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Biomedical subjects

G C Wang

Publications and source records attributed to G C Wang.

At least 19 recordsLinked to original sources
PubMed2005

Mechanical testing of isolated amorphous silicon slanted nanorods.

Mechanical testing was performed on a new class of nanostructures-amorphous Si slanted nanorods of rectangular cross section, fixed at one end to the substrate. These nanorods were grown spatially well separated on nano-pillars under the oblique angle physical vapor deposition technique. Various samples with different dimensions and inclination angles were tested in bending using an atomic force microscope. The material response was elastic up to large stresses/deflections. The Young's modulus was calculated from the slope of the experimentally observed stiffness versus the geometrical factor common to all the samples and was found to be (94.14 +/- 10.21) GPa. No size effect of this parameter was observed within the accuracy of the present measurement.

Biomechanical Phenomena↗
PubMed2003

QTL x environment interactions in rice. I. heading date and plant height.

One hundred twenty six doubled-haploid (DH) rice lines were evaluated in nine diverse Asian environments to reveal the genetic basis of genotype x environment interactions (GEI) for plant height (PH) and heading date (HD). A subset of lines was also evaluated in four water-limited environments, where the environmental basis of G x E could be more precisely defined. Responses to the environments were resolved into individual QTL x environment interactions using replicated phenotyping and the mixed linear-model approach. A total of 37 main-effect QTLs and 29 epistatic QTLs were identified. On average, these QTLs were detectable in 56% of the environments. When detected in multiple environments, the main effects of most QTLs were consistent in direction but varied considerably in magnitude across environments. Some QTLs had opposite effects in different environments, particularly in water-limited environments, indicating that they responded to the environments differently. Inconsistent QTL detection across environments was due primarily to non- or weak-expression of the QTL, and in part to significant QTL x environment interaction effects in the opposite direction to QTL main effects, and to pronounced epistasis. QTL x environment interactions were trait- and gene-specific. The greater GEI for HD than for PH in rice were reflected by more environment-specific QTLs, greater frequency and magnitude of QTL x environment interaction effects, and more pronounced epistasis for HD than for PH. Our results demonstrated that QTL x environment interaction is an important property of many QTLs, even for highly heritable traits such as height and maturity. Information about QTL x environment interaction is essential if marker-assisted selection is to be applied to the manipulation of quantitative traits.

Chromosome Mapping↗
PubMed2003

Mechanics of patterned helical Si springs on Si substrate.

The elastic response, including the spring constant, of individual Si helical-shape submicron springs, was measured using a tip-cantilever assembly attached to a conventional atomic force microscope. The isolated, four-turn Si springs were fabricated using oblique angle deposition with substrate rotation, also known as the glancing angle deposition, on a templated Si substrate. The response of the structures was modeled using finite elements, and it was shown that the conventional formulae for the spring constant required modifications before they could be used for the loading scheme used in the present experiment.

Elasticity↗
PubMed2001

Morphology transition during low-pressure chemical vapor deposition.

Assuming a reemission model, we have studied, in detail, the effect of sticking coefficient on the morphology evolution in low-pressure chemical vapor deposition processes. We have shown that the surface morphology changes from a self-affine fractal to a columnarlike morphology with increasing sticking coefficient, which agrees qualitatively with experimental observations.

Journal Article↗
PubMed2001

Epidemiological analysis of Salmonella enteritidis isolates in Singapore.

