bluuebunny/crossref_metadata_2025 huggingface dataset:
A three-point velocity estimation method for two-dimensional coarse-grained imaging data
Authors: Losada J. M. , Helgeland A. D. , Terry J. L. , Garcia O. E.
Published: September 2024

Time delay and velocity estimation methods have been widely studied subjects in the context of signal processing, with applications in many different fields of physics. The velocity of waves or coherent fluctuation structures is commonly estimated as the distance between two measurement points divided by the time lag that maximizes the cross correlation function between the measured signals, but this is demonstrated to result in erroneous estimates for two spatial dimensions. We present an improved method to accurately estimate both components of the velocity vector, relying on three non-aligned measurement points. We introduce a stochastic process describing the fluctuations as a superposition of uncorrelated pulses moving in two dimensions. Using this model, we show that the three-point velocity estimation method, using time delays calculated through cross correlations, yields the exact velocity components when all pulses have the same velocity. The two- and three-point methods are tested on synthetic data generated from realizations of such processes for which the underlying velocity components are known. The results reveal the superiority of the three-point technique. Finally, we demonstrate the applicability of the velocity estimation on gas puff imaging data of strongly intermittent plasma fluctuations due to the radial motion of coherent, blob-like structures at the boundary of the Alcator C-Mod tokamak.
When do multiple pulses of environmental variation trigger tipping in an ecological system?
Authors: Basak Ayanava , Dana Syamal K. , Bairagi Nandadulal , Feudel Ulrike
Published: September 2024

Climate change and anthropogenic impacts have a significant effect on natural ecosystems. As a response, tipping phenomena, i.e., abrupt qualitative changes in the dynamics of ecosystems, like transitions between alternative stable states, can be observed. We study such critical transitions, caused by an interplay between B-tipping, the rate of change of environmental forcing, and a rate-dependent basin boundary crossing. Instead of a slow trend of environmental change, we focus on pulses of variation in the carrying capacity in a simple ecological model, the spruce budworm model, and show how one pulse of environmental change can lead to tracking the current stable state or to tipping to an alternative state depending on the strength and the duration of the pulse. Moreover, we demonstrate that applying a second pulse after the first one, which can track the desired state, can lead to tipping, although its rate is slow and does not even cross the critical threshold. We explain this unexpected behavior in terms of the interacting timescales, the intrinsic ecological timescale, the rate of environmental change, and the movement of the basin boundaries separating the basins of attraction of the two alternative states.
Temperature-dependent charge transport measurements unveil morphological insights in non-fullerene organic solar cells
Authors: Zhang Chujun , Feng Erming , Gao Yaxin , Wong Vox Kalai , Li Hengyue , Liu Biao , Mahadevan Sudhi , Tsang Sai-Wing , Yang Junliang , So Shu Kong
Published: September 2024

The morphological analysis of bulk heterojunction (BHJ) active layer stands as a critical imperative for advancing the performance of future organic solar cells. Conventional characterization tools employed for morphological investigation often require substantial resources, both in cost and physical space, thereby imposing restraints on research endeavors in this domain. Here, we extend the application of charge carrier transport characterization beyond conventional mobility assessments, utilizing it as a table-top method for preliminary morphological screening in organic thin films. The investigation focuses on several high-performance BHJ systems that utilize typical “Y” non-fullerene acceptors. It involves in-depth transport studies, including temperature- and field-dependent transport characterizations. The resulting transport data are analyzed in detail using the Gaussian disorder model to extract key transport parameters, specifically the high-temperature limited mobility (μ∞) and positional disorder (∑). Integrating these transport parameters with morphological insights obtained through various characterization tools—including x-ray scattering, sensitive spectroscopy, and quantum chemistry simulation—provides a deep understanding of the intricate interplay between charge transport properties and morphological characteristics. The results reveal explicit relationships, associating μ∞ with the degree of molecular stacking in BHJs and ∑ with the structural disorder in molecule skeleton. Our findings point to the promising potential of utilizing a simple transport characterization technique for the early stage evaluation of thin film packing and geometric properties of organic materials.
Laboratory demonstration of an off-axis optical bench design for future gravity missions
Authors: Peng Bo , Wu Kailan , Wu Jingui , Guo Zhongkai , Wang Yun , Li Ming , Zheng Yongchao , Li Xu , Xia Chenhui , Bai Shaojun , Wang Yiqun , Lin Xuling
Published: September 2024

The inter-satellite laser ranging interferometer is one of the core components of future gravity missions to achieve high ranging precision. This work builds a preliminary breadboard of the off-axis optical bench design, which integrates the merits of the off-axis optical bench design of GRACE Follow-On mission and other on-axis designs. The study finds that the displacement noise between two optical benches has been reduced to 20nm/Hz at a frequency of 10 mHz, and the differential wavefront sensing noise has been suppressed to 10−5rad/Hz at 1 kHz as well. In addition, the tilt-to-length coupling noise related to the piston effect is restricted within 30 μm/rad, and the relative parallelism error of the transmitting beam and receiving beam is less than 4.5%. The results show that this off-axis optical bench design is an important candidate for China’s future gravity missions.
Improving near-stall performance of axial flow compressors using variable rotor tandem stage. A steady analysis
Authors: Fathi Sahar , Boroomand Masoud , Eshraghi Hamzeh
Published: September 2024

