Showing papers by "Sun Yat-sen University published in 2002"

Segmented contraction scheme for small-core lanthanide pseudopotential basis sets

Abstract: Gaussian (14s13p10d8f6g)/[10s8p5d4f3g] valence basis sets using a segmented contraction scheme have been derived for relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart-Bonn variety. The present basis sets are only slightly larger than previously published (14s13p10d8f6g)/[6s6p5d4f3g] atomic natural orbital basis sets, which use a generalized contraction scheme, and achieve a similar accuracy in atomic and molecular calculations. For calibration purposes multi-configuration self-consistent field and subsequent multi-reference averaged coupled-pair functional calculations are presented for the first to fourth ionization potentials of all lanthanide elements. In addition, results of molecular calibration studies using the coupled-cluster singles, doubles and perturbative triples approach as well as gradient-corrected density functional theory are reported for the monohydrides, monoxides and monofluorides of lanthanum and lutetium.

Hydroxylation of N-heterocycle ligands observed in two unusual mixed-valence Cui/Cuii complexes

Abstract: The chelate ligands 2,2 -bipyridine (bpy), 1,10-phenanthroline (phen), and their substituted derivatives have played an important role in the development of coordination chemistry,[1, 2] and over the decades a number of so-called anomalies have been reported in reactions of their metal complexes. To rationalize the anomalous properties of complexes such as [M(bpy)3] and [M(phen)3] , Gillard borrowed the idea of TMcovalent hydrates∫ from the organic literature and proposed an interesting mechanism,[3] the core of which is nucleophilic attack of a hydroxide ion on a coordinated heterocyclic ligand to form a covalent hydrate (CH); this may react further by intramolecular shift of OH or H2O onto the metal before the formation of the final products (Scheme 1). The mechanism

Double‐Stranded Helices and Molecular Zippers Assembled from Single‐Stranded Coordination Polymers Directed by Supramolecular Interactions

Abstract: Using three nonlinear dicarboxylates, isophthalate (ipa), 4,4'-oxybis(benzoate) (oba), and ethylenedi(4-oxybenzoate) (eoba), we have prepared five neutral infinite copper(II) dicarboxylate coordination polymers containing lateral aromatic chelate ligands, namely [Cu(ipa)(2,2'-bpy)]n.2nH2O (1), [Cu2(ipa)2(phen)2H2O]n (2), [Cu(oba)(phen)]n (3), [Cu(oba)(2,2'-bpy)]n (4), and [Cu(eoba)(phen)]n (5; 2,2'-bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) by hydrothermal synthesis. X-ray single-crystal structural analyses of these complexes reveal that the nonlinear flexible or V-shaped dicarboxylates can induce the helicity or flexuousity of the polymeric chains and aromatic chelate ligands are important in providing potential supramolecular recognition sites for pi-pi aromatic stacking interactions. An appropriate combination of the bridging dicarboxylate and aromatic chelate can induce a pair of single-stranded helical or flexuous chains to generate a double-stranded helix or molecular zipper through supramolecular interactions, respectively.

Impact and wear resistance of polymer nanocomposites at low filler content

Abstract: It is well known that inorganic filler particles enhance the mechanical and tribological properties of polymers. The stiffness, toughness, and wear performance of the composites are extensively determined by the size, shape, volume content, and especially the dispersion homogeneity of the particles. In the present study, various amounts of micro- and nano-scale particles (titanium dioxide TiO 2 , 200-400 nm, calcium silicate CaSiO 3 , 4-15 μm) were introduced into an epoxy polymer matrix for its reinforcement. The influence of these particles on the impact strength, dynamic mechanical thermal properties, and block-on-ring wear behavior was investigated. Using only the nano-particles, the results demonstrate the best improvement in stiffness, impact strength, and wear resistance of the epoxy at a nano-particle content of 4 vol% TiO 2 . Therefore, this nanocomposite was used to act as a matrix for the CaSiO 3 micro-particles, in the hope of finding synergistic effects between the micro- and the nano-particles. Results show, in fact, a further improvement of wear resistance and stiffness, whereas the impact strength suffers. Geometrical properties of the particles, the homogeneous dispersion state, energy dissipating fracture mechanisms, and a transition of wear mechanisms mostly contribute to the increase in performance.

