214 research outputs found
Exact description of the magnetoelectric effect in the spin-1/2 XXZ-chain with Dzyaloshinskii-Moriya interaction
We consider a simple integrable model of a spin chain exhibiting the
Magnetoelectric Effect (MEE). Starting from the periodic S=1/2 XXZ-chain with
Dzyaloshinskii-Moriya terms, which we consider as a local electric polarization
in the spirit of the Katsura-Nagaosa-Baladsky (KNB) mechanism, we perform the
mapping onto the conventional XXZ-chain with twisted boundary conditions. Using
the techniques of Quantum Transfer Matrix (QTM) and Non-Linear Integral
Equations (NLIE) we obtain the magnetization, electric polarization and
magnetoelectric tensor as functions of magnetic and electric field for
arbitrary temperatures. We investigate these dependencies as well as the
thermal behavior of the above mentioned physical quantities, especially in the
low-temperature regime. We found several regimes of polarization. Adjusting the
magnetic field one can switch the system from one regime to another. The
features of the critical properties connected with the MEE are also
illustrated.Comment: 11 pages; 6 figure
On the theory of microwave absorption by the spin-1/2 Heisenberg-Ising magnet
We analyze the problem of microwave absorption by the Heisenberg-Ising magnet
in terms of shifted moments of the imaginary part of the dynamical
susceptibility. When both, the Zeeman field and the wave vector of the incident
microwave, are parallel to the anisotropy axis, the first four moments
determine the shift of the resonance frequency and the line width in a
situation where the frequency is varied for fixed Zeeman field. For the
one-dimensional model we can calculate the moments exactly. This provides exact
data for the resonance shift and the line width at arbitrary temperatures and
magnetic fields. In current ESR experiments the Zeeman field is varied for
fixed frequency. We show how in this situation the moments give perturbative
results for the resonance shift and for the integrated intensity at small
anisotropy as well as an explicit formula connecting the line width with the
anisotropy parameter in the high-temperature limit.Comment: 4 page
Leukoencephalopathy with accumulated succinate is indicative of SDHAF1 related complex II deficiency
Does human bocavirus infection depend on helper viruses? A challenging case report
A case of severe diarrhoea associated with synergistic human bocavirus type 1 (HBoV) and human herpes virus type 6 (HHV6) is reported. The case supports the hypotheses that HBoV infection under clinical conditions may depend on helper viruses, or that HBoV replicates by a mechanism that is atypical for parvoviruses, or that HBoV infection can be specifically treated with cidofovir
The complete conformal spectrum of a invariant network model and logarithmic corrections
We investigate the low temperature asymptotics and the finite size spectrum
of a class of Temperley-Lieb models. As reference system we use the spin-1/2
Heisenberg chain with anisotropy parameter and twisted boundary
conditions. Special emphasis is placed on the study of logarithmic corrections
appearing in the case of in the bulk susceptibility data and in
the low-energy spectrum yielding the conformal dimensions. For the
invariant 3-state representation of the Temperley-Lieb algebra with
we give the complete set of scaling dimensions which show huge
degeneracies.Comment: 18 pages, 5 figure
Cryo-EM structural studies of the agonist complexed human TRPV4 ion-channel reveals novel structural rearrangements resulting in an open-conformation
The human transient receptor potential vanilloid 4 (hTRPV4) ion channel plays a critical role in a variety of biological processes. Whilst the activation of hTRPV4 gating properties has been reported for a broad spectrum of stimuli, including synthetic 4α-phorbols, the molecular basis of the activation is poorly understood. Here we report the novel cryo-EM structure of the hTRPV4 determined in the presence of the archetypical phorbol acid agonist, 4α-PDD. Complementary mutagenesis experiments support the EM-identified binding site as well as allowing rationalization of disruptive mutants located outside of the 4α-PDD binding site. This work represents the first structural information of hTRPV4 in a ligand-induced open conformation. Together, our data reveal the underlying molecular mechanisms resulting in the opening of the central pore and ion-channel activation and provide a structural template for designing inhibitors targeting the open-state conformation of hTRPV4
On the absorption of microwaves by the one-dimensional spin-1/2 Heisenberg-Ising magnet
We analyze the absorption of microwaves by the Heisenberg-Ising chain
combining exact calculations, based on the integrability of the model, with
numerical calculations. Within linear response theory the absorbed intensity is
determined by the imaginary part of the dynamical susceptibility. The moments
of the normalized intensity can be used to define the shift of the resonance
frequency induced by the interactions and the line width independently of the
shape of the spectral line. These moments can be calculated exactly as
functions of temperature and strength of an external magnetic field, as long as
the field is directed along the symmetry axis of the chain. This allows us to
discuss the line width and the resonance shift for a given magnetic field in
the full range of possible anisotropy parameters. For the interpretation of
these data we need a qualitative knowledge of the line shape which we obtain
from fully numerical calculations for finite chains. Exact analytical results
on the line shape are out of reach of current theories. From our numerical work
we could extract, however, an empirical parameter-free model of the line shape
at high temperatures which is extremely accurate over a wide range of
anisotropy parameters and is exact at the free fermion point and at the
isotropic point. Another prediction of the line shape can be made in the
zero-temperature and zero magnetic field limit, where the sufficiently
anisotropic model shows strong absorption. For anisotropy parameters in the
massive phase we derive the exact two-spinon contribution to the spectral line.
From the intensity sum rule it can be estimated that this contribution accounts
for more than 80% of the spectral weight if the anisotropy parameter is
moderately above its value at the isotropic point.Comment: 23 pages, revtex4-1, 11 figure
Outbreak of leptospirosis among triathlon participants in Germany, 2006
<p>Abstract</p> <p>Background</p> <p>In August 2006, a case of leptospirosis occurred in an athlete after a triathlon held around Heidelberg and in the Neckar river. In order to study a possible outbreak and to determine risk factors for infection an epidemiological investigation was performed.</p> <p>Methods</p> <p>Participants of the triathlon were contacted by e-mail and were asked to fill out a standardized questionnaire. In addition, they were asked to supply a serum sample for laboratory diagnosis of leptospirosis. A confirmed case patient was defined as a clinical case (i.e. fever and at least one additional symptom suggestive for leptospirosis) with at least two of the following tests positive: ELISA IgM, latex agglutination testing, or microscopic agglutination testing. Rainfall and temperature records were obtained.</p> <p>Results</p> <p>A total of 142 of 507 triathletes were contacted; among these, five confirmed leptospirosis cases were found. Open wounds were identified as the only significant risk factor for illness (p = 0.02). Heavy rains that preceded the swimming event likely increased leptospiral contamination of the Neckar River.</p> <p>Discussion</p> <p>This is the first outbreak of leptospirosis related to a competitive sports event in Germany. Among people with contact to freshwater, the risk of contracting leptospirosis should be considered by health care providers also in temperate countries, particularly in the summer after heavy rains.</p
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