223 research outputs found
Near-optimal mean value estimates for multidimensional Weyl sums
We obtain sharp estimates for multidimensional generalisations of
Vinogradov's mean value theorem for arbitrary translation-dilation invariant
systems, achieving constraints on the number of variables approaching those
conjectured to be the best possible. Several applications of our bounds are
discussed
KamLAND-experiment and Soliton-like Nuclear Georeactor. Part 1. Comparison of Theory with Experiment
We give an alternative description of the data produced in the KamLAND
experiment, assuming the existence of a natural nuclear reactor on the boundary
of the liquid and solid phases of the Earth's core. Analyzing the uncertainty
of antineutrino spectrum of georeactor origin, we show that the theoretical
(which takes into account the soliton-like nuclear georeactor) total reactor
antineutrino spectra describe with good accuracy the experimental KamLAND-data
over the years of 2002-2007 and 2002-2009, respectively. At the same time the
parameters of mixing ({\Delta}(m21)^2=2.5\cdot 10^-5 eV^2,
tan^2{\theta}12=0.437) calculated within the framework of georeactor hypothesis
substantially differ from the parameters of mixing ({\Delta}(m21)^2=7.49\cdot
10^-5 eV^2, tan^2{\theta}12=0.436) obtained in KamLAND-experiment for total
exposure over the period of 2002-2009. By traingulation of KamLAND and Borexino
data we have constructed the coordinate location of soliton-like nuclear
georeactors on the boundary of the liquid and solid phases of the Earth core.
Based on the necessary condition of full synchronization of geological
(magnetic) time scale and time evolution of heat power of nuclear georeactor,
which plays the role of energy source of the Earth magnetic field, and also the
strong negative correlation between magnetic field of the solar tachocline zone
and magnetic field of the Earth liquid core (Y-component) we have obtain the
estimation of nuclear georeactor average heat power ~30 TW over the years
2002-2009.Comment: 50 pages; 17 figures; 1 table. A substantially revised, corrected and
enhanced editio
Theory of magnetization precession induced by a picosecond strain pulse in ferromagnetic semiconductor (Ga,Mn)As
A theoretical model of the coherent precession of magnetization excited by a
picosecond acoustic pulse in a ferromagnetic semiconductor layer of (Ga,Mn)As
is developed. The short strain pulse injected into the ferromagnetic layer
modifies the magnetocrystalline anisotropy resulting in a tilt of the
equilibrium orientation of magnetization and subsequent magnetization
precession. We derive a quantitative model of this effect using the
Landau-Lifshitz equation for the magnetization that is precessing in the
time-dependent effective magnetic field. After developing the general
formalism, we then provide a numerical analysis for a certain structure and two
typical experimental geometries in which an external magnetic field is applied
either along the hard or the easy magnetization axis. As a result we identify
three main factors, which determine the precession amplitude: the
magnetocrystalline anisotropy of the ferromagnetic layer, its thickness, and
the strain pulse parameters
Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR
Substantial experimental and theoretical efforts worldwide are devoted to
explore the phase diagram of strongly interacting matter. At LHC and top RHIC
energies, QCD matter is studied at very high temperatures and nearly vanishing
net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was
created at experiments at RHIC and LHC. The transition from the QGP back to the
hadron gas is found to be a smooth cross over. For larger net-baryon densities
and lower temperatures, it is expected that the QCD phase diagram exhibits a
rich structure, such as a first-order phase transition between hadronic and
partonic matter which terminates in a critical point, or exotic phases like
quarkyonic matter. The discovery of these landmarks would be a breakthrough in
our understanding of the strong interaction and is therefore in the focus of
various high-energy heavy-ion research programs. The Compressed Baryonic Matter
(CBM) experiment at FAIR will play a unique role in the exploration of the QCD
phase diagram in the region of high net-baryon densities, because it is
designed to run at unprecedented interaction rates. High-rate operation is the
key prerequisite for high-precision measurements of multi-differential
observables and of rare diagnostic probes which are sensitive to the dense
phase of the nuclear fireball. The goal of the CBM experiment at SIS100
(sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD
matter: the phase structure at large baryon-chemical potentials (mu_B > 500
MeV), effects of chiral symmetry, and the equation-of-state at high density as
it is expected to occur in the core of neutron stars. In this article, we
review the motivation for and the physics programme of CBM, including
activities before the start of data taking in 2022, in the context of the
worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal
Functional Relationship between Protein Disulfide Isomerase Family Members during the Oxidative Folding of Human Secretory Proteins
We systematically depleted PDI family members and show that whereas ERp72 and P5 contributed minimally to oxidative protein folding, PDI and ERp57 were the predominant catalysts. Depletion of PDI or ERp57 alone modestly delayed folding, but depletion of both led to generalized protein misfolding and degradation
Increased cholinergic contractions of jejunal smooth muscle caused by a high cholesterol diet are prevented by the 5-HT(4 )agonist – tegaserod
BACKGROUND: Excess cholesterol in bile and in blood is a major risk factor for the respective development of gallbladder disease and atherosclerosis. This lipid in excess negatively impacts the functioning of other smooth muscles, including the intestine. Serotonin is an important mediator of the contractile responses of the small intestine. Drugs targeting the serotonin receptor are used as prokinetic agents to manage intestinal motor disorders, in particular irritable bowel syndrome. Thus, tegaserod, acting on 5-HT(4 )receptor, ideally should obviate detrimental effects of excessive cholesterol on gastrointestinal smooth muscle. In this study we examined the effect of tegaserod on cholesterol-induced changes in the contractile responses of intestinal smooth muscle. METHODS: The effects of a high cholesterol (1%) diet on the in vitro contractile responses of jejunal longitudinal smooth muscle from Richardson ground squirrels to the cholinergic agonist carbachol were examined in the presence or absence of tetrodrodotoxin (TTX). Two groups of animals, fed either low (0.03%) or high cholesterol rat chow diet, were further divided into two subgroups and treated for 28 days with either vehicle or tegaserod. RESULTS: The high cholesterol diet increased, by nearly 2-fold, contractions of the jejunal longitudinal smooth muscle elicited by carbachol. These cholinergic contractions were mediated by muscarinic receptors since they were blocked by scopolamine, a muscarinic receptor antagonist, but not by the nicotinic receptor antagonist, hexamethonium. Tegaserod treatment, which did not affect cholinergic contractions of tissues from low cholesterol fed animals, abrogated the increase caused by the high cholesterol diet. With low cholesterol diet TTX enhanced carbachol-evoked contractions, whereas this action potential blocker did not affect the augmented cholinergic contractions seen with tissues from animals on the high cholesterol diet. Tegaserod-treatment removed the effects of a high cholesterol diet on neuronal muscarinic receptors, as the potentiating effect of TTX on carbachol-elicited contractions was maintained in these animals. CONCLUSION: A high cholesterol diet causes significant changes to cholinergic neurotransmission in the enteric nerves of the jejunum. The mechanisms by which these effects of cholesterol are reversed by tegaserod are unknown, but relate to removal of an inhibitory effect of cholesterol on enteric nerves
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