1,988 research outputs found
Anisotropic charge dynamics in detwinned Ba(FeCo)As
We investigate the optical conductivity as a function of temperature with
light polarized along the in-plane orthorhombic - and -axes of
Ba(FeCo)As for =0 and 2.5 under uniaxial pressure.
The charge dynamics at low frequencies on these detwinned, single domain
compounds tracks the anisotropic transport properties across their
structural and magnetic phase transitions. Our findings allow us to estimate
the dichroism, which extends to relatively high frequencies. These results are
consistent with a scenario in which orbital order plays a significant role in
the tetragonal-to-orthorhombic structural transition
Charge dynamics of the Co-doped BaFeAs
We report on a thorough optical investigation over a broad spectral range and
as a function of temperature of the charge dynamics in
Ba(CoFe)As compounds for Co-doping ranging between 0 and
18%. For the parent compound as well as for =0.025 we observe the opening of
a pseudogap, due to the spin-density-wave phase transition and inducing a
reshuffling of spectral weight from low to high frequencies. For compounds with
0.051 0.11 we detect the superconducting gap, while at =0.18 the
material stays metallic at all temperatures. We describe the effective metallic
contribution to the optical conductivity with two Drude terms, representing the
combination of a coherent and incoherent component, and extract the respective
scattering rates. We establish that the transport properties in the normal
phase are dominated by the coherent Drude term for 00.051 and by the
incoherent one for 0.0610.18, respectively. Finally through spectral
weight arguments, we give clear-cut evidence for moderate electronic
correlations for 00.061, which then crossover to values appropriate
for a regime of weak interacting and nearly-free electron metals for
0.11
Mathematical Structure of Rabi Oscillations in the Strong Coupling Regime
In this paper we generalize the Jaynes--Cummings Hamiltonian by making use of
some operators based on Lie algebras su(1,1) and su(2), and study a
mathematical structure of Rabi floppings of these models in the strong coupling
regime. We show that Rabi frequencies are given by matrix elements of
generalized coherent operators (quant--ph/0202081) under the rotating--wave
approximation.
In the first half we make a general review of coherent operators and
generalized coherent ones based on Lie algebras su(1,1) and su(2). In the
latter half we carry out a detailed examination of Frasca (quant--ph/0111134)
and generalize his method, and moreover present some related problems.
We also apply our results to the construction of controlled unitary gates in
Quantum Computation. Lastly we make a brief comment on application to Holonomic
Quantum Computation.Comment: Latex file, 24 pages. I added a new section (Quantum Computation), so
this paper became self-contained in a certain sens
Chow's theorem and universal holonomic quantum computation
A theorem from control theory relating the Lie algebra generated by vector
fields on a manifold to the controllability of the dynamical system is shown to
apply to Holonomic Quantum Computation. Conditions for deriving the holonomy
algebra are presented by taking covariant derivatives of the curvature
associated to a non-Abelian gauge connection. When applied to the Optical
Holonomic Computer, these conditions determine that the holonomy group of the
two-qubit interaction model contains . In particular, a
universal two-qubit logic gate is attainable for this model.Comment: 13 page
Multiresistant Salmonella enterica serovar 4,[5],12:i:- in Europe: a new pandemic strain?
A marked increase in the prevalence of S. enterica serovar 4,[5],12:i:- with resistance to ampicillin, streptomycin, sulphonamides and tetracyclines (R-type ASSuT) has been noted in food-borne infections and in pigs/pig meat in several European countries in the last ten years. One hundred and sixteen strains of S. enterica serovar 4,[5],12:i:- from humans, pigs and pig meat isolated in England and Wales, France, Germany, Italy, Poland, Spain and the Netherlands were further subtyped by phage typing, pulsed-field gel electrophoresis and multilocus variable number tandem repeat analysis to investigate the genetic relationship among strains. PCR was performed to identify the fljB flagellar gene and the genes encoding resistance to ampicillin, streptomycin, sulphonamides and tetracyclines. Class 1 and 2 integrase genes were also sought. Results indicate that genetically related serovar 4,[5],12:i:- strains of definitive phage types DT193 and DT120 with ampicillin, streptomycin, sulphonamide and tetracycline resistance encoded by blaTEM, strA-strB, sul2 and tet(B) have emerged in several European countries, with pigs the likely reservoir of infection. Control measures are urgently needed to reduce spread of infection to humans via the food chain and thereby prevent the possible pandemic spread of serovar 4,[5],12:i:- of R-type ASSuT as occurred with S. Typhimurium DT104 during the 1990s
A new formulation of oral viscous budesonide in treating of paediatric eosinophilic oesophagitis: a pilot study
OBJECTIVES:
Oral viscous budesonide is a recent therapeutic option for eosinophilic oesophagitis (EoE) compared with dietary restriction and inhaled steroids. This single-centre, open-label, not blinded study aims to evaluate the efficacy and safety of a new, preprepared oral viscous budesonide suspension (PVB) in children and adolescents with EoE.
