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S T Wang

Publications and source records attributed to S T Wang.

At least 19 recordsLinked to original sources
PubMed2006

Smectic-Calpha*-smectic-C* phase transition and critical point in binary mixtures.

We have investigated the smectic-Calpha*-smectic-C* (SmCalpha*-SmC*) transition in a series of binary mixtures with resonant x-ray diffraction, differential optical reflectivity, and heat capacity measurements. Results show that the phases are separated by a first-order transition that ends at a critical point. We report the observation of such a critical point. We have proposed the appropriate order parameter and obtained values of two critical exponents associated with this transition. The values of the critical exponents suggest that long-range interactions are present in the SmCalpha*-SmC* critical region.

Journal Article↗
PubMed2006

Optical studies on the surface-induced tilted layers in freestanding films of two no-layer-shrinkage liquid crystal compounds.

Null transmission ellipsometry has been employed to study the molecular arrangements in freestanding films of two no-layer-shrinkage liquid crystal homologous compounds above the bulk smectic A-smectic C* (Sm C*) transition temperature. An unusual nonplanar-parallel or nonplanar-antiparallel-parallel transition has been observed in both compounds under a proper electric field. With the addition of one CH2 group, while the SmC* phase is more stable thermally, the magnitude of the critical field needed to induce a parallel-antiparallel transition decreases dramatically.

Journal Article↗
PubMed2006

Surface-induced multiple reentrant transitions.

We have studied tilted surface layers in the bulk SmA temperature window of one liquid crystal using null transmission ellipsometry. Five distinct nonplanar surface structures were observed. We present analyses of the tilt and azimuthal profiles of the structures and examine the transitions between the structures. The transitions are identified as a double reentrant synclinic-anticlinic-synclinic-anticlinic transition. Meanwhile, the transitions also display reentrant ferroelectric-antiferroelectric-ferroelectric behavior.

Journal Article↗
PubMed2006

Optical and resonant X-ray diffraction studies confirm a SmC*FI2-SmC* liquid crystal phase sequence reversal.

Employing both null transmission ellipsometry and resonant x-ray diffraction, we confirmed the SmC*FI2-SmC* phase sequence reversal in one liquid crystal compound and specially prepared binary mixtures. This phase sequence reversal was predicted by two recent theoretical advances. Moreover, the temperature range for the SmC*FI2 phase increases significantly in the mixture suggesting that such a phase sequence may exist in other compounds.

Journal Article↗
PubMed2005

Calorimetric investigations of liquid-crystal compounds exhibiting almost no layer-shrinkage behavior through the smectic-A-smectic- C* transition.

Heat-capacity measurements have been made on liquid-crystal compounds exhibiting almost no layer-shrinkage (NLS) behavior through the Sm-A-Sm- C(*) phase transition. The transition was found to be second order for two of the substances studied. It was found that the heat-capacity anomaly accompanying a second-order Sm-A-Sm- C(*) transition with NLS behavior is quite similar to that observed for typical antiferroelectric liquid crystals of the 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) group, showing three-dimensional (3D) XY behavior in the vicinity of the transition. On the other hand, for one compound which shows a weakly first-order transition, the anomaly is almost symmetric above and below T(c) , with a significant fluctuation effect in the Sm-A phase. For this compound, the critical behavior of the heat-capacity anomaly is almost tricritical in the immediate vicinity of T(c) , while away from T(c) the behavior can be explained with the 3D XY model. This suggests that the underlying transition with the 3D XY critical behavior is driven to almost being tricritical but remaining weakly first order. No indication of low-dimensional character in the critical behavior was found in both cases.

Journal Article↗
PubMed2005

Temperature variation of film tension above the bulk smectic-A-isotropic transition in freestanding liquid-crystal films.

We have measured the temperature variation of film tension above the bulk smectic-A-isotropic transition in freestanding films of two liquid-crystal compounds. Above the transition, the tension increases sharply with temperature, and the slope is proportional to the film's thickness regardless of whether or not the compound exhibits regular layer-by-layer thinning. The data can be interpreted in the context of theoretical models for layer thinning.

