Nonuniform Systems Research Articles

The immiscible to miscible transition and its consequences for 3-phase displacements in porous media of arbitrary wettability: Basic theory

In this paper, a “process-based” 3-phase model is applied to explore how multiphase fluid flow behaviour in two non-uniform wettability systems, named weakly oil-wet (WOW) and mixed-wet large (MWL), change when gas and oil move towards miscibility (σgo → 0). In the course of the theoretical development, we indicate how parts of the theory have been validated and confirmed satisfactorily by summarising experimental data from the literature. To demonstrate how the complexities of the three-phase physics interact with the system wettability, we use a capillary bundle (CB) model for the porous medium. This is sufficient to show the main processes which occur in the transition from immiscible to miscible behaviour. Even although the CB model is the simplest possible case for a porous medium, the results demonstrate a high level of unpredictable complexity which cover key parameters of the physics of 3-phase flow within porous media. In addition, for each case, the results point to the specific physical parameter that controls the phase separation lines. In some cases, gas injection or oil injection in a WOW system, the phase displacement changes quite radically as the system goes towards miscibility since there is a transition in wetting order from O/W/G to O/G/W. The differences and similarities between saturation paths in WOW and MWL are described in detail. For a given pore size distribution (PSD), the 3-phase displacements are controlled by the parameters of the rock wettability structure (see text) and the 3 interfacial tensions. Moving towards miscibility, 3-phase fluid displacement for gas injection and oil invasion are controlled by IFTs, while for water flooding, wettability structure plays the key role at all miscibility conditions. Although the simple CB model cannot describe all phenomena, such as phase trapping, the phase displacement paths, still the pore occupancies are qualitatively correct. Results of various phase injection in WOW are broadly consistent with pore occupancy sequences observations from pore scale X-Ray image analysis in literature despite simplicity of the theory which is validated in terms of its underling physics.

Visualizing and Controlling of Photogenerated Electron-Hole Pair Separation in Monolayer WS2 Nanobubbles under Piezoelectric Field.

The piezoelectric properties of two-dimensional semiconductor nanobubbles present remarkable potential for application in flexible optoelectronic devices, and the piezoelectric field has emerged as an efficacious pathway for both the separation and migration of photogenerated electron-hole pairs, along with inhibition of recombination. However, the comprehension and control of photogenerated carrier dynamics within nanobubbles still remain inadequate. Hence, this study is dedicated to underscore the importance of in situ detection and detailed characterization of photogenerated electron-hole pairs in nanobubbles to enrich understanding and strategic manipulation in two-dimensional semiconductor materials. Utilizing frequency modulation kelvin probe force microscopy (FM-KPFM) and strain gradient distribution techniques, the existence of a piezoelectric field in monolayer WS2 nanobubbles was confirmed. Combining w/o and with illumination FM-KPFM, second-order capacitance gradient technique and in situ nanoscale tip-enhanced photoluminescence characterization techniques, the interrelationships among the piezoelectric effect, interlayer carrier transfer, and the funneling effect for photocarrier dynamics process across various nanobubble sizes were revealed. Notably, for a WS2/graphene bubble height of 15.45 nm, a 0 mV surface potential difference was recorded in the bubble region w/o and with illumination, indicating a mutual offset of piezoelectric effect, interlayer carrier transfer, and the funneling effect. This phenomenon is prevalent in transition metal dichalcogenides materials exhibiting inversion symmetry breaking. The implication of our study is profound for advancing the understanding of the dynamics of photogenerated electron-hole pair in nonuniform strain piezoelectric systems, and offers a reliable framework for the separation and modulation of photogenerated electron-hole pair in flexible optoelectronic devices and photocatalytic applications.

