Showing papers by "The Chinese University of Hong Kong published in 1998"

Quantitative Analysis of Fetal DNA in Maternal Plasma and Serum: Implications for Noninvasive Prenatal Diagnosis

Abstract: Summary We have developed a real-time quantitative PCR assay to measure the concentration of fetal DNA in maternal plasma and serum. Our results show that fetal DNA is present in high concentrations in maternal plasma, reaching a mean of 25.4 genome equivalents/ml (range 3.3–69.4) in early pregnancy and 292.2 genome equivalents/ml (range 76.9–769) in late pregnancy. These concentrations correspond to 3.4% (range 0.39%–11.9%) and 6.2% (range 2.33%–11.4%) of the total plasma DNA in early and late pregnancy, respectively. Sequential follow-up study of women who conceived by in vitro fertilization shows that fetal DNA can be detected in maternal serum as early as the 7th wk of gestation and that it then increases in concentration as pregnancy progresses. These data suggest that fetal DNA can be readily detected in maternal plasma and serum and may be a valuable source of material for noninvasive prenatal diagnosis.

Toward A Taxonomy of Multidimensional Constructs

Abstract: We propose a taxonomy of multidimensional constructs based on the relations between the construct and its dimensions. Multidimensional constructs that exist at deeper levels than their dimensions we term latent model. We call constructs formed as algebraic functions of their dimensions aggregate model, whereas constructs formed as different profiles of dimensional characteristics we term profile model. We discuss the nature of multidimensional constructs defined under these models and their operationalizations in empirical research.

Explaining International and Intertemporal Variations in Income Inequality

Abstract: This paper explores the propositions that, income inequality is relatively stable within countries; and that it varies significantly among countries. A new and expanded data set provides broad support for both propositions. Drawing on a political economy and capital market imperfection arguments to explain the intertemporal and international variation in inequality, the empirical analysis shows that the predicted variables associated with the first argument (a measure of civil liberties and the initial level of secondary schooling) and the second argument (a measure of financial depth and the initial distribution of land) are indeed important determinants of inequality. This paper explores two propositions regarding income inequality. They are: first, income inequality is relatively stable within countries; and second, it varies significantly across countries.' To illustrate, note that the Gini coefficient in India remained almost constant for forty years (1951-92) with mean 32.6 and standard deviation 2.0.2 In contrast, the variation in Gini coefficients across countries is large: 61.9 in Honduras in 1968 compared with 17.8 in Bulgaria in 1976. If substantiated, these propositions have potentially significant implications for poverty. The significance of the first is obvious - barring any fundamental socio-political change, poverty reduction will depend crucially on the rate of economic growth. Given this, the significance of the second is that in inegalitarian economies the poor will enjoy a smaller share of any national increment in income than in more egalitarian ones. Drawing on a new and expanded data set on inequality (Deininger and Squire, 1996a), the first of the paper's three sections conducts standard statistical tests of the two propositions. The sample comprises 573 observations on the most common measure of inequality - the Gini coefficient - for 49 developed and developing countries covering the period 1947-94. The results broadly confirm our two propositions. Specifically, analysis of variance (ANOVA) shows that about 90% of the total variance in the Gini coefficients

Prenatal diagnosis of fetal RhD status by molecular analysis of maternal plasma.

Abstract: Background The ability to determine fetal RhD status noninvasively is useful in the treatment of RhD-sensitized pregnant women whose partners are heterozygous for the RhD gene. The recent demonstration of fetal DNA in maternal plasma raises the possibility that fetal RhD genotyping may be possible with the use of maternal plasma. Methods We studied 57 RhD-negative pregnant women and their singleton fetuses. DNA extracted from maternal plasma was analyzed for the RhD gene with a fluorescence-based polymerase-chain-reaction (PCR) test sensitive enough to detect the RhD gene in a single cell. Fetal RhD status was determined directly by serologic analysis of cord blood or PCR analysis of amniotic fluid. Results Among the 57 RhD-negative women, 12 were in their first trimester of pregnancy, 30 were in their second trimester, and 15 were in their third trimester. Thirty-nine fetuses were RhD-positive, and 18 were RhD-negative. In the samples obtained from women in their second or third trimester of pregnancy, t...

Income Inequality is not Harmful for Growth: Theory and Evidence

Abstract: The paper shows that income inequality may theoretically lead to higher economic growth if public consumption enters the utility function. Empirically, baseline estimations and a sensitivity analysis show that income inequality is positively, and most of the time significantly, associated with economic growth. These findings stand in sharp contrast to the negative association between inequality and growth propounded by Alesina and Rodrik and by Persson and Tabellini.