Journal Article↗
PubMed2005

Increased plasma concentration of nitric oxide in type 2 diabetes but not in nondiabetic individuals with insulin resistance.

OBJECTIVE: Insulin resistance (IR) is a key element in the pathogenesis of type 2 diabetes. The results of recent experiments on insulin-mediated vasodilatation have suggested that vascular insensitivity is a component of IR. However, it is still controversial that patients with type 2 diabetes have a decreased ability of insulin to increase endothelial nitric oxide (NO) release. METHOD: Plasma concentration of NO was examined in 26 patients with type 2 diabetes and 78 nondiabetic volunteers during an insulin suppression test. The test measured the efficacy of insulin in promoting disposal of the infused glucose load, in which the steady state plasma glucose (SSPG) during the 150-180 min of the test was used as an index of IR. Plasma NO levels were assayed by measurement of the stable end products of their metabolism. Comparison of plasma NO levels between groups were performed by Mann-Whitney test and relationships between SSPG and different variables were analyzed by partial correlations. RESULTS: Our results showed that the plasma NO levels were significantly higher in the diabetic group. When the nondiabetic subjects were analyzed according to their SSPG levels, there was no difference of plasma NO levels between those with SSPG>160 mg/dl and those with SSPG<160 mg/dl. There were also no difference of NO levels between those with a family history of type 2 diabetes and those without. In the nondiabetic group, SSPG correlated with BMI, fasting insulin, triglyceride and HDL-cholesterol, but neither with plasma NO levels nor fasting plasma glucose. CONCLUSION: Our data suggests that the impairment of NO activity in patients with type 2 diabetes is due to an impaired effect rather than its production. This altered NO signaling pathway is not an early event in insulin resistant individuals. Any such changes will not be apparent until type 2 diabetes with overt hyperglycemia develops.

Blood Pressure↗
PubMed2004

Optical investigations on the biaxial smectic- A phase of a bent-core compound.

Several unique optical properties have been obtained from freestanding films of a bent-core compound. Our experimental results indicate the existence of the antiferroelectric biaxial smectic-A (Sm A) phase. The critical exponent associated with the biaxiality through the uniaxial-antiferroelectric biaxial Sm A transition has been measured to be 0.82+/-0.04 , which is in good agreement with our theoretical calculation. Our theoretical advances further demonstrate that the critical behavior of the optical biaxiality with the order parameter being a vector is described by the secondary-order parameter of the three-dimensional XY model. We also observe a remarkable even-odd layering effect exhibited by the surface layers of freestanding films under an applied electric field (approximately 20 V/cm) in the film plane.

Journal Article↗
PubMed2004

Experimental investigations of one liquid-crystal compound exhibiting the no-layer-shrinkage effect near the Sm-A-Sm- C(*) transition.

Three experimental probes have been employed to investigate the nature of the smectic- A -smectic- C ( Sm-A-Sm- C(*) ) phase transition of one liquid-crystal compound showing almost no layer-shrinkage effect through the transition. Results from both x-ray diffraction and optical studies indicate that the compound exhibits a crossover behavior of different molecular packing arrangements within the bulk Sm-A phase window. The calorimetry results show a significant critical anomaly near the Sm-A-Sm- C(*) transition, although it was found to be weakly first order.

Journal Article↗
PubMed2003

Unusual behavior of the surface-induced tilted layers in free-standing films of a non-layer-shrinkage liquid crystal compound.

Null-transmission ellipsometry has been conducted to study the molecular arrangements in free-standing films of one chiral compound above the bulk smectic-A-smectic-C* transition temperature. Upon cooling under a proper electric field, a nonplanar-anticlinic-synclinic or a nonplanar-synclinic transition has been observed. The nonplanar structure continuously evolves into the anticlinic or synclinic structures. Increasing electric field can induce a rare transition from a synclinic to an anticlinic structure.

