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Osmotic Pressures and Second Virial Coefficients for Aqueous Saline Solutions of Lysozyme
Dynamic Phases of Vortices in Superconductors with Periodic Pinning
We present results from extensive simulations of driven vortex lattices
interacting with periodic arrays of pinning sites. Changing an applied driving
force produces a rich variety of novel dynamical plastic flow phases which are
very distinct from those observed in systems with random pinning arrays.
Signatures of the transition between these different dynamical phases include
sudden jumps in the current-voltage curves as well as marked changes in the
vortex trajectories and the vortex lattice order. Several dynamical phase
diagrams are obtained as a function of commensurability, pinning strength, and
spatial order of the pinning sites.Comment: 4 pages, 3 figures. To appear in Physical Review Letters. Movies
available at http://www-personal.engin.umich.edu/~nor
Anomalous Exponent of the Spin Correlation Function of a Quantum Hall Edge
The charge and spin correlation functions of partially spin-polarized edge
electrons of a quantum Hall bar are studied using effective Hamiltonian and
bosonization techniques. In the presence of the Coulomb interaction between the
edges with opposite chirality we find a different crossover behavior in spin
and charge correlation functions. The crossover of the spin correlation
function in the Coulomb dominated regime is characterized by an anomalous
exponent, which originates from the finite value of the effective interaction
for the spin degree of freedom in the long wavelength limit. The anomalous
exponent may be determined by measuring nuclear spin relaxation rates in a
narrow quantum Hall bar or in a quantum wire in strong magnetic fields.Comment: 4 pages, Revtex file, no figures. To appear in Physical Revews B,
Rapid communication
Teleworking practice in small and medium-sized firms: Management style and worker autonomy
In an empirical study of teleworking practices amongst small and medium-sized enterprises (SMEs) in West London, organisational factors such as management attitudes, worker autonomy and employment flexibility were found to be more critical than technological provision in facilitating successful implementation. Consequently, we argue that telework in most SMEs appears as a marginal activity performed mainly by managers and specialist mobile workers
Spin Degeneracy and Conductance Fluctuations in Open Quantum Dots
The dependence of mesoscopic conductance fluctuations on parallel magnetic
field is used as a probe of spin degeneracy in open GaAs quantum dots. The
variance of fluctuations at high parallel field is reduced from the low-field
variance (with broken time-reversal symmetry) by factors ranging from roughly
two in a 1 square-micron dot at low temperature, to four or greater in 8
square-micron dots. The factor of two is expected for simple Zeeman splitting
of spin degenerate channels. A possible explanation for the unexpected larger
factors in terms of field-dependent spin orbit scattering is proposed.Comment: Includes new reference to related theoretical work, cond-mat/0010064.
Other minor changes. Related papers at http://marcuslab.harvard.ed
Scaling behavior of impurities in mesoscopic Luttinger liquids
Using a functional renormalization group we compute the flow of the
renormalized impurity potential for a single impurity in a Luttinger liquid
over the entire energy range - from the microscopic scale of a lattice-fermion
model down to the low-energy limit. The non-perturbative method provides a
complete real-space picture of the effective impurity potential. We confirm the
universality of the open chain fixed point, but it turns out that very large
systems (10^4-10^5 sites) are required to reach the fixed point for realistic
choices of the impurity and interaction parameters.Comment: 4 pages, 4 figures include
Steady state properties of a mean field model of driven inelastic mixtures
We investigate a Maxwell model of inelastic granular mixture under the
influence of a stochastic driving and obtain its steady state properties in the
context of classical kinetic theory. The model is studied analytically by
computing the moments up to the eighth order and approximating the
distributions by means of a Sonine polynomial expansion method. The main
findings concern the existence of two different granular temperatures, one for
each species, and the characterization of the distribution functions, whose
tails are in general more populated than those of an elastic system. These
analytical results are tested against Monte Carlo numerical simulations of the
model and are in general in good agreement. The simulations, however, reveal
the presence of pronounced non-gaussian tails in the case of an infinite
temperature bath, which are not well reproduced by the Sonine method.Comment: 23 pages, 10 figures, submitted for publicatio
Dynamic Vortex Phases and Pinning in Superconductors with Twin Boundaries
We investigate the pinning and driven dynamics of vortices interacting with
twin boundaries using large scale molecular dynamics simulations on samples
with near one million pinning sites. For low applied driving forces, the vortex
lattice orients itself parallel to the twin boundary and we observe the
creation of a flux gradient and vortex free region near the edges of the twin
boundary. For increasing drive, we find evidence for several distinct dynamical
flow phases which we characterize by the density of defects in the vortex
lattice, the microscopic vortex flow patterns, and orientation of the vortex
lattice. We show that these different dynamical phases can be directly related
to microscopically measurable voltage - current V(I) curves and voltage noise.
By conducting a series of simulations for various twin boundary parameters we
derive several vortex dynamic phase diagrams.Comment: 5 figures, to appear in Phys. Rev.
Phase Locking, Devil's Staircases, Farey Trees, and Arnold Tongues in Driven Vortex Lattices with Periodic Pinning
Using numerical simulations, we observe phase locking, Arnold tongues, and
Devil's staircases for vortex lattices driven at varying angles with respect to
an underlying superconducting periodic pinning array. This rich structure
should be observalble in transport measurments. The transverse curves
have a Devil's staircase structure, with plateaus occurring near the driving
angles along symmetry directions of the pinning array. Each of the plateaus
corresponds to a different dyanmical phase with a distinctive vortex structure
and flow pattern.Comment: accepted to Physical Review Letter
The search for magnetic fields in mercury-manganese stars
We performed a highly sensitive search for magnetic fields on a large set of
HgMn stars. With the aid of a new polarimeter attached to the HARPS
spectrometer at the ESO 3.6m-telescope, we obtained high-quality circular
polarization spectra of 41 single and double HgMn stars. Using a multi-line
analysis technique on each star, we co-added information from hundreds of
spectral lines resulting in significantly greater sensitivity to the presence
of magnetic fields, including very weak fields. For the 47 individual objects
studied, including 6 components of SB2 systems, we do not detect any magnetic
fields at greater than the 3 sigma level. The lack of detection in the circular
polarization profiles indicates that if strong fields are present on these
stars, they must have complex surface topologies. For simple global fields, our
detection limits imply upper limits to the fields present of 2-10 Gauss in the
best cases. We conclude that HgMn stars lack large-scale magnetic fields,
typical for spotted magnetic Ap stars, sufficient to form and sustain the
chemical spots observed on HgMn stars. Our study confirms that in addition to
magnetically altered atomic diffusion, there exists another differentiation
mechanism operating in the atmospheres of late-B main sequence stars which can
compositional inhomogeneities on their surfaces.Comment: 12 pages, 8 figures, 2 table
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