Characteristics of proppant transport and placement within rough hydraulic fractures

A three-dimensional reconstruction of rough fracture surfaces of hydraulically fractured rock outcrops is carried out by casting process,a large-scale experimental setup for visualizing rough fractures is built to perform proppant transport experiments.The typical characteristics of proppant transport and placement in rough fractures and its intrinsic mechanisms are investigated,and the influences of fracture inclination,fracture width and fracturing fluid viscosity on proppant transport and placement in rough fractures are analyzed.The results show that the rough fractures cause variations in the shape of the flow channel and the fluid flow pattern,resulting in the bridging buildup during proppant transport to form unfilled zone,the emergence of multiple complex flow patterns such as channeling,reverse flow and bypassing of sand-carrying fluid,and the influence on the stability of the sand dune.The proppant has a higher placement rate in inclined rough fractures,with a maximum increase of 22.16 percentage points in the experiments compared to vertical fractures,but exhibits poor stability of the sand dune.Reduced fracture width aggravates the bridging of proppant and induces higher pumping pressure.Increasing the viscosity of the fracturing fluid can weaken the proppant bridging phenomenon caused by the rough fractures.

Transportation characteristics of motor vehicle pollutants near Beijing typical expressway

As a major source of air pollution in urban areas, the motor vehicle exhaust has attracted more and more attention due to its growing amount and serious harm to human health. It is of benefit to the pollutant control to make clear the transportation characteristics of vehicle exhausts. In this paper, the transportation characteristics of vehicle exhaust pollutants are investigated by means of the on-site measurement based on a typical Beijing expressway-Badaling expressway （G6 state expressway）. The concentrations of CO, NOx, S02 and particles near the expressway were obtained, by which the variations of the particle num- ber and mass concentrations, as well as the gas pollutant volume concentrations in the vicinity of the roadways with the dis- tance from the expressway were fitted. The results show that the gas pollutant concentrations and particle concentrations de- crease almost exponentially with the distance from the expressway, which is helpful for the air pollutant database establish- ment and future pollution control in big cities.

Effects of Rattling Behavior of K and Cd Atoms along Different Directions in Anisotropic KCdAs on Lattice Thermal Transport and Thermoelectric Properties

We employ advanced first principles methodology,merging self-consistent phonon theory and the Boltzmann transport equation,to comprehensively explore the thermal transport and thermoelectric properties of KCdAs.Notably,the study accounts for the impact of quartic anharmonicity on phonon group velocities in the pursuit of lattice thermal conductivity and investigates 3ph and 4ph scattering processes on phonon lifetimes.Through various methodologies,including examining atomic vibrational modes and analyzing 3ph and 4ph scattering processes,the article unveils microphysical mechanisms contributing to the lowκL within KCdAs.Key features include significant anisotropy in Cd atoms,pronounced anharmonicity in K atoms,and relative vibrations in non-equivalent As atomic layers.Cd atoms,situated between As layers,exhibit rattling modes and strong lattice anharmonicity,contributing to the observed lowκL.Remarkably flat bands near the valence band maximum translate into high PF,aligning with ultralowκL for exceptional thermoelectric performance.Under optimal temperature and carrier concentration doping,outstanding ZT values are achieved:4.25(a(b)-axis,p-type,3×10^(19)cm^(−3),500 K),0.90(c-axis,p-type,5×10^(20)cm^(−3),700 K),1.61(a(b)-axis,n-type,2×10^(18)cm^(−3),700 K),and 3.06(c-axis,n-type,9×10^(17)cm^(−3),700 K).

Nonvolatile ferroelectric control of electronic properties of Bi2Te3

Nonvolatile electric-field control of the unique physical characteristics of topological insulators (TIs) is essential forthe fundamental research and development of practical electronic devices. Electrically tunable transport properties throughgating materials have been extensively investigated. However, the relatively weak and volatile tunability limits its practicalapplications in spintronics. Here, we demonstrate the nonvolatile electric-field control of Bi2Te3 transport properties viaconstructing ferroelectric Rashba architectures, i.e., 2D Bi2Te3/a-In2Se3 ferroelectric field-effect transistors. By switchingthe polarization states of a-In2Se3, the Fermi level, resistance, Fermi wave vector, carrier mobility, carrier density andmagnetoresistance (MR) of the Bi2Te3 film can be effectively modulated. Importantly, a shift of the Fermi level towards aband gap with a surface state occurs as switching to a negative polarization state, the contribution of the surface state to theconductivity then increases, thereby increasing the carrier mobility and electron coherence length significantly, resulting inthe enhanced weak anti-localization (WAL) effect. These results provide a nonvolatile electric-field control method to tunethe electronic properties of TI and can further extend to quantum transport properties.

