Search PubMed⌕ Search

Biomedical subjects

S M Yu

Publications and source records attributed to S M Yu.

At least 19 recordsLinked to original sources
PubMed2002

Confinement-induced order of tethered alkyl chains at the water/vapor interface.

Packing of tethered alkyl chains in Langmuir monolayers of a hairy-rod polypeptide poly[gamma-4-(n-hexadecyloxy)benzyl alpha,L-glutamate] on water has been studied by x-ray scattering measurements at room temperature. The rods lie parallel to the surface while the alkyl side chains segregate toward the vapor. Results indicate that the herringbone order of the alkyl chains is established initially by one-dimensionally confined chains between aligned rods and grows laterally with compression.

Journal Article↗
PubMed2002

The impact of sea water flushing on biological nitrification-denitrification activated sludge sewage treatment process.

The process performance of the two largest activated sludge processes in Hong Kong, the Sha Tin and the Tai Po Sewage Treatment Works (STW), deteriorated in the initial period after the introduction of seawater flushing in 1995 and 1996, respectively. High effluent ammonia nitrogen (NH4-N) and total suspended solids (TSS) in excess of the discharge standards resulted from incomplete nitrification and changes in floc characteristics. A desktop study on the inhibitory effects of salinity, particularly on nitrification, was subsequently conducted using the Tai Po STW operating data. To assist the upgrade of the Sha Tin STW a five-month extensive bench-scale investigation on a simple but flexible modified Ludzack-Ettinger configuration with bio-selector was conducted to quantify the inhibitory effects due to the saline concentration. The Sha Tin STW upgrade consists of restoration of its original design capacity (conventional process) of 205,000 m3/day from its currently much reduced capacity as a Bardenpho process. Only the volume of the existing biological process and clarifier is to be utilized. The saline concentration ranges from 3,500 up to 6,500 mg Cl-/L, both daily and seasonally. High and greatly fluctuating saline concentrations have been known to inhibit nitrification. Design consideration should also be given to the peak daily and seasonal TKN loading of up to three times the average. Although the nitrifiers maximum specific growth rate was significantly reduced to a low 0.25 day(-1), the inhibition was considered to be tolerable with effluent NH4-N and NO3-N consistently at < 1 and < 6 mg/L. The bio-selector was demonstrated to be efficient in control of sludge foaming and bulking with SVI consistently < or = 125 mL/g. Results from the IAWO Model No. 1 and the hydraulic model of the secondary clarifiers allowed overall process capacity maximization. With an anoxic mass fraction of 25-30%, operating sludge age of 9-14 days and SVI < or = 125 mL/g, both the design requirements and the effluent discharge standards could be met. Without these investigations, an unnecessarily large reaction basin and secondary clarifier volume, and hence capital investment, would have resulted.

Ammonia↗
PubMed2001

Protective effects of treadmill training on infarction in rats.

This study was undertaken to determine the protective effects of treadmill training on brain ischemic lesions caused by middle cerebral artery (MCA) occlusion in male rats. Rats were divided into four groups: control, 1-week treadmill pre-training, 2-week treadmill pre-training, and 4-week treadmill pre-training. Cerebral infarction was induced by MCA occlusion for 60 min, followed by reperfusion. After 24 h, rats were killed and brain slices were then stained to assess lesion size. Treadmill training at least for 2 weeks can reduce the infarction size and edema caused by MCA occlusion (P<0.01). The present study provides evidence that treadmill training reduces ischemic brain damage in an animal model of cerebral ischemia.

Animals↗
PubMed2001

Factors associated with use of preventive dental and health services among U.S. adolescents.

