Showing papers by "National University of Singapore published in 2000"

Embryonic stem cell lines from human blastocysts: somatic differentiation in vitro.

Abstract: We describe the derivation of pluripotent embryonic stem (ES) cells from human blastocysts. Two diploid ES cell lines have been cultivated in vitro for extended periods while maintaining expression of markers characteristic of pluripotent primate cells. Human ES cells express the transcription factor Oct-4, essential for development of pluripotential cells in the mouse. When grafted into SCID mice, both lines give rise to teratomas containing derivatives of all three embryonic germ layers. Both cell lines differentiate in vitro into extraembryonic and somatic cell lineages. Neural progenitor cells may be isolated from differentiating ES cell cultures and induced to form mature neurons. Embryonic stem cells provide a model to study early human embryology, an investigational tool for discovery of novel growth factors and medicines, and a potential source of cells for use in transplantation therapy.

Factors influencing the adoption of Internet banking

Abstract: A research framework based on the theory of planned behavior (Ajzen 1985) and the diffusion of innovations theory (Rogers 1983) was used to identify the attitudinal, social and perceived behavioral control factors that would influence the adoption of Internet banking. An online questionnaire was designed on the World Wide Web (WWW). Respondents participated through extensive personalized email invitations as well as postings to newsgroups and hyperlinks from selected Web sites.

Quantifying the Bullwhip Effect in a Simple Supply Chain: The Impact of Forecasting, Lead Times, and Information

Abstract: An important observation in supply chain management, known as the bullwhip effect, suggests that demand variability increases as one moves up a supply chain. In this paper we quantify this effect for simple, two-stage supply chains consisting of a single retailer and a single manufacturer. Our model includes two of the factors commonly assumed to cause the bullwhip effect: demand forecasting and order lead times. We extend these results to multiple-stage supply chains with and without centralized customer demand information and demonstrate that the bullwhip effect can be reduced, but not completely eliminated, by centralizing demand information.

Arabidopsis NAC1 transduces auxin signal downstream of TIR1 to promote lateral root development

Abstract: Auxin plays a key role in lateral root formation, but the signaling pathway for this process is poorly understood. We show here that NAC1, a new member of the NAC family, is induced by auxin and mediates auxin signaling to promote lateral root development. NAC1 is a transcription activator consisting of an N-terminal conserved NAC-domain that binds to DNA and a C-terminal activation domain. This factor activates the expression of two downstream auxin-responsive genes, DBP and AIR3. Transgenic plants expressing sense or antisense NAC1 cDNA show an increase or reduction of lateral roots, respectively. Finally, TIR1-induced lateral root development is blocked by expression of antisense NAC1 cDNA, and NAC1 overexpression can restore lateral root formation in the auxin-response mutant tir1, indicating that NAC1 acts downstream of TIR1.

Improvements to the SMO algorithm for SVM regression

Abstract: This paper points out an important source of inefficiency in Smola and Scholkopf's (1998) sequential minimal optimization (SMO) algorithm for support vector machine regression that is caused by the use of a single threshold value. Using clues from the Karush-Kuhn-Tucker conditions for the dual problem, two threshold parameters are employed to derive modifications of SMO for regression. These modified algorithms perform significantly faster than the original SMO on the datasets tried.

New potential functions for mobile robot path planning

Abstract: The paper first describes the problem of goals unreachable with obstacles nearby when using potential field methods for mobile robot path planning. Then, new repulsive potential functions are presented by taking the relative distance between the robot and the goal into consideration, which ensures that the goal position is the global minimum of the total potential.

