bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the spin dynamics of a room-temperature diamond maser using an extended rate equation model
Authors: Wen Yongqiang , Diggle Philip L. , Alford Neil McN. , Arroo Daan M.
Published: November 2023

Masers—the microwave analog of lasers—are coherent microwave sources that can act as oscillators or quantum-limited amplifiers. Masers have historically required high vacuum and cryogenic temperatures to operate, but recently, masers based on diamond have been demonstrated to operate at room temperature and pressure, opening a route to new applications as ultra-low noise microwave amplifiers. For these new applications to become feasible at a mass scale, it is important to optimize diamond masers by minimizing their size and maximizing the power of signals that can be amplified. Here, we develop and numerically solve an extended rate equation model to present a detailed phenomenology of masing dynamics and determine the optimal properties required for the copper cavity, dielectric resonator, and gain medium in order to develop portable maser devices. We conclude by suggesting how the material parameters of the diamond gain media and dielectric resonators used in diamond masers can be optimized, and how rate equation models could be further developed to incorporate the effects of temperature and nitrogen concentration on spin lifetimes.
Large-area single-crystal hexagonal boron nitride: From growth mechanism to potential applications
Authors: Lee Joo Song , Basu Nilanjan , Shin Hyeon Suk
Published: November 2023

To date, chemical vapor deposition has been employed to grow large-area polycrystalline (PC) films of hexagonal boron nitride (hBN). However, PC hBN thin films exhibit abundant grain boundaries, small grain sizes, and structural imperfections, which collectively degrade the performance as well as hinder the scalability and potential applications of hBN films. Recently, demonstrated deposition methods for growing large-area single-crystalline (SC) hBN films can break through these bottlenecks and have opened avenues for new opportunities. Large-area SC hBN films outperform their PC counterparts owing to the presence of fewer grain boundaries and a more homogeneous surface morphology. This review article presents a consolidated overview of the growth mechanisms of SC hBN films and role of metal catalysts (substrates) in the growth process. Applications, in which SC hBN outperforms PC hBN as well as the potential applications of SC hBN, are also discussed.
Hybrid nanostructure with two-dimensional grating for resonance waves self-referenced sensing
Authors: Zhu Xiaoqing , Wang Bo
Published: November 2023

Self-referenced sensors have attracted significant interest in recent years due to their ability to provide more reliable detection results than conventional sensors. In this paper, we propose a hybrid structure based on a two-dimensional grating surface for self-referenced refractive index sensing in the near-infrared operating band. The hybrid structure can support the metal-assisted guided-mode and Fabry–Pérot resonances. Meanwhile, the resonance mechanism of the proposed structure is analyzed in detail through the electric field distribution characteristics, and the feasibility of the structure as self-referenced sensing is also confirmed. In addition, the influences of structural parameters, structure shape, and polarization angle on the optical properties are systematically discussed. Notably, calculations at different refractive indices of the analytes show that the structure has a more stable reference signal and better sensing performance than previously reported self-referenced sensors, with a sensitivity and figure of merit of 680 nm/RIU and 1852 RIU−1, respectively. These results illustrate that the proposed structure can provide more accurate measurements in some unstable measurement environments, implying its promising application in the fields of biological, pharmaceutical, and chemical sensing.
Evidence for intrinsic magnetic scatterers in the topological semimetal (Bi2)5(Bi2Se3)7
Authors: Gehring Pascal , Merckling Clement , Meng Ruishen , Fonck Valentin , Raes Bart , Houssa Michel , Van de Vondel Joris , De Gendt Stefan
Published: November 2023

We report the synthesis and characterization of high-quality thin films of the topological semimetal (Bi2)5(Bi2Se3)7. Cryogenic magneto-transport experiments reveal strong metallic character and spin–orbit coupling in the films. By studying the temperature dependence of the electrical resistance of the topological semimetal, we observe a pronounced Kondo effect, which points toward the presence of magnetic scatterers. With the aid of density functional theory calculations, we identify Bi vacancies as intrinsic magnetic scatterers in this topological semimetal.
Unlocking the potential of hexaferrite–spinel ferrite composites: Microstructure-induced colossal permittivity and relaxation phenomena
Authors: Karnajit Singh Hodam , Mohapatra Prajna P. , Pandey Subingya , Dobbidi Pamu
Published: November 2023

