bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppression of stimulated Raman scattering by angularly incoherent light, towards a laser system of incoherence in all dimensions of time, space, and angle
Authors: Guo Yi , Zhang Xiaomei , Xu Dirui , Guo Xinju , Shen Baifei , Lan Ke
Published: April 2023

Laser–plasma instability (LPI) is one of the main obstacles to achieving predictable and reproducible fusion at high gain through laser-driven inertial confinement fusion (ICF). In this paper, for the first time, we show analytically and confirm with three-dimensional particle-in-cell simulations that angular incoherence provides suppression of the instability growth rate that is additional to and much stronger than that provided by the well-known temporal and spatial incoherence usually used in ICF studies. For the model used in our calculations, the maximum field ratio between the stimulated Raman scattering and the driving pulses drops from 0.2 for a Laguerre–Gaussian pulse with a single nonzero topological charge to 0.05 for a super light spring with an angular momentum spread and random relative phases. In particular, angular incoherence does not introduce extra undesirable hot electrons. This provides a novel method for suppressing LPI by using light with an angular momentum spread and paves the way towards a low-LPI laser system for inertial fusion energy with a super light spring of incoherence in all dimensions of time, space, and angle, and may open the door to the use of longer-wavelength lasers for inertial fusion energy.
Fast uncertainty estimates in deep learning interatomic potentials
Authors: Zhu Albert , Batzner Simon , Musaelian Albert , Kozinsky Boris
Published: April 2023

Deep learning has emerged as a promising paradigm to give access to highly accurate predictions of molecular and material properties. A common short-coming shared by current approaches, however, is that neural networks only give point estimates of their predictions and do not come with predictive uncertainties associated with these estimates. Existing uncertainty quantification efforts have primarily leveraged the standard deviation of predictions across an ensemble of independently trained neural networks. This incurs a large computational overhead in both training and prediction, resulting in order-of-magnitude more expensive predictions. Here, we propose a method to estimate the predictive uncertainty based on a single neural network without the need for an ensemble. This allows us to obtain uncertainty estimates with virtually no additional computational overhead over standard training and inference. We demonstrate that the quality of the uncertainty estimates matches those obtained from deep ensembles. We further examine the uncertainty estimates of our methods and deep ensembles across the configuration space of our test system and compare the uncertainties to the potential energy surface. Finally, we study the efficacy of the method in an active learning setting and find the results to match an ensemble-based strategy at order-of-magnitude reduced computational cost.
Trotter–Kato approximations of semilinear stochastic evolution equations in Hilbert spaces
Authors: Liu Ming , Zhang Xia , Dai Lingfei
Published: April 2023

This article deeply studies a class of semilinear stochastic evolution equations in real separable Hilbert spaces. The main goal here is to consider Trotter–Kato approximations for mild solutions of such equations. After proving the existence and uniqueness of mild solutions, the Trotter–Kato approximation system is introduced and studied in detail. Based on this, the weak convergence of probability measures induced by mild solutions of Trotter–Kato approximation equations and the approximation error estimator are established. Finally, as an application, the classical limit theorem about the parameter dependence of this kind of equations is exhibited. To deal with the general additive diffusion term, which not only depends on the state but also depends on the probability distribution of the solution process at that time, we adopt some specific techniques of measure theory and random functional analysis.
Excellent energy storage properties, domain mechanism, and temperature stability of lead-free BaTiO3-Bi(Mg1/2Sn1/2)O3 bulk ferroelectrics
Authors: Qie Dan , Tang Zhenhua , Fang Junlin , Yao Dijie , Zhang Li , Jiang Yan-Ping , Sun Qi-Jun , Zhang Dan , Fan Jing-Min , Tang Xin-Gui , Liu Qiu-Xiang , Zhou Yi-Chun
Published: April 2023

Pulsed power systems require high-performance capacitors with high energy storage density. In this work, (1 − x)BaTiO3-xBi(Mg1/2Sn1/2)O3 ferroelectric ceramics were synthesized in a solid-state solution. The sample of x = 0.12 (0.88BT-0.12BMS) has excellent energy storage density, wide temperature, and wide frequency stability. The excellent energy density of 4.87 J/cm3 at 315 kV/cm and the energy efficiency of 72% at room temperature for 0.88BT-0.12BMS ceramics were achieved. Furthermore, the 0.88BT-0.12BMS ceramics demonstrated well temperature stabilities in the range of 20–100 °C and very good frequency stability in the range of 1–100 Hz. Through pulsed charging–discharging testing, the current density is calculated as 314.01 A/cm2, and the power density is 21.98 MW/cm3. Moreover, the oxygen vacancies' defects and ferroelectric domain mechanism for enhanced breakdown strength as well as high energy density were discussed. These findings broaden the horizon for lead-free dielectrics and show promising applications for pulse power capacitors.
Study of device characteristics of intrinsic Josephson junction terahertz emitters related to annealing conditions of the crystals
Authors: Nakagawa S. , Shizu T. , Imai T. , Nakayama M. , Kim J. , Minami H. , Kadowaki K. , Tsujimoto M. , Nakao H. , Eisaki H. , Ishida S. , Mochiku T. , Hasegawa Y. , Kashiwagi T.
Published: April 2023