BIM Data Model Based on Multi-Scale Grids in Civil Engineering Buildings

The construction of digital twin cities is a current research hotspot; GIS technology and BIM technology are widely used in the field of digital twin cities. However, BIM is still subject to major limitations in its applications, mainly due to huge amounts of model data, low query efficiency and accuracy, non-uniform marking systems, etc. The reason is that the BIM model itself focuses more on the expression of visual effects and lacks spatial calculation ability and the utilization of spatial location information. Secondly, the current lightweight processing methods for BIM models are mostly based on geometric transformation and rendering optimization, focusing more on the data compression and visual quality of the model, which essentially does not change the data structure of the BIM model, and it is difficult to establish the mapping relationship between spatial location and spatial data, information, and resources. In addition, current coding methods proposed for BIM models are mostly based on the line classification method, which realizes the identification of components based on the classification of their attributes, and the location information is stored according to the attributes or natural language descriptions, which need to be parsed and translated when they are used, and this procedure ignores the importance of spatial location in daily management and emergency management. The importance of spatial location in daily management and emergency management is also ignored. Based on this kind of identification code, it is impossible to directly analyze and apply spatial location data. Therefore, this paper takes the combination of GIS technology and BIM technology as the starting point and proposes a BIM data modeling method based on the BeiDou grid code, based on the efficiency of its underlying data organization and the accuracy of its real geographic location expression on the one hand and the completeness of the information expression by BIM and fine three-dimensional visualization on the other hand. Finally, a series of experiments are carried out based on the method. Through visualization modeling and efficiency experiments, different feature models are meshed to verify the feasibility and efficiency of the model. Through coding and information query experiments, the model′s data organization capability, data dynamic carrying capability, and efficient spatial computation capability and practical application capability are verified.

A transient transformation theory for the design of convective thermal metamaterials: Cloaks, concentrators, and rotators

Convective thermal metamaterials have attracted particular attention since they can simultaneously manipulate the fluid flow and heat transfer. However, the current transformation theory for designing convective thermal metamaterials is only applied to steady state heat-transfer systems or porous media systems. Therefore, we prove the weak forms of convective heat-transfer governing equations with time-dependent terms for non-porous media flows possess form invariant under coordinate transformation and develop the transient transformation theory for creeping viscous potential flows. Based on this theory, three convective thermal metamaterials are designed under transient heat-transfer systems, including cloaks, concentrators, and rotators. The validity of the transient transformation theory is verified through quantitative numerical simulation, which validate the functionalities of the metamaterials in uniform, non-uniform, steady-state, and transient heat-transfer systems. These cloaks, concentrators, and rotators in the transient convective heat-transfer system ensure that the heat fluxes and flows are transported around the object, amplified at specified times in the center region, and are rotated to a specified angle, respectively, without disturbing the background. Especially, the convective thermal cloak is characterized by approximately drag-free characteristics in transient velocity fields. Furthermore, comparative results reveal that transient convective thermal metamaterials constitute an extension of their steady-state counterparts. The established transient theory of transformation heat transfer not only guides the design of more richly functional thermal metamaterials but also broadens their application scenarios.

Modeling nuclear quantum effects on long-range electrostatics in nonuniform fluids

Nuclear quantum effects play critical roles in a variety of molecular processes, especially in systems that contain hydrogen and other light nuclei, such as water. For water under ambient conditions, nuclear quantum effects are often interpreted as local effects resulting from a smearing of the hydrogen atom distribution. However, the orientational structure of water at interfaces determines long-range effects, such as electrostatics, through the O–H bond ordering that is impacted by nuclear quantum effects. In this work, I examine nuclear quantum effects on long-range electrostatics of water confined between hydrophobic walls using path integral simulations. To do so, I combine concepts from local molecular field theory with path integral methods at varying levels of approximation to develop efficient and physically intuitive approaches for describing long-range electrostatics in nonuniform quantum systems. Using these approaches, I show that quantum water requires larger electrostatic forces to achieve interfacial screening than the corresponding classical system. This work highlights the subtleties of electrostatics in nonuniform classical and quantum molecular systems, and the methods presented here are expected to be of use to efficiently model nuclear quantum effects in large systems.

Combined reaction and diffusion across the interface in reactive nonuniform liquid systems

A recently introduced theoretical framework is generalized to multicomponent reactive nonuniform systems. The modified and generalized Cahn-Hilliard equation is combined with a chemical kinetics model. Kinetic rate equations, which are formulated with activities rather than concentrations, are combined with non-Fickian diffusion driven by gradients in chemical potential. Based on the incompressible density gradient theory, which provides an expression for the Gibbs energy of a nonuniform system, a generalized method is developed to model the combined reaction and diffusion associated with reactive liquid-liquid systems. A set of partial differential equations describing the temporal evolution of the mole fractions of all the involved components in the bulk phases and the spatial and temporal evolution of the mole fractions in the interface has been derived. The obtained equations were used to investigate the dynamics of the interfacial properties of a ternary mixture with a simple chemical reaction. Special attention is given to reacting mixtures with reaction rates that are much smaller than diffusion rates. In particular, it was found that the mixture will remain in phase equilibrium upon reaction and that the interfacial chemical reaction will not affect the dynamics of the overall system, the latter being only affected by the bulk phase kinetics.

