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Biomedical subjects

K H Chen

Publications and source records attributed to K H Chen.

At least 19 recordsLinked to original sources
PubMed2006

Influence of oxygen on the elastic properties of nanocrystalline diamond films studied by laser-induced surface acoustic waves.

Laser-induced surface acoustic waves (SAWs) were used to study the influence of oxygen on the elastic properties of nanocrystalline diamond films. A series of samples was grown by chemical vapor deposition (CVD) on the (100) plane of p-type silicon for 3h under different O(2)/(CH(4)+H(2)) flow ratios from 0% to 8%. The elastic properties of these nanocrystalline diamond films were determined from the SAW dispersion curves. The maximum frequency realized was about 310 MHz in wideband SAW experiments and about 700 MHz using a narrowband mask method with several higher harmonics. It was found that the densities of all samples were surprisingly high, approaching the ideal value of diamond, whereas the Young's modulus increased from 700 to 950 GPa with the addition of oxygen. It is concluded that oxygen has a significant positive effect on the elastic properties of nanocrystalline diamond.

Journal Article↗
PubMed2006

Singular meshless method using double layer potentials for exterior acoustics.

Time-harmonic exterior acoustic problems are solved by using a singular meshless method in this paper. It is well known that the source points cannot be located on the real boundary, when the method of fundamental solutions (MFS) is used due to the singularity of the adopted kernel functions. Hence, if the source points are right on the boundary the diagonal terms of the influence matrices cannot be derived. Herein we present an approach to obtain the diagonal terms of the influence matrices of the MFS for the numerical treatment of exterior acoustics. By using the regularization technique to regularize the singularity and hypersingularity of the proposed kernel functions, the source points can be located on the real boundary and therefore the diagonal terms of influence matrices are determined. We also maintain the prominent features of the MFS, that it is free from mesh, singularity, and numerical integration. The normal derivative of the fundamental solution of the Helmholtz equation is composed of a two-point function, which is one of the radial basis functions. The solution of the problem is expressed in terms of a double-layer potential representation on the physical boundary based on the potential theory. The solutions of three selected examples are used to compare with the results of the exact solution, conventional MFS, boundary element method, and Dirichlet-to-Neumann finite element method. Good numerical performance is demonstrated by close agreement with other solutions.

Journal Article↗
PubMed2004

Blue luminescence of Au nanoclusters embedded in silica matrix.

Photoluminescence study using the 325 nm He-Cd excitation is reported for the Au nanoclusters embedded in SiO(2) matrix. Au clusters are grown by ion beam mixing with 100 KeV Ar(+) irradiation on Au [40 nm]/SiO(2) at various fluences and subsequent annealing at high temperature. The blue bands above approximately 3 eV match closely with reported values for colloidal Au nanoclusters and supported Au nanoislands. Radiative recombination of sp electrons above Fermi level to occupied d-band holes are assigned for observed luminescence peaks. Peaks at 3.1 and 3.4 eV are correlated to energy gaps at the X- and L-symmetry points, respectively, with possible involvement of relaxation mechanism. The blueshift of peak positions at 3.4 eV with decreasing cluster size is reported to be due to the compressive strain in small clusters. A first principle calculation based on density functional theory using the full potential linear augmented plane wave plus local orbitals formalism with generalized gradient approximation for the exchange correlation energy is used to estimate the band gaps at the X- and L-symmetry points by calculating the band structures and joint density of states for different strain values in order to explain the blueshift of approximately 0.1 eV with decreasing cluster size around L-symmetry point.

Journal Article↗
PubMed2002

Genetic polymorphism of the CYP2E1 gene and susceptibility to Parkinson's disease in Taiwanese.

Cytochrome p450IIE1 (CYP2E1), an ethanol-inducible cytochrome p450 enzyme, is expressed in the basal ganglia and is probably involved in the activation of neurotoxicants, producing free radical metabolites and resulting in oxidative stress. To examine the association between CYP2E1 polymorphism and the risk of Parkinson's disease (PD), we performed a case-control study on a large population of Taiwanese PD patients, focusing especially on early-onset PD patients (onset at, or before, the age of 50). Two hundred and thirty-four PD patients and 251 age- and sex-matched controls were recruited. A much higher frequency of the uncommon c2 allele was seen in our control subjects than in Caucasians (0.23 vs. 0.02). There were no significant differences between PD patients and controls in the distribution of either allelic or genotype frequencies. Our results suggest that CYP2E1 is not a major or independent determinant in the occurrence of PD in Taiwanese.

