Search

The in-plane thermal conductivity of hexagonal boron nitride (h-BN) with varying thicknesses is a key property that affects the performance of various applications from electronics to optoelectronics. However, the transition of the thermal conductivity from two-dimensional (2D) to three-dimensional (3D) h-BN remains elusive. To answer this question, we have developed a machine learning interatomic potential within the neuroevolution potential (NEP) framework for h-BN, achieving a high accuracy akin to ab initio calculations in predicting its thermal conductivity and phonon transport from monolayer to multilayers and bulk. Utilizing molecular dynamics simulations based on the NEP, we predict the thermal conductivity of h-BN with a thickness up to ∼100 nm, demonstrating that its thermal conductivity quickly decreases from the monolayer and saturates to the bulk value above four layers. The saturation of its thermal conductivity is attributed to the little change in phonon group velocity and lifetime as the thickness increases beyond four layers. In particular, the weak thickness dependence of phonon lifetime in h-BN with a nanoscale thickness results from its extremely high phonon focusing along the in-plane direction. This research bridges the knowledge gap of phonon transport between 2D and 3D h-BN and will benefit the thermal design and performance optimization of relevant applications. [ABSTRACT FROM AUTHOR]

We present experimental demonstration and modeling of mechanical wave propagation in a quasi-one-dimensional (quasi-1D) phononic crystal (PnC) waveguide (WG) constructed from a periodic array of single-crystal cubic-silicon carbide (3C-SiC) coupled micromechanical resonators, with an exceptional dynamic range exceeding 92 dB. The PnC design comprises 50 periodic cells, enabling the propagation of flexural mechanical waves in high-frequency and very-high-frequency bands, featuring a broad PnC bandgap spanning approximately 24–27.5 MHz. Furthermore, the 3C-SiC PnC WG exhibits excellent characteristics, including a high group velocity of 350 m/s and a low transmission loss of 0.69 dB/mm, enabling efficient guidance and support for mechanical waves across extended distances before reaching the noise level of the device. These attributes of the PnC WG, as demonstrated in this study, may open possibilities for the development of device platforms with applications in on-chip signal processing, sensing, and quantum transducer technologies. [ABSTRACT FROM AUTHOR]

We investigate the formation and transport of gas bubbles across a model porous electrode/catalyst using lattice Boltzmann simulations. This approach enables us to systematically examine the influence of a wide range of morphologies, flow velocities, and reaction rates on the efficiency of gas production. By exploring these parameters, we identify critical parameter combinations that significantly contribute to an enhanced yield of gas output. Our simulations reveal the existence of an optimal pore geometry for which the product output is maximized. Intriguingly, we also observe that lower flow velocities improve gas production by leveraging coalescence-induced bubble detachment from the electrode/catalyst. [ABSTRACT FROM AUTHOR]

Background: Local high-frequency percussive (HFP) massage has recently found widespread application in physical therapy. Although HFP massage reportedly improves range of motion (ROM), the mechanism underlying its action has not yet been proven. This study aimed to clarify whether a 5-minute percussive massage regimen affects muscular or connective tissues, such as the deep fascia and deep intermuscular fascia and the change in joint ROM. Method: The study sample was calculated using G*Power analysis program, and this study enrolled 15 healthy men who underwent 5-minute HFP massage to the medial gastrocnemius muscle. Shear-wave elastography was used to measure tissue stiffness in the deep fascia, muscle, and deep intermuscular fascia through shear-wave velocity as well as the ROM of the volunteers' ankle joint dorsiflexion before and after the HFP massage. A value of P < .05 was used to declare statistical significance, and post hoc was used to calculate the effect size using G*Power. Results: Shear-wave velocity revealed a significant change in the deep fascia (P = .003; shear-wave velocity: -0.7 m/s) and significant increase in ROM of ankle dorsiflexion (P = .002; increase in ROM: 3.0°) after 5 minutes of HFP massage. However, the muscle and deep intermuscular fascia did not exhibit any significant changes. Conclusions: HFP massage for 5 minutes modified the stiffness of the deep fascia and concurrently improved the ankle joint-dorsiflexion ROM. This method can be used as an intervention to decrease stiffness of the deep fascia and increase the ROM efficiently. [ABSTRACT FROM AUTHOR]

The propagation characteristics of magneto-quasistatic waves, more commonly, known as magnetostatic waves in a long, metallic rectangular waveguide filled with a metamaterial slab are comprehensively investigated. The metamaterial slab consists of split-ring resonators as an anisotropic uniaxial medium with transversal negative effective permeability. Some analytical relations and numerical validations on the characteristics of these waves are presented. The results include the dispersion relations, mode patterns (field distributions) that can be supported by such media, and their corresponding cutoff frequencies, group velocities, power flows, and storage energies of magnetostatic waves. The findings from the present research study can be advantageous to advance the synthesis and development of negative permeability materials with peculiar features in guiding structures. [ABSTRACT FROM AUTHOR]

