Domain wall conduction in multiaxial ferroelectrics

The conductance of domain wall structures consisting of either stripes or cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed. The effects of the domain size, wall tilt and curvature, on charge accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory for polarization combined with Poisson equation for charge distributions. Both the classical ferroelectric parameters including expansion coefficients in 2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling, inhomogeneous elastic strains and electrostriction are included in the present analysis. Spatial distributions of the ionized donors, free electrons and holes were found self-consistently using the effective mass approximation for the respective densities of states. The proximity and size effect of the electron and donor accumulation/depletion by thin stripe domains and cylindrical nanodomains are revealed. In contrast to thick domain stripes and thicker cylindrical domains, in which the carrier accumulation (and so the static conductivity) sharply increases at the domain walls only, small nanodomains of radius less then 5-10 correlation length appeared conducting across entire cross-section. Implications of such conductive nanosized channels may be promising for nanoelectronics.Comment: 39 pages, 11 figures, 3 tables, 4 appendice

STUDY OF LAKES MORPHOMETRY IN THE BORDERS OF PLEISTOCENE GLACIATIONS OF THE NORTHWEST RUSSIA

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Reconstruction of palaeoecological and palaeoclimatic conditions of the Holocene in the south of the Taimyr according to an analysis of lake sediments

© 2017, Pleiades Publishing, Ltd. A sediment core from Khatanga-12 Lake (Taimyr Peninsula, Krasnoyarsk krai) has been studied. The 131.5-cm-long core covers ca. 7100 years of sedimentation. Chironomid analysis, a qualitative reconstruction of the paleoenvironment in the region, and a quantitative reconstruction of variations of the mean July air temperature and in the water depth of the lake have been performed using Northern Russia chironomid-inferred mean July temperature models (Nazarova et al., 2008, 2011, 2015). Khatanga-12 Lake was formed during the Middle Holocene warming as a result of thermokarst processes. The development of the lake ecosystem at different stages of its development was influenced by climatic and cryolithogenic factors. The Middle Holocene warming, which occurred around 7100–6250 cal. years BP, activated thermokarst processes and resulted in the formation of the lake basin. Later, between 6250 and 4500 cal. years BP, a period of cooling took place, as is proved by chironomid analysis. The bottom sediments of the lake during this period were formed by erosion processes on the lake shores. The reconstructed conditions were close to the modern after 2500 cal. years BP

The relationship of clinical and morphological parameters with the BRAF status of the tumor in patients with stage I skin melanoma

Aim: to study the relationship between clinical and morphological parameters of skin melanoma and the BRAF status of the tumor in patients with stage I of the disease. Materials and methods. The study was retrospective and included 200 patients with stage I skin melanoma (pT1-2aN0M0), of which BRAF status was assessed in 88 patients. All patients underwent clinical data analysis, an extended morphological study and a molecular genetic study to determine the BRAF V600E mutation in the primary tumor. Results. The median age of patients in the total sample was 61.5 years. Mutation in the BRAF V600E gene was detected in 25 patients (28.4%). Patient age, tumor location and Breslow thickness were recognized as independent predictors of BRAF status of stage I skin melanoma. With an increase in the patient's age by 1 year, the chance of having a BRAF V600E mutation decreased by 3.4% or 1.04 times (OR = 0.966; 95% CI = 0.935–0.999; p = 0.045). When melanoma was localized in the lumbar region, the chance of having a BRAF V600E mutation increased by 15.311 times (95% CI = 1.239–189.142; p = 0.033). With a tumor thickness according to Breslow of more than 0.7 mm, the chance of having a BRAF V600E mutation increased by 2.939 times (95% CI = 1.031-8.376; p = 0.044). With a threshold value of the logistic function of 50%, the sensitivity and specificity of the proposed model were 28.0% and 93.7%, respectively. When the threshold function value is reduced to 25.3%, the sensitivity of the model increases to 68% with a simultaneous drop in specificity to 61.9%. Conclusion. Younger age, greater tumor thickness according to Breslow, and tumor localization in the lumbar region in patients with stage I skin melanoma increase the chance of having a BRAF V600E mutation, while other morphological parameters of the tumor are not associated with BRAF status. However, moderate sensitivity does not allow for a sufficiently accurate determination of the presence of a mutation, thereby strengthening the belief in the need for molecular genetic testing

Paleolimnological studies in Russian northern Eurasia: A review

© 2017, Pleiades Publishing, Ltd. This article presents a review of the current data on the level of paleolimnological knowledge about lakes in the Russian part of the northern Eurasia. The results of investigation of the northwestern European part of Russia as the best paleolimnologically studied sector of the Russian north is presented in detail. The conditions of lacustrine sedimentation at the boundary between the Late Pleistocene and Holocene and the role of different external factors in formation of their chemical composition, including active volcanic activity and possible large meteorite impacts, are also discussed. The results of major paleoclimatic and paleoecological reconstructions in northern Siberia are presented. Particular attention is given to the databases of abiotic and biotic parameters of lake ecosystems as an important basis for quantitative reconstructions of climatic and ecological changes in the Late Pleistocene and Holocene. Keywords: paleolimnology, lakes, bottom sediments, northern