bluuebunny/crossref_metadata_2025 huggingface dataset:
Feynman–Kac formula for parabolic Anderson model in Gaussian potential and fractional white noise
Authors: Han Yuecai , Wu Guanyu
Published: February 2024

In this paper, we establish a Feynman–Kac formula for the stochastic parabolic Anderson model with Gaussian potential in space and fractional white noise in time with Hurst parameter H > 1/2. We obtain the necesscary and suffcient condition for the integrability of the Gaussian potential and the exponential integrability of the solution which is defined by Feynman–Kac formula. By the smoothing of the fractional white noise and techniques from Malliavin calculus, we prove that the Feynman–Kac representation is a mild solution of the stochastic parabolic Anderson equation.
Stochastic model for barrier crossings and fluctuations in local timescale
Authors: Bhaskaran Rajeev , Sadhasivam Vijay Ganesh
Published: February 2024

The problem of computing the rate of diffusion-aided activated barrier crossings between metastable states is one of broad relevance in physical sciences. The transition path formalism aims to compute the rate of these events by analysing the statistical properties of the transition path between the two metastable regions concerned. In this paper, we show that the transition path process is a unique solution to an associated stochastic differential equation, with a discontinuous and singular drift term. The singularity arises from a local time contribution, which accounts for the fluctuations at the boundaries of the metastable regions. The presence of fluctuations at the local time scale calls for an excursion theoretic consideration of barrier crossing events. We show that the rate of such events, as computed from excursion theory, factorizes into a local time term and an excursion measure term, which bears empirical similarity to the transition state theory rate expression. Since excursion theory makes no assumption about the presence of a transition state in the potential energy landscape, the mathematical structure underlying this factorization ought to be general. We hence expect excursion theory (and local times) to provide some physical and mathematical insights in generic barrier crossing problems.
Superintegrable quantum mechanical systems with position dependent masses invariant with respect to three parametric Lie groups
Authors: Nikitin A. G.
Published: February 2024

Quantum mechanical systems with position dependent masses (PDM) admitting four and more dimensional symmetry algebras are classified. Namely, all PDM systems are specified which, in addition to their invariance with respect to a three parametric Lie group, admit at least one second order integral of motion. The presented classification is partially extended to the more generic systems which admit one or two parametric Lie groups.
Wave propagation of a reaction-diffusion cholera model with hyperinfectious vibrios and spatio-temporal delay
Authors: Song Chenwei , Xu Rui
Published: February 2024

In this paper, we consider a reaction-diffusion cholera model with hyperinfectious vibrios and spatio-temporal delay. In the model, it is assumed that cholera has a fixed latent period and the latent individuals can diffuse, and a non-local term is incorporated to describe the mobility of individuals during the latent period. It is shown that the existence and nonexistence of traveling wave solutions are fully determined by the basic reproduction number R0 and the critical wave speed c*. Firstly, when R0>1 and the wave speed c > c*, the existence of strong traveling waves is obtained by using Schauder’s fixed point theorem and Lyapunov functional approach. By employing a limiting argument, the existence of strong traveling waves is established when R0>1 and c = c*. Next, when R0≤1, the nonexistence of traveling wave solutions is established by contradiction. Besides, when R0>1 and c < c*, the nonexistence of traveling wave solutions is obtained by means of two-sided Laplace transform. This indicates that c* is indeed the minimal wave speed. Numerical simulations are carried out to illustrate the theoretical results.
Dispensing uniform droplets of phosphate buffer saline using electrohydrodynamic jetting
Authors: Baghel Kuldeep , Zahra  , Cho Seongsu , Lee Jinkee
Published: February 2024

Generating a stable cone jet regime in electrohydrodynamic (EHD) jetting for water or water-based solutions is difficult due to the high surface tension of the liquid. To overcome this challenge and produce uniform droplets of ∼O(100) μm, alternative EHD jetting regimes need to be investigated. This study presents EHD jetting characteristics using phosphate buffered saline (PBS). Three blunt-tip steel needles with internal diameters (IDs) of 100, 260, and 400 μm were used as electrodes. A high-speed camera was used to capture electrospray phenomena. The effect of flow rate and voltage on electrospray regimes, droplet size, generation frequencies, and velocities are presented. Regime maps are generated for PBS 1X, PBS 10X, and DI water, highlighting differences in spray characteristics due to electrical conductivity. The focus is on the Spindle regime, revealing unique observations not previously reported. The study demonstrates that a droplet generation frequency of 4314 Hz can be achieved in the Spindle regime, which is 308% of frequency in Microdripping, and the mean droplet size is ∼67% of size in the Microdripping regime. Based on these findings, recommendations are made for generating uniform droplets of PBS, including suggestions regarding the choice of the regime, nozzle dimensions, and electrode spacing.
Osteogenically committed hUCMSCs-derived exosomes promote the recovery of critical-sized bone defects with enhanced osteogenic properties
Authors: Li Shuyi , Rong Qiong , Zhou Yang , Che Yuejuan , Ye Ziming , Liu Junfang , Wang Jinheng , Zhou Miao
Published: February 2024

