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C S Leung

Publications and source records attributed to C S Leung.

At least 19 recordsLinked to original sources
PubMed2001

A pruning method for the recursive least squared algorithm.

The recursive least squared (RLS) algorithm is an effective online training method for neural networks. However, its conjunctions with weight decay and pruning have not been well studied. This paper elucidates how generalization ability can be improved by selecting an appropriate initial value of the error covariance matrix in the RLS algorithm. Moreover, how the pruning of neural networks can be benefited by using the final value of the error covariance matrix will also be investigated. Our study found that the RLS algorithm is implicitly a weight decay method, where the weight decay effect is controlled by the initial value of the error covariance matrix; and that the inverse of the error covariance matrix is approximately equal to the Hessian matrix of the network being trained. We propose that neural networks are first trained by the RLS algorithm and then some unimportant weights are removed based on the approximate Hessian matrix. Simulation results show that our approach is an effective training and pruning method for neural networks.

Algorithms↗
PubMed2000

Difference in susceptibilities of different cell lines to bilirubin damage.

OBJECTIVE: To investigate if there are differences in susceptibilities to bilirubin toxicity of different cell lines. METHODOLOGY: A modified 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method was adopted to study the cytotoxic effect of bilirubin on several commercially available cell lines including human glioblastoma (ATCC CRL 1690, T98G), human neuroblastoma (ATCC HTB-10, SK-N-MC), human liver (ATCC CCL 13, Chang Liver, HeLa markers) and a mouse fibroblast (ATCC CCL-1, NCTC Colon 929). RESULTS: Cytotoxicity was observed when certain bilirubin:albumin molar ratios were exceeded in the medium of a cell line in culture. Different cells exhibited different susceptibilities to the cytotoxic effects of bilirubin; neuroblastoma and glioblastoma were most susceptible, fibroblasts were the least vulnerable. CONCLUSIONS: Our findings have confirmed the clinical impression that different cells sustain different degrees of cytotoxicities caused by bilirubin.

Albumins↗
PubMed2000

A local training and pruning approach for neural networks.

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition.

Algorithms↗
PubMed1999

An adaptive Bayesian pruning for neural networks in a non-stationary environment.

Pruning a neural network to a reasonable smaller size, and if possible to give a better generalization, has long been investigated. Conventionally the common technique of pruning is based on considering error sensitivity measure, and the nature of the problem being solved is usually stationary. In this article, we present an adaptive pruning algorithm for use in a nonstationary environment. The idea relies on the use of the extended Kalman filter (EKF) training method. Since EKF is a recursive Bayesian algorithm, we define a weight-importance measure in term of the sensitivity of a posteriori probability. Making use of this new measure and the adaptive nature of EKF, we devise an adaptive pruning algorithm called adaptive Bayesian pruning. Simulation results indicate that in a noisy nonstationary environment, the proposed pruning algorithm is able to remove network redundancy adaptively and yet preserve the same generalization ability.

Bayes Theorem↗
PubMed1998

Porokeratotic eccrine ostial and dermal duct naevus with dermatomal trunk involvement: literature review and report on the efficacy of laser treatment.

Porokeratotic eccrine ostial and dermal duct naevus (PEODDN) is a rare, benign hamartomatous malformation involving the eccrine sweat duct. The existence of filiform keratinous plugs that represent cornoid lamellae overlying dilated infundibula of eccrine ducts is a distinctive feature and the presence of associated abnormal dermal ducts is frequent. We report a patient with PEODDN who exhibited lesions on the left side of her chest. Cases of PEODDN reported in the literature are reviewed. Our experience in treating this patient with ultrapulsed carbon dioxide laser is also presented.

Eccrine Glands↗
PubMed1998

Clinical evaluation of ceftibuten in gonorrhea. A pilot study in Hong Kong.

BACKGROUND: The escalating rates of gonococcal resistance to quinolone in Hong Kong have prompted a search for an alternative first-line antimicrobial agent for use in treating uncomplicated gonococcal urethritis. Ceftibuten is an orally active third-generation cephalosporin with potent in vitro activity against Neisseria gonorrhoeae. Its pharmacokinetic properties allow single-dose administration. OBJECTIVE: To evaluate the efficacy, safety, and tolerability of ceftibuten in the treatment of uncomplicated gonorrhea in men. STUDY DESIGN: Ceftibuten was evaluated in an open-label, noncomparative, multicenter study. Eligible men with uncomplicated gonococcal urethritis were treated with a single 400-mg oral dose of ceftibuten and reassessed 1 week and 3 weeks after treatment. The main outcome measures were the isolation of N. gonorrhoeae, patient-reported side effects, and other safety parameters (e.g., blood counts and renal and hepatic function tests). RESULTS: One hundred twenty-five men were enrolled in the study. The overall cure rate was 98.2% (110 of 112 evaluable patients). Adverse events, which occurred in 4.5% of patients, were all mild, well tolerated, and of short duration. No significant changes in laboratory test results were noted. Of the 125 isolates, 4.8% were -lactamase positive. Susceptibility to ofloxacin was found to be low in 59.2% of isolates (MIC 0.1 to < 1g/mL) and 25.6% of isolates were resistant (MIC1g/mL) to ofloxacin. CONCLUSIONS: A single 400-mg oral dose of ceftibuten is highly effective and well tolerated in the treatment of uncomplicated gonococcal urethritis in men.

