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Crowd movement analysis (CMA) is a key technology in the field of public safety. This technology provides reference for identifying potential hazards in public places by analyzing crowd aggregation and dispersion behavior. Traditional video processing techniques are susceptible to factors such as environmental lighting and depth of field when analyzing crowd movements, so cannot accurately locate the source of events. Radar, on the other hand, offers all-weather distance and angle measurements, effectively compensating for the shortcomings of video surveillance. This paper proposes a crowd motion analysis method based on radar particle flow (RPF). Firstly, radar particle flow is extracted from adjacent frames of millimeter-wave radar point sets by utilizing the optical flow method. Then, a new concept of micro-source is defined to describe whether any two RPF vectors originated from or reach the same location. Finally, in each local area, the internal micro-sources are counted to form a local diffusion potential, which characterizes the movement state of the crowd. The proposed algorithm is validated in real scenarios. By analyzing and processing radar data on aggregation, dispersion, and normal movements, the algorithm is able to effectively identify these movements with an accuracy rate of no less than 88%.

We present a Mach 15 air flow over a blunt two-dimensional wedge simulated using the direct molecular simulation method. As electronically excited states are not modelled, the resulting air mixture around the wedge contains the electronic ground states only, namely ${\\rm N}_2(\\text {X}^1 \\varSigma _g^{+})$, ${\\rm O}_2(\\text {X}^3 \\varSigma _g^{-})$, ${\\rm NO}(\\text {X}^2\\varPi _r)$, ${\\rm N}(^4{\\rm S})$ and ${\\rm O}(^3{\\rm P})$. All the potential energy surfaces (PESs) that are used to model the various interactions between air particles are ab initio, with two notable exceptions, namely ${\\rm N}_2+{\\rm NO}$ and ${\\rm O}_2+{\\rm NO}$. At the selected free-stream conditions, strong vibrational non-equilibrium is observed in the shock layer. The flow is characterized by significant chemical activity, with near-complete oxygen dissociation, considerable formation of NO and minimal molecular nitrogen dissociation. Complex mass diffusion kinetics, driven by composition, temperature and pressure gradients, are identified in the shock layer. All these physical phenomena are directly coupled to, and responsible for, the mechanics of the gas flow and are all solely traceable to the PESs’ inputs, without the need for any thermochemical models, mixing rules or constitutive laws for transport properties. Because the flow is entirely at near-continuum conditions, it is a gas-phase thermophysics benchmark that is useful to enhance the fidelity of continuum models used in computational fluid dynamics of hypersonic flows.

We present a flexible and noninvasive approach for efficient continuous micromixing and microreaction based on direct current-induced thermal buoyancy convection in a single microfluidic unit. Theoretically, microfluids in this microsystem are unevenly heated by powering the asymmetrically arranged microheater. The thermal buoyancy convection is then formed to induce microvortices that cause effective fluidic interface disturbance, thereby promoting the diffusion and convective mass transfer. The temperature distribution and the convection flow in the microchip are first characterized and studied, which can be flexibly adjusted by changing the DC voltage. Then the mixing performance of the presented method is validated by joint numerical and experimental analyses. Specifically, at U = 7 V, the mixing efficiencies are higher than 90% as the flow rate is lower than Qv= 600 nL/s. So high-quality chemical or biochemical reactions needing both suitable heating and efficient mixing can be achieved using this method. Finally, as one example, we use this method to synthesize nano-sized cuprous oxide (Cu2O) particles by effectively mixing the Benedict’s solution and glucose buffer. Remarkably, the particle size can be tuned by changing the voltage and the concentration of Benedict’s solution. Therefore, this micromixer can be attractive for diverse applications needing homogeneous sample mixtures.

We have studied the effect of strong magnetic field on the viscous properties of hot QCD matter at finite chemical potential by calculating the shear viscosity (η) and the bulk viscosity (ζ). The viscosities have been calculated using the relativistic Boltzmann transport equation within the relaxation time approximation. The interactions among partons are incorporated through their quasiparticle masses at finite temperature, strong magnetic field and finite chemical potential. From this study, one can understand the influence of strong magnetic field and the influence of chemical potential on the sound attenuation through the Prandtl number (Pl), on the nature of the flow by the Reynolds number (Rl), and on the relative behavior between the shear viscosity and the bulk viscosity through the ratio ζ/η. We have observed that, both shear and bulk viscosities get increased in the presence of a strong magnetic field and the additional presence of chemical potential further enhances their magnitudes. With the increase of temperature, η increases for the medium in the presence of a strong magnetic field as well as for the isotropic medium in the absence of magnetic field, whereas ζ is found to decrease with the temperature, contrary to its increase in the absence of magnetic field. We have observed that, the Prandtl number gets increased in the presence of strong magnetic field and finite chemical potential as compared to that in the isotropic medium, but it always remains larger than unity, thus instead of the thermal diffusion, the momentum diffusion largely affects the sound attenuation in the medium and this is more vigorous in the presence of both strong magnetic field and finite chemical potential. However, the Reynolds number becomes lowered than unity in an ambience of strong magnetic field and even gets further decreased in an additional presence of chemical potential, thus it implies the dominance of kinematic viscosity over the characteristic length scale of the system. Finally, the ratio ζ/η is amplified to the value larger than unity, contrary to its value in the absence of magnetic field and chemical potential where it is less than unity, thus it is inferred that the bulk viscosity prevails over the shear viscosity for the hot and dense QCD matter in the presence of a strong magnetic field.

