bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalized model of laser-induced peak asymmetry in Raman lines
Authors: Dörfler Andreas , Asgariyan Tabrizi Afsaneh , Stubler Timo , Ruediger Andreas
Published: August 2022

The rate and precision at which samples can be scanned by Raman spectroscopy strongly depend on laser and material parameters. In this article, we describe the trade-off between parameters that increased laser intensities to improve resolution and reduce integration times, and its effect on thermally induced shift and asymmetric broadening of the line profile, especially in the case of resonant Raman. We present an analytical approximation to describe this phenomenon for all volumetrically absorbing materials and a wide range of laser parameters. This allows the determination of an optimal scan rate for the sample material and the required optical resolution, or vice versa, the determination and accurate correction for thermally induced shifts and asymmetries. This study provides an analytical quantification of this often-neglected line asymmetry and allows us to correct for its impact on the signal with few material properties and laser parameters. It may, in particular, allow us to discriminate this effect against other sources of peak asymmetry due to intrinsic properties. We obtain this analytical expression by condensing a parametrized finite element method model into a heuristic probability density function of temperature that describes the full parameter space. This function can be applied to any thermally undistorted line shape by convolution to determine a corrected line profile. This profile then provides a parameter-dependent optimized fitting function for an optimal determination of Raman signal parameters.
Spiropyran-functionalized photochromic nylon webbings for long-term ultraviolet light sensing
Authors: Zhang Peng , Ohanian Osgar John , Porfiri Maurizio
Published: August 2022

Webbing structures are extensively employed in engineering systems as load-bearing components. In a field setting, webbings are frequently subject to extended ultraviolet (UV) light irradiation, which can affect their integrity and reduce their mechanical strength. Despite technological advancements in structural health monitoring, long-term UV sensing techniques for webbings remain under-developed. To fill this gap, we propose a photochromic nylon webbing that demonstrates color variation in response to extended UV exposure. The webbing offers a rich, yet controlled, color variation over multiple time scales that is conducive to UV sensing. A mathematical model grounded in photochemistry is developed to interpret experimental observations, unveiling the photochromic phenomenon as a multi-step, multi-timescale photochemical process involving several chemical species. The model captures the evolution of the coexisting species through a system of nonlinear, coupled ordinary differential equations, offering the basis for the inference of the webbing’s color. The proposed photochromic webbing and the photochemistry-based mathematical model could inform future designs of UV-sensitive structures that maintain sensitivity under weeks of continuous sunlight UV exposure.
Diversity-induced resonance in a globally coupled bistable system with diversely distributed heterogeneity
Authors: Liu Cong , Wang Chong-Yang , Wu Zhi-Xi , Yang Han-Xin , Guan Jian-Yue
Published: August 2022

A moderate degree of diversity, in form of quenched noise or intrinsic heterogeneity, can significantly strengthen the collective response of coupled extended systems. As yet, related discoveries on diversity-induced resonance are mainly concentrated on symmetrically distributed heterogeneity, e.g., the Gaussian or uniform distributions with zero-mean. The necessary conditions that guarantee the arise of resonance phenomenon in heterogeneous oscillators remain largely unknown. In this work, we show that the standard deviation and the ratio of negative entities of a given distribution jointly modulate diversity-induced resonance and the concomitance of negative and positive entities is the prerequisite for this resonant behavior emerging in diverse symmetrical and asymmetrical distributions. Particularly, for a proper degree of diversity of a given distribution, the collective signal response behaves like a bell-shaped curve as the ratio of negative oscillator increases, which can be termed negative-oscillator-ratio induced resonance. Furthermore, we analytically reveal that the ratio of negative oscillators plays a gating role in the resonance phenomenon on the basis of a reduced equation. Finally, we examine the robustness of these results in globally coupled bistable elements with asymmetrical potential functions. Our results suggest that the phenomenon of diversity-induced resonance can arise in arbitrarily distributed heterogeneous bistable oscillators by regulating the ratio of negative entities appropriately.
Degradation mechanisms of Mg-doped GaN/AlN superlattices HEMTs under electrical stress
Authors: Li Shanjie , Sun Peiye , Xing Zhiheng , Wu Nengtao , Wang Wenliang , Li Guoqiang
Published: August 2022

GaN-based high electron mobility transistors (HEMTs) have exhibited great application prospects in power and radio frequency devices, thanks to the superior properties of GaN. Despite the significant commercialization progress, the reliability of GaN-based HEMTs remains a challenge. This work experimentally investigates the time-dependent degradation of Mg-doped GaN/AlN superlattice HEMTs under both OFF-state and SEMI-ON-state bias conditions and proposes that GaN/AlN superlattices as a barrier can solve the Vth instability issues of GaN HEMTs under OFF-state and SEMI-ON-state bias conditions. On the one hand, in the SEMI-ON-state, the hot electron effect leads to the degradation of Ig, gm,max, and Id,sat to varying degrees. However, the as-prepared GaN-based HEMTs exhibit excellent Vth stability (almost no change) under hot electron injection, on the account of the excellent two-dimensional electron gas confinement in the GaN/AlN superlattice structure. On the other hand, in the OFF-state, positive Vth shift (about 0.12 V) is induced by the hole emission in the GaN/AlN superlattice structure under reverse bias stress. In addition, the stress-induced destruction of MgO gate dielectric gives rise to the gate leakage, which increases by 2 orders of magnitude and triggers an irreversible degradation (about 10%) of the gm,max. These results are expected to provide a solution to the Vth instability of GaN HEMTs.
Concurrence of auxetic effect and topological phase transition in a 2D phosphorous nitride
Authors: Liu Jiangxin , Wu Chao , Xie Yuee , Yan Xiaohong , Peng Qing , Chen Yuanping
Published: August 2022

