Entire Regime Research Articles

Studies on the melting dynamics of PCM in a semicircular cavity with straight and wavy heating surfaces

Several kinds of curved confinements for phase changing material storages are found application in natural systems, latent heat storages, metal furnaces, and thermal control devices. Semi-circular enclosures have an inherent advantage of decreasing unmelt volume on top with an increase in melt height when heated from bottom. Hence the melt dynamics differs from conventional rectangular enclosures of similar orientation and realizes faster thermal response during the entire regimes of melting. Experimental and numerical studies on Rayleigh Benard convection in a semi-circular enclosure having straight, corrugated, and wavy bottom surface with constant heat flux conditions are presented. Melt front evolution, thermal convection, and unsteady surface heat transfer characteristics of a phase changing material contained in a semicircular confinement are presented in this study. Enthalpy-porosity method based finite volume solver is used to simulate the unsteady thermal convection of PCM in semi-circular enclosure. Experimental thermal response at various locations inside the confinement and shadowgraph images are used to verify the numerical results quantitatively and qualitatively. Present results and correlations (103 < Ra < 109) are useful in design, analysis, and thermal characterization of PCM enclosures of minimum volume and better thermal response finding application in electronic cooling devices and latent energy storages.

Entropy engineering in I–V–VI2 family: a paradigm to bestow enhanced average ZT in the entire operating temperature regime

Highly symmetrical stabilized cubic structure in the operating temperature range of 300–800 K.

מאבק הממסד נגד הפעלת כוח משטרתי פסול בעשור הראשון למדינת ישראל

The use of unlawful force by British Mandate police was embedded into the Jewish consciousness as a symbol for the entire regime's inherent faults. In contrast, the desired image of the Israeli police force was shaped as the complete opposite: A police force whose actions are justified, enacts law and order, and applies force with restraint. Thus, as opposed to the Mandate's model of colonial policing founded on oppressive military components, the Israeli police, upon its inception, espoused – in theory, at least – the metropolitan model, based on the public's consent to its actions. In practice, however, this was not enough to uproot the phenomenon entirely: since the Israeli police's very first years, members of the Knesset, government and media have voiced their complaints about an unlawful use of force by police officers. Although it is difficult to gauge the true scope of the problem, the state had worked to fight it due to both its practical and symbolic severity. This study will focus on the measures taken by the police, Knesset and government – sometimes with the influence of public and media discussions and sometimes without it – to eradicate it, on three levels: educational – through training courses for new police officers that included laws, regulations and content defining proper use of force; legal – which involved disciplinary and criminal action against policemen who used unlawful force; and structural – which comprised of inquiry committees that examined the use of force by the police and its officers systemically. The failure of these efforts is often explained on a universal level using Brodeur's stance, that the use of force is tantamount to fighting fire with fire: fighting an inherently wrong action by employing an equally wrong means of doing so. Our research will focus on the limited success of these efforts using a local analysis that focuses on Israeli police and society during the state's first decade: on the micro level, we will examine the characteristics of police officers, while the macro level will follow the broad political and social contexts of that time, which led to a reproduction of mandatory-military practices even within a police force that raised the banner of civic policing.

Energy build-up factors estimation for BaZr0.10Ti0.90O3, Ba0.90La0.10TiO3 and Ba0.90La0.10Zr0.10Ti0.90O3 ceramics in shielding applications

The search for materials that serve as good shields for radiation has become very important in light of the increasing exposure to ionizing radiation in various vital sectors. The aim is to search for novel materials with better radiation shielding properties that are stable, nontoxic, and abundant and environment friendly. The solid-state reaction approach has been used to synthesize a few ceramics, including BaZrXTi1-XO3, Ba1-XLaXTiO3 and Ba1-XLaXZrXTi1-XO3 (with x = 0.10) i.eBaZr0.10Ti0.90O3 (BZT), Ba0.90La0.10TiO3 (BLT), and Ba0.90La0.10Zr0.10Ti0.90O3 (BLZT). The density of the prepared samples varies from 6.3471 to 11.6003 g/cm3. The X-ray diffraction technique, shows strong peaks to confirm the crystalline structure of prepared ceramic samples. Using the G-P fitting approach, the advanced radiation shielding parameters (build-up factor) have been evaluated in the photon energy region of 1.5 keV–15 MeV. It is observed from the results that exposure buildup factor (EBF) and energy absorption buildup factor (EABF) are maximum for BLZT and has the minimum value for BZT in the entire photon energy regime. The results of this work should be useful in radiation shielding applications such as in industry, medicine, and nuclear engineering.

