137 research outputs found
Effects of Fermi energy, dot size and leads width on weak localization in chaotic quantum dots
Magnetotransport in chaotic quantum dots at low magnetic fields is
investigated by means of a tight binding Hamiltonian on L x L clusters of the
square lattice. Chaoticity is induced by introducing L bulk vacancies. The
dependence of weak localization on the Fermi energy, dot size and leads width
is investigated in detail and the results compared with those of previous
analyses, in particular with random matrix theory predictions. Our results
indicate that the dependence of the critical flux Phi_c on the square root of
the number of open modes, as predicted by random matrix theory, is obscured by
the strong energy dependence of the proportionality constant. Instead, the size
dependence of the critical flux predicted by Efetov and random matrix theory,
namely, Phi_c ~ sqrt{1/L}, is clearly illustrated by the present results. Our
numerical results do also show that the weak localization term significantly
decreases as the leads width W approaches L. However, calculations for W=L
indicate that the weak localization effect does not disappear as L increases.Comment: RevTeX, 8 postscript figures include
Paired accelerated arames: The perfect interferometer with everywhere smooth wave amplitudes
Rindler's acceleration-induced partitioning of spacetime leads to a
nature-given interferometer. It accomodates quantum mechanical and wave
mechanical processes in spacetime which in (Euclidean) optics correspond to
wave processes in a ``Mach-Zehnder'' interferometer: amplitude splitting,
reflection, and interference. These processes are described in terms of
amplitudes which behave smoothly across the event horizons of all four Rindler
sectors. In this context there arises quite naturally a complete set of
orthonormal wave packet histories, one of whose key properties is their
"explosivity index". In the limit of low index values the wave packets trace
out fuzzy world lines. By contrast, in the asymptotic limit of high index
values, there are no world lines, not even fuzzy ones. Instead, the wave packet
histories are those of entities with non-trivial internal collapse and
explosion dynamics. Their details are described by the wave processes in the
above-mentioned Mach-Zehnder interferometer. Each one of them is a double slit
interference process. These wave processes are applied to elucidate the
amplification of waves in an accelerated inhomogeneous dielectric. Also
discussed are the properties and relationships among the transition amplitudes
of an accelerated finite-time detector.Comment: 38 pages, RevTex, 10 figures, 4 mathematical tutorials. Html version
of the figures and of related papers available at
http://www.math.ohio-state.edu/~gerlac
Conserved Quasilocal Quantities and General Covariant Theories in Two Dimensions
General matterless--theories in 1+1 dimensions include dilaton gravity,
Yang--Mills theory as well as non--Einsteinian gravity with dynamical torsion
and higher power gravity, and even models of spherically symmetric d = 4
General Relativity. Their recent identification as special cases of
'Poisson--sigma--models' with simple general solution in an arbitrary gauge,
allows a comprehensive discussion of the relation between the known absolutely
conserved quantities in all those cases and Noether charges, resp. notions of
quasilocal 'energy--momentum'. In contrast to Noether like quantities,
quasilocal energy definitions require some sort of 'asymptotics' to allow an
interpretation as a (gauge--independent) observable. Dilaton gravitation,
although a little different in detail, shares this property with the other
cases. We also present a simple generalization of the absolute conservation law
for the case of interactions with matter of any type.Comment: 21 pages, LaTeX-fil
Generation of defects and disorder from deeply quenching a liquid to form a solid
We show how deeply quenching a liquid to temperatures where it is linearly
unstable and the crystal is the equilibrium phase often produces crystalline
structures with defects and disorder. As the solid phase advances into the
liquid phase, the modulations in the density distribution created behind the
advancing solidification front do not necessarily have a wavelength that is the
same as the equilibrium crystal lattice spacing. This is because in a deep
enough quench the front propagation is governed by linear processes, but the
crystal lattice spacing is determined by nonlinear terms. The wavelength
mismatch can result in significant disorder behind the front that may or may
not persist in the latter stage dynamics. We support these observations by
presenting results from dynamical density functional theory calculations for
simple one- and two-component two-dimensional systems of soft core particles.Comment: 25 pages, 11 figure
Macromolecular theory of solvation and structure in mixtures of colloids and polymers
The structural and thermodynamic properties of mixtures of colloidal spheres
and non-adsorbing polymer chains are studied within a novel general
two-component macromolecular liquid state approach applicable for all size
asymmetry ratios. The dilute limits, when one of the components is at infinite
dilution but the other concentrated, are presented and compared to field theory
and models which replace polymer coils with spheres. Whereas the derived
analytical results compare well, qualitatively and quantitatively, with
mean-field scaling laws where available, important differences from ``effective
sphere'' approaches are found for large polymer sizes or semi-dilute
concentrations.Comment: 23 pages, 10 figure
Non-monotonic variation with salt concentration of the second virial coefficient in protein solutions
The osmotic virial coefficient of globular protein solutions is
calculated as a function of added salt concentration at fixed pH by computer
simulations of the ``primitive model''. The salt and counter-ions as well as a
discrete charge pattern on the protein surface are explicitly incorporated. For
parameters roughly corresponding to lysozyme, we find that first
decreases with added salt concentration up to a threshold concentration, then
increases to a maximum, and then decreases again upon further raising the ionic
strength. Our studies demonstrate that the existence of a discrete charge
pattern on the protein surface profoundly influences the effective interactions
and that non-linear Poisson Boltzmann and Derjaguin-Landau-Verwey-Overbeek
(DLVO) theory fail for large ionic strength. The observed non-monotonicity of
is compared to experiments. Implications for protein crystallization are
discussed.Comment: 43 pages, including 17 figure
The relationship between the perception of distributed leadership in secondary schools and teachers' and teacher leaders' job satisfaction and organizational commitment
This study investigates the relation between distributed leadership, the cohesion of the leadership team, participative decision-making, context variables, and the organizational commitment and job satisfaction of teachers and teacher leaders. A questionnaire was administered to teachers and teacher leaders (n=1770) from 46 large secondary schools. Multiple regression analyses and path analyses revealed that the study variables explained significant variance in organizational commitment. The degree of explained variance for job satisfaction was considerably lower compared to organizational commitment. Most striking was that the cohesion of the leadership team and the amount of leadership support was strongly related to organizational commitment, and indirectly to job satisfaction. Decentralization of leadership functions was weakly related to organizational commitment and job satisfaction
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