Genome-wide scan for familial nasopharyngeal carcinoma reveals evidence of linkage to chromosome 4

Abstract: Nasopharyngeal carcinoma (NPC) occurs with high frequency in Asian populations, especially among people of Cantonese ancestry. In areas with high incidence, NPC clusters in families, which suggests that both geography and genetics may influence disease risk. Although the HLA-Bw46 locus is associated with increased risk of NPC, no predisposing genes have been identified so far. Here we report the results of a genome-wide search carried out in families at high risk of NPC from Guangdong Province, China. Parametric analyses provide evidence of linkage to the D4S405 marker on chromosome 4 with a logarithm of odds for linkage (lod) score of 3.06 and a heterogeneity-adjusted lod (hlod) score of 3.21. Fine mapping with additional markers flanking D4S405 resulted in a lod score of 3.54 and hlod score of 3.67 for the region 4p15.1-q12. Multipoint nonparametric linkage analysis gives lod scores of 3.54 at D4S405 (P = 5.4 x 10(-5)) and 4.2 at D4S3002 (P = 1.1 x 10(-5)), which is positioned 4.5 cM away from D4S405. When Epstein Barr virus antibody titer was included as a covariate, the lod scores reached 4.70 (P = 2.0 x 10(-5)) and 5.36 (P = 4.36 x 10(-6)) for D4S405 and D4S3002, respectively. Our findings provide evidence of a major susceptibility locus for NPC on chromosome 4 in a subset of families.

Pseudo-polyrotaxane and beta-sheet layer-based three-dimensional coordination polymers constructed with silver salts and flexible pyridyl-type ligands.

Abstract: A fascinating 3D pseudo-polyrotaxane architecture with 1D polymeric [Ag(bpp)]n chains penetrating 2D (6,3) [Ag2(bpp)2(ox)]n sheets and a 3D coordination network constructed with 2D infinite [Ag(ppa...

Primary angle closure glaucoma in Chinese and Western populations.

Abstract: Objective To review the major progress in primary angle closure glaucoma (PACG). Methods Contents of this article were selected from the original papers or reviews related to primary angle closure glaucoma published in Chinese and foreign journals. A total of 76 articles were selected from several hundred original articles or reviews. The content of selected articles is in accordance with our purpose and the authors are authorized scientists in the study of glaucoma. Results Primary angle closure glaucoma is the most common type of glaucoma in the Sino-Mongoloid population. PACG in Chinese can be classified into three types depending on the mechanism of angle closure: 1. Multimechanism: 54.8% of Chinese PACG is caused by co-existing factors. The pattern of angle closure appears to mainly be creeping closure. After iridectomy, almost 40% of the cases still manifest a positive response to the darkroom provocative test and progressive synechial closure or recurrent angle closure may occur. Several mechanisms are involved in this form of PACG such as pupillary blocking component, iris crowding component and anterior positioned ciliary body. These factors can coexist in the follow patterns: pupillary blocking and iris crowding coexist; pupillary blocking and anterior positioned ciliary body coexist or three of them co-exist. 2. Pupillary block: (38.1% of Chinese PACG) is caused by iris bombe due to pupillary block with acute or subacute attack. It responds well to iridectomy or laser iridotomy. 3. Non-pupillary blocking: (7.8% of Chinese PACG). They usually have a deeper anterior chamber, and tend to be younger (below 40 years of age). Angle closure in this form of PACG is caused by: iris crowding mechanism or/and anteriorly positioned ciliary body against iris root to angle. It is critical to distinguish multi-mechanism PACG from other types. The initial treatment for this type of PACG is also iridectomy, but after the pupillary block component is eliminated by iridectomy, the residual non-pupillary blocking components should be highlighted by a diagnostic treatment procedure or by a ultrasound biomicroscopy (UBM) provocative test. Finally, the role of UBM in the observation and evaluation of the mechanism of angle closure is discussed and future research directions on PACG in Asians are proposed. Conclusion Chinese eyes have been recognized to be prone to the development of creeping angle closure. There is some direct evidence that creeping angle closure is caused by multiple mechanisms. Further study on this topic is needed.

Syntheses, crystal structures, and physical properties of dinuclear copper(I) and tetranuclear mixed-valence copper(I,II) complexes with hydroxylated bipyridyl-like ligands.

