4,143 research outputs found
Temperature-stable Gunn-diode oscillator
Oscillator consisting of Gunn diode embedded in coaxial circuit has excellent temperature stability and low fabrication costs as compared with automatic-frequency-control crystal oscillators
Formation of magnetic impurities and pair-breaking effect in a superfluid Fermi gas
We theoretically investigate a possible idea to introduce magnetic impurities
to a superfluid Fermi gas. In the presence of population imbalance
(, where is the number of Fermi atoms with
pseudospin ), we show that nonmagnetic potential
scatterers embedded in the system are magnetized in the sense that some of
excess -spin atoms are localized around them. They destroy the
superfluid order parameter around them, as in the case of magnetic impurity
effect discussed in the superconductivity literature. This pair-breaking effect
naturally leads to localized excited states below the superfluid excitation
gap. To confirm our idea in a simply manner, we treat an attractive Fermi
Hubbard model within the mean-field theory at T=0. We self-consistently
determine superfluid properties around a nonmagnetic impurity, such as the
superfluid order parameter, local population imbalance, as well as
single-particle density of states, in the presence of population imbalance.
Since the competition between superconductivity and magnetism is one of the
most fundamental problems in condensed matter physics, our results would be
useful for the study of this important issue in cold Fermi gases.Comment: 27 pages, 14 figure
The small mixing angle and the lepton asymmetry
We present the correlation of low energy CP phases, both Dirac and Majorana,
and the lepton asymmetry for the baryon asymmetry in the universe, with a
certain class of Yukawa matrices that consist of two right-handed neutrinos and
include one texture zero in themselves. For cases in which the amount of the
lepton asymmetry turns out to be proportional to , we
consider the relation between two types of CP phases and the relation of
versus the Jarlskog invariant or the amplitude of neutrinoless double beta
decay as varies.Comment: 17 pages, 14 figures, information for figures added, version
published in PR
Sound propagation in density wave conductors and the effect of long-range Coulomb interaction
We study theoretically the sound propagation in charge- and spin-density
waves in the hydrodynamic regime. First, making use of the method of comoving
frame, we construct the stress tensor appropriate for quasi-one dimensional
systems within tight-binding approximation. Taking into account the screening
effect of the long-range Coulomb interaction, we find that the increase of the
sound velocity below the critical temperature is about two orders of magnitude
less for longitudinal sound than for transverse one. It is shown that only the
transverse sound wave with displacement vector parallel to the chain direction
couples to the phason of the density wave, therefore we expect significant
electromechanical effect only in this case.Comment: revtex, 14 pages (in preprint form), submitted to PR
Cystatins as calpain inhibitors: Engineered chicken cystatin- and stefin B-kininogen domain 2 hybrids support a cystatin-like mode of interaction with the catalytic subunit of μ-calpain
Within the cystatin superfamily, only kininogen domain 2 (KD2) is able to inhibit μ- and m-calpain. In an attempt to elucidate the structural requirements of cystatins for calpain inhibition, we constructed recombinant hybrids of human stefin B (an intracellular family 1 cystatin) with KD2 and Delta L110 deletion mutants of chicken cystatin-KD2 hybrids. Substitution of the N-terminal contact region of stefin B by the corresponding KD2 sequence resulted in a calpain inhibitor of K-i = 188 nM. Deletion of L110, which forms a beta -bulge in family 1 and 2 cystatins but is lacking in KD2, improved inhibition of mu -calpain 4- to 8-fold. All engineered cystatins were temporary inhibitors of calpain due to slow substrate-like cleavage of a single peptide bond corresponding to Gly9-Ala10 in chicken cystatin. Biomolecular interaction analysis revealed that, unlike calpastatin, the cystatin-type inhibitors do not bind to the calmodulin-like domain of the small subunit of calpain, and their interaction with the mu -calpain heterodimer is completely prevented by a synthetic peptide comprising subdomain B of calpastatin domain 1. Based on these results we propose that (i) cystatin-type calpain inhibitors interact with the active site of the catalytic domain of calpain in a similar cystatin-like mode as with papain and (ii) the potential for calpain inhibition is due to specific subsites within the papain-binding regions of the general cystatin fold
Recent Advances in Unconventional Density Waves
Unconventional density wave (UDW) has been speculated as a possible
electronic ground state in excitonic insulator in 1968. Recent surge of
interest in UDW is partly due to the proposal that the pseudogap phase in high
T_c cuprate superconductors is d-wave density wave (d-DW).
Here we review our recent works on UDW within the framework of mean field
theory. In particular we have shown that many properties of the low temperature
phase (LTP) in alpha-(BEDT-TTF)_2MHg(SCN)_4 with M=K, Rb and Tl are well
characterized in terms of unconventional charge density wave (UCDW). In this
identification the Landau quantization of the quasiparticle motion in a
magnetic field (the Nersesyan effect) plays the crucial role. Indeed the
angular dependent magnetoresistance and the negative giant Nernst effect are
two hallmarks of UDW.Comment: 18 pages, 12 figure
Combined Electroweak Analysis
Recent developments in the measurement of precision electroweak measurements
are summarised, notably new results on the mass of the top quark and mass and
width of the W boson. Predictions of the Standard Model are compared to the
experimental results which are used to constrain the input parameters of the
Standard Model, in particular the mass of the Higgs boson. The agreement
between measurements and expectations from theory is discussed.
Invited talk presented at the EPS HEP 2007 conference
Manchester, England, July 19th to 25th, 2007Comment: 7 pages and 6 figure
Neutrino Mixing and Leptonic CP Phase in Neutrino Oscillations
Oscillations of the Dirac neutrinos of three generations in vacuum are
considered with allowance made for the effect of the CP-violating leptonic
phase (analogue of the quark CP phase) in the lepton mixing matrix. The general
formulas for the probabilities of neutrino transition from one sort to another
in oscillations are obtained as functions of three mixing angles and the CP
phase. It is found that the leptonic CP phase can, in principle, be
reconstructed by measuring the oscillation-averaged probabilities of neutrino
transition from one sort to another. The manifestation of the CP phase as a
deviation of the probabilities of direct processes from those of inverse
processes is an effect that is practically unobservable as yet
Glucose metabolism and oscillatory behavior of pancreatic islets
A variety of oscillations are observed in pancreatic islets.We establish a
model, incorporating two oscillatory systems of different time scales: One is
the well-known bursting model in pancreatic beta-cells and the other is the
glucose-insulin feedback model which considers direct and indirect feedback of
secreted insulin. These two are coupled to interact with each other in the
combined model, and two basic assumptions are made on the basis of biological
observations: The conductance g_{K(ATP)} for the ATP-dependent potassium
current is a decreasing function of the glucose concentration whereas the
insulin secretion rate is given by a function of the intracellular calcium
concentration. Obtained via extensive numerical simulations are complex
oscillations including clusters of bursts, slow and fast calcium oscillations,
and so on. We also consider how the intracellular glucose concentration depends
upon the extracellular glucose concentration, and examine the inhibitory
effects of insulin.Comment: 11 pages, 16 figure
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