Age of Onset↗
PubMed2001

Relationship between base excision repair capacity and DNA alkylating agent sensitivity in mouse monocytes.

Base excision repair (BER) capacity and the level of DNA polymerase beta (beta-pol) are higher in mouse monocyte cell extracts when cells are treated with oxidative stress-inducing agents. Consistent with this, such treated cells are more resistant to the cytotoxic effects of methyl methanesulfonate (MMS), which produces DNA damage considered to be repaired by the BER pathway. In contrast to the up-regulation of BER in oxidatively stressed cells, cells treated with the cytokine interferon-gamma (IFN-gamma) are down-regulated in both BER capacity of the cell extract and level of beta-pol. We find that cells treated with IFN-gamma are more sensitive to MMS than untreated cells. These results demonstrate concordance between beta-pol level, BER capacity and cellular sensitivity to a DNA methylation-inducing agent. The results suggest that BER is a significant defense mechanism in mouse monocytes against the cytotoxic effects of methylated DNA.

Alkylating Agents↗
PubMed2001

Enantioseparation of phenothiazines in capillary zone electrophoresis using cyclodextrins as chiral selectors.

In this study, enantioseparations of five phenothiazines, including promethazine, ethopropazine, trimeprazine, methotrimeprazine, and thioridazine, in cyclodextrin (CD)-modified capillary zone electrophoresis were investigated using a phosphate buffer (40 mM) at pH 3.0. We focussed on the separation of phenothiazines with the use of CDs at low concentrations. Three different CDs, including beta-CD, hydroxypropyl-beta-CD (HP-beta-CD) and gamma-CD, were chosen as chiral selectors. The results indicate that effective enantioseparation of phenothiazines, except for methotrimeprazine, is simultaneously achievable with addition of gamma-CD at a concentration of 2.5-6.0 mM. The enantiomers of ethopropazine and trimeprazine are effectively separated with addition of HP-beta-CD at low concentrations, in the range 0.4-6.0 mM, whereas those of promethazine and trimeprazine are baseline resolved with beta-CD at much lower concentrations (0.02-3.0 mM) than with HP-beta-CD. The results also confirm that the separation window is greatly enlarged at low CD concentrations. Moreover, the drastic variations of the electrophoretic mobility of phenothiazines as a function of CD concentration reveal that phenothiazines interact very strongly with CDs in the order gamma-CD<HP-beta-CD<beta-CD.

Cyclodextrins↗
PubMed2001

Catalytic growth and characterization of gallium nitride nanowires.

The preparation of high-purity and -quality gallium nitride nanowires is accomplished by a catalytic growth using gallium and ammonium. A series of catalysts and different reaction parameters were applied to systematically optimize and control the vapor-liquid-solid (VLS) growth of the nanowires. The resulting nanowires show predominantly wurtzite phase; they were up to several micrometers in length, typically with diameters of 10-50 nm. A minimum nanowire diameter of 6 nm has been achieved. Temperature dependence of photoluminescence spectra of the nanowires revealed that the emission mainly comes from wurtzite GaN with little contribution from the cubic phase. Moreover, the thermal quenching of photoluminescence was much reduced in the GaN nanowires. The Raman spectra showed five first-order phonon modes. The frequencies of these peaks were close to those of the bulk GaN, but the modes were significantly broadened, which is indicative of the phonon confinement effects associated with the nanoscale dimensions of the system. Additional Raman modes, not observed in the bulk GaN, were found in the nanowires. The field emission study showing notable emission current with low turn-on field suggests potential of the GaN nanowires in field emission applications. This work opens a wide route toward detailed studies of the fundamental properties and potential applications of semiconductor nanowires.

Journal Article↗
PubMed2001

X-ray absorption studies of carbon-related materials.

