96 research outputs found
Constraining the dark energy with galaxy clusters X-ray data
The equation of state characterizing the dark energy component is constrained
by combining Chandra observations of the X-ray luminosity of galaxy clusters
with independent measurements of the baryonic matter density and the latest
measurements of the Hubble parameter as given by the HST key project. By
assuming a spatially flat scenario driven by a "quintessence" component with an
equation of state we place the following limits on the
cosmological parameters and : (i) and (1) if the
equation of state of the dark energy is restricted to the interval (\emph{usual} quintessence) and (ii) and
() if violates the null energy condition and assume values (\emph{extended} quintessence or ``phantom'' energy). These results are in
good agreement with independent studies based on supernovae observations,
large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe
Current lookback time-redshift bounds on dark energy
We investigate observational constraints on dark energy models from lookback
time (LT) estimates of 32 old passive galaxies distributed over the redshift
interval . To build up our LT sample we combine the age
measurements for these 32 objects with estimates of the total age of the
Universe, as obtained from current CMB data. We show that LT data may provide
bounds on the cosmological parameters with accuracy competitive with type Ia
Supernova methods. In order to break possible degeneracies between models
parameters, we also discuss the bounds when our lookback time versus redshift
sample is combined with with the recent measurement of the baryonic acoustic
oscillation peak and the derived age of the Universe from current CMB
measurements.Comment: 6 pages, 4 figures, LaTe
Observational constraints on the time-dependence of dark energy
One of the most important questions nowadays in physics concerns the nature
of the so-called dark energy. It is also a consensus among cosmologists that
such a question will not be answered on the basis only of observational data.
However, it is possible to diminish the range of possibilities for this dark
component by comparing different dark energy scenarios and finding which models
can be ruled out by current observations. In this paper, by asssuming three
distinct parametrizations for the low-redshift evolution of the dark energy
equation of state (EOS), we consider the possibility of discriminating between
evolving dark energy and CDM models from a joint analysis involving
the most recent radio sources gravitational lensing sample, namely, the Cosmic
All Sky Survey (CLASS) statistical data and the recently published \emph{gold}
SNe Ia sample. It is shown that this particular combination of observational
data restricts considerably the dark energy parameter space, which enables
possible distinctions between time-dependent and constant EOS's.Comment: 5 pages, 1 figure, to appear in Nuclear Physics
Astrophysically important 19Ne states studied with the 2H(18F, α+15 O)n reaction
The nuclear structure of 19Ne near the proton threshold is of interest for understanding the rates of proton-induced reactions on 18F in novae. Analogues for several states in the mirror nucleus 19F have not yet been identified in 19Ne indicating the level structure of 19Ne in this region is incomplete. The 18F(d,n)19Ne and 18F(d, p)19F reactions have been measured simultaneously at Ec.m. = 14.9 MeV. The experiments were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) of Oak Ridge National Laboratory (ORNL) by bombarding a 720-μg/cm2 CD2 target with a radioactive 18F beam. The 19Ne states of interest near the proton threshold decay by breakup into a and 15O particles. These decay products were detected in coincidence with position-sensitive E-ΔE silicon telescopes. The α and 15N particles from the break up of the mirror nucleus 19F were also measured with these detectors. Particle identification, coincidence, and Q-value requirements enable us to distinguish the reaction of interest from other reactions. The reconstruction of relative energy of the detected particles reveals the excited states of 19Ne and 19F which are populated. The neutron (proton) angular distributions for states in 19Ne (19F) were extracted using momentum conservation. The observed states in 19Ne and 19F will be presented
Early- Onset Stroke and Vasculopathy Associated with Mutations in ADA2
Adenosine deaminase 2 (ADA2) is an enzyme involved in purine metabolism and a growth factor that influences the development of endothelial cells and leukocytes. This study shows that defects in ADA2 cause recurrent fevers, vascular pathologic features, and mild immunodeficiency. Patients with autoinflammatory disease sometimes present with clinical findings that encompass multiple organ systems.(1) Three unrelated children presented to the National Institutes of Health (NIH) Clinical Center with intermittent fevers, recurrent lacunar strokes, elevated levels of acute-phase reactants, livedoid rash, hepatosplenomegaly, and hypogammaglobulinemia. Collectively, these findings do not easily fit with any of the known inherited autoinflammatory diseases. Hereditary or acquired vascular disorders can have protean manifestations yet be caused by mutations in a single gene. Diseases such as the Aicardi-Goutieres syndrome,(2),(3) polypoidal choroidal vasculopathy,(4) sickle cell anemia,(5) livedoid vasculopathy,(6) and the small-vessel vasculitides(7),(8) are examples of systemic ...</p
S-wave scattering lengths for the Be 7 +p system from an R-matrix analysis
The astrophysical S factor for the radiative proton capture reaction on Be7 (S17) at low energies is affected by the s-wave scattering lengths. We report the measurement of elastic and inelastic scattering cross sections for the Be7+p system in the center-of-mass energy range 0.474-2.740 MeV and center-of-mass angular range 70-150. A radioactive Be7 beam produced at Oak Ridge National Laboratory's (ORNL) Holifield Radioactive Ion Beam Facility was accelerated and bombarded a thin polypropylene (CH2)n target. Scattered ions were detected in the segmented Silicon Detector Array. Using an R-matrix analysis of ORNL and Louvain-la-Neuve cross-section data, the s-wave scattering lengths for channel spins 1 and 2 were determined to be 17.34-1.33+1.11 and -3.18-0.50+0.55 fm, respectively. The uncertainty in the s-wave scattering lengths reported in this work is smaller by a factor of 5-8 compared to the previous measurement, which may reduce the overall uncertainty in S17 at zero energy. The level structure of B8 is discussed based upon the results from this work. Evidence for the existence of 0+ and 2+ levels in B8 at 1.9 and 2.21 MeV, respectively, is observed
Transmission of porcine circovirus 2 (PCV2) by semen and viral distribution in different piglet tissues
Self-emulsifying therapeutic system: a potential approach for delivery of lipophilic drugs
Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station
A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.</p
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