The Biermann battery effect at the interfaces in stratified plasmas

The Biermann battery arises because an inhomogeneous electron pressure acts as a source term for the magnetic field. In order to better understand its effects, we consider a simplified model formed by the boundary between two fluids with different mean molecular weight and look for magnetic fields generated by the battery and localized in a band around the interface. We show that a parallel field is generated, which tends to push the original flow away from the boundary creating a rarefaction band. The specific forms of magnetic field and velocity are detailed.     

Vibrational cavitation at interfaces between solid and liquid metals

The author demonstrates the existence of cavitation bubbles in liquid zinc and establishes a relationship between the intensity of cavitation and the vibration of the cavitation bubbles.     

Numerical study of nanoscale lubrication and friction at solid interfaces

This study investigates lubrication and related frictional phenomena on the nanoscale using numerical simulations. Two models of lubrication, a two-layer and a three-layer, are considered, and for the three-layer model, a lubricant layer is introduced between the two solids. The kinetic frictional force shows resonance behaviour caused by multi-phonon excitations at the interface. It is found that these frictional effects cause a peculiar stick-slip motion of the driven plate and lubricants.     

Spreading and two-dimensional mobility of long-chain alkanes at solid/gas interfaces

Long-chain n alkanes on solid surfaces can form partially wetting liquid alkane droplets coexisting with solid multilayer terraces. We propose a diffusivelike alkane flow between terrace edge and droplet perimeter through a molecularly thin "precursorlike" film. Depending on the (uniform!) sample temperature, either droplet or terrace edge are not in thermodynamic equilibrium. This leads to a chemical potential gradient, which drives the reversible alkane flow. The gradient can be adjusted and calculated independently from the phenomenological diffusion coefficient.     

Effect of non-uniform reaction rates at solid–oxide interfaces on the electrochemical impedance

An impedance model is developed for a porous oxygen electrode on top of a solid oxide conductor, taking into account adsorption and surface transport along the pore walls, interfacial diffusion and reaction along the interface, as well as current distribution (2D) in the electrolyte. All parameters are in principal measurable. Simulated impedance spectra typically exhibit two semicircles, one related to the charge transfer reaction at the interface (high frequencies), and one related to mass transfer limitations (low frequencies). The resolution of these two semicircles, however, depend on the relative contributions of these two processes to the overall potential losses, and the magnitude of the interfacial capacitance relative to the other kinetic and transport parameters, as well as geometrical parameters.     

Boundary conditions for distribution functions at interfaces between crystalline grains

The paper concerns a derivation of boundary conditions at a planar interface between two crystalline grains for distribution functions of quasiparticles of a given kind. The derivation is performed under the assumption that the equi-energy surfaces (in thek-space) which, in general, need not be the same in both the grains, are convex. The boundary conditions take into account a jump of the (electro) chemical potential and temperature induced when a current of the quasiparticles passes through the interface. The Bezák-Krempaský boundary conditions that were originally formulated for longitudinal currents are thus generalized to the case when the currents may have a transversal component.The author thanks Dr. V.Bezák for many helpful comments.     

Free energies of surface steps in the solid on solid model of interfaces: The large system limit

Monte Carlo simulation results for the free energy associated with steps in the solid on solid model of interfaces are extrapolated to infinite system size. Within the accuracy of the machine calculations, the free energy is observed to vanish above a reduced temperature, T = 1.25 ± 0.05. It is shown that the major finite size effect is due to the interaction between steps periodically imposed in the Monte Carlo simulation.     

On the statistical distribution in a deformed solid

A modification of the Gibbs distribution in a thermally insulated mechanically deformed solid, where its linear dimensions (shape parameters) are excluded from statistical averaging and included among the macroscopic parameters of state alongside with the temperature, is proposed. Formally, this modification is reduced to corresponding additional conditions when calculating the statistical sum. The shape parameters and the temperature themselves are found from the conditions of mechanical and thermal equilibria of a body, and their change is determined using the first law of thermodynamics. Known thermodynamic phenomena are analyzed for the simple model of a solid, i.e., an ensemble of anharmonic oscillators, within the proposed formalism with an accuracy of up to the first order by the anharmonicity constant. The distribution modification is considered for the classic and quantum temperature regions apart.     

