7,727 research outputs found
Correlations in hot and dense quark matter
We present a relativistic three-body equation to investigate three-quark
clusters in hot and dense quark matter. To derive such an equation we use the
Dyson equation approach. The equation systematically includes the Pauli
blocking factors as well as the self energy corrections of quarks. Special
relativity is realized through the light front form. Presently we use a
zero-range force and investigate the Mott transition.Comment: 6 pages, 4 figure, Few-Body Systems style file
Hemodynamic and inotropic effects of endothelin-1 in vivo
Endothelin-1 (ET-1) is known to have strong vasoactive properties. Contradictory results have been reported with regard to its inotropic effects. This study examined the dose-dependent (500, 1000, 2500, 5000 and 10,000 ng ET-1/kg vs. NaCl controls) hemodynamic and inotropic effects of ET-1 in 53 open-chest rats during and after a 7-min infusion. Besides measurements in the intact circulation the myocardial function was examined by isovolumic registrations independent of peripheral vascular effects. A transient ET-1 induced (500, 1000, 2500, 5000 ng ET-1/kg) decrease of the left ventricular systolic pressure (LVSP) and the mean aortic pressure (AoPmean) was followed by a dose-related rise of these pressures (LVSP: -1%, -1%, +8%, +16% vs. preinfusion values; AoPmean: -11%, +9%, +39%, +52%). Heart rate (HR) was not influenced by ET-1. Due to the dose-dependent decrease of the stroke volume (SV) the cardiac output (CO) was reduced (CO: -8%, -23%, -40%, -50%). After an initial vasodilatation ET-1 elevates the total peripheral resistance (TPR: -1%, +49%, +139%, +215%) dose-dependently. 10,000 ng ET-1/kg was a lethal dose resulting in cardiac failure within minutes (low output). Since the maximum of the isovolumic LVSP (peak LVSP) and the corresponding dP/dtmax (peak dP/dtmax) were unchanged under ET-1, the isovolumic measurements do not indicate a positive inotropic effect of ET-1 in vivo in contrast to published results of in vitro experiments. It may be possible that a direct positive inotropic effect of ET-1 observed in in vitro studies is counterbalanced in vivo by an indirect negative inotropic effect due to the coronary-constrictive effect of ET-1
Dynamics of few-body states in a medium
Strongly interacting matter such as nuclear or quark matter leads to few-body
bound states and correlations of the constituents. As a consequence quantum
chromodynamics has a rich phase structure with spontaneous symmetry breaking,
superconductivity, condensates of different kinds. All this appears in many
astrophysical scenarios. Among them is the formation of hadrns during the early
stage of the Universe, the structure of a neutron star, the formation of nuclei
during a supernova explosion. Some of these extreme conditions can be simulated
in heavy ion colliders. To treat such a hot and dense system we use the Green
function formalism of many-body theory. It turns out that a systematic Dyson
expansion of the Green functions leads to modified few-body equations that are
capable to describe phase transitions, condensates, cluster formation and more.
These equations include self energy corrections and Pauli blocking. We apply
this method to nonrelativistic and relativistic matter. The latter one is
treated on the light front. Because of the medium and the inevitable truncation
of space, the few-body dynamics and states depend on the thermodynamic
parameters of the medium.Comment: 3 pages, 2 figures, talk presented at the 19th European Conference on
Few-Body System
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
Fractional Calculus via Functional Calculus: Theory and Applications
This paper demonstrates the power of the functional-calculus definition of linear fractional (pseudo-)differential operators via generalised Fourier transforms. Firstly, we describe in detail how to get global causal solutions of linear fractional differential equations via this calculus. The solutions are represented as convolutions of the input functions with the related impulse responses. The suggested method via residue calculus separates an impulse response automatically into an exponentially damped (possibly oscillatory) part and a ''slow' relaxation. If an impulse response is stable it becomes automatically causal, otherwise one has to add a homogeneous solution to get causality. Secondly, we present examples and, moreover, verify the approach along experiments on viscolelastic rods. The quality of the method as an effective few-parameter model is impressively demonstrated: the chosen reference example PTFE (Teflon) shows that in contrast to standard classical models our model describes the behaviour in a wide frequency range within the accuracy of the measurement. Even dispersion effects are included. Thirdly, we conclude the paper with a survey of the required theory. There the attention is directed to the extension from the L-2-approach on the space of distributions cal D-
Violations of Lorentz Covariance in Light Front Quark Models
Electromagnetic form factors of the nucleon from relativistic quark models
are analyzed: results from null-plane projection of the Feynman triangle
diagram are compared with a Bakamjian-Thomas model. The magnetic form factors
of the models differ by about 15% at spacelike momentum transfer 0.5 GeV^2,
while the charge form factors are much closer. Spurious contributions to
electromagnetic form factors due to violations of rotational symmetry are
eliminated from both models. One method changes magnetic form factors by about
10%, whereas the charge form factors stay nearly the same. Another one changes
the charge form factor of the Bakamjian-Thomas model by more than 50%.Comment: 19 pages, 9 figures, Late
Macroscopic evidence for quantum criticality and field-induced quantum fluctuations in cuprate superconductors
We present macroscopic experimental evidence for field-induced microscopic
quantum fluctuations in different hole- and electron-type cuprate
superconductors with varying doping levels and numbers of CuO layers per
unit cell. The significant suppression of the zero-temperature in-plane
magnetic irreversibility field relative to the paramagnetic field in all
cuprate superconductors suggests strong quantum fluctuations due to the
proximity of the cuprates to quantum criticality.Comment: 3 figures. To appear in Phys. Rev. B, Rapid Communications (2007).
For correspondence, contact: Nai-Chang Yeh (e-mail: [email protected]
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