Measurement of lattice damage caused by ion-implantation doping of semiconductors†

Two new techniques have been used to measure the lattice damage produced in gallium arsenide by the implantation of 60 keV cadmium ions. In one of these methods, optical reflection spectra of the ion-implanted samples were measured in the wavelength range from 2000 to 4600Å. The decrease in reflectivity resulting from ion- implantation was used to determine the relative amount of lattice damage as a function of ion dose. The second technique employed the scanning electron microscope. Patterns very similar in appearance to Kikuchi electron diffraction patterns are obtained when the secondary and/or backscattered electron intensity is displayed in the scanning electron microscope as a function of the angle of incidence of the electron beam on a single crystal surface. The degradation of these ‘Coates-Kikuchi’ patterns resulting from ion implantation was used to obtain a quantitative measure of the lattice damage caused by the implantation process. The results of measurements made by both of the methods described have been compared with each other, and with data obtained by the more established method of measuring lattice damage by Rutherford scattering of 1 MeV helium ions.     

Thermally induced birefringence in Nd:YAG ceramics

Analytical expressions for eigenpolarizations and phase delays in grains of thermally loaded Nd:YAG ceramic rods have been derived. It is shown that the depolarization of radiation in polycrystalline ceramics results in beam modulation with a characteristic size of the order of the ceramic grain size. It is reasonable to increase the ratio of rod length to grain length both to diminish this modulation depth and to compensate for birefringence by use of known techniques.     

Jordan Superalgebras Defined by Brackets

Jordan superalgebras defined by brackets on associative commutativesuperalgebras are studied. It is proved that any such superalgebrais imbedded into a superalgebra defined by Poisson brackets.In particular, all Jordan superalgebras of brackets are i-special.The speciality of these superalgebras is also examined, andit is proved, in particular, that the Cheng–Kac superalgebrais special.     

Stability of motion of a two-mass system with nonlinear friction

This paper concerns the motion of different elastically coupled masses. One of the masses is subjected to a motive force, while the other mass is acted upon by friction. The motive force decreases linearly, while friction changes nonlinearly. The differential equations of motion are derived and are reduced to the standard form (after Bogolyubov). The averaging method is used to find steady-state solutions, one of which agrees with the exact steady-state solution of the initial system of equations. It is found that the actual conditions of stability of the steady-state solution are differ greatly from the conditions calculated on the basis of avaraged equations. These differences are due to the difference in the degrees of the characteristic Rouse-Hurwitz polynomials calculated on the basis of the initial and averaged equations. The analytical results are illustrated by modeling on a microcomputer. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev; Regional Scientific Research and Experimental Design Institute, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 8, pp. 94–100, August, 1999.     

Transverse Elastic–Friction Vibrations of a Running Aircraft

An analytical model of the plane-parallel running of an aircraft under crosswind load is proposed. The compliance of the internal constraints of the aircraft and the nonlinearity of the side force on the landing gear wheels are taken into account. The model is intended to study the transverse elastic friction vibrations of the aircraft hull and landing gears. The steady motion of the aircraft is considered. The dependence of the lateral friction force on the slip angle is assumed to have the form of a sinusoidal segment. The Routh–Hurwitz instability conditions are derived in an explicit form     

Critical shimmy speed of nonswiveling landing-gear wheels subject to lateral loading

The paper presents a nonlinear model describing vibration of the landing gear relative to the fuselage. The model is intended to analyze the dynamic stability of nonswiveling main-gear wheels. The model is used to show that the lateral component of the fuselage speed has a significant effect on the critical shimmy speed __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 134–142, September 2006.     

On the motion stability of an airplane on a runway under wind loading

A nonlinear mathematical model is constructed for an airplane in high-speed plane-parallel motion along a runway when the airplane's weight exceeds slightly the lift of its wings in the presence of a cross wind. The airplane is considered a two-weight mechanical object. A system of second-order equations is obtained that describes the airplane's behavior. A system of three phase variables is suggested in which the dynamics of transverse motion is described by a set of three second-order equations. A stationary solution of this system is obtained. A stability criterion for the plane-parallel motion of the airplane is established using the Routh-Hurwitz criterion. Analysis of the data of other authors indicates that the mathematical model is adequate for some objects of aviation technology. Translated from Prikladnaya Mekhanika, Vol. 35, No. 10, pp. 101–107, October, 1999.     

Possibility of separationless flow in a nozzle with strongly curved walls

An example is given of calculation of the flow in a two-dimensional Laval nozzle whose profile in the subsonic part is concave with respect to the direction of the oncoming flow. Under the hypothesis of a separationless flow of ideal gas on the walls of the nozzle, regions of deceleration of the flow are absent. Then the well-known criteria suggest the existence of a separationless boundary layer, which must ensure that the flow as a whole is separationless.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 188–189, September–October, 1980.     

Flow past a thin wedge in a wind tunnel with partially perforated walls at high subsonic velocities

The problem of flow past a thin two-dimensional wedge at high subsonic velocity in a wind tunnel with partially perforated walls is considered for low suction flow rates. The solution of this model problem may be used in determining the optimal parameters of the suction system for which the aerodynamic characteristics in the tunnel are closest to those in an unbounded stream.In conclusion the author wishes to thank E. M. Kalinin for suggesting the study of this problem.