Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition

An unusual temperature and concentration behavior of resistivity in $La_{0.7}Ca_{0.3}Mn_{1-x}Cu_xO_3$ has been observed at slight $Cu$ doping ($0\leq x \leq 0.05$). Namely, introduction of copper results in a splitting of the resistivity maximum around a metal-insulator transition temperature $T_0(x)$ into two differently evolving peaks. Unlike the original $Cu$-free maximum which steadily increases with doping, the second (satellite) peak remains virtually unchanged for $x<x_c$, increases for $x\ge x_c$ and finally disappears at $x_m\simeq 2x_c$ with $x_c\simeq 0.03$. The observed phenomenon is thought to arise from competition between substitution induced strengthening of potential barriers (which hamper the charge hopping between neighboring $Mn$ sites) and weakening of carrier's kinetic energy. The data are well fitted assuming a nonthermal tunneling conductivity theory with randomly distributed hopping sites.Comment: 10 REVTEX pages, 2 PostScript figures (epsf.sty); to be published in JETP Letter

Features of the crystal structure and electrical properties of sodium chloride at pressure 20-50 GPa

The electrical properties of polycrystalline samples of sodium chloride are studied at direct and alternating current in a wide range of frequencies at high pressure and room temperature. Graphic analysis of the experimental data [1-3] in the view of equivalent circuits allowed us to separate the contributions to conductivity caused by grains and intergrain boundaries. Features of impedance at pressure up to 37 GPa are in good agreement with earlier data and structural changes. It is shown that in the studied materials the electrical resistance of grains is much greater than the resistance of intergrain boundaries. © 2013 Allerton Press, Inc

A phenomenological model for the pressure sensitivity of the Curie temperature in hole-doped manganites

We performed high pressure experiments on La(0.8)Ca(0.2-x)Sr(x)MnO(3) (LCSMO) (0<x< 0.2) ceramic samples in order to analyze the validity of the well known relation between the A mean ionic radius () and the Curie temperature Tc of hole-doped manganites at a fixed doping level and for doping values below the 0.3 (Mn+4/Mn+3) ratio. By considering our results and collecting others from the literature, we were able to propose a phenomenological law that considers the systematic dependence of Tc with structural and electronic parameters. This law predicts fairly well the pressure sensitivity of Tc, its dependence with the A-cation radius disorder and its evolution in the high pressure range. Considering a Double Exchange model, modified by polaronic effects, the phenomenological law obtained for Tc can be associated with the product of two terms: the polaronic modified bandwidth and an effective hole doping.Comment: 5 pages, 7 figures, corresponding author: C. Acha ([email protected]

Role of Genetic and Environmental Factors in Determining the Response to Metformin

Metformin is one of the most commonly prescribed drugs for the treatment and prevention of type 2 diabetes mellitus (T2DM). Numerous evidence accumulates indicating that both genetic and environmental factors underlie adverse side effects of metformin, as well as individual differences in patient response to treatment The present review summarizes information on genetic factors and environmental modifiers determining patients’ individual response to metformin treatment. The data on the role of polymorphism of the most significant genes and protein products encoded by them both in the development of adverse effects and in determining the therapeutic response are summarized, and the place of metformin in the realization of the phenotypic effects of these genes is discussed.Endogenous conditions and exogenous effects modifying the response to metformin are considered. Among them are factors that affect the functional state of the genome (the level of methylation of genes, one way or another associated with the response to metformin, etc.), reflecting the biological characteristics of the organism (gender, age), health level (the presence of concomitant diseases, the supply of biometals and vitamins), taking other medications, etc. Thus, there is a wide range of factors modifying the response to metformin, which, unlike genetic characteristics, are largely controllable. At the same time, both genetic and environmental factors may differ in significance in different ethno-territorial groups of the population. This information should be taken into account when developing a personalized approach to prescribing metformin for the treatment of type 2 diabetes, as well as when recommending its use for the treatment of other diseases

