1,219 research outputs found
Link between the diversity, heterogeneity and kinetic properties of amorphous ice structures
Based on neutron wide-angle diffraction and small-angle neutron scattering
experiments, we show that there is a correlation between the preparational
conditions of amorphous ice structures, their microscopic structural
properties, the extent of heterogeneities on a mesoscopic spatial scale and the
transformation kinetics. There are only two modifications that can be
identified as homogeneous disordered structures, namely the very high-density
vHDA and the low-density amorphous LDA ice. Structures showing an intermediate
static structure factor with respect to vHDA and LDA are heterogeneous phases.
This holds independently from their preparation procedure, i.e. either obtained
by pressure amorphisation of ice I_h or by heating of vHDA. The degree of
heterogeneity can be progressively suppressed when higher pressures and
temperatures are applied for the sample preparation. In accordance with the
suppressed heterogeneity the maximum of the static structure factor displays a
pronounced narrowing of the first strong peak, shifting towards higher
Q-numbers. Moreover, the less heterogeneous the obtained structures are the
slower is the transformation kinetics from the high--density modifications into
LDA. The well known high-density amorphous structure HDA does not constitute
any particular state of the amorphous water network. It is formed due to the
preparational procedure working in liquid nitrogen as thermal bath, i.e. at
about 77 K
A phenomenological theory of zero-energy Andreev resonant states
A conceptual consideration is given to a zero-energy state (ZES) at the
surface of unconventional superconductors. The reflection coefficients in
normal-metal / superconductor (NS) junctions are calculated based on a
phenomenological description of the reflection processes of a quasiparticle.
The phenomenological theory reveals the importance of the sign change in the
pair potential for the formation of the ZES. The ZES is observed as the
zero-bias conductance peak (ZBCP) in the differential conductance of NS
junctions. The split of the ZBCP due to broken time-reversal symmetry states is
naturally understood in the present theory. We also discuss effects of external
magnetic fields on the ZBCP.Comment: 12 page
Terbinafine Resistance of Trichophyton Clinical Isolates Caused by Specific Point Mutations in the Squalene Epoxidase Gene.
Terbinafine is one of the allylamine antifungal agents whose target is squalene epoxidase (SQLE). This agent has been extensively used in the therapy of dermatophyte infections. The incidence of patients with tinea pedis or unguium tolerant to terbinafine treatment prompted us to screen the terbinafine resistance of all javax.xml.bind.JAXBElement@dc06fb4 clinical isolates from the laboratory of the Centre Hospitalier Universitaire Vaudois collected over a 3-year period and to identify their mechanism of resistance. Among 2,056 tested isolates, 17 (≈1%) showed reduced terbinafine susceptibility, and all of these were found to harbor javax.xml.bind.JAXBElement@374d721c gene alleles with different single point mutations, leading to single amino acid substitutions at one of four positions (Leu javax.xml.bind.JAXBElement@4655f570 , Phe javax.xml.bind.JAXBElement@112b804a , Phe javax.xml.bind.JAXBElement@1f18e014 , and His javax.xml.bind.JAXBElement@4319ac79 ) of the SQLE protein. Point mutations leading to the corresponding amino acid substitutions were introduced into the endogenous javax.xml.bind.JAXBElement@2a0e3f1f gene of a terbinafine-sensitive javax.xml.bind.JAXBElement@67eac3c4 (formerly javax.xml.bind.JAXBElement@3f2a876d ) strain. All of the generated javax.xml.bind.JAXBElement@315e9e95 transformants expressing mutated SQLE proteins exhibited obvious terbinafine-resistant phenotypes compared to the phenotypes of the parent strain and of transformants expressing wild-type SQLE proteins. Nearly identical phenotypes were also observed in javax.xml.bind.JAXBElement@6af3a966 transformants expressing mutant forms of javax.xml.bind.JAXBElement@5bb6b31f SQLE proteins. Considering that the genome size of dermatophytes is about 22 Mb, the frequency of terbinafine-resistant clinical isolates was strikingly high. Increased exposure to antifungal drugs could favor the generation of resistant strains
Dynamical and stationary critical behavior of the Ising ferromagnet in a thermal gradient
In this paper we present and discuss results of Monte Carlo numerical
simulations of the two-dimensional Ising ferromagnet in contact with a heat
bath that intrinsically has a thermal gradient. The extremes of the magnet are
at temperatures , where is the Onsager critical temperature.
