Research into displacement cascade processes in alloy systems has received little attention, yet is potentially of interest because issuessuch as the effect of solutes on the displacement threshold and the defectdistribution and movement in cascades are important. As part of a widerstudy, we have initially considered the minor substitutional solute Au in a Cu matrix, and have used molecular dynamics to investigate the properties of point defects, the threshold displacement energy Ed, and temporal and spatial distribution of defects in low-energy (≤500 eV) displacement cascades. The results show that the influence of the solute on the properties of defects is important and that Edis dramatically different from its form in pure copper. In comparison with pure copper,the recoil of the Au solute gives rise to a higher peak at longer timesin the number of displaced atoms in the generation of a displacement cascade. The influence of this on defect density in the cascade and thefinal number and arrangement of defects has been investigated.

A molecular-dynamics study has been made of the influence of solute content on low-energy displacement cascade processes in copper containing up to 15 at. % Au in solid solution. This alloy system was chosen to illustrate the effects of heavy, oversized solute atoms in a fcc matrix. Cascades of up to 2ke Vin energy were considered. The presence of the solute was found to have a significant impact on all phases of cascade development, but not on the final defect number. The ballistic phase is increased in duration, and the number of temporarily displaced atoms is increased by the solute, and the thermal spike that follows is also increased in intensity and duration. As a consequence, the atomic mixing associated with these two phases was highest in the Cu–15% Au alloy that contained the most solute. However, as a result of self-healing in the thermal spike, the final number of Frenkel defects is independent of alloy composition. To test the influence of solute atomic mass, simulations were carried out on copper containing solute atoms with the same size as Au, but a lighter mass than copper. The alloys with this fictitious element did not show the ballistic-and thermal-spike effects exhibited by those containing "normal" gold. The results are discussed in terms of the likely roles of solutes in damage evolution in alloys under cascade-producing irradiation.

The Active Queue Management (AQM) strategies are important in Internet congestion control, which bear the PmIlPlD Structure esscntially. But it is hard to configure thc controlling parameters to achieve good tradcoff among a series of,$erformancc objectives. In this paper, we derivc the approximate First Order Lag Plus Delay (FOLPD) model of TCP/AQM and present a guideline to design PIPID, AQM in. the network routers. Both positional and incremental PIIPTDd: implementations arc considered. Simulation results manifest the effectiveness of thc proposed tuning method.

In this paper, we consider a pariicular model of electron-beam-inducedpair excitation. This model takes account of thickness dependence and istherefore considerably more realistic than the constant generation rate assumedwe in a previous paper. The surface recombination velocity (SRVo) n the uppersurface can be varied independently of that on the lower surface. An exactanalytical expression for the Green function (GF) has been found. Funher, generalexpressions for the minoriiy carrier concentration profile (MCCPa), nd hence forthe cathodoluminescence intensity (cu) are constructed merely by convolving theGF with the pair-generation function which is allowed to assume arbitrary form.Here a 'correlation function' form of the pair excitation density is considered whichnon-trivially makes the entire problem be of completely analytical formulation. Theinfluence of various physical parameters, especially the SRV, the diffusion length(oL), and the incident vonage on the MCCP and cu, are discussed in more detailtheoretically and numerically. Explicit analytical forms of the GF, MCCP, and cuare given for various surface-recombination conditions as well as expressionsfor junction current (JC) in the charge-collecting modes. An example is givenof a model prediction in agreement with experimental results which cannot beobtained by previously existing models. It is found that the present formalism canalso be used to tackle the problems of dislocation-or defect-imaging contrastand resolution in thin film materials within some approximation scheme andthat many past models can be reproduced from the present model as specialcases. It is anticipated that the generality of the model which we propose willbe of considerable interest in seeking an understanding of experimental resuns.Quantitative calculations reveal many interesting and even unusual featurescontained in the new model

e, fcc solid solution: we have taken Ni3Al and a Au solute in copper as examples of these systems. Many-body interatomic potentials for these alloys have been used, but modified at small separations to provide suitable descriptions of collisions at near-threshold energies. The properties of point defects associated with a single Au solute atom in a copper matrix are presented, and it is then shown that the threshold energy, Ed, for the Au recoil in this alloy is smaller and has much less orientation-dependence than is found for a Cu recoil in the pure metal. This effect is related to the number of atoms temporarily displaced from their sites during the creation of a stable Frenkel pair. Ed for Al in Ni3Al is much higher than in pure aluminium and similar in size to that of a Ni atom. The stable defect arrangements produced at threshold are in general much more complex than for pure metals, and defects on the Ni sublattices are usually the majority species. A striking effect occurs for 110 recoils along mixed Ni-Al-Ni-Al- … rows, for chains of antisite defects created by replacement sequences break to form two Frenkel pairs for each primary recoil atom.