Adolescent↗
PubMed1998

Scleredema in Chinese patients: a local retrospective study and general review.

The records from 12 Chinese adult patients with scleredema, who had attended the Social Hygiene Service of the Hong Kong Department of Health between 22 January 1990 and 19 March 1996, were retrieved and analysed. The neck was the commonest site of involvement (75%), followed by the back (42%), and the shoulder (17%). The vast majority (83%) of scleredema cases were associated with diabetes mellitus; half of these were insulin-dependent. Most of the patients (92%) had hypertension for which medical treatment was needed. No cases of skin disease were preceded by acute infection, and none had any associated paraproteinaemia. The degree of skin involvement did not affect the daily activities of most of the patients. This study revealed differences between the disease in our locality and those described in the western literature.

Journal Article↗
PubMed1997

Comparison of ThinPrep and conventional preparations: nongynecologic cytology evaluation.

ThinPrep processing, an automated cytopreparatory method, has been reported to show good correlation with conventional preparations and to reduce the rate of false-negative diagnoses. In a retrospective review of 230 consecutive nongynecologic cytology cases, we compare the ThinPrep (TP) method with conventional preparations (CP). There were 129 fine-needle aspiration (FNA) specimens from various sites, including 51 breasts, 40 thyroids, 14 lungs, 8 livers, and 16 miscellaneous sites. The sources of 101 body cavity fluids included 68 pleural/peritoneal effusions, 25 peritoneal/pelvic washings, and 8 miscellaneous sites. Each case was evaluated for cellularity, morphologic, details, and obscuring background material. Diagnoses of the TP slides were classified as insufficient, normal, benign, suspicious, or malignant. Each case was then correlated with the tissue diagnosis when available. In TP slides, cellular arrangements, nuclear details, and nuclear cytoplasmic ratio were preserved, while blood and diathesis were eliminated. There was no statistically significant difference between TP and CP in the diagnostic categories. However, in six cases of "insufficient for diagnosis" on FNA by CP, TP yielded sufficient cells and tissue fragments for diagnosis. One case each of FNA and body fluid with a diagnosis of "suspicious for malignancy" by CP was considered "positive" on TP slides. The overall sensitivity of TP was 97.6%, and the specificity was 92.9%. The positive predictive value was 93.0%. We conclude that the ThinPrep method shows good correlation with conventional preparations in both FNA and body fluids.

Biopsy, Needle↗
PubMed1997

Solitary angiokeratoma of the oral cavity.

Angiokeratoma is a rare, cutaneous disorder that typically occurs at multiple sites and is often associated with a number of metabolic disorders. Although solitary cutaneous forms have been reported, to date localized lesions within the oral cavity have not been described. We report on an 82-year-old man with a history of squamous cell carcinoma of the ear and scalp who also had a solitary pigmented lesion of the oral cavity. Excisional biopsy of the buccal mucosal lesion showed features consistent with angiokeratoma. We report the first intra-oral solitary angiokeratoma and review the clinical and pathologic features of this unusual condition.

Aged↗
PubMed1997

p53 mutations detected in colorectal carcinoma patients in Hong Kong.

A mutational spectrum for exons 5-8 of the p53 tumor suppressor gene in colorectal carcinomas in Hong Kong Chinese was established. Ninety-nine colorectal carcinomas from Hong Kong patients were analyzed for mutations in p53 gene by PCR-single-strand conformation polymorphism analysis and direct DNA sequencing. Thirty-five of the 99 tumors (35.4%) contained mutations. Point mutations accounted for 80% of all genetic changes and were predominantly base transitions at CpG dinucleotide sites, mutations that were also predominant in Caucasian carcinomas. The major hot spots at codons 175 and 248 of p53 in Caucasians are also hot spots in the Chinese gene. Identical mutations in codons 152 and 306 were detected in two independent tumors in the Chinese, which were reported only rarely in Caucasians. Moreover, a significantly higher frequency (20%) of deletion and insertion mutations was observed in Hong Kong colorectal cancer patients. Distinct genetic and/or environmental factors may contribute to these findings.

Adult↗
PubMed1996

Attraction basin of bidirectional association memories.