Low viability of seed cells and the concern about biosafety restrict the application of cell-based tissue-engineered bone (TEB). Exosomes that bear similar bioactivities to donor cells display strong stability and low immunogenicity. Human umbilical cord mesenchymal stem cells-derived exosomes (hUCMSCs-Exos) show therapeutic efficacy in various diseases. However, little is known whether hUCMSCs-Exos can be used to construct TEB to repair bone defects. Herein, PM-Exos and OM-Exos were separately harvested from hUCMSCs which were cultured in proliferation medium (PM) or osteogenic induction medium (OM). A series of in-vitro studies were performed to evaluate the bioactivities of human bone marrow mesenchymal stem cells (hBMSCs) when co-cultured with PM-Exos or OM-Exos. Differential microRNAs (miRNAs) between PM-Exos and OM-Exos were sequenced and analyzed. Furthermore, PM-Exos and OM-Exos were incorporated in 3D printed tricalcium phosphate scaffolds to build TEBs for the repair of critical-sized calvarial bone defects in rats. Results showed that PM-Exos and OM-Exos bore similar morphology and size. They expressed representative surface markers of exosomes and could be internalized by hBMSCs to promote cellular migration and proliferation. OM-Exos outweighed PM-Exos in accelerating the osteogenic differentiation of hBMSCs, which might be attributed to the differentially expressed miRNAs. Furthermore, OM-Exos sustainably released from the scaffolds, and the resultant TEB showed a better reparative outcome than that of the PM-Exos group. Our study found that exosomes isolated from osteogenically committed hUCMSCs prominently facilitated the osteogenic differentiation of hBMSCs. TEB grafts functionalized by OM-Exos bear a promising application potential for the repair of large bone defects.
Effect of axial and radial components of the magnetic field on the electrostatic resistive instabilities in Hall thruster plasma
Authors: Bharti Saty Prakash , Singh Sukhmander
Published: February 2024

A two-fluid model is used to investigate the influence of the axial component of the magnetic field on the growth rate of electrostatic resistive instabilities with cross field electron transport in a Hall thruster. The axial component of the magnetic field plays an important role in instabilities. It provides additional confinement to electrons and ions near the channel axis. Also, it helps to protect the walls from the direct impacts of particles, thereby reducing erosion and extending the operational lifetime of the system. A fourth-order dispersion equation is derived using plasma perturbed densities into Poisson's equation to observe the various effects on the growing waves in plasma. It is observed that the growth rate and the real frequency increase with axial and radial components of the magnetic field, respectively. The order of the real frequency of the wave is found to be 106/s. For the fixed value of the azimuthal wavenumber (ky=500/m), the amplitude of the growth rate of the instability dropped to almost 40% if the axial component of the magnetic field is considered. Similarly, the amplitude of the real frequency increases by almost 74% (at  ky=500/m) by incorporating the contribution of the axial component of the magnetic field. In addition, it is also observed that the amplitude of the growth rate increases with low values of radial and axial components of the magnetic field, but it decreases at the higher value of the magnetic field due to the resonance of electron cyclotron frequency with plasma frequency.
Demonstration of controllable Si doping in N-polar AlN using plasma-assisted molecular beam epitaxy
Authors: Khan Md Irfan , Lee Cindy , Ahmadi Elaheh
Published: February 2024

In this study, we present the demonstration of controllable Si doping in N-polar AlN films grown on single-crystal AlN substrates by plasma-assisted molecular beam epitaxy. Through optimization of growth conditions, we obtained high-quality N-polar AlN films at 950 °C. However, our studies revealed that Si incorporation dramatically decreases at such high growth temperature. To enable higher Si incorporation, a hybrid low-temperature and high-temperature growth condition was developed by using Ga as a surfactant at low-temperature growth. By lowering the growth temperature of AlN to 750 °C, we were able to incorporate Si with concentrations as high as 2×1020 cm−3 and demonstrated an electron concentration as high as 1.25×1019 cm−3 at room temperature. The secondary ion mass spectrometry analysis revealed that, <0.2% Ga is incorporated in the AlN films grown with Ga as a surfactant at low temperature.
PZT-based flexible piezoelectric sensors for real-time condition monitoring
Authors: Jin Liang , Song Juheng , Liu Lu , Jia Yufang
Published: February 2024

Endowed with high sensitivity, fast response, and excellent flexibility, flexible piezoelectric sensors proffer substantial advantages for establishing efficacious contact with coarse object surfaces. They exhibit remarkable potential for application in wearable devices, motion state recognition, and device vibration monitoring. This paper introduces the development of a novel pliable piezoelectric nanocomposite harnessing modified lead zirconate titanate (PZT) and a flexible photosensitive resin. The PZT-based flexible piezoelectric sensors were fabricated using the light-curing molding technique. By establishing a sensor test platform, the performance parameters of the PZT-based sensors were obtained. Compared to conventional flexible piezoelectric sensors, the output voltage of the PZT-based sensors increased by 1.67 times under the same excitation, resulting in an improved response time and sensitivity. Moreover, the sensors demonstrated an excellent voltage output performance for recognizing human motion states and monitoring electrical equipment vibrations, both in real-time motion state changes and in core vibration under high-frequency operating conditions. These 3D-printed flexible piezoelectric sensors assume paramount significance across diverse domains, including motion science and real-time equipment condition monitoring.
Future stability of expanding spatially homogeneous FLRW solutions of the spherically symmetric Einstein–massless Vlasov system with spatial topology R3
Authors: Taylor Martin
Published: February 2024

