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Biomedical subjects

J N Wang

Publications and source records attributed to J N Wang.

At least 19 recordsLinked to original sources
PubMed2007

Age-hardening behavior of a low-gold dental alloy.

The age-hardening behaviors of a low gold dental alloy were studied by means of differential scanning calorimetry, hardness testing, X-ray diffraction, optical microscopy and transmission election microscopy. Two distinct hardening behaviors were found at two different aging temperatures. Age-hardening at 290 degrees C was attributed to the formation of the metastable AuCuI' ordered phase, and the gradual softening in the overaging stage resulted from the slow growth of this phase. The rapid increase in hardness in the early stage at 495 degrees C was due to the precipitation of the metastable AuCuI' or/and AuCuII' ordered phases, and the rapid decrease in hardness in the overaging stage was a consequence of the growth of these phases and the loss of the coherency strain at the interface between the spindal-like AuCuI platelets and the matrix.

Calorimetry, Differential Scanning↗
PubMed2006

Strengthening of a Pd-free high gold dental alloy for porcelain bonding by a pre-firing heat treatment.

OBJECTIVES: The purpose of the present investigation was to report a Pd-free high gold alloy for porcelain bonding based on the ternary system of Au-Pt-Zn with a nominal composition of 86Au-11Pt-1.5Zn-0.5In-0.7Rh-0.2Fe-0.1Ir (wt.%). Emphasis was put on the effect of a pre-firing heat treatment on the mechanical properties of the alloy. METHODS: The strengthening effect of the pre-firing heat treatment was investigated by means of hardness measurement, tensile testing, X-ray diffraction, optical microscopy and scanning electron microscopy. RESULTS: Experimental results showed that both the hardness and tensile strength of the alloy can be significantly improved after heat treatment at the temperature of 980 degrees C for 15 min. The strengthening could be attributed to homogenization of microstructure and alloying elements and precipitation of new fine particles. SIGNIFICANCE: The cast framework of the present new Pd-free alloy could be heat treated before actual firing, and this would improve the processing properties of the alloy during firing.

Dental Alloys↗
PubMed2006

Spectral dependence of spin photocurrent and current-induced spin polarization in an InGaAs/InAlAs two-dimensional electron gas.

The converse effects of spin photocurrent and current induced spin polarization are experimentally demonstrated in a two-dimensional electron gas system with Rashba spin splitting. Their consistency with the strength of the Rashba coupling as measured for the same system from beating of the Shubnikov-de Haas oscillations reveals a unified picture for the spin photocurrent, current-induced spin-polarization, and spin-orbit coupling. In addition, the observed spectral inversion of the spin photocurrent indicates a system with dominating structure inversion asymmetry.

Journal Article↗
PubMed2005

Effective dose evaluation for chest and abdomen X-ray tests.

The radiation doses resulting from diagnostic X-ray examinations are routinely measured in terms of entrance skin exposure (ESE). In this study, for the purpose of radiation protection, the radiation doses received from chest and abdomen X-ray tests were evaluated in terms of equivalent dose and effective dose. The dose calculations were conducted by using the MCNP Monte Carlo code and an adult hermaphrodite mathematical phantom. The effects of both operating high voltage and projection geometry on the effective dose were investigated. The absolute values of the effective doses may be provided from the national average ESE.

Body Burden↗
PubMed2004

Low energy electron irradiation induced deep level defects in 6H-SiC: the implication for the microstructure of the deep levels E1/E2.

N-type 6H-SiC samples irradiated with electrons having energies of E(e)=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E(e)>/=0.3 MeV, deep levels ED1, E(1)/E(2), and E(i) appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E(1)/E(2), as well as ED1 and E(i), involves the displacement of the C atom in the SiC lattice.

Journal Article↗
PubMed2004

Structural analysis of the epitopes on erbB2 interacted with inhibitory or non-inhibitory monoclonal antibodies.

erbB2 oncogene encodes a growth factor receptor. The overexpression of erbB2 was correlated with more aggressive tumors and a poorer prognosis. Some antibodies directed to this molecule have an antitumor effect in vivo, but some antibodies do not. In an attempt to understand the molecular basis of the anti-erbB2 antibody interaction with erbB2 ectodomain (ECD), we analyzed binding epitopes on erbB2 for inhibitory and non-inhibitory antibodies, Herceptin and HF by computer-guided protein engineering and site-directed mutagenesis. Two different interaction domains were identified by molecular docking, computer graphics and distance geometry method and confirmed through studies on a series of mutants of erbB2 ECD. Non-inhibitory antibody HF only recognized N-terminal portion of erbB2 ECD, but inhibitory antibody Herceptin bound to C-terminal portion of it exclusively. The region interacted with inhibitory antibody Herceptin can be an important target for anticancer therapies.

Antibodies, Monoclonal↗
PubMed2003

Age-dependent protection quantities for external neutron irradiation.