X-ray absorption near-edge structure (XANES) measurements have been performed on nitrogen-doped diamond films with three different dopant concentrations and iron-layer-stabilized carbon nanotube (CNT) structures with various diameters at the C K-absorption edge using the sample drain current mode. The C K-edge XANES spectra of these N-doped diamond films resemble that of the undoped diamond regardless of the dopant concentration, which suggest that the overall bonding configuration of the C atom is unaltered. N dopants are found to reduce the intensities of both the sp2- and sp3-bond-derived resonance features in the XANES spectra. On the other hand, the C K-edge XANES spectra of CNTs indicate that the intensities of the pi* and sigma* bands and the interlayer-state features vary with the diameter of the CNT. This phenomenon may be caused by the Fe-layer-catalysed bending of the graphite sheet and the interaction between C and Fe atoms.

Journal Article↗
PubMed2001

The COMT L allele modifies the association between MAOB polymorphism and PD in Taiwanese.

OBJECTIVE: Reports suggest that catechol-O-methyltransferase (COMT(L/L)) (Val(158)/Met) and monoamine oxidase B (MAOB) intron 13 genotype polymorphism is associated with PD. To understand the ethnicity-specific effects of genetic polymorphism, we performed a case-control study of the association between PD susceptibility and polymorphism of MAOB and COMT, both separately and in combination, in Taiwanese. METHODS: Two hundred twenty-four patients with PD and 197 controls, matched for age, sex, and birthplace, were recruited. MAOB and COMT polymorphism genotyping was performed by using PCR-based restriction fragment length polymorphism (RFLP) analyses. chi(2), OR, and Fisher's exact tests were used to compare differences in allelic frequencies and genotypes. RESULTS: The MAOB G genotype (G in men and G:/G in women) was associated with a 2.07-fold increased relative risk of PD. COMT polymorphism, considered alone, showed no correlation with PD risk; however, a significant synergistic enhancement was found in PD patients harboring both the COMT(L) and MAOB G genotypes. CONCLUSIONS: These results suggest that, in Taiwanese, PD risk is associated with MAOB G intron 13 polymorphism, and this association is augmented in the presence of the COMT(L) genotype, indicating an interaction of these two dopamine-metabolizing enzymes in the pathogenesis of sporadic PD. However, the relatively low frequencies of these combined genotypes in our study necessitates confirmation with a larger sample size.

Aged↗
PubMed2001

Apoptosis in atherosclerosis: pathological and pharmacological implications.

Normal embryonic development, tissue differentiation and repair in the eukaryote requires a tightly regulated apoptosis, or programmed cell death. Apoptosis also plays an essential role in different pathological processes including atherosclerosis, in which it affects all cell types in the atherosclerotic lesion, including endothelial cells, vascular smooth muscle cells, and macrophages. During atherosclerosis progression, pro- and anti-apoptotic signals abound in the evolving lesion. Apoptosis limits the number of a particular cell type that accumulates in the lesion and slows down the overall progression of the lesion. On the other hand, it contributes to the production of unstable plaques. Many pharmacological agents used to treat cardiovascular and lipid disorders have pro- or/and anti-apoptotic effects. Pharmaceuticals that modulate apoptosis in specific types of cell can potentially serve as anti-atherogenic agents. However, to develop agents for clinical use requires a thorough knowledge of the pathophysiology of apoptosis in atheromatous lesions, a highly cell-specific process. Here we review our current understanding of the process to provide a background for future pharmacological research in the area.

Animals↗
PubMed2001

Serratia Marcescens corneal ulcer as a complication of orthokeratology.

PURPOSE: To report a case of Serratia Marcescens corneal ulcer as a complication of orthokeratology treatment. METHODS: Case report. RESULTS: A 9-year-old male who underwent orthokeratology treatment for 6 months suffered from a corneal ulcer. The refractive state of lesion eye was -5.5D/-1.25D x 180 degrees, and visual acuity was hand motion at 30 cm. He wore a retainer lens, rigid gas permeable lens, overnight for 2 months before the corneal ulcer occurred. Ulcer became worse after tobramycin and gentamycin treatment for 2 days. After ciprofloxacin treatment, the ulcer healed and visual acuity recovered to 20/20 with spectacle correction. Cultures of the cornea tissue and contact lens storage solution both grew Serratia Marcescens, which was sensitive to ciprofloxacin. CONCLUSION: Overnight wearing of a rigid contact lens is a risk factor for a corneal ulcer.