We fabricated terahertz (THz) wave emitters from high-temperature superconductor Bi2Sr2CaCu2O8+δ (Bi2212) single crystals annealed under oxygen gas (O2) flow and nitrogen gas (N2) flow conditions. To better understand the annealing effects of the crystal for the device, we evaluated both device properties and a c-axis lattice constant using x-ray diffraction. Compared to the N2-annealed sample, the O2-annealed sample shows higher critical current in the current–voltage characteristics and no clear emission. In addition, multiple hysteresis loops were observed above 75 K. Based on the x-ray diffraction measurements, it is suggested that the presence of multiple hysteresis loops observed in the I–V characteristics of the O2-annealed sample is caused by the existence of layers that have varying levels of oxygen content along the c-axis direction of the crystal. The formation of these layers is attributed to the deposition process of metallic thin films during the device fabrication procedure. This result indicates that the Bi2212 crystal surface of the O2-annealed sample is more sensitive than that of the N2-annealed one. The information is useful for preparing the Bi2212 crystals for THz-wave emitting devices.
Study on the influence of metal phase transition on transport coefficient calculation of gas–metal plasma mixtures
Authors: Cui Jian , Zhang Guogang , Al-Dweikat Mohmmad , Zhang Weizhen , Geng Yingsan
Published: April 2023

In most industrial applications, plasma has an important feature that the erosion products produced by plasma will undergo a phase transition and affect the properties of plasma mixtures. Calculating the transport coefficients of the plasma mixtures, usually, gas–metal mixtures, is an important approach to study this feature. However, most transport coefficient calculation methods have some difficulties in dealing with the solid and liquid components of gas–metal plasma mixtures. In this study, a modified method for calculating transport coefficients of gas–metal plasma mixtures containing solid and liquid status is proposed, considering that the liquid and solid components are usually in the form of clusters. Based on this modified method, the influence of the metal phase transition on the transport coefficients of gas–metal plasma mixture is explored with the example of H2–Cu plasma mixture. The findings revealed in this study are as follows: (1) The modified calculation method is applicable for not only gas–metal plasma mixtures but also other plasma mixtures containing solid and liquid status. (2) Ignoring the metal phase transition in the calculation of transport coefficients of gas–metal plasma mixtures will inevitably produce considerable variances. (3) The variances, caused by ignoring the metal phase transition, are tightly associated with the pressure, the proportion of metal, and the unbalanced degree of gas–metal plasma mixtures. In summary, the variances caused by ignoring the metal phase transition might be ignorable only when the pressure, proportion of metal, and unbalanced degree of gas–metal plasma mixture are all in extremely small values.
Feasible power for DLC deposition on alumina by RF-biased inductively coupled plasma: Effect of atmospheric parameters
Authors: Ai Zhijun , Wu Zhicheng , Feng Le , Zhang Qiaogen , Zhang Zehao , An Zhengjie , Hu Zhengyong
Published: April 2023

The high density and controllability of radio frequency (RF)-biased inductively coupled plasma offer significant potential for diamond-like carbon (DLC) deposition on alumina. However, the effects of power and atmospheric parameters on DLC deposition have been understudied due to multiple constraints, such as discharge conditions and carbon source requirements. In this study, considering the dual requirements of ion flux and ion kinetic energy for deposition, an RF-biased inductively coupled plasma-enhanced DLC deposition method was proposed. A total of 273 deposition experiments designed by response surface methodology were performed over wide parameter ranges to explore the influence of atmospheric parameters, such as gas pressure and Ar/H2 auxiliary gas fractions, on feasible power. The results showed that there was a power threshold for DLC deposition on alumina, which increased with gas pressure and slightly decreased with auxiliary gas addition. The effect of auxiliary gas on DLC deposition exhibited duality due to changes in the dominance of ion etching and methane dissociation. The feasible power region for DLC deposition in multicomponent atmosphere was jointly constrained by the power threshold and etching action. This research contributed to the DLC modification of alumina substrate in batches.
Transitional behaviors of fractional dimensional models of field-induced and space-charge limited emission from rough surfaces
Authors: Zubair Muhammad , Raheem Noreen , Mehmood Muhammad Qasim , Ang Yee Sin , Massoud Yehia
Published: April 2023

Electron emission is an important physical phenomenon in both vacuum and solid-state devices. Previously, the effects of surface roughness or interface irregularity have been incorporated in the fractional Fowler–Nordheim (FNα) equation for field emission, the fractional Child–Langmuir (CLα) law for space-charge limited emission (SCLE) in vacuum, and the fractional Mott–Gurney (MGα) law for SCLE in the presence of carrier collisions using a fractional dimensional approach, where the fractional dimensional parameter (0<α≤1) defines the degree of roughness at electrode surface or irregularity of the gap medium. Here, the transitions between FNα, CLα, and MGα regimes have been investigated for electron emission from rough surfaces. It is shown that the fractional second-order or third-order nexuses, where at least two or three of the FNα, CLα, and MGα regimes converge, respectively, have a strong dependence on the surface conditions as captured by the parameter α. This work provides an important insight into the mechanism of electron emission in electron emitters where surface roughness is inevitable due to practical experimental fabrication and/or emitter surface degradation over time. The model shall serve as a versatile analytical tool to characterize the roughness by fitting the model to the experimental measurements.
Stabilization mechanism of the feedback instability with height-resolved ionosphere and Alfvén resonator models
Authors: Watanabe T.-H. , Hiwatari J. , Maeyama S.
Published: April 2023