Spatially homogeneous Friedmann–Lemaître–Robertson–Walker (FLRW) solutions constitute an infinite dimensional family of explicit solutions of the Einstein–massless Vlasov system with vanishing cosmological constant. Each member expands toward the future at a decelerated rate. These solutions are shown to be nonlinearly future stable to compactly supported spherically symmetric perturbations, in the case that the spatial topology is that of R3. The decay rates of the energy momentum tensor components, with respect to an appropriately normalised double null frame, are compared to those around Minkowski space. When measured with respect to their respective t coordinates, certain components decay faster around Minkowski space, while others decay faster around FLRW.
Origin and suppression of kink effect in InP high electron mobility transistors at cryogenic temperatures
Authors: Zhou Fu-gui , Feng Rui-ze , Cao Shu-rui , Feng Zhi-yu , Liu Tong , Su Yong-bo , Shi Jing-yuan , Ding Wu-chang , Jin Zhi
Published: February 2024

The kink effect is a phenomenon that typically occurs in InP-based InAlAs/InGaAs high electron mobility transistors (HEMTs) at cryogenic temperatures. It results in higher output conductance (gDS) and non-monotonic behavior. This Letter discusses the origin and suppression of the kink effect in InP HEMTs at cryogenic temperatures, which is linked to the structure of gate recess passivation. At room temperature, two devices with different gate recess passivation structures show similar characteristics. However, a temperature-sensitive kink is observed in the non-passivated gate recess structure, leading to the discontinuous transconductance (gm) and the non-monotonic threshold voltage (Vth) shifts. Based on pulsed and static (non-pulsed) measurement data, surface traps and impact ionization in the high-field region are identified as the origin of the kink effect. Specifically, a positive Vth shift of +160 mV is caused by surface traps when the temperature drops to 150 K. A negative Vth shift of –60 mV is due to the enhanced impact ionization below 150 K. Conversely, the device with a passivated gate recess has a negligible kink effect and effectively improves discontinuous gm and the non-monotonic Vth shifts (+25 mV) when the temperature drops. Therefore, the device with a passivated gate recess is significant for suppressing the kink effect and maintaining the stability of the device in variable temperature environments.
Deep reinforcement learning for propulsive performance of a flapping foil
Authors: Bao Yan , Shi Xinyu , Wang Zhipeng , Zhu HongBo , Srinil Narakorn , Li Ang , Zhou Dai , Fan Dixia
Published: February 2024

While it is challenging for a traditional propulsor to achieve a wide range of force profile manipulation and propulsion efficiency, nature provides a solution for a flapping foil such as that found in birds and turtles. In this paper, we introduce a deep reinforcement learning (DRL) algorithm with great potential for solving nonlinear systems during the simulation to achieve a self-learning posture adjustment for a flapping foil to effectively improve its thrust performance. With DRL, a brute-force search is first carried out to provide intuition about the optimal trajectories of the foil and also a database for the following case studies. We implement an episodic training strategy for intelligent agent learning using the DRL algorithm. To address a slow data generation issue in the computational fluid dynamics simulation, we introduce a multi-environment technique to accelerate data exchange between the environment and the agent. This method is capable of adaptively and automatically performing an optimal foil path planning to generate the maximum thrust under various scenarios and can even outperform the optimal cases designed by users. Numerical results demonstrate how the proposed DRL is powerful to achieve optimization and has great potential to solve a more complex problem in the field of fluid mechanics beyond human predictability.
The effect of gamma ray irradiation on few layered MoSe2: A material for nuclear and space applications
Authors: Ozden Burcu , Aditya Teresa , Cherry Javari , Yu Zhuohang , Allain Jean-Paul , Terrones Mauricio
Published: February 2024

In recent years, emerging two-dimensional (2D) materials, such as molybdenum diselenide (MoSe2), have been at the center of attention for many researchers. This is due to their unique and fascinating physicochemical properties that make them attractive in space and defense applications that include shielding harsh irradiation environments. In this study, we examined the effects of gamma (γ) rays at various doses on the structural, chemical, and optical properties of MoSe2 layers. After the samples were exposed to intense gamma radiation (from a 60Co source) with various exposure times to vary the total accumulated dosage (up to 100 kGy), Raman and photoluminescence spectroscopies were used to study and probe radiation-induced changes to the samples. When compared to pristine materials, very few changes in optical properties were typically observed, indicating good robustness with little sensitivity, even at relatively high doses of gamma radiation. The imaging using scanning electron microscopy revealed a number of nano-hillocks that were connected to substrate alterations. X-ray photoelectron spectroscopies revealed that Mo’s binding energies remained the same, but Se’s binding energies blueshifted. We associated this shift with the decrease in Se vacancies that occurred after irradiation as a result of Mo atoms creating adatoms next to Se atoms. When compared to pristine materials, very few changes in optical, chemical, and structural properties were typically observed. These findings highlight the inherent resilience of MoSe2 in hostile radioactive conditions, which spurs additional research into their optical, electrical, and structural characteristics as well as exploration for potential space, energy, and defense applications.
Dual-component anomalous Hall effect in a helical spin-spiral metamagnet
Authors: Prestigiacomo Joseph C. , Jamer Michelle E. , Callahan Patrick G. , Bennett Steven P.
Published: February 2024

