Showing papers by "Xiamen University published in 2000"

A Review on the Currents in the South China Sea: Seasonal Circulation, South China Sea Warm Current and Kuroshio Intrusion

Abstract: Researches on the currents in the South China Sea (SCS) and the interaction between the SCS and its adjacent seas are reviewed Overall seasonal circulation in the SCS is cyclonic in winter and anticyclonic in summer with a few stable eddies The seasonal circulation is mostly driven by monsoon winds, and is related to water exchange between the SCS and the East China Sea through the Taiwan Strait, and between the SCS and the Kuroshio through the Luzon Strait Seasonal characteristics of the South China Sea Warm Current in the northern SCS and the Kuroshio intrusion to the SCS are summarized in terms of the interaction between the SCS and its adjacent seas

Taxol from Tubercularia sp. strain TF5, an endophytic fungus of Taxus mairei.

Abstract: The diterpenoid taxol is an important anticancer agent used widely in the clinic. The purpose of this work was to identify a taxol-producing endophytic fungus (strain TF5) isolated from Taxus mairei and study its anticancer activities. Strain TF5 was identified as a Tubercularia sp. according to the morphology of the fungal culture, the mechanism of spore production and the characteristics of the spores. Strain TF5 produced taxol, when grown in potato dextrose liquid medium and analyzed by thin layer chromatography, high performance liquid chromatography, ultraviolet and mass spectrometry. The fungal taxol, which was isolated from the organic extract of the TF5 culture, had strong cytotoxic activity towards KB and P388 cancer cells in vitro, tested by the MTT assay. Observed with immunofluorescence and electron microscopy, the fungal taxol enhanced microtubule stability and bundling in culture cells and induced tubulin polymerization in vitro similar to the authentic taxol.

Multiwavelength erbium-doped fibre laser based on a high-birefringence fibre loop mirror

Abstract: A novel multiwavelength fibre laser is proposed, which is based on a fibre loop mirror formed by a high-birefringence (HiBi) fibre, a polarisation controller, and a directional coupler By setting the polarisation controller properly, the HiBi fibre loop mirror acts as a polarisation-independent wavelength filter With this configuration, the wavelength spacing of the laser can be varied accurately by adjusting the length of the HiBi fibre Experimentally, by cooling the erbium-doped fibre with liquid nitrogen to reduce its homogeneous linewidth, stable emission at 16 wavelengths with a spacing of 08 nm and an amplitude variation of < 5 dB was achieved

Detection of antitumor and antimicrobial activities in marine organism associated actinomycetes isolated from the Taiwan Strait, China.

Abstract: The purpose of this work was to screen the actinomycetes having antitumor or antimicrobial activity, which were isolated from the surface, epidermis and intestines of sea plants and animals collected from the Taiwan Strait, China. Antitumor activity was studied by the MTT assay and DNA target activity was studied by the biochemical induction assay while antimicrobial activity was determined by observing bacterial and fungal growth inhibition. 20.6% of marine actinomycete cultures displayed cytotoxic activity on P388 cells at dilutions at and below 1:320 and 18.6% on KB cells. 2.96% of marine actinomycete cultures displayed inducing activity. Among all marine actinomycetes isolated, the genus Micromonospora has the highest positive rate of inducing activity. However, most antimicrobial activity was found in the genus Streptomyces. These results indicate that marine organism associated actinomycetes could be a promising source for antitumor and antimicrobial bioactive agents.

In Situ FTIR Spectroscopic Studies of Adsorption of CO, SCN-, and Poly(o-phenylenediamine) on Electrodes of Nanometer Thin Films of Pt, Pd, and Rh: Abnormal Infrared Effects (AIREs)

Abstract: Pt, Pd, and Rh films of a few nanometers in thickness supported on glassy carbon (GC) and other substrates were prepared by electrochemical voltammetry. STM patterns illustrated that the prepared thin films are composed of crystallites of layer structure and exhibit a low surface roughness. Studies of in situ FTIR spectroscopy on chemisorption of CO and SCN- and formation of a polymer of o-phenylenediamine (POPD) on electrodes of nanometer thin films have been conducted to explore the abnormal infrared effects (AIREs), which consist of two main characteristics: (1) inversion of IR bands; (2) the enhancement of IR absorption of adsorbates. The results demonstrated that the AIREs depend mainly on the structure and the chemical nature of nanometer thin films. In all cases of chemisorption on thin films of platinum-group metals supported on GC or supported on polymer-covered GC, the direction of IR bands of adsorbates is inverted in comparison with the direction of IR bands of the same adsorbates on correspo...