Weak differentiability to nonuniform nonlinear degenerate elliptic systems under p,q-growth condition on the Heisenberg group

The paper concerns the weak differentiability of weak solutions to two kinds of nonuniform nonlinear degenerate elliptic systems under the p,q-growth condition on the Heisenberg Group. We use the iteration to fractional difference quotients on the Heisenberg Group to get the weak differentiability of weak solution u in the vertical direction (i.e., Lp(1<p<4) integrability of Tu) and then the second order weak differentiability of weak solution in the horizontal directions (i.e., L2 integrability of ∇H2u) and weak differentiability of gradient of weak solution in the vertical direction (i.e., L2 integrability of T∇Hu)).

Shear viscosity of nuclear matter in the spinodal region

Based on IBUU simulations calibrated by previous efforts of the transport model evaluation project, we have studied the specific shear viscosity $\eta/s$ of nuclear matter in the spinodal region using the Green-Kubo method. With the momentum-independent mean-field potential which reproduces reasonably well empirical nuclear matter properties and nuclear phase diagram, we have generated dynamically stable and thermalized nuclear cluster systems in a box with the periodic boundary condition. Extensive results of the $\eta/s$ at different average densities and temperatures in uniform and non-uniform systems are compared, and we found that the shear viscosity is smaller with nuclear clusters due to the enhanced correlation of the energy-momentum tensor and the stronger collision effect. The temperature dependence of the $\eta/s$ has a minimum only at low average densities of $\rho<0.3\rho_0$. The present study serves as a rigorous baseline calculation of the $\eta/s$ in nuclear systems with clusters, and helps to understand the relation between the shear viscosity and the nuclear phase diagram.

Adaptive blind receiving for deep VLC coverage innon-uniform LED systems.

Recently, visible light communication (VLC) has become a promising technology for reliable communication in the industrial Internet of Things. In VLC, light sources with non-uniform parameters make uncontrollable signal blind zones and aliases. The unknown parameters also lead to the problem of channel estimation. Hence, deep coverage of VLC is challenging. In this paper, we design a dual-sensor elongated receiver. The receiver expands the signal receiving area by increasing the distance between photon detectors and realizes aliased signal recovery without channel estimation. Cooperatively, an adaptive blind receiving scheme is proposed. The scheme separates aliased signals by parameter estimation of a Gaussian mixture model without knowing transmitter parameters. It unifies the aliased and blind receiving cases by an adaptive signal combining method. Finally, the simulation results demonstrate that our scheme achieves better reliability and deeper communication coverage in the given system.

Observer Synthesis for Uncertain Nonlinear Systems With Nonuniformly Sampled and Delayed Output

This article presents a novel observer synthesis for nonuniform observable uncertain nonlinear systems with sampled (constant and non-uniform intervals) and disturbed delayed output. An observer with a cascade structure is proposed in order to obtain (in a continuous way) the estimated free-delay state vector. The base of the cascade structure is a continuous-discrete observer that achieve the continuous estimation of the delayed state, which reduces the convergence time and allows to reduce the remaining subsystems in the cascade. The rest of the cascade structure is composed by predictors that compensate the delay induced by the original signal. The performance of the observer is evaluated by estimating the state of an uncertain chaotic system with delayed measurements by considering different scenarios.

Use the Plasma Equation to Find the Statistical Distribution Laws of Unbalanced Systems

The plasma equation of motion of particles in the presence of afield potential per particle and a pressures force beside a resistive force have been used to find a useful expression of thermal pressure and non-thermal pressure. Another expression of ordinary Maxwell-Boltzmann distribution and Maxwell-Boltzmann distribution with stands for the kinetic energy is derived from the plasma equation with respect to x due to the potential changes only and due to potential changes with change in the density of the number of particles respectively. For non-uniform temperature systems, and non-uniform potential energy per particle, the statistical distribution law is described. This relation is different from where the temperature is assumed to be uniform when the thermal pressure changes due to the temperature change. The statistical distribution law is described when the thermal pressure change due to the temperature change. This relation is different from where the thermal pressure changes due to the change of both particle number density and temperature in this case the plasma equation. Also Statistical Distribution Law from the Plasma Equation in the Presence of Friction has been derived.