Anti-Infective Agents↗
PubMed2001

The oxidation of cholesterol in the yolk of selective traditional Chinese egg products.

The yolks of traditional chicken egg products (Tiedan, Ludan, and Chayedan) and duck egg products (raw and cooked Xiandan, immersed and coated Pidan) were subjected to moisture, lipid, and thiobarbituric acid (TBA) determinations as well as cholesterol and cholesterol oxidation products (COP) analysis. The main COP detected for these egg products included 20-hydroxycholesterol and 7beta-hydroxycholesterol, other types of COP were not detected. The contents of COP formed in traditional egg products varied, depending upon the types of egg products. The cholesterol oxidation ratio for traditional Chinese chicken egg products ranged from 1.14 to 1.75%, whereas that for traditional Chinese duck egg products ranged from 1.18 to 1.90%. Those traditional egg products that required pickling in salt or alkaline, cooking, hot air drying, and exposure to oxygen and heat all produced COP.

Animals↗
PubMed2001

Transplantation of adult human corneal endothelium ex vivo: a morphologic study.

PURPOSE: To investigate the feasibility of transplanting untransformed human corneal endothelial cells as a treatment strategy and possible alternative for penetrating keratoplasty by growing donor cells in culture and then transplanting them to denuded Descemet's membrane of recipient corneas. METHODS: Corneas from adult donors (50-80 years old) were obtained from eye banks. To grow corneal endothelial cells, Descemet's membrane with associated cells was dissected from the stroma. Endothelial cells were released by ethylenediaminetetraacetic acid treatment, grown in medium containing multiple growth factors, and identified as being of endothelial origin by morphology and by reverse-transcription polymerase chain reaction for keratin 12 and collagen type VIII. In transplantation experiments, cultured cells were seeded onto denuded Descemet's membrane of a second donor cornea at 5 x 10(5) cells/mL. The recipient cornea was incubated in organ culture for as long as 2 weeks. The morphology and ultrastructure of the endothelium were evaluated 7 and 14 days after transplantation by transmission electron microscopy, and by immunolocalization of zonula occludins-1 (ZO-1). Endothelial cell density was calculated in transplants by counting ZO-1-stained cells. RESULTS: Corneal endothelial cells cultured from adult donors consistently grew well in culture medium. Cells were identified as corneal endothelium by characteristic morphology and messenger RNA expression. Morphologic and ultrastructural studies of corneas containing transplanted endothelial cells demonstrated that with time there was an increase in endothelial cell-Descemet's membrane adhesion, in the extent of cell-cell contacts and lateral interdigitation, and in formation of a single cell layer. ZO-1 staining revealed tight junction formation similar to that of corneas in vivo. Mean endothelial cell density in transplanted corneas was 1,895 cells/mm(2) (range, 1,503-2,159 cells/mm(2) ). CONCLUSION: Untransformed adult human corneal endothelial cells can be efficiently and consistently cultured and transplanted onto denuded Descemet's membrane. Transplanted cells in organ culture exhibit morphologic characteristics and cell densities similar to corneal endothelial cells in vivo. These results provide evidence for the feasibility of developing methods for in vivo transplantation of untransformed corneal endothelial cells cultured from adult donor tissue.

Aged↗
PubMed2001

Pattern of skin diseases in a geriatric patient group in Taiwan: a 7-year survey from the outpatient clinic of a university medical center.