This paper investigates the idea of substituting the first stage of a conventional axial-flow compressor and its inlet guide vane (IGV) row with a variable rotor tandem (VRT) stage to reduce the size and weight of axial-flow compressors. It is expected that a tandem stage gains higher pressure ratio than a conventional stage, and simultaneously, its variable stagger rotor provides more flexibility in handling unsteady phenomena at low mass flow rates. A three-dimensional numerical model based on Reynolds-Averaged Navier–Stokes equations is developed to conduct this investigation. To validate the numerical model, experimental tests are conducted on a tandem single-stage axial-flow compressor test bench in the Dana laboratory of Amirkabir University of Technology, to compare the performance map with numerical results. The validated numerical model is then employed to simulate the performance of both front and aft variable rotor blades. The proposed tandem stage effectively performs the IGV duty, suppresses instabilities at low mass flow rates, and eventually extends the compressor's stable operational range. This proves that a VRT stage is an efficient active surge-control system tool. The detailed survey of the three-dimensional flow field reveals that the aft tandem rotor blade stagger angle is more effective in increasing the stall margin and decreasing the minimum operational mass flow rate than the front row of blades. It is observed that when the aft blades rotate in the direction of decreasing the tandem blades' gap area, the flow momentum increases and causes the compressor stability at lower mass flow rates.
Pressure-induced softening in bulk modulus due to magnetoelastic coupling in Nd2CoFeO6 double perovskite
Authors: Mukherjee Bidisha , Sahu Mrinmay , Samanta Debabrata , Ghosh Bishnupada , Joseph Boby , Dev Mukherjee Goutam
Published: September 2024

In the present work, we have investigated the structural response of transition metal double perovskite oxide Nd2CoFeO6 under pressure by XRD and Raman spectroscopic measurements. From XRD data, we have observed a pressure-induced structural transition from the orthorhombic phase to the monoclinic phase at about 14.8 GPa. An anomalous increase in compressibility at a much lower pressure (∼1.1 GPa) is seen where no structural transition occurs. At about the same pressure, a sudden drop in the slope of the Raman shift is observed. Further investigation at low temperatures reveals that the B1g Raman mode is strongly affected by magnetic interactions. Additional high-pressure Raman experiments with the application of a magnetic field have indicated that the mentioned anomaly around 1.1 GPa can be explained by a high-spin to low-spin transition of Co3+.
Soft bottles drain faster but glug slower
Authors: Velankar Rohit S. , Velankar Sachin S.
Published: September 2024

An inverted container of water drains with a periodic glugging process where bubbles of air enter through the bottom hole, thus replacing the exiting water. If the container is soft, its walls can flex with each glug. We examine the effect of container elasticity on the drainage process. Experiments are conducted to measure the drainage rate and the glug period as water drains out of a container through a bottom hole. The container compliance is varied by varying the diameter of a soft rubber membrane comprising the lid of the container. Increasing container compliance (i.e., making the container softer) is found to increase the drainage velocity, increase the glugging period, and increase the volume of each glug. Previously, Clanet and Searby (2004) modeled the glugging process as a spring-and-mass oscillator where the compressibility of air in the headspace acts as the spring. We adapt this model so that the membrane elasticity acts in series with the air compressibility. This adapted model qualitatively agrees with the observations but underpredicts the observed effect on the glug period.
Enhancing vacuum surface flashover voltage of alumina insulator by self-assembly of fluorine-containing molecule
Authors: Huo Yankun , Liu Wenyuan , He Yajiao , Wang Hongjie , Cheng Jun , Ke Changfeng
Published: September 2024

In this study, a fluorocarbon chain was grafted on the surface of the alumina insulator through the molecule self-assembly of perfluorododecyl trichlorosilane to enhance the vacuum surface flashover voltage. A hydrocarbon chain with the same molecular structure, devoid of fluorine element, was also grafted through the self-assembly of dodecyl trichlorosilane to enable comparison. The surface state examination of the self-assembled alumina insulators shows that both the molecules are attached to the alumina surface. The arrangement of the molecules on the surface is regular. Surface property tests reveal that the fluorocarbon chain endows the surface of alumina with a lower secondary electron emission yield and a lower gas adsorption volume than the hydrocarbon chain. Correspondingly, the surface flashover voltage of the fluorocarbon chain grafted insulator is higher than that of the hydrocarbon chain. This implies that the surface flashover voltage can be improved through surface fluorination, which converts hydrocarbon bonds to fluorocarbon bonds. The study demonstrates this possibility at the molecule level.
Effects of propeller boss cap fins on hydrodynamics and flow noise of a pump-jet propulsor
Authors: Zheng Sijie , Huang Qiaogao , Zhou Li , Li Han , He Xing , Li Xinming
Published: September 2024