Eigenvalue analysis of feedback instability in a magnetosphere–ionosphere (M–I) coupling model has been extended to study the stabilization mechanism of high-frequency shear Alfvén modes by introducing both an inhomogeneous conductivity profile and an ionospheric Alfvén resonator. Stabilization of high-frequency modes is attributed to change of the effective impedance due to the non-uniform ionospheric conductivity along the field line rather than the collision-induced flow shear, while low-frequency modes relevant to auroral arc excitation remain unstable. An effective impedance model incorporating the inhomogeneous conductivity profile is also developed as an extension of the height-integrated ionosphere model.
Meteotsunamis and other anomalous “tidal surge” events in Western Europe in Summer 2022
Authors: Renzi E. , Bergin C. , Kokina T. , Pelaez-Zapata D. S. , Giles D. , Dias F.
Published: April 2023

We investigate occurrences of anomalous tidal activity in coastal waters of north-west Europe during Summer 2022. Sightings of an anomalous “tidal surge” occurred on 18 June 2022 in Wales, followed by similar observations in Ireland, France, and Spain. Several anomalous long-wave events were also reported in south England and Wales in the morning of 19 July 2022. We analyzed surface and high-altitude air pressure fields, and sea level oscillations for both days. Our detailed analysis reveals that the 18 June events were a series of meteotsunamis, propagating over several countries in Western Europe and triggered by localized pressure perturbations, originating within a low-pressure area over the North Atlantic Ocean. A local analysis of the southern coast of Ireland suggests that Proudman resonance was the determinant mechanism that amplified the meteotsunami traveling eastward in the afternoon of 18 June. A similar analysis of the 19 July events suggests that the tidal surge reported in the UK and anomalous signals recorded in Ireland and France were episodes of seiching triggered by infragravity waves, resonated subharmonically by wind waves. Numerical simulations of the 18 June event were performed with Volna-OP2, which solves the non-linear shallow water equations using a finite volume discretization. The influence of the atmospheric wave velocity on the amplification of the sea surface elevation is analyzed.
Chemical phases in the solution-grown Zn(O,S) buffer of post-annealed Cu(In,Ga)Se2 solar cells investigated by transmission electron microscopy and electroreflectance
Authors: Jin Xiaowei , Schneider Reinhard , Popescu Radian , Seeger Jasmin , Grutke Jonas , Zerulla Benedikt , Hetterich Michael , Hariskos Dimitrios , Witte Wolfram , Powalla Michael , Gerthsen Dagmar
Published: April 2023

Thin-film solar cells with Cu(In,Ga)Se2 (CIGS) absorber layers have been intensively studied due to their high power conversion efficiencies. CIGS solar cells with Zn(O,S) buffer layers achieved record efficiencies due to their reduced parasitic absorption compared with the more commonly used CdS buffer. Accordingly, we have studied solution-grown Zn(O,S) buffer layers on polycrystalline CIGS absorber layers by complementary techniques. A bandgap energy Eg of 2.9 eV is detected by means of angle-resolved electroreflectance spectroscopy corresponding to Zn(O,S), whereas an additional Eg of 2.3 eV clearly appeared for a post-annealed CIGS solar cell (250 °C in air) compared with the as-grown state. To identify the chemical phase that contributes to the Eg of 2.3 eV, the microstructure and microchemistry of the Zn(O,S) buffer layers in the as-grown state and after annealing were analyzed by different transmission electron microscopic techniques on the submicrometer scale and energy-dispersive x-ray spectroscopy. We demonstrate that the combination of these methods facilitates a comprehensive analysis of the complex phase constitution of nanoscaled buffer layers. The results show that after annealing, the Cu concentration in Zn(O,S) is increased. This observation indicates the existence of an additional Cu-containing phase with Eg close to 2.3 eV, such as Cu2Se (2.23 eV) or CuS (2.36 eV), which could be one possible origin of the low power conversion efficiency and low fill factor of the solar cell under investigation.
O3 full photo-fragmentation TALIF spectroscopy for quantitative diagnostics of non-thermal O2-mixed plasmas
Authors: Qiao Jun-Jie , Xiong Qing , Yang Qi , Song Yi-Jia , Wang Da-Zhi
Published: April 2023

