Atomic relaxation,stability and electronic properties of Mg2Sn(100)surfaces from ab-initio calculations

Mg2Sn(100)surfaces were investigated using ab-initio method based on density functional theory in order to explore the surface properties.It is found that both the eleven-layers for Mg-termination surfaces and the nine-layers for Sn-termination surfaces are all converged very well.The effects of relaxation mainly occurred within the three outermost atomic layers for both Mg and Sn terminations during the surface relaxation.Mg-termination surfaces are more stable than Sn-termination surfaces according to the analysis of surface energy.The density of states reveals the metallic property of both Mg-termination and Sn-termination surfaces.Covalent bonding exists in Mg2Sn(100)surfaces according to the analysis of partial density of states.

First-principles study of electronic properties and stability of Nb_5SiB_2(001) surface

The density functional calculations are performed to study the electronic structure and stability of Nb5SiB2 （001） surface with different terminations. The calculated cleavage energies along the （001） planes in Nb5SiB2 are 5.015 J · m-2 and 6.593 J· m-2 with the break of Nb=Si and Nb-NbB bonds, respectively. There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy： the larger the cleavage energy, the larger the surface relaxation. Moreover, the surface stability of the NbsSiB2 （001） with different terminations has been investigated by the chemical potential phase diagram. From a thermodynamics point of view, the four terminations can be stabilized under different conditions. In chemical potential space, NbB （Nb） and Nb （Si） terminations are just stable in a small area, whereas Si （Nb） and Nb （NbB） terminations are stable in a large area （the letters in brackets represent the subsurface atoms）.

Baroclinic Instability in the Generalized Phillips＇Model PartI：Two－layer Model

By employing Arnol'd's method(energy-Casimr),this paper has studied the nonlinear stability of the two-layergeneralized Phillips'model for which the top and bottom surfaces are either rigid or free, and obtained somenonlinear stability criteria.In addition,some linear stability criteria are obtained by normal mode method.The results reveal the influences of the free surface parameter on the stability of atmospheric and oceanic motions.

Insight into the effect of graphene coating on cycling stability of LiNi_(0.5)Mn_(1.5)O_(4):Integration of structure-stability and surface-stability

Graphene has presented promising features for application in lithium ion batteries(LIBs)due to its superior electronic conductivity and high surface area.It has been successfully used for modifying cathode materials to meet the increasing demand for LIBs with longer cycle life.However,the improving effect of graphene on cycling stability is still unclear,which restricts its further application in LIBs.Herein,graphene coated hollow sphere-like structure LiNi0.5Mn1.5O4(LNMO)wasdesigned and the improvement mechanism of graphene coating on LNMO’s cycling stability was investigated.The results show that graphene coating not only contributes to suppress structural deformation from mechanistic reaction and extend solid-solution reaction,but also helps protect electrode from corrosion by the products from electrolyte decomposition and suppress the generation of surface defects,especially at high temperature.Owing to graphene coating,graphene coated LNMO can deliver a discharge capacity of 91 mAh g1 with high capacity retention of 82.5%after 1000 cycles under 20C and 83.8 mAh g1 with 94.5%capacity retention after 100 cycles under 2C at 55C.This work deeply explores the effect of graphene coating on cycling stability from crystal stability and surface stability,which will help a wider application of graphene in energy storage field.

Development of Slippery Liquid-Infused Porous Surface on AZ31 Mg Alloys for Corrosion Protection

The relatively poor corrosion resistance remarkably limits the wide applications of Mg alloys in practice,although they possess many attractive properties,like low density,high specific strength,and good biocompatibility.The formation of a protective coating can effectively suppress the corrosion.In this work,a slippery liquid-infused porous surface(SLIPS),with good surface hydrophobicity,stability,and self-healing property,was formed on AZ31 Mg alloys.The development of SLIPS requires suitable porous micro/nanostructures.Layered double hydroxide(LDH),with effective corrosion resistance for Mg alloys,was a good candidate to accommodate the liquid lubricant.Especially,different temperatures were applied to in situ form MgAl-LDH on AZ31 Mg alloys.The results showed that the temperature of 120℃was the best condition for the SLIPS to provide good corrosion protection for Mg alloys,with the lowest corrosion current density of 3.19×10^(-9)A cm^(−2).In addition,the SLIPS performed well in the long-term immersion test and abrasion test.The AZ31 Mg alloys with superior corrosion resistance and good mechanical and chemical stability can be extensively applied in areas of automotive,electronics,and aerospace.

