915 research outputs found
Diffuse transport and spin accumulation in a Rashba two-dimensional electron gas
The Rashba Hamiltonian describes the splitting of the conduction band as a
result of spin-orbit coupling in the presence of an asymmetric confinement
potential and is commonly used to model the electronic structure of confined
narrow-gap semiconductors. Due to the mixing of spin states some care has to be
exercised in the calculation of transport properties. We derive the diffusive
conductance tensor for a disordered two-dimensional electron gas with
spin-orbit interaction and show that the applied bias induces a spin
accumulation, but that the electric current is not spin-polarized.Comment: REVTeX4 format, 5 page
The ventral epithelium of Trichoplax adhaerens deploys in distinct patterns cells that secrete digestive enzymes, mucus or diverse neuropeptides
© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mayorova, T. D., Hammar, K., Winters, C. A., Reese, T. S., & Smith, C. L. The ventral epithelium of Trichoplax adhaerens deploys in distinct patterns cells that secrete digestive enzymes, mucus or diverse neuropeptides. Biology Open, 8, (2019): bio045674, doi:10.1242/bio.045674.The disk-shaped millimeter-sized marine animal, Trichoplax adhaerens, is notable because of its small number of cell types and primitive mode of feeding. It glides on substrates propelled by beating cilia on its lower surface and periodically pauses to feed on underlying microorganisms, which it digests externally. Here, a combination of advanced electron and light microscopic techniques are used to take a closer look at its secretory cell types and their roles in locomotion and feeding. We identify digestive enzymes in lipophils, a cell type implicated in external digestion and distributed uniformly throughout the ventral epithelium except for a narrow zone near its edge. We find three morphologically distinct types of gland cell. The most prevalent contains and secretes mucus, which is shown to be involved in adhesion and gliding. Half of the mucocytes are arrayed in a tight row around the edge of the ventral epithelium while the rest are scattered further inside, in the region containing lipophils. The secretory granules in mucocytes at the edge label with an antibody against a neuropeptide that was reported to arrest ciliary beating during feeding. A second type of gland cell is arrayed in a narrow row just inside the row of mucocytes while a third is located more centrally. Our maps of the positions of the structurally distinct secretory cell types provide a foundation for further characterization of the multiple peptidergic cell types in Trichoplax and the microscopic techniques we introduce provide tools for carrying out these studies.The work was supported by the Intramural Research Program of the National Institute of Neurological Disorders and Stroke and the National Institutes of Health
Critical properties of S=1/2 Heisenberg ladders in magnetic fields
The critical properties of the Heisenberg two-leg ladders are
investigated in a magnetic field. Combining the exact diagonalization method
and the finite-size-scaling analysis based on conformal field theory, we
calculate the critical exponents of spin correlation functions numerically. For
a strong interchain coupling, magnetization dependence of the critical
exponents shows characteristic behavior depending on the sign of the interchain
coupling. We also calculate the critical exponents for the Heisenberg
two-leg ladder with a diagonal interaction, which is thought as a model
Hamiltonian of the organic spin ladder compound
. Numerical results are compared with
experimental results of temperature dependence of the NMR relaxation rate
.Comment: REVTeX, 10 pages, 8 figures, accepted for Phys. Rev.
Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field
The T=0 dynamical properties of the one-dimensional (1D)
Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe
ansatz for cyclic chains of sites. The ground state at magnetization
, which can be interpreted as a state with spinons or as a
state of magnons, is reconfigured here as the vacuum for a different
species of quasiparticles, the {\em psinons} and {\em antipsinons}. We
investigate three kinds of quantum fluctuations, namely the spin fluctuations
parallel and perpendicular to the direction of the applied magnetic field and
the dimer fluctuations. The dynamically dominant excitation spectra are found
to be sets of collective excitations composed of two quasiparticles excited
from the psinon vacuum in different configurations. The Bethe ansatz provides a
framework for (i) the characterization of the new quasiparticles in relation to
the more familiar spinons and magnons, (ii) the calculation of spectral
boundaries and densities of states for each continuum, (iii) the calculation of
transition rates between the ground state and the dynamically dominant
collective excitations, (iv) the prediction of lineshapes for dynamic structure
factors relevant for experiments performed on a variety of quasi-1D
antiferromagnetic compounds, including KCuF,
Cu(CHN, and CuGeO.Comment: 13 pages, 12 figure
Neutron Scattering Study of Magnetic Ordering and Excitations in the Doped Spin Gap System Tl(CuMg)Cl
Neutron elastic and inelastic scattering measurements have been performed in
order to investigate the spin structure and the magnetic excitations in the
impurity-induced antiferromagnetic ordered phase of the doped spin gap system
Tl(CuMg)Cl with . The magnetic Bragg reflections
indicative of the ordering were observed at with integer
and odd below K. It was found that the spin structure
of the impurity-induced antiferromagnetic ordered phase on average in
Tl(CuMg)Cl with is the same as that of the
field-induced magnetic ordered phase for in the parent
compound TlCuCl. The triplet magnetic excitation was clearly observed in
the - plane and the dispersion relations of the triplet excitation
were determined along four different directions. The lowest triplet excitation
corresponding to the spin gap was observed at with integer
and odd , as observed in TlCuCl. It was also found that the spin gap
increases steeply below upon decreasing temperature. This strongly
indicates that the impurity-induced antiferromagnetic ordering coexists with
the spin gap state in Tl(CuMg)Cl with .Comment: 24 pages, 7 figures, 11 eps files, revtex style, will appear in Phys.