The Hole Transport Characteristics of 1,4,5,8,9 and 11-Hexaazatriphenylene-Hexacarbonitrile by Blending

The hole transport characteristics of molecule blends of 1, 4, 5, 8, 9 and 11-hexaazatriphenylene-hexacarbonitrile （HAT-CN）： N,N＇-di（naphthalene-l-yl）-N,N＇-diphenyl-benzidine （NPB） and HAT-CN： 4,4＇-cyclohexylidenebis[N,N- bis（4-methylphenyl）benzenamine] （TAPC） with various NPB and TAPC mixing concentrations （5 90wt%） are studied. When the concentration is in the range of 5-80wt%, it is found that the hole conductions in the two blends are space-charge-limited current （SCLC） with free trap distributions. The current-voltage characteristics of the two blends show SCLC with exponentiM trap distributions at the concentration of 90wt%. The hole mo- bilities of the two blends are very close （10^-4-10^-3 cm2 V^-1 s-X ）, the dependence of electric field and temperature can be described by the modified Poole-Frenkel model. The hole mobility and activation energy of the two blends depending on concentration are similar.

Comparison between the Causes and Transmission Characteristics of Two Sand and Dust Weather Processes with Heavy Pollution in Ulanqab City

The actual situation of two sand and dust weather processes with heavy pollution in Ulanqab City in 2021 was analyzed from the aspects of air quality,visibility,PM_(2.5)and PM_(10),and the causes of the sand and dust weather with heavy pollution were discussed.The differences between the two processes in transport characteristics of sand and dust were studied,and the roles of high-and low-altitude weather systems and their impact on sand and dust transport were explored.

Transport Patterns and Potential Sources of Atmospheric Pollution during the ⅩⅩⅣ Olympic Winter Games Period

The attainment of suitable ambient air quality standards is a matter of great concern for successfully hosting the ⅩⅩⅣ Olympic Winter Games(OWG). Transport patterns and potential sources of pollutants in Zhangjiakou(ZJK) were investigated using pollutant monitoring datasets and a dispersion model. The PM_(2.5) concentration during February in ZJK has increased slightly(28%) from 2018 to 2021, mostly owing to the shift of main potential source regions of west-central Inner Mongolia and Mongolian areas(2015–18) to the North China Plain and northern Shanxi Province(NCPS) after 2018.Using CO as an indicator, the relative contributions of the different regions to the receptor site(ZJK) were evaluated based on the source-receptor-relationship method(SRR) and an emission inventory. We found that the relative contribution of pollutants from NCPS increased from 33% to 68% during 2019–21. Central Inner Mongolia(CIM) also has an important impact on ZJK under unfavorable weather conditions. This study demonstrated that the effect of pollution control measures in the NCPS and CIM should be strengthened to ensure that the air quality meets the standard during the ⅩⅩⅣ OWG.

Low lattice thermal conductivity and high figure of merit in p-type doped K3IO

Based on first-principles calculations, Boltzmann transport equation and semiclassical analysis, we conduct a detailed study on the lattice thermal conductivity κL, Seebeck coefficient S, electrical conductivity σ, power factor S2σ and dimensionless figure of merit, zT, for K3IO. It is found that K3IO exhibits relatively low lattice thermal conductivity of 0.93 W·m-1·K-1 at 300 K, which is lower than the value 1.26 W·m-1·K-1 of the classical TE material PbTe. This is due to the smaller phonon group velocity νg and smaller relaxation time τλ. The low lattice thermal conductivity can lead to excellent thermoelectric properties. Thus maximum zT of 2.87 is obtained at 700 K, and the zT = 0.41 at 300 K indicate that K3IO is a potential excellent room temperature TE material. Our research on K3IO shows that it has excellent thermoelectric properties, and it is a promising candidate for applications in fields in terms of thermoelectricity.

Selective and asymmetric ion transport in covalent organic framework-based two-dimensional nanofluidic devices

Two-dimensional(2D)covalent organic framework(COF)mem-branes featuring well-aligned and programmable vertical nano-channels have emerged as a promising candidate for advanced nanofluidic devices and showcased vast potential in the fields of smart-gating,ion-separation,and energy-harvesting.However,the transverse interlayer nanochannels with a height of sub-nanometer-scale in 2D-COF membranes have scarcely been studied in com-parison.Here,we report the ion transport characteristics in 2D interlayer nanochannels of protonated CoF membranes.The dis-tinct surface-charge-governed ionic conductance in domination of electrolyte concentration below 1o-3 M as well as the exceptional anion/cation(Cl^(-)/K^(+))selectivity is revealed due to the pronounced charge and nano-confinement effects.Additionally,evident ion current rectification is witnessed when incorporating asymmetric geometry into the system,which is attributed to the dynamic process of ion enrichment and dissipation within the protonated nanochannels.This work offers immense prospects for 2D-COF membranes in the fields of biomimetic nanofluidic devices and cutting-edge electronic devices.