A seismologically consistent surface rupture length model for unbounded and width-limited events

A new surface-rupture-length (SRL) relationship as a function of magnitude [Formula: see text], fault thickness, and fault dip angle is presented in this article. The objective of this study is to model the change in scaling between unbounded and width-limited ruptures. This is achieved through the use of seismological-theory-based relationships for the average displacement scaling and the aid of dynamic fault rupture simulations to constrain the rupture width scaling. The empirical data set used in the development of this relationship is composed of [Formula: see text] events ranging from [Formula: see text] 5 to [Formula: see text] and SRL 1.1 to 432 km. The dynamic rupture simulations data set includes [Formula: see text] events ranging from [Formula: see text] 4.9 to 8.2 and [Formula: see text] 1 to 655 km. For the average displacement [Formula: see text] scaling, three simple models and two composite models were evaluated. The simple average displacement models are a square root of the rupture area [Formula: see text], a down-dip width [Formula: see text], and a rupture length [Formula: see text] proportional model. The two composite models have a [Formula: see text] scaling for unbounded ruptures and transition to [Formula: see text] and [Formula: see text] scaling for width-limited events, respectively. The empirical data favors a [Formula: see text] scaling for the entire regime (unbounded and width-limited ruptures) followed by a [Formula: see text] scaling for unbounded that changes to [Formula: see text] scaling for width-limited ruptures. The selected models exhibit better predictive performance compared to linear [Formula: see text] type models, especially in the large magnitude range, which is dominated by width-limited events. A comparison with published SRL models shows consistent scaling for different fault types and tectonic environments.

The equivalence between BE-LSE and NS-LSEs under continuum assumption

The linear stability theory, which is based on the Navier–Stokes equations, has been extensively studied in the field of hydrodynamic stability. However, due to the continuum assumption, there exist various limitations when attempting to solve problems that involve rarefaction effects. In contrast, based on kinetic theory, the Boltzmann equation is well-suited for analyzing linear stability throughout the entire regime, ranging from continuous to rarefied flows. In this paper, a linear stability equation derived from the Boltzmann–Bhatnagar–Gross–Krook (Boltzmann-BGK) equation is introduced, and the relationship between small perturbations of the velocity distribution function and macroscopic physical variables is established. Under the continuum assumption, the linear stability equation based on the Boltzmann equation (BE-LSE) and the linear stability equations based on the Navier–Stokes equations (NS-LSEs) have the same numerical solutions, which indicates that the microscopic BE-LSE can recover to macroscopic NS-LSEs theoretically. Nevertheless, there is still a lack of mathematical proof for this theoretical outcome. To address this issue, the research on the equivalence of BE-LSE and NS-LSEs under continuum assumption is carried out in this paper, which can establish the theoretical relationship between BE-LSE and NS-LSEs. These efforts lay a solid theoretical foundation for stability research based on the BE-LSE.

Flow Rate Dependency of Steady-State Two-Phase Flows in Pore Networks: Universal, Relative Permeability Scaling Function and System-Characteristic Invariants

The phenomenology of steady-state two-phase flow in porous media is conventionally recorded by the relative permeability diagrams in terms of saturation. Yet, theoretical, numerical and laboratory studies of flow in artificial pore network models and natural porous media have revealed a significant dependency on the flow rates—especially when the flow regime is capillary to capillary/viscous and part of the disconnected non-wetting phase remains mobile. These studies suggest that relative permeability models should incorporate the functional dependence on flow intensities. In the present work, a systematic dependence of the pressure gradient and the relative permeabilities on flow rate intensity is revealed. It is based on extensive simulations of steady-state, fully developed, two-phase flows within a typical 3D model pore network, implementing the DeProF mechanistic–stochastic model algorithm. Simulations were performed across flow conditions spanning 5 orders of magnitude, both in the capillary number, Ca, and the flow rate ratio, r, and for different favorable /unfavorable viscosity ratio fluid systems. The systematic, flow rate dependency of the relative permeabilities can be described analytically by a universal scaling function along the entire domain of the independent variables of the process, Ca and r. This universal scaling comprises a kernel function of the capillary number, Ca, that describes the asymmetric effects of capillarity across the entire flow regime—from capillarity-dominated to mixed capillarity/viscosity- to viscosity-dominated flows. It is shown that the kernel function, as well as the locus of the cross-over relative permeability values, are single-variable functions of the capillary number; they are both identified as viscosity ratio invariants of the system. Both invariants can be correlated with the structure of the pore network, through a function of Ca. Consequently, the correlation is associated with the wettability characteristics of the system. Among the potential applications, the proposed, universal, flow rate dependency scaling laws are the improvement of core analysis and dynamic rock-typing protocols, as well as integration into field-scale simulators or associated machine learning interventions for improved specificity/accuracy.

