Showing papers by "Hong Kong University of Science and Technology published in 2005"

A haplotype map of the human genome

Abstract: Inherited genetic variation has a critical but as yet largely uncharacterized role in human disease. Here we report a public database of common variation in the human genome: more than one million single nucleotide polymorphisms (SNPs) for which accurate and complete genotypes have been obtained in 269 DNA samples from four populations, including ten 500-kilobase regions in which essentially all information about common DNA variation has been extracted. These data document the generality of recombination hotspots, a block-like structure of linkage disequilibrium and low haplotype diversity, leading to substantial correlations of SNPs with many of their neighbours. We show how the HapMap resource can guide the design and analysis of genetic association studies, shed light on structural variation and recombination, and identify loci that may have been subject to natural selection during human evolution.

CoolStreaming/DONet: a data-driven overlay network for peer-to-peer live media streaming

Abstract: This paper presents DONet, a data-driven overlay network for live media streaming. The core operations in DONet are very simple: every node periodically exchanges data availability information with a set of partners, and retrieves unavailable data from one or more partners, or supplies available data to partners. We emphasize three salient features of this data-driven design: 1) easy to implement, as it does not have to construct and maintain a complex global structure; 2) efficient, as data forwarding is dynamically determined according to data availability while not restricted by specific directions; and 3) robust and resilient, as the partnerships enable adaptive and quick switching among multi-suppliers. We show through analysis that DONet is scalable with bounded delay. We also address a set of practical challenges for realizing DONet, and propose an efficient member and partnership management algorithm, together with an intelligent scheduling algorithm that achieves real-time and continuous distribution of streaming contents. We have extensively evaluated the performance of DONet over the PlanetLab. Our experiments, involving almost all the active PlanetLab nodes, demonstrate that DONet achieves quite good streaming quality even under formidable network conditions. Moreover, its control overhead and transmission delay are both kept at low levels. An Internet-based DONet implementation, called CoolStreaming v.0.9, was released on May 30, 2004, which has attracted over 30000 distinct users with more than 4000 simultaneously being online at some peak times. We discuss the key issues toward designing CoolStreaming in this paper, and present several interesting observations from these large-scale tests; in particular, the larger the overlay size, the better the streaming quality it can deliver.

Leader-Member Exchange as a Mediator of the Relationship Between Transformational Leadership and Followers' Performance and Organizational Citizenship Behavior

Abstract: We developed a model in which leader-member exchange mediated between perceived transformational leadership behaviors and followers' task performance and organizational citizenship behaviors. Our s...

Core Vector Machines: Fast SVM Training on Very Large Data Sets

Abstract: Standard SVM training has O(m3) time and O(m2) space complexities, where m is the training set size. It is thus computationally infeasible on very large data sets. By observing that practical SVM implementations only approximate the optimal solution by an iterative strategy, we scale up kernel methods by exploiting such "approximateness" in this paper. We first show that many kernel methods can be equivalently formulated as minimum enclosing ball (MEB) problems in computational geometry. Then, by adopting an efficient approximate MEB algorithm, we obtain provably approximately optimal solutions with the idea of core sets. Our proposed Core Vector Machine (CVM) algorithm can be used with nonlinear kernels and has a time complexity that is linear in m and a space complexity that is independent of m. Experiments on large toy and real-world data sets demonstrate that the CVM is as accurate as existing SVM implementations, but is much faster and can handle much larger data sets than existing scale-up methods. For example, CVM with the Gaussian kernel produces superior results on the KDDCUP-99 intrusion detection data, which has about five million training patterns, in only 1.4 seconds on a 3.2GHz Pentium--4 PC.

Synthesis of iron fertilization experiments: From the iron age in the age of enlightenment

