Magnetic Gaps related to Spin Glass Order in Fermionic Systems

We provide evidence for spin glass related magnetic gaps in the fermionic density of states below the freezing temperature. Model calculations are presented and proposed to be relevant for explaining resistivity measurements which observe a crossover from variable-range- to activated behavior. The magnetic field dependence of a hardgap and the low temperature decay of the density of states are given. In models with fermion transport a new metal-insulator transition is predicted to occur due to the spin-glass gap, anteceding the spin glass to quantum paramagnet transition at smaller spin density. Important fluctuation effects due to finite range frustrated interactions are estimated and discussed.Comment: 4 pages, 1 Postscript figure, revised version accepted for publication in Physical Review Letter

Stress and Strain State Analysis of Defective Pipeline Portion

The paper presents computer simulation results of the pipeline having defects in a welded joint. Autodesk Inventor software is used for simulation of the stress and strain state of the pipeline. Places of the possible failure and stress concentrators are predicted on the defective portion of the pipeline

Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions

The CHORUS experiment, designed to search for $\nu_{\mu}\to\nu_{\tau}$ oscillations, consists of a nuclear emulsion target and electronic detectors. In this paper, results on the production of charged particles in a small sample of charged-current neutrino-- and anti-neutrino--nucleus interactions at high energy are presented. For each event, the emission angle and the ionization features of the charged particles produced in the interaction are recorded, while the standard kinematic variables are reconstructed using the electronic detectors. The average multiplicities for charged tracks, the pseudo-rapidity distributions, the dispersion in the multiplicity of charged particles and the KNO scaling are studied in different kinematical regions. A study of quasi-elastic topologies performed for the first time in nuclear emulsions is also reported. The results are presented in a form suitable for use in the validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure

Strong localization of electrons in quasi-one-dimensional conductors

We report on the experimental study of electron transport in sub-micron-wide ''wires'' fabricated from Si $\delta$-doped GaAs. These quasi-one-dimensional (Q1D) conductors demonstrate the crossover from weak to strong localization with decreasing the temperature. On the insulating side of the crossover, the resistance has been measured as a function of temperature, magnetic field, and applied voltage for different values of the electron concentration, which was varied by applying the gate voltage. The activation temperature dependence of the resistance has been observed with the activation energy close to the mean energy spacing of electron states within the localization domain. The study of non-linearity of the current-voltage characteristics provides information on the distance between the critical hops which govern the resistance of Q1D conductors in the strong localization (SL) regime. We observe the exponentially strong negative magnetoresistance; this orbital magnetoresistance is due to the universal magnetic-field dependence of the localization length in Q1D conductors. The method of measuring of the single-particle density of states (DoS) in the SL regime has been suggested. Our data indicate that there is a minimum of DoS at the Fermi level due to the long-range Coulomb interaction.Comment: 12 pages, 11 figures; the final version to appear in Phys. Rev.

Manipulating the Tomonaga-Luttinger exponent by electric field modulation

We establish a theoretical framework for artificial control of the power-law singularities in Tomonaga-Luttinger liquid states. The exponent governing the power-law behaviors is found to increase significantly with an increase in the amplitude of the periodic electric field modulation applied externally to the system. This field-induced shift in the exponent indicates the tunability of the transport properties of quasi-one-dimensional electron systems.Comment: 7 pages, 3 figure

Single-particle excitations under coexisting electron correlation and disorder: a numerical study of the Anderson-Hubbard model