The auxetic effect and topological phase transition are interesting mechanical and electronic properties of some materials, respectively. Although each has been extensively studied separately, no material has been identified to possess both properties simultaneously. Here, we report that a two-dimensional phosphorous nitride monolayer simultaneously possesses auxetic behavior and undergoes a topological phase transition under tensile strain. The monolayer has a normal-auxeticity mechanical phase transition when a tensile strain above 0.055 is applied along the P–P zigzag direction. The negative Poisson ratio can even approach as abnormally high as −0.60. Furthermore, the material is an intrinsic Dirac material, but a phase transition from the semi-Dirac material to Dirac material is observed at nearly the same critical tensile strain as that in auxetic phase transition. An electronic orbital analysis reveals that the simultaneity of the normal-auxeticity phase transition and topological phase transition originates from the variation of orbital hybridization around the Fermi level.
A method to stabilize the unreconstructed MgO (111) polar surface
Authors: Godin Simon , Davidson Bruce A. , Sutarto Ronny , Liu Chong , Li Fengmiao , Elfimov Ilya S. , Sawatzky George A. , Zou Ke
Published: August 2022

The choice and quality of single-crystal substrates for epitaxial thin film growth drastically influence the properties of the synthesized films. Among them, high-quality substrates with a polar surface are particularly difficult to prepare due to their inherent structural instability against electrostatic forces of the polar discontinuity. As a commonly used insulating substrate, the (111) cut of MgO shows alternating planes of Mg2+ and O2− that form a hexagonal unit cell at the surface, which is useful for thin films with similar crystal symmetries. We present a method to prepare such a surface by first introducing (3×3)R30° reconstructed MgO (111) surface via face-to-face annealing in an O2 environment. We then dissolve the top layers in acid to achieve an unreconstructed and also passivated surface. The structure, stoichiometry, and stability of the resulting surfaces are characterized. This work provides an easy and reliable way to prepare a MgO (111) polar surface ready for subsequent epitaxial growth.
Mechanism of improved crystallinity by defect-modification in proton-irradiated GaAsPN photovoltaics: Experimental and first-principle calculations approach
Authors: Yamane Keisuke , Maki Yuito , One Shun , Wakahara Akihiro , Pavelescu Emil-Mihai , Ohshima Takeshi , Nakamura Tetsuya , Imaizumi Mitsuru
Published: August 2022

This study presents a new model for point-defect modification in III-V-N alloys through first-principle calculations and several validation experiments conducted in our previous study, which explain the enhanced crystallinity of III-V-N alloys caused by proton irradiation and rapid thermal annealing (RTA). Validation experiments clarified that the conversion efficiency of the GaAsPN solar cell increased after proton irradiation followed by RTA, whereas that of the GaP solar cell decreased after the same process. Thus, the improved crystallinity of the GaAsPN alloy by this process is attributed to the decrease in nitrogen-related point defects in the crystal. The detailed annihilation mechanism of the nitrogen-related point defect was then studied using first-principle calculations demonstrating that the representative nitrogen-related point defects can change to a lower-energy state when a vacancy forms at its neighboring group V site, leading to the annihilation of the defects. It was concluded that vacancies created by proton irradiation enhance the annihilation of nitrogen-related point defects.
Fano-resonant graphene metamaterials
Authors: Liu Qingjie , Yan Zhinan , Ao Yingquan , Wang Bing
Published: August 2022

The concept of Fano resonance originally discovered in quantum systems has been introduced to the field of optics for the last decade and more. One distinctive feature of the resonance lies in its asymmetric line shape. Graphene metamaterials have attracted much attention for making tunable devices due to the controllable carrier density of graphene. As realizing Fano resonance in graphene metamaterials, asymmetric and tunable optical responses are usually observed in transmission or reflectance spectra. This Perspective is intended to review the current developments on Fano-resonant graphene metamaterials, which are divided into three categories based on the participation of graphene plasmon in Fano resonance. Later, discussions on the applications in sensors, switches, modulators, and slow-light devices are given, and a future perspective is proposed.
Low-tortuosity, hierarchical porous structure Co3O4@carbonized wood integrated electrode for lithium-ion battery
Authors: Zhang Xi , Liu Yangai , Zhu Bing , Zhao Hang , Mi Ruiyu , Wang Zekun , He Peijie
Published: August 2022

