Showing papers by "Hong Kong University of Science and Technology published in 1999"

A chemically functionalizable nanoporous material (Cu3(TMA)2(H2O)3)n

Abstract: Although zeolites and related materials combine nanoporosity with high thermal stability, they are difficult to modify or derivatize in a systematic way. A highly porous metal coordination polymer [Cu3(TMA)2(H2O)3]n (where TMA is benzene-1,3,5-tricarboxylate) was formed in 80 percent yield. It has interconnected [Cu2(O2CR)4] units (where R is an aromatic ring), which create a three-dimensional system of channels with a pore size of 1 nanometer and an accessible porosity of about 40 percent in the solid. Unlike zeolites, the channel linings can be chemically functionalized; for example, the aqua ligands can be replaced by pyridines. Thermal gravimetric analysis and high-temperature single-crystal diffractometry indicate that the framework is stable up to 240 degreesC.

Multiuser OFDM with adaptive subcarrier, bit, and power allocation

Abstract: Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability.

Static scheduling algorithms for allocating directed task graphs to multiprocessors

Abstract: Static scheduling of a program represented by a directed task graph on a multiprocessor system to minimize the program completion time is a well-known problem in parallel processing. Since finding an optimal schedule is an NP-complete problem in general, researchers have resorted to devising efficient heuristics. A plethora of heuristics have been proposed based on a wide spectrum of techniques, including branch-and-bound, integer-programming, searching, graph-theory, randomization, genetic algorithms, and evolutionary methods. The objective of this survey is to describe various scheduling algorithms and their functionalities in a contrasting fashion as well as examine their relative merits in terms of performance and time-complexity. Since these algorithms are based on diverse assumptions, they differ in their functionalities, and hence are difficult to describe in a unified context. We propose a taxonomy that classifies these algorithms into different categories. We consider 27 scheduling algorithms, with each algorithm explained through an easy-to-understand description followed by an illustrative example to demonstrate its operation. We also outline some of the novel and promising optimization approaches and current research trends in the area. Finally, we give an overview of the software tools that provide scheduling/mapping functionalities.

Optical coherence tomography (OCT): a review

Abstract: This paper reviews the state of the art of optical coherence tomography (OCT), an interferometric imaging technique that provides cross-sectional views of the subsurface microstructure of biological tissue. Following a discussion of the basic theory of OCT, an overview of the issues involved in the design of the main components of OCT systems is presented. The review concludes by introducing new imaging modes being developed to extract additional diagnostic information.

Culture specific and cross-culturally generalizable implicit leadership theories: Are attributes of charismatic/transformational leadership universally endorsed?

Abstract: This study focuses on culturally endorsed implicit theories of leadership (CLTs). Although cross-cultural research emphasizes that different cultural groups likely have different conceptions of what leadership should entail, a controversial position is argued here: namely that attributes associated with charismatic/transformational leadership will be universally endorsed as contributing to outstanding leadership. This hypothesis was tested in 62 cultures as part of the Global Leadership and Organizational Behavior Effectiveness (GLOBE) Research Program. Universally endorsed leader attributes, as well as attributes that are universally seen as impediments to outstanding leadership and culturally contingent attributes are presented here. The results support the hypothesis that specific aspects of charismatic/transformational leadership are strongly and universally endorsed across cultures.

Speckle in Optical Coherence Tomography

Abstract: Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.

Ownership strategy of Japanese firms: transactional, institutional, and experience influences

Abstract: We compare the effects of transactional, institutional, and experience influences on the ownership strategies of Japanese investors. Our theoretical development suggests that the equity position of a foreign investor should increase as the specificity of the assets transferred to the foreign affiliate increases, but a lower equity position should be assumed when the foreign investor requires complementary assets to establish a foreign entry. International experience and a strong institutional environment also should lead to increases in the equity position of the foreign investor. These relationships were tested with data on more than 1000 Japanese investments in nine countries of East and South-East Asia. The results demonstrate that experience and institutional factors were the most important influences on the ownership position taken in the foreign investment, while transactional factors had a much less important and a more ambiguous role. Copyright © 1999 John Wiley & Sons, Ltd.