The Foreign Exchange Exposure of Japanese Multinational Corporations

Abstract: We find that about 25 percent of our sample of 171 Japanese multinationals' stock returns experienced economically significant positive exposure effects for the period January 1979 to December 1993. The extent to which a firm is exposed to exchange-rate fluctuations can be explained by the level of its export ratio and by variables that are proxies for its hedging needs. Highly leveraged firms, or firms with low liquidity, tend to have smaller exposures. Foreign exposure is found to increase with firm size. We also find that keiretsu multinationals are more exposed to exchange-rate risk than nonkeiretsu firms. IT IS CONVENTIONAL WISDOM that exchange-rate movements affect both the cash flows of a firm's operations and the discount rate employed to value these cash flows.' Measuring foreign exchange exposure is now a central issue of international financial management, and this issue has spawned a considerable amount of research. Existing empirical evidence on foreign exchange exposure, however, seems perplexing; studies have so far documented a weak link between contemporaneous exchange-rate fluctuations and stock returns of U.S. multinational firms.2 Gendreau (1994) finds it difficult and unconvincing that the weak results imply that exchange-rate changes have no effect on exporters' stock returns. Bartov arnd Bodnar (1994) attribute the observed insignificant relationship between exchange-rate changes and st;ock returns to probable problems associated with the previous studies' samiple selection procedure, or to mispricing caused by investors' errors in estimat

Texture information in run-length matrices

Abstract: We use a multilevel dominant eigenvector estimation algorithm to develop a new run-length texture feature extraction algorithm that preserves much of the texture information in run-length matrices and significantly improves image classification accuracy over traditional run-length techniques. The advantage of this approach is demonstrated experimentally by the classification of two texture data sets. Comparisons with other methods demonstrate that the run-length matrices contain great discriminatory information and that a good method of extracting such information is of paramount importance to successful classification.

Globule-to-Coil Transition of a Single Homopolymer Chain in Solution

Abstract: Using a nearly monodisperse high molar mass poly( $N$-isopropylacrylamide) (PNIPAM) sample, we successfully made the conformation change of individual PNIPAM chains from a coil to a fully collapsed stable single chain globule in an extremely dilute aqueous solution, which enabled us to study for the first time the globule-to-coil transition of a single homopolymer chain in solution. A comparison to the coil-to-globule and the globule-to-coil transitions revealed a hysteresis in the globule-to-coil transition. Our results also confirmed the existence of two additional thermodynamically stable states between the coil and the globule states, namely, the crumpled coil and the molten globule.

Mining fuzzy association rules in databases

Abstract: Data mining is the discovery of previously unknown, potentially useful and hidden knowledge in databases. In this paper, we concentrate on the discovery of association rules. Many algorithms have been proposed to find association rules in databases with binary attributes. We introduce the fuzzy association rules of the form, 'If X is A then Y is B', to deal with quantitative attributes. X, Y are set of attributes and A, B are fuzzy sets which describe X and Y respectively. Using the fuzzy set concept, the discovered rules are more understandable to human. Moreover, fuzzy sets handle numerical values better than existing methods because fuzzy sets soften the effect of sharp boundaries.

Finite element methods and their convergence for elliptic and parabolic interface problems

Abstract: In this paper, we consider the finite element methods for solving second order elliptic and parabolic interface problems in two-dimensional convex polygonal domains. Nearly the same optimal $L^2$ -norm and energy-norm error estimates as for regular problems are obtained when the interfaces are of arbitrary shape but are smooth, though the regularities of the solutions are low on the whole domain. The assumptions on the finite element triangulation are reasonable and practical.

Music training improves verbal memory

Abstract: Magnetic resonance imaging has shown that the left planum temporale region of the brain is larger in musicians than in non-musicians1. If this results from a change in cortical organization2,3, the left temporal area in musicians might have a better developed cognitive function than the right temporal lobe. Because verbal memory is mediated mainly by the left temporal lobe, and visual memory by the right4,5, adults with music training should have better verbal, but not visual, memory than adults without such training. Here we show that adults who received music training before the age of 12 have a better memory for spoken words than those who did not. Music training in childhood may therefore have long-term positive effects on verbal memory.

"It's Always More Difficult than You Plan and Imagine": Teachers' Perceived Difficulties in Introducing the Communicative Approach in South Korea.