Chemical shakers are active particles with zero propulsion velocity whose activity derives from chemical reactions on portions of their surfaces. Although they do not move, except through Brownian motion, the nonequilibrium concentration and velocity fields that they generate endow them with properties that differ from their equilibrium counterparts. In particular, collections of such shakers can actively move, reorient, and self-assemble into various cluster states, which are the subject of this paper. Elongated chemical shakers constructed from linked catalytic and noncatalytic spheres are considered, and it is shown how hydrodynamic, chemotactic, and shape-dependent interactions give rise to various self-assembled shaker structures. The chemical forces responsible for cluster formation are described in terms of a model based on pair-wise additive contributions. The forms of the self-assembled structures can be varied by changing the chemostat concentrations that control the nonequilibrium state. The resulting structures and their manipulation through chemical means suggest ways to construct a class of active materials for applications. [ABSTRACT FROM AUTHOR]

We present comprehensive numerical results from a study of model H, which describes phase separation kinetics in binary fluid mixtures. We study the pattern dynamics of both density and velocity fields in d = 2, 3. The density length scales show three distinct regimes, in accordance with analytical arguments. The velocity length scale shows a diffusive behavior. We also study the scaling behavior of the morphologies for density and velocity fields and observe dynamical scaling in the relevant correlation functions and structure factors. Finally, we study the effect of quenched random field disorder on spinodal decomposition in model H. [ABSTRACT FROM AUTHOR]

The influence of microstructure on the response of energetic structural materials (ESMs) under shock conditions remains inadequately quantified, and the energy release process is not thoroughly understood. In this work, taking the classical Ni/Al ESM as an example, the shock response was investigated by the shock compression theory with the microstructure-based chemical reaction kinetics model. This theory mainly refers to the equation of the state of multi-component materials with mixture rule, and the reaction at the particle contact interface is built to form the multiscale thermodynamics model. The physical states of material after shock, including relative volume, temperature, and extent of reaction, were analyzed. The results revealed the effect of the burn velocity, particle size and molar ratio on the shock response. Furthermore, the model facilitates a comprehensive understanding of energy release, the extent of the intermetallic reaction, and the oxidation reaction. Despite the involvement of only a small portion of materials in the oxidation reaction, the energy release proportion was comparable to that of the intermetallic reaction. Additionally, insights into the effect of the microstructure on the energy release revealed by the model matched the tests well. [ABSTRACT FROM AUTHOR]

Crossed-Field Vacuum Electron Devices are ubiquitous in the High-Power Microwave field in either an oscillator/source or amplifier variant. A typical configuration consists of a magnetically insulated laminar electron flow in an anode–cathode gap with crossed electric (∝ V , voltage) and magnetic (B-) fields and a series of open resonant cavities/vanes located on the anode block that serve as a slow-wave structure (SWS). The SWS slows the phase velocity of the electromagnetic signal down so that the wave becomes synchronous with a layer of the electron flow but is often neglected when calculating the Hull magnetic field necessary to insulate the electrons. In particular, the guiding design equation for the critical cutoff B-field assumes a smooth anode wall. In this paper, we show that such an assumption severely narrows the operating regime in B–V space and that upon inclusion of a revised Hull Cutoff condition taking into account the SWS, operation at lower B and higher V is possible. This revised Hull Cutoff criterion for magnetic insulation in crossed-field devices is corroborated by Particle-in-Cell simulations using CST Particle Studio. [ABSTRACT FROM AUTHOR]

ReaxFF reactive force field bridges the gap between nonreactive molecular simulations and quantum mechanical calculations and has been widely applied during the past two decades. However, its application to earth materials, especially those under high T-P conditions relevant to Earth's interior, is still limited due to the lack of available parameters. Here, we present the development and validation of a ReaxFF force field containing several of the most common elements in Earth's crust, i.e., Si/Al/O/H/Na/K. The force field was trained against a large data set obtained from density functional theory (DFT) calculations, including charges, bond/angle distortion curves, equation of states, ion migration energy profiles, and condensation reaction energies. Different coordination environments were considered in the training set. The fitting results showed that the current force field can well reproduce the DFT data (the Pearson correlation coefficient, Rp, is 0.95). We validated the force field on mineral–water interfaces, hydrous melts/supercritical geofluids, and bulk crystals. It was found that the current force field performed excellently in predicting the structural, thermodynamic, and transport properties of various systems (Rp = 0.95). Moreover, possible applications and future development have been discussed. The results obtained in this study suggest that the current force field holds good promise to model a wide range of processes and thus open opportunities to advance the application of ReaxFF in earth material modeling. [ABSTRACT FROM AUTHOR]

The identification and analysis of quantum state-specific effects can significantly deepen our understanding of detailed photodissociation dynamics. Here, we report an experimental investigation on the vibrational state-mediated photodissociation of the OCS+ cation via the A2Π1/2 (ν1 0 ν3) states by using the velocity map ion imaging technique over the photolysis wavelength range of 263–294 nm. It was found that the electronically excited S+ product channel S+(2Du) + CO (X1Σ+) was significantly enhanced when the ν1 and ν3 vibrational modes were excited. Clear deviations in the branching ratios of the electronically excited S+ channel were observed when the vibrational modes ν1 and ν3 were selectively excited. The results reveal that vibrationally excited states play a vital role in influencing the nonadiabatic couplings in the photodissociation process. [ABSTRACT FROM AUTHOR]

