Metal-insulator transition induced by 16O -18O oxygen isotope exchange in colossal negative magnetoresistance manganites

The effect of 16O-18O isotope exchange on the electric resistivity was studied for (La(1-y)Pr(y))0.7Ca0.3MnO3 ceramic samples. Depending on y, this mixed perovskite exhibited different types of low-temperature behavior ranging from ferromagnetic metal (FM) to charge ordered (CO) antiferromagnetic insulator. It was found that at y=0.75, the substitution of 16O by 18O results in the reversible transition from a FM to a CO insulator at zero magnetic field. The applied magnetic field (H >= 2 T) transformed the sample with 18O again to the metallic state and caused the increase in the FM transition temperature Tc of the 16O sample. As a result, the isotope shift of Tc at H = 2 T was as high as 63 K. Such unique sensitivity of the system to oxygen isotope exchange, giving rise even to the metal-insulator transition, is discussed in terms of the isotope dependence of the effective electron bandwidth which shifts the balance between the CO and FM phases.Comment: 5 pages (RevTeX), 2 eps figures included, to appear in J. Appl. Phys. 83, (1998

TRUST AS A VIRTUAL TEAM EFFECTIVENESS FACTOR

A relatively new phenomenon in management practice – a virtual team has been considered. Based on a study of a wide range of domestic and foreign sources, it has been shown, what problems arise during the formation and operation of virtual teams. Attention on the problem of mutual trust in the team has been focused. It has been concluded that the lack of common social norms and opportunities for mutual control, the lack of direct personal contacts, cross-cultural problems, and the lack of informal communication impede confidence building. However, the rapid idealization of a communication partner, the ability to create the effect of physical presence with minimal means can contribute to building trust and team spirit. The article is addressed to specialists in the field of personnel management and all interested in modern technologies of labor management

Semantic features of the phraseological units with the component light within the artistic discourse

Conduct lexical and semantic analysis on the concept light in the artistic discourse of postmodern fictio

Higher education reform and the landscape diversity of higher education institutions in the Kyrgyz Republic, 1991–2015

Following its independence from the Soviet Union in 1991, Kyrgyzstan experienced processes of change across all areas of social, political and economic life. Higher education reform has been central to this agenda, and between 1991 and today the Soviet-era system of state-funded and Communist Party controlled higher education institutions (HEIs) in Kyrgyzstan has been transformed into an expansive, diverse, unequal, semi-privatized and marketized higher education (HE) landscape. Mindful of arguments that the marketization of higher education does not necessarily generate institutional diversification, that government regulation does not necessarily lead to homogenization among institutions, and that universities’ own institutional strategies and responses to environmental changes shape processes of structural reform in complex ways, this paper assesses the specific character of these changes to the higher education landscape in post-Soviet Kyrgyzstan. After briefly describing the structure and financing of higher education in the Kirgiz Soviet Socialist Republic from 1917–1991, we consider some key factors which have shaped patterns of the differentiation and diversification of HE in the post-Soviet period. These include the historical legacies of Soviet HE infrastructures, new legal and political frameworks for HE governance and finance, changes to regulations for the licensing of institutions and academic credentials, the introduction of new multinational policy agendas for higher education in the Central Asian region, changes in the relationship between higher education and labor, the introduction of a national university admissions examination, and the adoption of certain principles of the European Bologna Process. The picture of HE reform that emerges from this analysis is one in which concurrent processes of diversification and homogenization are not driven wholly by either state regulation or forces of market competition, but mediated by universities’ strategic negotiations of these forces in the context of historical institutional formations in Kyrgyzstan

Development of Hydrometallurgical Process of Non-Ferrous and Rare Metals Recovery from Untraditional Mineral Raw Materials and Natural Brines

In connection with gradual lowering of supplies of tradit- ional ore raw materials involving non-ferrous and rare metals, winch is treated by well-known technologies, invo-lving into the production of untraditional, secondary and technogeneous raw materials appears to be actual task

Non-Perturbative Production of Multi-Boson States and Quantum Bubbles

The amplitude of production of $n$ on-mass-shell scalar bosons by a highly virtual field $\phi$ is considered in a $\lambda \phi^4$ theory with weak coupling $\lambda$ and spontaneously broken symmetry. The amplitude of this process is known to have an $n!$ growth when the produced bosons are exactly at rest. Here it is shown that for $n \gg 1/\lambda$ the process goes through `quantum bubbles', i.e. quantized droplets of a different vacuum phase, which are non-perturbative resonant states of the field $\phi$. The bubbles provide a form factor for the production amplitude, which rapidly decreases above the threshold. As a result the probability of the process may be heavily suppressed and may decrease with energy $E$ as $\exp (-const \cdot E^a)$, where the power $a$ depends on the number of space dimensions. Also discussed are the quantized states of bubbles and the amplitudes of their formation and decay.Comment: 20 pages in LaTeX + 3 figures (fugures not included, hardcopy available on request), TPI-MINN-93/20-

Catalyzed decay of false vacuum in four dimensions

The probability of destruction of a metastable vacuum state by the field of a highly virtual particle with energy $E$ is calculated for a (3+1) dimensional theory in the leading WKB approximation in the thin-wall limit. It is found that the induced nucleation rate of bubbles, capable of expansion, is exponentially small at any energy. The negative exponential power in the rate reaches its maximum at the energy, corresponding to the top of the barrier in the bubble energy, where it is a finite fraction of the same power in the probability of the spontaneous decay of the false vacuum, i.e. at $E=0$.Comment: 9 pages (standard LaTeX)+ 3 figures (one figure in LaTeX, two are appended in PostScript). TPI-MINN-92/31-

Superlattices Consisting of "Lines" of Adsorbed Hydrogen Atom Pairs on Graphene

The structures and electron properties of new superlattices formed on graphene by adsorbed hydrogen molecules are theoretically described. It has been shown that superlattices of the (n, 0) zigzag type with linearly arranged pairs of H atoms have band structures similar to the spectra of (n, 0) carbon nanotubes. At the same time, superlattices of the (n, n) type with a "staircase" of adsorbed pairs of H atoms are substantially metallic with a high density of electronic states at the Fermi level and this property distinguishes their spectra from the spectra of the corresponding (n, n) nanotubes. The features of the spectra have the Van Hove form, which is characteristic of each individual superlattice. The possibility of using such planar structures with nanometer thickness is discussed.Comment: 5 pages, 4 figure