In this study, we explore the potential of using laser-induced photo-fragmentation of O3 by UV radiation as a quantitative diagnostic tool in non-thermal O2-mixed plasmas. We analyze the optical processes of O3 using a comprehensive kinetic model with a 226 nm laser, which is typically used in the two-photon absorption laser-induced fluorescence (TALIF) measurement of O atoms. Our model demonstrates that the fluorescence intensity from atomic O fragments produced by the same laser is directly proportional to the population of precursor O3. This makes various diagnostic purposes achievable through the proposed O3 full photo-fragmentation (FPF) TALIF spectroscopy, including calibration of TALIF signals of O atoms and quantification of both O and O3 in O2-mixed plasmas. We present detailed theoretical principles, technical requirements, and successful examples of implementation for different diagnostic aims using the proposed O3 FPF-TALIF spectroscopy. However, we also specify the limitations of the developed diagnostic methods, particularly under low E/N conditions (<30 Td), where other interferential species such as the vibrationally excited ground-state O 2 ( X 3 Σ g − , v ≠ 0 ) are abundantly produced.
Vertical detachment energies of ammonia cluster anions using self-interaction-corrected methods
Authors: Ufondu Peter , Chang Po-Hao , Baruah Tunna , Zope Rajendra R.
Published: April 2023

Systems with weakly bound extra electrons impose great challenges to semilocal density functional approximations (DFAs), which suffer from self-interaction errors. Small ammonia clusters are one such example of weakly bound anions where the extra electron is weakly bound. We applied two self-interaction correction (SIC) schemes, viz., the well-known Perdew–Zunger and the recently developed locally scaled SIC (LSIC) with the local spin density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA), and the SCAN meta-GGA functionals to calculate the vertical detachment energies (VDEs) of small ammonia cluster anions (NH3)n−. Our results show that the LSIC significantly reduces the errors in calculations of VDE with LSDA and PBE-GGA functionals leading to better agreement with the reference values calculated with coupled cluster singles and doubles with perturbative triples [CCSD(T)]. Accurate prediction of VDE as an absolute of the highest occupied molecular orbital (HOMO) is challenging for DFAs. Our results show that VDEs estimated from the negative of HOMO eigenvalues with the LSIC-LSDA and Perdew–Zunger SIC-PBE are within 11 meV of the reference CCSD(T) results. The LSIC method performs consistently well for the VDE estimates, from both the total energy differences and the absolute HOMO eigenvalues.
Investigation of real-time strain responses of the insulating system of superconducting magnets by using fiber Bragg grating sensors
Authors: Zhao Wanyin , Xin Jijun , Zhang Hengcheng , Wang Wei , Fang Zhichun , Lyu Bingkun , Wu Longfeng , Wang Chundong , Shen Fuzhi , Shan Xinran , Huang Chuanjun , Sun Wentao , Zhou Yuan , Li Laifeng
Published: April 2023

The normal operation of various superconducting magnets is greatly influenced by the thermal stress of the insulating system, commonly made of epoxy resins with vacuum pressure impregnation (VPI) technology, throughout the curing and cooling processes. In this work, we developed a Fiber Bragg Grating (FBG) strain measurement method to monitor the real-time strain responses of an epoxy resin IR-3 and its glass fiber-reinforced composite during both curing and cooling processes. Then, we also monitored the same process of a Nb–Ti superconducting magnet coil prepared by VPI technology. With the help of FBG strain sensors, the residual strains of the coil at various positions and directions were investigated. The results show that the large residual strain occurred near the end of the coil in the axial direction. In addition, the interlaminar shear stress properties were measured at both room temperature and liquid nitrogen temperature. The strain characteristics of the epoxy resin IR-3 and the insulating system can provide useful guidance for the design and construction of high-field Nb–Ti superconducting magnets.
GaSb band-structure models for electron density determinations from Raman measurements
Authors: Ochoa Maicol A. , Maslar James E. , Bennett Herbert S.
Published: April 2023

We investigate the use of Raman spectroscopy to measure carrier concentrations in n-type GaSb epilayers to aid in the development of this technique for the nondestructive characterization of transport properties in doped semiconductors. The carrier concentration is quantified by modeling the measured coupled optical phonon-free carrier plasmon mode spectra. We employ the Lindhard–Mermin optical susceptibility model with contributions from carriers in the two lowest GaSb conduction-band minima, the Γ and L minima. Furthermore, we evaluate three conduction-band models: (1) both minima parabolic and isotropic, (2) the Γ minimum non-parabolic and isotropic and the L minima parabolic and isotropic, and (3) the Γ minimum non-parabolic and isotropic and the L minima parabolic and ellipsoidal. For a given epilayer, the carrier concentration determined from the spectral simulations was consistently higher for the ellipsoidal L minima model than the other two models. To evaluate the conduction-band models, we calculated the L to Γ electron mobility ratio necessary for the electron concentrations from the Raman spectral measurements to reproduce those from the Hall effect measurements. We found that the model with the ellipsoidal L minima agreed best with reported carrier-dependent mobility-ratio values. Hence, employing isotropic L minima in GaSb conduction-band models, a common assumption when describing the GaSb conduction band, likely results in an underestimation of carrier concentration at room temperature and higher doping levels. This observation could have implications for Raman spectral modeling and any investigation involving the GaSb conduction band, e.g., modeling electrical measurements or calculating electron mobility.
Surface plasmon-mediated enhanced field electron emission based on metasurfaces with a nano-gap driven by LEDs
Authors: Zhao Jing , Liu Jianlong , Jiang Ruirui , Yang Kaiqiang , Zeng Baoqing
Published: April 2023

