Comparative study of wall shear stress at the ascending aorta for different mechanical heart valve prostheses

An experimental study is reported which investigates the wall shear stress (WSS) distribution in a transparent model of the human aorta comparing a bileaflet mechanical heart valve (BMHV) with a trileaflet mechanical heart valve (TMHV) in physiological pulsatile flow. Elastic micro-pillar WSS sensors, calibrated by micro-Particle-Image-Velocimetry measurement, are applied to the wall along the ascending aorta. Peak WSS values are observed almost twice in BMHV compared to TMHV. Flow field analyses illuminate that these peaks are linked to the jet-like flows generated in the valves interacting with the aortic wall. Not only the magnitude but also the impact regions are specific for the different valve designs. The side-orifice jets generated by BMHV travel along the aortic wall in the ascending aorta and cause a whole range impact, while the jets generated by TMHV impact further downstream in the ascending aortic generating less severe WSS

Antikaon flow in heavy-ion collisions: the effects of absorption and mean fields

We study antikaon flow in heavy-ion collisions at SIS energies based on the relativistic transport model (RVUU 1.0). The production of antikaons from both baryon-baryon and pion-baryon collisions are included. Taking into account only elastic and inelastic collisions of the antikaon with nucleons and neglecting its mean-field potential as in the cascade model, a strong antiflow or anti-correlation of antikaons with respect to nucleons is seen as a result of the strong absorption of antikaons by nucleons. However, the antiflow of antikaons disappears after including also their propagation in the attractive mean-field potential. The experimental measurement of antikaon flow in heavy-ion collision will be very useful in shedding lights on the relative importance of antikaon absorption versus its mean-field potential.Comment: 12 pages, 2 postscript figures omitted in the original submission are included, to appear in Phys. Rev.

Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon

Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon is studied in the relativistic Vlasov-Uehling-Uhlenbeck model. The self-energies of the antiproton are determined from the nucleon self-energies by the G-parity transformation. Also, the final-state interactions of the antiproton including both rescattering and annihilation are explicitly treated. With a soft nuclear equation of state, the calculated antiproton momentum spectrum is in good agreement with recent experimental data from the heavy-ion synchrotron at GSI. The effect due to the reduced nucleon and antinucleon masses in a medium is found to be more appreciable than in earlier Bevalac experiments with lighter systems and at higher energies.Comment: 10 pages, 4 figures available upon request to [email protected]. TAMUNT-940

The Productivity Impact of Skills in English Manufacturing, 2001: Evidence from Plant-Level Matched Data

Microeconomic analyses of productivity for the UK have generally not been able to control for the quality of the labour input, primarily due to data availability, and yet the supply of suitably skilled labour is thought to be a major contributing factor to productivity levels. This paper combines the Annual Respondents Database with the Employers’ Skills Survey for 2001, which allows for a more detailed analysis of the role of skills in determining plant level productivity. Using an augmented Cobb-Douglas production function, the analysis shows that plants experiencing skills shortages were generally less productive than those who did not perceive a skills gap, having controlled for industry and regional effects. In more detail, the analysis reveals some interesting results: the impact that skills gaps have on productivity vary by industry, and higher qualifications do not always result in higher productivity, although innovative plants are seen to be on average 5 per cent more productive, as a result of their more qualified workforce.