Showing papers by "Sun Yat-sen University published in 1993"

Energy loss reduction by critical switches

Abstract: A systematic method to derive an optimal switching plan to achieve energy loss minimization for short term and long term operation of distribution systems is presented. The short term optimal switching criterion is developed by binary integer programming with a branch and bound technique. An overall optimization problem is formulated for the optimal switching operation. It is further divided into several subproblems to find the largest energy loss reduction among all possible switching operations between two feeders. A quick method is applied to estimate the largest loss reduction for each feeder-pair in the distribution system during short term switching operation. The composite load profile of each feeder is derived by field tests over a one year period. After determining the hourly optimal network configuration by taking into the account the typical daily load patterns for all the distributed feeders, the long term optimal criterion for each season is derived and the corresponding critical switches are determined. >

Indoor Air Pollution and Lung Cancer in Guangzhou, People's Republic of China

Abstract: A case-control study comprising 224 male and 92 female incident lung cancer cases and the same number of individually matched hospital controls was conducted from June 1983 to June 1984 in Guangzhou, People's Republic of China, to evaluate the association between indoor air pollution and lung cancer risk. Guangzhou residents were exposed to several sources of pollution in their homes, most importantly to cooking fumes. Increased risks were found among subjects living in a house without a separate kitchen (the exposure odds ratio was 2.4 (95% confidence interval (CI) 1.4-4.2) for men and 5.9 (95% CI 2.1-16.0) for women). Similarly, living in a house with poor air circulation was associated with an exposure odds ratio of 2.1 (95% CI 1.2-3.8) for men and 3.6 (95% CI 1.4-9.3) for women. A trend in the association between lung cancer risk and factors pertaining to house and kitchen ventilation was observed, and a decreasing risk of lung cancer was observed for several variables indicating better ventilation, even after adjustment for potential confounders such as education, occupation, living area, smoking, and history of chronic respiratory diseases. No statistically significant differences were found between cases and controls for frequency of cooking at home, presence of a chimney in the kitchen, or type of cooking fuel. Smoking was clearly related to risk of lung cancer in both men and women, and among nonsmoking women, exposure to tobacco smoke from their spouses was also associated with an increased risk. These results suggest that, in addition to smoking, indoor air pollution may be a risk factor for lung cancer.

Studies of the preparation, structure, and properties of an acrylic chelating fiber containing amidoxime groups

Abstract: Polyacrylonitrile fiber was treated with hydroxylamine to form a chelating fiber containing the amidoxime group with high adsorption capacity to the Au3+ ion (up to 626 mg/g, when the nitrile group conversion reaches 53.7%), reasonable mechanical properties, and good thermal stability; the relationship among reaction conditions, fiber structures, and properties were investigated. The amidoxime group content rapidly increases to a steady value with increasing reaction time or HONH2 • HCl concentration, the fiber strength drops linearly with increasing reaction time, when the reaction takes place at the temperature where the morphology and order structure begins to be destroyed, and the amidoxime group content increases significantly, while fiber strength decreases remarkably. It is suggested that, to prepare a chelating fiber with high adsorption capacity and reasonable mechanical property, the reaction could be carried out at temperatures from 70 to 75°C, time of about 30 min, and concentration around 75 g/L. © 1993 John Wiley & Sons, Inc.

Immunisation against gastric infection with Helicobacter species: First step in the prophylaxis of gastric cancer?

Abstract: Summary The discovery of the gastric bacterium, Helicobacter pylori and the demonstration of its role in the pathogenesis of gastroduodenal disease, has been one of the major microbiological advances in the last decade. Recent demonstration. of long term infection with this bacterium as a risk factor in gastric carcinoma suggests that intervention in a disease of major morbidity and mortality is possible. Using a model of Helicobacter infection in mice it has been shown that oral immunisation with a sonicate of Helicobacter felis plus the adjuvant cholera toxin results in protection against an oral challenge with large numbers of viable bacteria. The success of the immunising regimen has been shown to correlate with the development of local immunity. Formulation of equivalent safe vaccines of H. pylori will make possible the immunisation of children in countries such as China, Japan and Columbia and so prevent the establishment of long term inflammation and thus significantly reduce the incidence of gastric cancer in those societies. This animal model is proposed as a major tool in the development of effective oral immunisation.

Fracture characteristics of discontinuous carbon fibre-reinforced PPS and PES-C composites

Abstract: Tensile strength, σ b , Young's modulus, E, and critical stress intensity factor, K IC , of two types of short carbon fibre (CF) reinforced high performance brittle thermoplastics (CF/PPS and CF/PES-C) have been measured for different volume fraction, V f of CF. Young's modulus increases linearly with increasing of V f with a Krenchel's efficiency factor of 0.05, whereas σ b and K IC initially rise and then level up at V f of 25 vol.%. With the help of loas-deflection curves and fractography, the experimental results have been analysed in the light of fibre-matrix adhesion characteristics

Community Structure and Standing Crop Biomass of a Mangrove Forest in Futian Nature Reserve, Shenzhen, China