Abstract: Comparison of eight iron experiments shows that maximum Chl a, the maximum DIC removal, and the overall DIC/Fe efficiency all scale inversely with depth of the wind mixed layer (WML) defining the light environment. Moreover, lateral patch dilution, sea surface irradiance, temperature, and grazing play additional roles. The Southern Ocean experiments were most influenced by very deep WMLs. In contrast, light conditions were most favorable during SEEDS and SERIES as well as during IronEx-2. The two extreme experiments, EisenEx and SEEDS, can be linked via EisenEx bottle incubations with shallower simulated WML depth. Large diatoms always benefit the most from Fe addition, where a remarkably small group of thriving diatom species is dominated by universal response of Pseudo-nitzschia spp. Significant response of these moderate (10–30 μm), medium (30–60 μm), and large (>60 μm) diatoms is consistent with growth physiology determined for single species in natural seawater. The minimum level of “dissolved” Fe (filtrate < 0.2 μm) maintained during an experiment determines the dominant diatom size class. However, this is further complicated by continuous transfer of original truly dissolved reduced Fe(II) into the colloidal pool, which may constitute some 75% of the “dissolved” pool. Depth integration of carbon inventory changes partly compensates the adverse effects of a deep WML due to its greater integration depths, decreasing the differences in responses between the eight experiments. About half of depth-integrated overall primary productivity is reflected in a decrease of DIC. The overall C/Fe efficiency of DIC uptake is DIC/Fe ∼ 5600 for all eight experiments. The increase of particulate organic carbon is about a quarter of the primary production, suggesting food web losses for the other three quarters. Replenishment of DIC by air/sea exchange tends to be a minor few percent of primary CO2 fixation but will continue well after observations have stopped. Export of carbon into deeper waters is difficult to assess and is until now firmly proven and quite modest in only two experiments.

Progressive skyline computation in database systems

Abstract: The skyline of a d-dimensional dataset contains the points that are not dominated by any other point on all dimensions. Skyline computation has recently received considerable attention in the database community, especially for progressive methods that can quickly return the initial results without reading the entire database. All the existing algorithms, however, have some serious shortcomings which limit their applicability in practice. In this article we develop branch-and-bound skyline (BBS), an algorithm based on nearest-neighbor search, which is I/O optimal, that is, it performs a single access only to those nodes that may contain skyline points. BBS is simple to implement and supports all types of progressive processing (e.g., user preferences, arbitrary dimensionality, etc). Furthermore, we propose several interesting variations of skyline computation, and show how BBS can be applied for their efficient processing.

How Does Industry Affect Firm Financial Structure

Abstract: We examine the importance of industry to firm-level financial and real decisions. We find that in addition to standard industry fixed effects, financial structure also depends on a firm's position within its industry. In competitive industries, a firm's financial leverage depends on its natural hedge (its proximity to the median industry capital--labor ratio), the actions of other firms in the industry, and its status as entrant, incumbent, or exiting firm. Financial leverage is higher and less dispersed in concentrated industries, where strategic debt interactions are also stronger, but a firm's natural hedge is not significant. Our results show that financial structure, technology, and risk are jointly determined within industries. These findings are consistent with recent industry equilibrium models of financial structure. Copyright 2005, Oxford University Press.

Scalable collaborative filtering using cluster-based smoothing

Abstract: Memory-based approaches for collaborative filtering identify the similarity between two users by comparing their ratings on a set of items. In the past, the memory-based approach has been shown to suffer from two fundamental problems: data sparsity and difficulty in scalability. Alternatively, the model-based approach has been proposed to alleviate these problems, but this approach tends to limit the range of users. In this paper, we present a novel approach that combines the advantages of these two approaches by introducing a smoothing-based method. In our approach, clusters generated from the training data provide the basis for data smoothing and neighborhood selection. As a result, we provide higher accuracy as well as increased efficiency in recommendations. Empirical studies on two datasets (EachMovie and MovieLens) show that our new proposed approach consistently outperforms other state-of-art collaborative filtering algorithms.

Factional groups: a new vantage on demographic faultlines, conflict, and disintegration in work teams

Abstract: We develop the concept of factional groups, or those in which members are representatives from a small number of (often just two) social entities. Such groups include many merger integration teams,...