PURPOSE: To examine adolescents' use of preventive medical and dental services and its relationship to demographic characteristics and other variables reflecting access to and need for care. METHODS: Self- and parent-reported data from a sample of 5644 adolescents aged 11 to 21 years from the National Longitudinal Study of Adolescent Health (Add Health). Variables studied include the influence of both the adolescents' demographic and socioeconomic characteristics (age, race/ethnicity, place of birth, acculturation, insurance status, and perception of health), as well as those of their parents (race/ethnicity, income, level of education, place of birth) on their lifetime use and use within the past year of medical and dental services. Bivariate and logistic regression analyses were conducted using SAS and SUDAAN. RESULTS: Approximately 32% of respondents had not had a physical examination in the year before the survey, and the same percentage had not had a dental examination. Approximately 2% reported never having had either a physical or a dental examination. Logistic regression reveals that lack of insurance, low family income, and low parental education level are significantly associated with the lack of preventive medical care. Lack of an annual dental visit was associated with male gender; black, Hispanic, or mixed race/ethnicity; and lack of insurance. Never having had a dental visit was the only dependent variable found to be associated with place of birth. CONCLUSIONS: Health insurance and family income are most consistently related to adolescents' use of preventive medical and dental care. However, the relationship between lack of dental care and place of birth emphasizes the need to improve access to dental services for immigrant teens. These findings are particularly relevant as states design systems of care for adolescents under the State Children's Health Insurance Program.

Adolescent↗
PubMed2001

Prenatal care use among selected Asian American groups.

OBJECTIVES: This study examined the predictors of 3 patterns of prenatal care use (no care, late initiation of care, and inadequate use after early initiation) for 4 Asian American ethnic groups in the United States. METHODS: Single live births to US resident mothers of Chinese, Japanese, Korean, and Vietnamese ancestry (n = 273 604) were selected from the 1992-1996 US natality files. Logistic regression was used to analyze the effects of maternal characteristics on the 3 use measures. RESULTS: Korean Americans and Vietnamese Americans had the lowest levels of prenatal care use. Young or single motherhood, high parity for age, and low educational attainment were the main risk factors for low use. CONCLUSIONS: Considerable variability exists in prenatal care use among Asian American ethnic groups.

Adolescent↗
PubMed2001

The health status of rural and urban ambulatory elderly in Taipei County.

BACKGROUND: To study the differences in the health status of rural and urban ambulatory elderly in Taipei County. METHOD: Non-compulsory general health check-up for elderly people over 65 years old in rural and urban areas. The content of the health examination included past medical history, health behavior, physical examination, laboratory examination, electrocardiogram and x-ray. Chi square test, t-test and logistic regression were applied for analysis. Risk factors relating to the cardiovascular system were included in the study. Gender differences affecting the prevalence of diseases and health behavior were also considered in the analysis. RESULTS: Significantly higher proportions of the rural elderly men smoked, drank alcohol, and had hypertension and impaired renal function. On the other hand, higher proportions of rural elderly women were obese and had diabetes, hypertension and renal impairment. The mean plasma glucose level of newly-diagnosed diabetic patients in the rural area was significantly higher than that in the urban area (p < 0.05). Diabetes, obesity, hypercholesterolemia and smoking were significantly associated with hypertension. The odds ratio for hypertension between rural and urban areas was 1.45 (p < 0.0001). The cardiovascular risk-rating score of rural elderly was statistically higher than that of urban elderly (p < 0.001). CONCLUSION: There were some minor differences in health status between urban and rural elderly. Health promotion should be varied according to the needs of various communities and various risk groups. Further studies should concentrate on prospective cohort research with well-defined determinants to evaluate whether cost-effective biopsychosocial intervention is necessary.

Aged↗
PubMed2000

Prepregnancy body mass index and pregnancy weight gain: associations with preterm delivery. The NMIHS Collaborative Study Group.

