100 research outputs found
Nucleosynthesis Constraints on a Massive Gravitino in Neutralino Dark Matter Scenarios
The decays of massive gravitinos into neutralino dark matter particles and
Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may
alter the primordial light-element abundances. We present here details of a new
suite of codes for evaluating such effects, including a new treatment based on
PYTHIA of the evolution of showers induced by hadronic decays of massive,
unstable particles such as a gravitino. We also develop an analytical treatment
of non-thermal hadron propagation in the early universe, and use this to derive
analytical estimates for light-element production and in turn on decaying
particle lifetimes and abundances. We then consider specifically the case of an
unstable massive gravitino within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM). We present upper limits on its
possible primordial abundance before decay for different possible gravitino
masses, with CMSSM parameters along strips where the lightest neutralino
provides all the astrophysical cold dark matter density. We do not find any
CMSSM solution to the cosmological Li7 problem for small m_{3/2}. Discounting
this, for m_{1/2} ~ 500 GeV and tan beta = 10 the other light-element
abundances impose an upper limit m_{3/2} n_{3/2}/n_\gamma < 3 \times 10^{-12}
GeV to < 2 \times 10^{-13} GeV for m_{3/2} = 250 GeV to 1 TeV, which is similar
in both the coannihilation and focus-point strips and somewhat weaker for tan
beta = 50, particularly for larger m_{1/2}. The constraints also weaken in
general for larger m_{3/2}, and for m_{3/2} > 3 TeV we find a narrow range of
m_{3/2} n_{3/2}/n_\gamma, at values which increase with m_{3/2}, where the Li7
abundance is marginally compatible with the other light-element abundances.Comment: 74 pages, 40 Figure
Barium effect on germination, plant growth, and antioxidant enzymes in Cucumis sativus L. plants
Barium (Ba) is a nonessential element that can cause several deleterious effects in
most organisms. Elevated Ba concentrations can be toxic for plants and may affect
growth and disturbances in homeostasis. This study aimed to evaluate the Ba stress,
the plant-tolerance limits, and the detoxification strategy adopted by Cucumis sativus
L. The effect of Ba on seed's germination and vegetative development of this species
was evaluated. For germination test, different Ba concentrations were used (0, 200,
500, 1,000, and 2,000 μM). Results showed that germination was stimulated with
500 and 2,000 µM of Ba. The toxicity effect on plant development was studied by
treating the plants with increasing doses of Ba (100, 200, 300, and 500 μM) during
45 days. Shoot and root dry biomass production decreased significantly with elevated
Ba concentrations, although water content enhanced in the roots. The concentration
of Ba, 500 µM, induced high Ba accumulation in shoots and roots (9 times higher
than in the control plants). Moreover, results showed that catalase, guaiacol peroxidase, and ascorbate peroxidase activities were stimulated in the different tissues of
cucumber plants which highlight the occurring of an oxidative damage through Ba
treatments and the involvement of the plant enzymatic antioxidant defense system
A Bitter Pill: The Primordial Lithium Problem Worsens
The lithium problem arises from the significant discrepancy between the
primordial 7Li abundance as predicted by BBN theory and the WMAP baryon
density, and the pre-Galactic lithium abundance inferred from observations of
metal-poor (Population II) stars. This problem has loomed for the past decade,
with a persistent discrepancy of a factor of 2--3 in 7Li/H. Recent developments
have sharpened all aspects of the Li problem. Namely: (1) BBN theory
predictions have sharpened due to new nuclear data, particularly the
uncertainty on 3He(alpha,gamma)7Be, has reduced to 7.4%, and with a central
value shift of ~ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic
baryon density with an uncertainty reduced to 2.7%. (3) Observations of
metal-poor stars have tested for systematic effects, and have reaped new
lithium isotopic data. With these, we now find that the BBN+WMAP predicts 7Li/H
= (5.24+0.71-0.67) 10^{-10}. The Li problem remains and indeed is exacerbated;
the discrepancy is now a factor 2.4--4.3 or 4.2sigma (from globular cluster
stars) to 5.3sigma (from halo field stars). Possible resolutions to the lithium
problem are briefly reviewed, and key nuclear, particle, and astronomical
measurements highlighted.Comment: 21 pages, 4 figures. Comments welcom
Hard X-ray emission from the Galactic ridge
We present results of a study of the Galactic ridge X-ray emission (GRXE) in
hard X-rays performed with the IBIS telescope aboard INTEGRAL. The imaging
capabilities of this coding aperture telescope make it possible to account for
the flux from bright Galactic point sources whereas the wide field of view
permits to collect large flux from the underlying GRXE. Extensive study of the
IBIS/ISGRI detector background allowed us to construct a model that predicts
the detector count rate with % accuracy in the energy band 17-60 keV.