We report a dual-component anomalous Hall effect (AHE) in polycrystalline Fe3Ga4 thin films grown on STO (001) and Al2O3 substrates. Systematic magnetic and magnetotransport measurements reveal an AHE consisting of positive and negative contributions that coexist across a wide range of temperatures and magnetic phases. We find that both magnitudes are nearly equal in the low-temperature ferromagnetic (FM) phase, but that their relative ratio is reduced upon heating through the antiferromagnetic helical spin-spiral state where they compete with metamagnetism and topological Hall effects, maintaining finite values at least up to the high-temperature FM phase.
Global stability of Bénard–Marangoni convection in an anisotropic porous medium
Authors: Dev Kapil , Suthar Om P.
Published: February 2024

Surface tension is essential in many industrial applications, especially where the liquid surface is in contact with the environment, such as crystal growth, semiconductor manufacturing, and welding. The present article reports a numerical analysis of convection induced by the combined effects of buoyancy force and surface tension in an infinitely extended horizontal fluid-saturated anisotropic porous layer with high permeability. We assume that the bottom boundary is rigid and the top is exposed to the air. Biot numbers establish general thermal conditions at both ends instead of commonly used adiabatic and isothermal boundary conditions. The anisotropy of the porous structure results in thermal and mechanical anisotropy parameters while examining layer's stability. The Chebyshev Tau technique yields the critical Marangoni number, MaLc and MaEc, representing linear and energy stability boundaries. We compare the constraints obtained from linear and energy analyses and conclude that the energy bounds for the current problem are less than linear bounds, indicating subcritical instabilities may exist. It is also observed that thermal anisotropy and Biot numbers stabilize the system. In contrast, mechanical anisotropy and the Darcy number advance the onset of convection. The existing results of limiting cases of the present problem are recovered with remarkable accuracy.
Bipolar magnetic semiconductor and doping controllable spin transport property in 2D CoI2/MnBr2 heterostructure
Authors: Guo Tianxia , Xu Xiaokang , Zhang Huiyang , Xie Yue , Yang Huanning , Rui Xue , Sun Yi , Yao Xiaojing , Wang Bing , Zhang Xiuyun
Published: February 2024

The integration of two-dimensional heterostructure materials remains a fundamental way for the manipulation of spintronics in practical applications. Here, we predicted the transform of stripy antiferromagnetic (AFM) CoI2 and MnBr2 monolayers to interlayer AFM CoI2/MnBr2 heterostructure with intralayer ferromagnetic orders by using density functional theory. Interestingly, the CoI2/MnBr2 heterostructure exhibits a typical bipolar magnetic semiconducting state with type-I band alignments. Moreover, the half-metal/semiconductor transition and spin-up/spin-down polarization switching in CoI2/MnBr2 heterostructure can be effectively triggered by electron/hole doping. Our study provides the potential of AFM spintronics for information storage and processing.
Impact of net magnetization on spin–orbit torque switching of synthetic ferromagnets in magnetic tunnel junctions
Authors: Kateel Vaishnavi , Monteiro Maxwel Gama , Jeong Seyeob , Talmelli Giacomo , Jayakumar Ganesh , Sorée Bart , De Boeck Jo , Couet Sebastien , Rao Siddharth
Published: February 2024

Spin–orbit torque (SOT)-induced reversal of a ferromagnet in a magnetic tunnel junction (MTJ) is promising for next-generation novel magnetic memory and spin-logic devices. However, inherent limitations of single ferromagnetic-based free layer (FL) systems are low thermal stability and susceptibility to external magnetic stray fields. To overcome these challenges, synthetic antiferromagnets (SAFs) are integrated into MTJ devices to form hybrid free layers (HFLs); this FL system enables tunability of thermal stability and stray field experienced by the FL, simultaneously lowering the SOT-induced switching currents. Here, we investigate the impact of net magnetization of the SAF-based HFL on the field and current-driven switching behavior. We observe that nearly compensated SAF-HFL systems demonstrate a higher proportion of switching failures at the device level than the uncompensated SAF-HFL systems in both current and field-driven schemes. Micro-magnetic simulations and thin film characterization of SAF-HFL show that the device-level stochasticity arises due to a dynamic decoupling within the nearly compensated SAF systems. We show that optimizing the SAF-HFL systems to have uncompensated magnetization mitigates this stochasticity and improves the SOT switching current for Pt-based SOT channel by at least 20% across the entire tested pulse width range down to 300 ps, thus leading to reliable switching of SOT-MTJs with SAF-HFL stacks.
Direct numerical simulation of supersonic nanoparticles flow in free-molecule regime using the angular coefficient method
Authors: Cao Liangliang , Jiang Haokui , Bi Yuanjie , Chen Ran , Guo Jinsen , Pang Hongchao , Wang Chuangao
Published: February 2024

