Bootstrap models for interval estimation of longevity characteristics of sequential systems from small samples

A generator of random variables is presented for the computation of “bootstrap intervals” for estimating longevity characteristics of sequential systems from small samples. Translated fromStatisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 89–98, Perm, 1993.     

Decrease in the bond energy of arsenic atoms on the GaAs(100)-(2×4)/c(2×8) surface due to the effect of adsorbed cesium

It has been found experimentally that the bond energy of arsenic atoms on the GaAs(100) surface decreases under the influence of adsorbed cesium. This is manifested in the disordering of the As-stabilized surface and in a decrease of ～(100 K in the temperature of the transition to the Ga-stabilized (100)GaAs(4×2)/c(8×2) surface. This effect is caused by the redistribution of the valence electron density between the arsenic atoms in the upper layer and the gallium atoms in the lower-lying layer as a result of charge transfer from the electropositive adsorbate to the semiconductor. In combination with the analogous effect of a decrease in the bonding energy of gallium atoms on the Ga-stabilized GaAs surface upon the adsorption of electronegative adsorbates (halogens), the effect observed allows the atomic layer etching of the polar GaAs(100) face.     

The Role of a Metallocene Additive in Radically Initiated Polymerization when Solving Direct and Inverse Kinetic Problems

Polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, is considered from the point of view of formal kinetics. Based on the kinetic scheme of the process (which includes the reactions of classical radical polymerization, the reaction of benzoyl peroxide with titanocene dichloride, the reactions of the controlled radical polymerization of organometallic mediated radical polymerization (OMRP) and atom transfer radical polymerization (ATRP), the reaction of the formation of a coordinating active site and the coordinating chain propagation on a mathematical model of the kinetics of the process is created. This model also makes it possible to calculate the molecular-mass characteristics of poly(methyl methacrylate). As a result of the solution of the inverse kinetic problem at a temperature of 343 K, the values of the reaction rate constants of the kinetic scheme are found under which the discrepancy between the calculated models and experimental data is minimal. Using the developed model of the kinetics of the process, a numerical experiment is performed (i.e., a direct kinetic problem is solved). This problem revealed the following regularities of the process. (1) An increase in the initial concentration of titanocene dichloride at a constant initial concentration of benzoyl peroxide leads to an increase in the rate of consumption of benzoyl peroxide but not to an increase in the initial rate of the process compared to classical radical polymerization. (2) With an increase in the initial concentration of titanocene dichloride, the lifetime of the macroradicals at the initial stage of the process is reduced, and hence the molecular weight of the resulting polymethyl methacrylate is less than that of the polymethyl methacrylate obtained in the absence of titanocene dichloride, and it will increase during the process of approaching the final values. (3) During the polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, a smoothing gel effect (as in the case of the polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of ferrocene) does not occur since titanocene dichloride forms stable complexes with methyl methacrylate and, consequently, it participates in reactions consuming macroradicals to a lesser degree than ferrocene.     

Erratum to: Antitumor activity of carboplatin in the composition of a copolymer of lactic and glycolic acids

Russian Chemical Bulletin - To the article “Antitumor activity of carboplatin in the composition of a copolymer of lactic and glycolic acids,” by E. D. Nikolskaya, O. A. Zhunina, N. G....     

Observations of the magnetic-zenith effect using GPS/GLONASS satellite signals

We present the results of first studies of the modification of the ionosphere by high-power HF radiation, which were obtained using signals of high-orbit GPS/GLONASS navigation satellites. Enhancement of the ionospheric modification in the magnetic-field direction was observed for the first time. This leads to a total decrease in electron number density and the formation of electron density irregularities near the magnetic-zenith direction. The efficiency of using GSP/GLONASS satellite signals for the studies of the ionosphere modified by HF radiation is demonstrated. Prospects for further studies in this field are discussed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 934–938, November 2008.     

Catalytic properties of sodium zirconium molybdate phosphates in methanol transformations

Molybdate phosphates Na_1?y Zr₂(MoO₄) _y (PO₄)_{3 ? y} (y = 0, 0.25, 0.5) having the NaZr₂(PO₄)₃ structure were prepared by the sol-gel method. The catalytic properties of the molybdate phosphates in dehydration and dehydrogenation of methanol in inert and oxidizing atmospheres were studied.     

Modulation of the Dirac Point Band Gap in the Antiferromagnetic Topological Insulator MnBi2Te4 due to the Surface Potential Gradient Change

Journal of Experimental and Theoretical Physics - The possibility of significant modulation of the band gap open at the Dirac point (DP) in the range from 15 to 55 meV for different samples of the...     

Impact of Co Atoms on the Electronic Structure of Bi2Te3 and MnBi2Te4 Topological Insulators

Journal of Experimental and Theoretical Physics - This work is devoted to an experimental investigation of the electronic structure of the surface of topological insulators of various stoichiometry...     

Bimodal temporal distribution of photons in ultrashort laser pulse passed through a turbid medium

The criteria were determined for simultaneous observation of scattered and unscattered (ballistic) peaks in temporal distribution of a narrow pulsed laser beam passed through a strongly scattering medium. Conditions were found for such an observation on the basis of non-stationary two-flux model for radiation transport. Calculation results permitted the definition of a compromise between the parameters of the initial laser pulse and the properties of a scattering medium. This provided the separate observation of various types of photons. The theoretical calculations were confirmed by experiments on recording pulse profiles of passed radiation of fs-laser in a water–milk solution.