A Review of Water Hammer Theory and Practice

Abstract: Hydraulic transients in closed conduits have been a subject of both theoretical stud intense practical interest for more than one hundred years. While straightforward in te of the one-dimensional nature of pipe networks, the full description of transient fluid fl pose interesting problems in fluid dynamics. For example, the response of the turbu structure and strength to transient waves in pipes and the loss of flow axisymme pipes due to hydrodynamic instabilities are currently not understood. Yet, such u standing is important for modeling energy dissipation and water quality in transient flows. This paper presents an overview of both historic developments and presen research and practice in the field of hydraulic transients. In particular, the paper cusses mass and momentum equations for one-dimensional Flows, wavespeed, nu solutions for one-dimensional problems, wall shear stress models; two-dimensional and momentum equations, turbulence models, numerical solutions for two-dimen problems, boundary conditions, transient analysis software, and future practical an search needs in water hammer. The presentation emphasizes the assumptions and tions involved in various governing equations so as to illuminate the range of applic ity as well as the limitations of these equations. Understanding the limitations of cu models is essential for (i) interpreting their results, (ii) judging the reliability of the da obtained from them, (iii) minimizing misuse of water-hammer models in both research practice, and (iv) delineating the contribution of physical processes from the contribu of numerical artifacts to the results of waterhammer models. There are 134 refrences in this review article.@DOI: 10.1115/1.1828050 #

High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

Abstract: We report a novel approach in fabricating high-performance enhancement mode (E-mode) AlGaN/GaN HEMTs. The fabrication technique is based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing with an annealing temperature lower than 500/spl deg/C. Starting with a conventional depletion-mode HEMT sample, we found that fluoride-based plasma treatment can effectively shift the threshold voltage from -4.0 to 0.9 V. Most importantly, a zero transconductance (g/sub m/) was obtained at V/sub gs/=0 V, demonstrating for the first time true E-mode operation in an AlGaN/GaN HEMT. At V/sub gs/=0 V, the off-state drain leakage current is 28 /spl mu/A/mm at a drain-source bias of 6 V. The fabricated E-mode AlGaN/GaN HEMTs with 1 /spl mu/m-long gate exhibit a maximum drain current density of 310 mA/mm, a peak g/sub m/ of 148 mS/mm, a current gain cutoff frequency f/sub T/ of 10.1 GHz and a maximum oscillation frequency f/sub max/ of 34.3 GHz.

Web Personalization as a Persuasion Strategy: An Elaboration Likelihood Model Perspective

Abstract: With advances in tracking and database technologies, firms are increasingly able to understand their customers and translate this understanding into products and services that appeal to them. Technologies such as collaborative filtering, data mining, and click-stream analysis enable firms to customize their offerings at the individual level. While there has been a lot of hype about web personalization recently, our understanding of its effectiveness is far from conclusive. Drawing on the elaboration likelihood model (ELM) literature, this research takes the view that the interaction between a firm and its customers is one of communicating a persuasive message to the customers driven by business objectives. In particular, we examine three major elements of a web personalization strategy: level of preference matching, recommendation set size, and sorting cue. These elements can be manipulated by a firm in implementing its personalization strategy. This research also investigates a personal disposition, need for cognition, which plays a role in assessing the effectiveness of web personalization. Research hypotheses are tested using 1,000 subjects in three field experiments based on a ring-tone download website. Our findings indicate the saliency of these variables in different stages of the persuasion process. Theoretical and practical implications of the findings are discussed.

Epoxy Nanocomposites with Highly Exfoliated Clay: Mechanical Properties and Fracture Mechanisms

Abstract: Epoxy/clay nanocomposites with a better exfoliated morphology have been successfully prepared using a so-called “slurry-compounding” process. The microstructures of the nanocomposites (epoxy/S-clays) were characterized by means of optical microscopy and transmission electron microscopy (TEM). It was found that clay was highly exfoliated and uniformly dispersed in the resulting nanocomposite. Characterizations of mechanical and fracture behaviors revealed that Young's modulus increases monotonically with increasing the clay concentration while the fracture toughness shows a maximum at 2.5 wt % of clay. No R-curve behavior was observed in these nanocomposites. The microdeformation and fracture mechanisms were investigated by studying the microstructure of arrested crack tips and the damage zone using TEM and scanning electron microscopy (SEM). The initiation and development of microcracks are the dominant microdeformation and fracture mechanisms in the epoxy/S-clay nanocomposites. Most of the microcracks in...

Controlled growth of large-area, uniform, vertically aligned arrays of alpha-Fe2O3 nanobelts and nanowires.

Abstract: Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O2. The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (∼700 °C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (∼800 °C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.

Heterodimers of nanoparticles: Formation at a liquid-liquid interface and particle-specific surface modification by functional molecules

Abstract: On the basis of a fundamental property of nanoparticles, the self-assembling at a liquid−liquid interface to form “colloidosomes”, a heterogeneous reaction takes place on the exposed surface of the nanoparticles to produce the heterodimers of two distinct nanospheres, which can be modified by two different functional molecules in a particle-specific manner.