Applicability of the film-diffusion model for description of the adsorption kinetics at the solid/solution interfaces

The adsorption kinetics at the solid/solution interfaces has been described by using the kinetic model based on accepting the existence of the concentration gradient in the region of bulk solution close to the solid surface (external film-diffusion model). This model has also been adopted to explain some behaviours observed in the real adsorption systems. Simultaneously, the pseudo-first order (Lagergren) equation can be derived applying this model. The results indicate that the necessary condition to state that the “diffusion across the liquid film” mechanism is involved in controlling the rate of adsorption process is the linearity of the initial parts of kinetic isotherms plotted as the amount adsorbed vs. the time. The two methods have been proposed to distinguish between this mechanism and the classical Langmuir kinetics. The results presented here might be useful in identifying if the concentration gradient in the bulk solution influences the overall adsorption rate.     

A finite element model for laser-induced leaky waves at fluid–solid interfaces

The finite element method is firstly used to simulate the laser-induced leaky waves at fluid–solid interfaces. Corresponding models and arithmetic are developed, in that the fluid–solid interactions are described by a coupling matrix and the infinite boundary of fluid domain is modeled by acoustic absorption elements. Typical calculations are executed for air–aluminum plane and cylindrical interfaces. The results are in very good agreements with the experimental signals in available literatures, which verify the correctness of our finite element model for simulating laser-induced leaky wave at fluid–solid interfaces. And some elementary conclusions are obtained for the laser induced leaky waves.     

The net charge at interfaces between insulators

The issue of the net charge at insulating oxide interfaces is briefly reviewed with the ambition of dispelling myths of such charges being affected by covalency and related charge density effects. For electrostatic analysis purposes, the net charge at such interfaces is defined by the counting of discrete electrons and core ion charges, and by the definition of the reference polarization of the separate, unperturbed bulk materials. The arguments are illustrated for the case of a thin film of LaAlO(3) over SrTiO(3) in the absence of free carriers, for which the net charge is exactly 0.5e per interface formula unit, if the polarization response in both materials is referred to zero bulk values. Further consequences of the argument are extracted for structural and chemical alterations of such interfaces, in which internal rearrangements are distinguished from extrinsic alterations (changes of stoichiometry, redox processes), only the latter affecting the interfacial net charge. The arguments are reviewed alongside the proposal of Stengel and Vanderbilt (2009 Phys. Rev. B 80 241103) of using formal polarization values instead of net interfacial charges, based on the interface theorem of Vanderbilt and King-Smith (1993 Phys. Rev. B 48 4442-55). Implications for non-centrosymmetric materials are discussed, as well as for interfaces for which the charge mismatch is an integer number of polarization quanta.     

Electron-stimulated reactions at the interfaces of amorphous solid water films driven by long-range energy transfer from the bulk

The electron-stimulated production of D2 from amorphous solid D2O deposited on Pt(111) is investigated as a function of film thickness. The D2 yield has two components that have distinct reaction kinetics. Using isotopically layered films of H2O and D2O demonstrates that the D2 is produced in reactions that occur at both the Pt/amorphous solid water (ASW) interface and the ASW/vacuum interface, but not in the bulk. The energy for the reactions, however, is absorbed in the bulk of the films and electronic excitations diffuse to the interfaces where they drive the reactions.     

Direct experimental evidence of slip in hexadecane: solid interfaces

The boundary condition for the flow velocity of a Newtonian fluid near a solid wall has been probed experimentally with a novel setup using total internal reflection-fluorescence recovery after photobleaching leading to a resolution from the wall of the order of 80 nm. For hexadecane flowing on a hydrocarbon/lyophobic smooth surface, we give what we think to be the first direct experimental evidence of noticeable slip at the wall. We show that the surface roughness and the strength of the fluid-surface interactions both act on wall slip, in antagonist ways.     

