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Biomedical subjects

G H Tang

Publications and source records attributed to G H Tang.

At least 19 recordsLinked to original sources
PubMed2005

Gas slippage effect on microscale porous flow using the lattice Boltzmann method.

A lattice Boltzmann method is developed for gaseous slip flow at the pore scale in microscale porous geometries. Flow characteristics through various porous structures are studied for different Knudsen numbers and inlet to outlet pressure ratios. It is found that the gas permeability is larger than the absolute permeability of porous media due to the gas slippage effect. Furthermore, the rarefaction influence on the gas permeability is more evident for porous structures with low porosity. The Klinkenberg equation is confirmed for the simulated porous structures. However, the second-order term of the Knudsen number (Kn2) cannot be neglected for gaseous flow with relatively high Knudsen numbers. A model for predicting the pressure drop of the flow through microscale porous media is presented based on the Ergun equation and the Carman-Kozeny equation by taking into account the effects of gas rarefaction and compressibility.

Journal Article↗
PubMed2005

Thermal boundary condition for the thermal lattice Boltzmann equation.

A thermal boundary condition for a double-population thermal lattice Boltzmann equation (TLBE) is introduced and numerically demonstrated. The unknown distribution population at the boundary node is decomposed into its equilibrium part and nonequilibrium parts, and then the nonequilibrium part is approximated with a first-order extrapolation of the nonequilibrium part of the populations at the neighboring fluid nodes. Numerical tests with Dirichlet and Neumann boundary constraints show that the numerical results of the TLBE together with the present boundary schemes agree well with the analytical solutions and those of the finite-volume method.

Journal Article↗
PubMed2005

Runx2 regulates endochondral ossification in condyle during mandibular advancement.

Runx2 is a transcription factor prerequisite for chondrocyte maturation and osteoblast differentiation. We tested the hypothesis that Runx2 is responsible for signaling chondrocyte maturation and endochondral ossification in the condyle during mandibular advancement. Fifty 35-day-old Sprague-Dawley rats were fitted with functional appliances for 3, 7, 14, 21, and 30 days. Experimental animals with 50 matched controls were labeled with bromodeoxyuridine for evaluation of the invasion of chondroclasts and osteoblasts into condylar cartilage. Mandibular advancement elicited Runx2 expression in condylar cartilage, and subsequently led to an expansion of type X collagen domain in the hypertrophic layer. Stronger Runx2 mRNA signals in subchondral bone corresponded with the increase in the recruitment of osteoblasts and chondroclasts, which preceded the increase of new bone formation in the condyle. Thus, Runx2 mediates chondrocyte terminal maturation and endochondral ossification in the mandibular condyle in response to mandibular advancement.

Animals↗
PubMed2004

Indian hedgehog: a mechanotransduction mediator in condylar cartilage.

Indian hedgehog (Ihh) is a critical mediator transducing mechanical signals to stimulate chondrocyte proliferation. To clarify the cellular signal transduction pathway that senses and converts mechanical signals into tissue growth in mandibular condyle, we evaluated Ihh expression and its relation to the kinetics of replicating mesenchymal cells in condylar cartilage during natural growth and mandibular advancement. Thirty-five-day-old Sprague-Dawley rats were fitted with functional appliances. Experimental animals with matched controls were doubly labeled with iododeoxyuridine and bromodeoxyuridine so that we could evaluate the cycles of the proliferative mesenchymal cells. Mandibular advancement triggered Ihh expression in condylar cartilage. A higher level of Ihh expression coincided with the increase of the replicating mesenchymal cells' population and the shortening of the turnover time. These findings suggested that Ihh acts as a mediator of mechanotransduction that converts mechanical signals resulting from anterior mandibular displacement to stimulate cellular proliferation in condylar cartilage.

Animals↗
PubMed2003

PTHrP regulates chondrocyte maturation in condylar cartilage.

PTHrP is a key factor regulating the pace of endochondral ossification during skeletal development. Mandibular advancement solicits a cascade of molecular responses in condylar cartilage. However, the pace of cellular maturation and its effects on condylar growth are still unknown. The purpose of this study was to evaluate the pattern of expression of PTHrP and correlate it to cellular dynamics of chondrocytes in condylar cartilage during natural growth and mandibular advancement. We fitted 35-day-old Sprague-Dawley rats with functional appliances. Experimental animals with matched controls were labeled with bromodeoxyuridine 3 days before their death, so that mesenchymal cell differentiation could be traced. Mandibular advancement increased the number of differentiated chondroblasts and subsequently increased the cartilage volume. Higher levels of PTHrP expression in experimental animals coincided with the slowing of chondrocyte hypertrophy. Thus, mandibular advancement promoted mesenchymal cell differentiation and triggered PTHrP expression, which retarded their further maturation to allow for more growth.

