8,995 research outputs found
Current noise through a Kondo quantum dot in a SU(N) Fermi liquid state
The current noise through a mesoscopic quantum dot is calculated and analyzed
in the Fermi liquid regime of the SU(N) Kondo model. Results connect the
Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and
temperature, and show that temperature corrections are sizeable in usual
experiments. For the experimentally relevant SU(4) case, quasiparticle
interactions are shown to increase the shot noise.Comment: 4 pages, 2 figures, to be published in Phys. Rev. Lett. (revised
version
Coupled currents in cosmic strings
We first examine the microstructure of a cosmic string endowed with two
simple Abelian currents. This microstructure depends on two state parameters.
We then provide the macroscopic description of such a string and show that it
depends on an additional Lorentz-invariant state parameter that relates the two
currents. We find that in most of the parameter space, the two-current string
is essentially equivalent to the single current-carrying string, i.e., only one
field condenses onto the defect. In the regions where two currents are present,
we find that as far as stability is concerned, one can approximate the dynamics
with good accuracy using an analytic model based on either a logarithmic (on
the electric side, i.e., for timelike currents) or a rational (on the magnetic
side, i.e., for spacelike currents) worldsheet Lagrangian.Comment: 25 pages, 9 figure
Topological confinement in graphene bilayer quantum rings
We demonstrate the existence of localized electron and hole states in a
ring-shaped potential kink in biased bilayer graphene. Within the continuum
description, we show that for sharp potential steps the Dirac equation
describing carrier states close to the K (or K') point of the first Brillouin
zone can be solved analytically for a circular kink/anti-kink dot. The
solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations
as functions of the height of the potential step and/or the radius of the ring
High Resolution Crystal Structures of the Wild Type and Cys-55 right-arrow Ser and Cys-59 right-arrow Ser Variants of the Thioredoxin-like [2Fe-2S] Ferredoxin from Aquifex aeolicus
The [2Fe-2S] ferredoxin (Fd4) from Aquifex aeolicus adopts a thioredoxin-like polypeptide fold that is distinct from other [2Fe-2S] ferredoxins. Crystal structures of the Cys-55 right-arrow Ser (C55S) and Cys-59 right-arrow Ser (C59S) variants of this protein have been determined to 1.25 Å and 1.05 Å resolution, respectively, whereas the resolution of the wild type (WT) has been extended to 1.5 Å. The improved WT structure provides a detailed description of the [2Fe-2S] cluster, including two features that have not been noted previously in any [2Fe-2S] cluster-containing protein, namely, pronounced distortions in the cysteine coordination to the cluster and a Calpha -H-Sgamma hydrogen bond between cluster ligands Cys-55 and Cys-9. These features may contribute to the unusual electronic and magnetic properties of the [2Fe-2S] clusters in WT and variants of this ferredoxin. The structures of the two variants of Fd4, in which single cysteine ligands to the [2Fe-2S] cluster are replaced by serine, establish the metric details of serine-ligated Fe-S active sites with unprecedented accuracy. Both the cluster and its surrounding protein matrix change in subtle ways to accommodate this ligand substitution, particularly in terms of distortions of the Fe2S2 inorganic core from planarity and displacements of the polypeptide chain. These high resolution structures illustrate how the interactions between polypeptide chains and Fe-S active sites reflect combinations of flexibility and rigidity on the part of both partners; these themes are also evident in more complex systems, as exemplified by changes associated with serine ligation of the nitrogenase P cluster
Hybrid phase at the quantum melting of the Wigner crystal
We study the quantum melting of the two-dimensional Wigner crystal using a
fixed node quantum Monte-Carlo approach. In addition to the two already known
phases (Fermi liquid at large density and Wigner crystal at low density), we
find a third stable phase at intermediate values of the density. The third
phase has hybrid behaviors in between a liquid and a solid. This hybrid phase
has the nodal structure of a Slater determinant constructed out of the bands of
a triangular lattice.Comment: 5 pages, 4 figure
Rapid spectrophotometric determination of nitrates and nitrites in marine aqueous culture media
The spectrophotometric determination of nitrate in sea water broths for cultivation of, say, microalgae is complicated
by the frequent presence of nitrite. Two methods - sulphamic/perchloric acid method (also known as Cawse method) and sulphamic
acid method - both claimed to be able to eliminate nitrite interference, were tested using a set of standards, but statistical
treatment of the results proved their limitations in nitrate quantification. An improved method, based on former published
methods for quantification of nitrite and coupled determination of nitrate and nitrite, was designed and tested. This improved
method was compared with the reference method (based on use of a cadmium column) using several standards and biological
samples of two culture media for microalgae, in different phases of their growth curve. The results thus obtained have demonstrated
that there is no statistically significant difference between them at the 5% level. The precision of the method was tested
by repeating determinations with three sets of standard mixtures containing nitrate and nitrite. The method proposed has advantages
over conventional methods in reduced time of analysis, as well as high precision and accuracy, so it may be a good alternative
for determination of nitrite and nitrate in marine aqueous media
Finite dimensional quantizations of the (q,p) plane : new space and momentum inequalities
We present a N-dimensional quantization a la Berezin-Klauder or frame
quantization of the complex plane based on overcomplete families of states
(coherent states) generated by the N first harmonic oscillator eigenstates. The
spectra of position and momentum operators are finite and eigenvalues are
equal, up to a factor, to the zeros of Hermite polynomials. From numerical and
theoretical studies of the large behavior of the product of non null smallest positive and largest eigenvalues, we infer
the inequality (resp. ) involving, in suitable
units, the minimal () and maximal () sizes of
regions of space (resp. momentum) which are accessible to exploration within
this finite-dimensional quantum framework. Interesting issues on the
measurement process and connections with the finite Chern-Simons matrix model
for the Quantum Hall effect are discussed
Mixture of Kernels and Iterated Semidirect Product of Diffeomorphisms Groups
In the framework of large deformation diffeomorphic metric mapping (LDDMM),
we develop a multi-scale theory for the diffeomorphism group based on previous
works. The purpose of the paper is (1) to develop in details a variational
approach for multi-scale analysis of diffeomorphisms, (2) to generalise to
several scales the semidirect product representation and (3) to illustrate the
resulting diffeomorphic decomposition on synthetic and real images. We also
show that the approaches presented in other papers and the mixture of kernels
are equivalent.Comment: 21 pages, revised version without section on evaluatio
Doença de Behçet e linfoma. Associação fortuita?
A doença de Behçet (DB) caracteriza-se, classicamente, por uma
tríade sintomática de úlceras orais recorrentes, úlceras genitais
e uveíte.
A DB é sistémica, com desenvolvimento de lesões vasculíticas
ou vasculopáticas nas áreas afectadas. Estas áreas podem
apresentar evidência microscópica de infiltração tecidual com
células T e neutrófilos.
A associação com Linfoma não-Hodgkin tem sido reportada
em raros casos, não permitido afirmar relação causal.
Reportamos um caso de Linfoma não-Hodgkin em doente
com doença de Behçet, com revisão de literatura neste contexto
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