm–2) on the parameters of charge carrier scattering and superconducting transition characteristics in an optimally doped Y–Ba–Cu–O single crystal (Тc = 91.74 K) was studied. Irradiation with electrons leads to a significant increase in the residual resistance and the Debye temperature. The latter is associated with the isotropization of the phonon spectrum due to an increase in the concentration of defects. Irradiation also results in a decrease in Тc and an increase in the coherence length.
Infection prevention quality indicators in aged care: ready for a national approach
Authors: Bennett N. J. , Bradford J. M. , Bull A. L. , Worth L. J.
Published: August 2018

Accreditation standards for Australian aged care homes include the requirement for programs to ensure infections are controlled. Effective infection prevention programs are supported by surveillance data providing the impetus for quality improvement and facilitating evaluation of interventions at the facility level. In 2016, infection control professionals employed in Victorian public-sector residential aged care services were surveyed to examine the nature and resourcing of local infection prevention programs and monitoring activities. Overall, 164 services participated (90% response rate). A high proportion (84%) reported executive support for infection surveillance, with mean allocation of 12h per fortnight per facility for infection prevention activities. Current surveillance activities included monitoring of infections and antimicrobial use (90%), influenza vaccination compliance for staff (96%) and residents (76%) and monitoring of infection due to significant organisms (84%). A successful statewide program including eight quality indicators has subsequently been implemented in Victoria. We suggest that a national focus could strengthen this framework, ensuring a uniform strategy with enhanced benchmarking capacity. Stakeholder engagement and refinement of appropriate indicators for monitoring quality improvement in public, not-for-profit and private sectors within aged care is required.
Salinity improves growth, photosynthesis and bioenergy characteristics of Phragmites karka
Authors: Abideen Zainul , Qasim Muhammad , Hussain Tabassum , Rasheed Aysha , Gul Bilquees , Koyro Hans-Werner , Ansari Raziuddin , Khan M. Ajmal
Published: August 2018

Based on biomass composition of plants collected from saline habitats, Phragmites karka (Retz.) Trin. ex Steud. has emerged as a suitable feedstock for biofuel. In the present study, plant growth, eco-physiological responses and bioenergy characteristics of P. karka grown under conditions ranging from non-saline to ~80% seawater salinity are reported. Moderate salinity (NaCl at 100 mol m–3) increased plant fresh weight (20%), number of leaves (25%) and specific plant length, which were directly linked with increased net photosynthetic rate (25%) and stomatal conductance (25%) compared with the non-saline control. Higher photosynthetic efficiency was achieved by increasing electron transport rate (ETR, 20%), effective quantum yield (YII, 21%) and maximum efficiency of photosystem II (Fv/Fm, 20%). Decreased non-photochemical quenching (Y(NPQ)) and malondialdehyde content (18%) indicated an oxidative balance, which was also reflected in total carotenoids and chlorophylls. These eco-physiological parameters worked together to increase cellulose (34%) and hemicellulose (70%) at NaCl concentrations up to 200 mol m–3. Decreased growth under higher salinity could be linked with photosynthesis inhibition, due to stomatal closure and co-occurring reduction in CO2 uptake. Lower stomatal conductance increased water-use efficiency but led to over-production of reactive oxygen species, which disturbed oxidative stability (increasing ETR/PN) and imposed membrane leakage. Consequently, plants accumulated more carotenoids and soluble carbohydrates to stabilise PSII machinery (Fv/Fm, YII and Y(NPQ)), and to survive under high salinity. Such adaptations, however, led to growth penalty and reduced quality of lignocellulosic biomass. The above findings suggest that P. karka qualifies as a suitable raw material for biofuel under moderate salinity.
Long non-coding RNA HOX transcript antisense RNA (HOTAIR) suppresses the angiogenesis of human placentation by inhibiting vascular endothelial growth factor A expression
Authors: Wu Kejia , Liu Fulin , Wu Wanrong , Chen Yurou , Wu Hanshu , Zhang Wei
Published: August 2018

HOX transcript antisense RNA (HOTAIR) is a long non-coding RNA located within the Homeobox C (HOXC) gene cluster on chromosome 12. Previous studies have revealed that HOTAIR is overexpressed in many types of cancers and is associated with metastasis and poor survival rates; however, few reports have mentioned the relationship between HOTAIR and angiogenesis of the human placenta. The aim of the present study was to investigate the correlation between HOTAIR and vascular endothelial growth factor (VEGF) A in the human placenta. HOTAIR levels decreased significantly in human placenta with increasing gestational age, and were negatively correlated with VEGFA levels. Invitro assays revealed that HOTAIR overexpression suppressed the proliferation, migration, invasion and tube formation of human umbilical vein endothelial cells (HUVECs); however, inhibition of HOTAIR had the opposite effects. Furthermore, VEGFA overexpression reversed the inhibitory effect of HOTAIR on the proliferation, migration, invasion and tube formation of HUVECs. In addition, overexpression of HOTAIR significantly inhibited VEGFA expression. Notably, a luciferase reporter assay found that HOTAIR inhibited VEGFA transcription by directly targeting the VEGFA promoter. Together, these results suggest that HOTAIR plays an important role in suppressing angiogenesis of the human placenta by inhibiting the expression of VEGFA; thus, HOTAIR may represent a potential therapeutic target for patients with human placental vascularisation abnormalities.