Vacuum electronic devices have the advantages of no scattering, anti-irradiation, and extreme operating temperatures. With their superiorities, light-assisted field emission can be utilized to drive ultrafast micro-/nano-vacuum electronic devices. However, traditional multiphoton or optical field emission is limited by the access of the lasers with high power and energy. In this Letter, an asymmetric non-semiconductor nanostructure may be applied to reduce cost with a nano-level gas or vacuum channel. We find that the basic LED may be a candidate to enhance the electron emission current by utilizing the multi-stage field enhancement consisting of tip effects and plasmon-based enhancement. By designing a field electron emission device with LEDs in standard atmospheric environment, we realize a 25% increase in field electron emission current at the resonance frequency with the light intensity under W cm−2 and the voltage less than 5 V. By comparing with lasers, simple LEDs are beneficial to increase the scope of applications with low-energy requirements. Meanwhile, the structure paves the way to the application of microelectronic and nano-electronic components in the on-chip electronic devices, such as switches and modulators.
Interrelation between ferroelectric properties and defects based on
low-frequency noise analysis of HZO ferroelectric capacitor
Authors: Jin Seunghee , Jeon Juye , Kim Min Jung , Heo Kiseok , Kim Jeong Hun , Im Jong-Pil , Yoon Sung-Min , Moon Seung Eon , Woo Jiyong , Lee Jae Woo
Published: April 2023

Switching characteristics of ferroelectrics depend on the fabrication conditions and phase-transition results of each fabrication recipe. Here, the pulsed I–V and positive-up negative-down plots of hafnium zirconium oxide ferroelectric capacitors (FeCaps) are analyzed using low-frequency noise (LFN), an electrical method to investigate defects including oxygen vacancies that are key elements influencing polarization properties. This is a new trial at adopting the LFN method for analysis of FeCaps to find interrelation ferroelectric characteristics and defects depending on the annealing conditions. Increasing power spectral density (PSD) levels are observed with increasing annealing temperature and time. Moreover, the nature of the defects reflected in the PSD is examined via x-ray photoelectron spectroscopy. Correlations are observed between the defects, including oxygen vacancies and ZrOx defects, and FeCap properties. High intrinsic polarization is observed when the density of defects is large; this shows that oxygen vacancies and ZrOx defects in FeCaps may enhance the orthorhombic phase by inducing lattice strain. These findings are expected to facilitate LFN studies of ferroelectrics and the fundamental understanding of their electrical properties from defects and oxygen vacancy analyses.
Physically based equation of state for Mie ν-6 fluids
Authors: Reimer Anja , van Westen Thijs , Gross Joachim
Published: April 2023

We develop a physically based equation of state that describes Mie ν-6 fluids with an accuracy comparable to that of state-of-the-art empirical models. The equation of state is developed within the framework of the uv-theory [T. van Westen and J. Gross, J. Chem. Phys. 155, 244501 (2021)], which is modified by incorporating the third virial coefficient B3 in the low-density description of the model. The new model interpolates between a first-order Weeks–Chandler–Andersen (WCA) perturbation theory at high densities and a modified first-order WCA theory that recovers the virial expansion up to B3 at low densities. A new algebraic equation for the third virial coefficient of Mie ν-6 fluids is developed—other inputs are taken from previous work. Predicted thermodynamic properties and phase equilibria are compared to a comprehensive database of molecular simulation results from the literature, including Mie fluids of repulsive exponents 9 ≤ ν ≤ 48. The new equation of state is applicable to states with densities up to ρ*(T*)⪅1.1+0.12T* and temperatures T* > 0.3. For the Lennard-Jones fluid (ν = 12), the performance of the model is comparable to that of the best empirical equations of state available. As compared to empirical models, the physical basis of the new model provides several advantages, however: (1) the new model is applicable to Mie fluids of repulsive exponents 9 ≤ ν ≤ 48 instead of only ν = 12, (2) the model leads to a better description of the meta-stable and unstable region (which is important for describing interfacial properties by classical density functional theory), and (3) being a first-order perturbation theory, the new model (potentially) allows an easier and more rigorous extension to non-spherical (chain) fluids and mixtures.
Beamlet formation in negative ion sources for fusion applications: A computational grid system comparison
Authors: den Harder Niek , Fantz Ursel
Published: April 2023

Divergence is a crucial parameter for neutral beam injection heating systems, since it affects the transmission of the beam through a duct. The divergence is determined by properties of the extracted ions, in combination with a grid system that extracts ions from the plasma and subsequently accelerates them to full energy. To disentangle different contributions to the divergence, eight different negative ion-based grid systems are studied with the IBSimu code, treating volume produced deuterium ions only. To ensure that the observed differences can be attributed to grid features, the grid systems are modeled without magnetic field. The ratio between acceleration and extraction potential that gives the lowest divergence shows good agreement with calculated and measured literature values. The divergence in various grid systems is studied at the ITER-heating neutral beams D− current density and extraction potential. At similar normalized emittance, there is a large range of divergences due to the variation in the axial velocity at different acceleration potentials. The normalized emittance is mostly determined by the starting emittance and emittance growth in the extraction stage. The starting emittance is due to the initial perpendicular temperature of the negative ions, which is assumed as 1 eV in simulations. The emittance growth is due to space charge in the extraction stage. Some of the investigated grid systems produce lower divergence beamlets at similar emittance by trading off beamlet size and divergence. The optimum divergence is limited by three parameters at fixed beamlet size: the D− perpendicular velocity distribution upstream of the grid system, the space charge in the extraction stage, and the available high-voltage potential to accelerate the beamlet.
Surface modification of Ti3C2Tx using terminal groups and heteroatoms with excellent electrochemical performance in supercapacitors
Authors: Swapnalin Jhilmil , Koneru Bhargavi , Pothu Ramyakrishna , Banerjee Prasun , Boddula Rajender , Radwan Ahmed Bahgat , Al-Qahtani Noora
Published: April 2023

