A method for improving numerical stability of implicit time integration for nonlinear dynamical structural response

In this paper the consequence of unloading is explored under the framework of implicit time integration for elasto-plastic materials. It is shown that simple unloading problems cause numerical failure in the integration scheme due to divergence during equilibrium iteration and that this divergence will occur regardless of time step size.An improved logical scheme is presented which is capable of recognizing when material unloading occurs and suitably modifying the equilibrium iteration scheme. The incorporation of this solution algorithm in conventional implicit time integration schemes for nonlinear finite element structural analysis will significantly improve both the numerical stability and the accuracy of the structural response calculations.     

Description of Onchocerca dewittei n. sp. (Filarioidea), parasite of Sus scrofa, in Malaysia (author's transl)

Onchocerca dewittei n. sp. was collected from a wild Boar at the metatarse level (tendons and subcutaneous connective tissue); it can be differentiated from other species by the female cuticle showing straight ridges which overlap in the lateral fields, and by its relatively thick microfilaria (length 228-247 mu and width 6-7 mu). This suidean Onchocerca displays some primitive characters such as straight ridges and persistency of ten pairs of caudal papillae in the male; but as a whole this species is undoubtedly more highly evolved than O. raillieti Bain, Müller and coll., 1976, a parasite of Equidae.     

An Acoustic-Phonetic and a Model-Theoretic Analysis of Subspace Distribution Clustering Hidden Markov Models

Recently, we proposed a new derivative to conventional continuous density hidden Markov modeling (CDHMM) that we call subspace distribution clustering hidden Markov modeling (SDCHMM). SDCHMMs can be created by tying low-dimensional subspace Gaussians in CDHMMs. In tasks we tried, usually only 32–256 subspace Gaussian prototypes were needed in SDCHMM-based system to maintain recognition performance of its original CDHMM-based system—a reduction of Gaussian parameters by one to three orders of magnitude. Consequently, both recognition time and memory were greatly reduced. We also have showed that if the underlying subspace distribution tying structure is known, it may be used to train an SDCHMM-based system with as little as eight minutes of speech from scratch. All the results suggest that there is substantial redundancy in conventional CDHMM and that SDCHMM is a more compact model. In this paper, we analyze the tying structure from two perspectives: from the acoustic-phonetic perspective showing that the tying structure seems to capture prominent relationship among phones; and, from the model-theoretic perspective showing that SDCHMMs, if properly created from CDHMMs, may be preferred over the latter as they are less complex and have the potential of greater generalization power.     

Development of Dual-Station Automated Expressway Incident Detection Algorithms

Most automated expressway incident detection algorithms were successfully developed using loop-based traffic occupancy from their local conditions. However, the performance of these algorithms was not satisfactory on sites that have installed a video-based detector system. Due to different traffic detector technologies and varying driving behaviors from one region to another, it is of interest to develop an algorithm that uses video-based data. This paper used a total of 160 incidents collected along the 15-km central expressway (CTE) in Singapore to develop two new dual-station algorithms: the combined detector evaluation (CODE) and the flow-based CODE algorithms. On average, the flow-based CODE algorithm yielded better performance than the CODE in terms of average reduced false alarms of about 16%. Measures were also taken to ensure that the algorithms were properly developed and assessed. It was found that the CODE algorithm can detect, on average, up to 57% of the incidents faster than those of existing detection methods on CTE.     

Design Theory and Performance of 1-GHz CMOS Downconversion and Upconversion Mixers

A CMOS mixer topology capable of both downconversion and upconversion mixing for use in integrated wireless transceivers is presented. The mixing is based on two cross-coupled differential pairs as commutators with two source-followers as current modulators. Independence of the input and output bandwidths allows this topology to be optimized separately for either downconversion or upconversion mixer. The prototypes of both upconversion and downconversion mixers, optimized for linearity and realized in 0.8 m CMOS technology, have been demonstrated to fully operate at 1 GHz with good linearity and low power consumption. In addition, another mixer, optimized for noise figure and realized in 0.5 m CMOS technology, has been designed to achieve a NF of around 12 dB.     

Genetic design of cellular manufacturing systems

In this article, an approach based on the concept of genetic algorithms is proposed as a powerful but simple means of effecting the optimal formation of machine‐part cells in the design of cellular manufacturing systems. A mathematical model is formulated to maximize the intracell and minimize the intercell part movements in the manufacturing system, and to ensure the balance of part movements within each machine‐part cell. The proposed approach is described in some detail, and its effectiveness is demonstrated by using an industrial example and 13 benchmark problems reported in literature. © 2000 John Wiley & Sons, Inc.     

An Adaptive Genetic Algorithm for Manufacturing Cell Formation

An adaptive genetic approach is proposed as an effective means of providing the optimal solution to the manufacturing cell formation problem in the design of cellular manufacturing systems. The proposed approach generates the optimal formation of machine cells and part families by sequencing the rows and columns of a machine-part incidence matrix, so as to maximise the bond energy of the incidence matrix. In order to enhance the performance of the genetic search process, an adaptive scheme is adopted, so that the genetic parameters can be adjusted during the genetic search process. The effectiveness of the proposed approach is demonstrated by applying it to two numerical examples and 11 benchmark problems obtained from the literature. The computational results show that the proposed approach provides a powerful but simple means of solving the manufacturing cell formation problem and thus facilitates the design of cellular manufacturing systems.     

A study on mechano‐electro‐chemical behavior of chitosan/poly(propylene glycol) composite fibers

Chitosan (CS) and poly(ethylene glycol) (PEG) composite fibers were prepared via solution spinning. The fibers were then crosslinked with epichlorohydrin (ECH) and glutaraldehyde (GA). Data indicated that the swelling behavior of CS‐PEG fibers exhibited pH sensitivity, and crosslinking could change the mechanical properties of fibers. Moreover, the mechano‐electro‐chemical (MEC) performance showed that the bending direction of fiber specimen would invert at a critical concentration of both of the crosslinking agents. i.e., in a 0.1% HCl aqueous solution under a dc electric field, as the ECH concentration was more than 9.0 × 10⁻³ M or GA concentration was more than 5.64 × 10⁻⁴ M, the CS‐PEG fibers bent to the cathode, while they bent to the anode if ECH or GA concentration was less than the above values respectively. The mechanisms involve variation in the fixed charge density on the macromolecular network as well as difference in the mechanical properties of the fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 542–551, 2000     

Fabrication and degradation of poly(l-lactic acid) scaffolds with wool keratin

As a natural protein, wool keratin was used to improve the cell affinity of poly(l-lactic acid) (PLLA). Small keratin particles were prepared from keratin solution by the spray-drying process. Keratin particles were blended with PLLA/1,4-dioxane solution and paraffin micro-spheres which were used as progens. After the mixture was molded and dried, the paraffin micro-spheres were removed by cyclohexane. PLLA/keratin scaffolds with controlled pore size and well interconnectivity were fabricated. Keratin releasing rate was detected by Fourier transform infrared (FTIR) after the scaffold was immersed into PBS up to 4 weeks. The surface chemical structure was examined by X-ray photoelectron spectroscope (XPS). The results suggested that the keratin could be held into the scaffold which was expected to improve the interactions between osteoblasts and the polymeric scaffolds.