As an underwater thruster, the pump-jet propulsor (PJP) exhibits low radiation noise but generates significant line spectral noise in the low-frequency band. In this paper, we equipped the PJP hub with two types of propeller boss cap fins (PBCF): one fixed and the other rotating with the rotor. The hybrid large eddy simulation and Reynolds-averaged Navier–Stokes method, along with the Ffowcs Williams-Hawkings (FW-H) equation, are employed to systematically analyze the hydrodynamics, exciting force, flow noise, and flow field of PJPs. The results indicate that the fixed PBCF improves the hydrodynamic performance and reduces the exiting force, raising the rotor's thrust coefficient by 9.22%–14.99%. The fixed PBCF also modifies the characteristics of line spectrum noise but causes an increase in the flow noise. The rotating PBCF increases the rotor's thrust coefficient by 2.03%–3.15%, decreasing both exciting force and line spectrum noise. For instance, at the advance coefficient of 0.8, its sound pressure level at the rotor frequency drops to 49.6%. Additionally, the rotating PBCF increases the pressure of the hub wake and effectively reduces the hub vortices' strengths. This paper provides a theoretical foundation for designing PJPs that enhance concealment and minimize vibrations and noise.
Versatile tunable metastructure based on liquid crystal-VO2 for polarization conversion and refractive index sensing
Authors: Li Qi-Juan , Liao Si-Yuan , Liu Fa-Zhan , Zhang Hai-Feng
Published: September 2024

This paper presents a metastructure device (MSD) modulated by liquid crystal (LC) and vanadium dioxide (VO2), suitable for circular-to-linear polarization conversion and refractive index (RI) sensing. The MSD employs a 2 × 2 array as a unit cell, forming a circular-to-linear polarization conversion. Filling the MSD with analytes of different RIs can cause changes in the electromagnetic properties of the MSD, thus realizing the sensing function. Furthermore, the detection range of the sensing can be modified by changing the long-axis pointing of the LC molecules under an applied voltage, resulting in multi-range detection. The RI unit is denoted as RIU. Without an applied voltage, the RI detection range is 1.949–2.607, with a sensitivity of 199 GHz/RIU; under full-bias conditions, the detection range is 2.828–3.391, with a sensitivity of 143 GHz/RIU. In the initial state of LCs, this paper also explores the use of the phase transition of VO2 to adjust the conductivity of VO2 to achieve changes in the detection range. In the insulating state, the detection range is 2.12–2.607, with a sensitivity of 225 GHz/RIU, while in the metallic state, the detection range is 1–2, with a sensitivity of 183 GHz/RIU. Furthermore, altering the thickness of the analyte also affects the electromagnetic properties of the device, causing a shift in the peak axial ratio frequency, making the MSD suitable for analyte thickness detection. The MSD has a wide detection range, high sensitivity, and adaptability, making it suitable for identifying cancer cells and giving a new method of monitoring human health.
Diffusion of proteins in crowded solutions studied by docking-based modeling
Authors: Singh Amar , Kundrotas Petras J. , Vakser Ilya A.
Published: September 2024

The diffusion of proteins is significantly affected by macromolecular crowding. Molecular simulations accounting for protein interactions at atomic resolution are useful for characterizing the diffusion patterns in crowded environments. We present a comprehensive analysis of protein diffusion under different crowding conditions based on our recent docking-based approach simulating an intracellular crowded environment by sampling the intermolecular energy landscape using the Markov Chain Monte Carlo protocol. The procedure was extensively benchmarked, and the results are in very good agreement with the available experimental and theoretical data. The translational and rotational diffusion rates were determined for different types of proteins under crowding conditions in a broad range of concentrations. A protein system representing most abundant protein types in the E. coli cytoplasm was simulated, as well as large systems of other proteins of varying sizes in heterogeneous and self-crowding solutions. Dynamics of individual proteins was analyzed as a function of concentration and different diffusion rates in homogeneous and heterogeneous crowding. Smaller proteins diffused faster in heterogeneous crowding of larger molecules, compared to their diffusion in the self-crowded solution. Larger proteins displayed the opposite behavior, diffusing faster in the self-crowded solution. The results show the predictive power of our structure-based simulation approach for long timescales of cell-size systems at atomic resolution.
Charge regulation of nanoparticles in the presence of multivalent electrolytes
Authors: Colla Thiago , Bakhshandeh Amin , Levin Yan
Published: September 2024

We explore the charge regulation (CR) of spherical nanoparticles immersed in an asymmetric electrolyte of a specified pH. Using a recently developed reactive canonical Monte Carlo (MC) simulation method, titration isotherms are obtained for suspensions containing monovalent, divalent, and trivalent coions. A theory based on the modified Poisson–Boltzmann approximation, which incorporates the electrostatic ion solvation free energy and discrete surface charge effects, is used to compare with the simulation results. A remarkably good agreement is found without any fitting parameters, both for the ion distributions and titration curves, suggesting that ionic correlations between coions and hydronium ions at the nanoparticle surface play only a minor role in determining the association equilibrium between hydroniums and the functional sites on the nanoparticle surface. On the other hand, if suspension contains multivalent counterions, we observe a large deviation between theory and simulations, showing that the electrostatic correlations between counterions and hydronium ions at the nanoparticle surface are very significant and must be properly taken into account to correctly describe CR for such solutions.
Field-free multistate spin–orbit torque devices for programmable image edge recognition circuit
Authors: Yang Liu , Li Wendi , Zuo Chao , Tao Ying , Jin Fang , Li Huihui , Tang RuJun , Dong Kaifeng
Published: September 2024

