1,721,061 research outputs found
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
On the relaxation of some types of Dirichlet minimum problems for unbounded functionals
No full textIn this paper, considered a Borel function g on Rn taking its values in [0,+∞], verifying some weak hypothesis of continuity, such that (domg)^{o}=∅ and domg is convex, we obtain an integral representation result for the lower semicontinuous envelope in the L1(Ω)-topology of the integral functional G0(u0,Ω,u)=∫_{Ω}g(∇u)dx, where u∈W_{loc}^{1,∞}(Rn), u=u0 only on suitable parts of the boundary of Ω that lie, for example, on affine spaces orthogonal to aff(domg), for boundary values u0 satisfying suitable compatibility conditions and Ω is geometrically well situated respect to domg. Then we apply this result to Dirichlet minimum problems
Asymptotic approximation of the solution to the Robin problem in a thick multi-structure
No full textWe consider a mixed boundary value problem for the Poisson equation in a thick multistructure Ωɛ, which is the union of a domain Ω0 and a large number N of ɛ-periodically situated thin rings with variable thickness of order ɛ = O(N-1): The Robin conditions are given on the lateral boundaries of the thin rings. The leading terms of the asymptotic expansion for the solution are constructed and the corresponding estimates in the Sobolev space H1(Ωɛ) are proved (as ɛ-> 0) with minimal conditions for the right-hand side
Metal and molecule cooling in simulations of structure formation
No full textCooling is the main process leading to the condensation of gas in the dark matter potential wells and consequently to star and structure formation. In a metal-free environment, the main available coolants are H, He, H2 and HD; once the gas is enriched with metals, these also become important in defining the cooling properties of the gas. We discuss the implementation in GADGET-2 of molecular and metal cooling at temperatures lower than 104 K, following the time-dependent properties of the gas and pollution from stellar evolution. We have checked the validity of our scheme by comparing the results of some test runs with previous calculations of cosmic abundance evolution and structure formation, finding excellent agreement. We have also investigated the relevance of molecule and metal cooling in some specific cases, finding that inclusion of HD cooling results in a higher clumping factor of the gas at high redshifts, while metal cooling at low temperatures can have a significant impact on the formation and evolution of cold objects
A Tabulation of Absorbed Dose per Unit Fluence Conversion Coefficients for Slab Phantoms of Three Tissue Equivalent Materials for Electron Energies from 70 keV to 10 MeV
No full textOptimal boundary control problem for ill-posed elliptic equation in domains with rugous boundary. Existence result and optimality conditions
No full textThe main purpose is the study of optimal control problem in a domain with rough boundary for the mixed Dirichlet-Neumann boundary value problem for the strongly nonlinear elliptic equation with exponential nonlinearity. A density of surface traction u acting on a part of rough boundary is taken as a control. The optimal control problem is to minimize the discrepancy between a given distribution and the current system state. We deal with such case of nonlinearity when we cannot expect to have a solution of the state equation for a given control. After having defined a suitable functional class in which we look for solutions, we prove the consistency of the original optimal control problem and show that it admits a unique optimal solution. Then we derive a first-order optimality system assuming the optimal solution is slightly more regular
On Optimal L1-Control in Coefficients for Quasi-Linear Dirichlet Boundary Value Problems with BMO-Anisotropic p-Laplacian
No full textWe study an optimal control problem for a quasi-linear elliptic equation with anisotropic p-Laplace operator in its principal part and L1-control in coefficient of the low-order term. We assume that the matrix of anisotropy belongs to BMO-space. Since we cannot expect to have a solution of the state equation in the classical Sobolev space, we introduce a suitable functional class in which we look for solutions and prove existence of optimal pairs using an approximation procedure and compactness arguments in variable spaces
Absorbed Dose per Unit Fluence for Tissue Equivalent Slab Phantoms for Electrons from 50 keV to 10 MeV
No full textGoing 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
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