Joseph Hun Wei Lee

Neural network modelling of coastal algal blooms

An artificial neural network (ANN), a data driven modelling approach, is proposed to predict the algal bloom dynamics of the coastal waters of Hong Kong. The commonly used back-propagation learning algorithm is employed for training the ANN. The modeling is based on (a) comprehensive biweekly water quality data at Tolo Harbour (1982 � /2000); and (b) 4-year set of weekly phytoplankton abundance data at Lamma Island (1996 � /2000). Algal biomass is represented as chlorophyll-a and cell concentration of Skeletonema at the two locations, respectively. Analysis of a large number of scenarios shows that the best agreement with observations is obtained by using merely the time-lagged algal dynamics as the network input. In contrast to previous findings with more complicated neural networks of algal blooms in freshwater systems, the present work suggests the algal concentration in the eutrophic sub-tropical coastal water is mainly dependent on the antecedent algal concentrations in the previous 1 � /2 weeks. This finding is also supported by an interpretation of the neural networks’ weights. Through a systematic analysis of network performance, it is shown that previous reports of predictability of algal dynamics by ANN are erroneous in that ‘future data’ have been used to drive the network prediction. In addition, a novel real time forecast of coastal algal blooms based on weekly data at Lamma is presented. Our study shows that an ANN model with a small number of input variables is able to capture trends of algal dynamics, but data with a minimum sampling interval of 1 week is necessary. However, the sufficiency of the weekly sampling for real time predictions using ANN models needs to be further evaluated against longer weekly data sets as they become available. # 2002 Elsevier Science B.V. All rights reserved.

Antibiotics in the Hong Kong metropolitan area: Ubiquitous distribution and fate in Victoria Harbour.

We investigated the presence and fate of 16 antibiotics belonging to seven groups (beta-lactams, fluoroquinolones, macrolides, sulfonamides, tetracyclines, trimethoprim and amphenicols) in effluents of sewage plants and receiving waters in Hong Kong. Cefalexin, amoxicillin, ofloxacin and erythromycin-H(2)O were ubiquitous in sea water throughout Victoria Harbour, indicating continuous discharge to the environment. This is one of the few studies reporting the frequent occurrence of cefalexin and amoxicillin in sewage effluents and sea water (170-5070 and 64-1670 ng/L in sewage; 6.1-493 and 0.64-76 ng/L in sea water, respectively). Mass flows from seven sewage plants discharged an estimated total of 14.4 kg/day to the Harbour. Typhoon shelters also appeared to play an important role as sources of antibiotics, as evidenced by elevated concentrations within their boundaries. Mass balance estimations suggested significant quantities of antibiotics are discharged to the Harbour without passage through treatment plants.

Relationship between plasma lipids and all-cause mortality in nondemented elderly

Objectives: To investigate the relationship between plasma lipids and risk of death from all causes in nondemented elderly.

Decline in cognitive and functional skills increases mortality risk in nondemented elderly

Objective: To investigate the relation between rate of decline in cognitive and functional/physical abilities and risk of death in nondemented elderly. Methods: Data were included from individuals participating in a prospective study of aging and dementia in Medicare recipients, 65 years and older, residing in northern Manhattan. The authors included 878 members of the cohort who had measures of memory, cognitive, language, or functional scores over three study intervals, excluding all participants who were demented or had more than one problem in activity of daily living (ADL) skills at baseline. Participants were classified as showing no decline, slow, medium, or rapid rate of decline, based on the slope of change in cognitive and functional/physical factors. The authors used survival methods to examine the relation of rate of decline in cognitive and functional performance to subsequent mortality in younger and older nondemented elderly and across three ethnic groups, adjusting for potential confounders. Results: Nondemented elderly with preserved ADL skills who showed rapid rates of decline on measures of visuospatial reasoning/cognitive, language, ADL, and instrumental ADL functions were approximately twice as likely to die as nondemented elderly who showed no decline or slower rates of decline, while rate of decline in memory or in measures of extremity mobility was not related to risk of death. The association of the rate of decline to risk of death was stronger in relatively young (≤75 years) than in older participants. Conclusions: Rate of decline in cognitive and functional skills predicts mortality in nondemented elderly.