Molecular-scale interface engineering for polymer light-emitting diodes

Abstract: Achieving balanced electron-hole injection and perfect recombination of the charge carriers is central to the design of efficient polymer light-emitting diodes (LEDs). A number of approaches have focused on modification of the injection contacts, for example by incorporating an additional conducting-polymer layer at the indium-tin oxide (ITO) anode. Recently, the layer-by-layer polyelectrolyte deposition route has been developed for the fabrication of ultrathin polymer layers. Using this route, we previously incorporated ultrathin (<100 A) charge-injection interfacial layers in polymer LEDs. Here we show how molecular-scale engineering of these interlayers to form stepped and graded electronic profiles can lead to remarkably efficient single-layer polymer LEDs. These devices exhibit nearly balanced injection, near-perfect recombination, and greatly reduced pre-turn-on leakage currents. A green-emitting LED comprising a poly(p-phenylene vinylene) derivative sandwiched between a calcium cathode and the modified ITO anode yields an external forward efficiency of 6.0 per cent (estimated internal efficiency, 15-20 per cent) at a luminance of 1,600 candelas per m2 at 5 V.

Prevalence and risk factors for refractive errors in adult Chinese in Singapore.

Abstract: PURPOSE. To determine the epidemiology of refractive errors in an adult Chinese population in Singapore. METHODS. A disproportionate, stratified, clustered, random-sampling procedure was used to select names of 2000 Chinese people aged 40 to 79 years from the 1996 Singapore electoral register in the Tanjong Pagar district in Singapore. These people were invited to a centralized clinic for a comprehensive eye examination, including refraction. Refraction was also performed on nonrespondents in their homes. Myopia, high myopia, and hyperopia were defined as a spherical equivalent (SE) in the right eye of less than -0.5 D, less than -5.0 D, and more than +0.5 D, respectively. Astigmatism was defined as less than -0.5 D of cylinder. Anisometropia was defined as a difference in SE of more than 1.0 D between the two eyes. Only phakic eyes were analyzed. RESULTS. From 1717 eligible people, 1232 (71.8%) were examined. Adjusted to the 1997 Singapore population, the overall prevalence of myopia, hyperopia, astigmatism, and anisometropia was 38.7% (95% confidence interval [CI]: 35.5, 42.1), 28.4% (95% CI: 25.3, 31.3), 37.8% (95% CI: 34.6, 41.1), and 15.9% (95% CI: 13.5, 18.4), respectively. The prevalence of high myopia was 9.1% (95% CI: 7.2, 11.2), with women having significantly higher rates than men. The age pattern of myopia was bimodal, with higher prevalence in the 40 to 49 and 70 to 81 age groups and lower prevalence between those age ranges. Prevalence was reversed in hyperopia, with a higher prevalence in subjects aged 50 to 69. There was a monotonic increase in prevalence with age for both astigmatism and anisometropia. Increasing educational levels, higher individual income, professional or office-related occupations, better housing, and greater severity of nuclear opacity were all significantly associated with higher rates of myopia, after adjustment for age and sex. CONCLUSIONS. The results indicate that whereas myopia is 1.5 to 2.5 times more prevalent in adult Chinese residing in Singapore than in similarly aged European-derived populations in the United States and Australia, the sociodemographic associations are similar.

AiiA, an enzyme that inactivates the acylhomoserine lactone quorum-sensing signal and attenuates the virulence of Erwinia carotovora

Abstract: N-acylhomoserine lactones, known as autoinducers (AIs), are widely conserved signal molecules present in quorum-sensing systems of many Gram-negative bacteria. AIs are involved in the regulation of diverse biological functions, including expression of pathogenic genes in the plant pathogens Pseudomonas solanacearum, several Erwinia species, and the human pathogen Pseudomonas aeruginosa. A bacterial isolate, Bacillus sp. 240B1, is capable of enzymatic inactivation of AIs. The gene (aiiA) for AI inactivation from Bacillus sp. 240B1 has been cloned and shown to encode a protein of 250 amino acids. Sequence alignment indicates that AiiA contains a “HXHXDH” zinc-binding motif that is conserved in several groups of metallohydrolases. Site-directed mutagenesis showed that conserved aspartate and most histidine residues are required for AiiA activity. Expression of aiiA in transformed Erwinia carotovora strain SCG1 significantly reduces the release of AI, decreases extracellular pectolytic enzyme activities, and attenuates pathogenicity on potato, eggplant, Chinese cabbage, carrot, celery, cauliflower, and tobacco. Our results indicate that the AI-inactivation approach represents a promising strategy for prevention of diseases in which virulence is regulated by AIs.

