A Breakdown Criterion of Free Molecular Flows and an Optimum Analysis of EBPVD

Two important issues in electron beam physical vapor deposition (EBPVD) are addressed. The first issue is a validity condition of the classical cosine law widely used in the engineering context. This requires a breakdown criterion of the free molecular assumption on which the cosine law is established. Using the analytical solution of free molecular effusion flow, the number of collisions (N-c) for a particle moving from an evaporative source to a substrate is estimated that is proven inversely proportional to the local Knudsen number at the evaporation surface. N-c = 1 is adopted as a breakdown criterion of the free molecular assumption, and it is verified by experimental data and DSMC results. The second issue is how to realize the uniform distributions of thickness and component over a large-area thin film. Our analysis shows that at relatively low evaporation rates the goal is easy achieved through arranging the evaporative source positions properly and rotating the substrate.

A probability-based approach to setting annual catch levels.

The requirement of setting annual catch limits to prevent overfishing has been added to the Magnuson-Stevens Fishery Conservation and Management Reauthorization Act of 2006 (MSRA). Because this requirement is new, a body of applied scientific practice for deriving annual catch limits and accompanying targets does not yet exist. This article demonstrates an approach to setting levels of catch that is intended to keep the probability of future overfishing at a preset low level. The proposed framework is based on stochastic projection with uncertainty in population dynamics. The framework extends common projection methodology by including uncertainty in the limit reference point and in management implementation, and by making explicit the risk of overfishing that managers consider acceptable. The approach is illustrated with application to gag (Mycteroperca microlepis), a grouper that inhabits the waters off the southeastern United States. Although devised to satisfy new legislation of the MSRA, the framework has potential application to any fishery where the management goal is to limit the risk of overfishing by controlling catch.

Mechanisms of femtosecond laser-induced breakdown and damage in MgO

Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold. (c) 2005 Elsevier B.V. All rights reserved.

Femtosecond laser-induced breakdown of multilayers and gold film

unavailable<br>H. Sun's e-mail address is shy780327@siom.ac.cn.

Optical breakdown of 6H SiC induced by wavelength-tunable femtosecond laser pulses

The damage mechanisms and micromachining of 6H SiC are studied by using femtosecond laser pulses at wavelengths between near infrared (NIR) and near ultraviolet (NUV) delivered from an optical parametric amplifier (OPA). Our experimental results indicate that high quality microstructures can be fabricated in SiC crystals. On the basis of the dependence of the ablated area and the laser pulse energy, the threshold fluence of SiC is found to increase with the incident laser wavelength in the visible region, while it remains almost constant for the NIR laser. For the NIR laser pulses, both photoionization and impact ionization play important roles in electronic excitation, while for visible lasers, photoionization plays a more important role.