994,453 research outputs found
Effects of viscous dissipation and boundary conditions on forced convection in a channel occupied by a saturated porous medium
Forced convection with viscous dissipation in a parallel plate channel filled by a saturated porous medium is investigated numerically. Three different viscous dissipation models are examined. Two different sets of wall conditions are considered: isothermal and isoflux. Analytical expressions are also presented for the asymptotic temperature profile and the asymptotic Nusselt number. With isothermal walls, the Brinkman number significantly influences the developing Nusselt number but not the asymptotic one. At constant wall heat flux, both the developing and the asymptotic Nusselt numbers are affected by the value of the Brinkman number. The Nusselt number is sensitive to the porous medium shape factor under all conditions considered
Effects of viscous dissipation and boundary conditions on forced convection in a channel occupied by a saturated porous medium
Forced convection with viscous dissipation in a parallel plate channel filled by a saturated porous medium is investigated numerically. Three different viscous dissipation models are examined. Two different sets of wall conditions are considered: isothermal and isoflux. Analytical expressions are also presented for the asymptotic temperature profile and the asymptotic Nusselt number. With isothermal walls, the Brinkman number significantly influences the developing Nusselt number but not the asymptotic one. At constant wall heat flux, both the developing and the asymptotic Nusselt numbers are affected by the value of the Brinkman number. The Nusselt number is sensitive to the porous medium shape factor under all conditions considered
Stacks of uniform cyclic covers of curves and their Picard groups
We study the stack B_{h,g,n} of uniform cyclic covers of degree n between
smooth curves of genus h and g and, for h >> g, present it as an open substack
of a vector bundle over the universal Jacobian stack of M_g. We use this
description to compute the integral Picard group of B_{h,g,n}, showing that it
is generated by tautological classes of B_{h,g,n}.Comment: v3: (long overdue) final versio
Semi-infinite optimization: Structure and stability of the feasible set
The problem of the minimization of a functionf: ℝn→ℝ under finitely many equality constraints and perhaps infinitely many inequality constraints gives rise to a structural analysis of the feasible setM[H, G]={x∈ℝn¦H(x)=0,G(x, y)≥0,y∈Y} with compactY⊂ℝr. An extension of the well-known Mangasarian-Fromovitz constraint qualification (EMFCQ) is introduced. The main result for compactM[H, G] is the equivalence of the topological stability of the feasible setM[H, G] and the validity of EMFCQ. As a byproduct, we obtain under EMFCQ that the feasible set admits local linearizations and also thatM[H, G] depends continuously on the pair (H, G). Moreover, EMFCQ is shown to be satisfied generically
On homomorphism spaces of metrizable groups
For two not necessarily commutative topological groups G and T, let H(G,T)
denote the space of all continuous homomorphisms from G to T with the
compact-open topology. We prove that if G is metrizable and T is compact then
H(G,T) is a k-space. As a consequence we obtain that if G_1 is a dense subgroup
of G then H(G_1,T) is homeomorphic to H(G,T), and if G is separable h-complete,
then the natural map G --> C(H(G,T),T) is open onto its image.Comment: v3 (revision of March 17, 2003): slight changes in general, the proof
of the last theorem has been rewritte
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