Crystal Engineering of Acentric Diamondoid Metal–Organic Coordination Networks

Abstract: Acentric three-dimensional coordination polymers bis(isonicotinato)zinc (1) and bis(4-pyridylacrylato)cadmium⋅H2 O (2) were synthesized under hydro(solvo)thermal conditions; they exhibit a threefold (see picture) and fivefold diamondoid structure, respectively. Both 1 and 2 are active for second harmonic generation and exhibit remarkable thermal stability.

Photoluminescence and ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn

Abstract: We report a simple method for preparing polycrystalline ZnO thin films with good luminescent properties: the oxidization of metallic Zn films. In photoluminescence (PL) studies at room temperature for wavelengths between 370 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission and a small PL full width at half maximum (23 meV), indicating that the concentrations of the defects responsible for the deep-level emissions are negligible. We have also observed optically pumped lasing action in these films. The threshold intensity for lasing was ∼9 MW/cm2.

Geographic scope, product diversification, and the corporate performance of Japanese firms

Abstract: The study extends research on the geographic scope, product diversification, and performance relationship by exploring both the antecedents and consequences of geographic scope. In so doing, it addresses a fundamental criticism of the geographic scope–performance relationship; namely, that the observed positive relationship between geographic scope and performance is spurious because it is the possession of proprietary assets that is the foundation of superior performance, not expansion into international markets per se. We tested the research model with data on the corporate performance of 399 Japanese manufacturing firms. In the partial least squares analyses used to examine the study’s six main hypotheses, we demonstrate that geographic scope was positively associated with firm profitability, even when the competing effect of proprietary assets on firm performance was considered. Further, we find that performance was not related to the extent of product diversification, although investment levels in rent-generating, proprietary assets were related to the extent of product diversification. Copyright © 1999 John Wiley & Sons, Ltd.

Preparation, Alignment, and Optical Properties of Soluble Poly(phenylacetylene)-Wrapped Carbon Nanotubes†

Abstract: Carbon nanotube-containing poly(phenylacetylenes) (NT/PPAs) are prepared by in situ polymerizations of phenylacetylene catalyzed by WCl6−Ph4Sn and [Rh(nbd)Cl]2 (nbd = 2,5-norbornadiene) in the pres...

On the optimal placement of web proxies in the Internet

Abstract: Web caching or web proxy has been considered as the prime vehicle of coping with the ever-increasing demand for information retrieval over the Internet, the WWW being a typical example. Existing work on web proxy has primarily focused on content based caching; relatively less attention has been given to the development of proper placement strategies for the potential web proxies in the Internet. In this paper, we argue that the placement of web proxies is critical to the performance and further investigates the optimal placement policy of web proxies for a target web server in the Internet. The objective is to optimize a given performance measure for the target web server subject to system resources and traffic pattern. Specifically, we are interested in finding the optimal placement of multiple web proxies (M) among potential sites (N) under a given traffic pattern. We show this can be modeled a dynamic programming problem. We further obtain the optimal solution for the tree topology using O(N/sup 3/M/sup 2/) time.