In this work, we detail a novel application of inverse design and advanced manufacturing to rapidly develop and experimentally validate modifications to a shaped charge jet analog. The shaped charge jet analog comprises a copper liner, a high explosive (HE), and a silicone buffer. We apply a genetic algorithm to determine an optimal buffer design that can be placed between the liner and the HE that results in the largest possible change in jet velocity. The use of a genetic algorithm allows for discoveries of unintuitive, complex, yet optimal buffer designs. Experiments using the optimal design verified the effectiveness of the buffer and validated the machine learning approach to hydrodynamic design optimization. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion bags are composite topological spin textures with arbitrary topological charges. Here, we computationally study the transient rotational motion of skyrmion bags, which is characterized by a global rotation of inner skyrmions around the central point. Distinct from conventional rotational modes found in skyrmions, the observed rotation is a forced motion associated with the breathing mode induced solely by vertical microwave fields. The driving force behind this rotation originates from the interactions between outer and inner skyrmions, with the angular velocity determined by the phase difference resulting from their asynchronous breathing behaviors. It is also found that skyrmion bags with larger skyrmion numbers are more conducive to the occurrence of the rotation. Our results are useful for understanding the cluster dynamics of complex topological spin textures driven by dynamic fields. [ABSTRACT FROM AUTHOR]

In this study, laser Directed Energy Deposition technology is employed to fabricate internal structures within the hollow interiors of rotating parts such as tubes and cylinders. A three-dimensional transient multiphysics model for C276 material was developed, which anticipated the impact of angular velocity from tube rotation on various aspects. This model, validated by experiments, focused on the melt pool morphology, Marangoni convection, oriented crystal microevolution, and deposited material microhardness. It was found that at 150 ms deposition, the dimensions of the melt pool stabilized. With an increase in the Peclet number, heat transfer within the melt pool transitioned from conduction to convection. A rise in angular velocity reduced the melt pool deposition height, limited by the volume of the deposited material. Additionally, this angular velocity generated tangential forces, leading to an asymmetric melt distribution in the longitudinal section of the melt pool and a movement of the melt toward the melting front. At the bottom of the melt pool, the growth of C276 columnar crystals was notably inclined toward the center of Marangoni convection. The microhardness of the deposited material showed a stable distribution along the inclined crystal direction, whereas significant fluctuations were observed perpendicular to the cylinder substrate. These findings highlighted the considerable effect of Marangoni convection on microstructural evolution. [ABSTRACT FROM AUTHOR]

The so-called velocity correlated cluster emission (VCCE) effect is the recently reported emission of large clusters with nearly the same velocity from an atomically heavy target (such as coinage metals) following a single C 60 − impact at the keV kinetic energy range. The effect was observed to get weaker for a meaningfully lighter target (Al) down to its complete disappearance for C60–Be impact. Microscopic insight into the subpicosecond evolution and thermalization of the impact induced energy spike (driving the effect) is achieved using molecular dynamics simulations. It is shown that the weakening of the VCCE effect for aluminum (toward its complete disappearance for Be) is due to ultrafast decay of the atomic number density within the spike nanovolume, thus not enabling the buildup of sufficient subsurface pressure as required for driving the correlated emission. For the Be target, an extremely rapid decay of nearly 90% of the initial density within 200 fs from impact is observed. This finding provides further support for the conclusion that the emission of the velocity correlated clusters as observed for the heavier targets takes place within an ultra-short time window of only a few hundreds of femtoseconds, roughly extending from 200 to 500 fs from impact. The lower bound is dictated by the requirement for a relatively slow rate of decay of number density, enabling the buildup of a sufficiently intense pressure spike. The upper bound is dictated by the cooling rate of the spike (still maintaining an extremely high temperature of kT ≥ 1 eV, as experimentally observed) and the onset of the evolution of the impact crater. [ABSTRACT FROM AUTHOR]

The band-anticrossing (BAC) model provides the basis for the self-consistent Green's function method that we have previously developed to calculate the density of states of GaN x As 1 − x dilute nitride alloys. In this paper, we extend this Green's function method to include the complex energy states and to find the poles of the Green's function, thereby allowing one to calculate the dispersion relation, group velocity, and the carrier decay rate in disordered dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the conventional two-band BAC model, which assumes that all N states are located at the same energy, and (2) a model which includes N states distributed over a range of energies, as expected in actual dilute nitride samples. Our results for the second model show a much shorter carrier mean-free path, and lower carrier mobility for GaN x As 1 − x , with the magnitude of the calculated mobility in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness. [ABSTRACT FROM AUTHOR]