BACKGROUND: Geriatric health care has become a worldwide concern, but relatively few statistical studies are available about geriatric skin diseases. Moreover, no information exists regarding skin disorders among the elderly population in Taiwan that has become a geriatric country. OBJECTIVE: To determine the characteristic pattern and the prevalence of various skin disorders for the elderly who visited the National Taiwan University in the last 7 years. METHODS: Using a database from the Dermatology Outpatient Clinic of the National Taiwan University Hospital, 1993-1999 file, we conducted a retrospective cross-sectional study by evaluating the age, proportion, and gender of each specific cutaneous disease category, chi(2) tests were used for analyzing statistical significance. The analysis supplied odds ratios and 95% confidence intervals. RESULTS: A total of 16,924 patients aged 65 years and older, which constituted 11% of the total patients seen at the Clinic of Dermatology from 1993 through 1999, were studied. The male to female ratio was 1.3 to 1. The most common cutaneous disorder in the elderly was dermatitis (58.7%), followed by fungal infections (38.0%), pruritus (14.2%), benign tumors (12.8%), and viral infections (12.3%). Cutaneous malignant tumors were found in 2.1%. Basal cell carcinoma occurred in 29.8%, actinic keratosis in 22.4%, Bowen's disease in 13.3% and squamous cell carcinoma 13.3%. Interestingly, our cases of extramammary Paget's disease showed a male predominance. Most melanomas were acral lentiginous melanoma located on the soles. The prevalence of common diseases in elderly patients compared with those outpatients of less than 65 years showed a 3-fold increased risk for pruritus. Moreover, the pattern of geriatric skin diseases in Taiwan was significantly different from Western countries. CONCLUSION: The prevalence of skin diseases in elderly patients emphasizes the importance of health education in geriatric people in Taiwan concerning appropriate use of emollients, proper foot care, sun protection and early detection of skin cancers.

Aged↗
PubMed2000

Absence of perilipin results in leanness and reverses obesity in Lepr(db/db) mice.

Obesity is a disorder of energy balance. Hormone-sensitive lipase (HSL) mediates the hydrolysis of triacylglycerol, the major form of stored energy in the body. Perilipin (encoded by the gene Plin), an adipocyte protein, has been postulated to modulate HSL activity. We show here that targeted disruption of Plin results in healthy mice that have constitutively activated fat-cell HSL. Plin -/- mice consume more food than control mice, but have normal body weight. They are much leaner and more muscular than controls, have 62% smaller white adipocytes, show elevated basal lipolysis that is resistant to beta-adrenergic agonist stimulation, and are cold-sensitive except when fed. They are also resistant to diet-induced obesity. Breeding the Plin -/- alleles into Leprdb/db mice reverses the obesity by ncreasing the metabolic rate of the mice. Our results demonstrate a role for perilipin in reining in basal HSL activity and regulating lipolysis and energy balance; thus, agents that inactivate perilipin may prove useful as anti-obesity medications.

Adipose Tissue↗
PubMed2000

Modulation of base excision repair by low density lipoprotein, oxidized low density lipoprotein and antioxidants in mouse monocytes.

In the present study, we found that oxidized low density lipoprotein, but not low density lipoprotein, down-regulated base excision repair activity in extracts of mouse monocyte cell line PU5-1.8. An enzyme required in this pathway, DNA polymerase beta, was also down-regulated. In contrast, treatment of monocytes with a combination of ascorbate and alpha-tocopherol up-regulated base excision repair activity and expression of DNA polymerase beta. Co-treatment of monocytes with antioxidants plus oxidized low density lipoprotein prevented down-regulation by oxidized low density lipoprotein. Oxidative DNA damage, as measured by 8-hydroxyguanine accumulation in genomic DNA, was found in cells treated with oxidized low density lipoprotein; 8-hydroxyguanine was not found in the cells treated with low density lipoprotein, antioxidants or oxidized low density lipoprotein plus antioxidants. These results establish a linkage between the DNA base excision repair pathway, oxidative DNA damage and oxidized low density lipoprotein treatment in mouse monocytes. Since oxidized low density lipoprotein is implicated in chronic disease conditions such as atherogenesis, these findings facilitate understanding of genetic toxicology mechanisms related to human health and disease.

Animals↗
PubMed2000

Communicating outpatient perception to improve quality management.

The authors report a study of outpatients' perceptions of clinic waiting times in relation to their expectations and to waiting time norms. The waiting time norm for online registration was 10 minutes, and for blood sampling was 20 minutes. Satisfaction with the behavior of clinic nurses also is reported and analyzed.

Ambulatory Care↗