METHODS:
We treated 36 children with PVB (29 boys; median age 12 years) with EoE diagnosed according to European Society for Paediatric Gastroenterology Hepatology and Nutrition guidelines. Patients <150 and >150 cm height received 2 and 4 mg PVB daily, respectively, for 12 weeks. Upper gastrointestinal endoscopy was performed at baseline, after 12 weeks of therapy and 24 weeks after the end of therapy. Baseline and post-treatment scores were calculated for symptoms, endoscopy, and histology. Serum cortisol was performed at baseline, 12, and 36 weeks.
RESULTS:
At the end of PVB trial, endoscopy showed macroscopic remission in 32 patients (88.9%), whereas at histology median pre- and post-treatment peak eosinophil count/high power field (HPF) markedly decreased from 42.2 (range: 15-100) to 2.9 (range: 0-30); moreover, mean symptom and histology scores impressively improved compared with baseline (Pâ<â0.01). At 24 weeks after the end of PVB therapy, endoscopy showed oesophageal relapse in 21 patients (58.3%), whereas 15 (41.7%) were still in remission. Seven children (19.4%) with positive multichannel intraluminal impedance-pH were treated also with proton pump inhibitors. No significant difference between pre-/post-treatment morning cortisol levels occurred.
CONCLUSIONS:
The new PVB suspension presented in the present study is effective and safe for treating children with proven EoE. Larger placebo-controlled clinical trials would provide more information about dosing, efficacy, and long-term safety of this formulation, specifically designed for the oesophagus
Anisotropic in-plane optical conductivity in detwinned Ba(Fe1-xCox)2As2
We study the anisotropic in-plane optical conductivity of detwinned
Ba(Fe1-xCox)2As2 single crystals for x=0, 2.5% and 4.5% in a broad energy range
(3 meV-5 eV) across their structural and magnetic transitions. For temperatures
below the Neel transition, the topology of the reconstructed Fermi surface,
combined with the distinct behavior of the scattering rates, determines the
anisotropy of the low frequency optical response. For the itinerant charge
carriers, we are able to disentangle the evolution of the Drude weights and
scattering rates and to observe their enhancement along the orthorhombic
antiferromagnetic a-axis with respect to the ferromagnetic b-axis. For
temperatures above Ts, uniaxial stress leads to a finite in-plane anisotropy.
The anisotropy of the optical conductivity, leading to a significant dichroism,
extends to high frequencies in the mid- and near-infrared regions. The
temperature dependence of the dichroism at all dopings scales with the
anisotropy ratio of the dc conductivity, suggesting the electronic nature of
the structural transition. Our findings bear testimony to a large nematic
susceptibility that couples very effectively to the uniaxial lattice strain. In
order to clarify the subtle interplay of magnetism and Fermi surface topology
we compare our results with theoretical calculations obtained from density
functional theory within the full-potential linear augmented plane-wave method.Comment: 17 pages, 9 figure
Theoretical Investigation of Optical Conductivity in Ba [Fe(1-x)Co(x)]2 As2
We report on theoretical calculations of the optical conductivity of Ba
[Fe(1-x)Co(x)]2 As2, as obtained from density functional theory within the full
potential LAPW method. A thorough comparison with experiment shows that we are
able to reproduce most of the observed experimental features, in particular a
magnetic peak located at about 0.2 eV which we ascribe to antiferromagnetic
ordered magnetic stripes. We also predict a large in-plane anisotropy of this
feature, which agrees very well with measurements on detwinned crystals. The
effect of Co doping as well as the dependence of plasma frequency on the
magnetic order is also investigated
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