Size really matters: Further evidence on the negative relationship between board size and firm value

Abstract: This study examines the impact of corporate governance mechanisms on the firm value of Singapore and Malaysia firms (as measured by Tobin's Q ) We find little evidence of relationships between most corporate governance mechanisms and Tobin's Q However, consistent with Yermack [Higher market valuation of firms with a small board of directors J Financ Econ 40 (1996), 185–211] and Eisenberg et al [Larger board size and decreasing firm value in small firms J Financ Econ 48 (1998), 35–54], we find that there is an inverse relationship between board size and firm value in both countries This suggests that the negative relationship between board size and firm value transcends different corporate governance systems

Structures, electronic states, photoluminescence, and carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles.

Abstract: The excellent electroluminescent (EL) properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles, 1-methyl-1,2,3,4,5-pentaphenylsilole (MPPS), and 1,1,2,3,4,5-hexaphenylsilole (HPS) have been found. Despite some studies devoted to these materials, very little is known about the real origin of their unique EL properties. Therefore, we investigated the structures, photoluminescence (PL), and charge carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles as well as the effect of substituents on these characteristics. The single crystals of the three siloles involving 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS), MPPS, and HPS were grown and their crystal structures were determined by X-ray diffraction. Three siloles have nonplanar molecular structures. The substituents at 1,1-positions enhance the steric hindrance and have predominant influence on the twisted degree of phenyl groups at ring carbons. This nonplanar structure reduces the intermolecular interaction and the likelihood of e...

On discovering moving clusters in spatio-temporal data

Abstract: A moving cluster is defined by a set of objects that move close to each other for a long time interval. Real-life examples are a group of migrating animals, a convoy of cars moving in a city, etc. We study the discovery of moving clusters in a database of object trajectories. The difference of this problem compared to clustering trajectories and mining movement patterns is that the identity of a moving cluster remains unchanged while its location and content may change over time. For example, while a group of animals are migrating, some animals may leave the group or new animals may enter it. We provide a formal definition for moving clusters and describe three algorithms for their automatic discovery: (i) a straight-forward method based on the definition, (ii) a more efficient method which avoids redundant checks and (iii) an approximate algorithm which trades accuracy for speed by borrowing ideas from the MPEG-2 video encoding. The experimental results demonstrate the efficiency of our techniques and their applicability to large spatio-temporal datasets.

Enhancement of photocatalytic activity of mesoporous TiO2 by using carbon nanotubes

Abstract: Titanium dioxide/carbon nanotubes (TiO 2 /CNTs) composites were prepared with the aid of ultrasonic irradiation. Products of different TiO 2 :CNTs molar ratio were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) adsorption analysis, thermogravimetric and differential thermal analysis (TGA–DSC), photoluminescence (PL) and UV–vis spectroscopy measurements (UV–vis). The photocatalytic activity was evaluated by the degradation of acetone and by the detection of the hydroxyl radical (·OH) signals using electron paramagnetic resonance (EPR). It is found that the crystalline TiO 2 is composed of both anatase and brookite phases. The agglomerated morphology and the particle size of TiO 2 in the composites change in the presence of CNTs. The CNTs in the composites are virtually all covered by TiO 2 . Other than an increase of the surface area, the addition of CNTs does not affect the mesoporous nature of the TiO 2 . Meanwhile, more hydroxyl groups are available on the surface of the composite than in the case of the pure TiO 2 . The higher the content of CNTs, there is more effective in the suppression of the recombination of photo-generated e − /h + pairs. However, excessive CNTs also shield the TiO 2 from absorbing UV light. The optimal amount of TiO 2 and CNTs is in the range of 1:0.1 and 1:0.2 (feedstock molar ratio). These samples have much more highly photocatalytic activity than P25 and TiO 2 /activated carbon (AC) composite. The mechanism for the enhanced photocatalytic activity of TiO 2 by CNTs is proposed.

Analytic model of phononic crystals with local resonances

Abstract: A simple analytic model is presented to describe the low-frequency effective mass densities of three-component phononic crystals with local resonances. We show that the effective mass densities can turn negative close to the local resonances. Expressions for the effective mass densities are derived for both three-dimensional systems with coated spheres embedded in a host matrix, and two-dimensional systems with coated cylinders embedded in a host matrix.