We present a derivation from the first principles of the coupled equations of motion of an active self-diffusiophoretic Janus motor and the hydrodynamic densities of its fluid environment that are nonlinearly displaced from equilibrium. The derivation makes use of time-dependent projection operator techniques defined in terms of slowly varying coarse-grained microscopic densities of the fluid species number, total momentum, and energy. The exact equations of motion are simplified using time scale arguments, resulting in Markovian equations for the Janus motor linear and angular velocities with average forces and torques that depend on the fluid densities. For a large colloid, the fluid equations are separated into bulk and interfacial contributions, and the conditions under which the dynamics of the fluid densities can be accurately represented by bulk hydrodynamic equations subject to boundary conditions on the colloid are determined. We show how the results for boundary conditions based on continuum theory can be obtained from the molecular description and provide Green–Kubo expressions for all transport coefficients, including the diffusiophoretic coupling and the slip coefficient. [ABSTRACT FROM AUTHOR]

Using nonequilibrium molecular dynamics (NEMD) based direct method and spectral energy density (SED) method, we calculate the size-dependent thermal conductivities (TCs) of single layer graphene (SLG), AB-stacked bilayer graphene (AB-BLG), and 21.78 ° twisted BLG (tBLG) in a robust and consistent manner. Our NEMD analysis reveals discrepancies in high TC reported for graphene systems in some of the earlier studies. Similarly, some of the previous SED based studies were done with unreliable SED Φ ′ approach. We conduct size-dependent analysis of the graphene systems by the SED method for the first time and report that bulk TCs for SLG and tBLG systems are nearly the same when calculated by either the direct or the SED method. Contrary to studies that claim that phonon group velocities of AB-BLG and tBLG samples do not change, we find that although average group velocities in SLG and AB-BLG are almost the same, they are around 30% higher when compared to tBLG samples with different twist angles. On the other hand, average phonon lifetimes are almost similar for AB-BLG and 21.78 ° tBLG samples but around 43% lower than the average phonon lifetime of SLG. Together these trends suggest the reason behind the decreasing order of TCs across three systems. We also systematically study the basic phonon mode contributions to TCs and their properties and find that the high-symmetry modes contribute the most in all three systems. [ABSTRACT FROM AUTHOR]

In this work, we calculated the lattice thermal conductivity of monolayer InTe by means of phonon Boltzmann transport theory with first-principles calculated inter-atomic force constants. The higher-order phonon anharmonicity was found to play a strong impact on thermal transport in InTe. With the involvement of the phonon–phonon scattering process up to the fourth-order, the in-plane lattice thermal conductivity of monolayer InTe is 5.1 W m−1 K−1 at room temperature, which is 35% of that considering only third-order force constants. Furthermore, strain was found to be an effective way to manipulate the thermal transport in InTe, which reduces to one half when applying 5% in-plane tensile strain. The strain adjustment is due to the decreases in the phonon group velocity as well as the increase in the phonon scattering rates. These findings can enrich thermal transport properties of group-III monochalcogenides and benefit the material design of thermoelectrics and thermal management electronic devices. [ABSTRACT FROM AUTHOR]

The study of granular avalanches in rotating drums is not only essential to understanding various complex behaviors of interest in granular media from a scientific perspective; it also has valuable applications in regard to industrial processes and geological catastrophes. Despite decades of research studies on avalanches, a proper understanding of their dynamic properties still remains a great challenge to scientists due to a lack of state-of-the-art techniques. In this study, we accurately predict the avalanche dynamic features of three-dimensional granular materials in rotating drums, by using graph neural networks on the basis of their initial static microstructures alone. We find that our method is robust to changes in various model parameters, such as the interaction potential, size polydispersity, and noise in particle coordinates. In addition, with the grain-scale velocities obtained either from our network or from numerical simulations, we find an approximately equal and strong correlation between the global velocity and global velocity fluctuation in our 3D granular avalanche systems, which further demonstrates the predictive power of our trained graph neural networks to uncover the fundamental physics of granular avalanches. We expect our method to provide more insight into the avalanche dynamics of granular materials and other amorphous systems in the future. [ABSTRACT FROM AUTHOR]

The solid-state synthesized dense ceramic composite, consisting of M-type hexaferrite Ba 0.5 Sr 0.5 Fe 12 O 19 and inverse spinel ferrite Ni 0.3 Co 0.2 Zn 0.5 Fe 2 O 4 (NCZFO) with varying concentrations, demonstrates the presence of apparent colossal permittivity along with dielectric relaxation behaviors at the higher frequency regions for all the composites. This phenomenon manifests as a giant dielectric permittivity of approximately 10 5 at 1 kHz, gradually decreasing to around 10 3 at 1 MHz at room temperature. It can be attributed to the Maxwell–Wagner interfacial polarization, which arises from the presence of different conductivity regions within the microstructures of the composite. The dielectric permittivity and the activation energy are also increased with higher NCZFO content, indicating an intricate microstructure influencing the electrical response by impacting charge carrier movement and ion migration. The presence of both Fe and Co cation defects and oxygen vacancies enhanced non-uniformity in the microstructure with different conductivity regions. The appearance of relaxation peaks in the higher frequency region can be attributed to inhomogeneity in the microstructure. In conjunction with the equivalent circuit analysis, the Nyquist plot confirmed that the electrical response at a lower frequency primarily arises from grain boundaries. The departure from ideal Debye-type relaxation behavior in the electrical response is also confirmed by impedance analysis. Furthermore, the step-like increase in AC conductivity with frequency suggests that the electrical response observed at a lower frequency is not intrinsic. Rather, it indicates the depletion of insulating grain boundaries due to diffusive ion motions resulting from defects. This observation reinforces that the high dielectric permittivity observed in the composite is not an inherent characteristic of the constituent materials. Instead, it arises from the microstructure and the influence of defects within the material. [ABSTRACT FROM AUTHOR]