Three-dimensional integrated electrode materials have broad application prospects in the field of improving the specific energy of lithium-ion batteries. Metal-organic frameworks and their derivatives are potential anode materials for Li-ion batteries due to their highly controllable composition and structure. Here, we designed and synthesized the Co3O4@carbonized wood (Co3O4@CW) composite as the anode materials of Li-ion batteries by ZIF-67 in situ growth in the balsa wood and high-temperature carbonization. The composite keeps the low-tortuosity and porous structure with a high specific surface area (293.61 m2/g), providing a smooth electrolyte transport path and enabling sufficient reaction sites for lithium-ions, thereby enhancing the electrochemical reactivity. The integrated electrode exhibits a specific capacity of 486.65 mAh/g and good stable performance (90.71% capacity maintain rate) after 200 cycles at the current of 0.2 A/g. The specific capacity reaches 552.37 mAh/g at 0.1 A/g and possessed excellent pseudocapacitive capacity (92.3%, the pseudocapacitive contribution).
Constant-potential molecular dynamics simulations of molten salt double layers for FLiBe and FLiNaK
Authors: Langford Luke , Winner Nicholas , Hwang Andrea , Williams Haley , Vergari Lorenzo , Scarlat Raluca O. , Asta Mark
Published: August 2022

We report the results of constant-potential molecular dynamics simulations of the double layer interface between molten 2LiF–BeF2 (FLiBe) and 23LiF–6NaF–21KF (FLiNaK) fluoride mixtures and idealized solid electrodes. Employing methods similar to those used in studies of chloride double layers, we compute the structure and differential capacitance of molten fluoride electric double layers as a function of applied voltage. The role of molten salt structure is probed through comparisons between FLiBe and FLiNaK, which serve as models for strong and weak associate-forming salts, respectively. In FLiBe, screening involves changes in Be–F–Be angles and alignment of the oligomers parallel to the electrode, while in FLiNaK, the electric field is screened mainly by rearrangement of individual ions, predominantly the polarizable potassium cation.
Origin of the unusual property contrast in K2Bi8Se13 phase-change material
Authors: Chen Yuxuan , Wang Biao , Li Huashan
Published: August 2022

Phase-change materials are promising foundations for both nonvolatile storage and neuro-inspired computing applications. An attractive phase change material K2Bi8Se13 (KBS) was recently discovered to possess fast structural transition and outstanding property contrast, yet the underlying mechanism remains unclear. We conducted ab initio molecular dynamics simulations to investigate the transition of KBS from a crystalline to amorphous phase. Initiated by the Bi–Se bond breaking at the boundaries of atom blocks, the simulated phase transition proceeds through the conversion between BiSex octahedral and pyramid structures. Remarkable discrepancies in electronic structures and absorption spectra between the two phases are further illustrated by density functional theory simulations, which reproduce the experimental observations. The optical and electrical contrasts between the two phases are found to originate from the band edge states localized at various atom blocks that uniquely appear in the crystalline phase. These states provide pseudo one-dimensional transport channels with resonant bonding that may further intensify the electrical contrast. The distinct phase change properties compared with traditional phase change materials can be attributed to the hierarchical KBS crystal structure comprised of loosely bound atom blocks. The above findings pave an avenue toward the design of phase change materials beyond the traditional scope of the Ge–Sb–Te triangle map.
A stacking-based short-term wind power forecasting method by CBLSTM and ensemble learning
Authors: Wang Nier , Li Zhanming
Published: August 2022

Aiming at the problem that the traditional wind power forecasting is difficult to deal with a large amount of strong volatility data and limited processing capacity of time series, a wind power forecasting method based on multi-model combination under stacking framework was proposed. First, the wind turbine data are cleaned by density-based spatial clustering of applications with the noise clustering method. Considering the differences of data observation and training principles, the proposed stacking method embedded multiple machine learning algorithms to utilize their diversified strength. The stacking base-learner includes the CBLSTM model, which has the advantages of deep architecture feature extraction, and takes into account data timing and nonlinear relationship as well as XGBoost and other tree ensemble learning models that were suitable for complex data modeling. The feasibility of the algorithm was verified by using the actual wind power data of two wind farms in Northeast and Western China. Experimental results show that the stacking ensemble learning method proposed has better forecasting performance and stability than other single forecasting models, which is of great significance to guide wind power dispatching operation and improve wind power consumption capacity.
Kinetic simulation of the ideal multipole resonance probe
Authors: Gong Junbo , Friedrichs Michael , Oberrath Jens , Brinkmann Ralf Peter
Published: August 2022