The solid-state synthesized dense ceramic composite, consisting of M-type hexaferrite Ba0.5Sr0.5Fe12O19 and inverse spinel ferrite Ni0.3Co0.2Zn0.5Fe2O4 (NCZFO) with varying concentrations, demonstrates the presence of apparent colossal permittivity along with dielectric relaxation behaviors at the higher frequency regions for all the composites. This phenomenon manifests as a giant dielectric permittivity of approximately 105 at 1 kHz, gradually decreasing to around 103 at 1 MHz at room temperature. It can be attributed to the Maxwell–Wagner interfacial polarization, which arises from the presence of different conductivity regions within the microstructures of the composite. The dielectric permittivity and the activation energy are also increased with higher NCZFO content, indicating an intricate microstructure influencing the electrical response by impacting charge carrier movement and ion migration. The presence of both Fe and Co cation defects and oxygen vacancies enhanced non-uniformity in the microstructure with different conductivity regions. The appearance of relaxation peaks in the higher frequency region can be attributed to inhomogeneity in the microstructure. In conjunction with the equivalent circuit analysis, the Nyquist plot confirmed that the electrical response at a lower frequency primarily arises from grain boundaries. The departure from ideal Debye-type relaxation behavior in the electrical response is also confirmed by impedance analysis. Furthermore, the step-like increase in AC conductivity with frequency suggests that the electrical response observed at a lower frequency is not intrinsic. Rather, it indicates the depletion of insulating grain boundaries due to diffusive ion motions resulting from defects. This observation reinforces that the high dielectric permittivity observed in the composite is not an inherent characteristic of the constituent materials. Instead, it arises from the microstructure and the influence of defects within the material.
Non-destructive detection of sub-micrometer-sized micropipes in silicon carbide using mirror electron microscope
Authors: Kobayashi Keisuke , Mori Yuki , Konishi Kumiko , Hasegawa Masaki , Kobayashi Kenji , Shima Akio
Published: November 2023

A non-destructive method for detecting sub-micrometer-sized micropipes on an entire wafer surface is investigated. Since it is difficult to detect sub-micrometer-sized micropipes due to their small core size, a non-destructively and accurately detecting method is required. To solve the issue, we focus on a characteristic depression generated around micropipes, namely, line-shaped depressions. In this paper, the location of line-shaped depressions is identified by using optical inspection, and the line-shaped depressions are distinguished whether micropipes exhibit line-shaped depression or not by using mirror electron microscope observation as high-resolution inspection. The accuracy of the distinction results is confirmed by scanning electron microscope observation, and electrical characteristics of the P–N diode are fabricated using the inspected wafer. Furthermore, the sub-micrometer-sized micropipes are observed at the sites of leakage current identified by emission microscopy. Additionally, device simulation of the blocking-voltage characteristics of P–N diodes suggests that the increase in leakage current depends on the electric field at the sub-micrometer-sized micropipes, regardless of their core size.
Evidence for a build-in remnant field in symmetrically contacted MAPbBr3 x-ray detectors
Authors: Lédée Ferdinand , Mayén-Guillen Javier , Lombard Stéphanie , Zacarro Julien , Verilhac Jean-Marie , Gros-Daillon Eric
Published: November 2023

Millimeter-thick methylammonium lead tribromide (MAPbBr3) single crystal x-ray detectors have recently raised attention due to their high x-ray attenuation efficiency and good charge transport properties. However, an intriguing feature of the photocurrent response of MAPbBr3 detectors has been largely overlooked in the literature. After biasing, transient sensitivity is measured under x rays at short-circuit (bias = 0 V), thus revealing a large remnant electric field that builds up under bias. Here, we exploit the x-ray sensitivity of MAPbBr3 detectors at zero-bias in order to probe the internal built-in field, as well as to investigate the charge transport properties of the perovskite material. Our model derived from the Hecht equation is able to fully rationalize the response of the detectors both at short-circuit and under moderate applied bias. Moreover, we provide a method for the estimation of the internal electric field, and for the sum of the electrons and holes mobility–lifetime products μeτe+μhτh. This general method could extend to any perovskite-based x-ray detector exhibiting transient sensitivity at zero-bias.
Experimental realization of exceptional surfaces enhanced displacement sensing with robustness
Authors: Jiang Shuo , Li Jincheng , Li Zelei , Li Zigeng , Li Wenxiu , Huang Xinyao , Zhang Hao , Zhang Guofeng , Huang Anping , Xiao Zhisong
Published: November 2023

The application of exceptional points in non-Hermitian photonic systems has attracted attention in the field of ultra-high-sensitivity sensing. However, the realization of an exceptional point (EP) in experiments requires precise control of the multiple parameters of the sensor, which limits the practical applicability of EP-enhanced sensors. In this work, the exceptional surface (ES)-enhanced displacement sensing is experimentally demonstrated in a fiber ring resonator to break through this restriction. Expanding EPs to an ES makes the system immune to fabrication errors and environmental uncertainties, thereby improving the system's robustness and maintaining a high sensing sensitivity by working exactly at EPs. Compared with a diabolic point-based structure, a significant sensitivity enhancement of the displacement sensing is observed by monitoring the frequency splitting in the spectrum. Our proposed structure has strong robustness against changes in the resonator dissipation and frequency fluctuations and could, therefore, pave the way for practical non-Hermitian photonic sensing applications.
Raman scattering and vacuum fluctuation: An Einstein-coefficient-like equation for Raman cross sections
Authors: Min Wei , Gao Xin
Published: November 2023

