4,165 research outputs found
Collective effects in charge transfer within a hybrid organic-inorganic system
A collective electron transfer (ET) process was discovered by studying the
current noise in a field effect transistor with light-sensitive gate formed by
nanocrystals linked by organic molecules to its surface. Fluctuations in the ET
through the organic linker are reflected in the fluctuations of the transistor
conductivity. The current noise has an avalanche character. Critical exponents
obtained from the noise power spectra, avalanche distributions, and the
dependence of the average avalanche size on avalanche duration are consistent
with each other. A plausible model is proposed for this phenomenonComment: 15 pages 4 figures. Accepted for publication in Physical Review
Letter
Relative "-Numerical Ranges for Applications in Quantum Control and Quantum Information
Motivated by applications in quantum information and quantum control, a new
type of "-numerical range, the relative "-numerical range denoted
, is introduced. It arises upon replacing the unitary group U(N) in
the definition of the classical "-numerical range by any of its compact and
connected subgroups .
The geometric properties of the relative "-numerical range are analysed in
detail. Counterexamples prove its geometry is more intricate than in the
classical case: e.g. is neither star-shaped nor simply-connected.
Yet, a well-known result on the rotational symmetry of the classical
"-numerical range extends to , as shown by a new approach based on
Lie theory. Furthermore, we concentrate on the subgroup , i.e. the -fold tensor product of SU(2),
which is of particular interest in applications. In this case, sufficient
conditions are derived for being a circular disc centered at
origin of the complex plane. Finally, the previous results are illustrated in
detail for .Comment: accompanying paper to math-ph/070103
Comparison of two models for bridge-assisted charge transfer
Based on the reduced density matrix method, we compare two different
approaches to calculate the dynamics of the electron transfer in systems with
donor, bridge, and acceptor. In the first approach a vibrational substructure
is taken into account for each electronic state and the corresponding states
are displaced along a common reaction coordinate. In the second approach it is
assumed that vibrational relaxation is much faster than the electron transfer
and therefore the states are modeled by electronic levels only. In both
approaches the system is coupled to a bath of harmonic oscillators but the way
of relaxation is quite different. The theory is applied to the electron
transfer in with free-base porphyrin () being the donor, zinc porphyrin () being the bridge and
quinone () the acceptor. The parameters are chosen as similar as
possible for both approaches and the quality of the agreement is discussed.Comment: 12 pages including 4 figures, 1 table, 26 references. For more info
see http://eee.tu-chemnitz.de/~kili
Weak-Localization in Chaotic Versus Non-Chaotic Cavities: A Striking Difference in the Line Shape
We report experimental evidence that chaotic and non-chaotic scattering
through ballistic cavities display distinct signatures in quantum transport. In
the case of non-chaotic cavities, we observe a linear decrease in the average
resistance with magnetic field which contrasts markedly with a Lorentzian
behavior for a chaotic cavity. This difference in line-shape of the
weak-localization peak is related to the differing distribution of areas
enclosed by electron trajectories. In addition, periodic oscillations are
observed which are probably associated with the Aharonov-Bohm effect through a
periodic orbit within the cavities.Comment: 4 pages revtex + 4 figures on request; amc.hub.94.
Biochemische Serumparameter bei in Gefangenschaft gehaltenen Gazellen
Objective: This study aimed at comparing serum parameters of clinically healthy gazelles of Al Wabra Wildlife Preservation (AWWP), Qatar, with reference ranges of domestic and other wild ruminants, in order to gain, on the one hand, insight into the nutritional status of the animals, and, on the other hand, to establish reference ranges for the investigated species. Material and methods: Serum biochemistry parameters and mineral levels were measured in 250 clinically healthy individuals of the species Soemmering's gazelle (Gazella soemmerringii), Speke's gazelle (Gazella spekei), Dorcas gazelle (Gazella dorcas), Saudi gazelle (Gazella saudiya), Mountain gazelle (Gazella gazella), Arabian goitered gazelle (Gazella subgutturosa marica) and Chinkara Pakistani gazelle (Gazella benetti). Results: With respect to the nutritional status, the supplementation with trace elements (selenium, copper, zinc, iron) was adequate at AWWP according to measured serum levels. In contrast, serum levels of phosphorus, total protein and albumin indicated a suboptimal feeding situation, most likely due to the low quality of the roughage available in the region. The levels of sodium, potassium, calcium, magnesium, choride, triglycerides, cholesterol, creatinine, ALT- as well as GGT avtivity were -as in other wild ruminants-within the reference range of domestic ruminants, which therefore should be applicable to ruminants in general. The contents of glucose, blood urea nitrogen, creatine kinase and ALP, in contrast, seem to be generally elevated in wild ruminants. While other wild ruminants display an AST activity comparable to those of domestic ruminants, gazelles of both this and other studies had elevated values of this enzyme. Conclusion and clinical relevance: These peculiarities need to be accounted for when interpreting blood values
Semiclassical analysis of the quantum interference corrections to the conductance of mesoscopic systems
The Kubo formula for the conductance of a mesoscopic system is analyzed
semiclassically, yielding simple expressions for both weak localization and
universal conductance fluctuations. In contrast to earlier work which dealt
with times shorter than , here longer times are taken to
give the dominant contributions. For such long times, many distinct classical
orbits may obey essentially the same initial and final conditions on positions
and momenta, and the interference between pairs of such orbits is analyzed.
Application to a chain of classically ergodic scatterers connected in
series gives the following results: for the
weak localization correction to the zero--temperature dimensionless
conductance, and for the variance of its
fluctuations. These results interpolate between the well known ones of random
scattering matrices for , and those of the one--dimensional diffusive wire
for .Comment: 53 pages, using RevTeX, plus 3 postscript figures mailed separately.
A short version of this work is available as cond-mat/950207
Classical versus Quantum Structure of the Scattering Probability Matrix. Chaotic wave-guides
The purely classical counterpart of the Scattering Probability Matrix (SPM)
of the quantum scattering matrix is defined for 2D
quantum waveguides for an arbitrary number of propagating modes . We compare
the quantum and classical structures of for a waveguide
with generic Hamiltonian chaos. It is shown that even for a moderate number of
channels, knowledge of the classical structure of the SPM allows us to predict
the global structure of the quantum one and, hence, understand important
quantum transport properties of waveguides in terms of purely classical
dynamics. It is also shown that the SPM, being an intensity measure, can give
additional dynamical information to that obtained by the Poincar\`{e} maps.Comment: 9 pages, 9 figure
How Phase-Breaking Affects Quantum Transport Through Chaotic Cavities
We investigate the effects of phase-breaking events on electronic transport
through ballistic chaotic cavities. We simulate phase-breaking by a fictitious
lead connecting the cavity to a phase-randomizing reservoir and introduce a
statistical description for the total scattering matrix, including the
additional lead. For strong phase-breaking, the average and variance of the
conductance are calculated analytically. Combining these results with those in
the absence of phase-breaking, we propose an interpolation formula, show that
it is an excellent description of random-matrix numerical calculations, and
obtain good agreement with several recent experiments.Comment: 4 pages, revtex, 3 figures: uuencoded tar-compressed postscrip
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