Showing papers by "Sun Yat-sen University published in 1994"

Linkage between eurasian winter snow cover and regional chinese summer rainfall

Abstract: An inverse relationship has been documented by previous studies between antecedent Eurasian winter snow cover (EWSC) and all-India summer monsoon rainfall. Because both China and India are strongly influenced by the Asian monsoon system, it may be reasonable to ask whether a similar relationship exists between the EWSC and summer rainfall over China. This study seeks an answer to this question. Only a weak interannual relationship is found between the EWSC and summer rainfall over China as a whole. This weak EWSC-rainfall linkage occurs only when the averaged rainfall over the entire country is used. By dividing the country into several geographical regions based on observed features in the interannual variability of rainfall, we find much stronger regional rainfall-EWSC relationships. A strong in-phase EWSC-rainfall relationship is found in southern and northern China, whereas an inverse EWSC-rainfall relationship appears in the western, central, and north-eastern parts of China. Thus, EWSC may be a useful predictor for regional Chinese summer rainfall, but not for rainfall over the country as a whole.

A simplified domain-testing strategy

Abstract: A simplified form of domain testing is proposed that is substantially cheaper than previously proposed versions, and is applicable to a much larger class of programs. In particular, the traditional restrictions to programs containing only linear predicates and variables defined over continuous domains are removed. In addition, an approach to path selectlon is proposed to be used m conjunction with the new strategy.

Hepatitis A And Evidence Against The Community Dissemination Of Helicobacter Pylori Via Feces

Abstract: Seroprevalence data from 1501 subjects was used to test the hypothesis that Helicobacter pylori may be transmitted by the fecal-oral route. Antibody to hepatitis A virus was used as a marker of fecal-oral exposure. Of the 1501 subjects, 35.5% were seropositive for both H. pylori and hepatitis A, 19.1% were seronegative for both, 36.5% were seropositive for hepatitis A only, and 8.8% were seropositive for H. pylori only. Cross-sectional data from rural areas supported an association between hepatitis A and H. pylori. However, in the urban area there was no evidence of hepatitis A infection in persons < 10 years old, yet the seroprevalence of H. pylori was high in this group (approximately 32%). From our data, we suggest that communitywide fecal-oral spread of H. pylori may be of limited importance.

Survey of Cellular Radiosensitivity Parameters

Abstract: A model of the formation of particle tracks in emulsion has been extended through the use of biological target theory to formulate a theory of the response of biological cells and molecules of biological importance to irradiation with energetic heavy ions. For this purpose the response to gamma rays is represented by the single-hit, multitarget model with parameters m and D0, while additional parameters kappa (or a0) and sigma 0 are required to represent the size of internal cellular targets and the effective cross-sectional area of the cell nucleus, respectively, for heavy-ion bombardments. For one-or-more-hit detectors, only the first three of these parameters are required and m = 1. For cells m is typically 2 or more. The model is developed from the concept that response to secondary electrons follows the same functional form for gamma rays and for the gamma rays surrounding an ion's path. Originally applied to dry enzymes and viruses in 1967, the model of the one-hit detector has been extended to emulsions, to other physical and chemical detectors, to single- and double-strand breaks in DNA in EO buffer and to three E. coli strains. The two-hit response has been observed for "track core" effects in radiation chemistry, for supralinearity in thermoluminescent dosimeters and for desensitized nuclear emulsions, where hit numbers up to 6 have been observed. In its extension to biological cells, additional concepts are required relating to the character of the track, namely the grain-count and track-width regimes, and to the ability of multitarget systems to acquire damage from intertrack delta rays (called gamma kill) as well as from intratrack delta rays (called ion kill). The model has been applied to some 40 sets of radiobiological data obtained from gamma, track-segment heavy-ion and neutron irradiations. Here we elaborate on the meaning of these concepts, tabulate the cellular parameters, and display their systematic behavior and the relationships among them. In particular the parameter kappa, which serves to determine the location in Z*2/beta 2 of the maximum value of the RBE, shows little variation among cell types, while D0, which describes the response to gamma rays and sigma 0, which appears to indicate the target size, varies over many orders of magnitude.

Fertile transgenic Indica rice plants obtained by electroporation of the seed embryo cells.

Abstract: We have obtained fertile transgenic plants of Indica rice variety IR36, by using electroporation to transfer the neomycin phosphotransferase II (nptII) gene into cells of mature embryos. Resistant calli were selected in the presence of 30 μg/ml G418. Nearly thirty transgenic plants were regenerated within three months after transformation. Many of them yielded seeds following self-pollination. Data from molecular analysis and enzyme assay proved that the foreign gene was stably integrated into the genome of resistant calli, R0 and R1 plants, and also expressed. Mendelian segregation of the nptII gene was observed in R1 progeny plants.