Based on the recommendations issued by the International Commission on Radiological Protection (ICRP), equivalent doses and effective doses for different ages are obtained for external neutron sources. The calculations at 28 neutron energies from 1 x 10(-9) MeV to 20 MeV are carried out for six irradiation geometries: AP, PA, RLAT, LLAT, ROT and ISO. An age-dependent anthropomorphic mathematical phantom series of six age groups: newborn, 1, 5, 10, 15 years old and adult is used with the Monte Carlo computer code MCNP for the dose evaluations. The results for adults are compared with those in ICRP Publication 74 and are in good agreement. At low energies the effective doses increase as the phantom age increases, but at high energics they decrease with increasing age for the AP, PA, ROT and ISO irradiation geometries. In the whole energy region the effective doses decrease as the phantom age increases for the RLAT and LLAT irradiation geometries. The age-dependent equivalent doses behave similarly to the effective doses, with some exceptions caused by the influence of the organ position.

Adolescent↗
PubMed2001

Superconductivity in 4 angstrom single-walled carbon nanotubes.

Investigation of the magnetic and transport properties of single-walled small-diameter carbon nanotubes embedded in a zeolite matrix revealed that at temperatures below 20 kelvin, 4 angstrom tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent. The measured superconducting characteristics display smooth temperature variations owing to one-dimensional fluctuations, with a mean-field superconducting transition temperature of 15 kelvin. Statistical mechanic calculations based on the Ginzburg-Landau free-energy functional yield predictions that are in excellent agreement with the experiments.

Journal Article↗
PubMed2001

Age-dependent protection quantities for external photon irradiation.

The age-dependent conversion coefficients of the protection quantities, the equivalent dose and the effective dose defined by the International Commission on Radiological Protection (ICRP), are obtained. A Monte Carlo computer code and the age-dependent hermaphrodite mathematical phantoms of six age groups: newborn, 1, 5, 10, 15 years old and adult are used for the evaluation. Twenty-three photon source energies from 10 keV to 10 MeV and six kinds of irradiation geometries: AP, PA, RLAT, LLAT, ROT, and ISO are chosen in the calculation. The evaluated conversion coefficients for the adult are compared with those in ICRP Publication 74 with good agreement. The conversion coefficients of the equivalent dose and the effective dose increase while the age of the phantom decreases, but with some exceptions for the AP irradiation geometry under certain conditions.

Adolescent↗
PubMed2000

Procyanidins from the seeds of Vitis amurensis.

Three procyanidins, procyanidin B-5 3'-O-gallate, vitisinol, and amurensisin, were isolated from the seeds of Vitis amurensis, whose structures were elucidated on the basis of spectral and chemical evidence. Vitisinol and amurensisin contain a spiro-type biflavanyl linkage and a biphenyl-lactone partial structure, respectively.

Biflavonoids↗
PubMed2000

Dangerous impact--commotio cordis.

Sudden death following blunt chest trauma is a frightening occurrence known as 'commotio cordis' or 'concussion of the heart'. It is speculated that commotio cordis could be caused by ventricular fibrillation secondary to an impact-induced energy that was transmitted via the chest wall to the myocardium during its vulnerable repolarization period. We describe a survivor of commotio cordis caused by a baseball. In this patient, an initial ventricular fibrillation was documented and converted by direct current defibrillation. Serial electrocardiographic changes (bifascicular conduction block and T wave inversion in precordial leads) were noticed in this patient. Our case suggested that coronary vasospasm might also play a role in commotio cordis.

Baseball↗
PubMed2000

Ectopic atrial tachycardia in children.

BACKGROUND AND PURPOSE: Ectopic atrial tachycardia (EAT) is an unusual and potentially risky arrhythmia that can result in left ventricular dysfunction if not properly managed. In adults, EAT is mainly caused by diseased atrial myocardium and responds poorly to antiarrhythmic drugs. The characteristics of EAT in children might be different from those in adults because of their immature myocardium and the different electrophysiologic characteristics of their conduction tissue. We examined the natural history and treatment of EAT in children. METHODS AND RESULTS: From June 1990 through June 1999, 24 children (8 girls and 16 boys; median age 4 mo [1 d-10 yr]) were admitted to our hospital with a diagnosis of EAT. Fifteen had healthy hearts, six had congenital heart disease, one had myocarditis, one had bronchopulmonary dysplasia with severe pulmonary hypertension, and one had hypertrophic cardiomyopathy. Thirteen patients presented with congestive heart failure. Only four patients had symptoms of prodromal airway infection. The maximum atrial rate was 244 +/- 66 beats per minute. Atrioventricular block was documented at least once during tachycardia in 10 patients. Warm-up or cool-down phenomenon was seen at the initiation or termination of tachycardia in thirteen patients. Primary pharmacologic treatment was attempted in all patients. EAT was initially controlled in all patients using digoxin plus propranolol (18 patients), propranolol only (4), or digoxin plus procainamide (2). EAT was controlled using medication in 22 patients. Fifteen patients had sinus rhythm but did not receive medication for 39 +/- 25 months. Two patients died of uncontrolled arrhythmia, and two of underlying disease. Recurrence was seen within 3 months after initial therapy in five patients. Surgery was performed to correct the underlying heart disease in three patients with frequently recurring EAT, all of whom remained tachycardia-free after surgery, without pharmacologic treatment. The spontaneous remission rate was 75% (18/24). CONCLUSION: EAT in children without underlying heart disease can be effectively treated using antiarrhythmic drugs. Spontaneous resolution of EAT after medication in children was frequent (75%) in this series. The results of this study suggest that a step-wise approach using digoxin, a beta-blocker, and a class I antiarrhythmic drug may be the most effective treatment for EAT.