ASSOCIATION BETWEEN GENETIC VARIANTS IN SORL1 AND AUTOPSY-CONFIRMED ALZHEIMER DISEASE

Genetic variants within two distinct regions of SORL1 have recently been associated with both familial and sporadic Alzheimer disease (AD) in multiple cohorts composed of more than 6,000 individuals.1 The original report was subsequently confirmed in an independent cohort of unrelated patients with probable AD and healthy elderly control subjects from a prospective study in multiethnic communities in northern Manhattan.2 To extend these results, we investigated a series of autopsy-confirmed cases with AD (n = 103) of white, non-Hispanic origin, and compared them with controls (n = 93) from similar ethnic origins. These analyses revealed that the same alleles in a haplotype in the 5′ region of the gene and a haplotype in the same 3′ region are associated with autopsy-proven AD. ### Methods. Frozen brain tissue was obtained from 103 autopsy-confirmed cases of AD and from 17 elderly control subjects with a normal postmortem examination and without a history of dementia or another neurologic disorder. To augment the number of controls from the same ethnic background, we included 76 nondemented elderly participants who have been followed prospectively at approximately 18-month intervals as part of a study of …

Predicting Super Spreading Events during the 2003 Severe Acute Respiratory Syndrome Epidemics in Hong Kong and Singapore

Abstract One of the intriguing characteristics of the 2003 severe acute respiratory syndrome (SARS) epidemics was the occurrence of super spreading events (SSEs). Here, the authors report the results of identifying the occurrence of SSEs in the Hong Kong and Singapore epidemics using mathematical and statistical analysis. Their predicted occurrence of SSEs agreed well with the reported occurrence of all seven super spreaders in the two cities. Additional unidentified SSEs were also found to exist. It was found that 71.1% and 74.8% of the infections were attributable to SSEs in Hong Kong and Singapore, respectively. There also seemed to be “synchronized” occurrences of infection peaks in both the community and the hospitals in Hong Kong. The results strongly suggested that the infection did not depend on the total number of symptomatic cases, with only a very small proportion of symptomatic individuals being shown to be infectious (i.e., able to infect other individuals). The authors found that the daily infection rate did not correlate with the daily total number of symptomatic cases but with the daily number of symptomatic cases who were not admitted to a hospital within 4 days of the onset of symptoms.

Replication of the LINGO1 gene association with essential tremor in a North American population.

A marker in the LINGO1 gene, rs9652490, showing significant genome-wide association with essential tremor (ET), was recently reported in an Icelandic population. To replicate this association in an independent population from North America, we genotyped 15 SNPs in the LINGO1 gene in 257 Caucasian ET cases (‘definite,’ ‘probable’ or ‘possible’) and 265 controls enrolled in an epidemiological study at Columbia University. We observed a marginally significant association with allele G of the marker rs9652490 (P=0.0569, odds ratio (OR)=1.33). However, for ‘definite’ or ‘probable’ ET, rs9652490 was significantly associated with ET (P=0.03, OR=1.41). Our subsequent analysis of early-onset ET (age at onset <40 years) revealed that three SNPs, rs177008, rs13313467 and rs8028808, were significantly associated with ET (P=0.028, OR=1.52; P=0.0238, OR=1.54; and P=0.0391, OR=1.55, respectively). These three SNPs represent a 2.3 kb haplotype. Finally, a meta-analysis of three published studies confirms allelic association with rs9652490 and two adjacent SNPs. Our study independently confirms that the LINGO1 gene is a risk factor for ET in a Caucasian population in North America, and further shows that those with early-onset ET are likely to be at high risk.

