Traditional IDS (Intrusion Detection System) performs detection by matching the sample pattern with the intrusion pattern that has been defined, as a result the IDS loses the diversity and the self-adaptation and can not detect the variation intrusion and the unknown intrusion. This paper gives a distributed intrusion detection approach based on the Artificial Immune System. It defines the Self, Nonself and immune cell and builds an intrusion detection model composed of memory cell, mature cell and immature cell and also gives the environment definition, matching rule, training detection system, immune regulation and memory, monitor generation and so on. The result of the experiment show that this intrusion detection system model has the characters of distributed, error tolerance, dynamic learning, adaptation and this approach is efficient to the network intrusion detection.
Experimental studies on laser driven high-speed metallic flyers have been carried out wiht a moderate Q-switched YAG laser whose output is 1J and pulse FWHM of 10 ns. An aluminum film of thickness 5.5 micrometers was accelerated to a speed about 7 km/s. The experiments on initiation of explosives and spallation of metals were performed using laser driven flyer. A numerical model is explored here for a description of vaporization, ablation and ionization during the laser irradiation and can give reasonable results compared with the experiments.
The mechanism of original crack formation on cylindrical shells with inner-pressure and under laser beam irradiation was investigated. By high-speed photographer, it was found that the crack formed at the central area of the surface irradiated by laser beam. The mechanism of crack formation was examined and discussed on the base of fractography, metallographic inspection and stress analysis. A simple criterion is setup to judge the original crack formation on the shell irradiated by laser beam. All information provided here is conductive to a better understanding of this problem.
KEYWORDS: Aluminum, High power lasers, Neodymium glass lasers, Wave propagation, Pulsed laser operation, Scanning electron microscopy, Electron microscopes, Camera shutters, Sun, Fluid dynamics
The dynamic fracture of pure aluminum targets with thickness in the range of 100 to approximately 800 micrometers has been investigated experimentally under shock loading induced by Nd:glass laser pulses of 4 ns FWHM. The experimental results indicate that the spallation of aluminum at ultra high strain rate up to 107s-1 is still a ductile fracture in the way of voids' nucleation, growth, and coalescence in interior of the material, but the damage behavior is somewhat different from that obtained by ordinary loading methods at lower strain rate. The function of spall thickness versus the target thickness is nearly linear under the conditions of this experiment.
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