Functional Modification of Polypropylene

Abstract: Strong interest has been generated in recent years regarding the modification of polyolefins to be functionalized or engineered for new materials with superior properties. Functional and engineered polyolefins are becoming more and more commercially important and expanding their applications as demonstrated by the scientific research and publication in the field as well as by attendance at symposia on modified polymers [1–5]. Of all the modifications of polyolefins to be functionalized or engineered, chemical modification of polymers is important for two reasons: (a) modifying the bulk properties of polymers by grafting or copolymerization leads to increased intermolecular interactions and possible crosslinking of the macromolecules; (b) the surface chemistry and physics of polymers can be modified by several surface modifying techniques such as surface coating, surface degradation, surface hydrolysis, plasma discharge treatment, and radiation-induced, photochemistry-induced, or catalytic-initiat...

Stellettin A, a new triterpenoid pigment from the marine sponge Stelletta tenuis.

Abstract: A new isomalabaricane triterpenoid, stellettin A [1], was isolated from the sponge Stelletta tenuis collected off Hainan Island, People's Republic of China. Its structure and stereochemistry were established by analysis of its spectral data and reference to related compounds.

Sulfur K- and L-edge X-ray absorption spectroscopy of sphalerite, chalcopyrite and stannite

Abstract: Sulfur K-edge x-ray absorption spectra (XANES and EXAFS) and L-edge XANES of sphalerite (ZnS), chalcopyrite (CuFeS2) and stannite (Cu2FeSnS4) have been recorded using synchrotron radiation. The K- and L-edge XANES features are interpreted using a qualitative MO/energy band structure model. The densities of unoccupied states at the conduction bands of sphalerite, chalcopyrite and stannite are determined using S K- and L-edge XANES features (up to 15 eV above the edge), combined with published metal K-edge XANES. The SK- and L-edge XANES also indicate that, for sphalerite, the Fe2+ 3d band at the fundamental gap has little or no bonding hybridization with S 3p and S 3s orbitals; for chalcopyrite, the Cu+ 3d and Fe3+ 3d bands have strong mixing with S 3p and S 3s states, while for stannite the Cu+ 3d band strongly hybridizes with S 3p and S 3s orbitals, but the Fe2+ 3d band does not. The post-edge XANES features (15–50 eV above the edge) of sphalerite, chalcopyrite and stannite are similar. These features are related to the tetrahedral coordination of sulfur in all these structures, and interpreted by a multiple scattering model. The resonance energies from both the K-edge and L-edge XANES for these minerals are well correlated with reciprocal interatomic distances and lattice spaces. Sulfur K-edge EXAFS analyses using Fourier transform and curve fitting procedures are presented. Comparison of the structural parameters from EXAFS with x-ray structure data shows that the first shell bond distances (BD) from EXAFS are usually accurate to ±0.02 A, and that coordination numbers (CN) are generally accurate to ±20 percent. For sphalerite, EXAFS analysis yields the structure parameters for the first three neighbour shells around a sulfur atom; the BD and CN even for the third shell are in close agreement with the x-ray structure, and the Debye-Waller term decreases from the first shell to the third shell. It is shown that sphalerite (ZnS) is a good model compound for EXAFS analysis of sulfur in chalcogenide glasses and metalloproteins.

Specific reversal of MDR1/P-gp-dependent multidrug resistance by RNA interference in colon cancer cells

Abstract: No control cell line was available for previous RNA interference studies on reversal of multidrug resistance (MDR) in colon cancer cells. Here, human COLO 320DM, with HT-29 as the control, colon cancer cell lines were used to investigate the reversal of MDR1/P-gp-dependent MDR by siRNA (#4123 and #4029 MDR1 siRNAs) targeting to MDR1 mRNA. Both siRNAs inhibited expression of MDR1 and P-gp in COLO 320DM. The minimum inhibition concentrations were 5 nmol/l of #4123 and 25 nmol/l of #4029. #4123 MDR1 siRNA took effect in 4, 5 and 6 days at doses of 5, 25 and 100 nmol/l, respectively. Increased cytotoxicity of the antitumor drugs adriamycin and vincristine with increased intracellular adriamycin accumulation accompanied inhibition of MDR1 mRNA and P-gp expression. No such effects were found in the HT-29 control. MDR1 siRNAs specifically reversed the MDR of colon cancer cells demonstrating a possible new approach for treating MDR1/P-gp-dependent multidrug resistance.

CpG island methylation status in the EpCAM promoter region and gene expression.

Abstract: The epithelial cell adhesion molecule (EpCAM) gene has been found to be highly expressed in carcinomas of various origins; however, the molecular mechanisms underlying the transcriptional regulation of EpCAM remain poorly understood. The purpose of this experiment was to study the relationship between EpCAM gene overexpression and CpG island methylation status in the promoter region in cell cultures and normal colon epithelial and colorectal cancer tissues. Real-time quantitative PCR and bisulfite sequencing PCR were employed to detect EpCAM gene expression and to analyze the methylation status of the CpG islands. In addition, EpCAM gene expression and methylation status of CpG islands were studied in promoter methylation cell lines treated with a DNA methyltransferase inhibitor. It was found that most CpG dinucleotides were unmethylated in cell lines and cancer tissues where the EpCAM gene was highly expressed whereas most CpG dinucleotides were methylated in EpCAM gene unexpressed cell lines and normal colon tissues. When cells were treated with demethylating agent, CpG islands were demethylated, although EpCAM gene expression did not increase suggesting that unmethylation of the EpCAM promoter region was not responsible for EpCAM overexpression. The results of the study described herein suggest that unmethylation of the EpCAM promoter region was associated with EpCAM overexpression; however, it was not responsible for EpCAM overexpression by itself. Further research is required to determine which factors are responsible for EpCAM gene expression.

