Efficient optimal design of structures by generalized steepest descent programming

The purpose of this paper is to present refinements in a steepest descent algorithm for optimal design of structures and numerical experience that demonstrates its numerical efficiency. The algorithm is based on a state space optimization technique that was initially developed and applied to optimal control problems. Design constraints are divided into four distinct subsets, the special characteristics of which are exploited to improve computational efficiency of the algorithm. Some further improvements in structural analysis, design sensitivity analysis, and constrained steepest descent programming calculations are presented. Optimum designs for three test problems are obtained and convergence rates are compared with results presented in the literature.     

Conversion schemes in residue code

In this paper, an implementation scheme involving decoders and residue adders has been suggested to convert input data in fixed radix representation to residue representation. A method dealing with the reverse process is also demonstrated. A comparison has been made with the methods known hitherto.     

A recursive quadratic programming method with active set strategy for optimal design

Recursive quadratic programming methods have become popular in the field of mathematical programming owing to their excellent convergence characteristics. There are two recursive quadratic programming methods that have been published in the literature. One is by Han and the other is by Pshenichny, published in 1977 and 1970, respectively. The algorithm of Pshenichny had been undiscovered until now, and is examined here for the first time. It is found that the proof of global convergence by Han requires computing sensitivity coefficients (derivatives) of all constraint functions of the problem at every iteration. This is prohibitively expensive for large-scale applications in optimal design. In contrast, Pshenichny has proved global convergence of his algorithm using only an active-set strategy. This is clearly preferable for large-scale applications. The method of Pshenichny has been coded into a FORTRAN program. Applications of this method to four example problems are presented. The method is found to be very reliable. However, the method is found to be very sensitive to local minima, i.e. it converges to a local minimum nearest to the starting design. Thus, for optimal design problems (which usually possess multiple local minima) it is suggested that Pshenichny's method be used as part of a hybrid method.     

SPICE model and parameters for fully-depleted SOI MOSFET'sincluding self-heating

A simple methodology to accurately extract constant temperature model parameters from static measurements of fully-depleted SOI MOSFET current-voltage characteristics is demonstrated. Self-heating is included in an existing physically-based, short-channel bulk MOSFET model, PCIM, by allowing the temperature to change linearly with power dissipation at each bias point. Only a simple modification of the channel bulk charge in PCIM is necessary to adapt it for SOI. The temperature dependence of the physical parameters (mobility, flatband voltage, and saturation velocity) are also fitted and included in the model. Excellent fit to experimental fully-depleted SOI data is shown over a large range of bias conditions and channel lengths. Once the static SOI data is fitted, the constant temperature model parameters appropriate for circuit simulation are easily extracted     

A hybrid formulation for treatment of point-wise state variable constraints in dynamic response optimization

This paper presents methods of design sensitivity analysis and optimization of dynamic response of mechanical and structural systems. The point-wise state variable constraint function is divided into time sub-domains such that each sub-domain contains only one local maximum point. Then, the original constraint is replaced by a number of equivalent functional constraints. Each functional constraint is the integration of the positive value of the original constraint over its own time sub-domain. A direct differentiation method and three adjoint variable methods of design sensitivity analysis are presented. All of these methods are discussed and compared. It turns out that two of the adjoint variable methods are more efficient than others. A hybrid optimization algorithm based on these methods is proposed in detail. Two problems are solved for optimal design. Comparisons of results with those available in the literature are made. Numerical experience with the proposed method is discussed in detail. It is concluded that the new formulation is extremely efficient and converges to either optimal or near optimal solutions without any difficulty.     

Influence of variation in calcium content on casein micelle stability and techno-functional properties of buffalo milk

Changes in techno-functional properties of buffalo milk were evaluated due to variation in calcium content. Decalcification resulted in significant variation in ζ-potential, casein size, colour and η_app. However, calcium addition only influenced ζ-potential of milk. In case of acid gelation, the time and temperature required for coagulation decreased significantly for both calcium-depleted and -added milks. However, during chymosin gelation, only 20%–30% of calcium-depleted milk coagulated with an increased clotting time. Furthermore, calcium addition increased firmness, consistency and cohesiveness of both chymosin and acid-induced gelation.     

Review: Nanocomposites in Food Packaging

ABSTRACT:  The development of nanocomposites is a new strategy to improve physical properties of polymers, including mechanical strength, thermal stability, and gas barrier properties. The most promising nanoscale size fillers are montmorillonite and kaolinite clays. Graphite nanoplates are currently under study. In food packaging, a major emphasis is on the development of high barrier properties against the migration of oxygen, carbon dioxide, flavor compounds, and water vapor. Decreasing water vapor permeability is a critical issue in the development of biopolymers as sustainable packaging materials. The nanoscale plate morphology of clays and other fillers promotes the development of gas barrier properties. Several examples are cited. Challenges remain in increasing the compatibility between clays and polymers and reaching complete dispersion of nanoplates. Nanocomposites may advance the utilization of biopolymers in food packaging.