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Biomedical subjects

G K Wong

Publications and source records attributed to G K Wong.

At least 19 recordsLinked to original sources
PubMed2006

Polarization modulation instability in photonic crystal fibers.

Polarization modulation instability (PMI) in birefringent photonic crystal fibers has been observed in the normal dispersion regime with a frequency shift of 64 THz between the generated frequencies and the pump frequency. The generated sidebands are orthogonally polarized to the pump. From the observed PMI frequency shift and the measured dispersion, we determined the phase birefringence to be 5.3 x 10(-5) at a pump wavelength of 647.1 nm. This birefringence was used to estimate the PMI gain as a function of pump wavelength. Four-wave mixing experiments in both the normal and the anomalous dispersion regimes generated PMI frequency shifts that show good agreement with the predicted values over a 70 THz range. These results could lead to amplifiers and oscillators based on PMI.

Journal Article↗
PubMed2004

A review of isolated third nerve palsy without subarachnoid hemorrhage using computed tomographic angiography as the first line of investigation.

INTRODUCTION: Digital subtraction angiography is recognized as the standard investigation for isolated third nerve palsy thought to be caused by an expanding aneurysm. We reviewed our experience in using computed tomographic angiography (CTA) as the first line investigation for patients presenting with isolated third nerve palsy without subarachnoid hemorrhage. METHOD: We retrieved the medical records of 34 patients who had presented with isolated third nerve palsy without associated subarachnoid hemorrhage to our institution between January 1998 and July 2001. The clinical history, course and outcome as well as the radiological data was reviewed. RESULTS: A total of nine structural lesions (26%) were noted as the etiology of the third nerve palsy. All of the five posterior communicating artery aneurysms were picked up by the CTA. Neither the presence nor the absence of painful complete third nerve palsy was of diagnostic value for intracranial aneurysm. CONCLUSION: A good quality CTA is sufficient to detect a compressive aneurysm and may detect other structural lesions. This allows neurosurgeons to plan the management of patients with isolated third nerve palsy. Patients in whom CTA results are inconclusive should be further investigated with catheter angiography.

Adolescent↗
PubMed2004

Fluoroscopic frameless computer-assisted navigation for transsphenoidal surgery: a clinical assessment of accuracy in spatial position and trajectory.

OBJECTIVE: Fluoroscopic navigation technique in transsphenoidal surgery on the one hand provides multi-planar (antero-posterior and lateral views) navigation while on the other hand it does not need any preoperative preparation. To assess the clinical accuracy of the above technique in the transsphenoidal surgery, we performed this study. METHODS: 5 patients undergoing transsphenoidal surgery were assessed. Fluoroscopic images were compared with C-arm X-ray images for difference in spatial position and trajectory. RESULTS: 26 sets of data were collected for analysis. Mean pointer tip difference was 0.6 mm. The 95 % confidence interval was 1.3 mm. Mean trajectory difference was 1.2 degree. The 95 % confidence interval was 2.7 degree. CONCLUSION: With a good clinical accuracy, fluoroscopic navigation offers a distinct advantage to replace the traditional fluoroscopic approach for transsphenoidal surgery for its low X-ray exposure and multi-planar (antero-posterior and lateral views) navigation.

Adenoma↗
PubMed2003

LINAC radiosurgery in recurrent Cushing's disease after transsphenoidal surgery: a series of 5 cases.

INTRODUCTION: Oversecretion of ACTH from pituitary adenomas is associated with morbidity and reduced life expectancies. We hypothesized that radiosurgical treatment may provide effective tumour and hormonal control associated with minimal pituitary insufficiency. METHOD: Data of five patients who underwent LINAC radiosurgery for recurrent or residual Cushing's disease between 1999 and 2002 were prospectively collected. RESULT: Follow-up period ranged from 27 to 49 months (mean 38 months). All patients attained remission in 6-18 months (mean 8.4 months). One patient (20 %) developed biochemical recurrence 12 months after remission. One patient (20 %) developed hydrocortisone deficiency 24 months after radiosurgery. None of the patients had new visual field defect detected on follow-up. CONCLUSION: In this small case series, LINAC radiosurgery was shown to be an effective and safe treatment of persistent or recurrent Cushing's disease following transsphenoidal surgery. Long-term follow-up and larger patient series is recommended for further clarification.