Abstract: Four copper complexes with hydroxylated bipyridyl-like ligands, namely [Cu2(ophen)2] (1), [Cu4(ophen)4(tp)] (2), [Cu4(obpy)4(tp)] (3), and [Cu4(obpy)4(dpdc)]⋅2H2O (4), (Hophen=2-hydroxy-1,10-phenanthroline, Hobpy=6-hydroxy-2,2′-bipyridine, tp=terephthalate, dpdc=diphenyl-4,4′-dicarboxylate) have been synthesized hydrothermally. X-ray single-crystal structural analyses of these complexes reveal that 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) ligands are hydroxylated into ophen or obpy during the reaction, which provides structural evidence for the long-time argued Gillard mechanism. The dinuclear copper(I) complex 1 has three supramolecular isomers in the solid state, in which short copper–copper distances (2.66–2.68 A) indicate weak metal–metal bonding interactions. Each of the mixed-valence copper(i,ii) complexes 2–4 consists of a pair of [Cu2(ophen)2]+ or [Cu2(obpy)2]+ fragments bridged by a dicarboxylate ligand into a neutral tetranuclear dumbbell structure. Dinuclear 1 is an intermediate in the formation of 2 and can be converted into 2 in the presence of additional copper(II) salt and tp ligands under hydrothermal conditions. In addition to the ophen-centered π→π* excited-state emission, 1 shows strong emissions at ambient temperature, which may be tentatively assigned as an admixture of copper-centered d→s,p and MLCT excited states.

Met protein expression level correlates with survival in patients with late-stage nasopharyngeal carcinoma.

Abstract: Met tyrosine kinase, the receptor for HGF/SF, is important in various cellular functions, including proliferation, mitogenesis, formation of branching tubules, angiogenesis, and tumor cell invasion and metastasis. However, the role of Met/HGF signaling pathway in nasopharyngeal carcinoma (NPC) has not been evaluated. In this study, we determined the expression profile and clinical correlation of Met/HGF in 66 cases of advanced NPC and the activation mechanisms of Met receptor in five NPC cell lines. Immunofluorescent staining and quantitative image analysis showed that the Met protein was expressed throughout the tumors and normal nasopharyngeal epithelia. Compared with NPC, the Met expression level was higher in columnar nasopharyngeal epithelium but lower in squamous nasopharyngeal epithelium. The normal interstitial stromal tissue expressed the lowest level of Met protein. HGF was detected mainly in the normal interstitial tissue surrounding the tumor. Met protein expression level was inversely correlated with patients' survival time; the correlation coefficient was -0.319 (P = 0.009). The mean survival time was 118 months in low Met expression group versus 52 months in high expression group (P = 0.0004). The cumulative 5-year survival rate was 77.68% in low expression group versus 38.24% in high expression group. The clinical stage was also significantly more advanced in high Met expression group. In the multivariate analysis, both clinical stage and Met protein expression level were independent prognostic indicators for patient survival. All of the five NPC cell lines tested did not express hgf mRNA but expressed met mRNA, and tyrosine phosphorylation of Met protein was mainly induced by exogenous HGF stimulation in these cells. No mutation was found in the tyrosine kinase and the juxtamembrane domains of Met receptor in the five NPC cell lines tested. These results indicate that: (a) high Met protein expression level correlates with poorer survival in late-stage NPC and serves as an independent prognostic indicator; and (b) the Met receptor in NPC is activated by its paracrine ligand HGF from the interstitial tissues rather than by an autocrine loop or its activating mutation.

Lectures on Mean Curvature Flows

Abstract: The curve shortening flow for convex curves The short time existence and the evolution equation of curvatures Contraction of convex hypersurfaces Monotonicity and self-similar solutions Evolution of embedded curves or surfaces (I) Evolution of embedded curves and surfaces (II) Evolution of embedded curves and surfaces (III) Convexity estimates for mean convex surfaces Li-Yau estimates and type II singularities The mean curvature flow in Riemannian manifolds Contracting convex hypersurfaces in Riemannian manifolds Definition of center of mass for isolated gravitating systems References Index.

Organochlorine hydrocarbons in human breast milk collected in Hong Kong and Guangzhou.