The application of spin–orbit torque (SOT) devices to neuromorphic computing platforms is focused on the development of hardware circuit architectures. However, the inter-device variability, the integration modes of devices and peripheral circuits, and appropriate application scenarios are still unclear, limiting the development of SOT devices in neuromorphic computing. To solve this problem, this paper first proposes a circuit compensation scheme for the difference in resistance values of SOT devices, which solves this variability problem at the circuit level. Moreover, a synergistic scheme with the circuit is developed based on the correspondence between the multistate resistance characteristics of the SOT devices and a convolutional algorithm. To achieve this, a multichannel SOT convolutional kernel circuit architecture is built, which implements an image edge recognition application. Finally, based on a simulation model, an image edge recognition hardware circuit based on our CoPt-SOT devices is implemented, which is capable of performing image edge recognition with an accuracy of 96.33%. This scheme provides technical support and development prospects for SOT devices in neural network hardware applications.
In-operando microwave scattering-parameter calibrated measurement of a Josephson traveling wave parametric amplifier
Authors: Shin S.-H. , Stanley M. , Wong W. N. , Sweetnam T. , Elarabi A. , Lindström T. , Ridler N. M. , de Graaf S. E.
Published: September 2024

Superconducting traveling wave parametric amplifiers (TWPAs) are broadband near-quantum limited microwave amplifiers commonly used for qubit readout and a wide range of other applications in quantum technologies. The performance of these amplifiers depends on achieving impedance matching to minimize reflected signals. Here, we apply a microwave calibration technique to extract the S-parameters of a Josephson junction based TWPA in-operando. This enables reflections occurring at the TWPA and its extended network of components to be quantified, and we find that the in-operation performance can be well described by the off-state measured S-parameters.
Interactions of clathrate hydrate promoters sodium dodecyl sulfate and tetrahydrofuran investigated using 1H diffusion nuclear magnetic resonance at hydrate-forming conditions
Authors: Adkins Zoe , Yang Yuan , Hartman Ryan L. , Koh Carolyn A.
Published: September 2024

Thermodynamic hydrate promoters and kinetic hydrate promoters can be used to reduce the P–T conditions for clathrate hydrate synthesis to decrease the nucleation induction time while increasing growth rates. Two commonly used promoters for hydrate research are tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS), which can increase the overall hydrate promotion when used in tandem as compared to individually. There are several molecular theories regarding how SDS promotes hydrate growth. This study explores the micellular theory, for which hydrate formation depends on surfactant aggregates (micelles) at a critical micelle concentration (CMC) to increase the interfacial surface area. The micellular theory is the most investigated and criticized surfactant hydrate promotion theory. To address questions related to micellar behavior, this study investigates the intermolecular behavior between SDS and THF for the identification of micelles at hydrate-forming conditions. The systems explored contained THF at 3 and 5 wt. % with varying concentrations of SDS below and above the CMC. Several methods including a qualitative visual method, conductivity, interfacial tensiometry, 13C Liquid-state Nuclear Magnetic Resonance (NMR) spectroscopy, and 1H diffusion NMR spectroscopy were evaluated at temperatures below the Krafft point of SDS and above 0 °C. The presence of THF at low concentrations decreased the critical temperature for the formation of SDS micelles, where SDS is solubilized in THF/water solution at hydrate-forming temperatures without precipitation. The CMC of SDS was decreased significantly even at hydrate-forming conditions. Mixed surfactant–cosolvent micellular behavior of SDS in the presence of low concentrations of THF was confirmed at hydrate-forming conditions above 0 °C.
Slip velocity and field information of two-phase cavitating flows
Authors: Ge Mingming , Apte Dhruv , Wang Chuan , Zhang Guangjian , Zhang Xinlei , Coutier-Delgosha Olivier
Published: September 2024

In this work, laser-induced florescent particle image velocimetry was performed to measure simultaneously the liquid and vapor velocity fields at the mid-span of a small-scale Venturi type section to determine the presence of a slip velocity between the phases. Various dynamic behavior and Kelvin–Helmholtz (K-H) instability involved in the cloud cavity shedding regime are discussed at four different cavitation numbers. The velocity, vorticity, and turbulence field information of the two phases are analyzed. The liquid–vapor mixture in a cavitating flow is usually considered a homogeneous medium in currently used computational models, but it is shown in this study that the two phases have very different dynamics. The measurements of the time-averaged velocities highlight the existence of a noteworthy slippage between the liquid and the vapor phases, especially in the upstream part of the cavitation region, where the slippage between the two phases can reach about 50% of the liquid velocity. Using phase-locked average, it is shown that the slip velocity in the upstream region is mainly located at the upper liquid–vapor interface, while the slip velocity in the closure area is near the bottom wall, due to the reentrant jet. These results contradict a primary assumption of the current models, where the medium is usually considered as a homogeneous mixture with a unique velocity field, thus providing a reference for future computational model improvement.
How bulk nanobubbles respond to elevated external pressures
Authors: Li Mingbo , Gao Yawen , Ma Xiaotong , Chen Changsheng , Wang Benlong , Sun Chao
Published: September 2024