Active plasma resonance spectroscopy (APRS) is a process-compatible plasma diagnostic method, which utilizes the natural ability of plasmas to resonate on or near the electron plasma frequency. The multipole resonance probe (MRP) is a particular design of APRS that has a high degree of geometric and electric symmetry. The principle of the MRP can be described on the basis of an idealized geometry that is particularly suited for theoretical investigations. In a pressure regime of a few Pa or lower, kinetic effects become important, which cannot be predicted by the Drude model. Therefore, in this paper, a dynamic model of the interaction of the idealized MRP with a plasma is established. The proposed scheme reveals the kinetic behavior of the plasma that is able to explain the influence of kinetic effects on the resonance structure. Similar to particle-in-cell, the spectral kinetic method iteratively determines the electric field at each particle position, however, without employing any numerical grids. The optimized analytical model ensures the high efficiency of the simulation. Eventually, the presented work is expected to cover the limitation of the Drude model, especially for the determination of the pure collisionless damping caused by kinetic effects. A formula to determine the electron temperature from the half-width Δω is proposed.
Zeeman spectroscopy of the internal transition 4T1 to 6A1 of Fe3+ ions in ZnO
Authors: Müller Raphael , Mangold Martin , Bauer Sebastian , Huber Florian , Herr Ulrich , Thonke Klaus
Published: August 2022

In this work, internal 4T1→6A1 transitions within the half-filled 3d shell of Fe3+ in extremely pure chemical vapor deposition (CVD)-grown ZnO layers were investigated by means of high-resolution, low-temperature continuous wave (cw) photoluminescence (PL), time-resolved PL, photoluminescence excitation (PLE) spectroscopy, Zeeman spectroscopy, and deep level transient spectroscopy (DLTS). For comparison, Zeeman spectroscopy measurements were also performed on commercially available, hydrothermally grown ZnO bulk crystals. Magnetic fields up to 15T were applied parallel and perpendicular to the c-axis of the ZnO crystals in order to investigate the fine structure of included states. The splitting pattern of emission lines related to 4T1→6A1 Fe3+ transitions was theoretically modeled by a Hamiltonian matrix including the crystal field in cubic and trigonal symmetries and spin–orbit interaction for the complete excited 4T1 state. The extremely pure ZnO used in this study, in direct comparison to hydrothermally grown ZnO, allows the identification, investigation, and description of single isolated Fe3+ defects in ZnO for the first time—different from literature reports hitherto, which seemingly were recording data on Fe–Li complexes. The resulting exact energy-level scheme in combination with the experimental data leads to a re-evaluation of 4T1→6A1 Fe3+ transitions in ZnO.
Identifying the physical mechanisms of polycrystalline lead salt photoconductors
Authors: Jost Steven
Published: August 2022

Polycrystalline infrared lead salt detectors exhibit exceptionally high sensitivity near room temperature and, as such, are ubiquitous in commercial instruments such as spectrometers and flame detectors. The underlying physical mechanism behind this remarkable performance has been the subject of speculation for many years. In this treatise, data from work performed at BAE Systems and St. John's Optical Systems and from the published literature are analyzed to identify common mechanisms that contribute to the photoconductivity of polycrystalline lead salt detectors from a multitude of material deposition and process technologies, and it was concluded that much of the behavior can be attributed to surface-related phenomenon. Physical models are proposed to explain the observations. Finally, there is a brief description of measurements related to noise in these complex structures, indicating the importance of ohmic contacts, but the observed low frequency spectral noise density remains a mystery.
Polarization doping—Ab initio verification of the concept: Charge conservation and nonlocality
Authors: Ahmad Ashfaq , Strak Pawel , Kempisty Pawel , Sakowski Konrad , Piechota Jacek , Kangawa Yoshihiro , Grzegory Izabella , Leszczynski Michal , Zytkiewicz Zbigniew R. , Muziol Grzegorz , Monroy Eva , Kaminska Agata , Krukowski Stanislaw
Published: August 2022

In this work, we study the emergence of polarization doping in AlxGa1−xN layers with graded composition from a theoretical viewpoint. It is shown that bulk electric charge density emerges in the graded concentration region. The magnitude of the effect, i.e., the relation between the polarization bulk charge density and the concentration gradient is obtained. The appearance of mobile charge in the wurtzite structure grown along the polar direction was investigated using the combination of ab initio and drift-diffusion models. It was shown that the ab initio results can be recovered precisely by proper parameterization of drift-diffusion representation of the complex nitride system. It was shown that the mobile charge appears due to the increase of the distance between opposite polarization-induced charges. It was demonstrated that, for sufficiently large space distance between polarization charges, the opposite mobile charges are induced. We demonstrate that the charge conservation law applies for fixed and mobile charge separately, leading to nonlocal compensation phenomena involving (i) the bulk fixed and polarization sheet charge at the heterointerfaces and (ii) the mobile band and the defect charge. Therefore, two charge conservation laws are obeyed that induces nonlocality in the system. The magnitude of the effect allows obtaining technically viable mobile charge density for optoelectronic devices without impurity doping (donors or acceptors). Therefore, it provides an additional tool for the device designer, with the potential to attain high conductivities: high carrier concentrations can be obtained even in materials with high dopant ionization energies, and the mobility is not limited by scattering at ionized impurities.
Understanding the role of cross-link density in the segmental dynamics and elastic properties of cross-linked thermosets
Authors: Zheng Xiangrui , Guo Yafang , Douglas Jack F. , Xia Wenjie
Published: August 2022