The Decomposition of Promotional Response: An Empirical Generalization

Abstract: Price promotions are used extensively in marketing for one simple reason-consumers respond. The sales increase for a brand on promotion could be due to consumers accelerating their purchases i.e., buying earlier than usual and/or buying more than usual and/or consumers switching their choice from other brands. Purchase acceleration and brand switching relate to the primary demand and secondary demand effects of a promotion. Gupta 1988 captures these effects in a single model and decomposes a brand's total price elasticity into these components. He reports, for the coffee product category, that the main impact of a price promotion is on brand choice 84%, and that there is a smaller impact on purchase incidence 14% and stockpiling 2%. In other words, the majority of the effect of a promotion is at the secondary level 84% and there is a relatively small primary demand effect 16%. This paper reports the decomposition of total price elasticity for 173 brands across 13 different product categories. On average, we find that 25% of the elasticity is due to primary demand expansion i.e., purchase acceleration and 75% to secondary demand effects or brand switching. Thus, while Gupta's finding that the majority of promotional response stems from brand switching is supported, the average magnitude of the effect appears to be smaller than first thought. More important, there is ample evidence that promotions have a significant primary demand effect. The relative emphasis on purchase acceleration and brand switching varies systematically across categories, and the second goal of the paper is to explain this variation as a function of exogeneous covariates. In doing this, we recognize that promotional response is the consumer's reaction to a price promotion, and therefore develop a framework for understanding variability in promotional response that is based on the consumer's perspective of the benefits from a price promotion. These benefits are posited to be a function of: i category-specific factors, ii brand-specific factors, and iii consumer characteristics. The framework is formalized as a generalized least squares meta-analysis in which the brand's price elasticity is the dependent variable. Several interesting results emerge from this analysis. • Category-specific factors, brand-specific factors, and consumer demographics explain a significant amount of the variance in promotional response for a brand at both the primary and secondary demand levels. • Category-specific factors have greater influence on variability in promotional response and its decomposition than do brand-specific factors. • There are several instances where exogenous variables do not affect total elasticities yet significantly affect individual components of total elasticity. In fact, the lack of a significant relationship between the variables and total elasticity is often due to offsetting effects within two or more of the three behavioral components of elasticity. This is particularly true for brand-specific factors, which typically have no effect on total elasticity, yet have important effects on the individual behaviors. • There is some evidence to suggest that not all promotion-related increases in primary demand are due to forward-buying-in some cases promotions appear to increase consumption. We use these results to illustrate how category-and brand-specific factors work to drive primary and secondary demand elasticities in different directions. In short, this paper offers an empirical generalization of a key finding on promotional response-how elasticities decompose across brand choice, purchase incidence, and stockpiling-and new insights into factors that explain variance in promotional response. These findings are likely to be of interest to researchers who are concerned with theory development and the generalizability of marketing phenomena, and to managers who plan promotion campaigns.

The Removal of Dye Colours from Aqueous Solutions by Adsorption on Low-cost Materials

Abstract: The ability of five low cost adsorbents – rice husk, cotton, bark, hair and coal – to adsorb two basic dyes, namely, Safranine and Methylene Blue, has been studied Equilibrium isotherms have been determined and analysed using the Langmuir equations The monolayer saturation capacities for Safranine are 1119, 838, 875, 190 and 120 mg g-1adsorbent and for Methylene Blue are 914, 312, 277, 158 and 250 mg g-1adsorbent for bark, rice husk, cotton waste, hair and coal respectively A limited number of fixed bed column studies have been performed and the bed depth service time for each dye-adsorbent system has been determined

A finite-difference time-domain method without the Courant stability conditions

Abstract: In this paper, a finite-difference time-domain method that is free of the constraint of the Courant stability condition is presented for solving electromagnetic problems. In it, the alternating direction implicit (ADI) technique is applied in formulating the finite-difference time-domain (FDTD) algorithm. Although the resulting formulations are computationally more complicated than the conventional FDTD, the proposed FDTD is very appealing since the time step used in the simulation is no longer restricted by stability but by accuracy. As a result, computation speed can be improved. It is found that the number of iterations with the proposed FDTD can be at least three times less than that with the conventional FDTD with the same numerical accuracy.

M-PSK and M-QAM BER computation using signal-space concepts

Abstract: In this paper, we introduce a simple geometric approach that is based on signal-space concepts to efficiently evaluate the performance of M-ary phase-shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) schemes over an additive white Gaussian noise channel. In particular, new bit error rate approximations are derived and shown to be in excellent agreement with Monte Carlo simulation results.