Defect Chemistry of Spinel Cathode Materials-A Case Study of Epitaxial LiMn2O4 Thin Films.

Spinels of the general formula Li2-δM2O4 are an essential class of cathode materials for Li-ion batteries, and their optimization in terms of electrode potential, accessible capacity, and charge/discharge kinetics relies on an accurate understanding of the underlying solid-state mass and charge transport processes. In this work, we report a comprehensive impedance study of sputter-deposited epitaxial Li2-δMn2O4 thin films as a function of state-of-charge for almost the entire tetrahedral-site regime (1 ≤ δ ≤ 1.9) and provide a complete set of electrochemical properties, consisting of the charge-transfer resistance, ionic conductivity, volume-specific chemical capacitance, and chemical diffusivity. The obtained properties vary by up to three orders of magnitude and provide essential insights into the point defect concentration dependences of the overall electrode potential. We introduce a defect chemical model based on simple concentration dependences of the Li chemical potential, considering the tetrahedral and octahedral lattice site restrictions defined by the spinel crystal structure. The proposed model is in excellent qualitative and quantitative agreement with the experimental data, excluding the two-phase regime around 4.15 V. It can easily be adapted for other transition metal stoichiometries and doping states and is thus applicable to the defect chemical analysis of all spinel-type cathode materials.

Parallel arrays of clay nanosheets sandwiched in two-dimensional nanofluidic membrane for enhanced ion transport properties

High ion selectivity and high structural stability have always been the pursuit of nanofluidic ion exchange membranes but they are often trade-offs. Herein, we built a sandwich structure by introducing parallel arrays of clay nanosheets in two-dimensional nanofluidic membrane to improve the ion transport performance. The introduction of an appropriate amount of clay nanosheets can not only redistributes internal stress and thereby increases the tensile strength but also provides higher surface charge density and thereby effectively increases ion selectivity of the membrane. The current density obtained from the sandwich structure membrane is ∼5 times than that of the homogeneous membrane and the cation mobility can reach a maximum of 0.98. When simulating the energy conversion of seawater and river water, the maximum output power density achieved through the membrane is 0.70 W m−2, which is increased by ∼6 times. Interestingly, it significantly weakens the internal resistance from 100 to 30 kΩ and the energy barriers from 4.56 to 2.13 kJ mol−1 of ion permeation in the entire regime although the clay nanosheets arrays increases the thickness of the membrane. This strategy of introducing negatively charged nanosheets of natural minerals to enhance ion transport properties provides a new idea for the enhancement and application of salinity gradient energy harvesting membranes.

Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments.

Frequency-dependent dielectric relaxation in three deep eutectic solvents (DESs), (acetamide+LiClO4/NO3/Br), was investigated in the temperature range, 329 ≤ T/K ≤ 358, via molecular dynamics simulations. Subsequently, decomposition of the real and the imaginary components of the simulated dielectric spectra was carried out to separate the rotational (dipole-dipole), translational (ion-ion), and ro-translational (dipole-ion) contributions. The dipolar contribution, as expected, was found to dominate all the frequency-dependent dielectric spectra over the entire frequency regime, while the other two components together made tiny contributions only. The translational (ion-ion) and the cross ro-translational contributions appeared in the THz regime in contrast to the viscosity-dependent dipolar relaxations that dominated the MHz-GHz frequency window. Our simulations predicted, in agreement with experiments, anion-dependent decrement of the static dielectric constant (ɛs ∼ 20 to 30) for acetamide (ɛs ∼ 66) in these ionic DESs. Simulated dipole-correlations (Kirkwood g factor) indicated significant orientational frustrations. The frustrated orientational structure was found to be associated with the anion-dependent damage of the acetamide H-bond network. Single dipole reorientation time distributions suggested slowed down acetamide rotations but did not indicate presence of any "rotationally frozen" molecule. The dielectric decrement is, therefore, largely static in origin. This provides a new insight into the ion dependence of the dielectric behavior of these ionic DESs. A good agreement between the simulated and the experimental timescales was also noticed.

