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In this paper we presentcrashα, the first radiative transfer code for cosmological application that follows the parallel propagation of Lyα and ionizing photons.crashα is a version of the continuum radiative transfer codecrash with a new algorithm to follow the propagation of Lyα photons through a gas configuration whose ionization structure is evolving. The implementation introduces the time evolution for Lyα photons (a feature commonly neglected in line radiative transfer codes) and, to reduce the computational time needed to follow each scattering, adopts a statistical approach to the Lyα treatment by making extensive use of pre-compiled tables. These tables describe the physical characteristics of a photon escaping from a gas cell where it was trapped by scattering as a function of the gas temperature/density and of the incoming photon frequency. With this statistical approach we experience a drastic increase of the computational speed and, at the same time, an excellent agreement with the full Lyα radiative transfer computations of the codemclyα. We find that the emerging spectra keep memory of the ionization history which generates a given ionization configuration of the gas and, to properly account for this effect, a self-consistent joint evolution of line and ionizing continuum radiation as implemented incrashα is necessary. A comparison between the results from our code and from Lyα scattering alone on a fixed H i density field shows that the extent of the difference between the emerging spectra depends on the particular configuration considered, but it can be substantial and can thus affect the physical interpretation of the problem at hand. These differences should furthermore be taken into account when computing the impact of the Lyα radiation on e.g. the observability of the 21-cm line from neutral hydrogen at epochs preceding complete reionization. [ABSTRACT FROM AUTHOR]

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this ‘dark energy’ corresponds to a ‘cosmological constant’, perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter β = 0.70 ± 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 ± 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift. [ABSTRACT FROM AUTHOR]

Background Over the 1980s several education campaigns for prevention and early diagnosis of cutaneous melanoma have been reported from various parts of the world. Aim To improve incidence and prognosis of cutaneous melanoma in 1985 we started, in our area, an information and health education campaign aimed at identifying precursors of melanoma (congenital melanocytic nevi), suspicious lesions (changing moles) and subjects with increased risk of melanoma. Method Precursors and suspicious lesions were promptly removed, and high-risk persons entered the follow-up program. Result As a general effect of these activities the percentage of thin melanomas diagnosed in our division after 1985 increased from 25 to 37. Conclusion We believe that education campaigns and screening of a targeted population. particularly of subjects presenting increased risk of melanoma. may be helpful in the early diagnosis of melanoma. [ABSTRACT FROM AUTHOR]