Landscape science: a Russian geographical tradition

The Russian geographical tradition of landscape science (landshaftovedenie) is analyzed with particular reference to its initiator, Lev Semenovich Berg (1876-1950). The differences between prevailing Russian and Western concepts of landscape in geography are discussed, and their common origins in German geographical thought in the late nineteenth and early twentieth centuries are delineated. It is argued that the principal differences are accounted for by a number of factors, of which Russia's own distinctive tradition in environmental science deriving from the work of V. V. Dokuchaev (1846-1903), the activities of certain key individuals (such as Berg and C. O. Sauer), and the very different social and political circumstances in different parts of the world appear to be the most significant. At the same time it is noted that neither in Russia nor in the West have geographers succeeded in specifying an agreed and unproblematic understanding of landscape, or more broadly in promoting a common geographical conception of human-environment relationships. In light of such uncertainties, the latter part of the article argues for closer international links between the variant landscape traditions in geography as an important contribution to the quest for sustainability

THERMOELECTRIC PROPERTIES OF HOT-PRESSED p-TYPE Mg2Si0.3Sn0.7 SOLID SOLUTION

It is shown that thermoelectric energy conversion which gives the possibility for utilizing a low potential heat is one of the ways for adoption of energy-saving technologies; and semiconductor materials with p-type and n-type conductivities having high thermoelectric figure of merit are necessary for operation of thermoelectric generators. The paper deals with possibility of usage of the p-Mg2Si0.3Sn0.7 solid solution (with a nanostructured modification) as a couple for the well studied thermoelectric material based on n-Mg2Si-Mg2Sn. A technological scheme for fabrication of heavily doped Mg2Si0.3Sn0.7 solid solution of p-type by hot pressing from nanopowder is developed. The given technology has made it possible to reduce duration of a homogeneous material fabrication and has improved its physical and chemical properties. The samples were made by three ways: direct fusion for polycrystals fabrication; hot pressing from microparticles; nanostructuring, i.e. hot pressing from nanoparticles. By X-ray diffraction it is shown that sizes of structural elements in the fabricated samples are about 40 nm. The probe technique is used for measurement of electric conductivity and Seebeck coefficient. The stationary absolute method is used for measurement of thermal conductivity. Thermoelectric figure of merit is defined by measured values of kinetic coefficients in the temperatures range of 77 – 800 K. It was demonstrated, that electric conductivity, Seebeck coefficient and the power factor do not depend practically on a way of solid solution preparation. Thermal conductivity of samples pressed from nanoparticles has appeared to be higher, than of samples, obtained by direct fusion; i.e. in this case nanostructuring has not led to increase of thermoelectric figure of merit. The conclusion is drawn, that polycrystalline semiconductor Mg2Si0.3Sn0.7 can be used as a p-branch for a thermoelectric generator though nanostructuring has not led to the figure of merit growth. The assumption is made, that thermoelectric figure of merit improvement can be expected at the further reduction of the nanograins size

The Influence of Weak Tin Doping on the Thermoelectric Properties of Zinc Antimonide

ZnSb would be a good thermoelectric material with carrier concentration above 10^(19)/cm^3, but unfortunately this has been shown to be difficult to achieve, particularly with Sn as a dopant. Two series ZnSb samples doped with Sn and ZnSn were prepared using hot-pressing technics, and their thermoelectric properties were investigated in the temperature range from 300 K to 700 K. The tin content of the samples was in the range from 0.1 to 0.5 at.%. Surprisingly, samples with lower tin content achieved higher carrier concentration, which is beneficial for thermoelectric performance. Samples doped with 0.1 at.% Sn achieved Hall carrier concentration above 1 × 10^(19)/cm^3, reaching ZT of 0.9, while for samples doped with 0.5 at.% Sn, the Hall carrier concentration was close to the hole concentration of pure ZnSb. Also, by analyzing hysteresis present in the heating–cooling cycles, we conclude that the role of intrinsic defects in ZnSb is important and that these defects clearly determine the ability of ZnSb to achieve ZT near 1

On Obtaining of Irreducible Polynomials on Galois Fields for Information Security Systems

The article is dedicated to the problem of generating the indecomposable polynomials over Galois fields used in cryptographic information security, generation of pseudo random numbers and sequences, data compression and error-correction during data transmission. New properties of polynomials over finite fields was discovered after theoretical and experimental research. The approach to increase speed of searching indecomposable polynomials is proposed and relies on the optimization of the procedure of their selection and testing using discovered features.В статье рассматривается проблема получения неразложимых полиномов на полях Галуа для использования в системах криптографической защиты информации, генерации псевдослучайных чисел и последовательностей, сжатия данных, а также исправления ошибок при их передаче. На основе теоретических и экспериментальных исследований выявлены новые свойства полиномов на конечных полях. Предложен подход к ускорению поиска неразложимых полиномов за счет оптимизации процедуры их селекции и тестирования на основе выявленных свойств