Bulk nanobubbles, nanoscopic gaseous domains in aqueous solutions, exhibit surprising long-term stability and unique properties under varying environmental conditions. This study investigates the effects of external pressure on nanobubble stability and behavior through three experimental setups: pressurization at room temperature, pressurization at elevated temperatures, and constant pressure loading. Our findings reveal that increasing external pressure reduces nanobubble concentration and reshapes the bubble size distribution. Larger nanobubbles either disappeared or transformed into microbubbles, while smaller ones expanded, significantly narrowing the size distribution. These changes were found to be irreversible. Additionally, nanobubble stability is influenced by both the magnitude and duration of the applied pressure. Elevated temperatures further narrowed the size distribution at atmospheric pressure, and subsequent pressurization caused these nanobubbles to shrink, showing different response characteristics compared to room temperature. This research highlights the complex interplay between pressure, temperature, and nanobubble stability, offering valuable insight for practical applications in fields such as drug delivery, water treatment, and nanomaterial synthesis.
Selective adsorption of divalent and trivalent cations in porous electrodes
Authors: Kawai Yusuke , Yamamoto Yuji , Kiyohara Kenji
Published: September 2024

The capacitive deionization technology uses the electrochemical adsorption of ions in porous electrodes to desalinate seawater or brackish water. Recently, capacitive deionization has gained significant attention as a technology for selective adsorption of ionic species from multicomponent aqueous electrolytes. To investigate the mechanism of selective adsorption at the molecular level, we performed molecular dynamics simulations of aqueous electrolytes and porous electrodes with different divalent or trivalent ions, electrode pore sizes, and applied voltages. We calculated the free energy barriers preventing ions from entering the pores of the electrode and the structure of the water molecules near the ions and the electrode surface under various conditions. Our results suggest that, when the pore and ion sizes are comparable, the steric and electrostatic interactions between the hydrated ions and electrode pores are comparable in magnitude. Moreover, the relative importance of the two interactions can be reversed by slight changes in the external conditions, such as the ion size, valence of the ions, electrode pore size, and applied voltage. Thus, by finely tuning the electrode pore size and the applied voltage, it may be possible to selectively adsorb a particular ionic species from a multicomponent electrolyte through capacitive deionization using a porous electrode.
Dynamic behavior and stability control of skyrmionium in periodic PMA/damping gradient nanowires
Authors: Wang Luowen , Wang Sunan , Li Wenjin , Gao Xiaoping , Yu Ziyang , Liu Qingbo , Xiong Lun , Lu Zhihong , Zhang Yue , Xiong Rui
Published: September 2024

Magnetic skyrmioniums—with a composite structure comprising two skyrmions with opposite topological charges, exhibit unique dynamic behaviors that are crucial for technological advancements and have application potential for high-density and nonvolatile memory. This study explores the impact of periodic perpendicular magnetic anisotropy (PMA) and damping gradients on skyrmioniums. Utilizing the object oriented micromagnetic framework for detailed simulations, the effective control and enhancement of the skyrmionium stability and mobility through the periodic modulation of PMA and damping gradients is demonstrated. The results demonstrate the dynamic behavior and stability control of skyrmioniums in periodic PMA/damping gradient nanowires. Moreover, the critical influence of the periodic gradient on the skyrmionium motion and stability is highlighted. The results present new avenues for developing advanced memory technologies, leveraging skyrmionium's unique nonlinear behaviors to improve the device performance and reliability.
Phase transitions in typical fluorite-type ferroelectrics
Authors: Yu Heng , Xue Kan-Hao , Mao Ge-Qi , Feng Nan , Zheng Yunzhe , Yang Shengxin , Huang Jinhai , Chen Zihui , Yang Wei , Cheng Yan , Xu Ben , Miao Xiangshui
Published: September 2024

While ferroelectric hafnia (HfO2) has become a technically important material for microelectronics, the physical origin of its ferroelectricity remains poorly understood. The tetragonal P42/nmc phase is commonly assigned as its paraelectric mother phase but has no soft mode at the Brillouin zone center. In this work, we propose that the paraelectric—ferroelectric transition in the fluorite-type Pca21 ferroelectric family can be described by a Pcca—Pca21 transition, where the Pcca mother phase will evolve into either the Pca21 ferroelectric phase or the centrosymmetric P21/c monoclinic phase, depending on the strain conditions. The Pcca phase is directly linked to both phases in the context of continuous phase transition. Hafnia is regarded as a special case of this family in that it has accidental atomic degeneracy because all anions are oxygen. The theory is also correlated with the seven-coordination theory that explains the ferroelectricity in hafnia from a chemical perspective. In addition, the strain conditions to promote the ferroelectric phase in hafnia are discussed.
A contactless in situ EFISH method for measuring electrostatic potential profile of semiconductor/electrolyte junctions
Authors: Zhao Fengyi , Xu Zihao , Suo Sa , Lin Lu , Hill Craig L. , Musaev Djamaladdin G. , Lian Tianquan
Published: September 2024