Distribution of ephemeral plants and their significance in dune stabilization in Gurbantunggut Desert

Based on systematically monitoring plants on dune ridges in the southern part of the Gurbantunggut Desert in 2002, this paper, from the angle of dune stabilization by vegetation, describes the temporal and spatial distribution patterns of ephemeral plants on isolated sand dunes, analyses the natural invasion processes of ephemeral plants on human-disturbed sand surface and expounds the importance of ephemeral plants in stabilizing sand dune surface. A total of 45 plant species were identified in the study area, 29 of which are ephemeral plants. Ephemeral plants sprouted in early April and completed their life-circle within about two months. Just as aeolian sand activities came to the strongest stage from April to June in desert regions of northern Xinjiang, the total coverage of trees, shrubs and herbs of long vegetational period on most dune ridges was less than 10%, while the mean coverage of ephemeral plants reached 13.9% in April, 40.2% in May and 14.1% in June. Therefore ephemeral plants acted as the major contributor to dune surface stabilization in the Gurbantunggut Desert. Investigations of vegetation restoration on engineering-disturbed dune surface show that ephemeral plants first recolonized the disturbed dune surface.

Fluorite Ce_(0.8)Sm_(0.2)O_(2-δ) porous layer coating to enhance the oxygen permeation behavior of a BaCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ) mixed conductor

Fluorite Ce0.8Sm0.2O2-δ（SDC） nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo0.7Fe0.2Nb0.1O3-δ（BCFN） mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux（JO2） than the uncoated BCFN in the partial oxidation of coke oven gas（COG）. The maximum JO2 value of the SDC-coated BCFN is 18.28 mL ·min^-1·cm^-2 under a COG/air flux of 177 mL ·min^-1/353 mL ·min^-1 at 875℃ when the thickness of the BCFN membrane is 1 mm; this JO2 value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen vacancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.

A time-dependent numerical model of the mild-slope equation

On the basis of the previous studies, the simplest hyperbolic mild-slope equation has been gained and the linear time - dependent numerical model for the water wave propagation has been established combined with different boundary conditions. Through computing the effective surface displacement and transforming into the real transient wave motion, related wave factors will be calculated. Compared with Lin＇s model, analysis shows that calculation stability of the present model is enhanced efficiently, because the truncation errors of this model are only contributed by the dissipation terms, but those of Lin＇s model are induced by the convection terms, dissipation terms and source terms. The tests show that the present model succeeds the merit in Lin＇ s model and the computational program is simpler, the computational time is shorter, and the computational stability is enhanced efficiently. The present model has the capability of simulating transient wave motion by correctly predicting at the speed of wave propagation, which is important for the real - time forecast of the arrival time of surface waves generated in the deep sea. The model is validated against analytical solution for wave diffraction and experimental data for combined wave refraction and diffraction over a submerged elliptic shoal on a slope. Good agreements are obtained. The model can be applied to the theory research an d engineering applications about the wave propagation in a biggish area.

On the stability of the flow over a shrinking cylinder with prescribed surface heat flux

This study investigates the steady stagnation point flow and heat transfer passes a horizontal shrinking permeable cylinder.The free stream velocity and the prescribed surface heat flux arc assumed to vary linearly with the distance from a fixed point on the cylinder.The partial differential equations governing the flow and heat transfer are transformed into a system of ordinary differential equations via similarity transformation.These equations are solved numerically for several values of the governing parameters,such as suction parameter s,curvature parameter γ,and shrinking parameter λ.The equations arc solved numerically by employing the boundary value problem solver package available in MATLAB software,bvp4c.The effects of the governing parameters on the skin friction coefficient,surface temperature,velocity,and temperature profiles are examined.Given the existence of dual solutions in the present study for a certain range of the curvature parameter,stability analysis is carried out to determine which one of the solutions is stable as time passes.The outcome of the stability analysis demonstrates that only the first solution,with lower boundary layer thickness,appeared to be stable and thus physically reliable,while the other is not.It is also discovered that the boundary layer separation is delayed by reducing the curvature parameter.

Precipitate-stabilized surface enabling high-performance Na_(0.67)Ni_(0.33-x)Mn_(0.67)Zn_(x)O_(2) for sodium-ion battery

Electrode interfacial degradations are the key challenges for high-performance rechargeable batteries,usually mitigated through surface modification/coating strategies.Herein,we report a novel mechanism to enhance the surface stability of P2 layered cathodes by introducing a high density of dopant-enriched precipitates.Based on microscopic analysis,we show that forming a high density of precipitates at the grain surface can effectively suppress surface cracking and corrosion,which not only improves the surface/interface stability but also effectively suppresses the intergranular cracking issue.Increasing the doping level can lead to a greater density of precipitates at the surface region,which results in higher surface stability and increased cycling stability of the P2 layered cathode for a sodium-ion battery.We further reveal that prolonged cycling can induce the formation of a precipitate-free surface region due to the loss of Zn dopant and Na.Our in-depth microanalysis reveals cycling-induced dynamic structural evolution of the P2 layered cathodes,highlighting that dopant segregation-induced precipitation is a new approach to achieving high interfacial stability.

