608 research outputs found
Confining properties of 2-color QCD at finite density
We study the confining properties of QCD with two colors across the finite
density phase transition. A disorder parameter detecting dual superconductivity
of the QCD vacuum is used as a probe for the confinement/deconfinement phase
transition.Comment: 7 pages, 3 figures, talk presented at Lattice 2006 (High Temperature
and Density
Transmission Oscillator Ultrasonic Spectrometer (TOUS): A new research instrument
TOUS is capable for measuring very small changes in acoustic attenuation and phase velocity. Its high sensitivity to small changes in ultrasonic absorption results in part from operation under marginal conditions. In spite of high sensitivity, TOUS system is relatively simple, inexpensive, and compact
Confining properties of QCD at finite temperature and density
A disorder parameter detecting dual superconductivty of the vacuum is used as
a probe to characterize the confining properties of the phase diagram of two
color QCD at finite temperature and density. We obtain evidence for the
disappearing of dual superconductivity (deconfinement) induced by a finite
density of baryonic matter, as well as for a coincidence of this phenomenon
with the restoration of chiral symmetry both at zero and finite density. The
saturation transition induced by Pauli blocking is studied as well, and a
general warning is given about the possible effects that this unphysical
transition could have on the study of the QCD phase diagram at strong values of
the gauge coupling.Comment: 13 pages, 23 figure
Nuclear Magnetic Resonance Probe for Supercritical Water and Aqueous Solutions
A nuclear magnetic resonance (NMR) probe for high pressure, high temperature studies is presented. While applicable to many physical systems, the device is optimized for the study of the physics and chemistry of supercritical water and its solutions. The design is modular and is particularly simple, using readily available parts and materials. A new approach is presented for elimination of the magnetic field from the heater currents. The probe has been used to 600 °C and 400 bar. The rf performance is quite good; the NMR linewidth is about 0.1 ppm full width at half-height at any pressure and temperature
Initial Conditions for a Universe
In physical theories, boundary or initial conditions play the role of
selecting special situations which can be described by a theory with its
general laws. Cosmology has long been suspected to be different in that its
fundamental theory should explain the fact that we can observe only one
particular realization. This is not realized, however, in the classical
formulation and in its conventional quantization; the situation is even worse
due to the singularity problem. In recent years, a new formulation of quantum
cosmology has been developed which is based on quantum geometry, a candidate
for a theory of quantum gravity. Here, the dynamical law and initial conditions
turn out to be linked intimately, in combination with a solution of the
singularity problem.Comment: 7 pages, this essay was awarded First Prize in the Gravity Research
Foundation Essay Contest 200
High-pressure spin shifts in the pseudogap regime of superconducting YBa2Cu4O8 as revealed by 17O NMR
A new NMR anvil cell design is used for measuring the influence of high
pressure on the electronic properties of the high-temperature superconductor
YBaCuO above the superconducting transition temperature . It is found that pressure increases the spin shift at all temperatures in
such a way that the pseudo-gap feature has almost disappeared at 63 kbar. This
change of the temperature dependent spin susceptibility can be explained by a
pressure induced proportional decrease (factor of two) of a temperature
dependent component, and an increase (factor of 9) of a temperature independent
component, contrary to the effects of increasing doping. The results
demonstrate that one can use anvil cell NMR to investigate the tuning of the
electronic properties of correlated electronic materials with pressure.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.
Effective medium theory of elastic waves in random networks of rods
We formulate an effective medium (mean field) theory of a material consisting
of randomly distributed nodes connected by straight slender rods, hinged at the
nodes. Defining novel wavelength-dependent effective elastic moduli, we
calculate both the static moduli and the dispersion relations of ultrasonic
longitudinal and transverse elastic waves. At finite wave vector the waves
are dispersive, with phase and group velocities decreasing with increasing wave
vector. These results are directly applicable to networks with empty pore
space. They also describe the solid matrix in two-component (Biot) theories of
fluid-filled porous media. We suggest the possibility of low density materials
with higher ratios of stiffness and strength to density than those of foams,
aerogels or trabecular bone.Comment: 14 pp., 3 fig
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