1,113 research outputs found
Soft-mode turbulence in electrohydrodynamic convection of a homeotropically aligned nematic layer
The experimental study of electroconvection in a homeotropically aligned nematic ~MBBA! is reported. Thesystem undergoes a supercritical bifurcation ‘‘rest state-spatiotemporal chaos.’’ The chaos is caused by longwavelengthmodulation of the orientation of convective rolls. For the first time the observations both below andbeyond the Lifshitz point are accompanied by quantitative analysis of temporal autocorrelation functions ofturbulent modes. The dependence of the correlation time on the control parameter is obtained. A secondarybifurcation from normal to abnormal rolls is discussed
Effective matrix model for deconfinement in pure gauge theories
We construct matrix models for the deconfining phase transition in SU(N)
gauge theories, without dynamical quarks, at a nonzero temperature T. We
generalize models with zero and one free parameter to study a model with two
free parameters: besides perturbative terms ~T^4, we introduce terms ~T^2 and
~T^0. The two N-dependent parameters are determined by fitting to data from
numerical simulations on the lattice for the pressure, including the latent
heat. Good agreement is found for the pressure in the semi-quark gluon plasma
(QGP), which is the region from Tc, the critical temperature, to about ~4 Tc.
Above ~1.2 Tc, the pressure is a sum of a perturbative term, ~ +T^4, and a
simple non-perturbative term, essentially just a constant times ~ -Tc^2 T^2.
For the pressure, the details of the matrix model only enter within a very
narrow window, from Tc to ~1.2 Tc, whose width does not change significantly
with N. Without further adjustment, the model also agrees well with lattice
data for the 't Hooft loop. This is notable, because in contrast to the
pressure, the 't Hooft loop is sensitive to the details of the matrix model
over the entire semi-QGP. For the (renormalized) Polyakov loop, though, our
results disagree sharply with those from the lattice. Matrix models provide a
natural and generic explanation for why the deconfining phase transition in
SU(N) gauge theories is of first order not just for three, but also for four or
more colors. Lastly, we consider gauge theories where there is no strict order
parameter for deconfinement, such as for a G(2) gauge group. To agree with
lattice measurements, in the G(2) matrix model it is essential to add terms
which generate complete eigenvalue repulsion in the confining phase.Comment: 80 pages, 26 figure
Two-dimensional quantum interference contributions to the magnetoresistance of Nd{2-x}Ce{x}CuO{4-d} single crystals
The 2D weak localization effects at low temperatures T = (0.2-4.2)K have been
investigated in nonsuperconducting sample Nd{1.88}Ce{0.12}CuO{4-d} and in the
normal state of the superconducting sample Nd{1.82}Ce{0.18}CuO{4-d} for B>B_c2.
The phase coherence time and the effective thickness of a conducting CuO_2
layer have been estimated by the fitting of 2D weak localization theory
expressions to the magnetoresistivity data for the normal to plane and the
in-plane magnetic fields.Comment: 5 pages, 4 postscript figure
Spectral Function of Fermion Coupled with Massive Vector Boson at Finite Temperature in Gauge Invariant Formalism
We investigate spectral properties of a fermion coupled with a massive gauge
boson with a mass m at finite temperature (T) in the perturbation theory. The
massive gauge boson is introduced as a U(1) gauge boson in the Stueckelberg
formalism with a gauge parameter \alpha. We find that the fermion spectral
function has a three-peak structure for T \sim m irrespective of the choice of
the gauge parameter, while it tends to have one faint peak at the origin and
two peaks corresponding to the normal fermion and anti-plasmino excitations
familiar in QED in the hard thermal loop approximation for T \gg m. We show
that our formalism successfully describe the fermion spectral function in the
whole T region with the correct high-T limit except for the faint peak at the
origin, although some care is needed for choice of the gauge parameter for T
\gg m. We clarify that for T \sim m, the fermion pole is almost independent of
the gauge parameter in the one-loop order, while for T \gg m, the one-loop
analysis is valid only for \alpha \ll 1/g where g is the fermion-boson coupling
constant, implying that the one-loop analysis can not be valid for large gauge
parameters as in the unitary gauge.Comment: 28pages, 11figures. v2: typos fixe
Fatigue crack analysis of ferrite material by acoustic emission technique
Among various methods of Non-destructive techniques (NDT), analysis using released acoustic emission (AE) waves due to crack propagation is very effective due to its dynamic monitoring features. In fragmentation theory for AE there are some proportional relationships among the AE parameters i.e. AE event, AE energy, area and volume of cracks etc., which are calculated from the released AE waves from the dynamic crack inside any material. The necessity of calculating the fractal dimension has been found in such relationships and the value is emphasized for determining the geometry of the irregularity in crack surface and crack volume. In this paper a novel approach for evaluating that value based on image processing by MATLAB is proposed. The images of the cracks during propagation are preserved and utilized to find out the fractal dimension for analyzing the crack propagation characteristics. The AE energy is also estimated from the received AE waves. The positioning of the sensors plays a great impact on this calculation. Finally, the theoretical proportionality relations of AE parameters are interpreted experimentally during crack propagation behavior in ferrite cast iron under fatigue loading
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques
Molecular gas, CO, and star formation in galaxies: emergent empirical relations, feedback, and the evolution of very gas-rich systems
We use time-varying models of the coupled evolution of the HI, H_2 gas phases
and stars in galaxy-sized numerical simulations to: a) test for the emergence
of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a
realistic H_2-regulated star formation recipe which brings forth a neglected
and potentially significant SF-regulating factor, and c) go beyond typical
galactic environments (for which these galactic empirical relations are
deduced) to explore the early evolution of very gas-rich galaxies. In this work
we model low mass galaxies (M_{\rm baryon} \le 10^9 \msun), while
incorporating an independent treatment of CO formation and destruction, the
most important tracer molecule of H2 in galaxies, along with that for the H2
gas itself. We find that both the K-S and the H_2-pressure empirical relations
can robustly emerge in galaxies after a dynamic equilibrium sets in between the
various ISM states, the stellar component and its feedback. (abridged)Comment: 32 pages, 9 figures, accepted for publication in Ap
- …