A bstract We study fermion number non-conservation (or chirality breaking) in Abelian gauge theories at finite temperature. We consider the presence of a chemical potential μ for the fermionic charge, and monitor its evolution with real-time classical lattice simula- tions. This method accounts for short-scale fluctuations not included in the usual effective magneto-hydrodynamics (MHD) treatment. We observe a self-similar decay of the chemi- cal potential, accompanied by an inverse cascade process in the gauge field that leads to a production of long-range helical magnetic fields. We also study the chiral charge dynamics in the presence of an external magnetic field B , and extract its decay rate Γ 5 ≡ d log μ dt . We provide in this way a new determination of the gauge coupling and magnetic field de- pendence of the chiral rate, which exhibits a best fit scaling as Γ 5 ∝ 11 2 B 2 . We confirm numerically the fluctuation-dissipation relation between Γ5 and Γ diff , the Chern-Simons diffusion rate, which was obtained in a previous study. Remarkably, even though we are outside the MHD range of validity, the dynamics observed are in qualitative agreement with MHD predictions. The magnitude of the chiral/diffusion rate is however a factor ∼ 10 times larger than expected in MHD, signaling that we are in reality exploring a dif- ferent regime accounting for short scale fluctuations. This discrepancy calls for a revision of the implications of fermion number and chirality non-conservation in finite tempera- ture Abelian gauge theories, though no definite conclusion can be made at this point until hard-thermal-loops are included in the lattice simulations.

This paper extends the analysis of solute dispersion in electrohydrodynamic flows to the case of band broadening in polyelectrolyte-grafted (soft) capillaries by accounting for the effects of ion partitioning, irreversible catalytic reaction and pulsatile flow actuation. In the Debye–Hückel limit, we present the benchmark solutions of electric potential and velocity distribution pertinent to steady and oscillatory mixed electroosmotic–pressure-driven flows in soft capillaries. Afterwards, the mathematical models of band broadening based on the Taylor–Aris theory and generalized dispersion method are presented to investigate the late-time asymptotic state and all-time evolution of hydrodynamic dispersion, respectively. Also, to determine the heterogeneous dispersion behaviour of solute through all spatiotemporal stages and to relax the constraint of small zeta potentials, a full-scale numerical simulation of time-dependent solute transport in soft capillaries is presented by employing the second-order-accurate finite difference method. Then, by inspecting the dispersion of passive tracer particles in Poiseuille flows, we examine the accuracy of two analytical approaches against the simulation results of a custom-built numerical algorithm. Our findings from hydrodynamic dispersion in Poiseuille flows reveal that, compared to rigid capillaries, more time is required to approach the longitudinal normality and transverse uniformity of injected solute in soft capillaries. For the case of dispersion in mixed electrohydrodynamic flows, it is found that the characteristics of the soft interface, including the thickness, permittivity, fixed charge density and friction coefficient of the polymer coating layer, play a significant role in determining the Taylor diffusion coefficient, advection speed and dispersion rate of solutes in soft capillaries.

Electroosmotic flow through porous media is a crucial contemporary research field that finds its application in the areas of various engineering, geological, and biological settings. Obeying Darcy’s law for electroosmotic flow through porous media in similar lines to that of pressure-driven flow yields a very important physical property of electro-permeability. This work aims to examine the influence of wall zeta potential, Debye length, the solid particle shape, and preferential orientation on the electro-permeability tensor using multiscale homogenization methodology for a single-phase fluid flow. For determining the range of possible particle shapes from prolate-oblate ellipsoid to sphere, the parameter of aspect ratio is employed. Additionally, anisotropy ratio and tortuosity have been explored. The governing equations for this study comprise a mass continuity equation, an advection–diffusion equation, a Poisson–Boltzmann equation for electric double layer, and a Laplace equation for solving the electric field in a fully coupled manner. A two-scale computational homogenization technique is employed to model the fluid-saturated periodic media subjected to external electric effects. The finite element approach is adopted to solve the multiscale and multi-physics problem in a coupled manner. The results indicate that the electro-permeability is significantly affected by wall zeta potential, aspect ratio, and orientation of solid particles. Also, one of the major findings is that the EDL thickness has a vital effect on the electro-permeability, anisotropy ratio, and tortuosity of the porous media. Article Highlights Permeability of porous media is estimated for a Newtonian fluid when subjected to an external electric field. Electrical double layer (EDL) thickness impacts the tortuosity and anisotropy ratio of the porous media. Wall zeta potential, EDL thickness, solid phase aspect ratio, and orientation affect the permeability.

