2,497 research outputs found
Two liquid states of matter: A new dynamic line on a phase diagram
It is generally agreed that the supercritical region of a liquid consists of
one single state (supercritical fluid). On the other hand, we show here that
liquids in this region exist in two qualitatively different states: "rigid" and
"non-rigid" liquid. Rigid to non-rigid transition corresponds to the condition
{\tau} ~ {\tau}0, where {\tau}is liquid relaxation time and {\tau}0 is the
minimal period of transverse quasi-harmonic waves. This condition defines a new
dynamic line on the phase diagram, and corresponds to the loss of shear
stiffness of a liquid at all available frequencies, and consequently to the
qualitative change of many important liquid properties. We analyze the dynamic
line theoretically as well as in real and model liquids, and show that the
transition corresponds to the disappearance of high-frequency sound,
qualitative changes of diffusion and viscous flow, increase of particle thermal
speed to half of the speed of sound and reduction of the constant volume
specific heat to 2kB per particle. In contrast to the Widom line that exists
near the critical point only, the new dynamic line is universal: it separates
two liquid states at arbitrarily high pressure and temperature, and exists in
systems where liquid - gas transition and the critical point are absent
overall.Comment: 21 pages, 8 figure
Phase separation and vortex states in binary mixture of Bose-Einstein condensates in the trapping potentials with displaced centers
The system of two simultaneously trapped codensates consisting of
atoms in two different hyperfine states is investigated theoretically in the
case when the minima of the trapping potentials are displaced with respect to
each other. It is shown that the small shift of the minima of the trapping
potentials leads to the considerable displacement of the centers of mass of the
condensates, in agreement with the experiment. It is also shown that the
critical angular velocities of the vortex states of the system drastically
depend on the shift and the relative number of particles in the condensates,
and there is a possibility to exchange the vortex states between condensates by
shifting the centers of the trapping potentials.Comment: 4 pages, 2 figure
Positive energy unitary irreducible representations of D=6 conformal supersymmetry
We give a constructive classification of the positive energy (lowest weight)
unitary irreducible representations of the D=6 superconformal algebras
osp(8*/2N). Our results confirm all but one of the conjectures of Minwalla (for
N=1,2) on this classification. Our main tool is the explicit construction of
the norms of the states that has to be checked for positivity. We give also the
reduction of the exceptional UIRs.Comment: 27 pages, TeX with harvmac, amssym.def, amssym.tex; v.2: minor
corrections and references added; v.3: minor corrections; v.4: to appear in
J. Phys.
Experimental evidence for a universal threshold characterizing wave-induced sea ice break-up
Waves can drastically transform a sea ice cover by inducing break-up over
vast distances in the course of a few hours. However, relatively few detailed
studies have described this phenomenon in a quantitative manner, and the
process of sea ice break-up by waves needs to be further parameterized and
verified before it can be reliably included in forecasting models. In the
present work, we discuss sea ice break-up parameterization and demonstrate the
existence of an observational threshold separating breaking and non-breaking
cases. This threshold is based on information from two recent field campaigns,
supplemented with existing observations of sea ice break-up. The data used
cover a wide range of scales, from laboratory-grown sea ice to polar field
observations. Remarkably, we show that both field and laboratory observations
tend to converge to a single quantitative threshold at which the wave-induced
sea ice break-up takes place, which opens a promising avenue for robust
parametrization in operational forecasting models.Comment: 18 pages, 8 figures, 1 tabl
Supersymmetry of Tensionless Rotating Strings in AdS_5 x S^5, and Nearly-BPS Operators
It is shown that a class of rotating strings in AdS_5 x S^5 with SO(6)
angular momenta (J,J',J') preserve 1/8-supersymmetry for large J,J', in which
limit they are effectively tensionless; when J=0, supersymmetry is enhanced to
1/4. These results imply that recent checks of the AdS/CFT correspondence
actually test a nearly-BPS sector.Comment: 12 pages, no figures; v2: new section on CFT operators and new
references added, discussion section and acknowledgements modified, abstract
rephrashe
Monte Carlo simulation of a two-dimensional continuum Coulomb gas
We study the classical two-dimensional Coulomb gas model for thermal vortex
fluctuations in thin superconducting/superfluid films by Monte Carlo simulation
of a grand canonical vortex ensemble defined on a continuum. The
Kosterlitz-Thouless transition is well understood at low vortex density, but at
high vortex density the nature of the phase diagram and of the vortex phase
transition is less clear. From our Monte Carlo data we construct phase diagrams
for the 2D Coulomb gas without any restrictions on the vortex density. For
negative vortex chemical potential (positive vortex core energy) we always find
a Kosterlitz-Thouless transition. Only if the Coulomb interaction is
supplemented with a short-distance repulsion, a first order transition line is
found, above some positive value of the vortex chemical potential.Comment: 10 pages RevTeX, 7 postscript figures included using eps
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