The derived longitude and latitude profiles of the ridge emission are in good
agreement with the Galactic distribution of stars obtained from infrared
observations. This, along with the measured hard X-ray spectrum of the Galactic
ridge emission strongly indicates its stellar origin. The derived unit stellar
mass emissivity of the ridge in the energy band 17-60 keV, \lummass (assuming a bulge mass of )
agrees with that of local (in the Solar neigborhood) accreting magnetic white
dwarf binaries - dominant contributors to the GRXE at these energies. In
addition, the shape of the obtained GRXE spectrum can be used to determine the
average mass of white dwarfs in such systems in the Galaxy as \sim0.5
M_{\sun}. The total hard X-ray luminosity of the GRXE is \lum in the 17--60 keV band. At energies 70--200 keV
no additional contribution to the total emission of the Galaxy apart from the
detected point sources is seen.Comment: 13 pages, 19 figures, submitted to Astronomy and Astrophysic
X-ray micro-tomography and pore network modeling of single-phase fixed-bed reactors.
A three-dimensional (3D) irregular and unstructured pore network was built using local topological and geometrical properties of an isometric bead pack imaged by means of a high-resolution X-ray computed micro-tomography technique. A pore network model was developed to analyze the 3D laminar/inertial(non-Darcy) flows at the mesoscopic (pore level) and macroscopic (after ensemble-averaging) levels. The non-linear laminar flow signatures were captured at the mesoscale on the basis of analogies with contraction and expansion friction losses. The model provided remarkably good predictions of macroscopic frictional loss gradient in Darcy and non-Darcy regimes with clear-cut demarcation using channel-based Reynolds number statistics. It was also able to differentiate contributions due to pore and channel linear losses, and contraction/expansion quadratic losses. Macroscopic mechanical dispersion was analyzed in terms of retroflow channels, and transverse and longitudinal Péclet numbers. The model qualitatively retrieved the Péclet-Reynolds scaling law expected for heterogeneous networks with predominance of mechanical dispersion. Advocated in watermark is the potential of pore network modeling to build a posteriori constitutive relations for the closures of the more conventional macroscopic Euler approaches to capture more realistically single-phase flow phenomena in fixed-bed reactor applications in chemical engineering
Impact of renal impairment on atrial fibrillation: ESC-EHRA EORP-AF Long-Term General Registry
Background: Atrial fibrillation (AF) and renal impairment share a bidirectional relationship with important pathophysiological interactions. We evaluated the impact of renal impairment in a contemporary cohort of patients with AF. Methods: We utilised the ESC-EHRA EORP-AF Long-Term General Registry. Outcomes were analysed according to renal function by CKD-EPI equation. The primary endpoint was a composite of thromboembolism, major bleeding, acute coronary syndrome and all-cause death. Secondary endpoints were each of these separately including ischaemic stroke, haemorrhagic event, intracranial haemorrhage, cardiovascular death and hospital admission. Results: A total of 9306 patients were included. The distribution of patients with no, mild, moderate and severe renal impairment at baseline were 16.9%, 49.3%, 30% and 3.8%, respectively. AF patients with impaired renal function were older, more likely to be females, had worse cardiac imaging parameters and multiple comorbidities. Among patients with an indication for anticoagulation, prescription of these agents was reduced in those with severe renal impairment, p <.001. Over 24 months, impaired renal function was associated with significantly greater incidence of the primary composite outcome and all secondary outcomes. Multivariable Cox regression analysis demonstrated an inverse relationship between eGFR and the primary outcome (HR 1.07 [95% CI, 1.01–1.14] per 10 ml/min/1.73 m2 decrease), that was most notable in patients with eGFR <30 ml/min/1.73 m2 (HR 2.21 [95% CI, 1.23–3.99] compared to eGFR ≥90 ml/min/1.73 m2). Conclusion: A significant proportion of patients with AF suffer from concomitant renal impairment which impacts their overall management. Furthermore, renal impairment is an independent predictor of major adverse events including thromboembolism, major bleeding, acute coronary syndrome and all-cause death in patients with AF
- …