Extending the chain of relationships among organizational justice, social exchange, and employee reactions: the role of contract violations

Abstract: This study extends prior research on the chain of relationships among organizational justice, social exchange relationships, and employee reactions by investigating the proposed mediating role of psychological contract violations. Results obtained from a longitudinal design examining a sample of 191 employees provide strong support for the proposal, enhance support for chain directionality, validate theoretical predictions about determinants of contract violations, and provide initial evidence supporting a proposed integration of perceived organizational support and psychological contract theory.

National character does not reflect mean personality trait levels in 49 cultures

Abstract: Most people hold beliefs about personality characteristics typical of members of their own and others' cultures. These perceptions of national character may be generalizations from personal experience, stereotypes with a "kernel of truth," or inaccurate stereotypes. We obtained national character ratings of 3989 people from 49 cultures and compared them with the average personality scores of culture members assessed by observer ratings and self-reports. National character ratings were reliable but did not converge with assessed traits. Perceptions of national character thus appear to be unfounded stereotypes that may serve the function of maintaining a national identity.

Enhancement of adsorption and photocatalytic activity of TiO2 by using carbon nanotubes for the treatment of azo dye

Abstract: The effect of carbon nanotubes (CNTs) on the adsorption and the photocatalytic properties of TiO 2 (P25) for the treatment of azo dyes, including one monoazo dye Procion Red MX-5B, and two diazo dyes Procion Yellow HE4R and Procion Red HE3B, are investigated by Brunauer–Emmett–Teller (BET) measurement, spectrophotometer, total organic carbon (TOC), high proficiency liquid chromatography (HPLC), Raman spectroscopy (Raman), photoluminescence (PL), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM) analyses. The results show that compared with activated carbon (AC), CNTs can comparatively better improve the adsorption of the dyes onto P25 due to the strong interaction between P25 and CNTs. Residual TOC in the solutions and the amount of cyanuric acid evolved after degradation both confirm that the adsorption ability of P25 is enhanced by CNTs. CNTs also facilitate the photocatalytic activity of P25 in the degradation of the three azo dyes more efficiently than AC. With PL and EPR analysis, the mechanism of the enhancement of the photocatalytic activity of P25 by CNTs is proposed. The excited e − in conduction band of TiO 2 may migrate into CNTs, of which have special structure and the ability for e − transport. Thus, the possibility of the recombination of e − /h + pairs decreases. Meanwhile, O 2 adsorbed on the surface of CNTs may accept e − and form O 2 − , which also leads to the formation of OH in the system. Therefore, there are more radicals in the system, resulting in the quicker degradation of the dyes.

Local color transfer via probabilistic segmentation by expectation-maximization

Abstract: We address the problem of regional color transfer between two natural images by probabilistic segmentation. We use a new expectation-maximization (EM) scheme to impose both spatial and color smoothness to infer natural connectivity among pixels. Unlike previous work, our method takes local color information into consideration, and segment image with soft region boundaries for seamless color transfer and compositing. Our modified EM method has two advantages in color manipulation: first, subject to different levels of color smoothness in image space, our algorithm produces an optimal number of regions upon convergence, where the color statistics in each region can be adequately characterized by a component of a Gaussian mixture model (GMM). Second, we allow a pixel to fall in several regions according to our estimated probability distribution in the EM step, resulting in a transparency-like ratio for compositing different regions seamlessly. Hence, natural color transition across regions can be achieved, where the necessary intra-region and inter-region smoothness are enforced without losing original details. We demonstrate results on a variety of applications including image deblurring, enhanced color transfer, and colorizing gray scale images. Comparisons with previous methods are also presented.

Service discovery in pervasive computing environments

Abstract: Pervasive computing environments pose unique service discovery challenges. We have developed a taxonomy of existing protocols as a basis for analyzing their approaches and identifying problems and open issues relative to service discovery in pervasive computing environments.

An integrative view of international experience

Abstract: Integrating multiple theoretical perspectives, we differentiated international experience into current and past experience. In addition, we organized past international experience along two dimensions: domain (work/travel) and cultural specificity (U.S./ non-U.S.). We examined the effects of expatriates' current assignment experience and past international experience on cross-cultural adjustment. The results indicate that past international experience moderates the relationship between current assignment tenure and general and work adjustment and also that general and work adjustment directly affect expatriates' early return intentions.