257 research outputs found
Orbital diamagnetism in multilayer graphenes: Systematic study with the effective mass approximation
We present a theoretical study on the orbital magnetism in multilayer
graphenes within the effective mass approximation. The Hamiltonian and thus
susceptibility can be decomposed into contributions from sub-systems equivalent
to monolayer or bilayer graphene. The monolayer-type subband exists only in odd
layers and exhibits a delta-function susceptibility at . The
bilayer-type subband appearing in every layer number gives a singular structure
in the vicinity of due to the trigonal warping as well as a logarithmic
tail away from . The integral of the susceptibility over energy is
approximately given only by the layer number.Comment: 12 pages, 5 figure
Tight--binding description of the quasiparticle dispersion of graphite and few--layer graphene
A universal set of third--nearest neighbour tight--binding (TB) parameters is
presented for calculation of the quasiparticle (QP) dispersion of stacked
graphene layers () with stacking sequence. The QP
bands are strongly renormalized by electron--electron interactions which
results in a 20% increase of the nearest neighbour in--plane and out--of--plane
TB parameters when compared to band structure from density functional theory.
With the new set of TB parameters we determine the Fermi surface and evaluate
exciton energies, charge carrier plasmon frequencies and the conductivities
which are relevant for recent angle--resolved photoemission, optical, electron
energy loss and transport measurements. A comparision of these quantitities to
experiments yields an excellent agreement. Furthermore we discuss the
transition from few layer graphene to graphite and a semimetal to metal
transition in a TB framework.Comment: Corresponding author: A. Gr\"uneis Tel.: +49 351 4659 519 e--mail:
[email protected]
Magneto-Optical Studies of Exciton Effects in Layer-Type Semiconductors
Both experimental and theoretical works were performed with particular reference to a layer-type semiconductor, GaSe, for a coherent treatment of the exciton-like and the oscillatory Landau-like spectra appearing in a form of their combination in semiconductors in magnetic fields. The interband magneto-absorption and the Faraday rotation were measured in pulsed magnetic fields up to ïœ200 kOe at low temperatures. The theoretical analysis was based mainly on the exact solution for an extremely anisotropic semiconductor in the magnetic field of arbitrary intensity. The exciton effects are discussed in terms of the energy spectrum, the spectral intensity, and the spectral width by the use of the band parameters deduced from the experimental results
A Pulse Compression Ultrasonic Test Instrument and Its Applications
In recent years, so called âdigital ultrasonic test instrumentsâ have been commercially available. These conventional instruments employ electrical impulse excitation of ultrasonic probes. In this configuration, waveforms of ultrasonic pulses into a test object are determined only by the characteristics of probes. This means that variation of probe characteristics causes variation of evaluated results and reproducibility of evaluation is poor. Furthermore, some of the conventional instruments do not provide enough information required for quantitative nondestructive evaluation (QNDE) about a test object, since ultrasonic echo signals are A/D converted after an envelope detector in a receiver and only information of echo height and position is obtained
Application of Gaussian expansion method to nuclear mean-field calculations with deformation
We extensively develop a method of implementing mean-field calculations for
deformed nuclei, using the Gaussian expansion method (GEM). This GEM algorithm
has the following advantages: (i) it can efficiently describe the
energy-dependent asymptotics of the wave functions at large , (ii) it is
applicable to various effective interactions including those with finite
ranges, and (iii) the basis parameters are insensitive to nuclide, thereby many
nuclei in wide mass range can be handled by a single set of bases. Superposing
the spherical GEM bases with feasible truncation for the orbital angular
momentum of the single-particle bases, we obtain deformed single-particle
wave-functions to reasonable precision. We apply the new algorithm to the
Hartree-Fock and the Hartree-Fock-Bogolyubov calculations of Mg nuclei with the
Gogny interaction, by which neck structure of a deformed neutron halo is
suggested for Mg.Comment: 17 pages, 4 eps figure
Inverse Correlation between Serum Levels of Selenoprotein P and Adiponectin in Patients with Type 2 Diabetes