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum. [ABSTRACT FROM AUTHOR]

Bipolar gradual resistive switching was investigated in ITO/InGaZnO/ITO resistive switching devices. Controlled intrinsic oxygen vacancy formation inside the switching layer enabled the establishment of a stable multilevel memory state, allowing for RESET voltage control and non-degradable data endurance. The ITO/InGaZnO interface governs the migration of oxygen ions and redox reactions within the switching layer. Voltage–stress-induced electron trapping and oxygen vacancy formation were observed before conductive filament electroforming. This device mimicked biological synapses, demonstrating short- and long-term potentiation and depression through electrical pulse sequences. Modulation of post-synaptic currents and pulse frequency-dependent short-term potentiation were successfully emulated in the InGaZnO-based artificial synapse. The ITO/InGaZnO/ITO memristor exhibited spike–amplitude-dependent plasticity, spike–rate-dependent plasticity, and potentiation–depression synaptic learning with low energy consumption, making it a promising candidate for large-scale integration. [ABSTRACT FROM AUTHOR]

Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks. Each periarterial element is modeled as a slender annular space bounded internally by a circular tube supporting a periodic traveling (peristaltic) wave. Under reasonable assumptions of a small Reynolds number flow, small radii, and small-amplitude peristaltic waves, we use lubrication theory and regular perturbation methods to derive theoretical expressions for the directional net flow and pressure distribution in the perivascular network. The reduced model is used to derive closed-form analytical expressions for the net flow for simple network configurations of interest, including single elements, two elements in tandem, and a three element bifurcation, with results compared with numerical predictions. In particular, we provide a computable theoretical estimate of the net flow induced by peristaltic motion in perivascular networks as a function of physiological parameters, notably, wave length, frequency, amplitude, and perivascular dimensions. Quantifying the maximal net flow for specific physiological regimes, we find that vasomotion may induce net pial periarterial flow velocities on the order of a few to tens of μ m/s and that sleep-related changes in vasomotion pulsatility may drive a threefold flow increase. [ABSTRACT FROM AUTHOR]

Fluid-based methods for particle sorting demonstrate increasing appeal in many areas of biosciences due to their biocompatibility and cost-effectiveness. Herein, we construct a microfluidic sorting system based on a swirl microchip. The impact of microchannel velocity on the swirl stagnation point as well as particle movement is analyzed through simulation and experiment. Moreover, the quantitative mapping relationship between flow velocity and particle position distribution is established. With this foundation established, a particle sorting method based on swirl induction is proposed. Initially, the particle is captured by a swirl. Then, the Sorting Region into which the particle aims to enter is determined according to the sorting condition and particle characteristic. Subsequently, the velocities of the microchannels are adjusted to control the swirl, which will induce the particle to enter its corresponding Induction Region. Thereafter, the velocities are adjusted again to change the fluid field and drive the particle into a predetermined Sorting Region, hence the sorting is accomplished. We have extensively conducted experiments taking particle size or color as a sorting condition. An outstanding sorting success rate of 98.75% is achieved when dealing with particles within the size range of tens to hundreds of micrometers in radius, which certifies the effectiveness of the proposed sorting method. Compared to the existing sorting techniques, the proposed method offers greater flexibility. The adjustment of sorting conditions or particle parameters no longer requires complex chip redesign, because such sorting tasks can be successfully realized through simple microchannel velocities control. [ABSTRACT FROM AUTHOR]

Reactive burn models for heterogeneous energetic materials (EMs) must account for chemistry as well as microstructure to predict shock-to-detonation transition (SDT). Upon shock loading, the collapse of individual voids leads to ignition of hotspots, which then grow and interact to consume the surrounding material. The sub-grid dynamics of shock-void interactions and hotspot development are transmitted to macro-scale SDT calculations in the form of a global reactive "burn model." This paper presents a physically evocative model, called meso-informed sub-grid source terms for energy localization (MISSEL), to close the macro-scale governing equations for calculating SDT. The model parameters are explicitly related to four measurable physical quantities: two depending on the microstructure (the porosity ϕ and average pore size D ¯ v o i d ), one depending on shock–microstructure interaction (the fraction of critical voids ξ c r ), and the other depending on the chemistry (the burn front velocity V h s ). These quantities are individually quantifiable using a small number of rather inexpensive meso-scale simulations. As constructed, the model overcomes the following problems that hinder the development of meso-informed burn models: (1) the opacity of more sophisticated surrogate/machine-learning approaches for bridging meso- and macro-scales, (2) the rather large number of high-resolution mesoscale simulations necessary to train machine-learning algorithms, and (3) the need for calibration of many free parameters that appear in phenomenological burn models. The model is tested against experimental data on James curves for a specific class of pressed 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane materials. The simple, evocative, and fast-to-construct MISSEL model suggests a route to develop frameworks for physics-informed, simulation-derived meso-informed burn models. [ABSTRACT FROM AUTHOR]