We employ molecular flow methods to numerically simulate the supersonic nanoparticles flow in free-molecule regime. To streamline the computational complexity, interaction forces between the gas and solid particles are disregarded. We first develop a discrete phase model (DPM) method that integrates the non-rigid body collision model, enabling an accurate simulation of nanoparticle diffusion under the influence of the drag force and Brownian motion force. The nanoparticles considered in this study have sizes below 10 nm, and the accuracy of the DPM method is verified by comparing its results with experimental data. Subsequently, we theoretically and numerically investigate the transmission probability and number density of N2 molecules flowing through two-dimensional (2D) channels and three-dimensional (3D) tubes by using the angular coefficient (AC) method and the direct simulation Monte Carlo (DSMC) method. The findings indicate that as the diameter of the nanoparticle (dp) decreases to 1 nm, the diffusion coefficient (D) and the root mean square displacement (x) of nanoparticles approach the N2 molecules. The microscopic velocity of most N2 molecules falls within the range of 62–1400 m/s, and the macroscopic velocity of N2 flow falls within the range of Ma = 1.28–1.35. In contrast to the DSMC method, the AC method exhibits enhanced accuracy even with a reduced number of grids and obviates the process for large-scale sampling. Additionally, the solution time required by the AC method is approximately 1/10 and 1/13–1/32 of the DSMC method in 3D cylindrical tubes and 2D channels, respectively. Moreover, the AC method demonstrates superior adaptability when dealing with complex geometries.
Stacked space-folded acoustic metasurfaces for the flexible control of sound absorption
Authors: Wang Xin , Wang Jiahao , Ma Zedong , Deriy Ilya , Song Mingzhao , Bogdanov Andrey , Chen Yongyao
Published: February 2024

Sound absorbing materials capable of working in harsh environments (e.g., fire resistance, moisture resistance, and pressure resistance) while having excellent low-frequency sound absorption properties are highly desirable for many practical applications. Recently, a new class of acoustic absorbers based on space coiling and folding metamaterials (SCFMs) has emerged. The SCFMs could be comprised of rigid plastics, ceramics, and metals and could be a good candidate for developing sound-absorbing devices capable of working in harsh environments. The SCFMs also enable flexible control of low-frequency sound with subwavelength structures, addressing the problem of poor absorption of low-frequency noise encountered by conventional acoustic materials. However, the current geometries of SCFM meta-atoms do not take full advantage of the configuration of three-dimensional space, limiting their ability for flexible control of sound absorption properties. Here, we propose an acoustic absorber based on stacked SCFMs with side openings, which could effectively absorb line-spectrum noise as well as broadband noise. The effects associated with the geometry and resonance modes of SCFMs are shown to significantly influence the sound absorption properties. To understand the sound-metamaterial interaction, an analytical model is obtained to study the acoustic response of SCFMs, which is further validated by numerical simulations. Further experiments have demonstrated the acoustic properties of our proposed metamaterial structure and confirmed the capability of stacked SCFMs for flexible control of the acoustic absorption spectrum. This work provides new possibilities for the development of novel sound absorption metamaterials desirable for many practical applications.
WindCline: Sloping wind tunnel for characterizing flame behavior under variable inclines and wind conditions
Authors: Makowiecki Amanda S. , Coburn Sean C. , Sheppard Samantha , Bitterlin Brendan , Breda Timothy , Dawlatzai Abdul , Giannella Robert , Jaros Alexandra , Kling Christopher , Kolb Eric , Lapointe Caelan , Simons-Wellin Sam , Michelsen Hope A. , Daily John W. , Hannigan Michael , Hamlington Peter E. , Farnsworth John , Rieker Gregory B.
Published: February 2024

Developing accurate computational models of wildfire dynamics is increasingly important due to the substantial and expanding negative impacts of wildfire events on human health, infrastructure, and the environment. Wildfire spread and emissions depend on a number of factors, including fuel type, environmental conditions (moisture, wind speed, etc.), and terrain/location. However, there currently exist only a few experimental facilities that enable testing of the interplay of these factors at length scales <1 m with carefully controlled and characterized boundary conditions and advanced diagnostics. Experiments performed at such facilities are required for informing and validating computational models. Here, we present the design and characterization of a tilting wind tunnel (the “WindCline”) for studying wildfire dynamics. The WindCline is unique in that the entire tunnel platform is constructed to pivot around a central axis, which enables the sloping of the entire system without compromising the quality of the flow properties. In addition, this facility has a configurable design for the test section and diffuser to accommodate a suite of advanced diagnostics to aid in the characterization of (1) the parameters needed to establish boundary conditions and (2) flame properties and dynamics. The WindCline thus allows for the measurement and control of several critical wildfire variables and boundary conditions, especially at the small length scales important to the development of high-fidelity computational simulations (10–100 cm). Computational modeling frameworks developed and validated under these controlled conditions can expand understanding of fundamental combustion processes, promoting greater confidence when leveraging these processes in complex combustion environments.
Nanomechanical mass measurements through feature-based time series clustering
Authors: Neumann Adam P. , Gomez Alfredo , Nunn Alexander R. , Sader John E. , Roukes Michael L.
Published: February 2024

Recent years have seen explosive growth in miniaturized sensors that can continuously monitor a wide variety of processes, with applications in healthcare, manufacturing, and environmental sensing. The time series generated by these sensors often involves abrupt jumps in the detected signal. One such application uses nanoelectromechanical systems (NEMS) for mass spectrometry, where analyte adsorption produces a quick but finite-time jump in the resonance frequencies of the sensor eigenmodes. This finite-time response can lead to ambiguity in the detection of adsorption events, particularly in high event-rate mass adsorption. Here, we develop a computational algorithm that robustly eliminates this often-encountered ambiguity. A moving-window statistical test together with a feature-based clustering algorithm is proposed to automate the identification of single-event jumps. We validate the method using numerical simulations and demonstrate its application in practice using time-series data that are experimentally generated by molecules adsorbing onto NEMS sensors at a high event rate. This computational algorithm enables new applications, including high-throughput, single-molecule proteomics.
Theory based recommendations to the resistive wall mode stability studies in tokamaks
Authors: Pustovitov V. D.
Published: February 2024