Analysis of Variance↗
PubMed2001

Body size at birth and blood pressure among children in developing countries.

BACKGROUND: Studies in developed countries have shown that reduced fetal growth is related to raised blood pressure in childhood and adult life. Little is known about this association in developing countries, where fetal growth retardation is common. METHODS: In 1994-1995, we measured blood pressure in 1570 3-6-year-old children living in China, Guatemala, Chile, Nigeria and Sweden. We related their blood pressure to patterns of fetal growth, as measured by body proportions at birth. The children were all born after 37 weeks gestation and weighed more than 2.5 kg at birth. RESULTS: In each country, blood pressure was positively related to the child's current weight. After adjusting for this and gender, systolic pressure was inversely related to size at birth in all countries except Nigeria. In Chile, China and Guatemala, children who were proportionately small at birth had raised systolic pressure. For example, in Chile, systolic pressure adjusted for current weight increased by 4.9 mmHg (95% CI : 2.1, 7.7) for every kilogram decrease in birthweight, by 1 mmHg (95% CI : 0.4, 1.6) for every centimetre decrease in birth length, and by 1.3 mmHg (95% CI : 0.4, 2.2) for every centimetre decrease in head circumference at birth. In Sweden, systolic pressure was higher in children who were disproportionately small, that is thin, at birth. Systolic pressure increased by 0.3 mmHg (95% CI : 0.0, 0.6) for every unit (kg/m3) decrease in ponderal index at birth. These associations were independent of the duration of gestation. CONCLUSIONS: Raised blood pressure among children in three samples from China, Central and South America is related to proportionate reduction in body size at birth, which results from reduced growth throughout gestation. The relation between fetal growth and blood pressure may be different in African populations. Proportionately reduced fetal growth is the prevalent pattern of fetal growth retardation in developing countries, and is associated with chronic undernutrition among women. Improvement in the nutrition and health of girls and young women may be important in preventing cardiovascular disease in developing countries.

Birth Weight↗
PubMed2001

[Synthesis and determination for enantiomeric purity of 6-fluoro-L-DOPA].

AIM: To study the synthesis and determination for enantiomeric purity of 6-fluoro-L-3, 4-dihydroxyphenylalanine (6-fluoro-L-DOPA, 6-FDOPA). METHODS: 2-(2-Fluoro-4, 5-dimethoxybenzyl)-N-(diphenylmethylene) glycine tert-butyl ester (8), a new compound, was synthesized from the starting material nitroveratraldehyde via the nucleophilic displacement, reductive iodination, and chiral catalytic phase-transfer alkylation, and 6-FDOPA was prepared from hydrolysis of 8. The enantiomeric purity of 6-FDOPA was determined by HPLC method using a chiral mobil phase and reversed-phase C18 column. RESULTS: The total time of synthesis was less than 90 min, the overall chemical yield from potassium fluoride was about 33%, and the enantiomeric purity was above 95%. CONCLUSION: Large scale production of 6-FDOPA and automatic synthesis of 6-[18F]fluoro-L-DOPA with excellent chemical and entiomeric purity are available. The practical technique was provided for the radiochemical synthesis and entiomeric purity of 6-[18F]fluoro-L-DOPA.

Dihydroxyphenylalanine↗
PubMed2001

[Congenital absence of upper anterior teeth a dentofacial morphologic analysis].

OBJECTIVE: This study was designed to examine the dentofacial morphology of the children in Shanghai with congenital absence of upper anterior teeth. METHODS: Cephalometric analysis for 37 children with congenital absence of upper anterior teeth was conducted and was compared with that of the normal ones. RESULTS: (1) There was no significant difference in all measurements between gender. (2) Craniofacial defection included a small SNA a small ANB a small AoBo a small angle of convexity,and a large AB plane angle. Vertical facial dimensions which was shown by Y axis and mandibular plane angle significantly decreased. Examination for soft tissue also revealed a small convexity of soft tissue and a large CmSnUL. (3) A compensative proclination of the upper central incisors as well as the upper lip was also found. CONCLUSION: Patients with congenital absence of upper anterior teeth might have a small maxilla a relatively normal mandibular dimension an anticlock rotation of the mandible plane, and a compensative proclination of the upper central incisors and the upper lip.