We consider a cylinder immersed in viscous fluid moving near a flat substrate covered by an incompressible viscoelastic fluid layer, and study the effect of the fluid viscoelasticity on the lift force exerted on the cylinder. The lift force is zero when the viscoelastic layer is not deformed, but becomes non-zero when it is deformed. We calculate the lift force by considering both the tangential stress and the normal stress applied at the surface of the viscoelastic layer. Our analysis indicates that as the layer changes from the elastic limit to the viscous limit, the lift force decreases with the decrease of the Deborah number (De). For small De, the effect of the layer elasticity is taken over by the surface tension and the lift force can become negative. We also show that the tangential stress and the interface slip velocity (the surface velocity relative to the substrate), which have been ignored in the previous analysis, give important contributions to the lift force. Especially for thin elastic layers, they give dominant contributions to the lift force. [ABSTRACT FROM AUTHOR]

The behavior of four algebraic closure models for anomalous electron transport is investigated using a fluid Hall thruster code. The models, which were selected because they have been previously described in the literature, are calibrated against a baseline experimental condition of a 9-kW-class magnetically shielded Hall thruster operating at 300 V and 15 A on xenon propellant. The extensibility of the models is then assessed by using this calibrated model to simulate three additional operating conditions—300 V and 30 A, 600 V and 15 A, and 300 V and 15 A operating on krypton propellant. The quality of the model prediction is quantified by comparing the model outputs to experimental measurements of discharge current, thrust, and ion velocity. It is found that while none of the models can predict the ion acceleration characteristics accurately, some compare favorably in terms of the scaling of thrust and discharge current across operating conditions. The limitations of the models are attributed to the coupling between the functional scaling of the closure models with respect to the local plasma properties and the fluid model. The role of the electron energy balance in this coupling is also highlighted. These results are discussed in the context of motivating improved closure models of the anomalous electron transport in Hall thrusters. [ABSTRACT FROM AUTHOR]

The Cattaneo–Vernotte model has been widely studied to take momentum relaxation into account in transport equations. Yet, the effect of reactions on the Cattaneo–Vernotte model has not been fully elucidated. At present, it is unclear how the current density associated with reactions can be expressed in the Cattaneo–Vernotte model. Herein, we derive a modified Cattaneo–Vernotte model by applying the projection operator method to the Fokker–Planck–Kramers equation with a reaction sink. The same modified Cattaneo–Vernotte model can be derived by a Grad procedure. We show that the inertial effect influences the reaction rate coefficient differently depending on whether the intrinsic reaction rate constant in the reaction sink term depends on the solute relative velocity or not. The momentum relaxation effect can be expressed by a modified Smoluchowski equation including a memory kernel using the Cattaneo–Vernotte model. When the intrinsic reaction rate constant is independent of the reactant velocity and is localized, the modified Smoluchowski equation should be generalized to include a reaction term without a memory kernel. When the intrinsic reaction rate constant depends on the relative velocity of reactants, an additional reaction term with a memory kernel is required because of competition between the current density associated with the reaction and the diffusive flux during momentum relaxation. The competition effect influences even the long-time reaction rate coefficient. [ABSTRACT FROM AUTHOR]

A model has been developed to predict the response of an eddy current flow meter (ECFM) to the passage of a non-conductive inclusion moving in a cylindrical tube filled with a liquid metal. The model can be solved analytically for small inclusion diameters and moderate AC frequencies of the excitation signal. This condition is expressed as v b S ω ≪ 1 , where v b is the dimensionless inclusion volume and S ω is a function of the ratio between the characteristic length of the system and the penetration depth of the magnetic field. The magnetic induction equation for this problem has also been solved numerically. A very good agreement between the analytical model and numerical solutions has been found for v b S ω ≪ 1. Two experimental setups have been designed. First, the ECFM model has been validated by comparing the response due to the passage of traveling beads of known diameters in a low melting point alloy. In a second experiment, the diameters of ascending argon bubbles have been estimated with the ECFM model. The numerical model predicts the gas volume with very good accuracy in the range of bubble diameters studied, between 1.5 and 6 mm, while the analytical model only deviates significantly from the experimental data when v b S ω ≳ 0.1. Moreover, we establish that the ECFM can also measure the radial deviation of the bubble trajectory, and the results are consistent with the theoretical limit for isolated bubbles between the regimes of oscillating/zigzag motion of ellipsoidal bubbles and non-oscillating motion of spherical bubbles. Another observation is that the dependence of the ECFM response on the shape of the bubble is negligible; indeed, the ECFM response is well approximated by a linear relation with the bubble volume as is assumed in the analytical model. Finally, an estimation of the terminal rising velocity of bubbles was also carried out. [ABSTRACT FROM AUTHOR]