The problem of the plasma stability against the resistive wall modes is considered from two sides, theoretical and experimental. The main subject is the dispersion relation and its verification, which is commonly understood as a comparison of the predicted and observed stability thresholds. As in the conventional magnetohydrodynamics, the growth rate γ and the angular rotation frequency ω of the mode are found from the energy balance with account of some dissipation in the plasma, additional to the resistive losses in the vacuum vessel wall. The resulting relations are integral, which allows the same γ and ω with different integrands. It is shown explicitly that only two fitting parameters are needed for getting a perfect agreement of such results with measured γ and ω. This explains why all attempts with so-called kinetic relations have been good in that. This also reveals the reason for the earlier finding [A. M. Garofalo, Fusion Sci. Technol. 48, 918 (2005)] that a number of models provided the stability regardless of the type of dissipation as long as the dissipation was sufficiently large. It is shown here that such “degeneracy” is a general property. One consequence is that a similar success with any model cannot guarantee its validity, and none of them can be recommended to ITER immediately. It is also explained that the edge harmonic oscillations can be a promising candidate for testing the dissipation channels missing in the kinetic dispersion relations.
Adaptive exponential integrate-and-fire model with fractal extension
Authors: Souza Diogo L. M. , Gabrick Enrique C. , Protachevicz Paulo R. , Borges Fernando S. , Trobia José , Iarosz Kelly C. , Batista Antonio M. , Caldas Iberê L. , Lenzi Ervin K.
Published: February 2024

The description of neuronal activity has been of great importance in neuroscience. In this field, mathematical models are useful to describe the electrophysical behavior of neurons. One successful model used for this purpose is the Adaptive Exponential Integrate-and-Fire (Adex), which is composed of two ordinary differential equations. Usually, this model is considered in the standard formulation, i.e., with integer order derivatives. In this work, we propose and study the fractal extension of Adex model, which in simple terms corresponds to replacing the integer derivative by non-integer. As non-integer operators, we choose the fractal derivatives. We explore the effects of equal and different orders of fractal derivatives in the firing patterns and mean frequency of the neuron described by the Adex model. Previous results suggest that fractal derivatives can provide a more realistic representation due to the fact that the standard operators are generalized. Our findings show that the fractal order influences the inter-spike intervals and changes the mean firing frequency. In addition, the firing patterns depend not only on the neuronal parameters but also on the order of respective fractal operators. As our main conclusion, the fractal order below the unit value increases the influence of the adaptation mechanism in the spike firing patterns.
Defect-assisted hole transport through transition metal oxide-based injection layers for passivated nanocrystalline CsPbBr3 emissive thin films: A combined experimental and modeling study
Authors: Akhtar Parvez , Hung Hsiao-Chun , Devi Henam Sylvia , Wu Yuh-Renn , Singh Madhusudan
Published: February 2024

The acidic (pKa ≈1.5–2.5) and hygroscopic nature of poly(3,4-ethylene dioxythiophene) polystyrene sulfonate, used as a common hole-injection layer in optoelectronic devices, has a detrimental effect on device stability and is associated with well established device failure mechanisms. In this work, a process with a high green index hole-injection layer material (V2O5) and low surface roughness (RMS roughness ≈1.3 nm) was developed for demonstrating a hybrid polymer–inorganic perovskite light-emitting diode. Test devices with the new hole-injection layer demonstrate nearly identical maximum current efficiencies (4.23 vs 4.19 cd/A), and luminous efficacies (2.99 vs 2.32 lm/W) when compared to a control device fabricated with the conventional hole-injection layer. Furthermore, the peak brightness was achieved at a current density one-third of the value for the control device. To examine the transport of holes in the above hole-injection layer, we carried out device simulations based on a physical charge control model, including defect-assisted tunneling for hole injection. Close agreement for current–voltage characteristics is observed. Experimentally measured mobility in the device and measured radiative lifetimes were found to be sufficient to achieve this agreement without resorting to the introduction of a sheet charge at the injection interface. Despite the use of a bulk-heterojunction device architecture, the model predicts high radiative recombination rates [≈5.6×1022/(cm3s)] in the emissive layer, consistent with the measured photophysical properties for the active film, suggesting effective passivation of non-radiative surface states.
P-i-N and Schottky P-i-N diamond diodes for high power limiters
Authors: Surdi Harshad , Bressler Mason , Ahmad Mohammad Faizan , Koeck Franz , Winters Bryce , Goodnick Stephen , Thornton Trevor , Nemanich Robert J. , Chang Josephine
Published: February 2024