Studies on preparation and ion‐exchange properties of weakly acidic cation exchange fiber by preirradiation‐induced graft copolymerization with electron beam

Abstract: Weak acidic cational exchange fibers were obtained by means of preirradiation-induced graft copolymerization of methacrylic acid, acrylic acid, and diglycol acrylate onto polypropylene nonwoven fabric with electron beam. Effects that influence grafting and the exchange adsorptive property of the ion-exchange fibers obtained toward transition and rare-earth metal ions have been investigated. © 1994 John Wiley & Sons, Inc.

Preparation and adsorption properties of the chelating fibers containing amino groups

Abstract: Four kinds of amino-group-containing chelating fibers were prepared by reacting diethylenetriamine, diethanolamine, diethylamine, and aminopyridine, respectively, with a grafted fiber PVA-g-GMA containing epoxy groups. The γ-ray preirradiation initiated graft copolymerization of GMA onto PVA fiber, the functionalization of the grafted fiber PVA-g-GMA with amino compounds, and the adsorption properties of the obtained chelating fibers were systematically investigated. It is concluded that with increasing monomer concentration, reaction time, and temperature, the grafting percentage increases significantly. In the functionalization of the grafted fiber, reaction time, temperature, solvent, and amount of amine used greatly influence the reaction. 1,4-Dioxane is a reasonable solvent for the reaction. The chelating fibers present great adsorption amounts and high adsorption rates for Cu2+ ion and Au3+ ion. Among the chelating fibers, the fiber with diethylenetriamine group is the most reasonable chelating fiber for the adsorption of Cu2+ and Au3+. The chelating fibers present good selectivities for Cu2+ in the solution with Cu2+, Mn2+, Ni2+, Co2+, and Zn2+, while presenting quite high selectivities for Au3+ ion in the solution with Cu2+, Au3+, Zn2+, and Cr3+ ions. The chelating fiber with diethanolamine or diethylamine can reduce the adsorbed Au3+ into metallic gold. © 1994 John Wiley & Sons, Inc.

Double melting phenomena of polyphenylene sulfide and its blends

Abstract: The melting behavior of PPS (polyphenylene sulfide) and its blends with PSF (bisphenol A polysulfone) and PEK-C (polyetherketone with phthalidylidene groups) are investigated with DSC technique. It is found that, with a rise in melt temperature Tmelt and melt time tmelt, the intensities of the lower melting peaks of PPS increase while those of the upper ones decrease or disappear in some cases, which can be attributed to the obstructive effect of branching or crosslinking of PPS macromolecules on the crystallization of PPS at higher temperature. As the annealing crystallization temperature increases, both the peak temperatures and intensities of the lower melting peaks of PPS increase. PSF and PEK-C have no influence on the lower melting peaks of PPS but are unfavorable to the crystallization of the higher melting species. The double melting behavior of the PPS component in the blends is much more susceptible to the changes in Tmelt and tmelt than that of neat PPS. © 1994 John Wiley & Sons, Inc.

Mössbauer study of the Jilin and Xinyang meteorites

Abstract: The Xinyang and Jilin meteorites were investigated using Mossbauer spectroscopy. In addition to troilites and silicates, the Jilin meteorite contains taenite and kamacite, while the Xinyang meteorite contains kamacite only. The Mossbauer data of these two meteorites confirm them as ordinary H chondrites. The Mossbauer parameters can be interpreted by a model based on the cooling history of these meteorites.

Analytic calculation of the vacuum wave function for (2+1)-dimensional SU(2) lattice gauge theory.

Abstract: The long wavelength vacuum wave function of (2+1)-dimensional SU(2) lattice gauge theory is calculated by the method of truncated eigenvalue equation. Third order results are consistent with Monte Carlo measurement and display a good scaling behavior extending to the deep weak coupling region.

Aldehyde-selective polymeric membrane electrodes based on a calix[4]arene ionophore

Abstract: A novel type of aldehyde-selective electrode was designed based on the host–guest interaction between p-tert-butylcalix[4]arene ionophore and hydrazone generated in situ from heptanal and Girard's reagent P. The poly(vinyl chloride) membrane electrode contains 3.5–8% m/m of a tetraester derivative of calix[4]arene as the neutral carrier and dioctyl phthalate as the plasticizer. At pH 5.5, the electrode exhibits a Nernstian response in the range 1 × 10–2–9 × 10–7 mol l–1 heptanal with a slope of 67.7 mV per concentration decade. The electrode has a fast response time and a constant Nernstian response after 2 months of continuous measurement. The viability of using the electrode for the micro-determination of heptanal was also demonstrated. The minimum detectable concentration of aldehyde is 3 × 10–5 mol l–1, or, as little as 3.4 µg of heptanal can be determined accurately by the method.