Imaging the edge of a 4He prewetting film on a cesium metal surface

The edge of a metastable ⁴ He prewetting film on a cesium metal surface is investigated using polarization interference microscopy. This technique images the local gradient of the coverage through its optical thickness. The cesium metal is a film evaporated on a polished copper substrate. A liquid helium film is deposited on the surface through raising and lowering the bulk liquid surface. Its edge is clearly observed for temperatures below 1.6 K. The apparent optical thicknesses of the films, larger than what is expected for a normal saturated film, remain to be explained.     

On the change in the modulus of elasticity with a decrease in the size of a nanocrystal

A model of nanocrystal in the form of a rectangular parallelepiped with a variable surface shape is used to show that, at high temperatures, modulus of elasticity B decreases with a decrease in size of the nanocrystal N, which is due to the increase in the surface pressure. However, at low temperatures, dependence B(N) is less pronounced and can even rise with a decrease in the nanocrystal size. This is because, at low temperatures, the increase in the surface pressure (which is larger than at high temperatures) leads to an increase in the modulus of elasticity for the entire nanocrystal. The more the nanocrystal shape deviates from the most energetically stable shape, the more pronounced the change in the dependence B(N) is.     

Modeling the Ultrasonic Radiation of a Planar Transducer Through a Plane Fluid—Solid Interface

Three types of transducer beam models are developed for obtaining the bulk waves generated by a plane piston transducer radiating through a planar fluid—solid interface. The first type, called the surface integral model, is based on a Rayleigh—Sommerfeld-like integral that requires a two-dimensional surface integral to be evaluated. The second model, called the boundary diffraction wave (BDW) paraxial model, simplifies the two-dimensional integration of the surface integral model to a one-dimensional line integration. The third type of model, called the edge element model, is shown to be a novel way of efficiently evaluating the two-dimensional surface integration of the surface integral model. The limitations of these models for simulating inspections near critical refracted angles and near the interface are discussed. It is shown that the introduction of the paraxial approximation in the BDW model allows that model to be computed with a very large (300—1) speed advantage over the surface integral while retaining the same accuracy in most cases. The edge element model, while having a smaller (5—1) advantage over the direct numerical integration of the surface integral model, retains the accuracy of the surface integral model in cases where the paraxial approximation fails and can be easily generalized to more complex testing situations (focused probes, curved interfaces, etc.).     

Modifying the composition of a brass and bronze surface layer under a high power ion beam of a nanosecond duration

The change in the composition of the surface layers of brass LS59-1 and bronze BrOS10-10 under the action of a high power ion beam has been studied. Zinc depletion of the brass surface at a beam current density of j ～50 A/cm² is shown; zinc enrichment of the surface layer is observed at j > 150 A/cm², and a thin zinc layer is found to be formed across the entire surface. For bronze BrOS10-10, tin enrichment of the surface is registered only under a multiple effect of the beam at j >150 A/cm². Various mechanisms of modifying the elemental composition are considered.     

Fluctuational electromagnetic interaction of the tip of a scanning microscope with the surface of a solid

A general formula for the lateral frictional force acting on the tip of a scanning microscope moving parallel to a surface with a velocity V is obtained within fluctuational electromagnetic theory. The contributions of various polarization mechanisms to this force are analyzed. The dependences of the lateral forces on the velocity, radius of curvature, and distance of the tip from the surface, as well as the temperature and the dielectric properties of the tribological contact are obtained. It is shown for the first time that the lateral forces can change sign and become accelerating for a definite combination of dielectric functions of the tip and the surface. Pis’ma Zh. Tekh. Fiz. 25, 10–16 (June 26, 1999)     

Scattering of the electromagnetic waves from a rough surface

The electromagnetic field scattered by a rough surface of a semi-infinite body is computed up to the second order of a perturbation scheme with the surface roughness as a perturbation parameter. The calculations are based on the equation of motion of the polarization within the Lorentz–Drude (plasma) model of polarizable, non-magnetic, homogeneous matter. The surface roughness contributes both to the main (specularly) reflected and refracted fields and diffuse scattering, or gives rise to secondary (second-order) diffraction peaks for a regular grating. The calculations are performed both for the s- and p-waves. Two-dimensional modes, resonant at certain frequencies, are identified, confined to and propagating only on the surface, as a consequence of the surface roughness.     

