Transport properties of microstructured ultrathin films of La0.67Ca0.33MnO3 on SrTiO3

We have investigated the electrical transport properties of 8 nm thick La0.67Ca0.33MnO3 films, sputter-deposited on SrTiO3 (STO), and etched into 5 micrometer-wide bridges by Ar-ion etching. We find that even slight overetching of the film leads to conductance of the STO substrate, and asymmetric and non-linear current-voltage (I-V) characteristics. However, a brief oxygen plasma etch allows full recovery of the insulating character of the substrate. The I-V characteristics of the bridges are then fully linear over a large range of current densities. We find colossal magnetoresistance properties typical for strained LCMO on STO but no signature of non-linear effects (so-called electroresistance) connected to electronic inhomogeneites. In the metallic state below 150 K, the highest current densities lead to heating effects and non-linear I-V characteristics.Comment: 3 pages, 5 figure

An algorithm for solving the pulsar equation

We present an algorithm of finding numerical solutions of pulsar equation. The problem of finding the solutions was reduced to finding expansion coefficients of the source term of the equation in a base of orthogo- nal functions defined on the unit interval by minimizing a multi-variable mismatch function defined on the light cylinder. We applied the algorithm to Scharlemann & Wagoner boundary conditions by which a smooth solu- tion is reconstructed that by construction passes success- fully the Gruzinov's test of the source function exponent.Comment: 4 pages, 4 figures, accepted for publication in ApSS (a shortened version of the previous one

Características comparativas da estabilidade térmica dos ácidos húmicos dos sapropels da região OB do meio e sul da bacia de OB-Irtysh da Sibéria Ocidental

The study of humic acids has more than a century history with a natural and logical evolution of focuses on their development processes, composition and properties. Despite the considerable material accumulated to date, the nature of this group of organic compounds still has not been sufficiently studied. We have decided that the distinctive features of hydrochemical and hydrobiological factors in the formation of sapropels of the studied lakes will be reflected in the thermal stability of humic acids extracted from them. Thermal analysis of humic acids extracted from the upper layers of bottom sediments of lakes of Kondinsk district of Khanty-Mansi Autonomous okrug and Barabinsk district of the Novosibirsk region, made using modern synchronous thermal analysis, has been resulted in the article. According to the obtained data, it is observed that with increasing of maximum temperature of the thermal effect, the value of Z decreases (the ratio of the mass loss in the low temperature space to the mass loss in the high temperature space), which indicates the increase in thermal stability, formation of humic acids. The indicator of humic acids of sapropels of the Kondinsk lakes varies from 0,56 to 0,67, and these intervals are much wider from 0.45 to 0.75 in the Barabinsk lakes. According to thermogravimetric analysis the only statement of changes in chemical structure is possible, and the direction of the process can be assumed taking into account the data of the structural chemistry in combination with other spectral and chemical analysis methods.El estudio de los ácidos húmicos tiene más de un siglo de historia con una evolución natural y lógica de enfoques en sus procesos de desarrollo, composición y propiedades. A pesar del considerable material acumulado hasta la fecha, la naturaleza de este grupo de compuestos orgánicos aún no ha sido suficientemente estudiada. Hemos decidido que las características distintivas de los factores hidroquímicos e hidrobiológicos en la formación de sapropeles de los lagos estudiados se reflejarán en la estabilidad térmica de los ácidos húmicos extraídos de ellos. El resultado del análisis térmico de los ácidos húmicos extraídos de las capas superiores de los sedimentos del fondo de los lagos del distrito de Kondinsk de Okrug Autónomo de Khanty-Mansi y el distrito de Barabinsk de la región de Novosibirsk, realizado con el moderno análisis térmico sincrónico, ha sido publicado. Según los datos obtenidos, se observa que al aumentar la temperatura máxima del efecto térmico, el valor de Z disminuye (la relación entre la pérdida de masa en el espacio de baja temperatura y la pérdida de masa en el espacio de alta temperatura), lo que indica El aumento de la estabilidad térmica, formación de ácidos húmicos. El indicador de ácidos húmicos de sapropeles de los lagos de Kondinsk varía de 0,56 a 0,67, y estos intervalos son mucho más amplios de 0,45 a 0,75 en los lagos de Barabinsk. Según el análisis termogravimétrico, la única declaración de cambios en la estructura química es posible, y la dirección del proceso se puede asumir teniendo en cuenta los datos de la química estructural en combinación con otros métodos de análisis espectral y químico.O estudo dos ácidos húmicos tem mais de um século de história com uma evolução natural e lógica de focos em seus processos de desenvolvimento, composição e propriedades. Apesar do considerável material acumulado até hoje, a natureza desse grupo de compostos orgânicos ainda não foi suficientemente estudada. Decidimos que as características distintivas dos fatores hidroquímicos e hidrobiológicos na formação de sapropelas dos lagos estudados serão refletidas na estabilidade térmica dos ácidos húmicos extraídos dos mesmos. Análises térmicas de ácidos húmicos extraídos das camadas superiores de sedimentos de fundo dos lagos do distrito de Kondinsk, distrito de Okrug e autônomo de Khanty-Mansi, na região de Novosibirsk, usando análise térmica síncrona moderna, resultaram no artigo. De acordo com os dados obtidos, observa-se que com o aumento da temperatura máxima do efeito térmico, o valor de Z diminui (a razão da perda de massa no espaço de baixa temperatura para a perda de massa no espaço de alta temperatura), o que indica o aumento da estabilidade térmica, formação de ácidos húmicos. O indicador de ácidos húmicos de sapropels dos lagos de Kondinsk varia de 0,56 a 0,67, e estes intervalos são muito mais largos de 0,45 a 0,75 nos lagos de Barabinsk. De acordo com a análise termogravimétrica, a única declaração de alterações na estrutura química é possível, e a direção do processo pode ser assumida levando em conta os dados da química estrutural em combinação com outros métodos de análise espectral e química