Difference in Endothelium-Derived Hyperpolarizing Factor–Mediated Hyperpolarization and Nitric Oxide Release Between Human Internal Mammary Artery and Saphenous Vein

Abstract: Background —The greater nitric oxide (NO) release that occurs in the internal mammary artery (IMA) when compared with the saphenous vein (SV) has been suggested by more endothelium-dependent relaxation in the IMA or measured by bioassay; however, no direct measurement of NO- or endothelium-derived hyperpolarizing factor (EDHF)–mediated hyperpolarization has been reported. The present study measured such hyperpolarization, as well as NO release, in these vessels. Methods and Results —IMA (n=46) and SV (n=61) segments taken from patients undergoing coronary surgery were studied in the organ chamber. Hyperpolarization (by intracellular glass microelectrode) and NO release (by NO-sensitive electrode) in response to acetylcholine and bradykinin, with and without incubation with NG-nitro-l-arginine, indomethacin, and oxyhemoglobin, were measured. The resting membrane potential of the smooth muscle cells from the IMA (58±0.8 mV; n=15) was higher than that in those from the SV (−62±0.9 mV; n=23; P =0.0001). The EDHF-mediated hyperpolarization induced by acetylcholine (10−5 mol/L: −9.4±1.5 mV in IMA, n=10, versus −4.5±1.0 mV in SV, n=17; P <0.01) and bradykinin (10−7 mol/L: −10.9±1.5 mV in IMA, n=8, versus −5.1±0.5 mV in SV, n=8; P <0.01) and the basal release of NO (16.8±1.6 nmol/L in IMA, n=13, versus 9.9±2.8 nmol/L in SV, n=13; P <0.001) were significantly greater in the IMA than in the SV. The duration of acetylcholine- and bradykinin-induced NO release was longer in the IMA than in the SV. Conclusions —The basal release of NO and EDHF-mediated hyperpolarization were significantly greater in the IMA than in the SV. In addition, the duration of the stimulated release of NO was longer in the IMA than in the SV. These differences may contribute to the superior long-term patency of IMA grafts.

A complementary study of surface-enhanced Raman scattering and metal nanorod arrays

Abstract: The two-dimensional arrays of various metal nanowires with diameters ranging from 15 to 70 nm have been fabricated by electrodepositing metals of Cu, Ag, Au, Ni, and Co into the nanoholes of the anodic aluminum oxide (AAO) films, followed by partial removal of the film. The strong surface-enhanced Raman scattering (SERS) effects were observed from the metal nanowire arrays including Ni, Co metals that were normally considered to be non-SERS active substrates. It has been shown that metal nanowire arrays can serve as very good SERS active substrates, especially for transition metals. The SERS intensity of the probe molecule adsorbed at the nanowires depends critically on the length of the nanowires explored at the surface. And the band frequency is very sensitive to the diameter, which reflects the change in the electronic property of metal nanowires. Applying this probe molecule strategy, SERS could develop into a diagnostic tool of metal nanowires (nanorods).

Study of Ag/La0.6Sr0.4MnO3 catalysts for complete oxidation of methanol and ethanol at low concentrations