Eutrophication dynamics of Tolo Harbour, Hong Kong

Abstract The time and spatial variation of water quality in Tolo Harbour, a eutrophic landlocked semi-enclosed bay frequented by algal blooms, is studied using a dynamic eutrophication model. Hourly changes of tide levels and currents are computed by a link-node model assuming M 2 tidal forcing. Phytoplankton growth is assumed to be limited by solar radiation, nitrogen and temperature. The model incorporates light acclimation by algae, self-shading, photosynthetic production, nutrient uptake, and a dynamic determination of the carbon to chlorophyll ratio. In particular, sediment-water-pollutant interactions are modelled via an anaerobic benthic layer segment. Using recorded pollution loads and environmental forcing as input, the model predictions of daily-averaged water quality are compared with the extensive water quality monitoring data of the Environmental Protection Department (EPD). The predicted spatial distribution and trends of algal biomass, inorganic nitrogen, dissolved oxygen (DO), as well as sediment oxygen demand (SOD), are in general agreement with field observations.

Temporal and spatial variations in nutrient stoichiometry and regulation of phytoplankton biomass in Hong Kong waters: Influence of the Pearl River outflow and sewage inputs

In 2001, the Hong Kong government implemented the Harbor Area Treatment Scheme (HATS) under which 70% of the sewage that had been formerly discharged into Victoria Harbor is now collected and sent to Stonecutters Island Sewage Works where it receives chemically enhanced primary treatment (CEPT), and is then discharged into waters west of the Harbor. The relocation of the sewage discharge will possibly change the nutrient dynamics and phytoplankton biomass in this area. Therefore, there is a need to examine the factors that regulate phytoplankton growth in Hong Kong waters in order to understand future impacts. Based on a historic nutrient data set (1986-2001), a comparison of ambient nutrient ratios with the Redfield ratio (N:P:Si=16:1:16) showed clear spatial variations in the factors that regulate phytoplankton biomass along a west (estuary) to east (coastal/oceanic) transect through Hong Kong waters. Algal biomass was constrained by a combination of low light conditions, a rapid change in salinity, and strong turbulent mixing in western waters throughout the year. Potential stoichiometric Si limitation (up to 94% of the cases in winter) occurred in Victoria Harbor due to the contribution of sewage effluent with high N and P enrichment all year, except for summer when the frequency of stoichiometric Si limitation (48%) was the same as P, owing to the influence of the high Si in the Pearl River discharge. In the eastern waters, potential N limitation and N and P co-limitation occurred in autumn and winter respectively, because of the dominance of coastal/oceanic water with low nutrients and low N:P ratios. In contrast, potential Si limitation occurred in spring and a switch to potential N, P and Si limitation occurred in eastern waters in summer. In southern waters, there was a shift from P limitation (80%) in summer due to the influence of the N-rich Pearl River discharge, to N limitation (68%) in autumn, and to N and P co-limitation in winter due to the dominance of N-poor oceanic water from the oligotrophic South China Sea. Our results show clear temporal and spatial variations in the nutrient stoichiometry which indicates potential regulation of phytoplankton biomass in HK waters due to the combination of the seasonal exchange of the Pearl River discharge and oceanic water, sewage effluent inputs, and strong hydrodynamic mixing from SW monsoon winds in summer and the NE monsoon winds in winter.

Discovering user access patterns on the World Wide Web

The World Wide Web provides its users with almost unlimited access to documents on the Internet. The use of intelligent agents is suggested to assist users to locate documents related to their interests instead of browsing the Web via primitive search engines. A number of key components in such intelligent systems are identified and a system architecture is proposed. In particular, a learning agent is designed along with the underlying algorithms for the discovery of areas of interest from user access logs. The discovered topics can be used to improve the efficiency of information retrieval by prefetching documents for the users and storing then in a document database in the system. A prototype system has also been implemented to illustrate the various concepts. Experiments are performed which show that the area of interest discovered can in fact be used to improve the efficiency of information retrieval on a distributed information system such as the Internet.