Cross-linking is known to play a pivotal role in the relaxation dynamics and mechanical properties of thermoset polymers, which are commonly used in structural applications because of their light weight and inherently strong nature. Here, we employ a coarse-grained (CG) polymer model to systematically explore the effect of cross-link density on basic thermodynamic properties as well as corresponding changes in the segmental dynamics and elastic properties of these network materials upon approaching their glass transition temperatures (Tg). Increasing the cross-link density unsurprisingly leads to a significant slowing down of the segmental dynamics, and the fragility K of glass formation shifts in lockstep with Tg, as often found in linear polymer melts when the polymer mass is varied. As a consequence, the segmental relaxation time τα becomes almost a universal function of reduced temperature, (T − Tg)/Tg, a phenomenon that underlies the applicability of the “universal” Williams–Landel–Ferry (WLF) relation to many polymer materials. We also test a mathematical model of the temperature dependence of the linear elastic moduli based on a simple rigidity percolation theory and quantify the fluctuations in the local stiffness of the network material. The moduli and distribution of the local stiffness likewise exhibit a universal scaling behavior for materials having different cross-link densities but fixed (T − Tg)/Tg. Evidently, Tg dominates both τα and the mechanical properties of our model cross-linked polymer materials. Our work provides physical insights into how the cross-link density affects glass formation, aiding in the design of cross-linked thermosets and other structurally complex glass-forming materials.
Active absorption modulation by employing strong coupling between magnetic plasmons and borophene surface plasmons in the telecommunication band
Authors: Yan Xiaofei , Lin Qi , Wang Lingling , Liu Guidong
Published: August 2022

The tunable and highly confined plasmon in 2D materials paves the way for designing 2D materials capable of manipulating light on a subwavelength scale, making them suitable for the design of optical modulators in ultracompact sizes. Herein, a continuously adjustable modulator in the telecommunication band is theoretically presented by the strong coupling between the magnetic plasmons (MPs) and borophene surface plasmons (BSPs). A remarkable Rabi splitting is observed and the coupling process is theoretically investigated by the model of two coupled oscillators. Results show that the splitting energy is determined by the coupling strength, which can be modulated by adjusting the distance between the borophene monolayer and silver grating. Moreover, by manipulating the electron density of the borophene to drive both two modes coupled or decoupled, the absorption can be continuously adjustable almost from 0 to 1 at 1544 nm, and the maximum modulation depth can be up to 94.8%. This work may provide a method to enhance light–matter interactions by the coupled multi-modes and design borophene-based plasmonic modulator.
Basic aspects of gold nanoparticle photo-functionalization using oxides and 2D materials: Control of light confinement, heat-generation, and charge separation in nanospace
Authors: Furube Akihiro , Yanagiya Shin-ichiro , Koinkar Pankaj M. , Katayama Tetsuro
Published: August 2022

Although the optical properties of localized surface plasmon resonance and the relaxation processes of excited hot electrons in gold nanoparticles (AuNPs) have been well understood, the phenomena that occur when AuNPs relax on solid surfaces of semiconductors or insulators remain largely unknown. Thermal energy diffusion and electron transfer are relatively simple physical processes, but the phenomena they induce are interesting because of a variety of new application developments. In this Perspective, we introduce the fundamental aspects as well as advanced applications of several new physical phenomena induced by AuNPs-based hybrid materials with oxides or 2D materials. Localized heat can induce a great force on the surrounding medium to control mass transport, and plasmon-induced charge transfer reactions are expected to have applications in photocatalysis and solar cells. We also review increasing reports on the development of nano-optical sensors, transistors, and nano-light sources based on precisely controlled device structures utilizing AuNPs.
Resonances in nitrobenzene probed by the electron attachment to neutral and by the photodetachment from anion
Authors: Ranković Miloš , Nag Pamir , Anstöter Cate S. , Mensa-Bonsu Golda , Kumar T. P. Ragesh , Verlet Jan R. R. , Fedor Juraj
Published: August 2022

We probe resonances (transient anions) in nitrobenzene with the focus on the electron emission from these. Experimentally, we populate resonances in two ways: either by the impact of free electrons on the neutral molecule or by the photoexcitation of the bound molecular anion. These two excitation means lead to transient anions in different initial geometries. In both cases, the anions decay by electron emission and we record the electron spectra. Several types of emission are recognized, differing by the way in which the resulting molecule is vibrationally excited. In the excitation of specific vibrational modes, distinctly different modes are visible in electron collision and photodetachment experiments. The unspecific vibrational excitation, which leads to the emission of thermal electrons following the internal vibrational redistribution, shows similar features in both experiments. A model for the thermal emission based on a detailed balance principle agrees with the experimental findings very well. Finally, a similar behavior in the two experiments is also observed for a third type of electron emission, the vibrational autodetachment, which yields electrons with constant final energies over a broad range of excitation energies. The entrance channels for the vibrational autodetachment are examined in detail, and they point to a new mechanism involving a reverse valence to non-valence internal conversion.
Correlative piezoresponse and micro-Raman imaging of CuInP2S6–In4/3P2S6 flakes unravels phase-specific phononic fingerprint via unsupervised learning
Authors: Checa M. , Ivanov I. , Neumayer S. M. , Susner M. A. , McGuire M. A. , Maksymovych P. , Collins L.
Published: August 2022