On the slow motion of a solid submerged in a fluid with a surfactant surface film

Summary This paper continues the work of Shail and Gooden [1–4] on the motion generated in a semi-infinite fluid by a singularity or submerged solid moving particle when the surface of the fluid is contaminated with a surfactant film. The fluid motion is assumed to be slow and quasi-steady, but the restriction to axially symmetric flows of earlier investigations is removed. The various linearised models of Shail and Gooden [3,4] governing the variation of film concentration are discussed, the constitutive properties of the film being expressed in terms of Boussinesq coefficients of surface shear and dilatational viscosities. The resulting film boundary conditions are applied to solve the non-axially symmetric problem of a Stokeslet placed in the bulk fluid with its axis parallel to the surface (assumed planar throughout the motion), and the results used to calculate approximate expressions for the resistive force on a particle which translates far from and parallel to the surface. A similar analysis is given for the case of a rotelet whose axis is parallel to the surface.     

Stress intensity in the vicinity of a surface flaw in the linear part of a pipeline

Real sharp-edted surface and subsurface flaws detected in a gas pipeline body are modeled by surface semi-elliptical mathematical cracks (cuts) in a closed cylindrical shell. A relationship is proposed that relates the geometrical dimensions of the flaws to the crack aspect ratio. Based on the line spring model, the problem of stress state and boundary equilibrium conditions of a closed cylindrical shell with a surface semi-elliptical crack is reduced to a system of singular integral equations. An algorithm was developed for computational solution of the problem, and numerical analysis was made for the dependence of stress intensity factors on loading conditions and geometrical parameters of shell and crack. For a shell subjected to internal pressure and weakened by a surface longitudinal semi-elliptical crack, a closed approximation formula is proposed that interrelates pressure level, shell/crack dimensions, and material mechanical properties in boundary equilibrium conditions. The maximal error value is indicated for the results obtained using this formula. Lvov Polytechnic State University, Lvov, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 38–47, July–August, 1999.     

Geodesic Gaussian Processes for the Parametric Reconstruction of a Free-Form Surface

Reconstructing a free-form surface from 3-dimensional (3D) noisy measurements is a central problem in inspection, statistical quality control, and reverse engineering. We present a new method for the statistical reconstruction of a free-form surface patch based on 3D point cloud data. The surface is represented parametrically, with each of the three Cartesian coordinates (x, y, z) a function of surface coordinates (u, v), a model form compatible with computer-aided-design (CAD) models. This model form also avoids having to choose one Euclidean coordinate (say, z) as a “response” function of the other two coordinate “locations” (say, x and y), as commonly used in previous Euclidean kriging models of manufacturing data. The (u, v) surface coordinates are computed using parameterization algorithms from the manifold learning and computer graphics literature. These are then used as locations in a spatial Gaussian process model that considers correlations between two points on the surface a function of their geodesic distance on the surface, rather than a function of their Euclidean distances over the xy plane. We show how the proposed geodesic Gaussian process (GGP) approach better reconstructs the true surface, filtering the measurement noise, than when using a standard Euclidean kriging model of the “heights”, that is, z(x, y). The methodology is applied to simulated surface data and to a real dataset obtained with a noncontact laser scanner. Supplementary materials are available online.     

Stress intensity factors for a semi-elliptical crack in the surface of a semi-infinite solid

The stress intensity factors are presented for a vertical semi-elliptical surface crack in an elastic semi-infinite body which is subjected to a constant pressure on the crack surface. The approach utilizes a singular integral equation which is defined over the crack area only, where the weakness of the stress singularity is taken into account near the corner points at which the crack periphery intersects the surface of the semi-infinite body.This pertinent approach provides the proper assessment of the stress intensity factors in the vicinity of the corner points, and reveals that the stress intensity factor reaches a maximum value near the corner point and then decreases to zero as the point is approached.

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Résumé On présente les facteurs d'intensité de contrainte pour une fissure de surface verticale semi-elliptique dans un corps élastique semi-infini soumis à une pression constante sur la surface de la fissure. L'approche utilisée recourt à une intégrale singulière définie uniquement sur la superficie de la fissure, où l'on prend en considération l'affaiblissement de la singularité des contraintes au voisinage des points où la périphérie de la fissure est en intersection avec la surface du corps semi-infini.Cette approche permet d'obtenir les facteurs d'intensité de contrainte au voisinage des points considérés et révèle que le facteur d'intensité des contraintes passe par un maximum en ceux-ci et décroît vers zéro lorsqu'on s'en éloigne.

     

Deformation of the Surface of a Conducting Liquid under the Action of a Pulse of a Strong Field

It has been shown that the development of the process of the so-called Frenkel–Tonks instability occurring in the case of application of an electric field to a plane surface of a conducting liquid is also determined by the size of the initial distortions of the surface.     