English Abstract↗
PubMed2001

[A clinical study on two forces orthodontic technique].

OBJECTIVE: Two Forces Technique was introduced in order to extend its use in daily clinical practice. The advantages of this technique were also mentioned. METHODS: Various kinds of malocclusion were treated by using Broussard brackets and auxiliary springs according to Two Forces Technique procedure. RESULTS: Satisfied treatment results were achieved based on the comparison of cephalometrics before and after orthodontic treatment. CONCLUSION: Auxiliary springs and light force were used in this technique, which moved teeth in three dimension precisely. It can be used in correction of various kinds of malocclusion and is easy to manipulate in clinics.

English Abstract↗
PubMed2000

Pharmacokinetics of perlolyrine in rats by stable isotope dilution in conjunction with GC-MS.

AIM: To determine the pharmacokinetics of perlolyrine in rats. METHODS: The plasma concentration and pharmacokinetic parameters of perlolyrine were determined by gas chromatography-mass spectrometry (GC-MS) with selected ion (m/z 247 and m/z 248) and [2-(15) N] perlolyrine (m/z 248) as internal standard. RESULTS: The concentration-time profile of perlolyrine after ig perlolyrine 2 mg.kg-1 fitted a two-compartment open model in rats. The pharmacokinetic parameters were T1/2 alpha = 0.33 h, T1/2 beta = 4.52 h, T1/2 (ka) = 0.14 h, Tmax = 0.35 h, Cmax = 18.84 micrograms/L, K12 = 0.88 h-1, K21 = 0.42 h-1, K10 = 0.32 h-1, V/F = 109.22 L.kg-1, AUC = 112.68 micrograms.h.L-1. CONCLUSION: The method was constant, sensitive, and accurate. It provides a useful method for the determination of pharmacokinetics of perlolyrine which are important for clinical use of perlolyrine.

Animals↗
PubMed2000

[A study on dental and cranioficial structure of normal shanghai adults occlusion-I the craniofacial structure analysis with posterioanterior cephalometric roentgenography]

OBJECTIVE: To evaluate the characteristics of normal transverse craniofacial structure in Shanghai area and to establish the database of normal Shanghai adults occlusion for posterioanterior cephalometric roentgenography.METHODS:Posterioanterior-cephalometric of the 92 adults subjects with normalocclusion were measured and analysed by Jiffy orthodontic evaluation 5.0 software package.RESULTS:The database of normal Shanghai adults occlusion for posterioanterior cephalometric roentgenography was established. Transverse measurements were intercorrelated, no statistically significant gender differences were demonstrated in craniofacial width, while the molar overjet of male was larger than that of female.CONCLUSION:The normal transverse cranioficial structure in Shanghai area has its own characteristics. The established database would provide a foundation for the diagnosis and treatment of malocclusion.

Journal Article↗
PubMed2000

[A Study On Dental and Craniofacial Structure Of Normal Shanghai Adults Occlusio-II The Dental Facial Symmetry Analysis with Posterioanterior Cephalometric Roentgenography]

OBJECTIVE:To evaluate the dental facial symmetry in normal Shanghai adults occlusion with posterioanterior cephalometric roentgenography. METHODS:Posterioanterior films of the 92 adults subjects with normal occlusion were measured. Five facial midlines commonly used in posterioanterior cephalometric were analyzed according to the middle structure index and side middle structure index. The midline deviations were measured. RESULTS:The middle line through ANS and perpendicular to zygomaticofrontal line has less mean of middle structure index and side middle structure index. There are midline deviations in population with normal occlusion.CONCLUSION:The facial midline mentioned above was suitable for posterioanterior cephalometrics, but the reliability is not absolute. Normal occlusion also has midline deviations. The asymmetry of face was larger than that of dental occlusion.

Journal Article↗
PubMed1997

[Properies of orthodontic wires in simulated teeth alignment test]

In this study,methods were developed to test and compare leveling archwires that commonly used in domestic practice.The results showed that the stainless steel arch wires were stiff.The Ni-Ti wires and the wires with loops were flexible and could deliver more constant force.The 0.014 Chinese Ni-Ti wires demonstrated the superelastic property,but 0.016 Ni-Ti wire did not appear the same property before they generated 250g force.

Journal Article↗