Vibrational and Thermal Properties of ZnX (X=Se, Te): Density Functional Theory (LDA and GGA) versus Experiment

We calculated the phonon dispersion relations of ZnX (X=Se, Te) employing ab initio techniques. These relations have been used to evaluate the temperature dependence of the respective specific heats of crystals with varied isotopic compositions. These results have been compared with mea- surements performed on crystals down to 2 K. The calculated and measured data are generally in excellent agreement with each other. Trends in the phonon dispersion relations and the correspond- ing densities of states for the zinc chalcogenide series of zincblende-type materials are discussed.Comment: 10 pages, submitted to PR

Computational aspects of probit model

Sometimes the maximum likelihood estimation procedure for the probit model fails. There may be two reasons: the maximum likelihood estimate (MLE) just does not exist or computer overflow error occurs during the computation of the cumulative distribution function (cdf). For example, the approximation explosive effect due to an inaccurate computation of the cdf for a large value of the argument occurs in a popular statistical package S-plus. The goal of the paper is to provide remedies for these two abnormalities. First, despite the availability of a criterion for the MLE existence, expressed in terms of a separation plane in the covariate space, there are no constructive criteria to verify whether such a separation exists. We develop constructive criteria for the MLE existence that are valid also for other link functions. Second, to avoid the overflow problem we suggest approximate formulae for the log-likelihood function and its derivatives in the case of possiblelarge value of the argument. Standard algorithms of the log-likelihood maximization like Newton-Raphson or Fisher Scoring are very sensitive to large values of the linear predictor, particularly outliers. Five algorithms are compared by the time to converge and reliability via statistical simulations. The corrected algorithms, based on the approximate formulae are more reliable and almost as fast as the standard one

Estimates for solutions to a class of time-delay systems of neutral type with periodic coefficients and several delays

We consider a class of nonlinear time-delay systems of neutral type with periodic coefficients in linear terms and several delays. We establish conditions under which the zero solution is exponentially stable and obtain estimates characterizing exponential decay of solutions at infinity. The conditions are formulated in terms of differential matrix inequalities. All the values characterizing the decay rate are written out in explicit form

Recent discoveries in the cycling, growing and aging of the p53 field

The P53 gene and it product p53 protein is the most studied tumor suppressor, which was considered as oncogene for two decades until 1990. More than 60 thousand papers on the topic of p53 has been abstracted in Pubmed. What yet could be discovered about its role in cell death, growth arrest and apoptosis, as well as a mediator of the therapeutic effect of anticancer drugs. Still during recent few years even more amazing discoveries have been done. Here we review such topics as suppression of epigenetic silencing of a large number of non-coding RNAs, role of p53 in suppression of the senescence phenotype, inhibition of oncogenic metabolism, protection of normal cells from chemotherapy and even tumor suppression without apoptosis and cell cycle arrest

Cerenkov generation of high-frequency confined acoustic phonons in quantum wells

We analyze the Cerenkov emission of high-frequency confined acoustic phonons by drifting electrons in a quantum well. We find that the electron drift can cause strong phonon amplification (generation). A general formula for the gain coefficient, alpha, is obtained as a function of the phonon frequency and the structure parameters. The gain coefficient increases sharply in the short-wave region. For the example of a Si/SiGe/Si device it is shown that the amplification coefficients of the order of hundreds of 1/cm can be achieved in the sub-THz frequency range.Comment: 4 pages, 2 figures. Submitted to AP

Statistical assessment of quality of credit activity of Ukrainian banks

The article conducts an economic and statistical analysis of the modern state of credit activity of Ukrainian banks and main tendencies of its development. It justifies urgency of the statistical study of credit activity of banks. It offers a complex system of assessment of bank lending at two levels: the level of the banking system and the level of an individual bank. The use of the system analysis allows reflection of interconnection between effectiveness of functioning of the banking system and quality of the credit portfolio. The article considers main aspects of management of quality of the credit portfolio – level of troubled debt and credit risk. The article touches the problem of adequate quantitative assessment of troubled loans in the credit portfolios of banks, since the methodologies of its calculation used by the National Bank of Ukraine and international rating agencies are quite different. The article presents a system of methods of management of credit risk, both theoretically and providing specific examples, in the context of prevention of occurrence of risk situations or elimination of their consequences