Surface Structures and Their Relative Stabilities of Orthorhombic YAlO_(3):A First-Principles Study

First-principles energetics calculations were performed to investigate the structures and relative stabilities of six low millerindex surfaces of orthorhombic YAlO_(3) (YAP).The stoichiometric YAP (100) and (001) were predicted to have the lowest surface energies of 1.91 and 1.96 J/m ^(2),respectively.Using a thermodynamic defect model,non-stoichiometric YAP surface energies were further predicted as a function of P_(O2)(P_(O2)<1 atm) and temperature (T).All the results were combined to construct the surface phase diagrams at T=300 and 1400 K,revealing the strong correlation of the surface stabilities of YAP with its surface stoichiometry.

Dual function of a high-contrast hydrophobic-hydrophilic coating for enhanced stability of perovskite solar cells in extremely humid environments

In spite of a continuous increase in their power conversion efficiency （PCE） and an economically viable fabrication process,organic-inorganic perovskite solar cells （PSCs） pose a significant problem when used in practical applications：They show fast degradation of the PCE when exposed to very humid environments.In this study,the stability of PSCs under very humid conditions is greatly enhanced by coating the surface of the PSC devices with a multi-layer film consisting of ultrahydrophobic and relatively hydrophilic layers.A hydrophobic composite of poly（methyl methacrylate） （PMMA）,polyurethane （PU）,and SiO2 nanoparticles successfully retards the water molecules from very humid surroundings.Also,the hydrophilic layer with moderately PMMA captures the residual moisture within the perovskite layer;subsequently,the perovskite layer recovers.This dual function of the coating film keeps the PCE of PSCs at 17.3% for 180 min when exposed to over 95% humidity.

Interaction between Cu^(2+) and different types of surface-modified nanoscale zero-valent iron during their transport in porous media

This study investigated the interaction between Cu^2＋and nano zero-valent iron（NZVI）coated with three types of stabilizers（i.e., polyacrylic acid [PAA], Tween-20 and starch） by examining the Cu^2＋ uptake, colloidal stability and mobility of surface-modified NZVI（SM-NZVI） in the presence of Cu^2＋. The uptake of Cu^2＋ by SM-NZVI and the colloidal stability of the Cu-bearing SM-NZVI were examined in batch tests. The results showed that NZVI coated with different modifiers exhibited different affinities for Cu^2＋, which resulted in varying colloidal stability of different SM-NZVI in the presence of Cu^2＋. The presence of Cu^2＋ exerted a slight influence on the aggregation and settling of NZVI modified with PAA or Tween-20. However, the presence of Cu^2＋caused significant aggregation and sedimentation of starch-modified NZVI, which is due to Cu^2＋complexation with the starch molecules coated on the surface of the particles. Column experiments were conducted to investigate the co-transport of Cu^2＋ in association with SM-NZVI in water-saturated quartz sand. It was presumed that a physical straining mechanism accounted for the retention of Cu-bearing SM-NZVI in the porous media. Moreover, the enhanced aggregation of SM-NZVI in the presence of Cu^2＋ may be contributing to this straining effect.

Charge distribution into illuminated dye-doped surface stabilized ferroelectric liquid crystal cell

Surface stabilized （anti） ferroelectric liquid crystal cells can be used as an optically addressed media for optical data processing. The structure of the cell has to contain a photo sensible agent, i.e, an absorbing dye-doped orienting layer. The all-optical generation of the diffractive grating can be done due to the switching parameters of the smectic slab within cells with a sensitive layer. This Letter considers a study of the optically induced charge generation into the dye-doped layer, and the explanation of the phenomena of the selective molecular director reorientation, while cell driving what leads to the induction of phase grating.

Surface potential uniformity and sensitivity of large-area PTFE electret discs of different thicknesses produced by a modified corona poling rotating system for dosimetry applications

In this study,large-area(6-cm diameter)Teflon polytetrafluoroethylene(PTFE)discs of different thicknesses(0.2-,0.5-and 1-mm)were negatively and positively charged by using the“modified single point-to-plane corona poling rotating system”.The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as.(a)PTFE disc thickness,(b)PTFE disc polarity and(c)needle-to-PTFE disc distance were successfully reported.Accordingly,closer needle-to-PTFE disc distance,positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity.However,the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness.Additionally,the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5-and 13-mm needle distances for the negative and positive charging modes,respectively.At the optimized charging conditions,large-area PTFE electret disc(0.5-mm-thick)with positive uniform surface charge potential especially at the edges up to
1.8 kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry.As also observed in this study,the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases.Meanwhile,0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.