Rev.
A low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V2O7
We report the results of measurements of the dc-susceptibility and the
23Na-NMR response of Na2V2O7, a recently synthesized, non metallic low
dimensional spin system. Our results indicate that upon reducing the
temperature to below 100 K, the V^{4+} moments are gradually quenched, leaving
only one moment out of 9 active. The NMR data reveal a phase transition at very
low temperatures. With decreasing applied field H, the critical temperature
shifts towards T = 0 K, suggesting that Na2V2O7 may be regarded as an insulator
reaching a quantum critical point at H = 0.Comment: 4 pages, 5 figure
Turning round the telescope. Centre-right parties and immigration and integration policy in Europe
This is an Author's Original Manuscript of 'Turning round the telescope. Centre-right parties and immigration and integration policy in Europe', whose final and definitive form, the Version of Record, has been published in the Journal of European Public Policy 15(3):315-330, 2008 [copyright Taylor & Francis], available online at: http://www.tandfonline.com/doi.org/10.1080/13501760701847341
Serum Calcium and the Risk of Breast Cancer: Findings from the Swedish AMORIS Study and a Meta-Analysis of Prospective Studies
To investigate the association between serum calcium and risk of breast cancer using a large cohort and a systematic review with meta-analysis. From the Swedish Apolipoprotein Mortality Risk (AMORIS) Study we included 229,674 women who had baseline measurements of serum total calcium and albumin. Multivariable Cox regression was used to assess the association between total and albumin-corrected calcium and breast cancer risk. For the systematic review, an electronic search of MEDLINE and EMBASE databases was performed to identify other prospective cohorts assessing the relationship between serum calcium and breast cancer risk. We pooled the results of our AMORIS cohort with other eligible studies in a meta-analysis using a random effects model. IÂČ test was used to assess heterogeneity. In the AMORIS study, 10,863 women were diagnosed with breast cancer (mean follow-up: 19 years). We found an inverse association between total serum calcium and breast cancer when comparing the fourth quartile to the first quartile (HR: 0.94, 95% CI: 0.88-0.99, p value for trend 0.04) and similar results using albumin-corrected calcium. In the systematic review, we identified another two prospective cohorts evaluating pre-diagnostic serum total calcium and breast cancer. Combining these studies and our findings in AMORIS in a meta-analysis showed a protective effect of serum calcium against breast cancer, with a summary RR of 0.80 (95% CI: 0.66-0.97). No substantial heterogeneity was observed. Our findings in AMORIS and the meta-analysis support an inverse association between serum calcium and breast cancer risk, which warrants mechanistic investigations
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Statistical design and monitoring of the Carotene and Retinol Efficacy Trial (CARET).
CARET is a chemoprevention trial of beta-carotene and vitamin A with lung cancer as the primary outcome. Participants at high risk for lung cancer are drawn from two populations: asbestos-exposed workers and heavy smokers. The intervention is a daily combination of 30 mg beta-carotene and 25,000 IU vitamin A as retinyl palmitate. Nearly 18,000 participants will be followed for a mean 6 years, yielding over 100,000 person-years of follow-up. We project that this sample size will have 80% power to detect a 23% decrease in the incidence of lung cancer cases. The purpose of this paper is to present the values of the key sample size parameters of CARET; our schemes for monitoring CARET for sample size adequacy, incidence of side effects, and efficacy of the study vitamins; an overview of the data collected; and plans for the primary, secondary, and ancillary analyses to be performed at the end of the trial. These approaches to the design, monitoring, and analysis of CARET are applicable for many other prevention trials
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