103,423 research outputs found
The Nature of Thermopower in Bipolar Semiconductors
The thermoemf in bipolar semiconductors is calculated. It is shown that it is
necessary to take into account the nonequilibrium distribution of electron and
hole concentrations (Fermi quasilevels of the electrons and holes). We find
that electron and hole electric conductivities of contacts of semiconductor
samples with connecting wires make a substantial contribution to thermoemf.Comment: 17 pages, RevTeX 3.0 macro packag
Continuous variable entanglement of phase locked light beams
We explore in detail the possibility of intracavity generation of
continuous-variable (CV) entangled states of light beams under mode
phase-locked conditions. We show that such quantum states can be generated in
self-phase locked nondegenerate optical parametric oscillator (NOPO) based on a
type-II phase-matched down-conversion combined with linear mixer of two
orthogonally polarized modes of the subharmonics in a cavity. A quantum theory
of this device, recently realized in the experiment, is developed for both
sub-threshold and above-threshold operational regimes. We show that the system
providing high level phase coherence between two generated modes, unlike to the
ordinary NOPO, also exhibits different types of quantum correlations between
photon numbers and phases of these modes. We quantify the CV entanglement as
two-mode squeezing and show that the maximal degree of the integral two-mode
squeezing(that is 50% relative to the level of vacuum fluctuations) is achieved
at the pump field intensity close to the generation threshold of self-phase
locked NOPO, provided that the constant of linear coupling between the two
polarizations is much less than the mode detunings. The peculiarities of CV
entanglement for the case of unitary, non-dissipative dynamics of the system
under consideration is also cleared up
Specific interplanetary conditions for CIR-, Sheath-, and ICME-induced geomagnetic storms obtained by double superposed epoch analysis
The comparison of specific interplanetary conditions for 798 magnetic storms
with Dst < -50 nT for the period 1976-2000 was made on the basis of the OMNI
archive data.We categorized various large-scale types of solar wind as
interplanetary drivers of storms: corotating interaction region (CIR), Sheath,
interplanetary CME (ICME) including magnetic cloud (MC) and Ejecta, separately
MC and Ejecta, and "Indeterminate" type. The data processing was carried out by
the method of double superposed epoch analysis which uses two reference times
(onset of storm and the minimum Dst index) and make a re-scaling of main phase
of storm a such way that after this transformation all storms have equal
durations of main phase in new time reference frame. This method reproduced
some well-known results and allowed us to obtain some new results.
Specifically, obtained results demonstrate high importance of Sheath in
generation of magnetic storms as well as a significant differences in
properties of MC and Ejecta and in their geoeffectiveness.Comment: 21 pages, 9 figures, 1 table, submitted to J. of Advances in Space
Research on 29 July, 2009 for Special Issue "Space Weather Advances
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