OBJECTIVE: To examine associations between rate of pregnancy weight gain and preterm delivery among women of varying prepregnancy body mass indices (BMI). METHODS: Subjects were 3511 mother-infant pairs from the 1988 National Maternal and Infant Health Survey. Prenatal weight measured between 14 and 28 weeks' gestation was used to calculate rate of pregnancy weight gain for each woman. Weight gain (lb/week) was categorized as low (under 0.5), average (0.5-1.5), or high (above 1.5). Prepregnancy BMI was calculated as weight divided by height in (kg/m(2)) and categorized as low (under 19.8), average (19.8-26.0), and high (above 26). Delivery before 37 weeks' gestation was considered preterm. Associations between BMI, weight gain, and preterm delivery were examined before and after exclusion of medically indicated preterm deliveries and pregnancies complicated by maternal medical conditions potentially related to weight gain or fetal growth restriction. Associations were expressed as odds ratios (OR) adjusted for several potential confounding factors. RESULTS: Women with low pregnancy weight gain were at increased risk of preterm delivery. The magnitude of risk varied according to a woman's prepregnancy BMI. After all exclusions and adjustments for confounders, ORs, and 95% confidence intervals (CI) for low pregnancy weight gain were 6.7 (1.1, 40.6) for underweight women, 3.6 (1.6, 8.0) for average-weight women, and 1.6 (0.7, 3.5) for overweight women compared with average-weight women with average pregnancy weight gain. CONCLUSIONS: Low weight gain in pregnancy was associated with increased risk of preterm delivery, particularly if women were underweight or of average weight before pregnancy.

Adolescent↗
PubMed2000

Thermal and structural properties of biologically derived monodisperse hairy-rod polymers.

Monodisperse derivatives of poly(gamma-4-(hexadecyloxy)benzyl alpha,L-glutamate) (PHBG-X, X = 3 or 4) with backbone sequence GluAsp(Glu17Asp)xGluGlu were prepared by reaction of 4-(hexadecyloxy)phenyldiazomethane with the corresponding monodisperse poly(alpha,L-glutamate) (PLGA) derivatives (PLGA-X, X = 3 or 4). PHBG-3 and -4 exhibited strong endotherms near 45 degrees C and weak endotherms near 86 degrees C when analyzed by differential scanning calorimetry. X-ray diffraction suggested that these polymers aggregate to form layerlike solid structures at room temperature, with extended alkyl side chains forming paraffinlike crystallites. Most of the side chain order disappears at the first melting transition; however, the layerlike structure remains. Both polymers are isotropic above the second melting transition; no ordered melts were observed at higher temperatures, possibly due to the small aspect ratios of PHBG-3 and -4. In contrast, polydisperse poly(gamma-4-(hexadecyloxy)benzyl alpha,L-glutamate) (PDI = 1.2, DP = 98) (PHBG-P1), prepared from commercial PLGA, formed liquid crystalline (LC) phases between 97 and 105 degrees C.

Calorimetry, Differential Scanning↗
PubMed2000

Multiple mode regulation of a cysteine proteinase gene expression in rice.

In many plants, cysteine proteinases play essential roles in a variety of developmental and physiological processes. In rice (Oryza sativa), REP-1 is a primary cysteine proteinase responsible for the digestion of seed storage proteins to provide nutrients to support the growth of young seedlings. In the present study, the gene encoding REP-1 was isolated, characterized, and designated as OsEP3A. An OsEP3A-specific DNA probe was used to study the effect of various factors on the expression of OsEP3A in germinating seeds and vegetative tissues of rice. The expression of OsEP3A is hormonally regulated in germinating seeds, spatially and temporally regulated in vegetative tissues, and nitrogen-regulated in suspension-cultured cells. The OsEP3A promoter was linked to the coding sequence of the reporter gene, gusA, which encodes beta-glucuronidase (GUS), and the chimeric gene was introduced into the rice genome. The OsEP3A promoter is sufficient to confer nitrogen regulation of GUS expression in suspension-cultured cells. Histochemical studies also indicate that the OsEP3A promoter is sufficient to confer the hormonal regulation of GUS expression in germinating seeds. These studies demonstrate that in rice the REP-1 protease encoded by OsEP3A may play a role in various physiological responses and processes, and that multiple mechanisms regulate the expression of OsEP3A.

Amino Acid Sequence↗
PubMed2000

Cloning and functional characterization of a constitutively expressed nitrate transporter gene, OsNRT1, from rice.