Thermophoresis beyond Local Thermodynamic Equilibrium.

We measure the thermophoresis of polysterene beads over a wide range of temperature gradients and find a pronounced nonlinear phoretic characteristic. The transition to the nonlinear behavior is marked by a drastic slowing down of thermophoretic motion and is characterized by a Péclet number of order unity as corroborated for different particle sizes and salt concentrations. The data follow a single master curve covering the entire nonlinear regime for all system parameters upon proper rescaling of the temperature gradients with the Péclet number. For low thermal gradients, the thermal drift velocity follows a theoretical linear model relying on the local-equilibrium assumption, while linear theoretical approaches based on hydrodynamic stresses, ignoring fluctuations, predict significantly slower thermophoretic motion for steeper thermal gradients. Our findings suggest that thermophoresis is fluctuation dominated for small gradients and crosses over to a drift-dominated regime for larger Péclet numbers in striking contrast to electrophoresis.

A Fluid Dynamic Development Like None Other

For more than 100 years, much uncertainty has surrounded fluid flow characteristics, both in open pipes and packed conduits. Not the least amongst this uncertainty has been the physics of the viscous boundary layer, in the former, and the so-called “wall-effect”, in the latter. Indeed, no fluid flow model has ever been able to reconcile both packed and empty conduits within the same theoretical framework, until now. In this paper, we describe the Quinn Fluid Flow Model (QFFM), which was first published in 2019 and represents the first model to capture, seamlessly, the physics of both empty and packed conduits, including all elements of wall-effects. This is not the only distinguishing feature of the model, which also includes, again, for the first time, a theoretical description of the so-called “constants” within the pressure flow relationship in closed conduits. Consequently, this model enables fluid dynamic validation over the entire fluid flow regime from creeping flow, at low Reynolds number values, to fully turbulent, at high Reynolds number values. This unique feature is possible because, on the one hand, in empty conduits, extremely large Reynolds number values are achievable at reasonable pressure drops but, very low Reynolds number values are not, due to the pressure drops being prohibitively low. In packed conduits, on the other hand, very low Reynolds number values are achievable at reasonable pressure drops but, large Reynolds number values are not, due to the pressure drops being prohibitively high. Accordingly, the QFFM enables simultaneous validation, at high Reynolds number values in the former and, at low Reynolds number values in the latter. This characteristic, therefore, to validate over the entire fluid flow regime using the same underlying physical and mathematical framework, sets this fluid flow model apart from all others. In addition to highlighting the many features of the QFFM in this paper, we will also demonstrate a comprehensive validation over ten orders of magnitude of the Reynolds number using published classical studies, as well as home grown experiments. To our knowledge, no extant fluid flow model comes even close to this comprehensive description of the fluid dynamics of fluid flow, not only in closed conduits, but also, by extrapolation, in other applications outside of this very narrow field of study.

A Parametric Study of the Bouc–Wen Model for Bolted Joint Dynamics

AbstractBuilt-up structures exhibit nonlinear dynamic phenomena due to friction at the surfaces that are held together using mechanical fasteners. This nonlinearity is hysteretic or history dependent. Additionally, interfacial slip results in stiffness and damping variations that are dependent on the vibration amplitude. In the microslip regime, the dissipation varies as a power of the amplitude. The four-parameter Iwan model can capture both the hysteretic and power-law dissipation behavior that is characteristic of many bolted joints. However, simulating the dynamic response of this model is computationally expensive since the states of several slider elements must be tracked implicitly, necessitating the use of fixed-step integration schemes with small time-steps. The Bouc–Wen model is an alternative hysteretic model in which the restoring force is given by a first-order nonlinear differential equation. Numerical integration of this model is much faster because it consists of just one additional state variable, i.e., the hysteretic variable. Existing literature predominantly focuses on studying the steady-state behavior of this model. This paper tests the effectiveness of the Bouc–Wen model in capturing power-law dissipation by comparing it to four-parameter Iwan models with various parameters. Additionally, the effect of each Bouc–Wen parameter on the overall amplitude-dependent damping is presented. The results show that the Bouc–Wen model cannot capture power-law behavior over the entire microslip regime, but it can be tuned to simulate the response over a smaller amplitude range.

