Initial Incident Angle Research Articles

The mechanism of vortex connection at a free surface

Vortex connections at the surface are fundamental and prominent features in free-surface vortical flows. To understand the detailed mechanism of such connection, we consider, as a canonical problem, the laminar vortex connections at a free surface when an oblique vortex ring impinges upon that surface. We perform numerical simulations of the Navier–Stokes equations with viscous free-surface boundary conditions. It is found that the key to understanding the mechanism of vortex connection at a free surface is the surface layers: a viscous layer resulting from the dynamic zero-stress boundary conditions at the free surface, and a thicker blockage layer which is due to the kinematic boundary condition at the surface. In the blockage layer, the vertical vorticity component increases due to vortex stretching and vortex turning (from the transverse vorticity component). The vertical vorticity is then transported to the free surface through viscous diffusion and vortex stretching in the viscous layer leading to increased surface-normal vorticity. These mechanisms take place at the aft-shoulder regions of the vortex ring. Connection at the free surface is different from that at a free-slip wall owing to the generation of surface secondary vorticity. We study the components of this surface vorticity in detail and find that the presence of a free surface accelerates the connection process. We investigate the connection time scale and its dependence on initial incidence angle, Froude and Reynolds numbers. It is found that a criterion based on the streamline topology provides a precise definition for connection time, and may be preferred over existing definitions, e.g. those based on free-surface elevation or net circulation.

Theoretical determination of parameters for optimum surface specificity in overlayer attenuated-total-reflection infrared spectroscopy

We investigate the feasibility of overlayer attenuated-total-reflectance (O-ATR) infrared spectroscopy as a surface analytical tool for studying reactions and molecular properties of adsorbates at surfaces exposed to aqueous nonelectrolyte solutions. Through modeling an O-ATR system by assuming it to comprise three, four, or n phases of homogeneous refractive index, one can use an electric-field analysis to determine how the parameters of adsorption free energy, overlayer thickness, initial angle of incidence, and internal-reflection element refractive-index influence solvent-subtracted O-ATR infrared-absorption spectra. The theory behind such an analysis is explained, and the results of its application are presented for hypothetical O-ATR systems consisting of either a zinc selenide or a germanium internal-reflection element, an iron or hematite overlayer, an adsorbate layer, and a solution of methylene chloride in water.

Inviscid dipole-vortex rebound from a wall or coast

A vortex approaching a no-slip wall ‘rebounds’ due to the creation of vorticity at the wall in a viscous boundary layer. Here it is demonstrated that a purely inviscid mechanism can also produce vortex rebound from a slip wall. In inviscid vortex rebound, vortex tube stretching generates the necessary vorticity to allow rebound, eliminating the need for viscous vorticity generation. This vortex stretching mechanism is demonstrated through numerical simulations and laboratory experiments on dipole-vortex rebound from a boundary. In an application to oceanography, numerical simulations of both quasi-geostrophic and shallow water dynamics are used to show that the β-effect at an eastern boundary can produce this inviscid rebound. Through a series of numerical experiments in which the strength of the β-effect is varied, a formula for predicting the point of separation of the vortices from the boundary in a dipole–coast collision is deduced. Through simulations, the flux of vorticity and fluid away from the boundary is measured as a function of β and initial angle of incidence. It is found that, in contrast to viscous vortex rebound, which typically does not produce a flux of material away from the boundary farther than a distance comparable to the initial vortex radius, the β-induced rebound does carry fluid far from the coast. Laboratory experiments in a rotating tank are used to show that a sloping bottom can also provide an inviscid mechanism for dipole-vortex rebound from the wall of the tank under certain conditions. A relation determining the conditions under which inviscid or viscous processes will dominate in the rebound of the dipole from a boundary is obtained.

A comparison of quantum and classical dynamics of H 2 dissociation on Cu(111)

A quantitative comparison of the results from quantum and classical computations of the dissociation of H 2 on the ab initio Cu(111) surface is presented. In order to initiate a detailed comparison of the classical and quantum methods, we chose to investigate motion on the vibrationally adiabatic ground state. This subtracts from the problem the largest quantum degree of freedom with the consequence that broadly speaking, quantum and classical results for the dissociation as a function of initial rotational state and incidence angle agree well. One feature arising from the calculation is that for the first time we have shown how the quantized nature of motion near the transition state affects experimental observables. We demonstrate that hitherto neglected structure in dissociation probabilities may be traced to quantized hindered rotational and translational motion. An additional consequence of the quantization is a pronounced J-dependent broadening in the dissociation probabilities when plotted as a function of the translational energy which should be experimentally observable.