A model of relational leadership: The integration of trust and leader–member exchange

Abstract: This article presents a model of relational leadership based on a review of leader-member exchange (LMX) and interpersonal trust. This model asserts that the LMX relationship is built through interpersonal exchanges in which parties to the relationship evaluate the ability, benevolence, and integrity of each other. These perceptions, in turn, influence the behaviors predicted by LMX researchers. This integrated model of relational leadership provides insights into the dynamics of leader-subordinate relationships and resolves some of the inconsistencies in the LMX research without losing the richness and uniqueness of the exchange theory. A number of propositions for future research in relational leadership are also suggested.

Error compensation in machine tools — a review: Part I: geometric, cutting-force induced and fixture-dependent errors

Abstract: Accuracy of machined components is one of the most critical considerations for any manufacturer. Many key factors like cutting tools and machining conditions, resolution of the machine tool, the type of workpiece etc., play an important role. However, once these are decided upon, the consistent performance of the machine tool depends upon its ability to accurately position the tool tip vis-a-vis the required workpiece dimension. This task is greatly constrained by errors either built into the machine or occurring on a periodic basis on account of temperature changes or variation in cutting forces. The three major types of error are geometric, thermal and cutting-force induced errors. Geometric errors make up the major part of the inaccuracy of a machine tool, the error caused by cutting forces depending on the type of tool and workpiece and the cutting conditions adopted. This part of the paper attempts to review the work done in analysing the various sources of geometric errors that are usually encountered on machine tools and the methods of elimination or compensation employed in these machines. A brief study of cutting-force induced errors and other errors is also made towards the end of this paper.

The trusted general manager and business unit performance: empirical evidence of a competitive advantage

Abstract: Employee trust for the general manager is proposed as an internal organizational characteristic that provides a competitive advantage for the firm. This paper empirically examines the relationship between trust for a business unit's general manager and organizational performance. Trust was found to be significantly related to sales, profits and employee turnover in the restaurant industry. Managers who were either more or less trusted differed significantly in perceptions of their ability, benevolence and integrity. Copyright © 2000 John Wiley & Sons, Ltd.

Toward the differentiation of trust in supervisor and trust in organization.

Abstract: Trust in supervisor and trust in organization are argued to be distinct but related constructs, each with its own set of antecedents and outcomes. Empirical field results supported the proposition. Although trust in supervisor and trust in organization were positively and significantly correlated, trust in supervisor was more strongly associated with proximal variables (ability, benevolence, and integrity of supervisor), whereas trust in organization was more strongly correlated with global variables (perceived organizational support and justice). This conclusion held despite the inclusion of proximal variables in the regression on trust in organization and the inclusion of global variables in the regression on trust in supervisor. In addition to the differential antecedents of trust in supervisor and trust in organization, the outcomes for both variables were different. Trust in supervisor was related to increased innovative behavior and satisfaction with supervisor, and trust in organization was related to higher organizational commitment and lower intention to leave. Therefore, the authors provide clear preliminary data on the distinctiveness of trust in supervisor and trust in organization. One implication of this set of results is that organizations should adopt a more holistic approach in building trust, which can be achieved by focusing on the various constituents of the organization and the various levels (e.g., the supervisor level and the organizational level).

Error compensation in machine tools — a review: Part II: thermal errors

Abstract: One of the major errors in machine tools namely geometric/kinematic errors was discussed at length in Part I of this paper. Here, in Part II, another major source of inaccuracy, namely thermal error that occurs due to extended usage of the machine is analysed. Continuous usage of a machine tool causes heat generation at the moving elements and this heat causes expansion of the various structural elements of the machine tool. It is this expansion of the structural linkages of the machine that leads to inaccuracy in the positioning of the tool. Such errors are called thermal errors and constitute a significant portion of the total error in a machine tool. Thus the overall volumetric error of a machine tool is not only dependent on errors due to the assembly and the specific kinematic structure of the machine but also on the thermal errors. In Part II of this paper, an attempt is made to review the work carried out over the last decade in the estimation and compensation of temperature dependent errors.