A novel approach for the quantitative kinetic study of reactions at solid/liquid interfaces in the presence of power ultrasound

A novel cell and procedure is described which permits the quantitative mechanistic study of ultrasonically enhanced reactions which occur at solid/liquid interfaces. A model of a controlled and calculable time-average rate of mass transport to and from the interface is used in order to compare experimental results with theoretical predictions based on mechanistic reaction schemes. In this way concentrations of mechanistically significant species near the interface can be related to those in bulk solution and hence the sonochemical effects of ultrasound dissected from those arising purely from mass transport. The effect of ultrasound is demonstrated for the reaction dissolution of p-chloranil in the presence of aqueous base and for the reaction of the same substrate with the aromatic amine, N,N-dimethyl-phenylenediamine, both systems which have been studied previously in the absence of ultrasound. Complementary atomic force microscopy images are also reported.     

The effect of wave reflection and refraction at soft tissue interfaces during ultrasound hyperthermia treatments.

An improved numerical model for calculating the ultrasonic power deposition in layered medium was developed and experimentally tested. The new model takes into account the ultrasound wave reflection and refraction at the tissue interfaces thereby providing improved accuracy in ultrasound hyperthermia treatment planning. The model was compared with a simplified model to evaluate when the tissue interfaces could be ignored in the hyperthermia treatment planning and evaluation. The effect of variations in water and tissue temperatures, the fat layer thicknesses, and the beam entrance angle were also investigated to establish guidelines for treatment execution. It was found that in most cases the effects of the soft tissue interfaces can be ignored. However, in some instances the acoustic focus may be shifted several millimeters off axis in layered medium. This is important when sharply focused transducers are used for ultrasound surgery or under the condition of pulsed, high-temperature hyperthermia treatments.     

Evaluating effect of surface state density at the interfaces in degraded bulk heterojunction organic solar cell

Degradation and short shelf life have been observed experimentally in poly(3-hexylthiophene) (P3HT): 6,6-phenyl C61-butyric acid methyl ester (PCBM) based blend solar cells. Both dark and illuminated current–voltage characteristics could be explained quantitatively with a proposed single model for a typical degraded organic solar cell-glass/ITO/PEDOT:PSS/P3HT:PCBM/Al. It has been found that surface state density, interface thickness, tunneling coefficient and occupation probabilities of the interface states becomes important with the passage of time. To look into the problem the activity at ITO/PEDOT:PSS and P3HT:PCBM/Al interfaces are studied using realistic values of the interfaces. The experimental J–V characteristics is well explained with the inclusion of tunneling current through these surface states and becomes the dominant current component for the degraded cell. It is also found that surface state density increases to 10¹²–10¹³ cm⁻² eV⁻¹, which has been verified with C–V measurements and also is in agreement with our proposed model for BHJ solar cell after 150 h of fabrication.     

The wavelet response as a multiscale characterization of scattering processes at granular interfaces

We perform a multiscale analysis of the backscattering properties of a complex interface between water and a layer of randomly arranged glass beads with diameter D = 1 mm. An acoustical experiment is done to record the wavelet response of the interface in a large frequency range from λ/D = 0.3 to λ/D = 15. The wavelet response is a physical analog of the mathematical wavelet transform which possesses nice properties to detect and characterize abrupt changes in signals. The experimental wavelet response allows to identify five frequency domains corresponding to different backscattering properties of the complex interface. This puts quantitative limits to the validity domains of the models used to represent the interface and which are flat elastic, flat visco-elastic, rough random half-space with multiple scattering, and rough elastic from long to short wavelengths respectively. A physical explanation based on Mie scattering theory is proposed to explain the origin of the five frequency domains identified in the wavelet response.