Since it was first predicted 100 years ago, Raman scattering has been a cornerstone of molecular spectroscopy with a widespread impact on science and technology. Nearly all theoretical frameworks have employed Raman cross sections (σRaman) to characterize and quantify molecular Raman response. The recently introduced absolute stimulated Raman scattering cross section (σSRS), on the other hand, provides an alternative way of interpreting molecular responses under two coherent laser sources. However, the theoretical connection between σRaman and σSRS remains unclear. Herein, we are inspired by Einstein’s A and B coefficients for spontaneous and stimulated emissions and derived an analogous equation [Eq. (16)] for Raman scattering from an approach along quantum electrodynamics. Equation (16) decomposes Raman cross sections into a contribution from the vacuum electromagnetic field and an underlying molecular response captured by stimulated Raman cross sections (in the unit of Göppert–Mayer). This theoretical relation is supported by recent experimental measurements on methanol as a model compound. Foremost, it provides a connection between experimentally defined σRaman and σSRS under certain approximations. In addition, it quantitatively shows that it is the weak vacuum field of the Stokes channel that makes Raman cross sections appear so small, corroborating the conventional Raman theory. Moreover, it suggests stimulated Raman cross sections to be a vacuum-decoupled intrinsic quantity for characterizing molecular response during Raman scattering. Remarkably, stimulated Raman cross sections turn out to be not weak when compared to two-photon absorption, narrowing the conventional gap of cross sections between spontaneous Raman and UV–vis absorption by more than 1010 folds.
Tunable electrocaloric effect in selective ferroelectric bilayers via electrostatics for solid-state refrigeration and microelectronics thermal management
Authors: Gupta Sanju , Saxena Avadh
Published: November 2023

Ferroelectric (FE) electrocaloric materials research has been blossoming worldwide for solid-state refrigeration and potential cooling systems replacing thermoelectric Peltier coolers in microelectronics. In this work, we report the outcomes from a systematic study of combined phase transition (thermodynamics) based on the phenomenological Landau theory and distributed electric field (electrostatics of thin film interfaces) in FE bilayer films. Specifically, the compositional variation of ferroelectric bilayers results in broken spatial inversion symmetry leading to asymmetric thermodynamic potentials due to a combination of normal (first- and second-order phase transition) and relaxor (dispersive dielectric constant) ferroelectric behaviors devised for efficient electrocaloric cooling effects. Extensive theoretical analyses conducted for bilayers consisting of insulating materials highlight modified phase transition temperature behavior and self-poling by effective electric field amplification arising due to bilayers’ electrostatic coupling yielding significant changes in isothermal entropy (ΔS) and adiabatic temperature (ΔT). The theoretical calculation insights supported with experimental results signify, through case studies for a combination of materials experimental parameters, that amplification of the local electric field and materials engineering maximize the number of coexisting phases at or away from the morphotropic phase boundary of constituent layers in bilayer thin film architectures, which can be applicable toward other classes of materials and multilayer systems. These are effective ways for efficient cooling, in general, and for microelectronics thermal management either directly or by developing a thermal switch with phase change materials integrated with thermoelectric coolers for residual heat dissipation, both at the system and on-chip levels.
Numerical study of cough droplet transmission in an indoor environment
Authors: Hu Liangquan , Ma Yong-Feng , Pourfattah Farzad , Deng Weiwei , Wang Lian-Ping
Published: November 2023

The Coronavirus Disease 2019 pandemic has become an unprecedented global challenge for public health and the economy. As with other respiratory viruses, coronavirus is easily spread through breathing droplets, particularly in poorly ventilated or crowded indoor environments. Therefore, understanding how indoor environmental conditions affect virus transmission is crucial for taking appropriate precautions. In this study, the effects of different natural wind-driven ventilation conditions and ambient relative humidities (RHs) on the cough droplet transmission in an indoor environment are investigated using the large eddy simulation approach with Lagrangian droplet tracking. The simulations show that the velocity and temperature of droplets significantly decrease in a short time after ejection. This feature for droplet velocity and temperature is more pronounced at smaller inlet wind speed (Vin) and larger Vin or lower RH, respectively. Wind-driven ventilation plays a crucial role in affecting the horizontal transmission distance of cough droplets. Under strong natural ventilation conditions (Vin = 4.17 m/s), cough droplets can spread more than 4 m within 1 s, whereas they can only travel within 2 m under weak ventilation with Vin = 0.05 m/s. The results confirm that the social distancing of 2 m is insufficient, while revealing that proper ventilation control can significantly remove virus-laden droplets from indoor air. We believe that there is no absolute safe social distancing because the droplet transmission and dispersion are mainly controlled by the local environmental conditions, and for safety, we recommend wearing a face mask and maintaining good indoor ventilation to reduce the release of potentially virus-laden droplets into the air.
Dynamic interaction between phonons and edge dislocations in LiF
Authors: Li Yang , Zheng Zexi , Chen Xiang , Chen Youping
Published: November 2023

