2,772 research outputs found
Experimental determination of the absorption strength in absorbing chaotic cavities
Due to the experimental necessity we present a formula to determine the
absorption strength by power losses inside a chaotic system (cavities, graphs,
acoustic resonators, etc) when the antenna coupling, always present in
experimental measurements, is taken into account. This is done by calculating
the average of the absorption coefficient as a function of the absorption
strength and the coupling of the antenna to the system, in the one channel
case.Comment: 6 pages, 3 figures, Submitted to Phys. Rev.
The Landau problem and noncommutative quantum mechanics
The conditions under which noncommutative quantum mechanics and the Landau
problem are equivalent theories is explored. If the potential in noncommutative
quantum mechanics is chosen as with defined in the
text, then for the value (that
measures the noncommutative effects of the space), the Landau problem and
noncommutative quantum mechanics are equivalent theories in the lowest Landau
level. For other systems one can find differents values for
and, therefore, the possible bounds for should be searched in
a physical independent scenario. This last fact could explain the differents
bounds for found in the literature.Comment: This a rewritten and corrected version of our previous preprint
hep-th/010517
Bilepton effects on the WWV^* vertex in the 331 model with right-handed neutrinos via a SU_L(2)XU_Y(1) covariant quantization scheme
In a recent paper, we investigated the effects of the massive charged gauge
bosons (bileptons) predicted by the minimal 331 model on the off-shell vertex
WWV^* (V=gamma, Z) using a SU_L(2) X U_Y(1) covariant gauge-fixing term for the
bileptons. We proceed along the same lines and calculate the effects of the
gauge bosons predicted by the 331 model with right-handed neutrinos. It is
found that the bilepton effects on the WWV^* vertex are of the same order of
magnitude than those arising from the SM and several of its extensions,
provided that the bilepton mass is of the order of a few hundred of GeVs. For
heavier bileptons, their effects on the WWV^* vertex are negligible. The
behavior of the form factors at high energies is also discussed as it is a
reflect of the gauge invariance and gauge independence of the WWV^* Green
function obtained via our quantization method.Comment: Replaced to match published versio
CFD code comparison for 2D airfoil flows
The current paper presents the effort, in the EU AVATAR project, to establish the necessary requirements to obtain consistent lift over drag ratios among seven CFD codes. The flow around a 2D airfoil case is studied, for both transitional and fully turbulent conditions at Reynolds numbers of 3 Ă 106 and 15 Ă 106. The necessary grid resolution, domain size, and iterative convergence criteria to have consistent results are discussed, and suggestions are given for best practice. For the fully turbulent results four out of seven codes provide consistent results. For the laminar-turbulent transitional results only three out of seven provided results, and the agreement is generally lower than for the fully turbulent case
Jarlskog-like invariants for theories with scalars and fermions
Within the framework of theories where both scalars and fermions are present,
we develop a systematic prescription for the construction of CP-violating
quantities that are invariant under basis transformations of those matter
fields. In theories with Spontaneous Symmetry Breaking, the analysis involves
the vevs' transformation properties under a scalar basis change, with a
considerable simplification of the study of CP violation in the scalar sector.
These techniques are then applied in detail to the two Higgs-doublet model with
quarks. It is shown that there are new invariants involving scalar-fermion
interactions, besides those already derived in previous analyses for the
fermion-gauge and scalar-gauge sectors.Comment: 12 pages, Latex, no figure
On The Low Frequency Quasi Periodic Oscillations of X-ray Sources
Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations
(kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries
(LMXBs) to the Keplerian and the periastron precession frequencies at the
magnetosphere-disk of X-ray neutron star (NS) respectively, we ascribe the low
frequency Quasi Periodic Oscillations (LFQPO) and HBO (15-60 Hz QPO for Z
sources or Atoll sources) to the periastron precession at some outer disk
radius.
The obtained conclusions include: all QPO frequencies increase with
increasing the accretion rate. The obtained theoretical relations between HBO
(LFQPO) frequency and the kHz QPO frequency are similar to the measured
empirical formula. Further, the possible dynamical mechanism for QPO production
is discussed.Comment: 6 pages, 2 figures, accepted by APSS, 200
Discovery of a Second Kilohertz QPO in the X-ray Binary 4U 1735-44
In recent observations with the Rossi X-Ray Timing Explorer we have detected
two simultaneous quasi-periodic oscillation (QPO) peaks in the low mass X-ray
binary and atoll source 4U 1735-44. The lower and higher frequency QPOs have
frequencies varying between 632 and 729 Hz, and 982 and 1026 Hz, respectively.
The fractional rms amplitudes are 3.7 to 8.1% and 5.0 to 5.8%. The frequency
separation between the two QPOs changes from 341+-7 Hz to 296+-12 Hz. The
inferred mass accretion rate during our observations is relatively low compared
to that during the previous observations, where only a single QPO was present.
There is weak evidence that the frequency of the QPOs correlates with the mass
accretion rate, as observed in other binaries. Five X-ray bursts were recorded
with no detectable oscillations with upper limits for the rms fraction of 4% to
13%.Comment: accepted by ApJ Letters, for more information see the QPO page at
http://www.astro.uva.nl/ecford/qpos.htm
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