1,721,249 research outputs found
Combined retrograde-antegrade external iliac artery occlusion recanalization through collaterals: Description of a new technique
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UV background fluctuations traced by metal ions at z ≈ 3
No full textHere we investigate how LyC-opaque systems present in the intergalactic medium at z ≈ 3 can distort the spectral shape of a uniform UV background (UVB) through radiative transfer (RT) effects. With this aim in mind, we perform a multifrequency RT simulation through a cosmic volume of 10 h-1 cMpc scale polluted by metals, and self-consistently derive the ions of all the species. The UVB spatial fluctuations are traced by the ratio of He II and H I column density, η, and the ratio of C IV and Si IV optical depths, ξ . We find that: (i) η spatially fluctuates through overdense systems (Δ) with statistically significant deviations δη > 25 per cent in 18 per cent of the volume; (ii) same fluctuations in ξ are also present in 34 per cent of the enriched domain (only 8 per cent of the total volume) and derive from a combination of RT induced effects and in-homogeneous metal enrichment, both effective in systems with Δ > 1.5
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Radiative transfer of ionizing radiation through gas and dust: the stellar source case
No full textWe present a new dust extension to the Monte Carlo radiative transfer code CRASH, which enables it to simulate the propagation of ionizing radiation through mixtures of gas and dust. The newcode is applied to study the impact of dust absorption on idealized galacticHII regions and on small-scale reionization. We find that HII regions are reduced in size by the presence of dust, while their inner temperature and ionization structure remain largely unaffected. In the small-scale reionization simulation, dust hardens ionization fronts and delays the overlap of ionized bubbles. This effect is found to depend only weakly on the assumed abundance of dust in underdense regions
Physics and metaphysics
No full textIn the recent debate scholars again discuss vividly the relation between physics and metaphysics (see DiSalle, 2006, pp. 57-58, Ladyman and Ross, 2007, Calosi, 2010 and Dorato, 2010). This is also consequence of the diffusion in contemporary philosophy of a metaphysical way of thinking, which either does not consider results of empirical sciences, or it uses them in a partial and distort manner (Lowe 2002 and 2006, Sider, 2001 and Varzi, 2001). The issue according to which there is a metaphysics before empirical sciences is an ancient new, if it already is in Aristotle (Met. E, 1026a, 10ss.), when he states that there is a proto-episteme (first science) concerning what is motionless and separated. Indeed Aristotle pays attention in avoiding that the proto-episteme neither coordinates nor contains in itself all the other disciplines . It follows that his “physics” – in our terms physics, biology and psychology – could not be deduced from the first science. In the Cartesian perspective, on the contrary, physics is the trunk of philosophy’s tree, whose roots are metaphysics (Descartes, Principes, 1647, AT, IX - 2, 14). Hence, in a certain sense, physics must be derived from metaphysics. Contemporary perspective is different. Scholars maintain that metaphysics is a conceptual (a priori) activity independent of physics. Nevertheless this does not mean the latter is derivable from the former. Ladyman and Ross (2007) and Dorato (2010) are against the contemporary perspective
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