686 research outputs found
Parasitoides de Ornidia obesa Fabricius (Diptera: Syrphidae) coletados em fezes de galinha no Brasil
Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
Nucleon electromagnetic form factor data (including recent data) is fitted
with models that respect the confinement and asymptotic freedom properties of
QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson
pole contributions and at high momentum transfer conform to the predictions of
perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also
include the width of the rho meson and the addition of higher mass vector meson
exchanges, but do not evolve into the explicit form of PQCD at high momentum
transfer. Different parameterizations of the GK model's hadronic form factors,
the effect of including the width of the rho meson and the addition of the next
(in mass) isospin 1 vector meson are considered. The quality of fit and the
consistency of the parameters select three of the combined HP/GK type models.
Projections are made to the higher momentum transfers which are relevant to
electron-deuteron experiments. The projections vary little for the preferred
models, removing much of the ambiguity in electron-nucleus scattering
predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure,
minor textual changes; email correspondence to [email protected]
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Double quantum dot turnstile as an electron spin entangler
We study the conditions for a double quantum dot system to work as a reliable
electron spin entangler, and the efficiency of a beam splitter as a detector
for the resulting entangled electron pairs. In particular, we focus on the
relative strengths of the tunneling matrix elements, the applied bias and gate
voltage, the necessity of time-dependent input/output barriers, and the
consequence of considering wavepacket states for the electrons as they leave
the double dot to enter the beam splitter. We show that a double quantum dot
turnstile is, in principle, an efficient electron spin entangler or
entanglement filter because of the exchange coupling between the dots and the
tunable input/output potential barriers, provided certain conditions are
satisfied in the experimental set-up.Comment: published version; minor error correcte
Reconciling Neutralino Relic Density with Yukawa Unified Supersymmetric Models
Supersymmetric grand unified models based on the gauge group SO(10) are
especially attractive in light of recent data on neutrino masses. The simplest
SO(10) SUSY GUT models predict unification of third generation Yukawa couplings
in addition to the usual gauge coupling unification. Recent surveys of Yukawa
unified SUSY GUT models predict an inverted scalar mass hierarchy in the
spectrum of sparticle masses if the superpotential mu term is positive. In
general, such models tend to predict an overabundance of dark matter in the
universe. We survey several solutions to the dark matter problem in Yukawa
unified supersymmetric models. One solution-- lowering the GUT scale mass value
of first and second generation scalars-- leads to u_R and c_R squark masses in
the 90-120 GeV regime, which should be accessible to Fermilab Tevatron
experiments. We also examine relaxing gaugino mass universality which may solve
the relic density problem by having neutralino annihilations via the Z or h
resonances, or by having a wino-like LSP.Comment: 21 page file plus 9 figures; updated version to coincide with
published versio
Large-amplitude driving of a superconducting artificial atom: Interferometry, cooling, and amplitude spectroscopy
Superconducting persistent-current qubits are quantum-coherent artificial
atoms with multiple, tunable energy levels. In the presence of large-amplitude
harmonic excitation, the qubit state can be driven through one or more of the
constituent energy-level avoided crossings. The resulting
Landau-Zener-Stueckelberg (LZS) transitions mediate a rich array of
quantum-coherent phenomena. We review here three experimental works based on
LZS transitions: Mach-Zehnder-type interferometry between repeated LZS
transitions, microwave-induced cooling, and amplitude spectroscopy. These
experiments exhibit a remarkable agreement with theory, and are extensible to
other solid-state and atomic qubit modalities. We anticipate they will find
application to qubit state-preparation and control methods for quantum
information science and technology.Comment: 13 pages, 5 figure
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