13,191 research outputs found
Multi-terminal far-from-equilibrium thermoelectric nano-devices in the Kondo regime
The quest for good thermoelectric materials and/or high-efficiency
thermoelectric devices is of primary importance from theoretical and practical
points of view. Low-dimensional structures with quantum dots or molecules are
promising candidates to achieve the goal. Interactions between electrons,
far-from-equilibrium conditions and strongly non-linear transport are important
factors affecting the usefulness of the devices. This paper analyses the
thermoelectric power of a two-terminal quantum dot under large thermal and voltage biases as well as the performance of the three-terminal
system as a heat engine. To properly characterise the non-linear effects under
these conditions, two different Seebeck coefficients are introduced,
generalizing the linear response expression. The direct calculations of
thermally induced electric and heat currents show, in agreement with recent
work, that the efficiency of the thermoelectric heat engine as measured by the
delivered power is maximal far from equilibrium. Moreover, the strong Coulomb
interactions between electrons on the quantum dot are found to diminish the
efficiency at maximum power and the maximal value of the delivered power, both
in the Kondo regime and outside of it.Comment: 29 pages, 8 figure
Projected Three-Pion Correlation Functions
We propose a new procedure for constructing projected three-pion correlation
functions which reduces undesirable artificial momentum dependences resulting
from the commonly used procedure and facilitates comparison of three-pion
correlation data with theoretical models.Comment: 6 pages revtex, incl. 1 figure. Submitted as Brief Report to Physical
Review C. Normalization error and typos correcte
Comparison of carbon and opal export rates between summer and spring bloom periods in the region of the Antarctic Polar Front, SE Atlantic.
Although primary production in the Antarctic Circumpolar Current is not above the world average and carbon burial rates are low, 70% of the world's opal burial occurs in this zone and it has been suggested that blooms of large diatoms are responsible for this extraordinary situation. Here we compare export fluxes during bloom and steady-state situations near the Antarctic Polar Front in the SE Atlantic.In a previous expedition during the austral spring, we observed the development of a bloom that led to the sudden export of particles (Rutgers van der Loeff et al., 1997). Here we report the results of a second expedition to the same area in summer (Dec-Jan), 3 years later. 234Th was monitored in the surface water and in Rosette casts down to a water depth of 500m as tracer of export production in an intensive sampling program within a box of 275 x 375 km.The distribution of particulate and dissolved 234Th was remarkably constant over time and location. Total (dissolved + particulate) 234Th activities were depleted relative to its parent 238U at the surface (234Th/238U activity ratio approximately 83%), reaching equilibrium at a depth of around 190m. This constant depletion corresponds to a 234Th export rate of 1115 dpm m-2 d-1, 35% of the value observed during the spring bloom
Yukawa coupling and anomalous magnetic moment of the muon: an update for the LHC era
We study the interplay between a soft muon Yukawa coupling generated
radiatively with the trilinear A-terms of the minimal supersymmetric standard
model (MSSM) and the anomalous magnetic moment of the muon. In the absence of a
tree-level muon Yukawa coupling the lightest smuon mass is predicted to be in
the range between 750 GeV and 2700 GeV at 2 sigma, if the bino mass M_1 is
below 1 TeV. Therefore, a detection of a smuon (in conjunction with a sub-TeV
bino) at the LHC would directly imply a non-zero muon Yukawa coupling in the
MSSM superpotential. Inclusion of slepton flavor mixing could in principle
lower the mass of one smuon-like slepton below 750 GeV. However, the
experimental bounds on radiative lepton decays instead strengthen the lower
mass bound, with larger effects for smaller M_1, We also extend the analysis to
the electron case and find that a light selectron close to the current
experimental search limit may prove the MSSM electron Yukawa coupling to be
non-zero.Comment: 6 pages, 2 figures, references added, version accepted for
publication in PR
Predominant utilization of V beta 8+ T cell receptor genes in the H-2Ld- restricted cytotoxic T cell response against the immediate-early protein pp89 of the murine cytomegalovirus
Cytotoxic T cell responses to the murine Cytomegalovirus (MCMV) were elicited in BALB/c mice (H-2d) by infectious virus. Eight days after infection, MCMV-primed local lymph node T cells were either depleted for T cells expressing a V beta 8+ TCR or separated into V beta 8+ and V beta 8- subpopulations by a cell sorter using the mAb F23.1. T cells were then expanded in vitro under limiting dilution conditions in the presence of IL-2 and in the absence of viral Ag to avoid selection by Ag in vitro. Frequencies of CTL precursors specific for the Immediate- Early-Ag 1 of MCMV and restricted to H-2Ld were determined. L cells of the endogenous haplotype H-2k cotransfected with the genes for MCMV-IE 1 and H-2Ld were used as target cells. Detection of a CTL response required previous priming of the animals by infection in vivo (less than 1/10(6) for nonimmunized animals). In primed animals CTL precursors of this specificity and restriction were three to fivefold more frequent in the V beta 8+ population (1/9.900 to 1/22.300) than in the V beta 8- population (1/57.000 to 1/87.200). Control experiments showed that frequencies were not influenced by the treatment with the anti-V beta 8-antibody and the fluorescein-labeled anti-Ig itself. V beta 8+ and V beta 8- T cells did not reveal any frequency differences when several other responses were determined (TNP-specific self- restricted CTL precursor; Th cells specific for keyhole limpet hemocyanin or Listeria monocytogenes)
Signatures of molecular correlations in the few-electron dynamics of coupled quantum dots
We study the effect of Coulomb interaction on the few-electron dynamics in
coupled semiconductor quantum dots by exact diagonalization of the few-body
Hamiltonian. The oscillation of carriers is strongly affected by the number of
confined electrons and by the strength of the interdot correlations.
Single-frequency oscillations are found for either uncorrelated or highly
correlated states, while multi-frequency oscillations take place in the
intermediate regime. Moreover, Coulomb interaction renders few-particle
oscillations sensitive to perturbations in spatial directions other than that
of the tunneling, contrary to the single-particle case. The inclusion of
acoustic phonon scattering does not modify the carrier dynamics substantially
at short times, but can damp oscillation modes selectively at long times.Comment: 4 pages, 5 figures, RevTex4 two-column format, to appear in Phys.
Rev.
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