The gastrointestinal tract: A major site of antioxidant action?

Abstract: Diets rich in fruits and vegetables delay the onset of many age-related diseases, and contain a complex mixture of antioxidants (including ascorbate, carotenoids, vitamin E and other phenolics such as the flavonoids). However, diet also contains pro-oxidants, including iron, copper, H2O2, haem, lipid peroxides and aldehydes. Nitrite is frequently present in diet, leading to generation of reactive nitrogen species in the stomach. In considering the biological importance of dietary antioxidants, attention has usually focussed on those that are absorbed through the gastrointestinal tract into the rest of the body. In the present paper we develop the argument that the high levels of antioxidants present in certain foods (fruits, vegetables, grains) and beverages (e.g. green tea) play an important role in protecting the gastrointestinal tract itself from oxidative damage, and in delaying the development of stomach, colon and rectal cancer. Indeed, carotenoids and flavonoids do not seem to be as well absorbed a...

The impact of exponential smoothing forecasts on the bullwhip effect

Abstract: An important phenomenon often observed in supply chain management, known as the bullwhip effect, implies that demand variability increases as one moves up the supply chain, i.e., as one moves away from customer demand. In this paper we quantify this effect for simple, two-stage, supply chains consisting of a single retailer and a single manufacturer. We demonstrate that the use of an exponential smoothing forecast by the retailer can cause the bullwhip effect and contrast these results with the increase in variability due to the use of a moving average forecast. We consider two types of demand processes, a correlated demand process and a demand process with a linear trend. We then discuss several important managerial insights that can be drawn from this research. c 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 269{286, 2000

Profitability of momentum strategies in the international equity markets

Abstract: This paper examines the profitability of momentum strategies implemented on international stock market indices. Our results indicate statiscally significant evidence of momentum profits. The momentum profits arise mainly from time-series predictability in stock market indices—very little profit comes from predictability in the currency markets. We also find higher profits for momentum portfolios implemented on markets with higher volume in the previous period, indicating that return continuation is stronger following an increase in trading volume. This result confirms the informational role of volume and its applicability in technical analysis.

A fast iterative nearest point algorithm for support vector machine classifier design

Abstract: In this paper we give a new fast iterative algorithm for support vector machine (SVM) classifier design. The basic problem treated is one that does not allow classification violations. The problem is converted to a problem of computing the nearest point between two convex polytopes. The suitability of two classical nearest point algorithms, due to Gilbert, and Mitchell et al., is studied. Ideas from both these algorithms are combined and modified to derive our fast algorithm. For problems which require classification violations to be allowed, the violations are quadratically penalized and an idea due to Cortes and Vapnik and Friess is used to convert it to a problem in which there are no classification violations. Comparative computational evaluation of our algorithm against powerful SVM methods such as Platt's sequential minimal optimization shows that our algorithm is very competitive.

The Multiple-Try Method and Local Optimization in Metropolis Sampling

Abstract: This article describes a new Metropolis-like transition rule, the multiple-try Metropolis, for Markov chain Monte Carlo (MCMC) simulations. By using this transition rule together with adaptive direction sampling, we propose a novel method for incorporating local optimization steps into a MCMC sampler in continuous state-space. Numerical studies show that the new method performs significantly better than the traditional Metropolis-Hastings (M-H) sampler. With minor tailoring in using the rule, the multiple-try method can also be exploited to achieve the effect of a griddy Gibbs sampler without having to bear with griddy approximations, and the effect of a hit-and-run algorithm without having to figure out the required conditional distribution in a random direction.