Abstract: Despite the widespread adoption of communicative language teaching (CLT) in ESL countries, research suggests that curricular innovations prompted by the adoption of CLT in EFL countries have generally been difficult. The literature on curriculum innovation suggests that teachers' understanding of an innovation is central to its success. A study of a group of South Korean secondary school English teachers' perceived difficulties in adopting CLT reveals that the difficulties have their source in the differences between the underlying educational theories of South Korea and those of Western countries. The results suggest that, to adopt CLT, EFL countries like South Korea will need to change their fundamental approach to education and that implementation should be gradual and grounded in the countries' own EFL situations. In the long run, EFL countries should establish their own contingent of language researchers in order to develop English teaching theories more suitable for their EFL contexts. Change agents must study teachers' perceptions of an innovation to ensure its success.

Mining association rules with weighted items

Abstract: Discovery of association rules has been found useful in many applications. In previous work, all items in a basket database are treated uniformly. We generalize this to the case where items are given weights to reflect their importance to the user. The weights may correspond to special promotions on some products, or the profitability of different items. We can mine the weighted association rules with weights. The downward closure property of the support measure in the unweighted case no longer exists and previous algorithms cannot be applied. In this paper, two new algorithms are introduced to handle this problem. In these algorithms we make use of a metric called the k-support bound in the mining process. Experimental results show the efficiency of the algorithms for large databases.

Detecting postnatal depression in Chinese women. Validation of the Chinese version of the Edinburgh Postnatal Depression Scale.

Abstract: BACKGROUND We evaluated the utility of the Chinese version of the Edinburgh Postnatal Depression Scale (EPDS) and measured the prevalence of major depression six weeks after confinement among Chinese women in Hong Kong. METHOD A prospective cohort of 145 women completed the EPDS, the 12-item General Health Questionnaire (GHQ) and the Beck Depression Inventory (BDI) six weeks after giving birth. They were then assessed with the Structured Clinical Interview for DSM-III-R, non-patient version (SCID-NP) to establish psychiatric diagnosis. The criterion validity of EPDS was tested against this clinical diagnosis, and the concurrent validity against the GHQ and BDI scores was also evaluated. The internal consistency of the scales was measured by Cronbach's alpha coefficient. RESULTS The Chinese EPDS had satisfactory psychometric properties and a cut-off score of 9/10 is recommended for screening depressive illness in a general postnatal population. At six weeks postpartum, 5.5% of the study population suffered from major depression. CONCLUSIONS The Chinese EPDS will be useful for screening for postnatal depression.

On characterization of entropy function via information inequalities

Abstract: Given n discrete random variables /spl Omega/={X/sub 1/, /spl middot//spl middot//spl middot/, X/sub n/}, associated with any subset /spl alpha/ of (1, 2, /spl middot//spl middot//spl middot/, n), there is a joint entropy H(X/sub /spl alpha//) where X/sub /spl alpha//={X/sub i/:i/spl epsiv//spl alpha/}. This can be viewed as a function defined on 2/sup {1, 2, /spl middot//spl middot//spl middot/, n}/ taking values in (0, +/spl infin/). We call this function the entropy function of /spl Omega/. The nonnegativity of the joint entropies implies that this function is nonnegative; the nonnegativity of the conditional joint entropies implies that this function is nondecreasing; and the nonnegativity of the conditional mutual information implies that this function has the following property: for any two subsets /spl alpha/ and /spl beta/ of {1, 2, /spl middot//spl middot//spl middot/, n} H/sub /spl Omega//(/spl alpha/)+H/sub /spl Omega//(/spl beta/)/spl ges/H/sub /spl Omega//(/spl alpha//spl cup//spl beta/)+H/sub /spl Omega//(/spl alpha//spl cap//spl beta/). These properties are the so-called basic information inequalities of Shannon's information measures. Do these properties fully characterize the entropy function? To make this question more precise, we view an entropy function as a 2/sup n/-1-dimensional vector where the coordinates are indexed by the nonempty subsets of the ground set {1, 2, /spl middot//spl middot//spl middot/, n}. Let /spl Gamma//sub n/ be the cone in R/sup 2n-1/ consisting of all vectors which have these three properties when they are viewed as functions defined on 2/sup {1, 2, /spl middot//spl middot//spl middot/, n}/. Let /spl Gamma//sub n/* be the set of all 2/sup n/-1-dimensional vectors which correspond to the entropy functions of some sets of n discrete random variables. The question can be restated as: is it true that for any n, /spl Gamma/~/sub n/*=/spl Gamma//sub n/? Here /spl Gamma/~/sub n/* stands for the closure of the set /spl Gamma//sub n/*. The answer is "yes" when n=2 and 3 as proved in our previous work. Based on intuition, one may tend to believe that the answer should be "yes" for any n. The main discovery of this paper is a new information-theoretic inequality involving four discrete random variables which gives a negative answer to this fundamental problem in information theory: /spl Gamma/~*/sub n/ is strictly smaller than /spl Gamma//sub n/ whenever n>3. While this new inequality gives a nontrivial outer bound to the cone /spl Gamma/~/sub 4/*, an inner bound for /spl Gamma/~*/sub 4/ is also given. The inequality is also extended to any number of random variables.

