Biomedical subjects
Publications and source records attributed to F J Uribe.
In this work we show that moment methods devised to solve the Boltzmann kinetic equation for a simple gas exhibit some inconsistencies. This puzzle, which also appears for the Chapman-Enskog method, is solved resorting to a perturbative expansion in the Knudsen number, thus allowing for a clear way to arrive at a closure condition.
We show that while Eu's claim is true that we made a mistake regarding the asymptotic behavior of his theory is true, the correct asymptotic behavior cannot have a physical meaning. We analyze in more detail his theory for a dilute gas of rigid spheres, and show that in some cases it predicts a negative value of the xx component of the pressure tensor.
The Grad ten-moment approximation (no heat flux) is analyzed for cylindrical symmetry in a stationary situation in which the gradients of the fluxes are assumed to be small. We show that if the collision term in the transport equation, resulting from the ten-moment approximation, is linearized in the fluxes, we can obtain a viscosity (etal) that depends on the gradient of the velocity with the correct limiting behavior for small gradients. The nonlinear contribution of the fluxes to the collision term are then taken into account to derive an expression for the viscosity (eta(nl)) as a function of the gradient of the velocity. A comparison between etal and eta(nl) is performed finding that the maximum percentage deviation between them is 0.52% when the gradient of the hydrodynamic velocity is positive, but when the gradient is negative the situation changes dramatically.
Two recent works have shown that at small Knudsen number (K) the pressure and temperature profiles in plane Poiseuille flow exhibit a different qualitative behavior from the profiles obtained by the Navier-Stokes equations. Tij and Santos [J. Stat. Phys. 76, 1399 (1994)] used the Bhatnagar-Gross-Kook model to show that the temperature profile is bimodal and the pressure profile is nonconstant. Malek-Mansour, Baras, and Garcia [Physica A 240, 255 (1997)] qualitatively confirmed these predictions in computer experiments using the direct simulation Monte Carlo method (DSMC). In this paper we compare the DSMC measurements of hydrodynamic variables and non-equilibrium fluxes with numerical solutions of the Burnett equations. Given that they are in better agreement with molecular-dynamics simulations [E. Salomons and M. Mareschal, Phys. Rev. Lett. 69, 269 (1992)] of strong shock waves than Navier-Stokes [F. J. Uribe, R. M. Velasco, and L. S. García-Colín, Phys. Rev. Lett. 81, 2044 (1998)], and that they are second order in Knudsen number suggests that the Burnett equations may provide a better description for large K. We find that for plane Poiseuille flow the Burnett equations do not predict the bimodal temperature profile but do recover many of the other anomalous features (e.g., nonconstant pressure and nonzero parallel heat flux).
A 4.5-mm filarial worm was removed from the anterior chamber of the left eye of a 56-year-old man who had lost the sight in the right eye due to trauma some years earlier. The worm was removed intact through an upper scleral incision with a corneal based flap. Within 2 months vision was normal. The worm was identified as a sexually mature male of an undescribed species of Loaina Eberhard and Orihel 1984, a genus related to Loa and Dirofilaria.