P-i-N and Schottky P-i-N diamond diodes are a promising technology for high-power limiters. Receivers, solid-state amplifiers, and detectors commonly use P-i-N and/or Schottky diodes for protection from high power incident signals. Here, we report on the RF power handling and power dissipation capability of diamond P-i-N and Schottky P-i-N diodes. We fabricate P-i-N diodes as vertical structures, with both majority and minority carriers involved in charge transport. Similarly, we fabricate vertical Schottky P-i-N diodes, with the doping in the n-layer reduced compared to P-i-N diodes such that the n-layer becomes fully depleted during operation, resulting in a majority-carrier device with a fast recovery time. Both P-i-N and Schottky P-i-N diodes were packaged in shunt-configuration and matched for 3 GHz operation, with a small signal insertion loss of ∼1.25 dB. P-i-N diodes operated up to 40 dBm before failing nondestructively at 45 dBm, demonstrating power dissipation handling that exceeds that of commercially available Si P-i-N diodes by more than a factor of five. Schottky P-i-N diodes operated up to 49 dBm before non-recoverable failure at 50 dBm.
Synthesis and characterization of novel iron-modified geopolymer cement from laterite clay as low energy material
Authors: Ali Akbar , Noor-ul-Amin  , Ahmad Hamza , Noor Sana , Sultana Sabiha , Umar Huzaifa , Ahmad Hijaz , Awwad Fuad A. , Ismail Emad A. A.
Published: February 2024

A new type of geopolymer with an iron–oxygen–silicon linkage is synthesized and reported for the first time. The aim was to enable the iron-rich clay material (laterite) as a raw material for the geopolymerization. Iron was used in different ratios ranging 1–3 wt. % in the raw mix designing geopolymer followed by activation with concentrated alkali solutions of NaOH and KOH in different concentrations. The bonding of Fe–O–Si was confirmed from the FTIR peaks in NaOH- and KOH-based geopolymers. X-ray diffraction studies confirmed the formation of zeolitic, sodalite, and almandite phases. The final product has shown a compressive strength of 2371.8 and 1503 kN/m2 and can be used as a construction material.
Development of a high-frequency dielectric spectrometer using a portable vector network analyzer
Authors: Erkoreka Aitor , Martinez-Perdiguero Josu
Published: February 2024

A simple and novel setup for high-frequency dielectric spectroscopy of materials has been developed using a portable vector network analyzer. The measurement principle is based on radio frequency reflectometry, and both its capabilities and limitations are discussed. The results obtained on a typical liquid crystal prove that the device can provide reliable spectra between 107 and 109 Hz, thus extending the capabilities of conventional impedance analyzers.
The sulfur dioxide–water complex: CCSD(T)/CBS anharmonic vibrational spectroscopy of stacked and hydrogen-bonded dimers
Authors: Hui Wallace C. H. , Lemke Kono H.
Published: February 2024

This study examines the structures, energies, and IR vibrational spectra of the sulfur dioxide–water SO2(H2O) complexes by employing coupled cluster theory CCSD(T) with Dunning style correlation consistent type basis sets aug-cc-pV(n+d)Z (n = D, T, Q, 5). Complete basis set (CBS) extrapolations have been carried out to predict binding energies for two isomers of the SO2(H2O) complex: a stacked global minimum (1A) structure and a hydrogen-bonded local minimum (1B) structure. The CCSD(T)/CBS extrapolation predicts an intermolecular S–O distance rS⋯O = 2.827 Å for the stacked isomer, which is in excellent agreement with an experimental measurement of 2.824 Å [K. Matsumura et al., J. Chem. Phys., 91, 5887 (1989)]. The CCSD(T)/CBS binding energy for the stacked dimer 1A and hydrogen-bonded form 1B is De = −4.37 kcal/mol and De = −2.40 kcal/mol, respectively. This study also employs anharmonic VPT2 MP2/aug-cc-pV(n+d)Z level corrections to CCSD(T)/aug-cc-pV(n+d)Z vibrational frequencies in both forms of SO2(H2O). The anharmonic CCSD(T)/aug-cc-pV(Q+d)Z OH stretching frequencies in the stacked structure 1A are 3743 cm−1 (ν3) and 3647 cm−1 (ν1), and these align well with the recorded IR spectroscopic values of 3745 and 3643 cm−1, respectively [C. Wang et al., J. Phys. Chem. Lett., 13, 5654 (2022)]. If we combine CCSD(T)/aug-cc-pV(n+d)Z De values with VPT2 vibrational frequencies, we obtain a new CCSD(T)/aug-cc-pV(Q+d)Z anharmonic dissociation energy D0 = −3.48 kcal/mol for 1A and D0 = −1.74 kcal/mol for 1B. In summary, the results presented here demonstrate that the application of CCSD(T) calculations with aug-cc-pV(n+d)Z basis sets and CBS extrapolations is critical in probing the structure and IR spectroscopic properties of the sulfur dioxide–water complex.
High-speed and sensitivity near-infrared organic photodetector achieved by halogen substitution strategy for optical wireless communication
Authors: Zhu Yu , Zhang Jing , Qin Hao , Song Guangkun , Yao Zhaoyang , Quan Zuhao , Yang Yanqing , Wan Xiangjian , Li Guanghui , Chen Yongsheng
Published: February 2024

