Showing papers by "Nanjing University published in 2003"

Hardness of covalent crystals.

Abstract: Based on the idea that the hardness of covalent crystal is intrinsic and equivalent to the sum of the resistance to the indenter of each bond per unit area, a semiempirical method for the evaluation of hardness of multicomponent crystals is presented. Applied to beta-BC2N crystal, the predicted value of hardness is in good agreement with the experimental value. It is found that bond density or electronic density, bond length, and degree of covalent bonding are three determinative factors for the hardness of a polar covalent crystal. Our method offers the advantage of applicability to a broad class of materials and initializes a link between macroscopic property and electronic structure from first principles calculation.

Fitness costs of R-gene-mediated resistance in Arabidopsis thaliana.

Abstract: Resistance genes (R-genes) act as an immune system in plants by recognizing pathogens and inducing defensive pathways. Many R-gene loci are present in plant genomes, presumably reflecting the need to maintain a large repertoire of resistance alleles. These loci also often segregate for resistance and susceptibility alleles that natural selection has maintained as polymorphisms within a species for millions of years. Given the obvious advantage to an individual of being disease resistant, what prevents these resistance alleles from being driven to fixation by natural selection? A cost of resistance is one potential explanation; most models require a lower fitness of resistant individuals in the absence of pathogens for long-term persistence of susceptibility alleles. Here we test for the presence of a cost of resistance at the RPM1 locus of Arabidopsis thaliana. Results of a field experiment comparing the fitness of isogenic strains that differ in the presence or absence of RPM1 and its natural promoter reveal a large cost of RPM1, providing the first evidence that costs contribute to the maintenance of an ancient R-gene polymorphism.

The Effect of Export Marketing Capabilities on Export Performance: An Investigation of Chinese Exporters

Abstract: The primary purpose of this article is to investigate the effect of export marketing capabilities on export performance. Drawing on the resource-based view, the authors develop a model that links an exporter’s product development capability, distribution capability, communication capability, and pricing capability with its positional advantages (low-cost advantage and branding advantage) and its performance in the export market. On the basis of a survey of Chinese export ventures, the authors find general support for their proposed model. The authors discuss the theoretical and managerial implications of their findings.

The iau 2000 resolutions for astrometry celestial mechanics and metrology in the relativistic framework: explanatory supplement

Abstract: We discuss the IAU resolutions B1.3, B1.4, B1.5, and B1.9 that were adopted during the 24th General Assembly in Manchester, 2000, and provides details on and explanations for these resolutions. It is explained why they present significant progress over the corresponding IAU 1991 resolutions and why they are necessary in the light of present accuracies in astrometry, celestial mechanics, and metrology. In fact, most of these resolutions are consistent with astronomical models and software already in use. The metric tensors and gravitational potentials of both the Barycentric Celestial Reference System and the Geocentric Celestial Reference System are defined and discussed. The necessity and relevance of the two celestial reference systems are explained. The transformations of coordinates and gravitational potentials are discussed. Potential coefficients parameterizing the post-Newtonian gravitational potentials are expounded. Simplified versions of the time transformations suitable for modern clock accuracies are elucidated. Various approximations used in the resolutions are explicated and justified. Some models (e.g., for higher spin moments) that serve the purpose of estimating orders of magnitude have actually never been published before.

An Early Cretaceous Tribosphenic Mammal and Metatherian Evolution

Abstract: Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous.

Synthesis of Inorganic Fullerene-Like Molecules

Abstract: The reaction of [Cp*Fe(eta5-P5)] with Cu(I)Cl in solvent mixtures of CH2Cl2/CH3CN leads to the formation of entirely inorganic fullerene-like molecules of the formula [[Cp*Fe(eta5:eta1:eta1:eta1:eta1:eta1-P5)]12[CuCl]10[Cu2Cl3]5[Cu(CH3CN)2]5] (1) possessing 90 inorganic core atoms. This compound represents a structural motif similar to that of C60: cyclo-P5 rings of [Cp*Fe(eta5-P5)] molecules are surrounded by six-membered P4Cu2 rings that result from the coordination of each of the phosphorus lone pairs to CuCl metal centers, which are further coordinated by P atoms of other cyclo-P5 rings. Thus, five- and six-membered rings alternate in a manner comparable to that observed in the fullerene molecules. The so-formed half shells are joined by [Cu2Cl3]- as well as by [Cu(CH3CN)2]+ units. The spherical body has an inside diameter of 1.25 nanometers and an outside diameter of 2.13 nanometers, which is about three times as large as that of C60.

Trends in temperature extremes during 1951–1999 in China

Abstract: [1] Based on the daily surface air temperature data from about 200 stations during 1951-1999 in China, changes in the frequency of some extreme temperature events were studied with a focus on trends. For China as a whole, the number of hot days (Tmax over 35°C) displays a slightly decreasing trend, while the number of frost days (Tmin below 0°C) exhibits a significant decreasing trend. Meanwhile, increasing trends were detected in the frequencies of warm days and warm nights. In addition, decreasing trends was found in the frequencies of cool days and even stronger decreasing trend was found in frequencies of cool nights in China.

Neural-network predictive control for nonlinear dynamic systems with time-delay

Abstract: A new recurrent neural-network predictive feedback control structure for a class of uncertain nonlinear dynamic time-delay systems in canonical form is developed and analyzed. The dynamic system has constant input and feedback time delays due to a communications channel. The proposed control structure consists of a linearized subsystem local to the controlled plant and a remote predictive controller located at the master command station. In the local linearized subsystem, a recurrent neural network with on-line weight tuning algorithm is employed to approximate the dynamics of the time-delay-free nonlinear plant. No linearity in the unknown parameters is required. No preliminary off-line weight learning is needed. The remote controller is a modified Smith predictor that provides prediction and maintains the desired tracking performance; an extra robustifying term is needed to guarantee stability. Rigorous stability proofs are given using Lyapunov analysis. The result is an adaptive neural net compensation scheme for unknown nonlinear systems with time delays. A simulation example is provided to demonstrate the effectiveness of the proposed control strategy.