The dynamic interaction between phonons and dislocations in LiF has been studied using molecular dynamics simulations. The simulations have captured the strong dynamic interactions between low-frequency slow transverse acoustic phonons and dislocations that were observed in experiments. Simulation results reveal that the strong dynamic interaction is attributed to resonant interactions between dislocations and slow transverse acoustic phonons. Each dislocation segment is found to possess a set of resonant modes characterized by large-amplitude out-of-phase vibrations of atoms on both sides of the dislocation slip plane. The resonant frequencies associated with these modes exhibit a nearly linear distribution with respect to the mode order. Contrary to previous beliefs, the resonant frequencies of dislocations exhibit only a weak correlation with the dislocation length. Additionally, each dislocation exhibits a dominant resonant mode that corresponds to the strongest vibration mode in response to phonons. This dominant resonant mode is not always the first resonant mode with the lowest frequency. Its specific order depends on the dislocation length. Simulation results have also demonstrated that the resonant modes of dislocations can be influenced by the interactions from neighboring dislocations.
Photothermal radiometry using normalized DC component for coating thickness evaluation
Authors: Chen Fei , Zhang Kai , Jiang Haijun , Shen Zhonghua , Chen Li
Published: November 2023

An improved photothermal technique for evaluating opaque coating thicknesses using a normalized DC component is proposed. The pump beam is modulated at a frequency that the generated thermal wave only exists in the coating layer and becomes invariant to the thickness changes. The DC component is normalized by the amplitude of the AC signal in order to eliminate the dependency on the pump intensity, surface absorptivity, and emissivity. Both theoretical analysis and experimental results demonstrate that the normalized DC component is linearly correlated to the coating thickness over a broad range. This method offers a significant advantage over existing photothermal methods by avoiding the tedious procedure of frequency trails for coatings of an unknown thickness. Also, the non-monotonic issue is successfully resolved.
Recombination activity of threading dislocations in MOVPE-grown AlN/Si {111} films etched by phosphoric acid
Authors: Pongrácz Jakub , Vacek Petr , Gröger Roman
Published: November 2023

Epitaxial growth of wurtzite AlN films on Si {111} results in 19% lattice misfit, which gives rise to a large density of threading dislocations with different recombination rates of electron–hole pairs. Here, we investigate types and distributions of threading dislocations of the MOVPE-grown 200 nm AlN/Si {111} film, whereby the dislocations are visualized using the technique of wet chemical etching. Atomic force microscopy suggests the existence of four different types of etch pits without any topological differences. Cross-sectional transmission electron microscope studies on etched samples are employed to associate the types of dislocations with the shapes of their etch pits. The recombination activity of individual dislocations was quantified by measuring the electron beam induced current and by correlative measurement of topography, secondary electron imaging, and the electron beam absorbed current. The strongest recombination activity was obtained for the m + c-type (mixed), c-type (screw), and a + c-type (mixed) threading dislocations, whereas the a-type (edge) threading dislocations were nearly recombination-inactive.
Entropy is a good approximation to the electronic (static) correlation energy
Authors: Martinez B Jessica A. , Shao Xuecheng , Jiang Kaili , Pavanello Michele
Published: November 2023

For an electronic system, given a mean field method and a distribution of orbital occupation numbers that are close to the natural occupations of the correlated system, we provide formal evidence and computational support to the hypothesis that the entropy (or more precisely −σS, where σ is a parameter and S is the entropy) of such a distribution is a good approximation to the correlation energy. Underpinning the formal evidence are mild assumptions: the correlation energy is strictly a functional of the occupation numbers, and the occupation numbers derive from an invertible distribution. Computational support centers around employing different mean field methods and occupation number distributions (Fermi–Dirac, Gaussian, and linear), for which our claims are verified for a series of pilot calculations involving bond breaking and chemical reactions. This work establishes a formal footing for those methods employing entropy as a measure of electronic correlation energy (e.g., i-DMFT [Wang and Baerends, Phys. Rev. Lett. 128, 013001 (2022)] and TAO-DFT [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)]) and sets the stage for the widespread use of entropy functionals for approximating the (static) electronic correlation.
Numerical analysis on the seakeeping performances of a full-scale container ship hull using strip theory
Authors: Bhatia Mohammed , Das Nachiketa , Dutta Prasun , Chattopadhyay Himadri
Published: November 2023

The race of taking more cargo on a ship has increased the size of ships as well as other aspects, such as their capacity and structural complexity, which affect the stability of ships. For naval architects and academics, accurately predicting seakeeping performances is difficult. In order to address this, the seakeeping performance of a container ship hall built by Korea Research Institute for Ships and Ocean Engineering (KRISO), i.e., KRISO container ship hall (KCS) is described in this research utilizing a numerical method. Maxsurf software based on strip theory was used to determine the results, where the containership hull was considered and input motions were applied with appropriate boundary conditions. Later, the ship's heading and speed were changed to see the effect of the seakeeping performance of the container ship. The current study is concentrated on systematic comparative research on the investigation of the ship's pitch, heave, and roll movements in irregular waves. It has been found that rolling motion was the highest at 22 kn at the 60° heading angle, potentially affecting ship stability. The significant amplitude analysis indicates that the roll motion is the largest at 60° of wave direction. The pitch motion response and the heave motion are near for each heading angle when the wave frequency exceeds 0.5 and 1 rad/s, respectively. The calculation findings show that seakeeping performance is directly related to ship direction and speed. Furthermore, threatening heading angles during sailing are classified, which could also help in enhancing ship stability.
Electron impact electronic excitation of benzene: Theory and experiment
Authors: Falkowski Alan G. , da Costa Romarly F. , Lima Marco A. P. , de A. Cadena Alexi , Pocoroba Ronald , Jones Regan , Mathur Mahak , Childers J. G. , Khakoo Murtadha A. , Kossoski Fábris
Published: November 2023