High-speed and sensitivity solution-processed organic photodetectors (OPDs) have drawn great attention for their promising applications in next-generation optoelectronics, including optical communication, imaging, autonomous driving, and military security. However, current OPDs commonly suffer from slow response speed due to low charge mobility, significantly hindering their applications in optical wireless communication. Herein, a pair of nonfullerene acceptors (NFAs), featuring a prominent π extension in the central units with respect to Y6, are synthesized with the same backbone but different halogenations in end cap groups, namely, CH-4Cl and CH-4F. The OPD based on CH-4Cl exhibits a remarkably short response time of 270 ns (λ = 850 nm) and detectivity of >1013 Jones in a self-powered mode, improving 34% and 500% compared to the values of OPD with CH-4F NFA, respectively, which ranks the highest speed among self-powered solution-processed binary OPD-based on NFAs. This outstanding performance is attributed to the low trap states and energetic disorders of OPDs with CH-4Cl. Furthermore, the high-speed OPD demonstrates a promising application in high-speed optical wireless communication.
Sliding-mediated ferroelectric phase transition in CuInP2S6 under pressure
Authors: Zhou Zhou , Zhang Jun-Jie , Turner Gemma F. , Moggach Stephen A. , Lekina Yulia , Morris Samuel , Wang Shun , Hu Yiqi , Li Qiankun , Xue Jinshuo , Feng Zhijian , Yan Qingyu , Weng Yuyan , Xu Bin , Fang Yong , Shen Ze Xiang , Fang Liang , Dong Shuai , You Lu
Published: February 2024

Interlayer stacking order has recently emerged as a unique degree of freedom to control crystal symmetry and physical properties in two-dimensional van der Waals (vdW) materials and heterostructures. By tuning the layer stacking pattern, symmetry-breaking and electric polarization can be created in otherwise non-polar crystals, whose polarization reversal depends on the interlayer sliding motion. Herein, we demonstrate that in a vdW layered ferroelectric, its existing polarization is closely coupled to the interlayer sliding driven by hydrostatic pressure. Through combined structural, electrical, vibrational characterizations, and theoretical calculations, we clearly map out the structural evolution of CuInP2S6 under pressure. A tendency toward a high polarization state is observed in the low-pressure region, followed by an interlayer-sliding-mediated phase transition from a monoclinic to a trigonal phase. Along the transformation pathway, the displacive-instable Cu ion serves as a pivot point that regulates the interlayer interaction in response to external pressure. The rich phase diagram of CuInP2S6, which is enabled by stacking orders, sheds light on the physics of vdW ferroelectricity and opens an alternative route to tailoring long-range order in vdW layered crystals.
Liouvillian exceptional points of an open driven two-level system
Authors: Seshadri Nikhil , Li Anqi , Galperin Michael
Published: February 2024

We study the applicability of the Liouvillian exceptional points (LEPs) approach to nanoscale open quantum systems. A generic model of the driven two-level system in a thermal environment is analyzed within the nonequilibrium Green’s function (NEGF) and Bloch quantum master equation formulations. We derive the latter starting from the exact NEGF Dyson equations and highlight the qualitative limitations of the LEP treatment by examining the approximations employed in its derivation. We find that the non-Markov character of evolution in open quantum systems does not allow for the introduction of the concept of exceptional points for a description of their dynamics. Theoretical analysis is illustrated with numerical simulations.
Chiral plasmonic sensing: From the perspective of light–matter interaction
Authors: Kim Ryeong Myeong , Han Jeong Hyun , Lee Soo Min , Kim Hyeohn , Lim Yae-Chan , Lee Hye-Eun , Ahn Hyo-Yong , Lee Yoon Ho , Ha In Han , Nam Ki Tae
Published: February 2024

Molecular chirality is represented as broken mirror symmetry in the structural orientation of constituent atoms and plays a pivotal role at every scale of nature. Since the discovery of the chiroptic property of chiral molecules, the characterization of molecular chirality is important in the fields of biology, physics, and chemistry. Over the centuries, the field of optical chiral sensing was based on chiral light–matter interactions between chiral molecules and polarized light. Starting from simple optics-based sensing, the utilization of plasmonic materials that could control local chiral light–matter interactions by squeezing light into molecules successfully facilitated chiral sensing into noninvasive, ultrasensitive, and accurate detection. In this Review, the importance of plasmonic materials and their engineering in chiral sensing are discussed based on the principle of chiral light–matter interactions and the theory of optical chirality and chiral perturbation; thus, this Review can serve as a milestone for the proper design and utilization of plasmonic nanostructures for improved chiral sensing.
Molecular-level design for a phosphate-based electrolyte for stable potassium-ion batteries
Authors: Geng Yuanhui , Fu Hongwei , Hu Yanyao , Rao Apparao M. , Fan Ling , Zhou Jiang , Lu Bingan
Published: February 2024

The safety and cycling stability of potassium-ion batteries are of paramount importance. This study investigates a class of phosphate electrolytes with different alkyl chains to understand the correlation between electrochemical properties and alkyl chains. Based on the traditional trimethyl phosphate, the impact of structural modifications on performance improvement was explored in a single-salt, single-solvent environment matched with 1 M bis(fluorosulfonyl)imide potassium salt (KFSI). The research findings indicate that appropriately altering the alkyl chain structure of the phosphate [1 M KFSI-tripropyl phosphate (TPP)] can enhance its electrochemical performance. Through characterization and calculations, it was revealed that TPP's weak solvation and steric hindrance properties favor the formation of a robust interphase on the electrode. Coupling with its excellent ion conductivity, the 1 M KFSI-TPP electrolyte enables good cycling stability of Kǁgraphite, KǁPrussian blue (PB), and PBǁgraphite full-cell configurations. This study provides essential guiding principles for electrolyte design and offers valuable insights into the molecular-level design of safe electrolytes.