Design and tuning of a 40-MeV electron linear accelerator

The 40-MeV electron linear accelerator RELUS-6 with a 100-mA pulse current has been designed. The standing wave accelerator with a biperiodic accelerating structure is composed of four sections and is powered from two 6-MW pulse klystrons. The operating frequency is 2856 MHz. The total length of the accelerating structure is 2.73 m. Calculations have been performed with the aim of selecting the lengths of the first three cells in the first accelerating section and the values of the accelerating field in them, so that the width of the energy spectrum at the end of the accelerator is 2%. The geometry of the accelerating structure and the power input cells has been designed. Four accelerating structures have been manufactured based on the simulation results. The structures have been tuned to the operating frequency, the predetermined accelerating field distribution, and a fixed coupling between the feed waveguide and the accelerating section.     

On the possibility for an autooscillatory system under external periodic drive action to exhibit universal behavior characteristic of the transition to chaos via period-doubling bifurcations in conservative systems

We propose a model of an autooscillatory system that admits the physical realization of the universal Hamiltonian-type critical behavior at a threshold of the transition to chaos that is characteristic of conservative systems. For this model, an approximate discrete map is obtained and the coordinates of the corresponding critical point are evaluated.     

Elastic wave propagation in a 3‐D unbounded random heterogeneous medium coupled with a bounded medium. Application to seismic soil–structure interaction (SSSI)

We present a sub‐structuring method for the coupling between a large elastic structure, and a stratified soil half‐space exhibiting random heterogeneities over a bounded domain and impinged by incident waves. Both media are also weakly dissipative. The concept of interfaces classically used in sub‐structuring methods is extended to ‘volume interfaces’ in the proposed approach. The random dimension of the stochastic fields modelling the heterogeneities in the soil is reduced by introducing a Karhunen–Loéve expansion of these stochastic fields. The coupled overall problem is solved by Monte‐Carlo simulation techniques. A realistic example of a large industrial structure interacting with an uncertain stratified soil medium under earthquake is finally presented. This case study and others validate the presented methodology and its ability to handle complex mechanical systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Static characteristics of conical multiple-wedge hydrodynamic liquid-friction bearings

Formulas are proposed for the state characteristics of conical multiple-wedge hydrodynamic liquid-friction bearings, with variation of the heat-transfer properties, a two-phase lubricant state, and variation in the load-carrying capacity, lubricant flow rate, and power loss on friction and pumping.     

Positive delayed photoconductivity in double heterostructures Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As of the p-type

Positive delayed photoconductivity was observed for the first time in double p-type heterostructures Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5 As upon exposure to the radiation of a red light-emitting diode. In this state, the concentration and mobility of two-dimensional holes are increased 1.5 and 1.7 times, respectively, as compared to the initial dark values. The delayed photoconductivity can be explained by the presence of deep electron traps located above the Fermi level at the inverted heterointerface.