While characterizing space-charge-limited current (SCLC) is important for numerous applications, no analytical solutions for SCLC with monoenergetic initial velocity exist for two-dimensional (2D) geometries. Here, we derive approximate closed-form solutions for uniform SCLC with monoenergetic emission of electrons in a 2D planar diode, where emission is restricted to a long patch of width W for electrodes separated by a distance D. We also derive a semiempirical approach for estimating the SCLC for these cases by treating the geometric and velocity correction factors as multiplicative corrections to the SCLC for a one-dimensional vacuum diode given by the Child–Langmuir (CL) law. We show that the SCLC for a finite patch with nonzero velocity can exceed the CL law by three orders of magnitude. The theoretically calculated SCLCs for various emission widths and initial velocities in the 2D diode agree well with particle-in-cell simulations using the over-injection method in XOOPIC; they agree with the semiempirical relationship for lower initial velocities. In the limit of high initial velocity, the geometry and velocity corrections to the CL law cannot be decoupled, invalidating the assumption of the semiempirical approach and causing it to diverge from the theoretical solution and XOOPIC simulations. These results provide valuable estimates for determining the onset of virtual cathode formation for photocathodes and thermionic cathodes, which operate in the over-injection regime to avoid beam quality degradation. [ABSTRACT FROM AUTHOR]

Context: Different resistance exercise determinants modulate the musculotendinous adaptations following eccentric hamstring training. The Nordic Hamstring Exercise (NHE) can be performed 2-fold: the movement velocity irreversibly increases toward the end of the range of motion or it is kept constant. Design: This cross-sectional study aimed to investigate if the downward acceleration angle (DWAangle) can be used as a classification parameter to distinguish between increasing and constant velocity NHE execution. Furthermore, the kinetic and kinematic differences of these 2 NHE execution conditions were examined by analyzing the DWAangle in relation to the angle of peak moment. Methods: A total of 613 unassisted NHE repetitions of 12 trained male sprinters (22 y, 181 cm, 76 kg) were analyzed. Results: The majority of analyzed parameters demonstrated large effects. NHEs with constant velocity (n = 285) revealed significantly higher impulses (P <.001; d = 2.34; + 61%) and fractional time under tension (P <.001; d = 1.29; +143%). Although the generated peak moments were significantly higher for constant velocity (P =.003; d = 0.29; +4%), they emerged at similar knee flexion angles (P =.167; d = 0.28) and revealed on average just low relationships to the DWAangle ( R mean 2 = 22.4 %). DWAangle highly correlated with the impulse ( R mean 2 = 60.8 %) and δ (DWAangle–angle of peak moment; R mean 2 = 83.6 %). Conclusions: Relating DWAangle to angle of peak moment assists to distinguish between significantly different NHE execution, which will potentially elicit different musculotendinous adaptations. These insights are essential for coaches and athletes to understand how to manipulate eccentric hamstring training to change its purpose. [ABSTRACT FROM AUTHOR]

We address the collision of two superfluid 4He droplets at non-zero initial relative velocities and impact parameters within the framework of liquid 4He time-dependent density functional theory at zero temperature. Despite the small size of these droplets (1000 He atoms in the merged droplet) imposed by computational limitations, we have found that quantized vortices may be readily nucleated for reasonable collision parameters. At variance with head-on collisions, where only vortex rings are produced, collisions with a non-zero impact parameter produce linear vortices that are nucleated at indentations appearing on the surface of the deformed merged droplet. Whereas for equal-size droplets, vortices are produced in pairs, an odd number of vortices can appear when the colliding droplet sizes are different. In all cases, vortices coexist with surface capillary waves. The possibility for collisions to be at the origin of vortex nucleation in experiments involving very large droplets is discussed. An additional surprising result is the observation of the drops coalescence even for grazing and distal collisions at relative velocities as high as 80 and 40 m/s, respectively, induced by the long-range van der Waals attraction between the droplets. [ABSTRACT FROM AUTHOR]

The design of novel materials requires a theoretical understanding of dynamical processes in the solid state, including polymorphic transitions and associated pathways. The organization of the potential energy landscape plays a crucial role in such processes, which may involve changes in the periodic boundaries. This study reports the implementation of a general framework for periodic condensed matter systems in our energy landscape analysis software, allowing for variation in both the unit cell and atomic positions. This implementation provides access to basin-hopping global optimization, the doubly nudged elastic band procedure for identifying transition state candidates, the missing connection approach for multi-step pathways, and general tools for the construction and analysis of kinetic transition networks. The computational efficacy of the procedures is explored using the state-of-the-art semiempirical method GFN1-xTB for the first time in this solid-state context. We investigate the effectiveness of this level of theory by characterizing the potential energy and enthalpy landscapes of several systems, including silicon, CdSe, ZnS, and NaCl, and discuss further technical challenges, such as translational permutation of the cell. Despite the expected limitations of the semiempirical method, we find that the resulting energy landscapes provide useful insight into solid-state simulations, which will facilitate detailed analysis of processes such as defect and ion migration, including refinement at higher levels of theory. [ABSTRACT FROM AUTHOR]