Abstract: In southern China, the awareness of persistent organic pollutant contamination has been increasing as a considerable number of past studies in Hong Kong had reported their trail in the coastal sediments, green-lipped mussels, muscle and viscera of pond fish, and foodstuffs. Hence there is an urgent need to assess their existence, contamination profiles, and potential impact on the public. In the present study, a survey was conducted to examine p,p'-DDT, p,p'-DDE, beta-HCH, and PCB concentrations in human breast milk, one of the most reliable bioaccumulation indicators. Milk samples (115 from Hong Kong and 54 from Guangzhou), in the lactation period from 3-5 weeks were analyzed. The results demonstrated that the mean levels of p,p'-DDT (Hong Kong: 0.39; Guangzhou: 0.70 microg/g of fat), p,p'-DDE (2.48; 2.85), and beta-HCH (0.95; 1.11) were 2-15-fold higher when compared with studies conducted elsewhere ( i.e., United Kingdom, Germany, Sweden, Spain, and Canada), and in contrast the concentration of PCBs (0.035; 0.031) was about 10 times lower. When compared to a similar study conducted 10 years ago in Hong Kong ( p,p'-DDT 2.17 microg/g of fat, p,p'-DDE 11.67, beta-HCH 15.96, and PCB 0.64), a considerable reduction in the levels of their contaminations was observed. The drastic reduction in body burdens in 10 years' time is presumably the result of effective regulatory actions. It is worth noting that body burden correlated positively with maternal age (total DDT, r = 0.93; beta-HCH, r = 0.91; PCBs, r = 0.77) and with historical record of seafood consumption (total DDT, r = 0.89; beta-HCH, r = 0.98; PCBs, r = 0.91) (p < 0.001) and potential uptake of the POPs by breastfed infants may pose adverse health hazards.

Understanding conflict avoidance: relationship, motivations, actions, and consequences

Abstract: Because of their relationship‐oriented values, avoiding conflict is thought to be particularly prevalent and appropriate in collectivist societies like China Although research in the West has assumed that avoiding conflict is one approach and a largely ineffective one, collectivists may use conflict avoidance in different ways, including protecting the other protagonist. Eighty‐five managers and employees in six State Owned Enterprises in South China described concrete incidents when they avoided conflict and responded to specific items to measure the prior relationship, motivation, strategies, and consequences. Results identify major motivations and strategies used in conflict avoidance. Findings indicate that Chinese managers and employees relied upon the other person, promoted task productivity, and strengthened the relationship when they had a prior strong relationship and cooperative goals. Cooperative goals and fear of revenge were both found to underlie outflanking (trying to work around the other). Results were interpreted as indicating that avoiding conflict can be useful and even reaffirm an already effective relationship, but like open conflict, it must be managed constructively.

Solutions of Euler-Poisson Equations¶for Gaseous Stars

Abstract: In this paper, we study the Euler-Poisson equations governing gas motion under self-gravitational force. We are interested in the evolution of the gaseous stars, for which the density function has compact support. We establish existence theory for the stationary solutions and describe the behavior of the solutions near the vacuum boundary. The boundary behavior thus obtained agrees with the physical boundary condition proposed and studied in [L, LY] for both Euler equations with damping and the Euler-Poisson equations. Existence, non-existence, uniqueness and instability of the stationary solutions with vacuum are also discussed in terms of the adiabatic exponent and the entropy function. And the phenomena of the blowup, that is, the collapsing of the star to a single point with finite mass, as well as the drifting of part of the star to infinity in space are also studied and shown to agree with the conjecture from the physical considerations.

Improvement of tribological performance of epoxy by the addition of irradiation grafted nano-inorganic particles

Abstract: To develop wear resistant nanocomposite coating materials, the authors of the present work treated nanosilica first by introducing a certain amount of grafting polymers onto the particles in terms of an irradiation technique. Throught irradiation grafting, the nanoparticle agglomerates turn into a nanocomposite microstructure (comprised of the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn built up a strong interfacial interaction with the surrounding epoxy matrix through chain entanglement and chemical bonding during the subsequent mixing and consolidation. The experimental results indicated that the addition of the grafted nanosilica into epoxy significantly reduced wear rate and frictional coefficient of the matrix at low filler loading. Compared with the cases of microsized silica and untreated nonosilica, the employment of grafted nanosilica provided composites with much higher tribological performance enhancement efficiency. Unlike the approaches for manufacturing of other types of nanocomposites, the current method is characterized by many advantages, suchs as simple, low cost, easy to be controlled, and broader applicability.