In photoelectrochemical cells, promising devices for directly converting solar energy into storable chemical fuels, the spatial variation of the electrostatic potential across the semiconductor–electrolyte junction is the key parameter that determines the cell performance. In principle, electric field induced second harmonic generation (EFISH) provides a contactless in situ spectroscopic tool to measure the spatial variation of electrostatic potential. However, the total second harmonic generation (SHG) signal contains the contributions of the EFISH signals of semiconductor space charge layer and the electric double layer, in addition to the SHG signal of the electrode surface. The interference of these complex quantities hinders their analysis. In this work, to understand and deconvolute their contributions to the total SHG signals, bias-dependent SHG measurements are performed on the rutile TiO2(100)–electrolyte junction as a function of light polarization and crystal azimuthal angle (angle of the incident plane relative to the crystal [001] axis). A quadratic response between SHG intensity and the applied potential is observed in both the accumulation and depletion regions of TiO2. The relative phase difference and amplitude ratio are extracted at selected azimuthal angles and light polarizations. At 0° azimuthal angle and s-in–p-out polarization, the SHG intensity minimum has the best match with the TiO2 flatband potential due to the orthogonal relative phase difference between bias-dependent and bias-independent SHG terms. We further measure the pH-dependent flatband potential and probe the photovoltage under open circuit conditions using the EFISH technique, demonstrating the capability of this contactless method for measuring electrostatic potential at semiconductor–electrolyte junctions.
The impact of feature representation on the accuracy of photonic neural networks
Authors: Gomes de Queiroz Mauricio , Jimenez Paul , Cardoso Raphael , Vidaletti Costa Mateus , Abdalla Mohab , O’Connor Ian , Bosio Alberto , Pavanello Fabio
Published: September 2024

Photonic neural networks (PNNs) are gaining significant interest in the research community due to their potential for high parallelization, low latency, and energy efficiency. PNNs compute using light, which leads to several differences in implementation when compared to electronics, such as the need to represent input features in the photonic domain before feeding them into the network. In this encoding process, it is common to combine multiple features into a single input to reduce the number of inputs and associated devices, leading to smaller and more energy-efficient PNNs. Although this alters the network’s handling of input data, its impact on PNNs remains understudied. This paper addresses this open question, investigating the effect of commonly used encoding strategies that combine features on the performance and learning capabilities of PNNs. Here, using the concept of feature importance, we develop a mathematical methodology for analyzing feature combination. Through this methodology, we demonstrate that encoding multiple features together in a single input determines their relative importance, thus limiting the network’s ability to learn from the data. However, given some prior knowledge of the data, this can also be leveraged for higher accuracy. By selecting an optimal encoding method, we achieve up to a 12.3% improvement in the accuracy of PNNs trained on the Iris dataset compared to other encoding techniques, surpassing the performance of networks where features are not combined. These findings highlight the importance of carefully choosing the encoding to the accuracy and decision-making strategies of PNNs, particularly in size or power constrained applications.
Dispersion in a slit with crossflow filtration through a porous wall
Authors: Dejam Morteza , Hassanzadeh Hassan
Published: September 2024

Crossflow filtration is a separation technique where fluid flows tangentially across a membrane or porous media, reducing clogging by sweeping away retained particles and allowing continuous filtration. Dispersion of solute matter in crossflow filtration plays an essential role in the separation performance of many industrial processes. The current work aims to generalize the Taylor dispersion theory and study the solute transport in a slit–porous medium system with a crossflow. The solute is depleted by the porous medium at the slit top porous wall or the interface between the slit and the porous medium, where the continuity of the solute concentration and mass flux is applied. The solute is simultaneously transported axially by the main flow along the slit and vertically by the crossflow perpendicular to the slit. Using the Reynolds decomposition and cross-sectional averaging techniques, the generalized reduced-order model for the advection-dispersion solute transport in the slit–porous medium system with the presence of a crossflow is established, where the effective velocity of the main flow and the effective dispersion coefficient are obtained. The analysis of the results reveals that the nondimensional Taylor dispersion coefficient scales with the Peclet numbers for the crossflow and the main flow, respectively, as DT∼Pev−5/3 (when Pev≥20) and DT∼Peu2. The proposed theoretical model, along with the findings of this study, paves the way for the fundamental study of dispersion in more complex systems.
Combustion modes of kerosene spray in a scramjet combustor with different injection schemes
Authors: Li Fan , Zhang Jincheng , Zhao Guoyan , Sun Mingbo , Li Fei , Ma Guangwei , Liu Mingjiang
Published: September 2024