Surface modification of Ti3C2Tx greatly enhances its charge storage mechanism as an electrode material. Herein, we demonstrate the role of surface terminals and heteroatoms in the electrochemical behavior of Ti3C2Tx electrodes. The abundance of –F and –OH surface terminals may be obtained with an acidic or base medium while etching of Ti3C2Tx. Further treatment with ammonia or glucose may help to get a thin layer of N or C at the surface of Ti3C2Tx. It is found that abundant reaction sites and larger interlayer spacing can help in improving the specific capacitance by nearly 2.5 times to unmodified Ti3C2Tx electrodes. This superior performance can be achieved without sacrificing the conductivity and accordion-like structure of Ti3C2Tx MXene two-dimensional material.
Modification of Lie's transform perturbation theory for charged particle motion in a magnetic field
Authors: Zheng Linjin
Published: April 2023

It is pointed out that the conventional Lie transform perturbation theory for the guiding center motion of charged particles in a magnetic field needs to be modified for ordering inconsistency. There are two reasons. First, the ordering difference between the temporal variation of gyrophase and that of the other phase space coordinates needs to be taken into account. Second, it is also important to note that the parametric limit of the derivative of a function is not equivalent to the derivative of the limit function. When these facts are taken into account, the near identity transformation rule for one form related to the Lagrangian is modified. With the modified near identity transformation rule, the drift motion of charged particles can be described in the first order, instead of the second order and beyond through a tedious expansion process as in the conventional formulation. This resolves the discrepancy between the direct and Lie transform treatments in the Lagrangian perturbation theory for charged particle motion in a magnetic field.
Effect of secondary atomization on blood backspatter affected by muzzle gases
Authors: Michael James B. , Yarin Alexander L.
Published: April 2023

Blood backspatter pattern analysis provides important evidence in firearm-related crime scenes. The mechanisms behind particular patterns have attracted significant recent attention in forensic sciences, in general, and in forensic-science-motivated fluid dynamics, in particular. However, investigations on the secondary atomization of blood drops in flight and its effects on trajectories and the corresponding blood stain distributions were scarce. The present work is especially concerned with the effect of secondary atomization on the blood backspatter interaction with muzzle gases at short-range shooting, where it can be very significant. A secondary breakup model is incorporated into the blood backspatter model accounting for interaction with a self-similar vortex ring formed by muzzle gases and moving with high speed in the direction opposite to that of the initial motion of blood drops. The behavior of blood drops of different sizes is investigated, and different scenarios are identified. The secondary atomization stems from high relative velocities of drops and air/muzzle gases and results in the formation of small blood droplets, which are swept easier by muzzle gases and even turned around toward a target. Overall, the secondary atomization in the presence of muzzle gases results in blood stains deposited on the floor closer to the target or even behind the target. It is revealed that in the cases of short-range shooting, the predicted blood stain locations on the floor without accounting for the secondary atomization could be misleading for realistic drop sizes observed experimentally.
Intense narrowband terahertz pulses produced by obliquely colliding laser pulses in helium gas
Authors: Lee Jaeho , Song Hyung Seon , Park Dohyun , Kumar Manoj , Ersfeld Bernhard , Yoffe Samuel R. , Jaroszynski Dino A. , Hur Min Sup
Published: April 2023

A practical configuration for generating narrowband terahertz (THz) pulses based on plasma dipole oscillations (PDOs) is studied using two-dimensional particle-in-cell simulations. In this scheme, two slightly detuned laser pulses collide obliquely in a helium gas. Plasma strips are generated along the paths of the laser pulses by field ionization. The PDO created in the overlap region of the two laser pulses emits a THz pulse with a peak electric field strength of a few gigavolt per meter. An energy conversion efficiency of 0.542 × 10 − 3 is achieved for laser pulse intensities 4.82 × 10 16   W / c m 2, a spot radii of 5  μ m, and a collision angle of 10.8 °. A force balance model is extended for the obliquely colliding configuration of the pulses. As the complications, such as generating plasmas separately or aligning the beams with preformed plasma, are eliminated from our new configuration, this makes a future experimental study of PDO more straightforward.
Liquid carrying capacity: From liquid bridge bearing to ferrofluid bearing
Authors: Dai Qingwen , Xu Hao , Ma Chenbo , Huang Wei , Wang Xiaolei
Published: April 2023