Numerous situations involve the capture of particles onto a functionalized surface in a laminar flow, such as classical biomedical assays, lab on a chip devices or even biological research protocols. Being able to control this capture is thus an important issue that we address in this paper. We focus on a simple and widely used geometry, the straight microfluidic channel, in which particles undergo two weak effects: diffusion towards the functionalized surface and lift forces expelling them away from it. We show that the competition between these two weak mechanisms yields strongly different capture behavior whose occurrence depends on the value of a new lifto-diffusive dimensionless number NLD. We show that tuning the flow rate and the channel dimension to get proper values of this number allow to trigger, via a pure hydrodynamic effect, the capture or non-capture of particles on surfaces. For example, we show that, under certain conditions, doubling the flow rate reduces the capture rate by four orders of magnitude. Additionally, we provide the particle distribution in the liquid along the channel, resulting from this competition, for different NLD values. We believe that this work opens new perspectives for analysis and biotechnology applications. More precisely, the proposed model should extend to any transverse force that can be written in the form of a potential energy.

It is of great significance to explore the osmotic transport mechanisms across nanopores for the design and applications of forward osmosis membranes. To deeply understand the quantitative relationship between pore diameters and water transport across nanopores of forward osmosis membrane at molecular level, systematic molecular dynamic simulations are conducted on water transport behaviors across nanopores with a length of 16 Å and with diameters ranging from 8.14 to 16.28 Å. The phase interface barrier on water flux across nanopores is predicted by the potential of mean force and hydrogen-bonding number. The combined effects of water structure, interface barrier and flow resistance of nanopores, and hydrogen bonds on the water flux are analyzed. A non-monotonic profile of the water flux with respect to pore diameters is observed due to the fact that the water flux of forward osmosis is determined by the interface barrier and flow resistance being the same order of magnitude with the naturally osmotic pressure rather than the driven pressure which is one order of magnitude higher than the naturally osmotic pressure. For the pore diameters between 8.14 and 10.85 Å where water structures are highly ordered, the water flux increases with the increasing diameter owing to the combined effects of the increasing diffusion coefficients and decreasing potential of mean force and hydrogen-bonding number. The increasing low resistance within nanopores caused by the water structure transition to be disordered at a critical diameter of 12.21 Å takes account for the obviously decreasing water flux. For the pore diameter being greater than12.21 Å, a linear increase of the water flux with increasing diameter is ascribed to the stabilized diffusion coefficient, potential of mean force, and hydrogen-bonding number.

Isopycnal diffusivity due to stirring by mesoscale eddies in an idealized, wind-forced, eddying, midlatitude ocean basin is computed using Lagrangian, in Situ, Global, High-Performance Particle Tracking (LIGHT). Simulation is performed via LIGHT within the Model for Prediction across Scales Ocean (MPAS-O). Simulations are performed at 4-, 8-, 16-, and 32-km resolution, where the first Rossby radius of deformation (RRD) is approximately 30 km. Scalar and tensor diffusivities are estimated at each resolution based on 30 ensemble members using particle cluster statistics. Each ensemble member is composed of 303 665 particles distributed across five potential density surfaces. Diffusivity dependence upon model resolution, velocity spatial scale, and buoyancy surface is quantified and compared with mixing length theory. The spatial structure of diffusivity ranges over approximately two orders of magnitude with values of O (10 5 ) m 2 s −1 in the region of western boundary current separation to O (10 3 ) m 2 s −1 in the eastern region of the basin. Dominant mixing occurs at scales twice the size of the first RRD. Model resolution at scales finer than the RRD is necessary to obtain sufficient model fidelity at scales between one and four RRD to accurately represent mixing. Mixing length scaling with eddy kinetic energy and the Lagrangian time scale yield mixing efficiencies that typically range between 0.4 and 0.8. A reduced mixing length in the eastern region of the domain relative to the west suggests there are different mixing regimes outside the baroclinic jet region.