Characterizing the novel properties of layered van der Waals materials is key for their application in functional devices. A better understanding of this type of material requires correlative imaging of diverse nanoscale material properties. Within this class of materials, CuInP2S6 (CIPS) has received a significant degree of interest due to its ionically mediated room temperature ferroelectricity. Moreover, it is possible to form stable self-assembled heterostructures of ferroelectric CuInP2S6 (CIPS) and non-ferroelectric (i.e., lacking Cu) In4/3P2S6 (IPS) phases, by controlling the targeted composition and kinetics of synthesis. In this work, we present a correlative nanometric imaging study of the phononic modes and piezoelectricity of the phase-separated thin heteroepitaxial CIPS/IPS flakes. We show that it is possible to isolate the different phononic modes of the two phases by spatially correlating them with their distinct ferroelectric behavior. The coupling of our experimental data with unsupervised learning statistical methods enables unraveling specific Raman peaks that are characteristic of each chemical phase (CIPS and IPS) present in the composite sample, discarding the less significant ones.
The effect of nanoparticle softness on the interfacial dynamics of a model polymer nanocomposite
Authors: Zhu Yuwen , Giuntoli Andrea , Zhang Wengang , Lin Zhongqin , Keten Sinan , Starr Francis W. , Douglas Jack F.
Published: August 2022

The introduction of soft organic nanoparticles (NPs) into polymer melts has recently expanded the material design space for polymer nanocomposites, compared to traditional nanocomposites that utilize rigid NPs, such as silica, metallic NPs, and other inorganic NPs. Despite advances in the fabrication and characterization of this new class of materials, the effect of NP stiffness on the polymer structure and dynamics has not been systematically investigated. Here, we use molecular dynamics to investigate the segmental dynamics of the polymer interfacial region of isolated NPs of variable stiffness in a polymer matrix. When the NP–polymer interactions are stronger than the polymer–polymer interactions, we find that the slowing of segmental dynamics in the interfacial region is more pronounced for stiff NPs. In contrast, when the NP–polymer interaction strength is smaller than the matrix interaction, the NP stiffness has relatively little impact on the changes in the polymer interfacial dynamics. We also find that the segmental relaxation time τα of segments in the NP interfacial region changes from values lower than to higher than the bulk material when the NP–polymer interaction strength is increased beyond a “critical” strength, reminiscent of a binding–unbinding transition. Both the NP stiffness and the polymer–surface interaction strength can thus greatly influence the relative segmental relaxation and interfacial mobility in comparison to the bulk material.
The rebounding-coalescing behaviors in drop-on-drop impact on a superhydrophobic surface
Authors: Yu Wenlong , Zhu Dong , Wang Wenhao , Yu Zhiyuan , Chen Shuo , Zhao Jiayi
Published: August 2022

The great anti-accumulation performance of drop-on-drop impact on a superhydrophobic surface is beneficial to self-cleaning and anti-icing. Hence, the rebounding-coalescing behaviors in drop-on-drop impingement with varying Weber number and offset ratio are studied experimentally in the present work. The complete regime map of rebounding states is proposed, which can be divided into no-coalesce, jug-like, pancake-like, and pendulum-like rebounding-coalescing behaviors. Subsequently, the increase in the contact time in pendulum-like rebounding-coalescing behaviors is captured and described by a linear model well. Finally, a theoretical prediction based on momentum conservation for the averaged maximal spreading radius of the coalesced droplet is provided. Our approach provides insight into a mechanism of the rebounding-coalescing behaviors, which is helpful for the improvement in related applications.
Propeller wake instabilities under turbulent-inflow conditions
Authors: Wang Lianzhou , Liu Xinyu , Wang Nian , Li Mijian
Published: August 2022

The wake instabilities of a propeller operating under turbulent-inflow conditions were studied by the improved delayed detached eddy simulation method on an unstructured mesh consisting of almost 82.5 × 106 cells, capturing propeller wakes extending to the downstream distance of 9D (where D is the propeller diameter). Two turbulent-inflow cases with the turbulence intensity of 5% and 20% were considered. The mean loads and phase-averaged flow field show good agreement with experiments. As the propeller blade interacts with the turbulent inflow, a wide peak extending approximately ±10 Hz in the power spectral density of the time histories of the thrust and torque coefficient. Simulation results reveal wake instability mechanisms of the propeller operating under different turbulent-inflow conditions. The turbulence added to the inlet boundary interacts with the tip vortices, which accelerates the destabilization processes of the tip vortex system from two aspects. First, the interaction between the inflow turbulence and the tip vortex promotes the diffusion of tip vortices. Second, the interaction between the inflow turbulence and the tip vortices magnifies the instability motion of the tip vortex. The wake vortex system of the high-turbulence inflow condition loses its stability after 2.2D downstream, while the initial instability behaviors for the low-turbulence inflow condition are observed at the location of 3.4D downstream. The present study presents a deeper insight into the flow physics driving the tip vortex pairing process for a propeller operating under turbulent-inflow conditions.
On orthogonal projections related to representations of the Hecke algebra on a tensor space
Authors: Bytsko Andrei
Published: August 2022