Metal-insulator transition in manganites: mixture of oxygen isotopes versus magnetic field

We have investigated the effect of oxygen isotope substitution on the metal-insulator transition temperature and the resistivity of the narrow band manganite (La0.25Pr0.75)0.7Ca0.3MnO3 in a constant magnetic field. A set of 16 samples having different mixtures of 16O, 17O and 18O isotopes with average mass varying from 16.0 to 17.8 a.m.u. was studied. We have found that the magnetoresistance and the isotope effect can be linked together with a single parameter - effective magnetic field, which decreases linearly with an increase of average oxygen mass with a slope of -2 T/a.m.u. The applicability of the small polaron model is discussed.Comment: Submitted to Moscow International Symposium on Magnetism MISM'0

Modification of the ground state in Sm-Sr manganites by oxygen isotope substitution

The effect of $^{16}$O $\to$ $^{18}$O isotope substitution on electrical resistivity and magnetic susceptibility of Sm$_{1-x}$Sr$_x$MnO$_3$ manganites is analyzed. It is shown that the oxygen isotope substitution drastically affects the phase diagram at the crossover region between the ferromagnetic metal state and that of antiferromagnetic insulator (0.4 $< x <$ 0.6), and induces the metal-insulator transition at for $x$ = 0.475 and 0.5. The nature of antiferromagnetic insulator phase is discussed.Comment: 4 pages, 3 eps figures, RevTeX, submitted to Phys. Rev. Let

Sequence of the Mrjp3 microsatellite Locus in honeybees of different origin

The sequencing of the nucleotide sequences of the mrjp3 repetitive region (mrjp3 microsatellite locus) in Siberian honeybees was carried out. A high similarity of the studied nucleotide sequences (≥99% identity) with reference sequences was observed, which indicates a high conservation of the mrjp3 repetitive region in different Apis mellifera subspecies

Theory of Insulator Metal Transition and Colossal Magnetoresistance in Doped Manganites

The persistent proximity of insulating and metallic phases, a puzzling characterestic of manganites, is argued to arise from the self organization of the twofold degenerate e_g orbitals of Mn into localized Jahn-Teller(JT) polaronic levels and broad band states due to the large electron - JT phonon coupling present in them. We describe a new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties. These explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence

Expression studies of tuberculosis susceptibility genes

The activating research interest in the problem of tuberculosis development is due to the increase in cases of drug resistance, coinfection with HIV and hepatitis, and the lack of an effective vaccine. However, the pathogenesis of tuberculosis remains insufficiently studied at present. A significant role is assigned to hereditary factors, as the majority of those infected with Mycobacterium tuberculosis remain resistant to tuberculosis, and only in 5—15% of cases does infection lead to the development of the disease. Despite a long history of research of genetic factors of susceptibility to tuberculosis infection — from the search for monogenic forms of immune dysfunction, associations of individual tuberculosis susceptibility genes, to the analysis of genome-wide associative studies and the assessment of the characteristics of the transcriptional profiles of patients, — the problem of obtaining clinically significant results for the identification and monitoring of risk groups remains particularly acute. The search of differentially expressed genes in groups with different status of the disease (non-infected, latent tuberculosis infection, presymptomatic state, active tuberculosis, recovery from tuberculosis, non-tuberculosis infection) led to identification of a large number of data which is not overlapped in different compared groups, different ethnic groups, in the studies of the whole blood and cellular models. Merging this wealth of data followed by its reanalysis helps to verify and update results. However, there still is a large number of questions concerning our understanding of the functioning of the human organism under the influence of M. tuberculosis. In recent years, new approaches have been used to develop test systems for the diagnosis of various forms of the disease. The review considers up to date results of expression studies of susceptibility to tuberculosis, namely, objects and approaches of research changing over time, forms of the host response to the mycobacteria infection studied, the influence of different factors on the results