Strong Scattering from Low-Frequency Rattling Modes Results in Low Thermal Conductivity in Antimonide Clathrate Compounds

Recent discoveries of materials with ultralow thermal conductivity open a pathway to significant developments in the field of thermoelectricity. Here, we conduct a comparative study of three chemically similar antimonides to establish the root causes of their extraordinarily low thermal conductivity (0.4–0.6 W m–1 K–1 at 525 K). The materials of interest are the unconventional type-XI clathrate K58Zn122Sb207, the tunnel compound K6.9Zn21Sb16, and the type-I clathrate K8Zn15.5Cu2.5Sb28 discovered herein. Calculations of the phonon dispersions show that the type-XI compound exhibits localized (i.e., rattling) phonon modes with unusually low frequencies that span the entire acoustic regime. In contrast, rattling in type I clathrate is observed only at higher frequencies, and no rattling modes are present in the tunnel structure. Modeling reveals that low-frequency rattling modes profoundly limit the acoustic scattering time; the scattering time of the type-XI clathrate is half that of the type-I clathrate and a quarter of that of the tunnel compound. For all three materials, the thermal conductivities are additionally suppressed by soft framework bonding that lowers the acoustic group velocities and structural complexity that leads to diffusonic character of the optical modes. Understanding the details of thermal transport in structurally complex materials will be crucial for developing the next generation of thermoelectrics.

Способы регулирования температуры приборного оборудования с помощью контурной тепловой трубы

The paper considers two ways of maintaining temperature of the instrumentation equipment: using the heat pipes equipped with thermoelectric cooling plate on the compensation cavity and the control valve installed at the outlet of the evaporating radiator. Since the temperature of the contour heat pipe is mainly controlled by the temperature of the compensation cavity positioned behind the evaporator, maintaining the high-precision temperature mode of this device is an urgent task for the entire spacecraft thermal regime. In the first method, the evaporating radiator is heated or cooled depending on the plate device polarity. In the second, the compensation chamber temperature could be changed using the steam supplied to the compensation cavity by a regulator installed at the outlet of the evaporator. Temperature control using a valve is due to the fact that the steam of the working fluid enters the bellows under pressure, which depends on the temperature in the evaporator. Pressure difference between steam and gas causes the bellows to contract and expand, while the valve associated with it partially closes the openings in the housing, through which the steam enters the condenser and the compensation cavity. Detailed description of these devices operation is provided, and thermal hydraulic models of the contour heat pipes equipped with these two devices are compiled.

Evaluation of radiation shielding parameters of SiO2-Na2O-K2O-P2O5-BaO glass system

Different glasses i.e. 20 SiO2-7.5 Na2O- 7.5 K2O- (65-x) P2O5- x BaO, have been synthesized using melt quench technique. The glass formation has been confirmed using X-Ray diffraction technique. The advance radiation shielding parameters (Build-up factor) has been evaluating using G-P fitting method. It is observed from results that EBF and EABF are maximum for GBa1 and minimum for GBa4 glass sample in the entire photon energy regime. Results revealed that EBF and EABF varies non-linearly in low photon energy regime due to photoelectric effect absorption role composition dependence. Whereas EBF and EABF, varies nearly linear in the mid and higher photon energy regions due to lower and insignificant compositional dependence respectively. Radiation analysis inferred that GBa4 containing 10 mol.% BaO is the most appropriate among other samples for absorption properties.

A 1D1V Continuum Vlasov–Poisson Multipactor Analysis From Onset to Saturation Across the Entire First-Order Multipactor Regime

This report employs a Vlasov–Poisson model to elucidate fundamental electron phase–space mechanics of a multipactor discharge from onset to saturation. At the onset of multipactor, the electron phase–space is primarily defined by sharp features in both the physical space and energy space. With increasing electron density, space-charge effects lead to debunching of the swarm in phase–space. The temporal evolution of the electron energy distribution is studied across a single impact cycle. The average and peak-to-peak saturation values for the entire first-order multipactor regime are presented. Comparisons between the third- and fifth-order multipactors highlight the nuanced similarities and differences in the energy distribution of the multipacting system. The Vlasov–Poisson approach, which neglects collisions, is well suited for such analysis since the multipactor phenomenon occurs under near-vacuum collisionless conditions. It also overcomes difficulties associated with kinetic schemes that require adequately sampling all of the electron phase–space, including sparely populated regions, or special treatments to model strong growths in carrier densities.

Functional central limit theorems for Wigner matrices

We consider the fluctuations of regular functions f of a Wigner matrix W viewed as an entire matrix f(W). Going beyond the well-studied tracial mode, Trf(W), which is equivalent to the customary linear statistics of eigenvalues, we show that Trf(W)A is asymptotically normal for any nontrivial bounded deterministic matrix A. We identify three different and asymptotically independent modes of this fluctuation, corresponding to the tracial part, the traceless diagonal part and the off-diagonal part of f(W) in the entire mesoscopic regime, where we find that the off-diagonal modes fluctuate on a much smaller scale than the tracial mode. As a main motivation to study CLT in such generality on small mesoscopic scales, we determine the fluctuations in the eigenstate thermalization hypothesis (Phys. Rev. A 43 (1991) 2046–2049), that is, prove that the eigenfunction overlaps with any deterministic matrix are asymptotically Gaussian after a small spectral averaging. Finally, in the macroscopic regime our result also generalizes (Zh. Mat. Fiz. Anal. Geom. 9 (2013) 536–581, 611, 615) to complex W and to all crossover ensembles in between. The main technical inputs are the recent multiresolvent local laws with traceless deterministic matrices from the companion paper (Comm. Math. Phys. 388 (2021) 1005–1048).

Time–frequency fusion for enhancement of deep learning-based physical layer identification

Existing studies on deep learning-based physical layer identification have mainly exploited raw in-phase/ quadrature (IQ) samples or power spectral density (PSD) samples as inputs independently. The raw IQ and PSD samples represent the information in the time and frequency domains, respectively. It has been observed from the results of existing studies that identification using raw IQ samples outperforms that using PSD in low signal-to-noise ratio (SNR) regimes, and that identification using PSD outperforms that using raw IQ in high SNR regimes. In this paper, we propose to use the fusion of raw IQ and PSD samples to enhance deep learning-based physical layer identification. In particular, we design three general fusion frameworks, i.e., input, feature, and decision fusions, and integrate them with three typical deep neural network architectures of fully connected neural network, convolutional neural network, and recurrent neural network to form fusion identification schemes. We conduct experiments using 50 off-the-shelf Wi-Fi devices to validate the concerned fusion schemes and investigate their performance gains in identification and model training. Our experimental results verify that the proposed fusion identification schemes can achieve comparable or superior identification performances to the state-of-the-art schemes in the entire SNR regime. Moreover, for the considered fusion schemes, we further investigate the impacts of fusion strategies, deep-learning networks, and SNR conditions on the identification performance and training time.

Secure Data Processing Technology of Distribution Network OPGW Line with Edge Computing

Promoted by information technology and scalable information systems, the network design and communication method of optical fiber composite overhead ground wire (OPGW) have been in great progress recently. As the overhead transmission line has strict requirements on the outer diameter and weight of OPGW, it is of vital importance to perform the physical-layer secure data processing for the distribution network OPGW line with edge computing. To this end, we examine a physical-layer secure distribution network OPGW with edge computing in this article, where there exists one transmitter S, one receiver D, one authorized legitimate monitor LM, and an interfering node I. To better analyze the system performance, we firstly give the definition of the system outage probability, based on the secure data rate. Then, we evaluate the system performance for the distribution network OPGW, by deriving analytical outage probability of secure data processing, to facilitate the system performance evaluation of secure data processing in the entire SNR regime. Finally, we demonstrate some simulation results to validate the analytical results on the physical-layer secure distribution network OPGW line with edge computing.