Background: We recently identified selenoprotein P (SeP) as a liver-derived secretory protein that causes insulin resistance in the liver and skeletal muscle; however, it is unknown whether and, if so, how SeP acts on adipose tissue. The present study tested the hypothesis that SeP is related to hypoadiponectinemia in patients with type 2 diabetes. Methodology/Principal Findings: We compared serum levels of SeP with those of adiponectin and other clinical parameters in 36 patients with type 2 diabetes. We also measured levels of blood adiponectin in SeP knockout mice. Circulating SeP levels were positively correlated with fasting plasma glucose (r = 0.35, P = 0.037) and negatively associated with both total and high-molecular adiponectin in patients with type 2 diabetes (r = 20.355, P = 0.034; r = 20.367, P = 0.028). SeP was a predictor of both total and high-molecular adiponectin, independently of age, body weight, and quantitative insulin sensitivity index (b = 20.343, P = 0.022; b = 20.357, P = 0.017). SeP knockout mice exhibited an increase in blood adiponectin levels when fed regular chow or a high sucrose, high fat diet. Conclusions/Significance: These results suggest that overproduction of liver-derived secretory protein SeP is connected with hypoadiponectinemia in patients with type 2 diabetes
New Discrete Basis for Nuclear Structure Studies
A complete discrete set of spherical single-particle wave functions for
studies of weakly-bound many-body systems is proposed. The new basis is
obtained by means of a local-scale point transformation of the spherical
harmonic oscillator wave functions. Unlike the harmonic oscillator states, the
new wave functions decay exponentially at large distances. Using the new basis,
characteristics of weakly-bound orbitals are analyzed and the ground state
properties of some spherical doubly-magic nuclei are studied. The basis of the
transformed harmonic oscillator is a significant improvement over the harmonic
oscillator basis, especially in studies of exotic nuclei where the coupling to
the particle continuum is important.Comment: 13 pages, RevTex, 6 p.s. figures, submitted to Phys. Rev.
Nuclear Skins and Halos in the Mean-Field Theory
Nuclei with large neutron-to-proton ratios have neutron skins, which manifest
themselves in an excess of neutrons at distances greater than the radius of the
proton distribution. In addition, some drip-line nuclei develop very extended
halo structures. The neutron halo is a threshold effect; it appears when the
valence neutrons occupy weakly bound orbits. In this study, nuclear skins and
halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov
and relativistic Hartree-Bogoliubov theories for spherical shapes. It is
demonstrated that skins, halos, and surface thickness can be analyzed in a
model-independent way in terms of nucleonic density form factors. Such an
analysis allows for defining a quantitative measure of the halo size. The
systematic behavior of skins, halos, and surface thickness in even-even nuclei
is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical
Review
Increased T-cell immunity against aquaporin-4 and proteolipid protein in neuromyelitis optica.
In neuromyelitis optica (NMO), B-cell autoimmunity to aquaporin-4 (AQP4) has been shown to be essential. However, the role of T cells remains ambiguous. Here, we first showed an increase in CD69+ activated T cells in PBMCs during NMO relapses. Next, T-cell responses to AQP4 and myelin peptides were studied in 12 NM0 patients, 10 multiple sclerosis (MS) patients and 10 healthy subjects (HS). Four hours after adding 1 of 28 overlapping AQP4 peptides, a mixture of AQP4 peptides (AQP4-M) or one of six distinct myelin peptides to 2-day cultured PBMC, CD69 expression on CD4+ T cells was examined. Data were analyzed by paired t-test, frequency of samples with 3-fold increase of CD69 on CD4+ cells (fSI3) and mean stimulation index (mSI). The T-cell response to AQP4-M was significantly increased in NMO (fSI3 = 10/12, mSI = 5.50), with AQP4 (11-30) and AQP4 (91-110) representing the two major epitopes (AQP4 (11-30), fSI3 = 11/12, mSI = 16.0 and AQP4 (91-110), fSI3 = 11/12, mSI = 13.0). Significant but less extensive responses to these two epitopes were also observed in MS and HS. Significant reactivities against AQP4 (21-40), AQP4 (61-80), AQP4 (101-120), AQP4 (171-190) and AQP4 (211-230) were exclusively found in NMO. In addition, responses to AQP4 (81-100) were higher and more frequently detected in NMO, without reaching statistical significance. Interestingly, among the six myelin peptides studied, proteolipid protein (95-116) induced a significant T-cell response in NMO (fSI3 = 7/12, mSI = 4.60). Our study suggests that cellular as well as humoral responses to AQP4 are necessary for NMO development and that the immune response to myelin protein may contribute to disease pathogenesis
- âŠ