Glutamate-receptor genes in plants.

Abstract: In animal brains, ionotropic glutamate receptors (GluRs) function as glutamate-activated ion channels in rapid synaptic transmission We have now discovered that genes encoding putative ionotropic GluRs exist in plants, and we present preliminary evidence for their involvement in light-signal transduction It may be that signalling between cells by excitatory amino acids in animal brains evolved from a primitive signalling mechanism that existed before the divergence of plants and animals Our findings also help to explain why neuroactive compounds made by plants work on receptors in human brains

Intracranial stenosis in Chinese patients with acute stroke

Abstract: We studied 100 consecutive acute stroke patients in a Chinese population with transcranial Doppler and CT. Twenty patients had intracerebral hemorrhage and 14 patients did not have adequate temporal windows for transcranial Doppler examination. Among the remaining 66 patients, 22 patients (33%) had intracranial occlusive diseases and 3 (6%) had extracranial carotid stenosis. Our data showed that intracranial occlusive disease is the most commonly found vascular lesion in our acute stroke patients.

Performance and Survival of Joint Ventures with Non-Conventional Ownership Structures

Abstract: The international joint venture (JV) literature has focused on two parent JVs formed between one foreign and one local firm. Yet, other types of JVs exist. This paper identifies four distinct forms of JVs based on the JV partners' nationality and equity affiliation. These are: (i) JVs that are formed between affiliated home-country based firms; (ii) JVs that are formed between unaffiliated home-country based firmsl; (iii) JVs that are formed between home-country based and local firms; and (iv) JVs that are formed between home-country and third-country based firms. Our analysis of 737 Japanese JVs in Asia demonstrates that the conventionally assumed form of JV represented only 30 percent of the total. Further, each of the four JV forms significantly differed in terms of incidence, performance, and survival likelihood.

Algebraic-geometry codes

Abstract: The theory of error-correcting codes derived from curves in an algebraic geometry was initiated by the work of Goppa as generalizations of Bose-Chaudhuri-Hocquenghem (BCH), Reed-Solomon (RS), and Goppa codes. The development of the theory has received intense consideration since that time and the purpose of the paper is to review this work. Elements of the theory of algebraic curves, at a level sufficient to understand the code constructions and decoding algorithms, are introduced. Code constructions from particular classes of curves, including the Klein quartic, elliptic, and hyperelliptic curves, and Hermitian curves, are presented. Decoding algorithms for these classes of codes, and others, are considered. The construction of classes of asymptotically good codes using modular curves is also discussed.

Underpricing and aftermarket performance of IPOs in Shanghai, China

Abstract: A-share initial public offerings (IPOs) in Shanghai were 289% underpriced, against a mere 26% for B-share IPOs. Regression analysis suggests that the `Chinese characteristic' of high equity retention by the state, a long time-lag between offering and listing and ex-ante risk of new issues were key determinants of market-adjusted IPO underpricing. After controlling for the market comovements, infrequent trading and a higher risk for new issues, the excess returns of overpriced A-share IPOs and B-share IPOs persisted over a long period of time. Rather than being a speculative conjecture, this represents a real phenomenon in that large excess returns accrue in the long run, albeit it meant less negative accumulated returns than the overall market, which had dropped sharply.

Scenarios for the Measurement of Collectivism and Individualism

Abstract: This article presents a method that uses scenarios for the measurement of horizontal (H)and vertical (V) individualism (I) and collectivism (C) across cultures, with university samples. The scenarios were developed by using focus groups, to cover a wide range of social situations often found among university students. Graduate student judges indicated which responses to each scenario represented HI, VI, HC, or VC judgments. When the judges did not agree on these judgments, the scenarios were eliminated. Scenarios that did not distinguish responses obtained from the Illinois and Hong Kong samples were also eliminated. This resulted in a set of 16 scenarios that provide efficient measurement of the constructs. The method converges with a method that uses attitude items.