In this way one can observe a phase transition between an ordered phase
() by means of a single simulation. By
starting the simulations with fully disordered initial configurations with
magnetization corresponding to , which are then suddenly
annealed to a preset thermal gradient, we study the short-time critical dynamic
behavior of the system. Also, by setting a small initial magnetization ,
we study the critical initial increase of the order parameter. Furthermore, by
starting the simulations from fully ordered configurations, which correspond to
the ground state at T=0 and are subsequently quenched to a preset gradient, we
study the critical relaxation dynamics of the system. Additionally, we perform
stationary measurements () that are discussed in terms of
the standard finite-size scaling theory. We conclude that our numerical
simulation results of the Ising magnet in a thermal gradient, which are
rationalized in terms of both dynamic and standard scaling arguments, are fully
consistent with well established results obtained under equilibrium conditions
A comparative study of transient characteristics of argon and argon-hydrogen pulse modulated induction thermal plasma
Solving a time-dependent two-dimensional local thermodynamic equilibrium (LTE) model simulation of Ar and Ar-H2 atmospheric pressure, a high-power RF-induction thermal plasma was performed. The effects of shimmer current level (SCL) in pulse-modulated mode and hydrogen concentrations on different flow fields were predicted. The radiation intensities of Ar I (751 nm) for different SCL were calculated from the temperature fields. For the same operating conditions as simulation, plasma was successfully generated in pulse-modulated mode and spectroscopic measurements were carried out to investigate the effects of SCL upon temporal plasma properties. Response times (rising, falling, on-delay, and off-delay time) of temporal radiation intensity were crosschecked for both experimental and simulated ones. The rising time increased gradually with the decrease of SCL, though the falling time remained almost unchanged with SCL. For example, for Ar plasma at 86 percent , 79 percent , 72 percent , 65 percent , 50 percent , and 40 percent SCL the rising times were 2.7, 3.0, 3.4, 3.4, 3.6, and 3.8 ms, respectively. And for Ar-H2 plasma (2.4 percent H2), at 87 percent , 77 percent , 72 percent , 63 percent , 55 percent , and 45 percent SCL, rising times were 2.5, 3.0, 3.0, 3.4, 3.7, 3.9, and 4.0 ms, respectively. Hydrogen inclusion slowed down the plasma response during the off-to-on pulsing transition at lower SCL and constricted the plasma axially. Finally, part of the simulated results was compared with experimental determinations and acceptable agreements were found. The discrepancies, in few cases, explicated mainly that the LTE assumption did not prevail in pulse-modulated plasma, especially around the on-pulse transitio
Theory of charge transport in diffusive normal metal / unconventional singlet superconductor contacts
We analyze the transport properties of contacts between unconventional
superconductor and normal diffusive metal in the framework of the extended
circuit theory. We obtain a general boundary condition for the Keldysh-Nambu
Green's functions at the interface that is valid for arbitrary transparencies
of the interface. This allows us to investigate the voltage-dependent
conductance (conductance spectrum) of a diffusive normal metal (DN)/
unconventional singlet superconductor junction in both ballistic and diffusive
cases. For d-wave superconductor, we calculate conductance spectra numerically
for different orientations of the junctions, resistances, Thouless energies in
DN, and transparencies of the interface. We demonstrate that conductance
spectra exhibit a variety of features including a -shaped gap-like
structure, zero bias conductance peak (ZBCP) and zero bias conductance dip
(ZBCD). We show that two distinct mechanisms: (i) coherent Andreev reflection
(CAR) in DN and (ii) formation of midgap Andreev bound state (MABS) at the
interface of d-wave superconductors, are responsible for ZBCP, their relative
importance being dependent on the angle between the interface normal
and the crystal axis of d-wave superconductors. For , the ZBCP is due
to CAR in the junctions of low transparency with small Thouless energies, this
is similar to the case of diffusive normal metal / insulator /s-wave
superconductor junctions. With increase of from zero to , the
MABS contribution to ZBCP becomes more prominent and the effect of CAR is
gradually suppressed. Such complex spectral features shall be observable in
conductance spectra of realistic high- junctions at very low temperature
Nonequilibrium excitations in Ferromagnetic Nanoparticles
In recent measurements of tunneling transport through individual
ferromagnetic Co nanograins, Deshmukh, Gu\'eron, Ralph et al.
\cite{mandar,gueron} (DGR) observed a tunneling spectrum with discrete
resonances, whose spacing was much smaller than what one would expect from
naive independent-electron estimates. In a previous publication,
\cite{prl_kleff} we had suggested that this was a consequence of nonequilibrium
excitations, and had proposed a ``minimal model'' for ferromagnetism in
nanograins with a discrete excitation spectrum as a framework for analyzing the
experimental data. In the present paper, we provide a detailed analysis of the
properties of this model: We delineate which many-body electron states must be
considered when constructing the tunneling spectrum, discuss various
nonequilibrium scenarios and compare their results with the experimental data
of Refs. \cite{mandar,gueron}. We show that a combination of nonequilibrium
spin- and single-particle excitations can account for most of the observed
features, in particular the abundance of resonances, the resonance spacing and
the absence of Zeeman splitting.Comment: 13 pages, 10 figure
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