4,258 research outputs found
Current-voltage correlations in interferometers
We investigate correlations of current at contacts and voltage fluctuations
at voltage probes coupled to interferometers. The results are compared with
correlations of current and occupation number fluctuations at dephasing probes.
We use a quantum Langevin approach for the average quantities and their
fluctuations. For higher order correlations we develop a stochastic path
integral approach and find the generating functions of voltage or occupation
number fluctuations. We also derive a generating function for the joint
distribution of voltage or occupation number at the probe and current
fluctuations at a terminal of a conductor. For energy independent scattering we
found earlier that the generating function of current cumulants in
interferometers with a one-channel dephasing or voltage probe are identical.
Nevertheless, the distribution function for voltage and the distribution
function for occupation number fluctuations differ, the latter being broader
than that of former in all examples considered here.Comment: 23 pages, 10 figures, minor changes, additional appendix, added
reference
Magnetoasymmetric transport in a mesoscopic interferometer: From the weak to the strong coupling regime
The microreversibility principle implies that the conductance of a
two-terminal Aharonov-Bohm interferometer is an even function of the applied
magnetic flux. Away from linear response, however, this symmetry is not
fulfilled and the conductance phase of the interferometer when a quantum dot is
inserted in one of its arms can be a continuous function of the bias voltage.
Such magnetoasymmetries have been investigated in related mesoscopic systems
and arise as a consequence of the asymetric response of the internal potential
of the conductor out of equilibrium. Here we discuss magnetoasymmetries in
quantum-dot Aharonov-Bohm interferometers when strong electron-electron
interactions are taken into account beyond the mean-field approach. We find
that at very low temperatures the asymmetric element of the differential
conductance shows an abrupt change for voltages around the Fermi level. At
higher temperatures we recover a smooth variation of the magnetoasymmetry as a
function of the bias. We illustrate our results with the aid of the electron
occupation at the dot, demonstrating that its nonequilibrium component is an
asymmetric function of the flux even to lowest order in voltage. We also
calculate the magnetoasymmetry of the current-current correlations (the noise)
and find that it is given, to a good extent, by the magnetoasymmetry of the
weakly nonlinear conductance term. Therefore, both magnetoasymmetries (noise
and conductance) are related to each other via a higher-order
fluctuation-dissipation relation. This result appears to be true even in the
low temperature regime, where Kondo physics and many-body effects dominate the
transport properties.Comment: 17 pages, 9 figure
Decrumpling membranes by quantum effects
The phase diagram of an incompressible fluid membrane subject to quantum and
thermal fluctuations is calculated exactly in a large number of dimensions of
configuration space. At zero temperature, a crumpling transition is found at a
critical bending rigidity . For membranes of fixed lateral
size, a crumpling transition occurs at nonzero temperatures in an auxiliary
mean field approximation. As the lateral size L of the membrane becomes large,
the flat regime shrinks with .Comment: 9 pages, 4 figure
Full counting statistics for voltage and dephasing probes
We present a stochastic path integral method to calculate the full counting
statistics of conductors with energy conserving dephasing probes and
dissipative voltage probes. The approach is explained for the experimentally
important case of a Mach-Zehnder interferometer, but is easily generalized to
more complicated setups. For all geometries where dephasing may be modeled by a
single one-channel dephasing probe we prove that our method yields the same
full counting statistics as phase averaging of the cumulant generating
function.Comment: 4 pages, 2 figure
Respiration rates of soil invertebrates from temperate and tropical zones as measured by infrared gas analysis.
The aim of our investigation was to measure the amount of carbon that is directly contributed by the soil fauna. Therefore a devide to measure the small amounts of CO2 released by soil invertebrates was developed. A commercially available portable photosynthesis measuring system, based on an infrared gas analyzer (IRGA) and designed to quantifity the CO2 uktake to single plant leaves, was modified in such a way that the CO2 production of soil invertebrates could be measured
Difference Equations and Highest Weight Modules of U_q[sl(n)]
The quantized version of a discrete Knizhnik-Zamolodchikov system is solved
by an extension of the generalized Bethe Ansatz. The solutions are constructed
to be of highest weight which means they fully reflect the internal quantum
group symmetry.Comment: 9 pages, LaTeX, no figure
Spatially Resolved Star Formation History Along the Disk of M82 Using Multi-Band Photometric Data
We present the results on the star formation history and extinction in the
disk of M82 over spatial scales of 10" (~180 pc). Multi-band photometric data
covering from the far ultraviolet to the near infrared bands were fitted to a
grid of synthetic spectral energy distributions. We obtained distribution
functions of age and extinction for each of the 117 apertures analyzed, taking
into account observational errors through Monte-Carlo simulations. These
distribution functions were fitted with gaussian functions to obtain the mean
ages and extinctions along with errors on them. The analyzed zones include the
high surface brightness complexes defined by O'Connell & Mangano (1978). We
found that these complexes share the same star formation history and extinction
as the field stellar populations in the disk. There is an indication that the
stellar populations are marginally older at the outer disk (450 Myr at ~3 kpc)
as compared to the inner disk (100 Myr at 0.5 kpc). For the nuclear regions
(radius less than 500 pc), we obtained an age of less than 10 Myr. The results
obtained in this work are consistent with the idea that the 0.5-3 kpc part of
the disk of M82 formed around 90% of the stellar mass in a star-forming episode
that started around 450 Myr ago lasting for about 350 Myr. We found that field
stars are the major contributors to the flux over the spatial scales analyzed
in this study, with stellar cluster contribution being 7% in the nucleus and
0.7% in the disk.Comment: 19 pages, 14 figures. Accepted for publication in The Astrophysical
Journa
K+ and K- production in heavy-ion collisions at SIS-energies
The production and the propagation of K+ and of K- mesons in heavy-ion
collisions at beam energies of 1 to 2 AGeV have systematically been
investigated with the Kaon Spectrometer KaoS at the SIS at the GSI. The ratio
of the K+ production excitation function for Au+Au and for C+C reactions
increases with decreasing beam energy, which is expected for a soft nuclear
equation-of-state. At 1.5 AGeV a comprehensive study of the K+ and of the K-
emission as a function of the size of the collision system, of the collision
centrality, of the kaon energy, and of the polar emission angle has been
performed. The K-/K+ ratio is found to be nearly constant as a function of the
collision centrality. The spectral slopes and the polar emission patterns are
different for K- and for K+. These observations indicate that K+ mesons
decouple earlier from the reaction zone than K- mesons.Comment: invited talk given at the SQM2003 conference in Atlantic Beach, USA
(March 2003), to be published in Journal of Physics G, 10pages, 7 figure
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