Two Sound Field Control Methods Based on Particle Velocity

In recent years, a variety of sound field control methods have been proposed for the generation of separated sound regions. Different algorithms control the physical properties of the generated sound field to different degrees. The existing methods mainly focus on sound pressure restoration and its related improvement. When the loudspeaker array is non-uniformly placed, the reconstruction system is not stable enough. To solve this problem, this paper proposes two sound field control methods related to particle velocity. The first method regulates the reconstruction error of particle velocity in the bright zone and the square of particle velocity in the dark zone; the second method regulates the reconstruction error of sound pressure and particle velocity in the bright zone and the square of sound pressure and particle velocity in the dark zone. Five channel and twenty-two channel non-uniform loudspeaker systems were used for two-dimensional and three-dimensional computer simulation testing. Experimental results show that the two proposed methods have better tradeoffs in terms of acoustic contrast, reproduction error and array effort than traditional methods, especially the second proposed method. In the two-dimensional experiment, the maximum reductions of the average array efforts generated by the proposed methods were about 10 dB and 11 dB compared with the average array efforts generated by two traditional methods. In the three-dimensional experiment, the maximum reductions of the average array efforts generated by the proposed methods were about 8 dB and 2 dB compared with the average array efforts generated by two traditional methods. The smaller the array effort, the more stable the loudspeaker system. Therefore, the reconstruction systems produced by the proposed methods are more stable than those produced by the traditional methods.

On the microscopic behaviour of the vapour-liquid interface of methane-xenon mixture

Although there are many simulation studies of mixtures, there remains a gap in the understanding of the phase transitions occurring when molecules are progressively added to a closed system. When molecules are added, the fluid passes from a rarefied state through metastable states where liquid droplets are dispersed in a gas phase. The droplets increase in size and when a sufficient number of molecules is present in the system, the droplets coalesce and the system splits into vapour and liquid phases separated by a planar interface. Here we have explored the microscopic details of these phase transitions for a methane/xenon mixture at 189 K by performing canonical ensemble simulations using the kinetic Monte Carlo scheme for uniform and non-uniform systems. When vapour and liquid are in equilibrium, the interface separating the vapour and liquid phases is planar. We have investigated variations in pressure and composition, in the interfacial region, when mixtures of molecules of constant compositions are added into the system. These changes are different from those in single-component systems because the increase in the number of particles affects the pressure of the system and the compositions of the liquid and gas phases.

Aggregation in non-uniform systems with advection and localized source

We explore analytically and numerically agglomeration driven by advection and localized source. The system is inhomogeneous in one dimension, viz along the direction of advection. It is characterized by the kinetic coefficients—the advection velocity, diffusion coefficient and the reaction kernel, quantifying the aggregation rates. We analyze a simplified model with mass-independent advection velocity, diffusion coefficient, and reaction rates. We also examine a model with mass-dependent coefficients arising in the context of aggregation with sedimentation. For the quasi-stationary case and simplified model, we obtain an exact solution for the spatially dependent agglomerate densities. For the case of mass-dependent coefficients we report a new conservation law and develop a scaling theory for the densities. For the numerical efficiency we exploit the low-rank approximation technique; this dramatically increases the computational speed and allows simulations of very large systems. The numerical results are in excellent agreement with the predictions of our theory.

Manipulation of dipole soliton for higher order nonlinear Schrödinger equation in the nonuniform management systems

The extended nonlinear Schrödinger equation which can be used to describe the propagation of the femtosecond soliton pulse has been investigated. A type of quartic and dipole soliton solutions is constructed based on the extended nonlinear Schrödinger equation with varying third-order and fourth-order dispersions, self-steepening and Raman effects. Parameter modulation of self-similar dipole soliton in some non-uniform management systems is also discussed in detail. The results show that with different forms of four-order dispersion and nonlinear coefficients, it exhibits different propagation dynamics. Modulation of the certain parameters, the amplitude and the trajectory of self-similar dipole soliton can be manipulated.