Anti-Arrhythmia Agents↗
PubMed2000

Antioxidant activity of polyphenols from seeds of Vitis amurensis in vitro.

AIM: To study the antioxidant action of five polyphenols (+) catechin, procyanidin B2, procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin isolated from the seeds of Vitis amurensis. METHODS: The mouse liver homogenate lipid peroxidation assay was applied for the evaluation of the antioxidant activity in vitro. RESULTS: (+) Catechin, procyanidin B2, procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin showed antioxidant activity with the IC50 values of 0.47, 0.25, 0.10, 0.02, and 0.03 mmol/L, respectively. The IC50 value of vitamin E used as a positive control was 0.13 mmol/L. The structural activity relationship was also analyzed. Procyanidins carrying a galloyl group possessed higher anti-lipid peroxidation activities. All dimers were found to be more potent than the non-galloylated momomer such as (+) catechin. However, the activity of the 4-->6 linked dimer seemed more preferable than 4-->8 linked dimer. CONCLUSION: Procyanidin B5, procyanidin B5 3'-O-gallate, and amurensisin showed a more antioxidant activity than vitamin E did, and their activity is dependent on their substitution and polymerization patterns.

Animals↗
PubMed2000

[Analysis of ginsenosides by high performance liquid chromatography/mass spectrometry/mass spectrometry(LC/MS/MS)].

Ginseng, one of the most popular medicinal herbs used in traditional Chinese medicines, has been studied to have biological effects attributing to its main constituents such as ginsenosides. There are more than 30 kinds of ginsenosides and some of them have similar polarity and structure. Thus, it is difficult to separate those ginsenosides with isocratic mobile phase owing to their similar polarity. A reversed-phase high performance liquid chromatographic method with gradient elution has been developed in this work. Nine ginsenosides can be separated by this method. Among them, five ginsenosides with different molecular weights can be determined by means of their molecular weight gained through LC/MS with an ESI interface. Re and Rd have the same Mw but belonging to two different kinds of ginsenosides. They can be differentiated from each other through their MS/MS gained by CID(collision induced decomposition) at the second stage quadrapole. Rc and Rb3 having the same molecular weight and belonging to the same kind of ginsenoside can be distinguished through their negative ion spectra gotten from LC/MS. So 9 ginsenosides can be determined by LC/MS/MS. This method can also be used to determine the ginsenosides contained in commercially available samples.

Chromatography, High Pressure Liquid↗
PubMed1999

Double-lumen aortic arch with anomalous left pulmonary artery origin from the main pulmonary artery--bilateral persistent fifth aortic arch--a case report.

Both double-lumen aortic arch (i.e., persistent fifth arch) and anomalous origin of the left pulmonary artery from the ascending aorta (failure of the development of the sixth arch) are rare diseases. They are frequently associated with cardiovascular anomalies. However, the co-occurrence of these two diseases has not been previously reported. We report such a case in a female baby with facial anomalies similar to conotruncal anomaly face syndrome.

Abnormalities, Multiple↗
PubMed1999

The role of pulmonary inflammation in the development of pulmonary hypertension in newborn with meconium aspiration syndrome (MAS).

1. There was no clear correlation between the tracheal aspirate cytokines and the elevation of pulmonary arterial pressure in newborn piglets with MAS. The use of dexamethasone significantly suppressed tracheal aspirate cytokines but did not significantly alter pulmonary arterial pressure. Dexamethasone significantly increased the cardiac stroke volume and blood pressure. 2. Early dexamethasone therapy (< 12 hrs) for one week in infants with MAS significantly improved pulmonary ventilation and facilitated weaning from mechanical ventilation. 3. The mechanisms for the improvement in cardiopulmonary status following early dexamethasone therapy in MAS remain unclear. An overall improvement in cardiac hemodynamics, along with a significant decrease in lung inflammation may be responsible for the improvement.

Animals↗