Journal Article↗
PubMed2003

Optical studies on free-standing films of an achiral smectic liquid crystal.

Employing null transmission ellipsometry and depolarized reflected light microscopy, we have studied two smectic phases, Sm-C1 and Sm-C2, of one achiral mesogen. Our results show that Sm-C1 and Sm-C2 are the synclinic Sm-C and anticlinic Sm-C(A) phases, respectively. We find no evidence to support recent claims that the Sm-C1 is chiral and ferroelectric [R. Stannarius et al., Phys. Rev. Lett. 90, 025502 (2003)].

Journal Article↗
PubMed2003

The association of a cystatin C gene polymorphism with late-onset Alzheimer's disease and vascular dementia.

A polymorphism in the cystatin C (CST3) gene was suggested to associate with Alzheimer's disease (AD). In the present study we attempted to determine the association between CST3 polymorphism and AD or vascular dementia (VD), and whether such effects are dependent of the APOE4 allele. The polymorphisms of CST3 genotype were determined using polymerase chain reactions (PCR) followed by gel electrophoresis in 124 AD, 70 VD, and 115 control individuals. No statistical difference in CST3B allele frequencies was observed among all three groups. Associations between CST3B/B genotype and AD patients older than 75-year-old, or VD patients younger than 75-year-old were evident. The APOE4 allele alone significantly increased the odds for the developing AD, but not VD. A logistic regression analysis revealed that either CST3 or its interaction with APOE4 were not significant predictors of AD. However, a synergistic association of CST3 and APOE4 alleles was observed in predicting VD patients. These results suggest that CST3 might interact with APOE4 on conferring vascular pathologies.

Aged↗
PubMed2003

Double reentrance of surface arrangements in freestanding liquid crystal films.

The molecular arrangement of tilted surface layers on freestanding films above the bulk smectic-A-smectic-C(*) transition has been studied by null transmission ellipsometry. In the presence of an applied in-plane electric field, a synclinic-anticlinic-synclinic-anticlinic double reentrance has been observed. Furthermore, we have characterized a novel transition from the synclinic arrangement to a structure in which the interior layers tilt in the same orientation and the outermost surface layers tilt oppositely with the interior layers.

Journal Article↗
PubMed2002

Effect of enantiomeric excess on surface structures and phase sequences in free-standing liquid-crystal films.

We present differential optical reflectivity and null transmission ellipsometry data from several mixtures of MHPBC enantiomers. From this data, we have determined the chiral smectic phase sequence as a function of enantiomeric excess. The data suggest a change in the structure of the smectic-C(*)(alpha) phase and the surface tilt state as the enantiomeric excess is reduced. The results also show that the intermediate phases, smectic C(*)(FI2), smectic C(*)(FI1), and smectic C(*)(alpha), disappear sequentially on reducing the net chirality.

Journal Article↗
PubMed2001

Kirsten ras mutations in patients with colorectal cancer: the 'RASCAL II' study.

Researchers worldwide with information about the Kirsten ras (Ki-ras) tumour genotype and outcome of patients with colorectal cancer were invited to provide that data in a schematized format for inclusion in a collaborative database called RASCAL (The Kirsten ras in-colorectal-cancer collaborative group). Our results from 2721 such patients have been presented previously and for the first time in any common cancer, showed conclusively that different gene mutations have different impacts on outcome, even when the mutations occur at the same site on the genome. To explore the effect of Ki-ras mutations at different stages of colorectal cancer, more patients were recruited to the database, which was reanalysed when information on 4268 patients from 42 centres in 21 countries had been entered. After predetermined exclusion criteria were applied, data on 3439 patients were entered into a multivariate analysis. This found that of the 12 possible mutations on codons 12 and 13 of Kirsten ras, only one mutation on codon 12, glycine to valine, found in 8.6% of all patients, had a statistically significant impact on failure-free survival (P = 0.004, HR 1.3) and overall survival (P = 0.008, HR 1.29). This mutation appeared to have a greater impact on outcome in Dukes' C cancers (failure-free survival, P = 0.008, HR 1.5; overall survival P = 0.02, HR 1.45) than in Dukes' B tumours (failure-free survival, P = 0.46, HR 1.12; overall survival P = 0.36, HR 1.15). Ki-ras mutations may occur early in the development of pre-cancerous adenomas in the colon and rectum. However, this collaborative study suggests that not only is the presence of a codon 12 glycine to valine mutation important for cancer progression but also that it may predispose to more aggressive biological behaviour in patients with advanced colorectal cancer.