Abstract: The community structure and standing crop biomass of a mangrove forest in Futian Nature Reserve, Shenzhen, the People’s Republic of China was studied. This mangrove, located towards the northern latitudinal limit of the mangrove development (22°N), had relatively simple structure and low diversity (the Shannon-Wiener index was 0.78). The three dominant species, namely Aegiceras corniculatum, Kandelia candel and Avicennia marina, possess importance values of 72, 19 and 9%, respectively. The average height of the mangrove community was 4.5 m with no vertical stratification. The values of tree density of A. corniculatum and A. marina were found to be 5290 and 260 ha−1, respectively. The biomass of both A. corniculatum and K. candel was best estimated from regression equations using a combination of height and diameter at breast height as the independent variables. For Avicennia marina, there was no simple correlation between biomass and height or diameter. The regression models suggested by previous workers did not give satisfactory estimation of biomass of A. marina in this mangrove forest. The total biomass of this mangrove forest was 12.1 kg m−2, with 73% of such production contributed by A. corniculatum and 8% by A. marina. Because of its small percentage, the inaccuracy in estimating biomass of A. marina did not affect the overall determination of biomass of the whole community. Average above-ground biomass was 8.7 kg m−2 (72% of the total biomass) and the major components were aerial woody tissues, stems and branches. The rootshoot ratio of this plant community was 0.4:1.

Models of competition in the chemostat with instantaneous and delayed nutrient recycling

Abstract: Two models for competition of two populations in a chemostat environment with nutrient recycling are considered. In the first model, the recycling is instantaneous, whereas in the second, the recycling is delayed. For each model an equilibrium analysis is carried out, and persistence criteria are obtained. This paper extends the work done by Beretta et al. (1990) for a single species.

Extraction of gold from Au(III) ion containing solution by a reactive fiber

Abstract: Metallic gold was extracted directly from a solution containing Au(III) ion by a reactive fiber with the amidoxime group. It is concluded that in the solution containing Au(III), Cu(II), Zn(II), and Cr(III) the reactive fiber presents high selectivity to Au(III). During the adsorption process, the adsorbed Au(III) is partially reduced into spongy metallic gold and the amidoxime group is finally oxidized into the carboxyl group. © 1993 John Wiley & Sons, Inc.

Energy dispersive X-ray spectroscopy analysis of YBa2Cu3−xSnxO7−δ superconductors fabricated by melt-texture-growth method

Abstract: Making use of the non-zero spatial temperature gradient at certain locations of a common tube furnace, we have fabricated bulk rectangular samples with nominal compositions YBa 2 Cu 3− x Sn x O 7−δ with highly oriented single crystal-like layers. The temperature range of 1028-930°C is believed to be a crucial period during which single crystal-like layers are formed in the MTG process and our report is based on samples prepared with a cooling rate of 5°C/h in the stated range. We have also carried out detailed energy dispersive X-ray spectroscopy analysis along a number of crystal layers, obtaining atomic percentages along these layers. With simple, plausible assumptions, we have found the phase amounts along the crystal layers. The process of analysis is repeated for the loose grains occurring in between the layers. Generally speaking, the amount of Y-123 present in the layers is around 50%-75%. The DC magnetization loops of these samples were also measured giving us very encouraging J c values of about 3.0 × 10 4 A cm −2 .

The regulatory effects of thyrotropin-releasing hormone on growth hormone secretion from the pituitary of common carp in vitro.

Abstract: The effects of thyrotropin-releasing hormone (TRH) on growth hormone (GH) and gonadotropin (GtH) release, and the influences of somatostatin (SRIF), the dopamine agonist apomorphine (APO) and extracellular calcium on basal and TRH-induced GH release were examined using an in vitro perifusion system for pituitary fragments of common carp (Cyprinus carpio). Five minute pulses of different dosages of TRH stimulated a rapid and dose-dependent increase in GH release from the perifused pituitary fragments with an ED50 of 9.7 ± 2.3 nM. TRH was ineffective on GtH release. SRIF significantly inhibited basal and TRH-induced GH release from the perifused pituitary fragments, and the effects of SRIF were dose-dependent. APO induced a dose-dependent increase in basal and TRH-stimulated GH release from the perifused pituitary fragments. Increasing the concentrations of extracellular calcium from 0 mM to 1.25 mM resulted in an increase in basal and TRH-induced GH release. The high dose of calcium (6.25 mM) caused a slight decrease in basal and TRH-induced GH release compared with those at a concentration of 1.25 mM.

Patagonicol: a diterpenoid from the Chinese soft coral Alcyonium patagonicum.

Abstract: Patagonicol [1], a diterpenoid with a eunicellin skeleton, was isolated from the soft coral Alcyonium patagonicum. The structure of 1 was determined by X-ray diffraction, and detailed 1H and 13C assignments were made via 1D and 2D nmr experiments.