Abstract: Ag-modified La 0.6 Sr 0.4 MnO 3 -based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al 2 O 3 -supported catalysts, Ag/γ-Al 2 O 3 , Pt/γ-Al 2 O 3 , and Pd/γ-Al 2 O 3 . The results showed that the Ag-modified La 0.6 Sr 0.4 MnO 3 -based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al 2 O 3 and 0.1%Pt/γ-Al 2 O 3 in the temperature range of 370–573 K. Over a 6%Ag/20%La 0.6 Sr 0.4 MnO 3 /γ-Al 2 O 3 catalyst, the T 95 temperature for methanol oxidation can be as low as 413 K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al 2 O 3 and 0.1%Pt/γ-Al 2 O 3 catalysts, the HCHO content in the reaction exit-gas reached ∼200 and ∼630 ppm at their T 95 temperatures. Over a 6%Ag/La 0.6 Sr 0.4 MnO 3 catalyst, the T 95 temperature for ethanol oxidation can be as low as 453 K, with a corresponding content of CH 3 CHO in the exit-gas at 782 ppm; when ethanol oxidation is performed at 493 K, the content of acetaldehyde in the exit-gas can be below 1 ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H 2 -TPR) and oxygen temperature-programmed desorption (O 2 -TPD) methods revealed that both the surface and the bulk phase of the perovskite La 0.6 Sr 0.4 MnO 3 played important roles in the catalytic oxidation of the alcohols, and that γ-Al 2 O 3 as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag + doped onto the surface of La 0.6 Sr 0.4 MnO 3 was able to partially occupy the positions of La 3+ and Sr 2+ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag + to the surface of La 0.6 Sr 0.4 MnO 3 resulted in an increase in relative content of the surface O 2 2− /O − species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag 2 O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO 3 would also lead to an increase in the content of the reducible Mn n + and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance.

Tax Policy for Emerging Markets: Developing Countries

Abstract: This paper discusses important tax policy issues facing developing countries today. It views tax policy from both the macroeconomic perspective, which focuses on broad questions such as the level and composition of tax revenue, and the microeconomic perspective, which focuses on certain design aspects of selected major taxes, such as the personal income tax, the corporate income tax, the value-added tax, excises, and import tariffs. It provides a review of the role of tax incentives in these countries, and identifies some policy challenges posed by the globalization of the world economy.

Optimal design of a multi-couple thermoelectric generator

Abstract: The performance of a multi-couple thermoelectric device as a generator is investigated. The general expressions of two important performance parameters, the efficiency and power output, are given. The -K characteristic curves of a thermoelectric generator are presented for some differently constrained conditions, where is the efficiency of the thermoelectric system and K is the total thermal conductance of the multi-couple thermoelectric device. The maximum efficiency of the system is calculated. The structure parameters of the device are optimized. The effect of the thermal conductances between the thermoelectric device and the external heat reservoirs on the performance of the system is expounded by using some representative numerical examples. The results obtained here will be useful for a more detailed investigation and for the optimal design of real thermoelectric generators.

Syntheses and spectroscopic and structural characterization of molybdenum(VI) citrato monomeric raceme and dimer, K4[MoO3(cit)].2H2O and K4[(MoO2)2O(Hcit)2].4H2O.

Abstract: Investigation of the aqueous coordination chemistry for citrate and molybdenum(VI) resulted in the isolation of molybdenum(VI) citrato monomeric raceme and dimer K4[MoO3(cit)]·2H2O (1) and K4[(MoO2)2O(Hcit)2]·4H2O (2) (H4cit = citric acid). Complex 1 can serve as the first structurally characterized monomeric citrato molybdate and may represent an early mobilized precursor in the biosynthesis of FeMo-co (FeMo-cofactor). The two complexes have been characterized by elemental analyses and IR and NMR spectroscopies. The IR and NMR spectra are consistent with a monomeric species or a monooxo-bridged dinuclear structure, as revealed by a single crystal X-ray diffraction study. Compound 1 is monoclinic space group P21/c with a = 7.225(1) A, b = 9.151(2) A, c = 22.727(2) A, β = 94.93(1)°, V = 1497.1(7) A3, and Z = 4. Full-matrix least-squares refinement resulted in residuals of R = 0.027 and Rw = 0.032. The molybdenum atom forms an octahedral coordination with three oxo groups and one tridentate citrate, in whic...