Interplay of electron correlation and randomness is studied by using the Anderson-Hubbard model within the Hartree-Fock approximation. Under the coexistence of short-range interaction and diagonal disorder, we obtain the ground-state phase diagram in three dimensions, which includes an antiferromagnetic insulator, an antiferromagnetic metal, a paramagnetic insulator (Anderson-localized insulator) and a paramagnetic metal. Although only the short-range interaction is present in this model, we find unconventional soft gaps in the insulating phases irrespective of electron filling, spatial dimensions and long-range order, where the single-particle density of states (DOS) vanishes with a power-law scaling in one dimension (1D) or even faster in two dimensions (2D) and three dimensions (3D) toward the Fermi energy. We call it soft Hubbard gap. Moreover, exact-diagonalization results in 1D support the formation of the soft Hubbard gap beyond the mean-field level. The formation of the soft Hubbard gap cannot be attributed to a conventional theory by Efros and Shklovskii (ES) owing the emergence of soft gaps to the long-range Coulomb interaction. Indeed, based on a picture of multivalley energy landscape, we propose a phenomenological scaling theory, which predicts a scaling of the DOS in perfect agreement with the numerical results. We further discuss a correction of the scaling of the DOS by the long-range part of the Coulomb interaction, which modifies the scaling of Efros and Shklovskii. Furthermore, explicit formulae for the temperature dependence of the DC resistivity via variable-range hopping under the influence of the soft gaps are derived. Finally, we compare the present theory with experimental results of SrRu_{1-x}Ti_xO_3.Comment: 22 pages, 19 figure

High Electron Mobility in Vacuum and Ambient for PDIF-CN2 Single-Crystal Transistors

We have investigated the electron mobility on field-effect transistors based on PDIF-CN$_{2}$ single crystals. The family of the small molecules PDI8-CN$_{2}$ has been chosen for the promising results obtained for vapour-deposited thin film FETs. We used as gate dielectric a layer of PMMA (spinned on top of the SiO$_{2}$), to reduce the possibility of electron trapping by hydroxyl groups present at surface of the oxide. For these devices we obtained a room temperature mobility of 6 cm$^{2}$/Vs in vacuum and 3 cm$^{2}$/Vs in air. Our measurements demonstrate the possibility to obtain n-type OFETs with performances comparable to those of p-type devices.Comment: published online in JAC

Conformational changes during pore formation by the perforin-related protein pleurotolysin

Membrane attack complex/perforin-like (MACPF) proteins comprise the largest superfamily of pore-forming proteins, playing crucial roles in immunity and pathogenesis. Soluble monomers assemble into large transmembrane pores via conformational transitions that remain to be structurally and mechanistically characterised. Here we present an 11 Å resolution cryo-electron microscopy (cryo-EM) structure of the two-part, fungal toxin Pleurotolysin (Ply), together with crystal structures of both components (the lipid binding PlyA protein and the pore-forming MACPF component PlyB). These data reveal a 13-fold pore 80 Å in diameter and 100 Å in height, with each subunit comprised of a PlyB molecule atop a membrane bound dimer of PlyA. The resolution of the EM map, together with biophysical and computational experiments, allowed confident assignment of subdomains in a MACPF pore assembly. The major conformational changes in PlyB are a ~70° opening of the bent and distorted central β-sheet of the MACPF domain, accompanied by extrusion and refolding of two α-helical regions into transmembrane β-hairpins (TMH1 and TMH2). We determined the structures of three different disulphide bond-trapped prepore intermediates. Analysis of these data by molecular modelling and flexible fitting allows us to generate a potential trajectory of β-sheet unbending. The results suggest that MACPF conformational change is triggered through disruption of the interface between a conserved helix-turn-helix motif and the top of TMH2. Following their release we propose that the transmembrane regions assemble into β-hairpins via top down zippering of backbone hydrogen bonds to form the membrane-inserted β-barrel. The intermediate structures of the MACPF domain during refolding into the β-barrel pore establish a structural paradigm for the transition from soluble monomer to pore, which may be conserved across the whole superfamily. The TMH2 region is critical for the release of both TMH clusters, suggesting why this region is targeted by endogenous inhibitors of MACPF function

Discovery of a Non-Peptidic Inhibitor of West Nile Virus NS3 Protease by High-Throughput Docking

An estimated 2.5 billion people are at risk of diseases caused by dengue and West Nile virus. As of today, there are neither vaccines to prevent nor drugs to cure the severe infections caused by these viruses. The NS3 protease is one of the most promising targets for drug development against West Nile virus because it is an essential enzyme for viral replication and because success has been demonstrated with the closely related hepatitis C virus protease. We have discovered a small molecule that inhibits the NS3 protease of West Nile virus by computer-aided high-throughput docking, and validated it using three experimental techniques. The inhibitor has potential to be developed to a drug candidate to combat West Nile virus infections