We consider the problem of finding orthogonal projections P of a rank r that gives rise to representations of the Hecke algebra HN(q) in which the generators of the algebra act locally on the Nth tensor power of the space Cn. It is shown that such projections are global minima of a certain functional. It is also shown that a characteristic property of such projections is that a certain positive definite matrix A has only two eigenvalues or only one eigenvalue if P gives rise to a representation of the Temperley–Lieb algebra. Apart from the parameters n, r, and Q = q + q−1, an additional parameter k proves to be a useful characteristic of a projection P. In particular, we use it to provide a lower bound for Q when the values of n and r are fixed and we show that k = rn if and only if P is of the Temperley–Lieb type. In addition, we propose an approach to constructing projections P and give some novel examples for n = 3.
Independent-noise provoked spiking, synchronized via coupling
Authors: Tiwari Ishant , Escalona J. , Rivera M. , Parmananda P.
Published: August 2022

We report experimental and numerical evidence of synchronized spiking phenomena provoked by the interaction of two bidirectionally coupled electrochemical systems subjected to independent stochastic input signals. To this end, the anodic potentials of two such systems were diffusively coupled. The corresponding anodic currents of these systems exhibited excitable fixed point behavior in the vicinity of a homoclinic bifurcation. Following this, the anodic potentials were perturbed by independent noise signals. The invoked oscillatory dynamics are analyzed using normalized variance and cross-correlation coefficient. By systematically varying the coupling strength between the systems and the level of external noise, regions exhibiting synchronized spiking behavior were identified.
On the thermodynamic properties of fictitious identical particles and the application to fermion sign problem
Authors: Xiong Yunuo , Xiong Hongwei
Published: August 2022

By generalizing the recently developed path integral molecular dynamics for identical bosons and fermions, we consider the finite-temperature thermodynamic properties of fictitious identical particles with a real parameter ξ interpolating continuously between bosons (ξ = 1) and fermions (ξ = −1). Through general analysis and numerical experiments, we find that the average energy may have good analytical properties as a function of this real parameter ξ, which provides the chance to calculate the thermodynamical properties of identical fermions by extrapolation with a simple polynomial function after accurately calculating the thermodynamic properties of the fictitious particles for ξ ≥ 0. Using several examples, it is shown that our method can efficiently give accurate energy values for finite-temperature fermionic systems. Our work provides a chance to circumvent the fermion sign problem for some quantum systems.
2D spectroscopies from condensed phase dynamics: Accessing third-order response properties from equilibrium multi-time correlation functions
Authors: Jung Kenneth A. , Markland Thomas E.
Published: August 2022

The third-order response lies at the heart of simulating and interpreting nonlinear spectroscopies ranging from two-dimensional infrared (2D-IR) to 2D electronic (2D-ES), and 2D sum frequency generation (2D-SFG). The extra time and frequency dimensions in these spectroscopic techniques provide access to rich information on the electronic and vibrational states present, the coupling between them, and the resulting rates at which they exchange energy that are obscured in linear spectroscopy, particularly for condensed phase systems that usually contain many overlapping features. While the exact quantum expression for the third-order response is well established, it is incompatible with the methods that are practical for calculating the atomistic dynamics of large condensed phase systems. These methods, which include both classical mechanics and quantum dynamics methods that retain quantum statistical properties while obeying the symmetries of classical dynamics, such as LSC-IVR, centroid molecular dynamics, and Ring Polymer Molecular Dynamics (RPMD), naturally provide short-time approximations to the multi-time symmetrized Kubo transformed correlation function. Here, we show how the third-order response can be formulated in terms of equilibrium symmetrized Kubo transformed correlation functions. We demonstrate the utility and accuracy of our approach by showing how it can be used to obtain the third-order response of a series of model systems using both classical dynamics and RPMD. In particular, we show that this approach captures features such as anharmonically induced vertical splittings and peak shifts while providing a physically transparent framework for understanding multidimensional spectroscopies.
Electrostatic control of magnetism: Emergent opportunities with van der Waals materials
Authors: Verzhbitskiy Ivan , Eda Goki
Published: August 2022

