257 research outputs found
Metal-insulator transition in 2D: a role of the upper Habbard band
To explain the main features of the metal-insulator transition (MIT) in 2D we
suggest a simple model taking into account strongly localized states in the
band tail of 2D conductivity band with a specific emphasize of a role of
doubly-occupied states (upper Hubbard band). The metallic behavior of
resistance is explained as result of activation of localized electrons to
conductance band leading to a suppression of non-linear screening of the
disorder potential. The magnetoresistance (MR) in the critical region is
related to depopulation of double occupied localized states also leading to
partial suppression of the nonlinear screening. The most informative data are
related to nearly activated temperature dependence of MR in strongly insulating
limit (which can be in particular reached from the metallic state in high
enough fields). According to our model this behavior originates due to a
lowering of a position of chemical potential in the upper Hubbard band due to
Zeeman splitting. We compare the theoretical predictions to the existing
experimental data and demonstrate that the model explains such features of the
2D MIT as scaling behavior in the critical region, saturation of MR and H/T
scaling of MR in the insulating limit. The quantitative analysis of MR in
strongly insulating limit based on the model suggested leads to the values of
g-factors being in good agreement with known values for localized states in
corresponding materials.Comment: 18 pages, 4 PNG figure
Zero-bias anomalies of point contact resistance due to adiabatic electron renormalization of dynamical defects
We study effect of the adiabatic electron renormalization on the parameters
of the dynamical defects in the ballistic metallic point contact. The upper
energy states of the ``dressed'' defect are shown to give a smaller
contribution to a resistance of the contact than the lower energy ones. This
holds both for the "classical" renormalization related to defect coupling with
average local electron density and for the "mesoscopic" renormalization caused
by the mesoscopic fluctuations of electronic density the dynamical defects are
coupled with. In the case of mesoscopic renormalization one may treat the
dynamical defect as coupled with Friedel oscillations originated by the other
defects, both static and mobile. Such coupling lifts the energy degeneracy of
the states of the dynamical defects giving different mesoscopic contribution to
resistance, and provides a new model for the fluctuator as for the object
originated by the electronic mesoscopic disorder rather than by the structural
one. The correlation between the defect energy and the defect contribution to
the resistance leads to zero-temperature and zero-bias anomalies of the point
contact resistance.
A comparison of these anomalies with those predicted by the Two Channel Kondo
Model (TCKM) is made. It is shown, that although the proposed model is based on
a completely different from TCKM physical background, it leads to a zero-bias
anomalies of the point contact resistance, which are qualitatively similar to
TCKM predictions.Comment: 6 pages, to be published in Phys. Rev.
Особливості перекладу англійських термінів ветеринарної медицини українською мовою
У статті аналізуються основні випадки і способи перекладу англійської ветеринарної лексики. Особлива увага
звертається на переклад науково-технічних термінів, які використовуються у сфері ветеринарної медицини.
(The article deals with the main cases and ways of translating of English veterinary terms, in particular scientific and technical terms used in the field of veterinary medicine. Studies of scientific and technical translation are very important, especially the translation of terminology, which is related to medicine, as this area is rapidly developing, new terms appear
that require adequate translation into Ukrainian. For submitting an adequate translation, a translator must be familiar with the relevant area of science or technology and be aware of special terminology. The analysis revealed that most terms used in the field of veterinary medicine are multicomponent. Analytical phase (i.e. the translation of components of the analyzed
terms) plays an important role in rendering the above-mentioned terms from one language into another. It is necessary to correctly identify the components of a complex term, because they can be not only words, but also phrases that make up the complex term. Special attention in the article is paid to suffixes and prefixes of Greek and Latin origin, which often constitute
veterinary medicine terms. Most of the analyzed terms consist of the following models: Noun plus Noun, Noun plus Participle II, Adjective plus Participle II plus Noun, Numeral plus Participle II plus Noun. The words which do not have match terms in
the language of translation are rendered into another language descriptively. The main task for specialists who try to convey a message of a technical nature is most accurately convey all the properties and parameters that the term characterizes.
Study of Genotype X Environment Interaction in Alfalfa Forage Yield
The response of alfalfa (Medicago sativa L.) forage yield to eight Alberta test sites was studied for the 1990 and 1991 production years. Cluster analysis was used to group locations and cultivars. Analyses of variances indicated genotype x environment (location) interaction for the first cut yield, the total yield and the difference between first and second cut yields. The Brooks, Bow Island (irrigation), Bow Island (dryland) and Provost locations always clustered together indicating that three of these four test sites may be eliminated without sacrificing reliability
- …