Inspired by liquid bridge bearings, a kind of ferrofluid (FF) bearing is proposed in this work. The bearing contains two plates with a drop of FF sandwiched between them. To restrain and position the FF, a cylindrical magnet is implanted in the lower plate. The carrying capacity of the liquid bridge and FF bearing is tested and compared. The results indicate that both bearings can provide a certain amount of liquid supporting force. For similar geometries, the maximum force generated by the FF bearing (1.60 N) is about 20 times higher than that of the liquid bearing (0.08 N). Moreover, due to the effect of the magnetic field, the supporting performance of the FF bearing is more stable, especially in small gap heights. To further understand the supporting mechanism, a model of the FF bearing for the carrying capacity was built and validated by the experiment. Theoretical analysis manifests that, compared with the Laplace force, the magnetic force acts as a dominant contribution to the FF bearing. This work provides an interesting way to create liquid support for MEMS applications that demand controllable micro-platforms or frictionless bearings.
Electro-optics of blue phase liquid crystal in field-perpendicular direction
Authors: Zhang Yuxian , Yoshida Hiroyuki , Wang Qiong-Hua , Ozaki Masanori
Published: April 2023

The electro-optic effect is the working principle of blue phase (BP) liquid crystals, and it describes the relationship between the field-induced birefringence of BPs and the field strength. Due to the electrostriction of BP crystals under the electric field, an orthorhombic or tetragonal crystal is usually obtained when the field is applied along one of the twofold axes of a BP crystal, leading to the optical biaxiality under electric field. Such field-induced optical biaxiality of BPs has been predicted and observed, but its dependence on the field strength has not been investigated. In this research, we analyze the electro-optics in the field-perpendicular direction by measuring the birefringence in highly ordered BP I(110) crystals perpendicular to the electric field. Results reveal that BP I crystals in the field-perpendicular direction show an electro-optic coefficient of the order of 10−10 m/V2 that may result from the large lattice deformation of BP crystals perpendicular to the electric field. Our research provides important experimental evidence for the tensorial properties of BP Kerr effect and may have important implications on the engineering of BP electro-optical devices in practical applications.
Dispersion of surface elastic waves on Z-LiNbO3 films on Z-sapphire
Authors: La Spina Léa , Micard Quentin , Mosset Alexis , Margueron Samuel , Bartasyte Ausrine , Laude Vincent
Published: April 2023

Epitaxial thin films of lithium niobate with a thickness of 160 nm, oriented along the crystallographic c axis, were grown by direct liquid injection chemical vapor deposition on c-sapphire substrates. Different families of very high-frequency surface acoustic waves with general polarization exist in such piezoelectric films on high-velocity substrates. Surface Brillouin light scattering measurements, complemented with fast finite element analysis of wave dispersion, demonstrate Rayleigh, leaky shear, and leaky longitudinal surface waves, excited at frequencies between 10 and 30 GHz. The Brillouin technique reveals dispersion and anisotropy of propagation without the implementation of high-frequency surface acoustic wave transducers.
Theoretical study of spin polarization in multiphoton ionization of Xe
Authors: Artemyev Anton N. , Kutscher Eric , Lagutin Boris M. , Demekhin Philipp V.
Published: April 2023

Spin polarization in the multiphoton above-threshold ionization of 5p3/2- and 5p1/2-electrons of Xe with intense 395nm, circularly polarized laser pulses, is investigated theoretically. For this purpose, we solve the time-dependent Schrödinger equation on the basis of spherical spinors. We, thus, simultaneously propagate the spin-up and spin-down single-active-electron wave packets, driven by the laser pulses in the ionic potential, which includes the spin–orbit interaction explicitly. The present theoretical results are in good agreement with the recent experimental results [D. Trabert et al., Phys. Rev. Lett. 120, 043202 (2018)].
Highly sensitive lock-in thermoreflectance temperature measurement using thermochromic liquid crystal
Authors: Takahagi Atsushi , Iguchi Ryo , Nagano Hosei , Uchida Ken-ichi
Published: April 2023

We show that the temperature measurement sensitivity in the lock-in thermoreflectance (LITR) can be improved by incorporating a thermochromic liquid crystal (TLC) into a transducer. The quantitatively estimated thermoreflectance coefficient of a TLC/Pt hybrid film depends on the excitation frequency and reaches >2 × 10−2 K−1 at low excitation frequencies, which is two orders of magnitude greater than typical values of 10−4 for metallic films. Using the TLC/Pt film, we detected the temperature changes due to Joule heating and the spin Peltier effect with the temperature resolution of ∼10 μK by the LITR method. We also performed the same measurements for an Au film and found that the temperature resolution for the TLC/Pt film is increased by a factor of >10 compared with that for the Au film despite the low reflected light intensity of the TLC/Pt film.
Effects of metamaterials on MIMO antennas for X-band radar applications and parameter optimization with a machine learning model: A review
Authors: Undrakonda Jyothsna , Upadhyayula Ratna Kumari
Published: April 2023

