48,598 research outputs found
Anisotropic Flow and Viscous Hydrodynamics
We report part of our recent work on viscous hydrodynamics with consistent
phase space distribution f(x,\p) for freeze out. We develop the gradient
expansion formalism based on kinetic theory, and with the constraints from the
comparison between hydrodynamics and kinetic theory, viscous corrections to
f(x,\p) can be consistently determined order by order. Then with the obtained
f(x,\p), second order viscous hydrodynamical calculations are carried out for
elliptic flow .Comment: 8 pages, 2 figures. Proceedings for the 28th Winter Workshop on
Nuclear Dynamics, Dorado Del Mar, Puerto Rico, United States Of America, 7 -
14 Apr 201
Pulsed THz radiation due to phonon-polariton effect in [110] ZnTe crystal
Pulsed terahertz (THz) radiation, generated through optical rectification
(OR) by exciting [110] ZnTe crystal with ultrafast optical pulses, typically
consists of only a few cycles of electromagnetic field oscillations with a
duration about a couple of picoseconds. However, it is possible, under
appropriate conditions, to generate a long damped oscillation tail (LDOT)
following the main cycles. The LDOT can last tens of picoseconds and its
Fourier transform shows a higher and narrower frequency peak than that of the
main pulse. We have demonstrated that the generation of the LDOT depends on
both the duration of the optical pulse and its central wavelength. Furthermore,
we have also performed theoretical calculations based upon the OR effect
coupled with the phonon-polariton mode of ZnTe and obtained theoretical THz
waveforms in good agreement with our experimental observation.Comment: 9 pages, 5 figure
Optical supercavitation in soft-matter
We investigate theoretically, numerically and experimentally nonlinear
optical waves in an absorbing out-of-equilibrium colloidal material at the
gelification transition. At sufficiently high optical intensity, absorption is
frustrated and light propagates into the medium. The process is mediated by the
formation of a matter-shock wave due to optically induced thermodiffusion, and
largely resembles the mechanism of hydrodynamical supercavitation, as it is
accompanied by a dynamic phase-transition region between the beam and the
absorbing material.Comment: 4 pages, 5 figures, revised version: corrected typos and reference
Electroweak Theory Without Higgs Bosons
A perturbative SU(2)_L X U(1)_Y electroweak theory containing W, Z, photon,
ghost, lepton and quark fields, but no Higgs or other fields, gives masses to
W, Z and the non-neutrino fermions by means of an unconventional choice for the
unperturbed Lagrangian and a novel method of renormalisation. The
renormalisation extends to all orders. The masses emerge on renormalisation to
one loop. To one loop the neutrinos are massless, the A -> Z transition drops
out of the theory, the d quark is unstable and S-matrix elements are
independent of the gauge parameter xi.Comment: 27 pages, LaTex, no figures; revised for publication; accepted by
Int. J. Mod. Phys. A; includes biographical note on A. F. Nicholso
Galaxy Formation with local photoionisation feedback I. Methods
We present a first study of the effect of local photoionising radiation on
gas cooling in smoothed particle hydrodynamics simulations of galaxy formation.
We explore the combined effect of ionising radiation from young and old stellar
populations. The method computes the effect of multiple radiative sources using
the same tree algorithm used for gravity, so it is computationally efficient
and well resolved. The method foregoes calculating absorption and scattering in
favour of a constant escape fraction for young stars to keep the calculation
efficient enough to simulate the entire evolution of a galaxy in a cosmological
context to the present day. This allows us to quantify the effect of the local
photoionisation feedback through the whole history of a galaxy`s formation. The
simulation of a Milky Way like galaxy using the local photoionisation model
forms ~ 40 % less stars than a simulation that only includes a standard uniform
background UV field. The local photoionisation model decreases star formation
by increasing the cooling time of the gas in the halo and increasing the
equilibrium temperature of dense gas in the disc. Coupling the local radiation
field to gas cooling from the halo provides a preventive feedback mechanism
which keeps the central disc light and produces slowly rising rotation curves
without resorting to extreme feedback mechanisms. These preliminary results
indicate that the effect of local photoionising sources is significant and
should not be ignored in models of galaxy formation.Comment: Accepted for Publication in MNRAS, 13 pages, 13 figure
Entropy in the NUT-Kerr-Newman Black Holes Due to an Arbitrary Spin Field
Membrane method is used to compute the entropy of the NUT-Kerr-Newman black
holes. It is found that even though the Euler characteristic is greater than
two, the Bekenstein-Hawking area law is still satisfied. The formula relating the entropy and the Euler characteristic becomes inapplicable for
non-extreme four dimensional NUT-Kerr-Newman black holes
Antiferromagnetism and phase separation in electronic models for doped transition-metal oxides
We investigate the ground state properties of electronic models for doped
manganites and nickelates. An effective t - J like Hamiltonian is derived from
the case of strong Hund coupling between the conduction electrons and localized
spins by means of the projection technique. An attractive interaction for
conduction electrons and an anti-ferromagnetic coupling of the localized spin
are obtained. A large ratio of the attraction to effective electron hopping,
which is modulated by the spin background, will lead to the phase separation.
The anti-ferromagnetic phase and the phase separation appear in the case of
either high or low density of electrons. The possible relevance of the phase
separation to the charge stripe phase in the manganites and nickelates is
discussed.Comment: 12 pages, ReVTEX, 3 figures. To appear in Phys. Rev. B (RC), (01Oct.,
1998
Numerical simulation of Quasi-Normal Modes in time-dependent background
We study the massless scalar wave propagation in the time-dependent
Schwarzschild black hole background. We find that the Kruskal coordinate is an
appropriate framework to investigate the time-dependent spacetime. A
time-dependent scattering potential is derived by considering dynamical black
hole with parameters changing with time. It is shown that in the quasinormal
ringing both the decay time-scale and oscillation are modified in the
time-dependent background.Comment: 10 pages, 8 figures; reference adde
Helical Flow in Healthy and Diseased Patient-specific Coronary Bifurcations
Helical flow (HF) exists in healthy and diseased coronary bifurcations and was found to have a protective atherosclerotic vascular effect in other vessels. However, the role of HF in patient-specific human coronary arteries still needs further study, and is therefore the objective of this study in both healthy and diseased bifurcations. Computational studies were conducted on 16 patient-specific coronary bifurcations, including eight healthy and eight identical cases with idealized narrowing to represent disease. In general, higher HF intensity may have a favorable effect as it corelated to the reduction of the percentage vessel area exposed to adverse time averaged wall shear stress (TAWSS%) in both healthy and diseased models. The HF intensity and distribution of each model varies due to the complex shape of patient-specific models. The presence of disease appears to have an important impact on the downstream HF patterns and the TAWSS distributions. Clinical Relevance - By understanding the relationship between HF and hemodynamics, HF may be used as a predictor for the formation and progression of atherosclerotic plaque in coronary arteries instead of near-wall WSS measures, which can be determined with higher accuracy in vivo
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