Combustion modes of kerosene spray in a scramjet combustor condition with different injection schemes are experimentally investigated at Mach 2.52. The study is based on two single injectors with nozzle diameters of 0.79 and 1.14 mm and two dual injectors with nozzle diameters of 0.56 and 0.72 mm, respectively. The results show that the weak combustion mode has little effect on the flow field, while the intensive combustion mode has the opposite effect. The dual injector can promote evaporation and mixing of the kerosene spray. Compared with the dual injector, intensive combustion cannot occur when a single injector is used, and the flame stability range is also narrower. As the nozzle diameter of the injector increases, the distribution and oscillation of kerosene spray change significantly, transition from the weak to intensive combustion mode occurs at a higher equivalence ratio, and the flame stability range increases. However, change in the nozzle diameter does not affect the overall process of combustion mode transition. For the single injector, intensive combustion still cannot occur when the nozzle diameter changes. In addition, change in the nozzle diameter has little effect on combustion heat release when the combustion mode remains unchanged.
A novel method for investigating the underwater explosion loads and bubble evolution
Authors: Gao Yang , Yang Tonghui , Wang Cheng , Sun Yuanbo
Published: September 2024

This paper presents an innovative experimental method for studying the evolution and energy output characteristics of underwater explosion bubbles. We independently constructed an experimental testing system for underwater electrical wire explosions (UEWE), in which electrodes connected to a metal wire serve as the load, and underwater explosions are initiated through instantaneous high-voltage discharge. By varying the diameter of the metal wire and configuring parallel wire arrays, we analyzed and discussed the explosion characteristic parameters and the current–voltage (I–V) signals under different conditions. The maximum bubble radius of the underwater metal wire explosion was compared with the corresponding equivalent explosive simulation results, and a numerical model for underwater metal wire explosion equivalent to explosive detonation was established. Subsequently, we discussed the characteristics of bubble generation and evolution under various conditions, clarifying the similarities and differences between wire explosions and explosive detonations. On this basis, we explored the propagation laws of shock waves and secondary pulsation waves (SPW) under different conditions. We also calculated and analyzed energy output characteristic parameters, such as shock wave energy and bubble energy. The results indicate that there are significant differences between copper wire and aluminum wire loads in UEWE. For copper wires with a diameter greater than 0.4 mm, the shock wave overpressure peak value significantly decreases, while for aluminum wires with a diameter greater than 0.5 mm, it slightly decreases. Both metals exhibit similar trends in parallel wire arrays, with the shock wave overpressure peak value initially increasing and then decreasing as the number of wires increases. Unlike underwater explosive detonations, the SPW peak value in UEWE may exceed that of the shock wave. For single wires, the SPW peak value of copper wires is generally higher than that of aluminum wires, but in wire arrays, the trend is reversed. The multi-wire parallel connection can improve the energy conversion efficiency of the shock waves. However, for bubble energy, under all conditions, a single aluminum wire with a diameter of 0.5 mm produced the maximum bubble energy, reaching 1023.1 J. These findings provide new insights into the energy features of UEWE.
Size dependence of transport coefficients of thin and long asphaltene molecules as determined using a mode-coupling theory approach
Authors: Wong Chi Pui Jeremy , Choi Phillip
Published: September 2024

Rotational diffusion coefficients (Dr) and viscosities (η) of rigid rod molecules consisting of N beads were first revisited for the situation at low density. Starting from this, the transport coefficients at high density condition were expressed in terms of different density pair correlation functions, such as intermolecular radial distribution function and structure factor. This was attained using a mode-coupling theory approach to approximate the intermolecular force–force correlation function, and thus the friction coefficient. As these density pair correlation functions are dependent on N, they determine how “entangled” the rigid rod molecules are, and therefore reproducing the crossover in the log –log plot of transport coefficients with N. It was found that there are crossovers in transport coefficients from Dr∼N−2.3 and η∼N2.3 at low N to Dr∼N−6.5 and η∼N6.5 at high N. The strength of N dependence is mainly determined by the competition between available free space and the compressibility of the system.
Orthonormal and periodic levels for quantum cascade laser simulation
Authors: Mohamed Zakaria , Önder D. Ekin , Wacker Andreas
Published: September 2024

A Python package to evaluate Wannier, Wannier–Stark, and EZ (both energy and location Z resolved) levels for quantum cascade lasers is presented. We provide the underlying theory in detail with a focus on the orthonormality and periodicity of the generated states.
Electronic structures and magnetic properties of Janus NbSSe monolayer controlled by carrier doping
Authors: Wu Yan-Ling , Zeng Zhao-Yi , Geng Hua-Yun , Chen Xiang-Rong
Published: September 2024

