14,783 research outputs found
Hydrodynamic fluctuations and the minimum shear viscosity of the dilute Fermi gas at unitarity
We study hydrodynamic fluctuations in a non-relativistic fluid. We show that
in three dimensions fluctuations lead to a minimum in the shear viscosity to
entropy density ratio as a function of the temperature. The minimum
provides a bound on which is independent of the conjectured bound in
string theory, , where is the entropy
density. For the dilute Fermi gas at unitarity we find \eta/s\gsim 0.2\hbar.
This bound is not universal -- it depends on thermodynamic properties of the
unitary Fermi gas, and on empirical information about the range of validity of
hydrodynamics. We also find that the viscous relaxation time of a hydrodynamic
mode with frequency diverges as , and that the shear
viscosity in two dimensions diverges as .Comment: 26 pages, 5 figures; final version to appear in Phys Rev
Neutron matter on the lattice with pionless effective field theory
We study neutron matter by combining pionless effective field theory with
non-perturbative lattice methods. The neutron contact interaction is determined
by zero temperature scattering data. We simulate neutron matter on the lattice
at temperatures 4 and 8 MeV and densities below one-fifth normal nuclear matter
density. Our results at different lattice spacings agree with one another and
match bubble chain calculations at low densities. The equation of state of pure
neutron matter obtained from our simulations agrees quantitatively with
variational calculations based on realistic potentials.Comment: 28 pages, 13 figure
Morphine Metabolism in Human Skin Microsomes
For patients with severe skin wounds, topically applied morphine is an option to induce efficient analgesia due to the presence of opioid receptors in the skin. However, for topical administration it is important to know whether the substance is biotransformed in the skin as this can eventually reduce the concentration of the active agent considerably. We use skin microsomes to elucidate the impact of skin metabolism on the activity of topically applied morphine. We are able to demonstrate that morphine is only glucuronidated in traces, indicating that the biotransformation in the skin can be neglected when morphine is applied topically. Hence, there is no need to take biotransformation into account when setting up the treatment regimen. Copyright (C) 2012 S. Karger AG, Base
Time-crystalline behavior in an engineered spin chain ?
Time crystals appear when systems display a commensurate spontaneous breaking
of the discrete time translational invariance imposed by an external periodic
drive. No consensus on the definition has been reached as yet, but important
aspects comprise robustness against small variations of the parameters and the
initial quantum state. Often, disorder and interaction are thought to be
essential ingredients for the occurrence of time crystals. We study a
finite-length polarized XX spin chain engineered to display a spectrum of
equidistant energy levels without drive and show that it keeps a spectrum of
equidistant quasienergies in Floquet theory for a large variety of periodic
driving schemes. This interesting behavior is explained by mapping the XX spin
chain with sites to a single large spin with invoking the closure
of the group SU(2). For suitably tuned parameters this system realizes time
crystals of various periodicities for \emph{all} initial states. The robustness
against variations of the parameters is also discussed. Thereby, we establish a
clean system without interaction which can display the phenomenon of time
crystallization.Comment: 17 pages, 5 figures. Title changed. Extended discussion of disorder
effects. Accepted for publication in Phys. Rev.
Production of Z^0 bosons with rapidity gaps: exclusive photoproduction in gamma p and p p collisions and inclusive double diffractive Z^0's
We extend the k_\perp-factorization formalism for exclusive photoproduction
of vector mesons to the production of electroweak Z^0 bosons. Predictions for
the gamma p \to Z^0 p and p p \to p p Z^0 reactions are given using an
unintegrated gluon distribution tested against deep inelastic data. We present
distributions in the Z^0 rapidity, transverse momentum of Z^0 as well as in
relative azimuthal angle between outgoing protons. The contributions of
different flavours are discussed. Absorption effects lower the cross section by
a factor of 1.5-2, depending on the Z-boson rapidity. We also discuss the
production of Z^0 bosons in central inclusive production. Here rapidity and
(x_{\Pom,1}, x_{\Pom,2}) distributions of Z^0 are calculated. The corresponding
cross section is about three orders of magnitude larger than that for the
purely exclusive process.Comment: 19 pages, 14 figs, A. Cisek is married name of A. Rybarsk
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