The velocity autocorrelation function (VACF) encapsulates extensive information about a fluid's molecular-structural and hydrodynamic properties. We address the following fundamental question: How well can a purely hydrodynamic description recover the molecular features of a fluid as exhibited by the VACF? To this end, we formulate a bona fide hydrodynamic theory of the tagged-particle VACF for simple fluids. Our approach is distinguished from previous efforts in two key ways: collective hydrodynamic modes and tagged-particle self-motion are modeled by linear hydrodynamic equations; the fluid's spatial velocity power spectrum is identified as a necessary initial condition for the momentum current correlation. This formulation leads to a natural physical interpretation of the VACF as a superposition of products of quasinormal hydrodynamic modes weighted commensurately with the spatial velocity power spectrum, the latter of which appears to physically bridge continuum hydrodynamical behavior and discrete-particle kinetics. The methodology yields VACF calculations quantitatively on par with existing approaches for liquid noble gases and alkali metals. Furthermore, we obtain a new, hydrodynamic form of the self-intermediate scattering function whose description has been extended to low densities where the Schmidt number is of order unity; various calculations are performed for gaseous and supercritical argon to support the general validity of the theory. Excellent quantitative agreement is obtained with recent MD calculations for a dense supercritical Lennard-Jones fluid. [ABSTRACT FROM AUTHOR]

The energy supply mode of a micro-cathodic arc thruster (μ-CAT) was adjusted based on the charge and discharge characteristics of the energy storage element, and the cathode discharge characteristics of μ-CAT were studied under different energy supply modes. We applied an electrical method to measure the discharge characteristics of μ-CAT, with an enhanced intensified charge coupled device spectrum detector to measure the plasma parameters of μ-CAT, allowing analysis of the internal logic among thruster plasma parameters, arc discharge characteristics, and thruster energy supply mode. The mechanisms of μ-CAT were analyzed and characteristics of accumulated discharge, energy distribution, and ion velocity distribution of thruster were compared under different energy supply modes to obtain the effect of the energy supply mode on the discharge characteristics of the interelectrode of μ-CAT. The results show that the energy supply mode of μ-CAT affected the ionization characteristics and ionization stability of the micro-cathodic arc thruster, causing a multistage ionization difference in the cathode metal target. This would not only affect the propulsion performance of the thruster, but also affect the change of the number of particles in the cathode region in a single discharge cycle. [ABSTRACT FROM AUTHOR]

The properties of bulk contribution to sum-frequency generation reflected and transmitted by a finite layer in a multilayer system are described. The leading term is essentially due to the processes emitting in the transmission geometry, in particular for macroscopic layers. For such transmission processes, phase mismatch leads to the production of interference fringes when the layer thickness or a wavelength is tuned, which may be mistaken for resonant processes inside or at the surface of the material. Experimental evidence of such fringes measured from centrosymmetric bulks is provided for a diamond window in the far infrared and suggested for other materials in previously published data. The existence of a stationary point in the phase mismatch, related to the group velocity mismatch, is shown to be the source of another pseudo-resonant process in centrosymmetric calcium and barium fluorides, for which theoretical predictions reproduce the experimental observations. [ABSTRACT FROM AUTHOR]

The nonadiabatic interactions between the C ̃ state and neighboring electronic states of SO2 have attracted much attention; however, the predissociation mechanisms are not yet completely understood. In this work, the predissociation dynamics of SO2 via its C ̃ state have been investigated at λ = 193–201 nm by using the time-sliced velocity map ion imaging technique. The translational energy distributions and the branching ratios of the O(3PJ=2,1,0) spin–orbit products at six photolysis wavelengths have been acquired. The SO(3Σ−) product population gradually decreases in v = 0 and increases in v = 2 as the photolysis wavelength decreases. The branching ratios of O(3P J=2,1,0) products are almost similar at most wavelengths, except at 194.8 nm. Our data suggest that the predissociation between 193 and 201 nm is via an avoided crossing between the C ̃ state and the repulsive triplet 23A′ state. The state-to-state dynamical pictures shown in this work provide a rigorous test of the potential energy surfaces (PESs) of the SO2 and the nonadiabatic couplings between these PESs. [ABSTRACT FROM AUTHOR]

The vibrationally excited reaction O(1D) + CHD3(ν1 = 1) has been investigated by crossed-molecular-beam experiments with a time-sliced velocity map imaging technique. Detailed and quantitative information is extracted on the C–H stretching excitation effects on the reactivity and dynamics of the title reaction, with the help of preparation of C–H stretching excited CHD3 molecules by direct infrared excitation. Experimental results show that the vibrational stretching excitation of the C–H bond almost does not affect the relative contributions between different dynamical pathways for all product channels. For the OH + CD3 product channel, the vibrational energy of the C–H stretching excited CHD3 reagent is channeled exclusively into the vibrational energy of the OH products. The vibrational excitation of the CHD3 reactant changes the reactivities for the ground-state and umbrella-mode-excited CD3 channels very modestly, while it significantly suppresses the corresponding CHD2 channels. For the CHD2(ν1 = 1) channel, the stretching excited C–H bond of the CHD3 molecule acts almost as a pure spectator. [ABSTRACT FROM AUTHOR]