Unified approach to structural optimization II: Variable segment boundaries and variable interior point constraints

Recently, Goh and Wang (1989) presented a unified approach for solving cross-section structural optimization problems under general constraints. In a continual development of the above unified approach, two important extensions have been made to enhance its versatility. They allow the optimization of variable piecewise segmental lengths and/or variable interior point constraint positions. This sequel paper shows how these extensions are incorporated in the unified approach and presents the derivation of gradient expressions (required in the optimization routine) of the objective functional and constraints with respect to these new variables. Some illustrative examples are solved to demonstrate the new features in the approach. Furthermore, a recent refinement in handling continuous state constraints is presented.On sabbatical leave from the Department of Civil Engineering, National University of Singapore, Kent Ridge, Singapore 0511     

Fabrication of Copper Nanowire Films and their Incorporation into Polymer Matrices for Antibacterial and Marine Antifouling Applications

With the ban of tributyltin, copper‐based biocides are now widely used in antifouling coatings as the major active ingredients. Given the past experience of heavy‐metal accumulation in harbors with limited water exchange, there is a significant interest in developing copper materials that greatly reduce the amount of copper ions released into marine surroundings. In this paper, copper nanowires (NWs) encapsulated in polymer matrices are investigated as the means to control the release of copper ions and to achieve a long‐lasting antifouling effect. Very long CuNWs with high aspect ratio in organic solution are drop‐coated onto substrates to fabricate uniform thin films. They are then incorporated into an elastomeric polydimethylsiloxane (PDMS) matrix. A small amount of CuNWs in PDMS can inhibit barnacle cyprid settlement, while it exhibits low mortality to cyprids and nauplii present in the surrounding seawater environment. The low levels of copper released after 50 days suggest that the intersecting and interconnected CuNWs embedded in PDMS could potentially release copper ions continuously over a few years in seawater. This approach provides a novel platform to use hybrid materials as effective marine antifouling coatings, and may be applied to fouling release materials to enhance their antifouling properties.     

Output Peak Control of Nonhomogeneous Markov Jump System with Unit-Energy Disturbance

This paper considers output peak controller design for discrete nonhomogeneous Markov jump systems under unit-energy disturbance. The mode-dependent output peak feedback controller is designed to ensure that the resulting closed-loop system is stochastically stable and the peak of the output is within a specified range. Furthermore, the optimal energy-to-peak gain indices of the mode-dependent and the mode-independent state feedback controllers are evaluated and compared. A numerical example is presented to illustrate the applicability of the results obtained.     

Approximate results for the bit error probability of binary phaseshift keying with noisy phase reference

Approximate results for the bit error probability (BEP) of binary phase shift keying (BPSK) in the presence of a noisy carrier phase reference are presented. The results show correctly the behavior or the BEP as a function of SNR. The accuracy of the approximations is verified by simulations and numerical integration of the BEP formulas. The results are compared with existing bounds     

Seroprevalence of hepatitis B and C viral markers in patients with primary hepatocellular carcinoma in Singapore

This paper reviews studies on the basic principles of biostimulation of wound healing by various low-energy lasers. It looks at the mechanism of action of biostimulation as well as the laser's effect on cell proliferation, collagen synthesis, and would healing.     

Effects of environmental uncertainty on organizational intention to adopt distributed work arrangements

Uncertainty in the external environmental context has been shown to affect organizational change and innovation. Distributed work arrangement is an organizational innovation that has the potential to enable a firm to meet the challenges of an uncertain environment more effectively. With the emergence of virtual organizations, such work arrangements are likely to gain increasing popularity. This exploratory empirical study employs a structural model to examine how environmental uncertainty affects organizational predisposition (adoption intention) toward distributed work arrangements. Environmental uncertainty has two different dimensions: environmental complexity (heterogeneity) and environmental variability (dynamism). In this paper, environmental dimensions are modeled to influence adoption of distributed work arrangements through shaping the organizational perceptions of three innovation characteristics: perceived relative advantage, compatibility and complexity. Data analyses using partial least squares statistical technique revealed that environmental complexity is negatively associated with perceived relative advantage, and perceived compatibility. Perceived relative advantage and perceived compatibility are in turn positively related to adoption intention for distributed work arrangements. However, environmental variability has no significant effect on the three innovation characteristics. Contrary to past findings that suggest organizations are more predisposed toward innovations in a complex environment, our study found that organizations in an environment of lower, rather than higher complexity are more likely to adopt distributed work arrangements. Implications for organizations are discussed.     

Racial differences in Helicobacter pylori seroprevalence in Singapore: correlation with differences in peptic ulcer frequency

The aim of this study was to determine, first, whether racial differences exist in the seroprevalence of Helicobacter pylori infection in Singapore, and second, whether these differences correlate with racial differences in peptic ulcer frequency. A commercial serological test for immunoglobulin (Ig)G antibody to H. pylori which was 90% sensitive and 83% specific in our population was used to screen 403 adult blood donors of Chinese, Malay and Indian origin, aged between 15-60 years. Serum specimens from 84 paediatric patients admitted to the Paediatrics Department, National University of Singapore, with non-gastroenterological illnesses were also tested. In all three races, seroprevalence of H. pylori increased with age. Indians have the highest prevalence of infection followed by Chinese and Malays. Peptic ulcer prevalences are known to be highest in Chinese, followed by Indians and Malays. The Malays have the lowest prevalence of H. pylori and peptic ulcer among the three races in Singapore. Indians have a higher prevalence of H. pylori antibodies but a lower frequency of peptic ulcer than the Chinese. Racial differences in peptic ulcer frequency between Chinese and Indians are not explained by the prevalence of H. pylori infection; other environmental or genetic factors may be involved.