Adenoma↗
PubMed2001

Polarity inversion in polar-nonpolar-polar heterostructures.

We have observed an epilayer-thickness-dependent polarity inversion for the growth of CdTe on Sb(Bi)/CdTe(111)B. For films with Sb(Bi) thicknesses of less than 40 A (15 A), the CdTe layer shows a B (Te-terminated) face, but it switches to an A (Cd-terminated) face for thicker layers. On the other hand, a CdTe layer grown on Bi(Sb)/CdTe(111)A always shows the A face regardless of Sb or Bi layer thicknesses. In order to address the observations we have performed ab initio calculations, which suggest that the polarity of a polar material on a nonpolar one results from the binding energy difference between the two possible surface configurations.

Journal Article↗
PubMed2001

Apolipoprotein E is upregulated in olfactory bulb glia following peripheral receptor lesion in mice.

Apolipoprotein E (apoE), a lipid transporting protein, has been postulated to participate in nerve regeneration. To better clarify apoE function in the olfactory system, we evaluated the amount and distribution of apoE in the olfactory bulb following olfactory nerve lesion in mice. Olfactory nerve was lesioned in 2- to 4-month-old mice by intranasal irrigation with Triton X-100. Olfactory bulbs were collected at 0, 3, 7, 21, 42, and 56 days postlesion, and both apoE concentrations and apoE distribution were determined. ApoE levels, as determined by immunoblot analysis, were twofold greater than normal during nerve degeneration at 3 days. ApoE levels remained elevated by approximately 1.5 times normal levels at 7 through 21 days after injury and returned to baseline by 56 days. Immunocytochemical studies supported these observations. ApoE immunoreactivity was prominent on the olfactory nerve at 3 days after lesion and decreased to baseline levels at later time periods. Double-labeling immunocytochemical studies confirmed that both reactive astroglia and microglia produced detectable amounts of apoE following the lesion. Return of apoE expression to baseline paralleled measures of olfactory nerve maturation as measured by olfactory marker protein. These data suggest that apoE increases concurrent with nerve degeneration. ApoE may facilitate efficient regeneration perhaps by recycling lipids from degenerating fibers for use by growing axons. The association of apoE genotype with dementing illnesses may represent a diminished ability to support a lifetime of nerve regeneration.

Animals↗
PubMed2001

Parental pediatric corticosteroid preferences.

Corticosteroids are often prescribed in the acute care management of asthma. Prednisolone can be administered intramuscularly (IM) or orally in 2 different concentrations. This study evaluated parental preference for three prednisolone preparations based on the route of administration, taste, and volume required. Accompanying adults (AAs) of pediatric patients were interviewed about their preferences based on the 3 factors. Those AAs who passed the health screen (51 of 214) were asked to taste 2 oral prednisolone preparations and reinterviewed about their corticosteroid preferences. Of the 214 AAs, 96% were parents. Of the group, 43% preferred IM corticosteroids whereas 40% preferred oral corticosteroids. Without considering taste as a factor for oral corticosteroids, 94% preferred the more concentrated syrup compared with the less concentrated one. When told that the less concentrated syrup tasted better, 58% preferred the less concentrated/better tasting syrup. After the 51 taste test subcohort subjects tasted the syrups, 96% preferred the less concentrated/ better tasting syrup over the more concentrated/poorer tasting syrup. Taste is more important than volume of administration for this particular corticosteroid comparison. Simply asking parents about their IM/oral and syrup formulation preferences may be the easiest way of optimizing their treatment plan.

Child, Preschool↗
PubMed2001

The impact of an armless frameless neuronavigation system on routine brain tumour surgery: a prospective analysis of 51 cases.