We report experimental differential cross sections (DCSs) for electron impact excitation of bands I to V of benzene at incident energies of 10, 12.5, 15, and 20 eV. They are compared to calculations using the Schwinger multichannel method while accounting for up to 437 open channels. For intermediate scattering angles, the calculations reveal that the most intense band (V) emerges from surprisingly similar contributions from all its underlying states (despite some preference for the dipole-allowed transitions). They further shed light on intricate multichannel couplings between the states of bands I to V and higher-lying Rydberg states. In turn, the measurements support a vibronic coupling mechanism for excitation of bands II and IV and also show an unexpected forward peak in the spin-forbidden transition accounting for band III. Overall, there is decent agreement between theory and experiment at intermediate angles and at lower energies and in terms of the relative DCSs of the five bands. Discrepancies between the present and previous experiment regarding bands IV and V draw attention to the need of additional experimental investigations. We also report measured DCSs for vibrational excitation of combined C–H stretching modes.
Influence of H on Sn incorporation in GeSnC alloys grown using molecular beam epitaxy
Authors: Dey Tuhin , Arbogast Augustus W. , Meng Qian , Reza Md. Shamim , Muhowski Aaron J. , Cooper Joshua J. P. , Ozdemir Erdem , Naab Fabian U. , Borrely Thales , Anderson Jonathan , Goldman Rachel S. , Wasserman Daniel , Bank Seth R. , Holtz Mark W. , Piner Edwin L. , Wistey Mark A.
Published: November 2023

GeSnC alloys offer a route to direct bandgap semiconductors for CMOS-compatible lasers, but the use of CBr4 as a carbon source was shown to reduce Sn incorporation by 83%–92%. We report on the role of thermally cracked H in increasing Sn incorporation by 6x–9.5x, restoring up to 71% of the lost Sn, and attribute this increase to removal of Br from the growth surface as HBr prior to formation of volatile groups such as SnBr4. Furthermore, as the H flux is increased, Rutherford backscattering spectroscopy reveals a monotonic increase in both Sn and carbon incorporation. X-ray diffraction reveals tensile-strained films that are pseudomorphic with the substrate. Raman spectroscopy suggests substitutional C incorporation; both x-ray photoelectron spectroscopy and Raman suggest a lack of graphitic carbon or its other phases. For the lowest growth temperatures, scanning transmission electron microscopy reveals nanovoids that may account for the low Sn substitutional fraction in those layers. Conversely, the sample grown at high temperatures displayed abrupt interfaces, notably devoid of any voids, tin, or carbon-rich clusters. Finally, the surface roughness decreases with increasing growth temperature. These results show that atomic hydrogen provides a highly promising route to increase both Sn and C to achieve a strongly direct bandgap for optical gain and active silicon photonics.
Effect of superhydrophilic surface on the cavitation behaviors of rotating blades
Authors: Choi Hongseok , Oh Seungtae , Lee Choongyeop , Choi Haecheon , Park Hyungmin
Published: November 2023

We experimentally confirmed the idea of mitigating (or delaying) the cavitation on the turbomachinery (rotating blades) by transforming the blade surface to be superhydrophilic, thereby the population of the cavitation nuclei is reduced near the surface. We focused on the changes in the cavitation incidence rate, amount of cavitation bubble, and bubble distribution on the superhydrophilic blade through the high-speed camera imaging, compared to the case with a regular (i.e., smooth) surface. With superhydrophilic blades, the cavitation incidence rate decreased significantly, indicating that fewer nuclei evolved into the actual cavitation bubbles. This is also associated with 8.6% delay of the critical rotational speed at which the cavitation process is almost completely established (incidence rate exceeds 80%), and the reduction in the total amount of cavitation bubbles was achieved as much as 18% (maximum 38% in the tested range of rotational Reynolds number). Additionally, the distribution of cavitation bubbles was generally pushed upstream, with fewer bubbles extending downstream, i.e., pushed away from the blade trailing edge. We believe the present results are promising enough to spur the follow-up investigation for the in-depth analysis and practical application toward the robust cavitation control without the substantial modulation of the geometry.
Numerical and experimental study of double-shock desensitization in triamino-tri-nitro-benzene based explosives
Authors: Peng Wenyang , Yang Shuqi , Zhang Xu , Shu Junxiang , Huang Kuibang , Pei Hongbo , Sun Yinao
Published: November 2023

