Theory Of Surface Effects Research Articles

Application of Gas Explosion Nanometer Powder Suppression Material in Coal Mine Safety

Mine gas explosion seriously threatens the safety of coal mine production. Existing gas explosion control materials and technologies cannot effectively control the occurrence of gas disasters. Aiming at the current limitations of powder explosion suppressants in suppressing gas explosions in mines, this paper analyzes the special flame retardant and explosion suppression effects of nano powders from the suppression effect of free radicals in the explosion process based on the theory of surface effects of nano powders. The anti-explosion mechanism of nano-powder on mine gas, and the performance characterization parameters of nano-anti-explosion powder were proposed. In this paper, the self-improved 20 L near-spherical gas explosion suppression experiment system is used to perform the explosion suppression experiment of nanometer powder. The results of this study show that compared with micron-level powders, nano-powders have a better anti-explosion effect. The maximum explosion pressure and average rate of pressure rise of methane have decreased by 70.5% and 90%, respectively, and the peak time of explosion pressure has been extended by 3 times. Therefore, thenano-explosion suppressing powder material can suppress the gas explosion in the mine and can effectively control the occurrence of gas disasters.

Nonlinear dynamics of fluid conveying double-walled nanotubes incorporating surface effect: A bifurcation analysis

The aim of this work is to analyze the effect of the residual surface stress on the dynamic instability of the fluid conveying double-walled nanotubes (DWNTs). To achieve this goal, the theory of surface effect, nonlocal elasticity and nonlinear von Karman theory are combined which lead to new insight in bifurcations of fluid conveying DWNTs. The conveying fluid is also modeled and analyzed based on modified Navier–Stokes relation considering Knudsen number. In addition, Galerkin technique and multiple time scales method is applied to solve the equation. By means of the bifurcation analysis, it is shown that a discontinuous bifurcation is always accompanied by a jump. Finally, stable and unstable regions in dynamic instability of DWNTs are addressed. We close this paper by stating that the residual surface stress enhances the stiffness of DWNTs. Furthermore, the results indicate and emphasize that the nanofluid velocity as an external excitation can significantly affect the instability behaviors of the system.

A clarification of the role of crack-tip conditions in linear elasticity with surface effects

We examine the role of crack-tip conditions in the reduction of stress at a crack tip in a theory of linear elasticity with surface effects. The maximum number of allowable end conditions for complete removal of a stress singularity is demonstrated for both plane and anti-plane problems. In particular, we show that the necessary and sufficient conditions for bounded stresses at a crack tip cannot be satisfied with a first-order (curvature-independent) theory of surface effects, which leads, at most, to the reduction of the classical strong square-root singularity to a weaker logarithmic singularity.

Observation of paramagnetic Meissner currents—evidence for Andreev bound surface states

We report the observation of anomalous Meissner currents (AMCs) in thin films of superconducting YBCO with oriented internal surfaces introduced by heavy-ion bombardment. High-precision measurements of the penetration depth λ( T) reveal an upturn in the temperature dependence of λ( T) below T≈15 K, which is strongly dependent on the orientation and density of the surfaces. The magnitude of the observed effect, its onset temperature and its dependence on the orientation of the surfaces are in quantitative agreement with the theory of surface effects in d-wave superconductors. The anomaly is interpreted as a consequence of surface-induced Andreev bound states (ABSs) carrying paramagnetic currents.

Low-Temperature Anomaly in the Penetration Depth ofYBa2Cu3O7Films: Evidence for Andreev Bound States at Surfaces

We report the observation of anomalous Meissner currents in thin films of superconducting YBCO with oriented internal surfaces introduced by heavy-ion bombardment. High-precision measurements of the penetration depth ( $\ensuremath{\lambda}$) reveal an upturn in the temperature dependence of $\ensuremath{\lambda}$ below ${T}^{*}\ensuremath{\approx}15\mathrm{K}$. The magnitude of the observed effect, its onset temperature, and its dependence on the orientation of the surfaces are in quantitative agreement with the theory of surface effects in $d$-wave superconductors. The anomaly is interpreted to arise from surface currents that are carried by surface-induced Andreev bound states.

Phenomenological theory of surface effects in ferroelectrics and its relationship with transverse Ising model

The relationship between the transverse field Ising model and the Landau phenomenological theory for ferroelectrics is analyzed, and the Landau free energy expression for ferroelectrics having surfaces is derived. It is pointed out that the traditional expression in which the surface integral has only a term of the square polarization is valid only for special cases, in general a term of the polarization to the four should be included as well. By use of the newly derived free energy expression, the thickness-dependence of the spontaneous polarization and Curie temperature of ferroelectric films is calculated; thereby some experimental results incompatible with the traditional phenomenological theory are successfully explained.

Theory of surface effects in binary alloys with fcc crystal structure: A Landau approach.

Theory of surface effects in binary alloys with fcc crystal structure: A Landau approach.