Domain wall velocity asymmetries driven by saturation magnetization gradients without a Dzyaloshinskii-Moriya interaction

The discovery of asymmetric domain wall velocities in magnetic alloys and multilayers without a heavy metal underlayer has given rise to claims of a large Dzyaloshinskii-Moriya interaction (DMI) driven by compositional non-uniformities. However, these non-uniformities also give rise to vertically non-uniform magnetic properties which can influence the dynamic properties of domain walls. In this work, we use micromagnetic simulations to show that vertical modulation of the saturation magnetization can give rise to asymmetric domain wall velocities for field and current driven motion, closely resembling the presence of a DMI. For field driven motion, by comparing the velocity asymmetries for varying saturation magnetization gradients, film thicknesses, and average saturation magnetization, we show that the magnitude of effective symmetry breaking field resulting from the non-uniformity can be comparable to those resulting from DMI. These effects scale with thickness and degree of modulation, mirroring recent results in single layer materials. However, the scaling of domain velocity asymmetries is largely suppressed for SOT driven domain dynamics. Therefore, great care needs to be taken when evaluating DMI in non-uniform systems.

Discrete vector-valued nonuniform Gabor frames

Gabor frames have interested many mathematicians and physicists due to their potential applications in time-frequency analysis, in particular, signal processing. A Gabor system is a collection of vectors which is obtained by applying modulation and shift operators to non-zero functions in signal spaces. In many applications, for example, signal processing related to Gabor systems, the corresponding shifts may not be uniform. That is, the set associated with shifts may not be a group under usual addition. We analyze discrete vector-valued nonuniform Gabor frames (DVNUG frames, in short) in discrete vector-valued nonuniform signal spaces, where the indexing set associated with shifts may not be a subgroup of real numbers under usual addition, but a spectrum which is based on the theory of spectral pairs. First, we give necessary and sufficient conditions for the existence of DVNUG Bessel sequences in discrete vector-valued nonuniform signal spaces in terms of Fourier transformations of the modulated window sequences. We provide a characterization of DVNUG frames in discrete vector-valued nonuniform signal spaces. It is shown that DVNUG frames are stable under small perturbation of window sequences associated with given discrete vector-valued nonuniform Gabor systems. We observed that the arithmetic mean sequences associated with window sequences of a given DVNUG frame collectively constitute a discrete nonuniform Gabor frame. Finally, we discuss an interplay between window sequences of DVNUG systems and their corresponding coordinates.

A new implicit finite difference method with a compact correction term for solving unsteady convection diffusion equations

A new implicit finite difference method with a compact correction term is established for solving unsteady convection-diffusion equations. The correction terms by connecting classical and compact finite difference formulas are proposed for improving the accuracies of numerical solutions. This new method with fourth order accuracy can be used for the numerical calculations of convection diffusion equation on both uniform and nonuniform grid systems. It can be extended not only from one-dimensional to multi-dimensional equations, but also from steady to unsteady convection-diffusion equations. Several convection-diffusion problems are stimulated for verifying the flexibility and high accuracy of this method.

WHO’s first scientific review of medicinal Cannabis: from global struggle to patient implications

Background“Cannabis” and “cannabis resin” are derived from the Cannabis plant, used as herbal medications, in traditional medicine and as active pharmaceutical ingredients. Since 1961, they have been listed in Schedule IV, the most restrictive category of the single convention on narcotic drugs. The process to scientifically review and reschedule them was launched by the World Health Organisation (WHO) on 2 December 2016; it survived a number of hindrances until finally being submitted to a delayed and sui generis vote by the UN Commission on Narcotic Drugs on 2 December 2020, withdrawing “cannabis” and “cannabis resin” from Schedule IV.Design/methodology/approachTo evaluate WHO’s scheduling recommendations, the process leading to the Commission vote and subsequent implications at global, national and patient/clinician levels. Narrative account of the four-year proceedings; review of the practical implications of both rejected and accepted recommendations.FindingsThe process was historically unprecedented, of political relevance to both medical Cannabis and evidence-based scheduling generally. Procedural barriers hampered the appropriate involvement of civil society stakeholders. The landscape resulting from accepted and rejected recommendations allow countries to continue creating decentralised, non-uniform systems for access to and availability of “cannabis” and “cannabis resin” for medical purposes.Originality/valuePerspective of accredited observers; highlight of institutional issues and the lay of the land; contrast of stakeholders’ interpretations and engagement.

Infection evolution and spreading models in non-uniform biological systems.

The paper investigates peculiarities of infection evolution and spreading models in non-uniform biological systems of individuals (humans, animals, plants) using the approach of mathematical modeling. The effects of different characteristic features are revealed. A robust tool for prediction of infection evolution (growth and spreading) under different external conditions is developed accounting for spatial non-uniformity of governing parameters.