2,513 research outputs found
Phase-sensitive quantum effects in Andreev conductance of the SNS system of metals with macroscopic phase breaking length
The dissipative component of electron transport through the doubly connected
SNS Andreev interferometer indium (S)-aluminium (N)-indium (S) has been
studied. Within helium temperature range, the conductance of the individual
sections of the interferometer exhibits phase-sensitive oscillations of
quantum-interference nature. In the non-domain (normal) state of indium
narrowing adjacent to NS interface, the nonresonance oscillations have been
observed, with the period inversely proportional to the area of the
interferometer orifice. In the domain intermediate state of the narrowing, the
magneto-temperature resistive oscillations appeared, with the period determined
by the coherence length in the magnetic field equal to the critical one. The
oscillating component of resonance form has been observed in the conductance of
the macroscopic N-aluminium part of the system. The phase of the oscillations
appears to be shifted by compared to that of nonresonance oscillations.
We offer an explanation in terms of the contribution into Josephson current
from the coherent quasiparticles with energies of order of the Thouless energy.
The behavior of dissipative transport with temperature has been studied in a
clean normal metal in the vicinity of a single point NS contact.Comment: 9 pages, 7 figures, to be published in Low Temp. Phys., v. 29, No.
12, 200
Why holes are not like electrons. II. The role of the electron-ion interaction
In recent work, we discussed the difference between electrons and holes in
energy band in solids from a many-particle point of view, originating in the
electron-electron interaction, and argued that it has fundamental consequences
for superconductivity. Here we discuss the fact that there is also a
fundamental difference between electrons and holes already at the single
particle level, arising from the electron-ion interaction. The difference
between electrons and holes due to this effect parallels the difference due to
electron-electron interactions: {\it holes are more dressed than electrons}. We
propose that superconductivity originates in 'undressing' of carriers from
electron-electron and electron-ion interactions, and that both aspects
of undressing have observable consequences.Comment: Continuation of Phys.Rev.B65, 184502 (2002) = cond-mat/0109385 (2001
Sensing cloud optimization to solve ED of units with valve-point effects and multi-fuels
In this paper a solution to an highly constrained and non-convex economical dispatch (ED) problem with a meta-heuristic technique named Sensing Cloud Optimization (SCO) is presented. The proposed meta-heuristic is based on a cloud of particles whose central point represents the objective function value and the remaining particles act as sensors "to fill" the search space and "guide" the central particle so it moves into the best direction. To demonstrate its performance, a case study with multi-fuel units and valve- point effects is presented
Ratio of Hadronic Decay Rates of J\psi and \psi(2S) and the \rho\pi Puzzle
The so-called \rho\pi puzzle of J\psi and \psi(2S) decays is examined using
the experimental data available to date. Two different approaches were taken to
estimate the ratio of J\psi and \psi(2S) hadronic decay rates. While one of the
estimates could not yield the exact ratio of \psi(2S) to J\psi inclusive
hadronic decay rates, the other, based on a computation of the inclusive ggg
decay rate for
\psi(2S) (J\psi) by subtracting other decay rates from the total decay rate,
differs by two standard deviations from the naive prediction of perturbative
QCD, even though its central value is nearly twice as large as what was naively
expected. A comparison between this ratio, upon making corrections for specific
exclusive two-body decay modes, and the corresponding experimental data
confirms the puzzles in
J\psi and \psi(2S) decays. We find from our analysis that the exclusively
reconstructed hadronic decays of the \psi(2S) account for only a small fraction
of its total decays, and a ratio exceeding the above estimate should be
expected to occur for a considerable number of the remaining decay channels. We
also show that the recent new results from the BES experiment provide crucial
tests of various theoretical models proposed to explain the puzzle.Comment: 8 pages, no figure, 4 table
Proton polarizability effect in the Lamb shift of the hydrogen atom
The proton polarizability correction to the Lamb shift of electronic and
muonic hydrogen is calculated on the basis of isobar model and experimental
data on the structure functions of deep inelastic lepton-nucleon scattering.
The contributions of the Born terms, vector-meson exchanges and nucleon
resonances are taken into account in the construction of the photoabsorption
cross sections for transversely and longitudinally polarized virtual photons
sigma_{T,L}.Comment: 11 pages, 3 figure
Anomalous k-dependent spin splitting in wurtzite AlxGa1-xN/GaN heterostructures
We have confirmed the k-dependent spin splitting in wurtzite AlxGa1-xN/GaN
heterostructures. Anomalous beating pattern in Shubnikov-de Haas measurements
arises from the interference of Rashba and Dresselhaus spin-orbit interactions.
The dominant mechanism for the k-dependent spin splitting at high values of k
is attributed to Dresselhaus term which is enhanced by the Delta C1-Delta C3
coupling of wurtzite band folding effect
Charmless decays using flavor SU(3) symmetry
The decays of mesons to a pair of charmless pseudoscalar () mesons are
analyzed within a framework of flavor SU(3). Symmetry breaking is taken into
account in tree () amplitudes through ratios of decay constants; exact SU(3)
is assumed elsewhere. Acceptable fits to and
branching ratios and CP asymmetries are obtained with tree, color-suppressed
(), penguin (), and electroweak penguin () amplitudes. Crucial
additional terms for describing processes involving and include
a large flavor-singlet penguin amplitude () as proposed earlier and a
penguin amplitude associated with intermediate and quarks. For
the mode a term associated with intermediate
and quarks also may be needed. Values of the weak phase are
obtained consistent with an earlier analysis of decays, where
denotes a vector meson, and with other analyses of CKM parameters.Comment: 26 pages, 1 figure. To be submitted to Phys. Rev. D. Reference
update
Low-Mass Baryon-Antibaryon Enhancements in B Decays
The nature of low-mass baryon-antibaryon enhancements seen in B decays is
explored. Three possibilities include (i) states near threshold as found in a
model by Nambu and Jona-Lasinio, (ii) isoscalar states with coupled to a pair of gluons, and (iii) low-mass enhancements favored by the
fragmentation process. Ways of distinguishing these mechanisms using angular
distributions and flavor symmetry are proposed.Comment: 8 pages, LaTeX, no figures, to be submitted to Phys. Rev. D. One
reference adde
Building a Better Racetrack
We find IIb compactifications on Calabi-Yau orientifolds in which all Kahler
moduli are stabilized, along lines suggested by Kachru, Kallosh, Linde and
Trivedi.Comment: 47 pages, 1 figure, harvmac (v2: added references, minor comments,
v3: improved discussion of metastability and explicit flux vacua
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