Mean field theory of the Mott-Anderson transition

We present a theory for disordered interacting electrons that can describe both the Mott and the Anderson transition in the respective limits of zero disorder and zero interaction. We use it to investigate the T=0 Mott-Anderson transition at a fixed electron density, as a the disorder strength is increased. Surprisingly, we find two critical values of disorder W_{nfl} and W_c. For W > W_{nfl}, the system enters a ``Griffiths'' phase, displaying metallic non-Fermi liquid behavior. At even stronger disorder, W=W_c > W_{nfl} the system undergoes a metal insulator transition, characterized by the linear vanishing of both the typical density of states and the typical quasiparticle weight.Comment: 4 pages, 2 figures, REVTEX, eps

Doping a semiconductor to create an unconventional metal

Landau Fermi liquid theory, with its pivotal assertion that electrons in metals can be simply understood as independent particles with effective masses replacing the free electron mass, has been astonishingly successful. This is true despite the Coulomb interactions an electron experiences from the host crystal lattice, its defects, and the other ~1022/cm3 electrons. An important extension to the theory accounts for the behaviour of doped semiconductors1,2. Because little in the vast literature on materials contradicts Fermi liquid theory and its extensions, exceptions have attracted great attention, and they include the high temperature superconductors3, silicon-based field effect transistors which host two-dimensional metals4, and certain rare earth compounds at the threshold of magnetism5-8. The origin of the non-Fermi liquid behaviour in all of these systems remains controversial. Here we report that an entirely different and exceedingly simple class of materials - doped small gap semiconductors near a metal-insulator transition - can also display a non-Fermi liquid state. Remarkably, a modest magnetic field functions as a switch which restores the ordinary disordered Fermi liquid. Our data suggest that we have finally found a physical realization of the only mathematically rigourous route to a non-Fermi liquid, namely the 'undercompensated Kondo effect', where there are too few mobile electrons to compensate for the spins of unpaired electrons localized on impurity atoms9-12.Comment: 17 pages 4 figures supplemental information included with 2 figure

Anderson-Mott transition as a quantum glass problem

We combine a recent mapping of the Anderson-Mott metal-insulator transition on a random-field problem with scaling concepts for random-field magnets to argue that disordered electrons near an Anderson-Mott transition show glass-like behavior. We first discuss attempts to interpret experimental results in terms of a conventional scaling picture, and argue that some of the difficulties encountered point towards a glassy nature of the electrons. We then develop a general scaling theory for a quantum glass, and discuss critical properties of both thermodynamic and transport variables in terms of it. Our most important conclusions are that for a correct interpretation of experiments one must distinguish between self-averaging and non-self averaging observables, and that dynamical or temperature scaling is not of power-law type but rather activated, i.e. given by a generalized Vogel-Fulcher law. Recent mutually contradicting experimental results on Si:P are discussed in the light of this, and new experiments are proposed to test the predictions of our quantum glass scaling theory.Comment: 25pp, REVTeX, 5 ps figs, final version as publishe

Экспериментальное определение тепловых потерь теплопроводов при применении сверхтонкой тепловой изоляции.

Объектом исследования является тонкопленочный теплоизоляционный материал торговой марки – «Корунд», Цель работы – Анализ тепловых потерь и исследование теплотехнических характеристик тонкопленочного теплоизоляционного материала торговой марки «Корунд». В результате исследования были найдены коэффициенты теплопроводности тонкопленочного теплоизоляционного материала при различных температурах поверхности ТЭНа.The object of study is the thin-film insulating material of the trademark "Emery", The work purpose – the Analysis of thermal losses and investigation of thermal characteristics of thin film insulating material of the trademark "Emery". The study was found the thermal conductivity of thin film insulating material at different temperatures the heating element surface

Behavior of the thermopower in amorphous materials at the metal-insulator transition

Published versio

Circulating Hepatitis B Surface Antigen Particles Carry Hepatocellular microRNAs

Hepatitis B virus (HBV) produces high quantities of subviral surface antigen particles (HBsAg) which circulate in the blood outnumbering virions of about 1\103–6 times. In individuals coinfected with the defective hepatitis Delta virus (HDV) the small HDV-RNA-genome and Delta antigen circulate as ribonucleoprotein complexes within HBsAg subviral particles. We addressed the question whether subviral HBsAg particles may carry in the same way cellular microRNAs (miRNAs) which are released into the bloodstream within different subcellular forms such as exosomes and microvescicles. Circulating HBsAg particles were isolated from sera of 11 HBsAg carriers by selective immunoprecipitation with monoclonal anti-HBs-IgG, total RNA was extracted and human miRNAs were screened by TaqMan real-time quantitative PCR Arrays. Thirty-nine human miRNAs were found to be significantly associated with the immunoprecipitated HBsAg, as determined by both comparative DDCT analysis and non-parametric tests (Mann-Whitney, p<0.05) with respect to controls. Moreover immunoprecipitated HBsAg particles contained Ago2 protein that could be revealed in ELISA only after 0.5% NP40. HBsAg associated miRNAs were liver-specific (most frequent = miR-27a, miR-30b, miR-122, miR-126 and miR-145) as well as immune regulatory (most frequent = miR-106b and miR-223). Computationally predicted target genes of HBsAg-associated miRNAs highlighted molecular pathways dealing with host-pathoge

Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment

In this paper, we review theoretical and experimental research on rare region effects at quantum phase transitions in disordered itinerant electron systems. After summarizing a few basic concepts about phase transitions in the presence of quenched randomness, we introduce the idea of rare regions and discuss their importance. We then analyze in detail the different phenomena that can arise at magnetic quantum phase transitions in disordered metals, including quantum Griffiths singularities, smeared phase transitions, and cluster-glass formation. For each scenario, we discuss the resulting phase diagram and summarize the behavior of various observables. We then review several recent experiments that provide examples of these rare region phenomena. We conclude by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative Ising chain fixed, references added, v3: final version as publishe

Complexity of the International Agro-Food Trade Network and Its Impact on Food Safety

With the world’s population now in excess of 7 billion, it is vital to ensure the chemical and microbiological safety of our food, while maintaining the sustainability of its production, distribution and trade. Using UN databases, here we show that the international agro-food trade network (IFTN), with nodes and edges representing countries and import-export fluxes, respectively, has evolved into a highly heterogeneous, complex supply-chain network. Seven countries form the core of the IFTN, with high values of betweenness centrality and each trading with over 77% of all the countries in the world. Graph theoretical analysis and a dynamic food flux model show that the IFTN provides a vehicle suitable for the fast distribution of potential contaminants but unsuitable for tracing their origin. In particular, we show that high values of node betweenness and vulnerability correlate well with recorded large food poisoning outbreaks