The desensitization characteristics of explosives significantly affect the shock initiation process of explosives, making it difficult to determine the initiation conditions of explosives. A one-dimensional Lagrange fluid dynamics code was developed based on the Arrhenius shock temperature state dependent Wescott–Stewart–Davis (AWSD) reactive burn model to investigate the response characteristics of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) based heterogeneous explosive TATB-2 under double-shock wave. The parameters of the equation of state and the reactive burn model were calibrated based on the experimental data of one-dimensional sustained pulse for TATB-2 explosive. The shock initiation process of TATB-2 explosive under double-shock wave was simulated and compared with the experiments. The results show that the AWSD model can well reproduce the shock initiation process of TATB-2 explosive under double-shock wave. In addition, the desensitization characteristics of TATB-2 explosive under double-shock wave were revealed by analyzing the distance to detonation, reaction degree, and temperature rise.
Multistable ghost attractors in a switching laser system
Authors: Sriram Gokulakrishnan , Parastesh Fatemeh , Natiq Hayder , Rajagopal Karthikeyan , Meucci Riccardo , Jafari Sajad
Published: November 2023

This paper studies the effects of a switching parameter on the dynamics of a multistable laser model. The laser model represents multistability in distinct ranges of parameters. We assume that the system’s parameter switches periodically between different values. Since the system is multistable, the presence of a ghost attractor is also dependent on the initial condition. It is shown that when the composing subsystems are chaotic, a periodic ghost attractor can emerge and vice versa, depending on the initial conditions. In contrast to the previous studies in which the attractor of the fast blinking systems approximates the average attractor, here, the blinking attractor differs from the average in some cases. It is shown that when the switching parameter values are distant from their average, the blinking and the average attractors are different, and as they approach, the blinking attractor approaches the average attractor too.
Aerodynamic interference analysis of multiple rotors in a heterogeneous unmanned aircraft system
Authors: Li Huadong , Kan Zi , Bie Dawei , Li Daochun , Zhao Shiwei
Published: November 2023

In recent years, with the development of intelligent technology, rotorcrafts have been widely used in unmanned collaborative missions due to their excellent maneuverability and vertical flight capability. However, the flight process of rotorcrafts generates a noticeable induced flow that affects the flight safety of surrounding aircrafts. In the current research on the aerodynamic interference of multiple rotorcrafts, scholars are focusing on the effects of the upper rotor on lower rotors, while ignoring the induced influence of lower rotors. In this research, the detached eddy simulation was used to analyze the numerical and flow characteristics of an upper small-ducted-rotor (SDR) disturbed by a large-rotor (LR). The Q-criterion and power spectrum density method were employed to analyze the wake vortex evolution characteristics of the SDR. The results indicate that the thrust loss of the duct is significantly positively correlated with the rotational speeds of both SDR and LR, whereas the thrust loss of the rotor is only associated with the rotational speed of LR. The thrust loss of the duct is significantly greater than that of the rotor, primarily due to the disruption of attachment vortices and the generation of new shear-layer shedding vortices. Wake analysis reveals that the disturbance from LR simultaneously enhances both the kinetic and turbulent kinetic energy around SD, resulting in the discovery of multiple energy peak frequencies in the near- and mid-field distinct from the blade-passing frequency. This research helps analyze rotorcrafts' flight safety during the collaborative processes.
Enhancement of Sn plasma EUV emission by double-sided laser illumination
Authors: Mazuz-Harpaz Yotam , Kliss Noa , Wengrowicz Jonathan M. , Papeer Jenya , Frank Yechiel
Published: November 2023

Advancements in state-of-the-art nanolithography technology over the past decade have been raising an ongoing demand for improvement of the power and efficiency of extreme-ultraviolet (EUV) light sources that stand at its heart. This study introduces a double-sided laser illumination scheme aimed at enhancing EUV emission from such a laser-produced Sn plasma source. Using a solid-state laser, experiments were conducted with suspended solid Sn targets of varying thicknesses, evaluating the resulting effect on EUV output intensity. A significant increase in EUV emission to the collection side was observed due to the addition of illumination of the other side, particularly for thinner targets. For targets with thicknesses of 60 and 20 nm, an increase between 50% and 150% in EUV emission was detected in comparison with single-sided illumination. Extrapolating to a long laser pulse that burns through the target, the enhancement is projected to be 17% for a 300 nm thick target. These results highlight a promising way for further improvement of output power and energy efficiency in next-generation EUV light sources.
Stability analysis of axial compressors with wire mesh casing treatment
Authors: Zhang Ming , Hu Jiahao , Fang Yibo , Dong Xu , Pan Tianyu , Sun Dakun , Sun Xiaofeng
Published: November 2023

Experimental results indicate that wire mesh casing treatment (WMCT) enhances the stability of low-speed compressors with little reduction in efficiency. The flow resistance on the surface of the grooves, which are formed by the wire mesh, provides a new variable for the design of WMCT. This paper investigates the stability improvement induced by three different meshes through experiments and steady numerical simulations. A stability prediction model incorporating the effect of WMCT is developed to assess the stability of the steady flow field, and the results show that the predicted stall points of the compressor are close to those of the experimental data. The stability analysis model has a well-defined theoretical foundation in which the meridional flow field of the compressor is considered as the basic flow and the blade is replaced with a body force. This formulation enables fast and accurate stability assessments of compressors incorporating WMCT during the design process. Finally, based on the influence of the different meshes on the steady flow field, the stability-enhancing mechanism of WMCT is analyzed in terms of flow field details and macroscopic physical quantities. WMCT improves the flow around the tip region, shifting the tip blade loading in the aft direction and reducing the tip leakage flow. Macroscopically, the installation of WMCT makes the flow structure in the tip region less sensitive to changes in the compressor operating conditions.
Effects of La/Ho co-substitution on structure and multiferroic characteristics of BiFeO3 ceramics
Authors: Li Qing Tian , Liu Lu , Zhu Xiao Li , Liu Xiao Qiang , Chen Xiang Ming
Published: November 2023

