33,776 research outputs found
Central Schemes for Porous Media Flows
We are concerned with central differencing schemes for solving scalar
hyperbolic conservation laws arising in the simulation of multiphase flows in
heterogeneous porous media. We compare the Kurganov-Tadmor, 2000 semi-discrete
central scheme with the Nessyahu-Tadmor, 1990 central scheme. The KT scheme
uses more precise information about the local speeds of propagation together
with integration over nonuniform control volumes, which contain the Riemann
fans. These methods can accurately resolve sharp fronts in the fluid
saturations without introducing spurious oscillations or excessive numerical
diffusion. We first discuss the coupling of these methods with velocity fields
approximated by mixed finite elements. Then, numerical simulations are
presented for two-phase, two-dimensional flow problems in multi-scale
heterogeneous petroleum reservoirs. We find the KT scheme to be considerably
less diffusive, particularly in the presence of high permeability flow
channels, which lead to strong restrictions on the time step selection;
however, the KT scheme may produce incorrect boundary behavior
Search for Spatial Structures at Scales Z~1. III. The Effect of Lensing on QSO ?
We carried out a search for peak inhomogeneities in the distribution of
matter - namely clumps and voids, within the range Z ~ 1-3. We used a new
method, based on the lensing of quasars by a combination of lenses, belonging
to the above sought inhomogeneities in the matter distribution. This work
confirms the evidence of the existence of inhomogeneities found by us earlier -
of a clump (superattractor N.1), and of a void (supervoid). Besides, the
existence of a new gigantic clump (superattractor N.2) was also discovered at Z
~ 3. These clumps could well serve as centers of the Bose-condensation in the
early Universe; in particular - as Anselm's arion condensate, which leads to
the formation of quasiperiodic structures with a period p ~ 100-200 Mpc.Comment: 22 pages, 2 figures, 6 tables. submitted to Astrophys.& Space Sc
Effect of dithiocarbamate thiram on Wistar rat growth plate and articular cartilage
Avaliou-se o efeito do tirame, ditiocarbamato largamente utilizado na agricultura como antifúngico e repelente de roedores, na ossificação endocondral de mamíferos, usando, como modelo, ratos Wistar. Não foram observadas lesões na cartilagem articular, nem nas placas de crescimento, o que pode ser atribuído à dose utilizada e à duração do ensaio. A diminuição da altura da placa de crescimento nos animais aos quais foi administrado o tirame parece traduzir o atraso verificado no crescimento em geral, e não um efeito específico na cartilagem, uma vez que as diferentes zonas da placa epifisária mantiveram as proporções dos animais do grupo-controle. Embora não tenham sido verificados, no presente trabalho, os efeitos registrados para outras espécies nos tecidos cartilaginosos, sugere-se a avaliação dos efeitos crónicos do tirame no crescimento e no desenvolvimento dos ossos longos em mamíferos
85% efficiency for cw frequency doubling from 1.08 to 0.54 μm
Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 μm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement
Some addition formulae for Abelian functions for elliptic and hyperelliptic curves of cyclotomic type
We discuss a family of multi-term addition formulae for Weierstrass functions
on specialized curves of genus one and two with many automorphisms. In the
genus one case we find new addition formulae for the equianharmonic and
lemniscate cases, and in genus two we find some new addition formulae for a
number of curves, including the Burnside curve.Comment: 19 pages. We have extended the Introduction, corrected some typos and
tidied up some proofs, and inserted extra material on genus 3 curve
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