Mechanical relaxations of a (Zr77.5Ti22.5)55(Ni48Cu52)21.25Be23.75 amorphous alloy studied using dynamic mechanical analysis

The dynamic mechanical properties of a (Zr_77.5Ti_22.5)₅₅(Ni₄₈Cu₅₂)_21.25Be_23.75 amorphous alloy were investigated by frequency-dependent elastic moduli and isothermal multi-frequency measurements. The frequency-dependent loss modulus showed a relaxation behavior resulting from a glass transition, and the variation of the peak frequency was related to the Arrhenius equation. Isothermal multi-frequency measurement data were used to construct the master curves of the elastic moduli and tan δ by applying the time-temperature superposition principle. The temperature dependence of the shift factor was found to follow the Arrhenius relationship, and the activation energies for the low temperature relaxation and glass transition were approximately 156.6kJ/mol and 554kJ/mol, respectively. The glass transition temperature (T _g) was manifested by the crossover region of the shift factor dependence, and from the relationship between the shift factors and the temperature aboveT _g), the fragility index of this alloy was estimated.     

Delay analysis of a unidirectional bus network with an erasure station

Fiber-based unidirectional bus networks offer attractive solutions for very high speed multiaccess communications over local and metropolitan areas. The transmission capacity of such networks can be increased considerably through the use of erasure stations that enable reuse of slots that have passed their destinations on the bus. An analysis of the mean packet delay performance of a unidirectional bus network with one erasure station is presented. The two bus sections separated by the erasure station are modeled as coupled queues. A functional equation for the joint generating function of the queue sizes in steady state is obtained and used to evaluate the mean packet delay under Poisson arrivals.     

Contribution of central and peripheral vision to the regulation of stance: developmental aspects

Postural oscillations in 6-, 8-, and 10-year-old children were analyzed in four conditions of vision of the environment (complete vision, peripheral vision, central vision and no-vision) and two conditions of ankle somatosensory information (normal and altered support surfaces with a 5-cm-thick foam). Children were more stable with than without vision. This was observed whether children had complete or partial vision (central or peripheral). They were also more stable with the normal than with the altered support surface. Overall, there was no effect of age. Beyond these well-established results, the present experiment showed the complementary role of peripheral and central vision in the regulation of children's posture. For the 6- and 10-year-olds, central and peripheral vision yielded similar postural stability, whereas for the 8-year-olds, central vision yielded greater postural stability than peripheral vision. The analysis of postural oscillations in the medio-lateral and antero-posterior planes showed that, for the three age groups, central vision was as efficient whatever the plane. On the other hand, after age 6, peripheral vision was more efficient for regulating antero-posterior than medio-lateral oscillations. The contribution of the different sensory systems and their interaction for stabilizing posture in children should be specifically interpreted with regard to the operating characteristics of each sensory system at each age.     

Integrating data traffic into a CDMA cellular voice system

Part one of this paper analyzes the effects of data traffic integration into a CDMA cellular voice system. The figure of merit used for the quality of service seen by the voice users is measured by the probability of blocking. The CDMA system under consideration is a power controlled, cellular architecture in which blocking occurs when the total interference level exceeds the background noise level by 10 dB [1]. It is shown that the introduction of data can be done at little or no increase in the probability of blocking on the voice users. In part two we propose and analyze a protocol which achieves the efficient integration of data by maximizing the utilization of the resources and minimizing the delay experienced by the voice users. The proposed protocol admits data traffic into the CDMA cellular system based on the current aggregate voice interference level, and allows for the efficient integration of voice and data without degrading the quality of service for the delay-critical voice traffic. A Markovian model for this protocol is developed, evaluated and compared to computer simulation results.     

Dual methods for optimizing finite element flexural systems

Modern numerical methods for the optimization of large discretized systems are now well developed and highly efficient in the case of thin walled elastic structures modeled by finite elements. However, this is not yet true for structures whose components are subject simultaneously to bending and extension loads. In this paper, the idea of Generalized Optimality Criterion (GOC), set forth in previous papers for bar, membrane, and pure bending elements, is extended to deal with general beam and flat shell elements. The modifications brought to the GOC result in explicit approximations for the behavior constraints that are correct up to the first order, but that exhibit a more complex algebraic form. Indeed these explicit expressions are no longer merely linear in the reciprocal design variables. However, they continue to be additively separable, and therefore dual methods remain fully applicable, just as in the original statement of the GOC approach. Numerical examples will be offered to demonstrate the efficiency of the method presented.     

A unified parametric design approach to structural shape optimization

This paper presents a general parametric design approach for 2-D shape optimization problems. This approach has been achieved by integrating practical design methodologies into numerical procedures. It is characterized by three features: (i) automatic selection of a minimum number of shape design variables based on the CAD geometric model; (ii) integration of sequential convex programming algorithms to solve equality constrained optimization problems; (iii) efficient sensitivity analysis by means of the improved semi-analytical method. It is shown that shape design variables can be either manually or systematically identified with the help of equality constraints describing the relationship between geometric entities. Numerical solutions are performed to demonstrate the applicability of the proposed approach. A discussion of the results is also given:     

Some applications of dual methods to optimal design of elastic structures

Dual methods of nonlinear mathematical programming are well suited to elastic structural synthesis of a finite element model. They provide a rational scheme for solving problems which are difficult to deal with by classical approaches. This paper is devoted to such special applications. First, after presenting the dual approach for thin-walled structures (bars, membrane elements), the case of discrete design variables (e.g. number of layers in a composite) is studied. The idea is extended to optimal selection of material properties and synthesis of fibre reinforced resins. Next, optimization of flexural system (beams, plates, shells) is reviewed. Lastly it is shown how some geometrical or dimensional limitations which are represented by separable constraints are taken into account exactly in dual algorithms (e.g. a linear increase in the number of layers in a laminate).