OBJECTIVES: Salmonella enteritidis is the most common non-typhoidal Salmonella species isolated in Singapore causing gastroenteritis and occasional bacteremia with secondary complications. The number of S. enteritidis isolates rose in 1993 and since then, it was the commonest Salmonella sp. isolated. In 1997, a total of 139 S. enteritidis was isolated and this comprised 19.2% of all non-typhoidal Salmonella sp. isolated. METHODS: We studied the antimicrobial susceptibilities, phage types and molecular epidemiology of 89 of these S. enteritidis strains. Fifty per cent were stool isolates whilst 33.3% were isolated from blood samples. RESULTS: All the isolates were susceptible to cephalothin, ceftriaxone, ciprofloxacin, aztreonam, gentamicin, amikacin, kanamycin, neomycin, streptomycin and nalidixic acid; whilst 75.3% were resistant to sulphonamide, 15.7% to tetracycline, 7.9% to co-trimoxazole, 6.7% to trimethoprim, 2.2% to ampicillin and 2.2% to chloramphenicol. The most frequent phage types were phage type 4 (64%), followed by phage type 1 (12.4%) and phage type 8 (2.2%). Seventy four of the 89 (83.1%) S. enteritidis isolates analysed by pulsed-field gel electrophoresis showed an indistinguishable pattern A when digested by restriction enzyme Xba I suggesting the presence of a predominant clone of S. enteritidis circulating in Singapore in 1997.

Animals↗
PubMed2001

[Screening, cloning and sequence analysis of the gene for pyruvate kinase from Achlya bisexualis cDNA library].

The gene for pyruvate kinase, which is involved in glycolysis and catalyze the biochemical reaction from phosphoenolpyruvate to pyruvate, was screened, cloned and sequenced from non-photosynthetic Oomycetes, Achlya bisexualis cDNA library. The size of the gene is about 1.6 kb. The amino acid sequence of the gene was deduced using the GCG program. On basis of analysis by the on-line PSORT II program the deduced amino acid sequence showed that the pyruvate kinase expressed by the gene was located in the cytosol. This result indicated that it is possible that the process of glycolysis for the lower form of eukaryotic cell such as Achlya bisexuali may occur in cytosol, which is different from Liaud's report.

Amino Acid Sequence↗
PubMed2000

Kinetic roughening in polymer film growth by vapor deposition.

The growth front roughness of linear poly( p-xylylene) films grown by vapor deposition polymerization has been investigated using atomic force microscopy. The interface width w increases as a power law of film thickness d, w approximately d(beta), with beta = 0. 25+/-0.03, and the lateral correlation length xi grows as xi approximately d(1/z), with 1/z = 0.31+/-0.02. This novel scaling behavior is interpreted as the result of monomer bulk diffusion, and belongs to a new universality class that has not been discussed previously.

Journal Article↗
PubMed1999

Cytokine profiles in Wegener's granulomatosis: predominance of type 1 (Th1) in the granulomatous inflammation.

OBJECTIVE: To determine whether a specific cytokine pattern (type 1 [Th1] or type 2 [Th2]) predominates in Wegener's granulomatosis (WG), by evaluating interferon-gamma (IFNgamma) and interleukin-4 (IL-4) expression in different compartments of the body (i.e., biopsied nasal mucosal tissue [NBS], bronchoalveolar lavage [BAL] fluid, and peripheral blood [PB]) and comparing the findings with those in disease and healthy control subjects. METHODS: Competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay were used to assess IFNgamma and IL-4 expression in T cell clones (TCC), T cell lines (TCL), and polyclonal CD4+ and CD8+ cells derived from NBS, BAL, and PB. RESULTS: Patients with WG and chronic rhinitis were found to share in situ production of messenger RNA (mRNA) specific for IFNgamma (Th1). Only 2 patients with WG expressed IL-4, whereas IL-4 mRNA PCR products were found in inflamed tissues of the disease control patients. The granuloma-derived T cells of WG patients produced only IFNgamma, while TCC, TCL, and CD4+ and CD8+ T cells from BAL and PB produced mainly IFNgamma. CONCLUSION: Our data indicate that a Thl cytokine pattern predominates in the granulomatous inflammation in patients with WG.

Adult↗
PubMed1999

Monte Carlo simulation of submonolayer vapor-deposition polymerization.