A passive infrared armless and frameless neuronavigation system was introduced in routine intracranial and skull base surgery, and its impact on 51 cases in a one year period was assessed. No cases were rejected by the operating surgeon for lack of accuracy (> 3 mm). Operating time was not significantly lengthened, except in transphenoidal cases (255 +/- SD 168 min versus 185 +/- SD 119 min, p = 0.02). Length of stay was shorter in navigation cases in supratentorial glioma (12 +/- SD 7.3 days versus 15 +/- SD 7.9 days) and meningioma (11 +/- SD 5.3 days versus 16 +/- SD 6.7 days, p = 0.01). Outcome at 3 months was comparable in both the supratentorial glioma and meningioma group. Problems such as setup time and brain shift are addressed and discussed.

Adolescent↗
PubMed2000

Intellectual property. Publication rights in the era of open data release policies.

The open data release policy adopted by the large-scale DNA sequencing centers has made accessible valuable information that facilitates research. Herein, we argue that the data producers' rights to receive credit for at least some portion of the analyses of the data must be protected. We suggest that this protection take the form of a specification of the probable content of the primary paper the data producers intend to publish when the data gathering is complete. Rights to publish that paper ought then be restricted to the producers unless they give permission otherwise.

Animals↗
PubMed2000

Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.

Pseudomonas aeruginosa is a ubiquitous environmental bacterium that is one of the top three causes of opportunistic human infections. A major factor in its prominence as a pathogen is its intrinsic resistance to antibiotics and disinfectants. Here we report the complete sequence of P. aeruginosa strain PAO1. At 6.3 million base pairs, this is the largest bacterial genome sequenced, and the sequence provides insights into the basis of the versatility and intrinsic drug resistance of P. aeruginosa. Consistent with its larger genome size and environmental adaptability, P. aeruginosa contains the highest proportion of regulatory genes observed for a bacterial genome and a large number of genes involved in the catabolism, transport and efflux of organic compounds as well as four potential chemotaxis systems. We propose that the size and complexity of the P. aeruginosa genome reflect an evolutionary adaptation permitting it to thrive in diverse environments and resist the effects of a variety of antimicrobial substances.

Bacterial Proteins↗
PubMed2000

Characterization of optical intrinsic signals and blood volume during cortical spreading depression.

Cortical spreading depression (CSD) was imaged in vivo in a rodent model with optical intrinsic signals (OIS). This is the first study to identify a triphasic OIS response and to characterize the rate and timing of the response. The initial OIS phase had a highly uniform wavefront, which spread at a rate characteristic of CSD, 3.5 mm/min. Later phases were more diffuse and inhomogeneous. Blood volume changes, measured with intravascular fluorescent dye, correlated in time and location with the later phases of OIS response. This suggests that the inhomogeneity of the late OIS response may be due to complex residual hemodynamic contributions, as opposed to underlying cortical circuitry.

Animals↗
PubMed2000

Sampling SNPs.

Explore the source record for details and available documents.

Alleles↗
PubMed2000

Is "junk" DNA mostly intron DNA?

Among higher eukaryotes, very little of the genome codes for protein. What is in the rest of the genome, or the "junk" DNA, that, in Homo sapiens, is estimated to be almost 97% of the genome? Is it possible that much of this "junk" is intron DNA? This is not a question that can be answered just by looking at the published data, even from the finished genomes. One cannot assume that there are no genes in a sequenced region, just because no genes were annotated. We introduce another approach to this problem, based on an analysis of the cDNA-to-genomic alignments, in all of the complete or nearly-complete genomes from the multicellular organisms. Our conclusion is that, in animals but not in plants, most of the "junk" is intron DNA.

Animals↗
PubMed2000

Enhancement of the antifungal activity of rapamycin by the coproduced elaiophylin and nigericin.