The effects of La/Ho co-substitution on multiferroic characteristics were investigated for BiFeO3 ceramics together with structure evolution. The symmetry in Bi1−x(La0.65Ho0.35)xFeO3 ceramics changed from R3c to Pna21 and finally Pbnm with increasing x. Ferroelectricity was significantly improved with La/Ho co-substitution, and Pr reached the maximum of 30.9 μC/cm2 at 160 kV/cm at x = 0.16, where the R3c/Pna21 morphotropic phase boundary was determined. The weak ferromagnetism was released as the symmetry changed from R3c to Pna21, and subsequently the saturated M–H loop could be determined gradually with increasing x, and Mr increased continuously. The electric field-controlled magnetism could be characterized by the significant magnetism variation due to the electric field-induced transition of Pna21/R3c, which occurred during the poling process, and this transition became reversible by the help of annealing after poling. Compared with the situation of Bi1−xNdxFeO3 (the ion radius is the same as the effective one of La0.65Ho0.35), the present co-substituted BiFeO3 ceramics exhibited superior electric field-induced transition of Pna21/R3c with a maximum change rate of 47.03% in remanent magnetization under an electric field, which enhanced the magnetoelectric effect.
Performance analysis of multiple structural parameters of injectors for hydrogen-mixed natural gas using orthogonal experimental methods
Authors: An Yongwei , Jia Guanwei , Xu Weiqing , Li Rui , Cai Maolin
Published: November 2023

Hydrogen is a clean energy source with high combustion calorific value and nonpolluting products. However, the high transportation costs hinder the development of hydrogen energy. A high flow rate, long-distance, and high-efficiency delivery can be realized by mixing natural gas with hydrogen, which significantly reduces the transportation cost. However, high concentrations of hydrogen aggregates risks hydrogen embrittlement in the natural-gas pipeline network and leakage. An injector is a highly efficient gas-blending device. Therefore, analyzing and optimizing the multiple structural parameters of the injector are necessary for improving the mixing efficiency and homogeneity of hydrogen and natural gas. First, eight structural parameters of the injector were selected and four levels were considered for each parameter. Subsequently, an orthogonal experiment table was constructed using the orthogonal experimental method. Finally, a modeling simulation was performed using Fluent simulation software. The results showed that the injectors can significantly shorten the distance of mixing uniformity and achieve faster mixing uniformity. The diameter of the mixing pipe was found to be the main factor affecting the overall score. Computational Fluid Dynamic-20 (CFD-20) had the highest overall score. The LCOV10% for CFD-20 improved by 21.5% over that of the initial model, and the composite score improved from 0.93 to 0.98. The results can provide a reference for the design of injector parameters and installation of metering equipment.
Influence of friction on the packing efficiency and short-to-intermediate range structure of hard-sphere systems
Authors: Tang Jiajun , Wen Xiaohui , Zhang Zhen , Wang Deyin , Huang Xinbiao , Wang Yujie
Published: November 2023

Using particle-resolved computer simulations, we investigate the effect of friction on the packing structure of hard-sphere mixtures with two kinds of particles under external compression. We first show that increasing friction between the particles results in a more disordered and less efficient packing of the local structure on the nearest neighbor scale. It is also found that standard two-point correlation functions, i.e., radial distribution function and static structure factor, show basically no detectable changes beyond short-range distances upon varying inter-particle friction. Further analysis of the structure using a four-point correlation method reveals that these systems have on the intermediate-range scale a three-dimensional structure with an icosahedral/dodecahedral symmetry that exhibits a pronounced dependence on friction: small friction gives rise to an orientational order that extends to larger distances. Our results also demonstrate that composition plays a role in that the degree of structural order and the structural correlation length are mainly affected by the friction coefficients associated with the more abundant species.
Directional transport of a droplet on biomimetic ratchet structure
Authors: Shan Fang , Chai Zhenhua , Shi Baochang , Xiao Junfeng , Wang Changli
Published: November 2023

Directional liquid transport is of importance in some engineering fields, and the problem is also very complicated since it involves interface moving, deforming, and pinning/depinning of the contact line. In this work, a consistent and conservative phase-field based lattice Boltzmann (LB) method is applied to study the phenomenon of directional liquid transport. We first test the LB method by conducting simulations and find that the numerical results agree well with the analytical solutions. We then design the biomimetic surface with the ratchet structure and consider the directional transport of a droplet on such a surface. Furthermore, a force analysis is conducted to analyze the transport mechanism of a droplet on the ratchet structure. It is worth pointing out that the results in the present work may play an instructive role on the design of microchannel for intelligently guiding fluid transportation.
Persistent photoconductivity of polycrystalline Pb1−xSnxTe:In films on an amorphous substrate in the telecom wavelength range
Authors: Kovalyuk Vadim , Sheveleva Evgeniia , Mel’nikov Andrey , Auslender Mark , Goltsman Gregory , Shneck Roni , Dashevsky Zinovi
Published: November 2023