Since the first reports on the observation of magnetic order in atomically thin crystals of FePS3, CrI3, and CrGeTe3 in 2016 and 2017, there has been a greatly renewed interest in the magnetism of van der Waals (vdW) layered magnets. Due to their dimensionality and structure, ultrathin vdW magnets offer tantalizing prospects for electrostatic control of magnetism for energy-efficient spintronic logic and memory devices. Recent demonstrations revealed unusually high susceptibility of some vdW magnets to electrostatic fields and shed light on a path to room temperature devices, a long-standing goal in spintronics research. In this Perspective, we discuss the potential of different classes of vdW magnets for electrostatic control of magnetism by comparing their properties with those of non-vdW magnets such as dilute magnetic III–V semiconductors and perovskite manganites that have been intensively studied in the past two decades.
PD-1 blockade following ART interruption enhances control of pathogenic SIV in rhesus macaques
Authors: Velu Vijayakumar , Titanji Kehmia , Ahmed Hasan , Shetty Ravi Dyavar , Chennareddi Lakshmi S. , Freeman Gordon J. , Ahmed Rafi , Amara Rama Rao
Published: August 2022

Programmed death-1 (PD-1) blockade during chronic Simian immunodeficiency virus (SIV) infection results in restoration of CD8 T-cell function and enhances viral control. Here, we tested the therapeutic benefits of PD-1 blockade administered soon after anti-retrovial therapy (ART) interruption (ATI) by treating SIV-infected and ART-suppressed macaques with either an anti-PD-1 antibody (
n
= 7) or saline (
n
= 4) at 4 wk after ATI. Following ATI, the plasma viremia increased rapidly in all animals, and the frequency of SIV-specific CD8 T cells also increased in some animals. PD-1 blockade post ATI resulted in higher proliferation of total memory CD8 and CD4 T cells and natural killer cells. PD-1 blockade also resulted in higher proliferation of SIV-specific CD8 T cells and promoted their differentiation toward better functional quality. Importantly, four out of the seven anti-PD-1 antibody-treated animals showed a rapid decline in plasma viremia by 100- to 2300-fold and this was observed only in animals that showed measurable SIV-specific CD8 T cells post PD-1 blockade. These results demonstrate that PD-1 blockade following ATI can significantly improve the function of anti-viral CD8 T cells and enhance viral control and strongly suggests its potential synergy with other immunotherapies that induce functional CD8 T-cell response under ART. These results have important implications for HIV cure research.
Insectivorous bats form mobile sensory networks to optimize prey localization: The case of the common noctule bat
Authors: Roeleke Manuel , Schlägel Ulrike E. , Gallagher Cara , Pufelski Jan , Blohm Torsten , Nathan Ran , Toledo Sivan , Jeltsch Florian , Voigt Christian C.
Published: August 2022

Animals that depend on ephemeral, patchily distributed prey often use public information to locate resource patches. The use of public information can lead to the aggregation of foragers at prey patches, a mechanism known as local enhancement. However, when ephemeral resources are distributed over large areas, foragers may also need to increase search efficiency, and thus apply social strategies when sampling the landscape. While sensory networks of visually oriented animals have already been confirmed, we lack an understanding of how acoustic eavesdropping adds to the formation of sensory networks. Here we radio-tracked a total of 81 aerial-hawking bats at very high spatiotemporal resolution during five sessions over 3 y, recording up to 19 individuals simultaneously. Analyses of interactive flight behavior provide conclusive evidence that bats form temporary mobile sensory networks by adjusting their movements to neighboring conspecifics while probing the airspace for prey. Complementary agent-based simulations confirmed that the observed movement patterns can lead to the formation of mobile sensory networks, and that bats located prey faster when networking than when relying only on local enhancement or searching solitarily. However, the benefit of networking diminished with decreasing group size. The combination of empirical analyses and simulations elucidates how animal groups use acoustic information to efficiently locate unpredictable and ephemeral food patches. Our results highlight that declining local populations of social foragers may thus suffer from Allee effects that increase the risk of collapses under global change scenarios, like insect decline and habitat degradation.
Whole-brain neuronal MCT2 lactate transporter expression links metabolism to human brain structure and function
Authors: Medel Vicente , Crossley Nicolás , Gajardo Ivana , Muller Eli , Barros L. Felipe , Shine James M. , Sierralta Jimena
Published: August 2022

Brain activity is constrained by local availability of chemical energy, which is generated through compartmentalized metabolic processes. By analyzing data of whole human brain gene expression, we characterize the spatial distribution of seven glucose and monocarboxylate membrane transporters that mediate astrocyte–neuron lactate shuttle transfer of energy. We found that the gene coding for neuronal MCT2 is the only gene enriched in cerebral cortex where its abundance is inversely correlated with cortical thickness. Coexpression network analysis revealed that MCT2 was the only gene participating in an organized gene cluster enriched in K

+

dynamics. Indeed, the expression of K

ATP

subunits, which mediate lactate increases with spiking activity, is spatially coupled to MCT2 distribution. Notably, MCT2 expression correlated with fluorodeoxyglucose positron emission tomography task-dependent glucose utilization. Finally, the MCT2 messenger RNA gradient closely overlaps with functional MRI brain regions associated with attention, arousal, and stress. Our results highlight neuronal MCT2 lactate transporter as a key component of the cross-talk between astrocytes and neurons and a link between metabolism, cortical structure, and state-dependent brain function.