1,509 research outputs found
Concepts of flywheels for energy storage using autostable high-T(sub c) superconducting magnetic bearings
A flywheel for energy storage using autostable high-T(sub c) superconducting magnetic bearings has been built. The rotating disk has a total weight of 2.8 kg. The maximum speed is 9240 rpm. A process that allows accelerated, reliable and reproducible production of melt-textured superconducting material used for the bearings has been developed. In order to define optimum configurations for radial and axial bearings, interaction forces in three dimensions and vertical and horizontal stiffness have been measured between superconductors and permanent magnets in different geometries and various shapes. Static as well as dynamic measurements have been performed. Results are being reported and compared to theoretical models
Phonon Assisted Multimagnon Optical Absorption and Long Lived Two-Magnon States in Undoped Lamellar Copper Oxides
We calculate the effective charge for multimagnon infrared (IR) absorption
assisted by phonons in the parent insulating compounds of cuprate
superconductors and the spectra for two-magnon absorption using interacting
spin-wave theory. Recent measured bands in the mid IR [Perkins et al. Phys.
Rev. Lett. {\bf 71} 1621 (1993)] are interpreted as involving one phonon plus a
two-magnon virtual bound state, and one phonon plus higher multimagnon
absorption processes. The virtual bound state consists of a narrow resonance
occurring when the magnon pair has total momentum close to .Comment: 4 page
Polarons and bipolarons in strongly interacting electron-phonon systems
The Holstein Hubbard and Holstein t--J models are studied for a wide range of
phonon frequencies, electron--electron and electron--phonon interaction
strengths on finite lattices with up to ten sites by means of direct Lanczos
diagonalization. Previously the necessary truncation of the phononic Hilbert
space caused serious limitations to either very small systems (four or even two
sites) or to weak electron--phonon coupling, in particular in the adiabatic
regime. Using parallel computers we were able to investigate the transition
from `large' to `small' polarons in detail. By resolving the low--lying
eigenstates of the Hamiltonian and by calculating the spectral function we can
identify a polaron band in the strong--coupling case, whose dispersion deviates
from the free--particle dispersion at low and intermediate phonon frequencies.
For two electrons (holes) we establish the existence of bipolaronic states and
discuss the formation of a bipolaron band. For the 2D Holstein t--J model we
demonstrate that the formation of hole--polarons is favoured by strong Coulomb
correlations. Analyzing the hole--hole correlation functions we find that hole
binding is enhanced as a dynamical effect of the electron--phonon interaction.Comment: 23 pages (Revtex) with 13 figures (ps, uuencoded
Neural Mechanism of a Sex-Specific Risk Variant for Posttraumatic Stress Disorder in the Type I Receptor of the Pituitary Adenylate Cyclase Activating Polypeptide
AbstractBackgroundPosttraumatic stress disorder (PTSD) is a frequent anxiety disorder with higher prevalence rates in female patients than in male patients (2.5:1). Association with a single nucleotide polymorphism (rs2267735) in the gene ADCYAP1R1 encoding the type I receptor (PAC1-R) of the pituitary adenylate cyclase activating polypeptide has been reported with PTSD in female patients. We sought to identify the neural correlates of the described PAC1-R effects on associative learning.MethodsIn a reverse genetic approach, we examined two independent healthy samples (N1 = 112, N2 = 73) using functional magnetic resonance imaging during cued and contextual fear conditioning. Skin conductance responses and verbal self-reports of arousal, valence, and contingency were recorded.ResultsWe found that PAC1-R modulates the blood oxygenation level–dependent response of the hippocampus. Specifically, we observed decreased hippocampal activity during contextual, but not during cued, fear conditioning in female participants carrying the PAC1-R risk allele. We observed no significant differences in conditionability for skin conductance responses, verbal reports, or activation in other brain regions between the genotype groups in female participants.ConclusionsOur results suggest that impaired contextual conditioning in the hippocampal formation may mediate the association between PAC1-R and PTSD symptoms. Our findings potentially identify a missing link between the involvement of PAC1-R in PTSD and the well-established structural and functional hippocampal deficits in these patients
Solution of the Multi-Channel Anderson Impurity Model: Ground state and thermodynamics
We present the solution of the SU(N) x SU(M) Anderson impurity model using
the Bethe-Ansatz. We first explain what extensions to the formalism were
required for the solution. Subsequently we determine the ground state and
derive the thermodynamics over the full range of temperature and fields. We
identify the different regimes of valence fluctuation at high temperatures,
followed by moment formation or intrinsic mixed valence at intermediate
temperatures and a low temperature non-Fermi liquid phase. Among other things
we obtain the impurity entropy, charge valence and specific heat over the full
range of temperature. We show that the low-energy physics is governed by a line
of fixed points. This describes non-Fermi-liquid behavior in the integral
valence regime, associated with moment formation, as well as in the mixed
valence regime where no moment forms.Comment: 28 pages, 8 figures, 1 tabl
Quasiparticle Effective Mass for the Two- and Three-Dimensional Electron Gas
We calculate the quasiparticle effective mass for the electron gas in two and
three dimensions in the metallic region. We employ the single particle
scattering potential coming from the Sj\"{o}lander-Stott theory and enforce the
Friedel sum rule by adjusting the effective electron mass in a scattering
calculation. In 3D our effective mass is a monotonically decreasing function of
throughout the whole metallic domain, as implied by the most recent
numerical results. In 2D we obtain reasonable agreement with the experimental
data, as well as with other calculations based on the Fermi liquid theory. We
also present results of a variety of different treatments for the effective
mass in 2D and 3D.Comment: 12 pages, 2 figure
The Influence of Social Evaluation on Heart Rate Variability and Motor Performance: A Study of “Real-Life” Competition
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Treatment of Infantile Inflammatory Bowel Disease and Autoimmunity by Allogeneic Stem Cell Transplantation in LPS-Responsive Beige-Like Anchor Deficiency
Inflammatory bowel disease (IBD) in young children can be a clinical manifestation of various primary immunodeficiency syndromes. Poor clinical outcome is associated with poor quality of life and high morbidity from the complications of prolonged immunosuppressive treatment and malabsorption. In 2012, mutations in the lipopolysaccharide-responsive beige-like anchor (LRBA) gene were identified as the cause of an autoimmunity and immunodeficiency syndrome. Since then, several LRBA-deficient patients have been reported with a broad spectrum of clinical manifestations without reliable predictive prognostic markers. Allogeneic hematopoietic stem cell transplantation (alloHSCT) has been performed in a few severely affected patients with complete or partial response. Herein, we present a detailed course of the disease and the transplantation procedure used in a LRBA-deficient patient suffering primarily from infantile IBD with immune enteropathy since the age of 6 weeks, and progressive autoimmunity with major complications following long-term immunosuppressive treatment. At 12 years of age, alloHSCT using bone marrow of a fully matched sibling donor-a healthy heterozygous LRBA mutant carrier-was performed after conditioning with a reduced-intensity regimen. During the 6-year follow-up, we observed a complete remission of enteropathy, autoimmunity, and skin vitiligo, with complete donor chimerism. The genetic diagnosis of LRBA deficiency was made post-alloHSCT by detection of two compound heterozygous mutations, using targeted sequencing of DNA samples extracted from peripheral blood before the transplantation
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