Two-dimensional spintronics has become a hot topic in recent years due to its advantages and potential in manipulating electron spins. In this paper, the electronic structures and magnetic properties of the Janus NbSSe monolayer are calculated using first-principles and Monte Carlo methods. Our study shows that the ground state of the material is a ferromagnetic metal. Under carrier doping, it undergoes a second-order phase transition from metal to half-metal, achieving 100% spin polarization, and enhancing or weakening ferromagnetic coupling. The value of the magnetocrystalline anisotropy energy is 570.96 μeV, and doping with an appropriate concentration of holes can transform the easy magnetization axis from in-plane to out-of-plane. Since the out-of-plane mirror symmetry is broken, we study the charge changes in the layer under the action of an external electric field. Due to the combined action of the external electric field and the built-in electric field, the layer exhibits a unique charge transfer mode. It is predicted that the Curie temperature of the material is about 156 K. When doped with 4.01 × 1013 cm−2 (0.04 holes per atom) concentration holes, the Curie temperature can reach about 350 K, indicating that the Curie temperature of the material can be reasonably controlled by regulating the carrier concentration. The coercive force calculated from the hysteresis loop is 0.01 T, and its hysteresis loss is low, showing its response to the external magnetic field. All of the above results indicate the application potential of this material in spin-electronic devices.
Generalized Einstein relations between absorption and emission spectra at thermodynamic equilibrium
Authors: Ryu Jisu , Yeola Sarang , Jonas David M.
Published: September 2024

We present Einstein coefficient spectra and a detailed-balance derivation of generalized Einstein relations between them that is based on the connection between spontaneous and stimulated emission. If two broadened levels or bands overlap in energy, transitions between them need not be purely absorptive or emissive. Consequently, spontaneous emission can occur in both transition directions, and four Einstein coefficient spectra replace the three Einstein coefficients for a line. At equilibrium, the four different spectra obey five pairwise relationships and one lineshape generates all four. These relationships are independent of molecular quantum statistics and predict the Stokes’ shift between forward and reverse transitions required by equilibrium with blackbody radiation. For Boltzmann statistics, the relative strengths of forward and reverse transitions depend on the formal chemical potential difference between the initial and final bands, which becomes the standard chemical potential difference for ideal solutes. The formal chemical potential of a band replaces both the energy and degeneracy of a quantum level. Like the energies of quantum levels, the formal chemical potentials of bands obey the Rydberg-Ritz combination principle. Each stimulated Einstein coefficient spectrum gives a frequency-dependent transition cross-section. Transition cross-sections obey causality and a detailed-balance condition with spontaneous emission, but do not directly obey generalized Einstein relations. Even with an energetic width much less than the photon energy, a predominantly absorptive forward transition with an energetic width much greater than the thermal energy can have such an extreme Stokes’ shift that its reverse transition cross-section becomes predominantly absorptive rather than emissive.
A cyberterrorist behind the keyboard
Authors: Etaywe Awni , Macfarlane Kate , Alazab Mamoun
Published: September 2024

Given the diverse backgrounds of people living in modern societies as well as the international nature of
cyber-terrorist threats, profiling the type of person behind cyber-mediated crimes has become a norm in terrorist profiling
practice. This study contributes to timely efficient terrorist profiling and threat assessment by showcasing an automated content
analysis of cyber-mediated terrorist texts, using natural language processing technology and AI-assisted analysis. To characterise
the terrorist type of texts and provide clues to threats, the study employs a ‘psycholinguistic profiling’ approach to authorship
analysis (Grant 2008). That is, it seeks to describe the likelihood of an author’s
engagement in violent extremist activity, identify motives for violence, and provide clues vis-a-vis would-be and actual violent
behaviours. The study takes twenty texts produced by international terrorists involved in jihadism and far-right violent extremism
as a case study. The findings reveal the investigative value of automated psycholinguistic profiling for security and intelligence
practitioners, with the semantic patterns yielding helpful information for an understanding of the criminal nature of terrorist
language. Also revealed is the attentional pattern of extremists and their discourse together with clues-based conclusions about
text type, as well as ‘warning’ behaviours and motives for aggression which vary according to the authors’ ideological
differences.
Conservation agriculture practices: Adaptation and yield
Authors: Rusinamhodzi Leonard
Published: September 2024

Conservation agriculture (CA) has been promoted in sub-Saharan Africa (SSA) to increase crop productivity and for climate change adaptation. CA is the simultaneous application of the three principles: no-till, mulch cover, and crop diversification. The potential benefits are largely linked to moisture conservation of crop residues, reduced run-off and erosion, increased infiltration, and reduced evaporative losses. This study uses a review of recent literature in SSA under rain-fed conditions to synthesize evidence of the effect of CA on yield and climate change adaptation. Web of Science and Google Scholar were used for literature searches. Crop productivity results in the literature suggest that CA increases yield in certain circumstances such as well-drained soils and moderate rainfall, and that poorly drained soils in combination with excessive rains lead to depressed yields. The yield benefits reported range from as low as 4% and as high as 16%, with negative effects also reported. Stability analysis used as a proxy for adaptation revealed only a marginal benefit of CA above conventional practices suggesting the significant effect of seasonal rainfall on crop productivity. The results suggest the need to target CA practices to different agroecologies and other pragmatic local agronomic practices that may be required in cases of excessive rainfall and extended mid-season dry spells. The benefits of CA reported are largely plot level, and only a few studies consider the whole farm, especially within the holistic livelihood framework. In addition, adoption of CA remains low among smallholder farmers, and the widespread benefits of the practices cannot be realized at multiple scales.