In this paper, we investigate the attraction basin of the bidirectional associative memory (BAM) model. The BAM is a two-layer heteroassociator that stores a prescribed set of bipolar library pairs. It consists of two layers of neurons. One layer has n neurons and the other has p neurons. We will first point out why the conventional energy approach cannot tell us about the attraction basin of each library pair. We then rigorously derive the statistical dynamics of the BAM, which shows how the upper bound on the number of errors changes during recalling for an arbitrary error pattern in the initial state. From the dynamics, we can estimate the attraction basin for the worst case errors, as well as the memory capacity and the number of errors in the retrieved pairs. The memory capacity is alpha rn, where alpha r (0 < alpha r < 1) depends on the ratio [formula: see text]. The number of errors in the retrieved pairs is [formula: see text] when the number of library pairs is alpha n. When r = 1, the lower bound on the attraction basin for the worst case errors is about 0.0068n.

Algorithms↗
PubMed1995

Distribution of lipochrome pigment in the prostate gland: biological and diagnostic implications.

Lipochrome pigment is characteristically found in Wolffian duct-derived structures including seminal vesicles and ejaculatory ducts. The presence of lipochrome pigment is helpful in identifying atypical histological patterns of seminal vesicle or ejaculatory duct that mimic prostatic adenocarcinoma. The authors studied the distribution of lipochrome pigment in 28 radical prostatectomy specimens using a modified Ziehl-Neelson stain and fluorescence microscopy. In all cases secretory epithelium of the central zone contained lipochrome pigment often in significant amounts (2 to 3+). Secretory epithelium from peripheral and transition zones in each of four specimens (14.3%) contained lipochrome pigment. In addition, occasional examples of nodular hyperplasia, prostatic intraepithelial neoplasia, and prostatic adenocarcinoma contained lipochrome pigment. The preferential distribution of lipochrome pigment in central zone epithelium adds further support to the hypothesis that central zone glands are derived embryologically from Wolffian duct (mesoderm) rather than urogenital sinus (endoderm), which gives rise to transition and peripheral zone glands. Furthermore, lipochrome pigment should not be used as the sole diagnostic criterion for separating atypical histological patterns of seminal vesicle and ejaculatory duct from those of prostatic origin.

Adenocarcinoma↗
PubMed1994

DNA image cytometry of prostatic carcinoma: a comparison of needle core biopsy and subsequent prostatectomy specimens.

DNA ploidy has recently been identified as an objective prognostic factor in prostatic carcinoma. Although the diagnosis of prostatic carcinoma is increasingly being made with the use of needle core biopsies, the optimal method for the cytometric analysis of these specimens has yet to be determined. In addition, the degree to which the biopsy is representative of the subsequent prostatectomy specimen with respect to DNA heterogeneity has not been adequately addressed. In this study, image cytometric (ICM) DNA analysis was performed on tissue sections from 12 prostatic needle core biopsies and the results were compared with similar ICM analysis of the subsequent prostatectomy specimens. Multiple blocks (n = 48) of the prostatectomy specimens were utilized to prepare tissue sections and nuclear suspensions and each set of preparations were analyzed by ICM in a parallel comparison study. There was concordance of 0.80 in the classification of DNA diploid and aneuploid tumors by ICM analysis of tissue sections and nuclear suspensions from paraffin blocks. In all of the discordant cases, DNA aneuploid populations were identified by ICM analysis of tissue sections only. This is attributed to difficulties in obtaining a representative nuclear suspension from disaggregated paraffin-embedded prostatic tissue which often has a very desmoplastic stroma. ICM analysis of tissue sections seems to be an optimal method for DNA ploidy analysis of prostatic carcinoma and is well suited to small volume biopsy material. Determination of DNA ploidy status in prostatic biopsies was predictive of the subsequent prostatectomy specimens with a concordance of 0.92.

Aged↗
PubMed1993

An old traditional herbal remedy for neonatal jaundice with a newly identified risk.

Yin-chen (Artemisia scoparia) is a very popular intravenous herbal preparation used for the treatment of neonatal jaundice in China. Bilirubin-protein titration studies with the horse radish peroxidase method have shown that the herb is highly effective in displacing bilirubin from its protein binding. Free bilirubin is liberated in this process and this could increase the risk of brain damage in jaundiced infants. With the present state of knowledge, the use of traditional herbal therapies should be strongly discouraged in neonates.

Bilirubin↗
PubMed1991

Biomonitoring of human exposure to alkylating agents by measurement of adducts to haemoglobin or DNA.

Recent analytical developments in the determination of adducts of DNA and protein with alkylating carcinogens are described which have considerably extended the number of carcinogens that can be examined. While sensitivity of detection equal to or better than one modified DNA base per 10(8) normal bases is now achievable for many specific alkylating carcinogens, further developments in the analytical methods are still needed for the identification and quantification of adducts derived from unknown and/or mixed exposures to carcinogens.

Alkylating Agents↗