An investigation on photocatalytic activities of mixed TiO2-rare earth oxides for the oxidation of acetone in air

Abstract: The photocatalytic activities of the mixtures of TiO2 (P25) with three rare earth oxides were investigated. The effects of the rare earth oxide contents and calcination temperature on the photocatalytic activities were studied. The results reveal that the mixtures of TiO2 with La2O3 (0.5 wt.%) or Y2O3 (0.5 wt.%) calcined at 700 °C or 650 °C exhibit higher photoactivity than pure TiO2 (P25) for the oxidation of acetone. On the other hand, the mixtures of TiO2 with CeO2 have lower photoactivity than pure TiO2. Experimental results of polycrystalline X-ray diffraction, photoexcited transient absorption decay and zeta potential measurements show that the presence of these rare earth oxides can inhibit anatase to rutile transformation at elevated temperatures. The lower photocatalytic activity of TiO2/CeO2 mixtures can be explained by the fast recombination rate of photogenerated electron-hole pairs and high isoelectric point in terms of pH value. The preparation method of these mixtures is also described.

A PII-like protein in Arabidopsis: Putative role in nitrogen sensing

Abstract: PII is a protein allosteric effector in Escherichia coli and other bacteria that indirectly regulates glutamine synthetase at the transcriptional and post-translational levels in response to nitrogen availability. Data supporting the notion that plants have a nitrogen regulatory system(s) includes previous studies showing that the levels of mRNA for plant nitrogen assimilatory genes such as glutamine synthetase (GLN) and asparagine synthetase (ASN) are modulated by carbon and organic nitrogen metabolites. Here, we have characterized a PII homolog (GLB1) in two higher plants, Arabidopsis thaliana and Ricinus communis (Castor bean). Each plant PII-like protein has high overall identity to E. coli PII (50%). Western blot analyses reveal that the plant PII-like protein is a nuclear-encoded chloroplast protein. The PII-like protein of plants appears to be regulated at the transcriptional level in that levels of GLB1 mRNA are affected by light and metabolites. To initiate studies of the in vivo function of the Arabidopsis PII-like protein, we have constructed transgenic lines in which PII expression is uncoupled from its native regulation. Analyses of these transgenic plants support the notion that the plant PII-like protein may serve as part of a complex signal transduction network involved in perceiving the status of carbon and organic nitrogen. Thus, the PII protein found in archaea, bacteria, and now in higher eukaryotes (plants) is one of the most widespread regulatory proteins known, providing evidence for an ancestral metabolic regulatory mechanism that may have existed before the divergence of these three domains of life.

Quasinormal-mode expansion for waves in open systems

Abstract: An open system is not conservative because energy can escape to the outside. As a result, the time-evolution operator is not Hermitian in the usual sense and the eigenfunctions (factorized solutions in space and time) are no longer normal modes but quasinormal modes (QNMs) whose frequencies $\ensuremath{\omega}$ are complex. Qausinormal-mode analysis has been a powerful tool for investigating open systems. Previous studies have been mostly system specific, and use a few QNMs to provide approximate descriptions. Here the authors review developments that lead to a unifying treatment. The formulation leads to a mathematical structure in close analogy to that in conservative, Hermitian systems. Hence many of the mathematical tools for the latter can be transcribed. Emphasis is placed on those cases in which the QNMs form a complete set and thus give an exact description of the dynamics. In situations where the QNMs are not complete, the ``remainder'' is characterized. Applications to optics in microspheres and to gravitational waves from black holes are given as examples. The second-quantized theory is sketched. Directions for further development are outlined.

Qualitative test and force optimization of 3-D frictional form-closure grasps using linear programming

Abstract: This paper formalizes qualitative test of 3D frictional form-closure grasps of n robotic fingers as a problem of linear programming (LP). It is well-known that a sufficient and necessary condition for form-closure grasps is that the origin of the wrench space lies inside the convex hull of primitive contact wrenches. We demonstrate that the problem of querying whether the origin lies inside the convex hull is equivalent to a ray-shooting problem, which is dual to a LP problem based on the duality between convex hulls and convex polytopes. Furthermore, this paper addresses a problem of minimizing the L/sub 1/ norm of the grasp forces balancing an external wrench, which can be also transformed to a ray-shooting problem. We have implemented the algorithms and confirmed their real-time efficiency for qualitative test and grasp force optimization.