Deep Potential Molecular Dynamics Systematic Study of Microstructure and Thermophysical Properties of NaCl-CaCl_(2) Molten Salt System across Phase Transition Temperature

Understanding the microscopic ionic structure and thermal properties of the NaCl-CaCl_(2) mixture is of great importance for improving its photothermal energy conversion efficiency.However,the measured values of thermophysical parameters are affected by the processes near the phase transition temperature,and the measured values often change abruptly.Classical and first-principles molecular dynamics studies have recently been performed to determine the thermal properties of molten salts,but such simulations for binary molten salts including NaCl-CaCl_(2) are still rare and limited to a range above the phase transition temperature(786.0 K),and the deviations from the measurements are still large.In this study,the molecular dynamics method based on the trained deep potential is used to systematically predict the variations of the ionic structure,phonon density of state,density and thermophysical properties including heat capacity,thermal conductivity,and diffusivity,and Prandtl number of the binary chloride system of NaCl-CaCl_(2) in a wide temperature range(600-1000 K)above the phase transition temperature.The variations and correlations of the properties(especially thermal diffusivity and Prandtl number)with temperature are deduced.It is found that an increase in temperature enhances ionic vibration,thus increasing the specific heat capacity.An increase in temperature weakens the interaction and vibrational transfer between ions,and hence the thermal conductivity tends to decrease.As the temperature increases,the heat capacity increases,while the density,thermal conductivity,thermal diffusion coefficient,and Prandtl number of the system all decrease.In general,the properties obtained by applying the deep potential trained in this work reflect the experimental values more accurately than the classical and first-principles molecular dynamics simulations.

Optimal Transportation for Generalized Lagrangian

This paper deals with the optimal transportation for generalized Lagrangian L = L（x, u, t）, and considers the following cost function： c（x, y） = inf x（0）=x x（1）=y u∈U∫0^1 L（x（s）, u（x（s）, s）, s）ds, where U is a control set, and x satisfies the ordinary equation x（s） = f（x（s）, u（x（s）, s））.It is proved that under the condition that the initial measure μ0 is absolutely continuous w.r.t. the Lebesgue measure, the Monge problem has a solution, and the optimal transport map just walks along the characteristic curves of the corresponding Hamilton-Jacobi equation：Vt（t, x） ＋ sup u∈U = 0,V（0, x） = Φ0（x）.

Study of limits to the rotation function in the SA-RC turbulence model

The Rotation and Curvature(RC)correction is an important turbulence model modifi-cation approach,and the Spalart-Allmaras model with the RC correction(SA-RC)has been exten-sively studied and used.As a multiplier of the modelling equation’s production term,the rotation function f_(r1)should have a cautiously designed value range,but its limit varies in different models and flow solvers.Therefore,the need of restriction is discussed theoretically,and the common range of f_(r1)is explored in Burgers vortexes.Afterwards,the SA-RC model with different limits is tested numerically.Negative f_(r1)always appears in the SA-RC model,and the difference between simula-tion results brought by the limits is not negligible.A lower limit of 0 enhances turbulence produc-tion,and therefore the vortex structures are dissipated faster and shrink in size,while an upper limit plays an opposite role.Considering that the lower limit of 0 usually promotes the simulation accu-racy and fixes the numerical defect,whereas the upper limit worsens the predictive performance in most cases,it is recommended to limit f_(r1)non-negative while utilizing the SA-RC model.In addi-tion,the RC-corrected model has a better prediction of the attached flow near curved walls,while the SA-Helicity model largely improves the simulation accuracy of three-dimensional large-scale vortices.The model combining both corrections has the potential to become more adaptive and more accurate.

Source,route and effect of Asian sand dust on environment and the oceans

We summarize in this overview achievements in current research frontiers in Asian sand dust with emphasis on the method for sand dust research, the sources of sand dust aerosols, emission of sand dust, mechanism of sand dust weather, chemical transformation during transport, and influences on climatic environment and oceans. Our main results show that most of Asian sand dust comes from Mongolia, the Gobi Desert, arid and semiarid desert areas in northwest China, which is divided into initial sources and enhanced sources. Half of the global production of dust originates from Asian dust source regions. Asian dust weather is so immense that it can cover a 5-？-day journey from the sources to the Korean Peninsula, Japan Islands, and the Pacific Ocean to even impact North America. Asian dust weather plays an active role in the hiogeochemical cycles of trace elements in the mid-latitude Northern Hemisphere.

TRANSPORT EFFICIENCY OF THE SPIRAL FLOW IN CIRCULAR PIPE

A concise definition of Transport Efficiency (TE) was given to examine the amount of transported grains in the pipe flow with certain energy consumption. The transport characteristics and the so-called 'roto-floating' characteristics were studied from the tests of sediment transport in the normal pipe flow and the spiral pipe flow, and hereby the energy gradients of the two kinds of pipe flows were obtained. By comparing the mean concentrations at the same gradient, it was concluded that the TE of the latter is several times to over ten times higher than that of the former, and the lift of the latter is 200 times larger than that of the former for the nearly same TE. The spiral flow in circular pipe is suitable for transporting fine grains of high concentration, and with sedimentation trend and coarse grains.