PbTe-based compounds are excellent candidates for the different types of optical detector applications from near to far IR ranges. In the present work, a technology has been developed for the fabrication of Pb1−xSnxTe compositions, doped with In, on a thin amorphous substrate (polyimide). The film preparation was performed by the electron gun evaporation method. The systematic study of structure and transport properties (Hall coefficient and electric conductivity) in the entire temperature range of 10–300 K for Pb1−xSnxTe:In films (x=0, 0.1, 0.2) was investigated. It was studied that the photoconductivity of the films in the telecom wavelength range, including kinetics, sensitivity, and noise equivalent power, has been conducted and it discovered persistent photoconductivity for all compositions at the temperature T<21 K. The results of the work have promising potential to use poly(nano) crystalline Pb1−xSnxTe:In films on an amorphous substrate both for photodetection in the telecom wavelength range and for the creation of all-optical neuromorphic systems, cooled memory, and logic elements operating at the low energy of laser pulses.
Chemically accurate singlet-triplet gaps of organic chromophores and linear acenes by the random phase approximation and σ-functionals
Authors: Dhingra Daniella , Shori Arjun , Förster Arno
Published: November 2023

Predicting the energy differences between different spin-states is challenging for many widely used ab initio electronic structure methods. We here assess the ability of the direct random phase approximation (dRPA), dRPA plus two different screened second-order exchange (SOX) corrections, and σ-functionals to predict adiabatic singlet-triplet gaps. With mean absolute deviations of below 0.1 eV to experimental reference values, independent of the Kohn–Sham starting point, dRPA and σ-functionals accurately predict singlet-triplet gaps of 18 organic chromophores. The addition of SOX corrections to dRPA considerably worsens agreement with experiment, adding to the mounting evidence that dRPA+SOX methods are not generally applicable beyond-RPA methods. Also for a series of linear acene chains with up to ten fused rings, dRPA, and σ-functionals are in excellent agreement with coupled-cluster single double triple reference data. In agreement with advanced multi-reference methods, dRPA@PBE and σ-functional@PBE predict a singlet ground state for all chain lengths, while dRPA@PBE0 and σ-functional@PBE0 predict a triplet ground state for longer acenes. Our work shows dRPA and σ-functionals to be reliable methods for calculating singlet-triplet gaps in aromatic molecules.
Canonical transformations and Poisson theory for second-order generalized mechanical systems with power-law Lagrangians
Authors: Zhu Lin , Zhang Yi
Published: November 2023

The canonical transformation and Poisson theory for the second-order generalized mechanical systems based on non-standard power-law Lagrangians are studied. First, the Euler–Lagrange equations and the Hamilton canonical equations for the second-order generalized mechanics with the power-law Lagrangians are established. Second, the canonical transformation theory of the systems is studied by establishing the relationship between old and new variables. Four basic forms of canonical transformation are given, and the transformation formulas in each case are derived. Third, the algebraic structure of the dynamical equations of the systems is studied, and the corresponding Poisson theory is established. Finally, the corresponding examples are presented to illustrate the application of the results we obtained.
Parallel ribbon vortex: A phenomenological flow feature in an atmospheric boundary layer near sloped terrain
Authors: Zhao Zhihang , Li Cruz Y. , Chen Zengshun , Wang Siyu , Xu Yemeng , Xue Xuanyi , Huang Lepeng
Published: November 2023

In this study, flow behaviors and vortex morphology around the sloping terrain that is covered by an atmospheric boundary layer are investigated using a combination of numerical and experimental methods. An array of wind tunnel experiments and high-fidelity large eddies simulations have been conducted, considering different slope angles θ = 90°, 45°, 26.5°, and 18.2°. Systematic analysis of turbulence phenomena pertaining to the flow field's topography-driven distortions and accelerations was performed quantitatively via time-averaged velocity field, terrain-induced turbulence intensity, velocity spectrum, and acceleration ratio. Two recirculation zones, one originating from the upstream boundary layer's gradual separation bubble (GSB) and the other from the forced separation bubble (FSB) behind the downstream sharp leading-edge, were confirmed by detailed visualization of the flow field. An acceleration zone of considerable magnitude is also observed, connecting the GSB and FSB. Subsequently, a new vortex structure—the parallel ribbon vortex (PRV)—was disclosed. The PRVs originate from the disordered turbulence structures inside the GSB, spiraling into coherent structures. The accelerated mainstream up the step then stretches and elongates the coherence structures into ribbon-like vortices parallel to the mainstream, completing the formation process. Finally, the PRVs transport fluid up the step before encountering the strong spanwise vortices and dissipating thereafter. The investigation into the slope flow characteristics and turbulence structure conducted in this study has the potential to enhance the prediction of wind characteristics and wind load specifications in mountainous regions.