A parallel iterative system solver

We study the adoption of iterative methods for numerically solving linear systems of the form Au=b on parallel machines. A new class of first order iterative schemes possessing a high level of parallelism is originated by the approximation of the Neumann series to A^?1. A preliminary study of the case where the sequence of parameters involved are constant and equal to unity reveals that the series is best approximated by its first two terms. This results in the derivation of a new iterative method which under certain conditions possesses an exceptionally high rate of convergence.     

pH and ionic strength effect on single fibrinogen molecule adsorption on mica studied with AFM

Although several investigations have been reported on the effect of pH or ionic strength on protein adsorption, most of them have been carried out with protein monolayers and not with single molecules. We have used atomic force microscopy to image, in phosphate buffer, single fibrinogen molecules adsorbed on mica and compare the surface coverage at variable pH (7.4, 5.8, 3.5) or ionic strength (15, 150, 500 mM) conditions. The images obtained and the statistical analysis of the surface coverage indicate adsorption enhancement at the IEP of fibrinogen (pH 5.8) and minimum adsorption at pH 3.5. On the other hand, more protein was adsorbed when the salt concentration of the buffer at pH 7.4 was increased from 15 to 150 mM. However, further increase of salt concentration up to 500 mM resulted in decreased adsorption. To confirm the aforementioned results an approaching bare Si(3)N(4) tip was used as an electrostatic analogue to a protein molecule and interaction force curves between it and the substrate were recorded. The results were in consistence with the double layer theory which justifies the screening of electrostatic repulsion as the salt concentration increases.     

结构非线性分析中求解预定荷载水平的改进弧长法

本文对目前广泛应用于结构非线性分析之中的弧长法进行改进。改进后的弧长法除保持原有优点外，能够在自动跟踪结构非线性平衡路径的同时，进一步求得位于结构平衡睡径任一区段的任意预先指定的荷载水平及相应的变形。本文的方法可以推广应用于求解预先指定的应力或位移。数值算例表明了本文方法的计算精度、效率及可靠性。     

Optimization of the design of recuperative heat exchangers in the exhaust nozzle of an aero engine

Today the needs for safer, cleaner and more affordable civil aero engines are found to be of great importance. Five years ago, the EU initiated an action for the design and the construction of efficient and environmentally friendly aero engines (EEFAE). One of the major European gas turbine industries, MTU, has presented a new technology for an advanced aero engine design, which uses an alternative thermodynamic cycle. The basis of this cycle is the adoption of a recuperation part with the use of a system of heat exchangers, installed in the exhaust nozzle of the aircraft engine. Thermal energy in the turbine exhaust is used in the recuperator to pre-heat the compressor outlet air before combustion. The benefits of this technique are focused on reduced pollutants and decreased fuel consumption. In this work, the procedure of the optimization of this installation, by means of the imposed pressure drop downstream the aircraft engine and the balanced mass inflow to the heat exchangers is presented. The optimization is based on experimental measurements in laboratory conditions and preliminary 2D CFD modeling for the flow inside the exhaust duct and through the heat exchangers. It is shown that with a careful approach, a better arrangement of the heat exchangers can be achieved in order to have a minimum pressure drop in the exhaust nozzle which can positively affect the engine’s performance.     

Effect of Immobilized Thiolated Glycosaminoglycans on Fibronectin Adsorption and Behavior of Fibroblasts

Glycosaminoglycans (GAGs) chondroitin sulfate, heparin, hyaluronan, and sulfated hyaluronan are lower and higher thiolated to enable a one?step covalent modification of gold or vinyl?terminated surfaces. Measurements of water contact angle and zeta potentials reveal that sulfated GAG?modified surfaces are more wettable and possess a negative surface potential. Additionally, higher thiolated GAGs (tGAGs) exhibit increased wettability and higher surface roughness. Fibronectin (FN) adsorption increases with sulfation degree of tGAGs. The tGAG?functionalized surfaces with higher degree of sulfation promote fibroblast adhesion most under serum‐free conditions. The preadsorption of FN allows for more cell adhesion on tGAG surfaces. Metabolic activity measurements show that cell growth is enhanced for tGAGs up to a certain thiolation degree. Overall, thiolation of GAGs does not hamper their bioactivity toward proteins and cells, which make them highly interesting for biomimetic surface modification of implants and tissue engineering scaffolds.     

Mass spectra of aminoacyl adenylate pentacoordinated phosphorus compounds

Aminoacyl adenylate pentacoordinated phosphorus compounds were analyzed by field desorption (FD) and fast atom bombardment (FAB) mass spectrometries, together with the B/E linked scan technique, and their mass spectral fragmentation pathways were investigated. For the five bonds (one P-N bond, three P-O bonds and one mixed anhydride bond P-O-CO), the cleavage usually occurred more on the P-N bond, the mixed anhydride bond and the O-C bond adjacent to the P-O bond, and less on the P-O bond. Ion YH(+), corresponding to water loss from protonated 2',3'-O-isopropylidene-adenosine, was the base peak. The results reflect the structural characteristics of aminoacyl adenylate pentacoordinated phosphorus compounds. Copyright 1999 John Wiley & Sons, Ltd.     

Cardiovascular Mechanics: Investigation of Two Components,Tissue Heart Valves and Blood Cells

A fundamental anatomical composition of the heart valves is presented along with its relationship to the tissue mechanical behavior. During the loading and unloading phases of the tissue different stress strain pathways are followed with the curves composing the characteristic hysteresis loop, exhibiting the viscoelastic mechanical behavior of valvular tissue. The storage modulus and the phase shift (tan ) as well as the collagen modulus of human heart valves were measured in orthotropic directions using uniaxial dynamic tensile tests at 10 Hz. Viscoelastic properties of human erythrocytes are presented as calculated from micropipette aspiration experiments. Employing the hemorheometre, from filtration experiments an index of rigidity (IR) of erythrocytes is estimated. A relationship between the global parameter IR and the shear elastic modulus of erythrocyte membrane, , is established. The same two techniques adapted for leukocytes and their subpopulations have been used and a relationship between the rigidity index of leukocytes (ILR) and their apparent bulk viscosity (_app), has been found.     

The modified alternating direction preconditioning method for the numerical solution of the elliptic self-adjoint second order and biharmonic equations

This paper introduces a generalised ADI method called the Modified Alternating Direction Preconditioning method (MADP method) for the numerical solution of the elliptic self-adjoint second order and biharmonic equations in a rectangle. The related theory of the MADP method is developed in detail and optimum values for the involved parameters are determined for both cases.