Elucidating how rice (Oryza sativa) takes up nitrate at the molecular level could help improve the low recovery rate (<50%) of nitrogen fertilizer in rice paddies. As a first step toward that goal, we have cloned a nitrate transporter gene from rice called OsNRT1. OsNRT1 is a new member of a growing transporter family called PTR, which consists not only of nitrate transporters from higher plants that are homologs of the Arabidopsis CHL1 (AtNRT1) protein, but also peptide transporters from a wide variety of genera including animals, plants, fungi, and bacteria. However, despite the fact that OsNRT1 shares a higher degree of sequence identity with the two peptide transporters from plants (approximately 50%) than with the nitrate transporters (approximately 40%) of the PTR family, no peptide transport activity was observed when OsNRT1 was expressed in either Xenopus oocytes or yeast. Furthermore, contrasting the dual-affinity nitrate transport activity of CHL1, OsNRT1 displayed only low-affinity nitrate transport activity in Xenopus oocytes, with a K(m) value of approximately 9 mM. Northern-blot and in situ hybridization analysis indicated that OsNRT1 is constitutively expressed in the most external layer of the root, epidermis and root hair. These data strongly indicate that OsNRT1 encodes a constitutive component of a low-affinity nitrate uptake system for rice.

Amino Acid Sequence↗
PubMed2000

An improved tripod amphiphile for membrane protein solubilization.

Intrinsic membrane proteins represent a large fraction of the proteins produced by living organisms and perform many crucial functions. Structural and functional characterization of membrane proteins generally requires that they be extracted from the native lipid bilayer and solubilized with a small synthetic amphiphile, for example, a detergent. We describe the development of a small molecule with a distinctive amphiphilic architecture, a "tripod amphiphile," that solubilizes both bacteriorhodopsin (BR) and bovine rhodopsin (Rho). The polar portion of this amphiphile contains an amide and an amine-oxide; small variations in this polar segment are found to have profound effects on protein solubilization properties. The optimal tripod amphiphile extracts both BR and Rho from the native membrane environments and maintains each protein in a monomeric native-like form for several weeks after delipidation. Tripod amphiphiles are designed to display greater conformational rigidity than conventional detergents, with the long-range goal of promoting membrane protein crystallization. The results reported here represent an important step toward that ultimate goal.

Animals↗
PubMed2000

Problem-based, small-group tutorial learning in clinical neurology for second-year medical students.

BACKGROUND: Problem-based learning (PBL) in small-group tutorials has been a trend in medical education. Chinese students are known to be reserved and passive; thus, they may not be adaptable to PBL. Neuroanatomy, important to clinical neurology, is difficult to learn. We incorporated clinical neurology with PBL, complementary to the traditional neuroanatomy curriculum, to evaluate the feasibility of PBL for Chinese students in Taiwan. METHODS: Forty-two second-year medical students and seven tutors participated in the clinical neurology PBL small-group tutorials. Twelve case reports were discussed weekly beginning in February, 1999. Each case was designed to meet the progressive curriculum of the neuroanatomy course. The tutors evaluated the students by the degree of their preparation, participation, key-point comprehension and interaction. All tutors and students filled out questionnaires at the end of each session. RESULTS: The majority of the students and tutors agreed that the case materials were clearly written. Ninety percent of the students agreed that the case materials matched the traditional content of neuroanatomy. Eighty-five percent of students and 71% of tutors were satisfied and found the class rewarding. Ninety-one percent of students and 74% of tutors were in favor of PBL being continued. CONCLUSIONS: This preliminary PBL, small-group tutorial learning in clinical neurology showed satisfactory results and was, indeed, complementary to a traditional neuroanatomy course. The students, as early as during the second year of their medical school education, were able to learn through the PBL. More integration of basic and clinical sciences by PBL may be considered in future curricula designs.

Education, Medical↗
PubMed1998

The 3' untranslated region of a rice alpha-amylase gene functions as a sugar-dependent mRNA stability determinant.

