440 research outputs found
The gamma ray background from large scale structure formation
Hierarchical clustering of dark matter halos is thought to describe well the
large scale structure of the universe. The baryonic component of the halos is
shock heated to the virial temperature while a small fraction of the energy
flux through the shocks may be energized through the first order Fermi process
to relativistic energy per particle. It has been proposed that the electrons
accelerated in this way may upscatter the photons of the universal microwave
background to gamma ray energies and indeed generate a diffuse background of
gamma rays that compares well to the observations. In this paper we calculate
the spectra of the particles accelerated at the merger shocks and re-evaluate
the contribution of structure formation to the extragalactic diffuse gamma ray
background (EDGRB), concluding that this contribution adds up to at most 10% of
the observed EDGRB.Comment: 19 pages, 4 figures. A few references and some comments added.
Version in press in Astropart. Phy
A class of neutral to the right priors induced by superposition of beta processes
A random distribution function on the positive real line which belongs to the class of neutral to the right priors is defined. It corresponds to the superposition of independent beta processes at the cumulative hazard level. The definition is constructive and starts with a discrete time process with random probability masses obtained from suitably defined products of independent beta random variables. The continuous time version is derived as the corresponding infinitesimal weak limit and is described in terms of completely random measures. It takes the interpretation of the survival distribution resulting from independent competing failure times. We discuss prior specification and illustrate posterior inference on a real data example.Bayesian nonparametrics; beta process; beta-Stacy process; completely random measures; neutral to the right priors; survival analysis
Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study
Quantitative, non-invasive and local measurements of arterial mechanical
properties could be highly beneficial for early diagnosis of cardiovascular
disease and follow up of treatment. Arterial shear wave elastography (SWE)
and wave velocity dispersion analysis have previously been applied to
measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D)
vary with age and pathology and may influence the shear wave propagation.
Nevertheless, the effect of arterial geometry in SWE has not yet been
systematically investigated. In this study the influence of geometry on the
estimated mechanical properties of plates (h = 0.5ā3 mm) and hollow
cylinders (h = 1, 2 and 3 mm, D = 6 mm) was assessed by experiments in
phantoms and by finite element method simulations. In addition, simulations
in hollow cylinders with wall thickness difficult to achieve in phantoms
were performed (h = 0.5ā1.3 mm, D = 5ā8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency
range 200ā1000 Hz and showed good agreement (R2 = 0.80 Ā± 0.07 for plates
and R2 = 0.82 Ā± 0.04 for hollow cylinders). Wall thickness had a larger effect
than diameter on the dispersion curves, which did not have major effects above
400 Hz. An underestimation of 0.1ā0.2 mm in wall thickness introduces an
error 4ā9 kPa in hollow cylinders with shear modulus of 21ā26 kPa. Therefore,
wall thickness should correctly be measured in arterial SWE applications for
accurate mechanical properties estimation
Prulifloxacin: a brief review of its potential in the treatment of acute exacerbation of chronic bronchitis
Exacerbations of chronic bronchitis (AECB) are a major cause of morbidity and mortality in patients with chronic obstructive pulmonary disease (COPD), and their impact on public health is increasing. The new fluoroquinolones have an excellent spectrum providing cover for the most important respiratory pathogens, including atypical and ātypicalā pathogens. Not surprisingly, different guidelines have inserted these agents among the drugs of choice in the empirical therapy of AECB. The pharmacokinetic and dynamic properties of the new fluoroquinolones have a significant impact on their clinical and bacteriological efficacy. They cause a concentration-dependent killing with a sustained post-antibiotic effect. This review discusses the most recent data on the new fluoroquinolone prulifloxacin and critically analyses its activity and safety in the management of AECB
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