Streptomyces hygroscopicus ATCC 29253 produces rapamycin, elaiophylin and nigericin. Although elaiophylin has no activity against Candida albicans ATCC 11651, it markedly enhances rapamycin's antifungal activity. Nigericin has only weak activity on its own but it also enhances rapamycin action. Surprisingly, elaiophylin does not enhance nigericin activity on C. albicans.

Anti-Bacterial Agents↗
PubMed1999

Characterization of the human endothelial nitric-oxide synthase promoter.

Understanding transcription initiation of the endothelial nitric-oxide synthase (eNOS) gene appears pivotal to gaining a comprehensive view of NO biology in the blood vessel wall. The present study therefore focused upon a detailed dissection of the functionally important cis-DNA elements and the multiprotein complexes implicated in the cooperative control of constitutive expression of the human eNOS gene in vascular endothelium. Two tightly clustered cis-regulatory regions were identified in the proximal enhancer of the TATA-less eNOS promoter using deletion analysis and linker-scanning mutagenesis: positive regulatory domains I (-104/-95 relative to transcription initiation) and II (-144/-115). Analysis of trans-factor binding and functional expression studies revealed a surprising degree of cooperativity and complexity. The nucleoprotein complexes that form upon these regions in endothelial cells contained Ets family members, Sp1, variants of Sp3, MAZ, and YY1. Functional domain studies in Drosophila Schneider cells and endothelial cells revealed examples of positive and negative protein-protein cooperativity involving Sp1, variants of Sp3, Ets-1, Elf-1, and MAZ. Therefore, multiprotein complexes are formed on the activator recognition sites within this 50-base pair region of the human eNOS promoter in vascular endothelium.

Animals↗
PubMed1998

The complete genomic sequence of 424,015 bp at the centromeric end of the HLA class I region: gene content and polymorphism.

We report here the genomic sequence of the centromeric portion of HLA class I, extending 424,015 bp from tumor necrosis factor alpha to a newly identified gene approximately 20 kb telomeric of Otf-3. As a source of DNA, we used cosmids centromeric of HLA-B that had been mapped previously with conventional restriction digestion and fingerprinting and previously characterized yeast artificial chromosomes subcloned into cosmids and mapped with multiple complete digest methodologies. The data presented provide a description of the gene content of centromeric HLA class I including new data on intron, promoter and flanking sequences of previously described genes, and a description of putative new genes that remain to be characterized beyond the structural information uncovered. A complete accounting of the repeat structure including abundant di-, tri-, and tetranucleotide microsatellite loci yielded access to precisely localized mapping tools for the major histocompatibility complex. Comparative analysis of a highly polymorphic region between HLA-B and -C was carried out by sequencing over 40 kb of overlapping sequence from two haplotypes. The levels of variation observed were much higher than those seen in other regions of the genome and indeed were higher than those observed between allelic HLA class I loci.

Centromere↗
PubMed1998

Antifungal activities of rapamycin and its derivatives, prolylrapamycin, 32-desmethylrapamycin, and 32-desmethoxyrapamycin.

The antifungal agent rapamycin is highly effective in inhibiting growth of yeast and mold strains. This study demonstrates that in liquid medium, rapamycin is more active than its derivatives (prolylrapamycin, 32-desmethylrapamycin, 32-desmethoxyrapamycin) against Candida albicans, Saccharomyces cerevisiae, and Fusarium oxysporum. All the rapamycins were more active than amphotericin B. Although four other molds were not inhibited in liquid medium, they were very sensitive to rapamycin and its derivatives when tested on agar. The latter assay showed that rapamycin is the most active and 32-desmethylrapamycin is more active than prolylrapamycin and 32-desmethoxyrapamycin. The conclusion of this study is that rapamycin is the most active antifungal agent of the compounds examined. The unexpected finding of high activity of rapamycin and its derivatives against filamentous fungi when assayed by the agar diffusion assay suggests that rapamycin or a derivative may hold promise for chemotherapy against pathogenic molds as well as yeasts.

Amphotericin B↗