A RECONSIDERATION OF THE PROPERTIES OF A PULSED RUBY LASER IN RELATION TO MICROSURGERY

Abstract— The properties of a pulsed ruby laser beam focused through a triocular microscope were studied in relation to microsurgery. Quantitative studies on 'model tissues' with different absorbencies at 6943 Å revealed that the spot diameter of the focused microbeam was dependent upon several factors. It decreased with (1) a decrease in the absorption by the object at 6943 Å; (2) a decrease in the energy of the microbeam; and (3) an increase in the magnification of the microscope. The existence of the 'tube of effect' in the optical path of the focused micro-beam was realized by irradiating the object at different planes. The depth of the tube of effect increased with (1) increase in laser energy or (2) decrease in magnification. By employing certain plant species ( Spirogyra praetensis Transeau, Ulva lactuca Linnaeus, Porphyra miniata (Lyngbye) C. Agardh and Elodea sp.) the reaction of the protoplasm to the laser microbeam in terms of 'primary damage' and 'secondary damage' was defined. Based on these experimental data the concept of minimal visible spot size in laser microsurgery and its limitations are discussed.     

On applications of the microlocal parameter method in modelling of temperature distributions in composite cylinders

Summary The problems of transient heat conduction in a periodically stratified medium consisting of a large number of alternating concentric cylinders of two homogeneous isotropic rigid materials and in a rotationally periodic cylinder consisting of a large number of circular homogeneous isotropic rigid sectors are considered. The equations of the homogenized models with microlocal parameters are derived by using the homogenization procedure given in [17]. The obtained models take into account certain microlocal effects connected with the microperiodic structure of the considered composites. Some examples of the application of the presented models to the problems of temperature distributions in composite cylinders are detailed. Received 10 March 1997; accepted for publication 23 October 1997     

Effect of time-dependent speed on frictional heat generation and wear in transient axisymmetrical contact of sliding

Summary A transient contact problem with frictional heating and wear for two nonuniform sliding half-spaces is considered. One of the two half-spaces is assumed to be slightly curved to give a Hertzian initial pressure distribution: the other is a rigid nonconductor. Under the assumption that the contact pressure distribution could be described by Hertz formulas during all the process of interaction, the problem is formulated in terms of one integral equation of Volterra type with unknown radius of contact area. A numerical solution of this equation is obtained using a piecewise-constant presentation of an unknown function. The influence of operating parameters on the contact temperature and the radius of the contact area is studied. Accepted for publication 3 November 1996     

Influence of the temporal profile of the contact pressure on the maximal temperature in pad/disc tribosystem

The solution to a thermal problem of friction during braking for a pad/disc (strip/semi-space) tribosystem with a time-dependence upon friction power is obtained. The convective cooling on an upper surface of a strip and the heat transfer through a contact surface are considered, too. The influence of duration of increase in pressure from zero (at the initial moment of time) to nominal value (at the moment of a stop) on the maximal temperature for a friction pair metal-ceramic pad/cast iron disc is studied.     

Testing Cyber-Physical Systems Using Timed Finite State Machines

Russian Physics Journal -     

AC-driven anomalous stochastic diffusion and chaotic transport in magnetic superlattices

We study regular and chaotic motion of the charge carriers in a two-dimensional electron gas subject to a spatially periodic magnetic field and to an AC electric field. We show how the interplay between the time-periodic electric and the spatially-periodic magnetic field leads to dynamical chaos and to fast stochastic diffusion of the electrons. The cases of a one-dimensional magnetic modulation with AC pumping and of a pure two-dimensional magnetic modulation are compared. We find the direct effect of anomalous diffusion and Lévy flights on the conductivity of a sample.     

The influence of the brakes friction elements thickness on the contact temperature and wear

This paper is the continuation of the author's investigations [11] where the mathematical model for determination of the contact temperature, sliding speed and wear during braking was proposed. On contrary to the previous investigation, where the working elements were considered as the half-spaces, at the present paper their thickness is taken into account. For three different dependences of the friction coefficient upon the temperature the influence of thickness on the contact temperature and wear is studied. Received on 26 April 1999     

Heat transfer in sliding of a plane-parallel layer over a base

An analytic solution of the thermal problem of friction for a plane-parallel layer–base tribosystem under conditions of incomplete thermal contact between contacting bodies is obtained. Asymptotics of the obtained solution for small and large values of time are determined. For the materials of a cermet layer–iron base friction pair, we investigate the influence of the thermal conductivity coefficient of the contact on the temperature distribution and intensity of a heat fluxes.     

Vortex and translational currents due to broken time-space symmetries

We consider the classical dynamics of a particle in a (d=2,3)-dimensional space-periodic potential under the influence of time-periodic external fields with zero mean. We perform a general time-space symmetry analysis and identify conditions, when the particle will generate a nonzero averaged translational and vortex currents. We perform computational studies of the equations of motion and of corresponding Fokker-Planck equations, which confirm the symmetry predictions. We address the experimentally important issue of current control. Cold atoms in optical potentials and magnetic traps are among possible candidates to observe these findings experimentally.     

The effect of the time structure of laser pulse on the temperature distribution in homogeneous body with coating

In the present paper an analytical solution of the transient heat conduction problem for the nonhomogeneous body, consisting of bulk foundation and thin coating of different material, is presented. This body is heated through the outer surface of coating by heat flux generated due to absorption of pulsed laser radiation. The dependence of nonstationary temperature on the thermophysical properties of the foundation and coating were studied.