Oxidation of the surface of a thin amorphous silicon film

The oxidation of clean crystalline silicon surfaces is self-limiting at moderate oxygen pressures (10^− 5 Pa) and temperatures (500 °C), forming 0.7-0.8 nm thick oxide layers. This study looks at the oxidation of a surface of a thin amorphous silicon film to establish if a similar mechanism is active in this case. We have devised a special experimental procedure to check the oxidation mechanism of thin amorphous silicon films. For the spectroscopic investigations we used photoemission with synchrotron radiation with the highest possible surface sensitivity and resolution. This permits a detailed decomposition of the Si 2p spectral details, using a mathematical decomposition procedure. The results clearly show that the oxidation mechanism of the surface of an amorphous silicon film under similar conditions is severely hindered compared to cases of crystalline substrates, indicating less reactivity at the surface and less transport of oxygen into the amorphous material.     

Constancy of the Surface Energy during the Melting of a Nanocrystal

The relation for the surface free energy @sgr; as a function of size and shape of a nanocrystal is derived. The nanocrystal has the form of a parallelepiped with a square base. The ratio of the lateral edge length to the base edge length f defines the shape of a system. It is shown that the value of @sgr; decreases with degreasing number of atoms N in a nanocrystal. The higher the deviation of the form parameter f from unity, the stronger the dependence @sgr;(N). It is found that the surface free energy decreases with the temperature T; in so doing, the quantity (d/T) is the greater, the smaller the size of the nanocrystal or the greater the deviation of the nanocrystal shape from the most thermodynamically stable, cubic, shape. It is shown that the nanocrystal melts when its surface energy decreases to a certain value independent of size and shape. The conditions are discussed under which the crystal fragmentation and dendritic growth are realized.     

Nonlinear dynamics of the free surface of a conducting liquid in an electric field

The nonlinear dynamics of the free surface of an ideal conducting liquid in an external electric field is investigated. It is found that in the absence of gravity and surface tension the equations of the two-dimensional motion of the medium can be solved in the approximation of small angles of inclination of the surface. It is shown that singularities of the square-root type, for which the curvature is infinite but the surface itself remains smooth, can form on the surface of a conducting liquid over a finite time. Pis’ma Zh. Tekh. Fiz. 24, 25–29 (June 26, 1998)     

Excitation of a phase-transformation wave in a metal under the action of a square surface heat pulse

We approximate the phase-transformation wave excited in a metal by the action of a square surface heat pulse when its surface density is given and the time of action is varied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 4, pp. 615–621, April, 1981.     

Direct photodesorption of ions from the surface of a crystal

A model of the direct photodesorption of ions from the surface of a crystal, reminiscent of the ionization of an atom in the external photoelectric effect, is studied. The model is based on the concept of a quasiclassical ion, whose motion in a surface potential well is described by a wave packet. The choice of wave function in the form of a packet may be justified by a variational principle, by finding the parameters of the packet. These parameters may also be selected from known experimental data. These methods are standard in solid state physics and make it unnecessary to take into account the form and magnitude of the operator describing the interaction between the ion and the crystal surface. Pis’ma Zh. Tekh. Fiz. 23, 23–26 (June 12, 1997)     

Concerning the shape of a growing dendrite

Time-independent growth of a dendrite with a nonisothermic surface is considered. The Gibbs-Thomson correction, kinetic supercooling and the curvature correction under conditions of thermal balance are taken into account. The solid- and liquid-phase heat capacities need not be equal. We obtain lower estimates for the degree of difference of the dendrite shape from paraboloidal (parabolic), valid for any — not necessarily small — values of the parameters (supercooling, surface tension, etc.).Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 5, pp. 808–815, November, 1991.     

Excitation of self-oscillations in flow past a surface with a recess and the possibility of preventing them

The results of experimental investigations of acoustic radiation initiated by hydrodynamic perturbations at the inlet to a cavity on a surface with a stream flowing past it are analyzed. A comparison is made between the processes of formation of large-scale hydrodynamic vibrations in a shear flow shed from the leading edge of the junction of the recess with the surface past which a stream flows and the processes in the region of transition from a laminar boundary layer on the surface of a wing to a turbulent one. The advisability of division of the flow inhomogeneity in the zone of the junction in order to prevent or weaken self-oscillations in the flow is estimated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 148–154, May–June, 2007.     

Averaged heat transfer during periodic fluctuations of the heat transfer intensity of the surface of a plate,a cylinder,or a sphere

Processes of heat transfer with periodically varying intensity on the surface of heated bodies of three typical geometries (plate, cylinder, sphere) are considered. The true heat transfer coefficient, which varies in time by the law of a periodic step function having two free parameters — amplitude and asymmetry, is specified on the heat transfer surface. Resultant relations are obtained for calculating the experimental heat transfer coefficient, which is the quantity measured in a traditional heat transfer experiment and used in applied calculations.Moscow Power Engineering Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 2, pp. 225–228, March–April, 1995.