Dmitrii Tumakov

Abstract: Regression and functional models of the main electrodynamic parameters for a family of balanced wire dipole antennas having arms similarly to the Koch first-order pre-fractal are developed. Each dipole differs from the remaining dipoles only in coordinates of the central vertices of arms. Conclusions on an influence of the wire’s diameter of the antenna on characteristics of the antenna are drawn. It is shown that a connection of electrodynamic parameters with the geometry of the antenna increases with an increase in the order of the pre-fractal. Algorithms for developing the antennas having preset characteristics are described. Examples describing an application of the algorithms to the modeling of the well matched Koch-type antennas to achieve some desired characteristics are provided.

Abstract: The microstrip antennas with symmetrical comb-shaped radiator are considered. The influence of depth of the cuts on main electrical characteristics of four- and eight-comb antennas is researched. The resonance frequency, the bandwidth and reflection coefficient are chosen as characteristics. The graphs of unknown dependencies are constructed for the two basic frequencies.

Abstract: The problem of diffraction of a plane elastic wave by a gradient transversely isotropic layer is considered. Using the method of overdetermined boundary value problem in combination with the Fourier transform method, the system of ordinary differential equations of the second order with boundary conditions of the third type is obtained which is solved by the grid method. Results of calculations obtained using the above-mentioned technique for the case of piecewise linear profiles for the Young modulus of the layer are given.

Abstract: The problem of diffraction of a plane TE-polarized electromagnetic wave by gaps between metal plates located in the same plane is investigated. The diffraction problem is formulated as a boundary-value problem for the Helmholtz equation with the boundary conditions on metal and a given asymptotic behavior at the edges of the screens. The solutions are sought in the class of waves propagating to infinity. The problem under consideration is reduced to an integral equation with a strongly singular kernel with respect to the trace of the electric field vector in the gap. In turn, the integral equation is reduced to an infinite system of linear algebraic equations with respect to the expansion coefficients of the derivative of the sought function. Some singular integrals involving generalized Chebyshev polynomials are analytically calculated.

Abstract: In this study, we investigated a one-dimensional diffraction problem of elastic wave propagation through gradient layer. The diffraction problem is reduced to an ordinary differential equation with the third type boundary conditions. The method of approximation of integral identities is applied to increase accuracy of the grid solution to the obtained boundary problem. The case when the elastic wave speed in the layer is constant and density changes continuously according to ρ0(1+A|sinmBx|) is considered in the paper.

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Abstract: It is estimated that over 90% of all new information produced in the world is being stored on magnetic media, most of it on hard disk drives. Despite their importance, there is relatively little published work on the failure patterns of disk drives, and the key factors that affect their lifetime. Most available data are either based on extrapolation from accelerated aging experiments or from relatively modest sized field studies. Moreover, larger population studies rarely have the infrastructure in place to collect health signals from components in operation, which is critical information for detailed failure analysis. We present data collected from detailed observations of a large disk drive population in a production Internet services deployment. The population observed is many times larger than that of previous studies. In addition to presenting failure statistics, we analyze the correlation between failures and several parameters generally believed to impact longevity. Our analysis identifies several parameters from the drive's self monitoring facility (SMART) that correlate highly with failures. Despite this high correlation, we conclude that models based on SMART parameters alone are unlikely to be useful for predicting individual drive failures. Surprisingly, we found that temperature and activity levels were much less correlated with drive failures than previously reported.