1,716 research outputs found
Non-linear vorticity-density coupling in Lagrangian dynamics
We present a general Lagrangian formalism that allows the treatment of
vorticity. We give solutions for the rotational perturbations up to the
third-order in a flat background universe. We show how the primordial vorticity
affects the evolution of the density fluctuation in high-density regions.Comment: 15 pages; submitted to Progress of Theoretical Physic
Weak Decay of in Nuclei: Direct Quark Mechanism vs Meson Exchange
Nonmesonic decays of in nuclear medium and light hypernuclei are
studied by using the weak transition potential derived from
the meson exchange mechanism and the direct quark mechanism. The long range
part of the transition potential is described by exchanges of the pseudoscalar
mesons (, , ), while the vector mesons (, ,
) may be considered as the medium- and short-range part in the meson
exchange picture. We propose the direct quark transition potential as the short
range part, which is derived from the matrix elements of the
effective weak Hamiltonian in the two baryon states. The results indicate that
the direct quark contribution is significantly large and its behavior is
qualitatively different from the vector meson exchanges. We also find that the
decay rate is sensitive to the choice of form factor and that a soft cutoff
must be used for the pion-baryon verteces so that the strong tensor transition
is suppressed. We find that the results are compatible with
experiment although the ratio is still too large. The decays of
light hypernuclei are related to the \DI=3/2 amplitudes of the nonmesonic
decay. The role of chiral symmetry for the pionic decays are discussed.Comment: 10 pages, Talk presented by Makoto Oka at the APCTP Workshop on
Strangeness Nuclear Physics (SNP'99), February, 199
Experimental Determination of the Gain Distribution of an Avalanche Photodiode at Low Gains
A measurement system for determining the gain distributions of avalanche
photodiodes (APDs) in a low gain range is presented. The system is based on an
ultralow-noise charge--sensitive amplifier and detects the output carriers from
an APD. The noise of the charge--sensitive amplifier is as low as 4.2 electrons
at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with
low average gains are presented, demonstrating the McIntyre theory in the low
gain range.Comment: 3 pages, 4 figure
Oxidative Stress and Ischemia-Reperfusion Injury in Gastrointestinal Tract and Antioxidant, Protective Agents
Exacerbation of hypoxic injury after reoxygenation is a crucial mechanism mediating organ injury in transplantation, and in myocardial, hepatic, gastrointestinal, cerebral, renal, and other ischemic syndromes. The occlusion and reperfusion of the splanchnic artery is a useful animal model to elucidate the mechanism of gastrointestinal injury induced by ischemia-reperfusion (I/R). Although xanthine oxidase is a major source of reactive oxygen species (ROS), which plays an important role in the I/R-induced intestinal injury, there are many other sources of intracellular ROS. Various treatment modalities have been successfully applied to attenuate the I/R injury in animal models. This review focuses on the role of oxidant stress in the mechanism of I/R injury and the use of antioxidant agents for its treatment
Studies toward the Synthesis of Biologically Important, Natural and Artificial Small Molecules
Shown in this article are our current research topics based on the organic syntheses of biologically important molecules. The synthetic studies on marine natural products, dysiherbaines, azaspiracids, and goniodomin are described. Another research aiming to discover biologically functional small molecules from artificial synthetic libraries is also described
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