A valence bond study of the Bergman cyclization: geometric features, resonance energy, and nucleus-independent chemical shift (NICS) values

Abstract: The Bergman cyclization of (Z)-hex-3-ene-1,5-diynes (1, enediynes), which produces pharmacologically important DNA-cleaving biradicals (1,4-benzyne, 2), was studied by using Hartree-Fock (HF) and density-functional theory (DFT) based valence bond (VB) methods (VB-HF and VB-DFT, respectively). We found that only three VB configurations are needed to arrive at results not too far from complete active space [CASSCF(6 x 6)] computations, while the quality of VB-DTF utilizing the same three configurations improves upon CASSCF(6 x 6) analogous to CASPT2. The dominant VB configuration in 1 contributes little to 2, while the most important biradical configuration in 2 plays a negligible role in 1. The avoided crossing of the energy curves of these two configurations along the reaction coordinate leads to the transition state (TS). As a consequence of the shape and position of the crossing section, the changes in geometry and in the electronic wavefunction along the reaction coordinate are non-synchronous; the TS is geometrically approximately 80% product-like and electronically approximately 70% reactant-like. While the pi resonance in the TS is very small, it is large (64.4 kcal mol(-1)) for 2 (cf. benzene=61.5 kcal mol(-1)). As a consequence, substituents operating on the sigma electrons should be much more effective in changing the Bergman reaction cyclization barrier. Furthermore, additional sigma resonance in 2 results in unusually high values for the nucleus-independent chemical shift (NICS, a direct measure for aromaticity). Similarly, the high NICS value of the TS is due mostly to sigma resonance to which the NICS procedure is relatively sensitive.

Changes in lipid peroxidation, the redox system and ATPase activities in plasma membranes of rice seedling roots caused by lanthanum chloride

Abstract: Highly purified plasma membranes were isolated by aqueous two-phase partitioning from rice (Oryza sativa) seedling roots. The effects of lanthanum chloride (LaCl3) on the activities of lipid peroxidation, the redox system and H+-ATPase, Ca2+-ATPase of plasma membranes were studied. The lipid peroxidation of plasma membranes could be depressed by certain low concentrations of LaCl3 and enhanced by high concentrations of LaCl3, while the lipid peroxidation was also dependent on the plasma membrane protein and incubation time. The relative activity of O2 uptake of plasma membranes was inhibited by all tested LaCl3 concentrations. In contrast, the reduction rate of Fe(CN)63− by plasma membranes was stimulated below 40 μM of LaCl3, but was reduced above 60 μM of LaCl3. The relative activities of both H+-ATPase and Ca2+-ATPase increased constantly from control to LaCl3 of concentration 60 μM where the activities of both enzymes were the maximum, but decreased remarkably at 80 μM LaCl3 concentrations various LaCl3 were added to culture solutions. In the other measurement case in which various LaCl3 concentrations were added directly to reaction medium and the plasma membrane vesicles only came from the control cultured rice seedling roots, the response of H+-ATPase activity to La3+ was similar to the response in culture solution. However, the La3+ concentration was only 20 μM when the activity of H+-ATPase was the maximum. In contrast to the case of LaCl3 addition to culture solution, Ca2+-ATPase activity was inhibited by all concentrations of La3+ which were added directly to the reaction medium. The above results revealed that REEs inhibited electron transfer from NADH to oxygen in plant plasma membranes, depressed the production of active oxygen radicals, and reduced the formation of lipid peroxides through plasma membrane lipid peroxidation. REEs ions also enhanced the H+ extrusion by both standard redox system and H+-ATPase in plasma membranes at certain concentrations. A possible role for the plant cell wall in REEs effects on plasma membranes was also suggested.

Analysis on the Performance of a Thermoelectric Generator

Abstract: An externally and internally irreversible heat engine model of thermoelectric generators is used to analyze the so-called device-design parameter introduced by Ozkaynak et al. The simple expression of the parameter is given and its physical meaning is expounded. Moreover, the optimal range of the parameter is determined and the problems relative to the maximum power output and maximum efficiency are discussed. Some meaningful results are obtained.

Some New Bounds for Singular Values and Eigenvalues of Matrix Products

Abstract: For two Hermitian matrices A and B, at least one of which is positive semidefinite, we give upper and lower bounds for each eigenvalue of AB in terms of the eigenvalues of A and B. For two complex matrices A,B with known singular values, upper and lower bounds are deduced for each singular value of AB.