In plants, sugar feedback regulation provides a mechanism for control of carbohydrate allocation and utilization among tissues and organs. The sugar repression of alpha-amylase gene expression in rice provides an ideal model for studying the mechanism of sugar feedback regulation. We have shown previously that sugar repression of alpha-amylase gene expression in rice suspension cells involves control of both transcription rate and mRNA stability. The alpha-amylase mRNA is significantly more stable in sucrose-starved cells than in sucrose-provided cells. To elucidate the mechanism of sugar-dependent mRNA turnover, we have examined the effect of alphaAmy3 3' untranslated region (UTR) on mRNA stability by functional analyses in transformed rice suspension cells. We found that the entire alphaAmy3 3' UTR and two of its subdomains can independently mediate sugar-dependent repression of reporter mRNA accumulation. Analysis of reporter mRNA half-lives demonstrated that the entire alphaAmy3 3' UTR and the two subdomains each functioned as a sugar-dependent destabilizing determinant in the turnover of mRNA. Nuclear run-on transcription analysis further confirmed that the alphaAmy3 3' UTR and the two subdomains did not affect the transcription rate of promoter. The identification of sequence elements in the alpha-amylase mRNA that dictate the differential stability has very important implications for the study of sugar-dependent mRNA decay mechanisms.

Base Sequence↗
PubMed1998

Sugar response sequence in the promoter of a rice alpha-amylase gene serves as a transcriptional enhancer.

Expression of alpha-amylase genes in both rice suspension cells and germinating embryos is repressed by sugars and the mechanism involves transcriptional regulation. The promoter of a rice alpha-amylase gene alphaAmy3 was analyzed by both loss- and gain-of-function studies and the major sugar response sequence (SRS) was located between 186 and 82 base pairs upstream of the transcription start site. The SRS conferred sugar responsiveness to a minimal promoter in an orientation-independent manner. It also converted a sugar-insensitive rice actin gene promoter into a sugar-sensitive promoter in a dose-dependent manner. Linker-scan mutation studies identified three essential motifs: the GC box, the G box, and the TATCCA element, within the SRS. Sequences containing either the GC box plus G box or the TATCCA element each mediated sugar response, however, they acted synergistically to give a high level glucose starvation-induced expression. Nuclear proteins from rice suspension cells binding to the TATCCA element in a sequence-specific and sugar-dependent manner were identified. The TATCCA element is also an important component of the gibberellin response complex of the alpha-amylase genes in germinating cereal grains, suggesting that the regulation of alpha-amylase gene expression by sugar and hormone signals may share common regulatory machinery.

Base Sequence↗
PubMed1998

Differential scanning calorimetric study of poly(3-hydroxyoctanoate) inclusions in bacterial cells.

Medium chain length polyhydroxyalkanoates, MCL-PHAs, produced by bacteria as inclusion bodies or granules were analyzed in situ by differential scanning calorimetry (DSC) without isolation from the cells. The kinetic DSC study of PHA granules, which contained mostly 3-hydroxyoctanoate units (PHO), in Pseudomonas putida BM01 cells showed that the polymer within the granules existed in an amorphous state, but it crystallized after dehydration of the cells under freeze-drying condition (below -50 degrees C) followed by annealing at ambient temperature. In this manner, PHO within the cells readily crystallized to the maximum degree of crystallinity within 24 h at room temperature, which was much faster than for the same polymer isolated by solvent extraction. This observation suggests that the polymer within the cellular granules may be well organized. The DSC endothermic melting peak areas for the room-temperature annealed polymers within the cells were directly proportional to the amount of polymer in the cell, and the results from this type of quantitative analysis were essentially identical to those obtained by gas chromatographic and gravimetric analysis of the polymers. X-Ray diffraction analysis of the polymer in the freeze-dried, whole cells and of the isolated, fully crystallized polymer showed that the two types of PHO samples had similar crystal structures, but the polymer in the granules exhibited better side-chain packing and higher crystallinity.

Calorimetry, Differential Scanning↗