Adolescent↗
PubMed2001

Working memory of school-aged children with a history of febrile convulsions: a population study.

OBJECTIVE: A prospective, population-based, case-control study was performed to ascertain whether febrile convulsion (FC) in early childhood is associated with specific working memory characteristics in school age. METHODS: From a population survey of 4,340 live-birth newborns in Tainan City, Taiwan, 103 children with confirmed FC by age 3 years were followed-up until they were at least 6 years old. Three analogous searching tasks dissociating the mnemonic and executive aspects of performances were administered to 87 of these school-aged children and to 87 randomly selected age-matched control subjects to assess the learning, spatial, and sequential working memory. RESULTS: The FC group performed significantly and consistently better than control subjects on all but one working memory measure, jumping errors. Multivariate analysis using linear regression revealed that the onset of FC before age 1 year was the only significant risk factor for deficits in mnemonic function. Prior neurodevelopmental delay was the only significant risk factor for deficits in executive function. Factors such as socioeconomic status, family predisposition for seizures, complex FC, recurrent FC, and subsequent unprovoked seizures were not risk factors for working memory deficits. CONCLUSION: The authors found that school-aged children with a history of FC demonstrated significantly better mnemonic capacity, more flexible mental processing, and higher impulsivity than their age-matched control subjects. The underlying mechanism for the facilitated working memory function in children with a history of FC needs further delineation.

Child↗
PubMed2001

Differential changes in regional bone mineral density in healthy Chinese: age-related and sex-dependent.

To investigate the pattern of age-related and sex-dependent bone mineral density (BMD) changes in the six skeletal regions in healthy Chinese, total-body and regional BMD were measured by dual-energy X-ray absorptiometry (DXA) in 310 women and 387 men aged 20-80 years. In women, a five-phase change was discernible in the axial bones: (1) gradual bone increase from 20-29 years old to maximal BMD at 35-39 years old; (2) maintenance of this level from 35-39 to 40-44; (3) a mild bone decrease from 40-44 to 45-49; (4) a rapid bone decrease from 45-49 to 55-59; and (5) a decelerated bone decrease after 55-59 years old. After validation of menopause status, the decrease of BMD in the late 40s became insignificant in premenopausal women. In appendicular bones, no obvious peak was observed, and significant bone decrease started at 50-54 years old. The overall bone decrease from 35-39 to 70-80 years old was 19.3% for the total body, 16.4% for the head, 29% for the spine, 23% for the pelvis, 18.2% for the ribs, 23.9% for the arms, and 20.4% for the legs. In men, the maximal bone mass was attained at 30-34 and 35-39 years old for axial and appendicular bones, respectively. The age-related bone decrease in the skeletal regions was small, except from 60-64 to 65-69 years old. The overall bone decrease in each region from maximal bone mass to 70-80 years old was 6.7% for the total body, 1.7% for the head, 7.6% for the spine, 11.3% for the pelvis, 9.5% for the ribs, 7.8% for the arms, and 10.4% for the legs. The overall magnitude of reduction in total-body BMD in women was about three times greater than that in men. The pattern of BMD changes differs in each region and is age-related as well as sex-dependent. There appeared to be no significant premenopausal bone decrease.

Absorptiometry, Photon↗