Angle measurement based on the internal-reflection effect: a new method

We describe a new method of angle measurement that is based on the internal-reflection effect at an air-glass boundary. The method uses a differential detection scheme to largely reduce the inherent nonlinearity of the reflectance versus the angle of incidence in internal reflection. With nonlinearity reduced, the displacement of the angle of incidence can be determined accurately by measuring the reflectance. The resolution and measurement range are determined by the initial angle of incidence, the polarization state of the light, and the number of reflections. Compared with interferometers and autocollimators, this method has the advantage of a simple sensor design for applications ranging from a wide measurement range to extremely high resolution. Other advantages are compact size, simple structure, and low cost. A theoretical analysis of the method and some experimental results of a prototype sensor are presented. The possible applications of the method are also discussed.

Effect of Initial Incident Angle on Magnetic Properties of Vacuum Deposited Co-Cr Films

The incident angle dependence of the magnetic properties of vacuum-deposited Co-Cr was investigated. Using a vacuum deposition system, continuous films and films were deposited onto polymer substrates in motion and held stationary, respectively, with the incident angle of evaporated atoms varying from 70° (initial) to 40° (final). In fixed films, which were cut into small pieces to perform measurements of regions in angular intervals of 2.5° the hep c-axis dispersion increases and the shape magnetic anisotropy increases with increasing angle of incidence. In films, both magnetocrystalline anisotropy and shape magnetic anisotropy contribute to the magnetic anisotropy. Compared with fixed films, the magnetic properties of are influenced by the initial film growth region at incident angles above 60°.

Coexistence of precursor and direct dynamics: The sticking of O2 on a Pt(111) surface

The initial sticking coefficient (probability for dissociative chemisorption) has been measured for O2 on a Pt(111) surface as a function of initial energy, incident angle, and surface temperature using molecular beam techniques. The results reveal two distinct mechanisms for sticking; precursor mediated and direct dissociation, either of which can dominate depending upon the initial adsorption conditions.

Effects of an Initial Layer on Co-Cr Films Sputtered on Continuous Film Substrates

Co-Cr films were fabricated by the targets facing type of sputtering method. It was already reported [2] that the smaller the initial incident angle (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> ), the better the magnetic properties and cryrstal orientation of the films. Mass production usually requires a large θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> . A double-layered Co-Cr film was fabricated with a small θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> -1) for the first layer and a large θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> -2) for the second layer. It was found that when the first layer was moore than 0.01 μm thick, the second layer grows in an epitaxial formation and the crystal orientation of the double-layered film is much better than that of a single-layered film with a large θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">init</sub> .

Crystalographic Orientation of Continuously Sputtered Co-Cr Films

The dependence of film crystal orientation on film thickness for several Co-Cr films formed by dc planar magnetron sputtering with a variety of deposition mask arrangements was investigated. Special attention was paid to the initial layer. The dependence of magnetic properties on film thickness was found to be strongly influenced by the mask arrangement, especially by the distance between the mask edge and the roll, and by the initial incidence angle for the sputtered atoms. It was found that controlling these parameters properly is extremely important in continuous sputtering.

Discussion of “Atmospheric refraction at College, Alaska, during the winter, 1947–1948”

Refraction by the Earth's atmosphere of the light from celestial bodies is simple to explain qualitatively, but extremely difficult to treat quantitatively, as was shown by Willis [1941], The statement cited by the authors from Humphreys, that the total refraction depends only on the initial angle of incidence and the speeds in the first and last media, applies only to monochromatic light traversing plane layers; for concentric spherical shells the problem is far more complex, as Humphreys went on to show.Basically, any computation of the amount of refraction involves some assumption about the rate of decrease of air density with height, in which the all‐important factor is the vertical temperature distribution, or lapse rate. This is particularly important for rays emanating a few degrees above the horizon; at higher altitudes, formulas based on almost any atmospheric model can be adjusted to agree with observed refractions. Various theories have used various lapse rates; almost all United States tables, including the 1885 Doolittle tables which the authors used as standard, are based on those of Bessel, whose development assumed a lapse rate of around 0.6° F per 1000 ft, decreasing very slightly with height.