ARCHITECTING EMERGING MEMORY TECHNOLOGIES FOR ENERGY-EFFICIENT COMPUTING IN MODERN PROCESSORS

Ph.DDOCTOR OF PHILOSOPH

Maximum Distance Separable Codes for Symbol-Pair Read Channels

We study (symbol-pair) codes for symbol-pair read channels introduced recently by Cassuto and Blaum (2010). A Singleton-type bound on symbol-pair codes is established and infinite families of optimal symbol-pair codes are constructed. These codes are maximum distance separable (MDS) in the sense that they meet the Singleton-type bound. In contrast to classical codes, where all known q-ary MDS codes have length O(q), we show that q-ary MDS symbol-pair codes can have length \Omega(q^2). In addition, we completely determine the existence of MDS symbol-pair codes for certain parameters

Dynamic characteristics of the railway ballast bed under water-rich and low-temperature environments

Studying the dynamic characteristics and evolution laws of the ballast bed under low-temperature, rain and snow environments has practical significance for the driving stability of railways in alpine. In this paper, a full-scale ballasted track model was constructed in a programmable temperature control laboratory, and the frequency response function (FRF) curves of the ballast bed under different temperature and humidity conditions were measured. Then the vibration characteristics and the evolution laws of the ballast bed under different conditions were analyzed. The longitudinal transfer behavior and the dissipation of the vibration energy in the ballast bed under different humidity and temperature environments were discussed combined with the finite element method. The results show that the influence of temperature on the vibration characteristics of the ballast bed is not significant in the dry and water-rich environments, but the vibration characteristics of the ballast bed in the frozen environment change dramatically with the decrease of temperature. The vibration energy is harder to dissipate in the frozen ballast bed than in the dry and water-rich ballast beds, and the frozen ballast bed is more prone to be sudden damaged when a train passes due to the significant increase in its stiffness. Thus, the performance monitoring and emergency maintenance of the ballast bed in those environments should be strengthened

A semi-analytical method for the dynamic analysis of cylindrical shells with arbitrary boundaries

The dynamic behavior of cylindrical shells with arbitrary boundaries is studied in this paper. Love's shell theory and Hamilton's principle are employed to derive the motion equations for cylindrical shells. A semi-analytical methodology, which incorporates Durbin's inverse Laplace transform, differential quadrature method and Fourier series expansion technique, is proposed to investigate this phenomenon. The use of the differential quadrature method provides a solution in terms of the axial direction whereas the use of Durbin's numerical inversion method generates a solution in the time domain. Comparison of calculated frequency parameters to that derived from the literature illustrates the effectiveness of the method. Specifically, convergence tests indicate that the present approach has a rapid convergence, the time-history response and the Navier's solution are in great agreement. Comparisons between time-history responses derived by two shell theories show that the results fit well with each other when the thickness-radius ratios are small enough. An analysis of the influences of boundaries on the time-history response of cylindrical shells indicates that the peak displacement is closely related to the degrees of freedom of boundaries. The influences of the length-radius ratios and the thickness-radius ratios on the peak displacement are further investigated

The Diagonally Dominant Degree and Disc Separation for the Schur Complement of Ostrowski Matrix

By applying the properties of Schur complement and some inequality techniques, some new estimates of diagonally and doubly diagonally dominant degree of the Schur complement of Ostrowski matrix are obtained, which improve the main results of Liu and Zhang (2005) and Liu et al. (2012). As an application, we present new inclusion regions for eigenvalues of the Schur complement of Ostrowski matrix. In addition, a new upper bound for the infinity norm on the inverse of the Schur complement of Ostrowski matrix is given. Finally, we give numerical examples to illustrate the theory results