In this paper, we propose a Monte Carlo simulation model for the initial growth of polymer films by considering only monomer surface diffusion in the vapor-deposition polymerization process. In the model, monomers are deposited randomly on a two-dimensional square lattice with periodic boundary conditions and are allowed to diffuse with nearest neighbor hops. Whenever monomers meet, they stop diffusing and form a stable dimer. When a diffusing or deposited monomer encounters one of the ends of a polymer (L>1), it stops moving and attaches to the polymer. Attachment of monomers or other polymers is allowed only at the two ends of the polymer. We have shown that there are three distinct growth regimes for surface coverages theta<0.5: a low-coverage initiation regime (I), a chain propagation regime (P), and a saturation regime (S). In both regimes I and P, the growth is similar to the molecular beam epitaxy model. We examine in detail the scaling relations for the chain length distribution, which agree quite well with results of a rate equation. However, in regime S, our model gives very different kinetics. The breakdown of scaling at higher coverages is due to the fact that long-chain polymers have partitioned the lattice with inactive sites. This inhibits further polymer growth and enhances production of dimers, shifting the chain distribution to favor shorter polymers and driving the average molecular weight down. The chain configuration initially is similar to a path taken in a diffusion-limited self-avoiding walk. However, at high coverages, due to the correlation of long polymer chains, the polymer chains tend to be compact.

Journal Article↗
PubMed1999

Reassortment and insertion-deletion are strategies for the evolution of influenza B viruses in nature.

The evolution of influenza B viruses is poorly understood. Reassortment of influenza B viruses in nature as a means of genetic variation has not been considered to be a major contributor to their evolution. However, the current practice of assigning evolutionary relationships by antigenic analysis of the hemagglutinin of influenza B viruses would fail to detect reassortants. In this study, influenza B viruses isolated within the past 10 years from sites in the United States and China were studied by nucleotide sequencing of the hemagglutinin and neuraminidase genes and construction of phylogenetic trees to assess evolutionary relationships. A group of viruses represented by B/Houston/1/92 possess a hemagglutinin derived from a B/Yamagata/16/88-like strain and a neuraminidase derived from a B/Victoria/2/87-like strain. A second reassortment event between the hemagglutinin of a B/Yamagata/16/88-like virus closely related to the B/Beijing/184/93 strain and the neuraminidase of a B/Victoria/2/87-like strain is represented by a single virus, B/Memphis/3/93. The neuraminidase of the reassortant viruses is most closely related to that of B/Victoria/2/87-like viruses currently circulating in Nanchang, China. A pattern of insertions and deletions in the hemagglutinin and the neuraminidase of different strains of influenza B viruses is observed. Reassortment plays a role in the evolution of influenza B viruses and may necessitate a change in the methods used to assess and identify new influenza viruses.

Animals↗
PubMed1997

Frequency of formation of chimeric molecules as a consequence of PCR coamplification of 16S rRNA genes from mixed bacterial genomes.

PCR is routinely used in amplification and cloning of rRNA genes from environmental DNA samples for studies of microbial community structure and identification of novel organisms. There have been concerns about generation of chimeric sequences as a consequence of PCR coamplification of highly conserved genes, because such sequences may lead to reports of nonexistent organisms. To quantify the frequency of chimeric molecule formation, mixed genomic DNAs from eight actinomycete species whose 16S rRNA sequences had been determined were used for PCR coamplification of 16S rRNA genes. A large number of cloned 16S ribosomal DNAs were examined by sequence analysis, and chimeric molecules were identified by multiple-sequence alignment with reference species. Here, we report that the level of occurrence of chimeric sequences after 30 cycles of PCR amplification was 32%. We also show that PCR-induced chimeras were formed between different rRNA gene copies from the same organism. Because of the wide use of PCR for direct isolation of 16S rRNA sequences from environmental DNA to assess microbial diversity, the extent of chimeric molecule formation deserves serious attention.

Actinomycetales↗
PubMed1995

Rapid differentiation of bacterial species with multiple probes of different lengths in a single slot blot hybridization.