Hybrid flow shop scheduling: a survey

Abstract: Extensive work has been done in hybrid flow shop scheduling. This paper reviews the state of art and discusses in details their contributions. The review is concluded with suggestions for future research directions.

Sorption of acid dyes from effluents using activated carbon

Abstract: The sorption of three acid dyes, namely, Acid Red 114, Polar Yellow and Polar Blue RAWL, onto activated carbon, has been studied. Equilibrium isotherms have been measured for three single component systems (AB, AR, AY) and one binary component system (AB+AY). The isotherms were determined by shaking 0.05 g activated carbon, particle size range 500–710 μm, with 0.05 dm3 dye solution of initial concentrations from 10 to 250 mg/dm3. A constant temperature agitating 400-rpm shaking water bath was used and the temperature maintained at 20±2°C. A contact time of 21 days was required to achieve equilibrium. Analysis of data has been carried out in two stages. (a) In single component analysis, the experimental isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich equations for each individual dye. The monolayer adsorption capacities are 101.0 mg Acid Red per g carbon, 100.9 mg Acid Blue per g carbon and 128.8 mg Acid Yellow per g carbon. (b) In multicomponent analysis, one binary system has been analysed using an extended form of the Langmuir equation. The correlation between theoretical data and experimental data only had limited success due to competitive and interactive effects between the dyes and dye-surface interactions.

Analysis and design of polysilicon thermal flexure actuator

Abstract: An analytical model that can accurately predict the performance of a polysilicon thermal flexure actuator has been developed. This model is based on an electrothermal analysis of the actuator, incorporating conduction heat transfer. Heat radiation from the hot arm of the actuator to the cold arm is also estimated. Results indicate that heat radiation becomes significant only at high input power, and conduction heat losses to both the substrate and the anchor are mainly responsible for the operating temperature of the actuator under routine operations. Actuator deflection is computed based on elastic analysis of structures. To verify the validity of the model, polysilicon thermal flexure actuators have been fabricated and tested. Experimental results are in good agreement with theoretical predications except at high input power. An actuator with a 240 µm long, 2 µm thick, 3 µm wide hot arm and a 180 µm long, 12 µm wide cold arm deflected up to 12 µm for the actuator tip at an input voltage of 5 V while it could be expected to deflect up to 22 µm when a 210 µm long cold arm is used.

Assimilation efficiencies of chemical contaminants in aquatic invertebrates: A synthesis

Abstract: Assimilation efficiencies of contaminants from ingested food are critical for understanding chemical accumulation and trophic transfer in aquatic invertebrates. Assimilation efficiency is a first-order physiological parameter that can be used to systematically compare the bioavailability of different contaminants from different foods. The various techniques used to measure contaminant assimilation efficiencies are reviewed. Pulse-chase feeding techniques and the application of gamma-emitting radiotracers have been invaluable in measuring metal assimilation efficiencies in aquatic animals. Uniform radiolabeling of food is required to measure assimilation, but this can be difficult when sediments are the food source. Biological factors that influence contaminant assimilation include food quantity and quality, partitioning of contaminants in the food particles, and digestive physiology of the animals. Other factors influencing assimilation include the behavior of the chemical within the animal's gut and its associations with different geochemical fractions in food particles. Assimilation efficiency is a critical parameter to determine (and to make predictions of) bioaccumulation of chemicals from dietary exposure. Robust estimates of assimilation efficiency coupled with estimates of aqueous uptake can be used to determine the relative importance of aqueous and dietary exposures. For bioaccumulation of metals from sediments, additional studies are required to test whether metals bound to the acid-volatile sulfide fraction of sediments can be available to benthic deposit-feeding invertebrates. Most assimilation efficiency studies have focused on chemical transfer in organisms at the bottom of the food chain; additional studies are required to examine chemical transfer at higher trophic levels.