Theory of Surface Effects in Binary Alloys

ABSTRACTThe chemical, ordering and magnetic properties of binary alloys at the surface are examined in terms of a model of pairwise interacting atoms. Both the case of segregating alloys and the case of alloys which form intermetallic compounds are examined. Some surprising results about surface concentration and surface ordering are found. Applications to a number of systems, including ferromagnets, are presented.

Theory of surface effects in binary alloys. III. Stepped surfaces

A theory of surface effects at stepped surfaces in binary ordering alloys is presented. The model is based on pairwise interactions between nearest neighbors and includes long- and short-range-order effects. An example of the [120] stepped surface with [$\overline{1}10$] monoatomic steps and terraces on the [110] plane of a body-centered-cubic alloy is presented. Results for the concentration at all the different sites on the stepped surface as well as for the short-range order parameters as functions of temperature are presented.

Theory of surface effects in binary alloys. IV. Ordering alloys with two ferromagnetic components

A theory of the surface concentration, spatial long-range order and magnetism for binary body-centered-cubic ordering alloys with ferromagnetic components is presented. It is a mean-field theory based on a model consisting of pairwise interactions between nearest neighbors only. We find that for an alloy ${A}_{x}{B}_{1\ensuremath{-}x}$ with spains ${S}_{A}$, ${S}_{B}$ and Ising exchange integrals ${J}_{\mathrm{AA}}$, ${J}_{\mathrm{AB}}$, and ${J}_{\mathrm{BB}}$, magnetism favors surface segregation of the $I$ component if ${S}_{I}^{2}{J}_{\mathrm{II}}l{S}_{{I}^{\ensuremath{'}}}^{2}{J}_{{I}^{\ensuremath{'}}{I}^{\ensuremath{'}}} (I,{I}^{\ensuremath{'}}=A,B)$. Results for the surface concentration and the long-range order parameters at $T=0$ are presented. At finite temperatures, alloys with several bulk behaviors are studied, i.e., (i) ${T}_{0}$ (spatial order-disorder critical temperature) $l{T}_{M}$ (Curie temperature), (ii) ${T}_{0}g{T}_{M}$, and (iii) ${J}_{\mathrm{AB}}\ensuremath{\ll}{J}_{\mathrm{AA}},{J}_{\mathrm{BB}}$. It is found that in case (iii) there is a range of temperatures where the surface is magnetic whereas the bulk is paramagnetic. Also studied is the effect on the surface properties produced by allowing the chemical and magnetic interactions to be location dependent. It is found in general that the results are more sensitive to changes in the chemical interactions. The FeCo system is examined along these lines, and the results are compared with existing experimental data.

Theory of surface effects in binary alloys. I. Ordering alloys

A theory of the (110) surface concentration and short- and long-range orders for an $\mathrm{AB}$ body-centered-cubic alloy is presented. It is based on a model consisting of pairwise interactions between nearest-neighbor atoms only. The entropy is calculated in the pair approximation following Kikuchi's method. It is found that depending on the values of the interaction parameters (a) the surface concentration decreases monotonically as a function of temperature from 100% of one component at $T=0$ to a random mixture as $T\ensuremath{\rightarrow}\ensuremath{\infty}$, or (b) it increases from a perfectly ordered $\mathrm{AB}$ layer of equal concentration of either component to a maximum concentration of one component at the order-disorder transition temperature ${T}_{c}$ and then decreases again to the disordered ${A}_{0.5}{B}_{0.5}$ alloy as $T\ensuremath{\rightarrow}\ensuremath{\infty}$. Long-range and short-range order parameters as functions of temperature are also discussed.

Theory of surface effects in binary alloys. II. Segregating alloys

Theory of surface effects in binary alloys. II. Segregating alloys

Theory of surface effect in photoassisted field emission

The influence of the surface on the photoassisted field emission from a metal is studied theoretically for two simple models of the solid. First, we consider the model of a half-space square well for the metal, and solve exactly for the current density after ignoring the Schottky effect. Next, we take into account the effect of the image charge, and calculate the current density in the WKB approximation. Numerical results based on the calculations are compared with the recent experimental data on photoassisted field emission from tungsten. Areas of agreement and discrepancy between the theory and experiment are pointed out and discussed.

Theory of Surface Effects on the Thermal Diffuse Scattering of X Rays or Electrons from Crystal Lattices

A theory has been developed for the effect of a free surface on the thermal diffuse scattering of x rays or electrons from a crystal lattice. The harmonic approximation is employed. It is assumed that the scattering is entirely from the surface layer. The results are presented both in terms of the eigenvalues and eigenvectors of the dynamical matrix and in terms of a function of the dynamical matrix itself. An alternative treatment based on thermodynamic Green's functions has also been developed and applied to the monatomic simple lattice with nearest- and next-nearest-neighbor central interactions. Explicit formulas are obtained for the isotropic case in the high-temperature limit when the difference between the outgoing and incoming wave vectors of the radiation is near a reciprocal lattice rod. A comparison between the surface and bulk cases is given.