César Nieto

Theoretic rates of potential tissue donation in a university hospital

BACKGROUND Catalonia and Spain have the highest rates of organ donation in the world. The National Transplant Organization studied the rates of potential and actual donors through the Quality Guarantee Program, but this research did not estimate potential tissue donation (PTD). The aim of this study was to define the theoretical rates of PTD at our university hospital in order to assess the main factors that exerted the greatest influence on tissue donation (TD). METHODS We prospectively studied all deaths from May 1, of 2001 to May 31, of 2002 using a specific protocol. The selection of cornea, vessels, skin, and bone had been established by the recommendations of the Spanish Association of Tissue Banks (AEBT). We considered each deceased person as a PTD when there was no medical contraindication (MC), and obtained blood samples for serologic determinations. RESULTS Among the 1960 deaths, 1444 (73.6%) displayed MC for TD. Only 516 (26.3%) patients were evaluated as PTD cases. Two hundred twenty-two cases (65%) were rejected due to lack of blood samples for serologic determination. The remaining 294 PTD cases were considered: family refusal of TD in 120 (40%) and consent in 174 (60%). All were corneal donors; 46 (26%) had been multitissue donors (20 vessels, 35 skin, and 30 bones) including 26 (56.5%) who were also organ donors. CONCLUSIONS PTD cases at a university hospital represented about 25% of deaths but only 30% of PTDs actually became donors.

Boundary element solution of thermal creeping flow in a nano single mixer

In order to employ continuum models in the analysis of the flow behaviour of a viscous Newtonian fluid in micro scale devices, it is necessary to consider at the wall surfaces appropriate slip boundary conditions instead of the classical non-slip condition. The slip behaviour in the case of micro fluid flow of rarefied gases is associated with the combined effect of reduction in momentum transfer due to the reduction in the number of molecules (shear creep) and the thermal creep or transpiration, which as a consequence of inequalities in temperatures, forces the fluid to slide over a surface from colder to hotter regions. In this work a boundary integral equation formulation for Stokes slip flow, based on the normal and tangential projection of the Green’s integral representational formulae for the Stokes velocity field, which directly incorporates into the integral equations the local tangential shear rate and heat flux at the wall surfaces, is presented. The tangential heat flux is evaluated in terms of the tangential gradient of the temperature integral representational formulae presenting singularity of the Cauchy type, which are removed by the use of an auxiliary field. These formulations are used to simulate a Single rotor mixer and analyze the combined effect of both shear and thermal creep effects over mixer performance.

Critical Sources of Aerodynamic Resistance in a Medium Distance Urban Train: a CFD approach

In this article, the aerodynamic behavior of a commuter train operating at average speeds is evaluated, by means of computational fluid dynamics; the main goal is to identify the main aerodynamic drag sources. The study consist of two phases; the first one is the aerodynamic analysis of the current train using certain mesh parameters and the turbulence model – to obtain a real condition of operation, with this analysis was obtained the total power consumption corresponding to the value of the aerodynamic drag thrown by the simulation process. These results were qualitatively compared with experimental data in order to validate the simulation process. The second part is the identification and analysis of the main aerodynamic drag zones that the Metro system generate in its interaction with the air, to make a preliminary evaluation of a few modifications that allowed the reduction in the drag in these critical

Boundary Integral Equation Approach for Stokes Flow with Non‐Linear Slip Boundary Condition

The numerical simulation of microfluid flow through the solution of governing equations based on continuum models has to be done under the consideration of appropriate slip boundary conditions to account for the velocity jump at the solid‐fluid interface. The linear model proposed by Navier states a relation between the tangential shear rate and the fluid‐wall velocity differences and has been successfully used in reproducing the characteristics of many types of flows (e.g. slit flows, rotating curved mixers, microbearings, among others), where the shear rate at solid‐fluid interfaces remains linear because of the geometry smoothness. Despite this, there are some situations for which this linear dependency fails leading to unrealistic behaviour and an expression for the slip condition at a solid‐liquid interface establishing the variation in the slip length in terms of the square root of the tangential shear rate needs to be used. This work employs a boundary integral equation formulation for Stokes slip ...

Unsteady Forced Convection in Packed Beds: Computational and Experimental Analysis

In this work, a process of unsteady forced convection in a packed bed of spheres was experimentally and computationally analyzed. A device was designed and constructed in order to run the experiments in packed beds. It was used to carry out an experimental run in a packing of ten aluminum spheres, which tube-to-particle diameter ratio was 2,4. Methane-air combustion products were kept flowing into the packed bed at constant inlet conditions, 2,8 m/s and 369°C. Packed spheres were heated from 25°C to gases temperature. While heating, temperature of spheres, tube wall and gases at different positions were measured to follow unsteady process. On the other hand, computational simulation was carried out by modeling the ten-spheres packing under the same flow conditions of the experimental run. Physical properties of gases were kept constant and fluid flow profile was solved before heating process. Results of unsteady temperature variation in different positions showed good agreement with the experimental measures. This result allowed inferring that flow field calculations were a satisfactory representation of the actual flow field, since temperature field variation depends strongly upon flow field. In conclusion, it was found that the Computational Fluid Dynamics (CFD) simulation is an accurate tool to analyze unsteady forced convection in packed beds. The device designed is a flexible and powerful tool to measure unsteady forced convection in packed beds. The behavior of the gas-to-solid heat transfer coefficient is a fundamental question to solve, and CFD supported on experimental measures is the way to solve it.Copyright