Large electric field effects on the resistance of La0.67_{0.67}Ca0.33_{0.33}MnO3_3 microstructures

We investigate electric field effects in thin film microbridges of La$_{0.7}$Ca$_{0.3}$MnO$_3$ with the focus on the regime of metal-insulator transition. A mechanically milled SrTiO$_3$ substrate is used as a backgate dielectric. Inside the metal-insulator transition we find a strong unipolar field-induced reduction in resistance, as well as a suppression of the nonlinear features in the I-V curves we observed earlier. We associate the observed effects with a phase separated state in which metallic regions coexist with short range correlated polaron regions. When the glassy polaron phase has fully developed, and closes off the microbridge, the field effects disappear leaving the strongly nonlinear behavior of the transport current unaltered.Comment: 3 pages, 5 figure

3D Simulations of MHD Jet Propagation Through Uniform and Stratified External Environments

We present a set of high-resolution 3D MHD simulations of steady light, supersonic jets, exploring the influence of jet Mach number and the ambient medium on jet propagation and energy deposition over long distances. The results are compared to simple self-similar scaling relations for the morphological evolution of jet-driven structures and to previously published 2D simulations. For this study we simulated the propagation of light jets with internal Mach numbers 3 and 12 to lengths exceeding 100 initial jet radii in both uniform and stratified atmospheres. The propagating jets asymptotically deposit approximately half of their energy flux as thermal energy in the ambient atmosphere, almost independent of jet Mach number or the external density gradient. Nearly one-quarter of the jet total energy flux goes directly into dissipative heating of the ICM, supporting arguments for effective feedback from AGNs to cluster media. The remaining energy resides primarily in the jet and cocoon structures. Despite having different shock distributions and magnetic field features, global trends in energy flow are similar among the different models. As expected the jets advance more rapidly through stratified atmospheres than uniform environments. The asymptotic head velocity in King-type atmospheres shows little or no deceleration. This contrasts with jets in uniform media with heads that are slowed as they propagate. This suggests that the energy deposited by jets of a given length and power depends strongly on the structure of the ambient medium. While our low-Mach jets are more easily disrupted, their cocoons obey evolutionary scaling relations similar to the high-Mach jets.Comment: Accepted in ApJ, 32 pages, 18 figures, animations available from: http://www.msi.umn.edu/Projects/twj/newsite/projects/radiojets/movies

Hydration of proteins: Excess partial volumes of water and proteins

High precision densitometry was applied to study the hydration of proteins. The hydration process was analyzed by the simultaneous monitoring of the excess partial volumes of water and the proteins in the entire range of water content. Five unrelated proteins (lysozyme, chymotrypsinogen A, ovalbumin, human serum albumin, and β-lactoglobulin) were used as models. The obtained data were compared with the excess partial enthalpies of water and the proteins. It was shown that the excess partial quantities are very sensitive to the changes in the state of water and proteins. At the lowest water weight fractions (w 1), the changes of the excess functions can mainly be attributed to water addition. A transition from the glassy to the flexible state of the proteins is accompanied by significant changes in the excess partial quantities of water and the proteins. This transition appears at a water weight fraction of 0.06 when charged groups of proteins are covered. Excess partial quantities reach their fully hydrated values at w1 > 0.5 when coverage of both polar and weakly interacting surface elements is complete. At the highest water contents, water addition has no significant effect on the excess quantities. At w1 > 0.5, changes in the excess functions can solely be attributed to changes in the state of the proteins. © 2012 American Chemical Society

Residual activity of α-chymotrypsin in water-1,2-propanediol mixtures

© 2017 Nova Science Publishers, Inc. All rights reserved.A novel experimental method was proposed to study the stability of enzymes in water-organic mixtures. This method is based on the analysis of the residual enzyme activity. Advantages of our method: (I) The residual activity curves can be determined in the entire range of the water content in organic liquids. (II) Enzyme activity values are measured at fixed reaction conditions. (III) Information on the changes in the state of the catalytically active site can be obtained separately from the other contributions (for example, changes in the solvation of the reagents and products in various water - organic mixtures). To show the efficiency of the proposed method we studied the residual activity of bovine pancreatic α-chymotrypsin (CT) in water-1,2- propanediol mixtures in the entire range of water content at 25°C. The obtained results show that the degree of stabilization/ destabilization of α- chymotrypsin depends strongly on the water content in organic solvent. (1) At high water content, the residual activity values are higher than 100%. (2) At low water content, the residual catalytic activity is~90-95%, compared with that observed after incubation in pure water. (3) A minimum on the residual activity curve was observed at intermediate water content

Effect of tetrahydrofuran on the binding of the competitive inhibitor proflavin and the storage stability of bovine pancreatic α-chymotrypsin

The binding of the competitive inhibitor proflavin by bovine pancreatic α-chymotrypsin in water-tetrahydrofuran mixtures was studied in the entire range of thermodynamic water activities at 25°C. The data on the binding of proflavin were compared with the results on the storage stability of α-chymotrypsin in water-organic mixtures. An analysis of the concentration dependency of these characteristics demonstrated that, at low water activity values, the interprotein contacts in the enzyme formed during its drying largely govern its functional properties, while at high water activity, they are determined by the interaction of the enzyme with the organic solvent. The interplay of these two factors is responsible for the complex shape observed for the isotherm of binding of proflavin, with a maximum degree of binding being attained at medium water activity values. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim