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C W Ma

Publications and source records attributed to C W Ma.

8 recordsLinked to original sources
PubMed2006

Linear relation on the correlation in complex networks.

Correlation in complex networks follows a linear relation between the degree of a node and the total degrees of its neighbors for six different classes of real networks. This general linear relation is an extension of the Aboav-Weaire law in two-dimensional cellular structures and provides a simple and different perspective on the correlation in complex networks, which is complementary to an existing description using Pearson correlation coefficients and a power law fit. Analytical expression for this linear relation for three standard models of complex networks: the Erdos-Renyi, Watts-Strogatz, and Barabasi-Albert networks is provided. The slope and intercept of this linear relation are described by a single parameter a together with the first and second moment of the degree distribution of the network. The assortivity of the network can be related to the sign of the intercept.

Journal Article↗
PubMed2005

Trends in the prevalence of peptic ulcer disease and Helicobacter pylori infection in family physician-referred uninvestigated dyspeptic patients in Hong Kong.

BACKGROUND: Peptic ulcer disease is mainly caused by Helicobacter pylori infection and the use of non-steroidal anti-inflammatory drugs. AIM: To investigate the trends in the prevalence of peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use in uninvestigated dyspeptic patients over recent years in Hong Kong. METHODS: Data from consecutive patients with uninvestigated dyspeptic symptoms referred by family physicians for open access upper endoscopy during 1997 and 2003 were analysed in relation to peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use. RESULTS: Among 2700 patients included, 405 (15%) had peptic ulcer disease and 14 (0.5%) had gastric cancer. There was a reduced trend from 1997 to 2003 in the prevalence of peptic ulcer disease (17, 20, 14, 16, 13, 14 and 14%, respectively, chi2 = 5.80, P = 0.016) (mainly because of decrease in duodenal ulcers), H. pylori infection (44, 50, 49, 44, 40, 40, 36 and 43%, respectively, chi2 = 13.55, P < 0.001) and non-steroidal anti-inflammatory drug use (13, 5, 5, 6, 3, 4, 4 and 5% respectively, chi2 = 13.61, P < 0.001). The prevalence of peptic ulcer disease, H. pylori infection and non-steroidal anti-inflammatory drug use between 2001 and 2003 were significantly lower than that between 1997 and 2000 (17% vs. 13%, OR = 0.78, 95% CI: 0.63-0.96, P = 0.020 for peptic ulcer disease; 47% vs. 39%, OR =0.72, 95% CI: 0.60-0.86, P < 0.001 for H. pylori infection; and 6% vs. 4%, OR = 0.56, 95% CI: 0.39-0.82, P = 0.002 for non-steroidal anti-inflammatory drug use). H. pylori infection was associated with both duodenal ulcer (OR = 15.87, 95% CI: 10.60-23.76, P < 0.001) and gastric ulcer (OR = 3.12, 95% CI: 2.15-4.53, P < 0.001) whereas non-steroidal anti-inflammatory drug use was only associated with gastric ulcer (OR = 2.97, 95% CI: 1.70-5.20, P < 0.001). CONCLUSIONS: The prevalence of peptic ulcer disease, mainly duodenal ulcers, was reduced in association with a decreasing trend in the prevalence of H. pylori infection and non-steroidal anti-inflammatory drug use from 1997 to 2003.

Adolescent↗
PubMed2002

Visual performance on detection tasks with double-targets of the same and different difficulty.

This paper reports a study of measurement of horizontal visual sensitivity limits for 16 subjects in single-target and double-targets detection tasks. Two phases of tests were conducted in the double-targets task; targets of the same difficulty were tested in phase one while targets of different difficulty were tested in phase two. The range of sensitivity for the double-targets test was found to be smaller than that for single-target in both the same and different target difficulty cases. The presence of another target was found to affect performance to a marked degree. Interference effect of the difficult target on detection of the easy one was greater than that of the easy one on the detection of the difficult one. Performance decrement was noted when correct percentage detection was plotted against eccentricity of target in both the single-target and double-targets tests. Nevertheless, the non-significant correlation found between the performance for the two tasks demonstrated that it was impossible to predict quantitatively ability for detection of double targets from the data for single targets. This indicated probable problems in generalizing data for single target visual lobes to those for multiple targets. Also lobe area values obtained from measurements using a single-target task cannot be applied in a mathematical model for situations with multiple occurrences of targets.

Attention↗
PubMed2001

Photodegradation mechanism and rate improvement of chlorinated aromatic dye in non-ionic surfactant solutions.

A typical insoluble chlorinated aromatic dye (CAD), disperse red (DR), was used to explore the reaction mechanism and kinetics of photodegradation in non-ionic surfactant solutions. The use of an additional hydrogen source and photosensitizer is also studied to improve the decay rates. The decay rate of dye in surfactants depends on the Km of surfactants and their ability to offering an effective hydrogen source. The photodegradation of CAD can be divided into three stages: the initial lag stage. the fast degradation stage and the final retardation stage. The lag stage will vanish and the decay rates of dye can be greatly improved by 2.5-3.6 times after adding an additional hydrogen source (NaBH4) or photosensitizer (acetone) to the surfactant micellar solution. However, the use of an additional hydrogen source or photosensitizer has dosage limitations in such applications. The photoreduction of DR is the main reaction mechanism, in which photodechlorination is observed first with the generation of HCI as the final product, then followed by photodecolorization by breaking the azo bond of the chromophore.

Acetone↗
PubMed1997

[Inhibition of parvovirus H-1 on transplantable human hepatoma and its histological and histobiochemical studies].

A transplantable human hepatoma model, the QGY-9204, was used in this study. The growth kinetics of hepatoma in nude mice were compared after injection of parvovirus H-1 into the tumor growth. Significant difference in growth curves were seen between injected groups with H-1 dosages of 5 x 10(7) PFU and 5 x 10(8) PFU and that of control. It indicated that parvovirus H-1 was capable of suppressing the growth of human hepatoma. Previous studies showed H-1 is oncotropic, oncosuppressive and oncolytic. For histological, ultrastructural and histochemical examinations, transplantable hepatomas were taken at different time interval post H-1 (1 x 10(8) PFU per tumor growth) injection. For H-1 DNA amplification and H-1 nonstructural protein expression, PCR and ABC approach in hepatoma paraffin sections were used. The H-1 treated groups exhibited obvious signs of necrosis. It started on 3rd day post infection (3 d.p.i.) and the area of necrosis enlarged consecutively on 7 d.p.i., 10 d.p.i. and 14 d.p.i., but none was seen in saline-injected group even on 14 d.p.i. H-1 virions were also detected in the damaged tumor cells with numerous vacuoles in cytoplasm. Specific band (908 bp) of H-1 DNA and ABC immunostaining indicated H-1 DNA replication and NS-1 expression in tumors of treated groups, their time course was well in accordance with that process of necrosis. These results suggest that parvovirus H-1 promotes tumor necrosis by its DNA replication and cytotoxic NS-1 protein expression, and thus, it inhibits hepatoma growth and induces oncosuppression and oncolysis.

Animals↗
PubMed1993

Two new rat alpha-globin sequences as identified by the conserved region PCR.

Based on the notion that regions of structural genes which encode critical domains of the corresponding proteins are highly conserved among closely related species, oligonucleotide primers were designed and used to amplify the alpha-globin sequence(s) of the Sprague-Dawley (SD) rat. Data of these amplified sequence constructs showed that two new rat alpha-globin specific sequences have been identified. Southern hybridization confirmed the presence of these sequences in the rat genome.

Animals↗
PubMed1987

The relationship of serum vitamin A, cholesterol, and triglycerides to the incidence of ovarian cancer.

Prospective and retrospective studies have suggested that serum vitamin A and total cholesterol levels may be associated with cancer. Our study showed that the mean (+/- SEM) concentrations of serum vitamin A 489 +/- 33.28 (mean +/- SEM micrograms/liter and serum total cholesterol 174.7 +/- 8.96 (mean +/- SEM) mg/dl from ovarian cancer patients in Singapore were significantly lower than the respective values of 668 +/- 25.10 (mean +/- SEM) microgram/liter and 210.7 4.48 (mean +/- SEM) mg/dl from noncancerous control subjects (P less than 0.0001 for both compounds). In addition, ovarian cancer patients did not show significantly lower serum triglyceride levels than the control subjects. Age did not significantly correlate the serum vitamin A and total cholesterol concentrations, but there was correlation with respect to the serum triglyceride levels. There were moderate correlations between vitamin A and cholesterol levels (r = 0.36, P less than 0.0027) and between cholesterol and triglyceride levels (r = 0.37, P less than 0.0024) in the control subjects but not in the cancer patients. Vitamin A levels correlated moderately with triglyceride levels in both the cancer patients (r = 0.42, P less than 0.0258) and the control subjects (r = 0.33, P less than 0.0069). The inverse relationship between the incidence of ovarian cancer and serum vitamin A and serum total cholesterol concentrations may have distinct implications for preventive medicine and public health.

Adult↗