We describe a highly efficient method for dot and slot blot hybridizations with multiple oligonucleotide probes for high throughput identification of organisms and studies of microbial community structures. Several probes with distinct specificities were designed to have the same melting temperature but unique lengths by adding different numbers of nonspecific nucleotides to one end. All of the probes were mixed, labelled with 32P, and hybridized to one piece of membrane on which genes coding for 16S rRNAs from different bacterial species had been immobilized. After hybridization, the bound probes were eluted and resolved on a denaturing polyacrylamide gel and the identities of the genes coding for 16S rRNAs were read from an autoradiograph of the gel. The results from the application of this technique to pure actinomycete cultures are reported here.

Bacteria↗
PubMed1991

Role of hair follicles in the repigmentation of vitiligo.

Vitiligo is a common pigment disease that is difficult to treat. The mechanism of repigmentation is not known. We combined Dopa-Toluidine Blue complex stain, hair follicle split-Dopa stain, and hair follicle split-scanning electron microscope (SEM) to observe the changes of melanocytes in 23 normal, 24 vitiliginous, and 36 repigmented skin specimens. We found that only active (Dopa-positive) melanocytes existed in the epidermis of normal skin. There were some inactive (Dopa-negative) melanocytes in the outer root sheaths of normal hair follicles, which form the melanocyte reservoir in human skin. In the patients with vitiligo the active melanocytes in the epidermis were totally missing, whereas the inactive melanocytes in the outer root sheaths of hair follicles were not affected. Treatment stimulated the inactive melanocytes in the middle and/or lower parts of the outer root sheaths of hair follicles to divide, proliferate, and migrate upward along the surface of the outer root sheath to the nearby epidermis, where the melanocytes continued to migrate radially to form the pigmented island visible clinically in repigmented vitiligo lesions. During the migration to the epidermis, the melanocytes matured gradually from an inactive phase to an active condition. In conclusion, the existence of these inactive melanocytes provided the melanocyte sources for repigmentation of vitiligo.

Biopsy↗
PubMed1989

A retrospective cohort study of leukemia and other cancers in benzene workers.

A retrospective cohort study was carried out in 1982-1983 among 28,460 benzene-exposed workers (15,643 males, 12,817 females) from 233 factories and 28,257 control workers (16,621 males, 12,366 females) from 83 factories in 12 large cities in China. All-cause mortality was significantly higher among the exposed (265.46/100,000 person-years) than among the unexposed (139.06/100,000 person-years), as was mortality from all malignant neoplasms (123.21/100,000 versus 54.7/100,000, respectively). For certain cancers, increased mortality was noted among benzene-exposed males in comparison with that among unexposed males; the standardized mortality ratios (SMR) were elevated for leukemia (SMR = 5.74), lung cancer (SMR = 2.31), primary hepatocarcinoma (SMR = 1.12), and stomach cancer (SMR = 1.22). For females only leukemia occurred in excess among the exposed. Risk of leukemia rose as duration to exposure to benzene increased up to 15 years, and then declined with additional years of exposure. Leukemia occurred among some workers with as little as 6 to 10 ppm average exposure and 50 ppm-years (or possibly less) cumulative lifetime exposure (based on all available measurements for the exposed work units). Among the 30 leukemia cases identified in the exposed cohort, the proportion of subjects with acute lymphocytic leukemia was substantially lower and the proportion with acute nonlymphocytic leukemias was higher than in the general population. During 1972 to 1981, the annual incidence of leukemia ranged from 5.83 to 28.33 per 100,000 with higher rates occurring in the interval 1977 to 1981 than in the earlier years of the study period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Metastatic liposarcoma of the brain with response to chemotherapy: case report.

Metastatic liposarcomas to the brain are rare. The authors describe a patient with a 20-year history of liposarcoma originating in the thigh and metastatic to the brain 18 years later. The brain metastasis was removed by surgery. Nine months later, the patient developed metastases to the retroperitoneum and liver. At that same time, she had recurrent brain metastasis. She was then treated with chemotherapy. The abdominal mass shrank considerably in the beginning, and the recurrent brain metastases totally disappeared. The patient eventually succumbed to widespread liposarcoma. Autopsy revealed extensive liposarcoma involving the retroperitoneum, liver, and lung, but no trace of tumor was found in the brain.

Brain Neoplasms↗