631 research outputs found
Finite Size and Current Effects on IV Characteristics of Josephson Junction Arrays
The effects of finite size and of finite current on the current-voltage
characteristics of Josephson junction arrays is studied both theoretically and
by numerical simulations. The cross-over from non-linear to linear behavior at
low temperature is shown to be a finite size effect and the non-linear behavior
at higher temperature, , is shown to be a finite current effect.
These are argued to result from competition between the three length scales
characterizing the system. The importance of boundary effects is discussed and
it is shown that these may dominate the behavior in small arrays.Comment: 5 pages, figures included, to appear in PR
Theoretical study of the absorption spectra of the sodium dimer
Absorption of radiation from the sodium dimer molecular states correlating to
Na(3s)-Na(3s) is investigated theoretically. Vibrational bound and continuum
transitions from the singlet X Sigma-g+ state to the first excited singlet A
Sigma-u+ and singlet B Pi-u states and from the triplet a Sigma-u+ state to the
first excited triplet b Sigma-g+ and triplet c Pi-g states are studied
quantum-mechanically. Theoretical and experimental data are used to
characterize the molecular properties taking advantage of knowledge recently
obtained from ab initio calculations, spectroscopy, and ultra-cold atom
collision studies. The quantum-mechanical calculations are carried out for
temperatures in the range from 500 to 3000 K and are compared with previous
calculations and measurements where available.Comment: 19 pages, 8 figures, revtex, eps
Exotic Meson Production in the System observed in the Reaction at 18 GeV/c
This letter reports results from the partial wave analysis of the
final state in collisions at 18GeV/c.
Strong evidence is observed for production of two mesons with exotic quantum
numbers of spin, parity and charge conjugation, in the decay
channel . The mass MeV/c^2 and
width MeV/c^2 of the first state are consistent
with the parameters of the previously observed . The second
resonance with mass MeV/c^2 and width MeV/c^2 agrees very well with predictions from theoretical
models. In addition, the presence of is confirmed with mass MeV/c^2 and width MeV/c^2
and a new state, , is observed with mass
MeV/c^2 and width MeV/c^2. The decay properties of
these last two states are consistent with flux tube model predictions for
hybrid mesons with non-exotic quantum numbers
Domain Walls Motion and Resistivity in a Fully-Frustrated Josephson Array
It is identified numerically that the resistivity of a fully-frustrated
Josephson-junction array is due to motion of domain walls in vortex lattice
rather than to motion of single vortices
Confirmation of a pi_1^0 Exotic Meson in the \eta \pi^0 System
The exclusive reaction , at 18 GeV has been studied with a partial wave analysis on a sample
of 23~492 events from BNL experiment E852. A mass-dependent fit
is consistent with a resonant hypothesis for the wave, thus providing
evidence for a neutral exotic meson with , a mass of MeV, and a width of MeV. New
interpretations of the meson exotics in neutral system observed in
E852 and Crystal Barrel experiments are discussed.Comment: p3, rewording the paragraph (at the bottom) about the phase
variations. p4, rewording paragrath "The second method ..." . p4, at the
bottom of paragrath "The third method ..." added consistent with the results
of methods 1 and 2
Low-dose CT for quantitative analysis in acute respiratory distress syndrome
Introduction: The clinical use of serial quantitative computed tomography (CT) to characterize
lung disease and guide the optimization of mechanical ventilation in patients with acute respiratory
distress syndrome (ARDS) is limited by the risk of cumulative radiation exposure and by the
difficulties and risks related to transferring patients to the CT room. We evaluated the effects of
tube current-time product (mAs) variations on quantitative results in healthy lungs and in
experimental ARDS in order to support the use of low-dose CT for quantitative analysis.
Methods: In 14 sheep chest CT was performed at baseline and after the induction of ARDS via
intravenous oleic acid injection. For each CT session, two consecutive scans were obtained
applying two different mAs: 60 mAs was paired with 140, 15 or 7.5 mAs. All other CT parameters
were kept unaltered (tube voltage 120 kVp, collimation 32x0.5 mm, pitch 0.85, matrix 512x512,
pixel size 0.625x0.625 mm ). Quantitative results obtained at different mAs were compared via
Bland-Altman analysis.
Results: Good agreement was observed between 60 mAs and 140 mAs and between 60 mAs and 15
mAs (all biases less than 1%). A further reduction of mAs to 7.5 mAs caused an increase in the bias
of poorly and non aerated tissue (-2.9 and 2.4%, respectively) and determined a significant
widening of the limits of agreement for the same compartments (-10.5 - 4.8 % for poorly aerated
and -5.9 - 10.8% for non aerated tissue). Estimated mean effective dose at 140, 60, 15 and 7.5 mAs
corresponded to 17.8, 7.4, 2.0 and 0.9 millisievert, respectively. Image noise of scans performed at
140, 60, 15 and 7.5 mAs corresponded to 10, 16, 38 and 74 Hounsfield Units, respectively.
Conclusions: A reduction of effective dose up to 70% has been achieved with minimal effects on
lung quantitative results. Low-dose computed tomography provides accurate quantitative results
and could be used to characterize lung compartment distribution and possibly monitor time-course
of ARDS with a lower risk of exposure to ionizing radiation. A further radiation dose reduction is
associated with lower accuracy in quantitative results
Observational Constraints on Teleparallel Dark Energy
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations
(BAO), and Cosmic Microwave Background (CMB) observations to constrain the
recently proposed teleparallel dark energy scenario based on the teleparallel
equivalent of General Relativity, in which one adds a canonical scalar field,
allowing also for a nonminimal coupling with gravity. Using the power-law, the
exponential and the inverse hyperbolic cosine potential ansatzes, we show that
the scenario is compatible with observations. In particular, the data favor a
nonminimal coupling, and although the scalar field is canonical the model can
describe both the quintessence and phantom regimes.Comment: 19 pages, 6 figures, version accepted by JCA
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