Radars are at the core of numerous real-world applications in healthcare monitoring and autonomous driving due to the rapid expansion of the communication system. MIMO (Multiple-Input Multiple-Output) antennas are an essential component of radar systems. The effect of mutual coupling degraded the performance of these antennas. This article comprehensively reviewed the metamaterial-based decoupling technique for antenna design and provided a comparison with other decoupling techniques. The occurrence and variety of current information, the sophistication of processing, and the low cost of data storage all contribute to the increased interest in using machine learning to find optimal solutions in a variety of fields. This article introduces and investigates machine learning applications in antenna design. This paper discusses implementing different machine learning models to optimize primary antenna performance, reduce mutual coupling, and increase the bandwidth. Various numerical results from synthetically generated and experimental datasets and about two specific applications are presented as a conclusion. These allow readers to evaluate the effectiveness of particular methods and compare them in terms of precision and computational effort.
Directional switches in network-organized swarming systems with delay
Authors: Xiao Rui , Li Wang , Zhao Donghua , Sun Yongzheng
Published: April 2023

Coordinated directional switches can emerge between members of moving biological groups. Previous studies have shown that the self-propelled particles model can well reproduce directional switching behaviors, but it neglects the impact of social interactions. Thus, we focus on the influence of social interactions on the ordered directional switching motion of swarming systems, in which homogeneous Erdös–Rényi networks, heterogeneous scale-free networks, networks with community structures, and real-world animal social networks have been considered. The theoretical estimation of mean switching time is obtained, and the results show that the interplay between social and delayed interactions plays an important role in regulating directional switching behavior. To be specific, for homogeneous Erdös–Rényi networks, the increase in mean degree may suppress the directional switching behaviors if the delay is sufficiently small. However, when the delay is large, the large mean degree may promote the directional switching behavior. For heterogeneous scale-free networks, the increase of degree heterogeneity can reduce the mean switching time if the delay is sufficiently small, while the increasing degree heterogeneity may suppress the ordered directional switches if the delay is large. For networks with community structures, higher communities can promote directional switches for small delays, while for large delays, it may inhibit directional switching behavior. For dolphin social networks, delay can promote the directional switching behavior. Our results bring to light the role of social and delayed interactions in the ordered directional switching motion.
Theoretical prediction of time-related performance of GaN-based p–n junction betavoltaic battery
Authors: Chen Ziyi , Lu Jingbin , Zheng Renzhou , Li Xiaoyi , Wang Yu , Zhang Xue , Zhang Yuehui , Cui Qiming , Yuan Xinxu , Zhao Yang , Li Haolin , Liu Yumin
Published: April 2023

Betavoltaic batteries can meet long-term energy supply needs. However, due to the decay of the radioactive source, the output performance of battery will change over time, and the laws of this change require elucidation to aid the battery engineer. In this study, the influences of time on the apparent power density and β-energy spectrum of the 63 Ni source were clarified. Moreover, the structural parameters, including the p-region, n-region doping concentrations, and junction depth of GaN-based (hexagonal) p–n junction, were optimized, which are 2 × 1017 cm–3, 1014 cm–3, and 0.1 μm, respectively. In particular, the time-related performance trends were analyzed, and a formula for the maximum output power density deterioration was obtained, which can be used to evaluate the performance of 63 Ni GaN-based p–n junction betavoltaic battery within 200 years. The simulation results showed that the maximum output power density of battery after 50 years is 0.243 μW cm−2, which is only 60% of the initial value. In addition, the other output performances, namely, the short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency are 0.096 μA cm−2, 2.67 V, 94.3%, and 20.5%, respectively.
Construction of a 3D/2D heterojunction based on a fluorinated cyclohexylamine 2D Ruddlesden–Popper perovskite for highly efficient and stable perovskite solar cells
Authors: Xu Jinghua , Qiao Hongwei , Chen Zhongliang , Wang Xue-Lu , Yao Ye-Feng
Published: April 2023

Nonradiative recombination at perovskite/charge transport layer interfaces is caused by surface defects and instability, and it is known to limit the long-term development of perovskite solar cells (PSCs). To overcome this issue, the three-dimensional/two-dimensional (3D/2D) perovskite heterojunction has emerged as a possible solution to improve the stabilities and efficiency of PSCs. Herein, we employ a simple one-step method to prepare n-i-p-structured PSCs using a 3D/2D perovskite heterojunction as the absorption layer. For this purpose, the large and non-centrosymmetric 4,4-difluorocyclohexylammonium (DFCHA+) cation, which has been confirmed to be a valid organic spacer in 2D Ruddlesden–Popper (RP) phase perovskites, is employed as an organic ligand for post-treatment of the surfaces of MAPbI3 films. The presence of an ultrathin 2D RP phase perovskite was confirmed on the surface, and the 3D/2D perovskite heterojunction was successfully constructed. Benefitting from surface post-treatment, the density of the surface trap states was reduced with effective passivation. In addition, nonradiative recombination was suppressed, and the interface bands were aligned. As a result, the optimal device achieved a power conversion efficiency of 21.93% with a remarkable open-circuit voltage (VOC) of 1.14 V, a current density (JSC) of 23.71 mA cm−2, and a fill factor of 0.82. Furthermore, owing to the hydrophobicity of the DFCHA+ cation, the unencapsulated device was able to maintain an initial efficiency of 82.3% after storage for 500 h at a relative humidity of ∼45%. We believe that this post-treatment strategy has wide application potential in the field of photovoltaic devices.