Wavelet solutions for time harmonic acoustic waves in a finite ocean

Abstract: In this paper, we show how wavelet analysis may be used to solve the parabolic approximate wave equation. The paper is naturally subdivided into three parts. The first entails a crash course in wavelet analysis with the aim of using it to solve partial differential equations. The second part develops the wavelet-Galerkin approximation for solving partial differential equations in variational form. Finally, the third section derives a range-depth adaptive wavelet approach, and, moreover, provides an algorithm for solving the propagation problem.

Mode locking with linear and nonlinear phase shifts

Abstract: The mode locking of a cw Nd:YAG laser by translation of one of the cavity mirrors is reported. The mode-locking effect is greatly enhanced when an intracavity nonlinear KTP crystal is used. Stable pulse trains with a 60-ps average pulse width are obtained. Theoretical analysis shows that the combined effect of linear phase shift imposed by the moving mirror and the nonlinear phase shift in the Kerr medium gives rise to a saturable-absorber-like behavior in a homogeneously broadened laser. The theory agrees well with the experimental results as well as with results obtained with a Ti:sapphire laser.

Nucleation and crystal growth of PEEK on carbon fiber

Abstract: The necleation and crystal growth of poly(ether ether ketone) (PEEK) on carbon fiber during isothermal crystallization were studied using optical microscopy. It was shown that the nucleation rate on the fiber is affected by the crystallization and melting temperatures. Transcrystallinity of PEEK was found to appear in the range 280–315°C after PEEK was melted at rather high temperature. Its linear growth rates at various temperatures were found to be similar to those of the spherulite in the bulk. Also, its thickness depends on the crystallization and melting temperatures. Variation of the molecular weight of PEEK within a small range has no obvious influence on its nucleation rate on the fiber, but affects the transcrystalline growth rate. © 1993 John Wiley & Sons, Inc.

Modes of angular motion in intrashell 2 S + 1 S o states of four-valence-electron atomic systems

Abstract: A model with all the radial degrees of freedom frozen is used to simulate the intrashell states of four-valence-electron atomic systems. By inspecting the two- and three-body densities, and by inspecting directly the eigenfunctions in appropriate subspaces, the features of geometric structure and of internal motion have been obtained. The effect of the spatial permutation symmetry has been emphasized. Although the interactions are spin independent, the correlations are found to be strongly spin dependent. All odd-parity states under consideration prefer the conjugate circles (CC) structure (two circles have a common diameter and have their planes vertical to each other). Two modes of motion are found in this structure, namely, the four-body head-on collision mode and the double two-body collisions mode. It is confirmed that the modes found in the quantum states are closely related to periodic solutions of classical mechanics.

A simple variational analysis of diffused channel waveguides

Abstract: The variational analysis of Ti:LiNbO3 strip waveguides is resolved into two related one-dimension problems, which provides a new iterative approach for the calculation of the mode parameters and the propagation constant. The analytical expressions of the local effective index profiles can be obtained from the variational analysis. The parameters of four trial solutions for the fundamental mode in a diffused-channel waveguide have been determined by using the present method. Comparison with results using the effective method shows that these four approximate expressions are accurate enough. It is also shown that this method converges very quickly and is suitable for both diffused channel waveguides and optical waveguides with rectangular cross-section.

Stereospecific polymerization of butene-1 with supported titanium catalyst

Abstract: Butene-1 was polymerized with a highly-active supported titanium catalyst which was developed in this laboratory. The influences of various conditions (e.g., catalyst composition, temperature, external ester, H 2 , triethylaluminum, and catalyst concentration) on the catalytic activity, decay of polymerization rate, molecular weight, and isotacticity of the products were studied in detail.

Fabrication of bulk superconductors YBa2Cu3−xTexO7−δ with highly oriented layer structure using the melt-texture growth process

Abstract: We report on the successful fabrication of bulk samples satisfying the nominal composition YBa2Cu3−x Te x O7−δ and containing highly single-crystal-like texture. While this type of crystal growing process is not new, our process requires only the existence of spatial temperature gradient in some parts of the common tube furnace. The samples with tellurium were found to be much more stable and better superconductors than the Y-123 specimen. Large layer textures with cross-section ∼50×500μm2 were observed to grow inside the usual bulk sample. The critical currents were measured by the d.c. magnetization method and found to be easily greater than 6000 A cm−2 for the samples with Te.

The synthesis, characterization and crystal structure of trans(N)-(1,10-phenanthroline)-bis(L-prolinato)cobalt(III) perchlorate hydrate

Abstract: The complex was prepared by reaction of cis-[Co(phen)2-Cl2] Cl·3H2O (phen = phenanthroline) with L-proline at pH 9, isolated by chromatography using an SP-Sephadex C-25 H+ form column, and characterized by elemental analysis, spectroscopy and thermogravimetry. The X-ray crystal structure has also been determined. There are 1.5 independent complex cations, 1.5 ClOinf4sup−anions and two H2O molecules in each asymmetric unit, and two complex cations of similar structure in the crystal. There is a crystallographic C2 symmetry in the first of these. In the octahedral coordination sphere of the metal the oxygen and nitrogen chelating prolinato ligands are arranged in the trans-N,N form.