The silica-like extended polymorphism of cobalt(II) imidazolate three-dimensional frameworks: X-ray single-crystal structures and magnetic properties.

Abstract: Five polymorphous frameworks of cobalt(II) imidazolates (1-5) have been prepared by solvatothermal syntheses. Of these, compound 3 has already been synthesized in a gas-phase reaction by Seel et al. in 1969 and structurally characterized by Sturm et al. in 1975. The new synthetic strategy affords four polymorphous frameworks of cobalt(II) imidazolates (1, 2, 4, 5) of crystalline substances, of which the compound 4 (a = b = 23.450(3), c = 12.460(3) A, tetragonal, I4(1)cd, Z = 16) is an isomorphous compound of [Zn(im)(2)]( infinity ), which was also synthesized in a gas-phase reaction in 1980. The frameworks of compounds 1 and 2 are porous and isostructural; they have the same framework topology that represents a novel uninodal (6,4)-net: 1: a = 18.513(4), b = 24.368(5), c = 9.2940(19) A, orthorhombic, Fdd2, Z = 16; 2: a = 17.635(4), b = 27.706(6), c = 9.0810(18) A, orthorhombic, Fdd2, Z = 16. The framework of compound 5 exhibits a topology of zeolitic structure with the unit-cell parameters: a = 24.3406(8), b = 9.4526(3), c = 24.8470(8) A, beta = 91.977(1) degrees, monoclinic, P2(1)/n, Z = 4. All polymorphous frameworks of cobalt(II) imidazolates reflect the structural features of silica (SiO(2)) and also exhibit different magnetic behaviors, although the imidazolates transmit the antiferromagnetic coupling between the cobalt(II) ions in all cases. However, the uncompensated antiferromagnetic couplings arise from spin-canting are sensitive to the structures: compound 1 is an antiferromagnet with T(N) = 13.11 K; compounds 2-4 are weak ferromagnets (canted antiferromagnets): 2 shows a very weak ferromagnetism below 15 K, 3 exhibits a relatively strong ferromagnetism below 11.5 K and a coercive field (H(C)) of 1800 Oe at 1.8 K, and 4 displays the strongest ferromagnetism of the three cobalt imidazolates and demonstrates a T(C) of 15.5 K with a coercive field, H(C), of 7300 Oe at 1.8 K. However, compound 5 seems to be a hidden canted antiferromagnet with a magnetic ordering temperature of 10.6 K.

Medical diagnosis with C4.5 rule preceded by artificial neural network ensemble

Abstract: Comprehensibility is very important when machine learning techniques are used in computer-aided medical diagnosis. Since an artificial neural network ensemble is composed of multiple artificial neural networks, its comprehensibility is worse than that of a single artificial neural network. In this paper, C4.5 Rule-PANE, which combines an artificial neural network ensemble with rule induction by regarding the former as a preprocess of the latter, is proposed. At first, an artificial neural network ensemble is trained. Then, a new training data set is generated by feeding the feature vectors of original training instances to the trained ensemble and replacing the expected class labels of original training instances with the class labels output from the ensemble. Additional training data may also be appended by randomly generating feature vectors and combining them with their corresponding class labels output from the ensemble. Finally, a specific rule induction approach, i.e., C4.5 Rule, is used to learn rules from the new training data set. Case studies on diabetes, hepatitis , and breast cancer show that C4.5 Rule-PANE could generate rules with strong generalization ability, which benefits from an artificial neural network ensemble, and strong comprehensibility, which benefits from rule induction.

Quasiparticle scattering interference in high-temperature superconductors

Abstract: We propose that the energy-dependent spatial modulation of the local density of states seen by Hoffman et al. [Science 297, 1148 (2002)] is due to the scattering interference of quasiparticles. In this paper we present the general theoretical basis for such an interpretation and lay out the underlying assumptions. As an example, we perform an exact T-matrix calculation for the scattering due to a single impurity. The results of this calculation is used to check the assumptions, and to demonstrate that quasiparticle scattering interference can indeed produce patterns similar to those observed by Hoffman et al.

A dual neural network for redundancy resolution of kinematically redundant manipulators subject to joint limits and joint velocity limits

Abstract: In this paper, a recurrent neural network called the dual neural network is proposed for online redundancy resolution of kinematically redundant manipulators. Physical constraints such as joint limits and joint velocity limits, together with the drift-free criterion as a secondary task, are incorporated into the problem formulation of redundancy resolution. Compared to other recurrent neural networks, the dual neural network is piecewise linear and has much simpler architecture with only one layer of neurons. The dual neural network is shown to be globally (exponentially) convergent to optimal solutions. The dual neural network is simulated to control the PA10 robot manipulator with effectiveness demonstrated.

Energy dissipation in gigahertz oscillators from multiwalled carbon nanotubes.

Abstract: Using atomistic models and molecular dynamics simulations, interlayer corrugation and resistant force in a biwalled carbon nanotube are shown to be strongly dependent upon the morphology combination of the bitube. Consequently, energy dissipation in a commensurate (e.g., armchair/armchair or zigzag/zigzag) bitube oscillator is found to be much larger than that in an incommensurate (e.g., zigzag/armchair) oscillator, resulting in a decay of oscillation amplitude within a few nanoseconds in the commensurate bitube and several tens of nanoseconds in the incommensurate bitube.

International ethical guidelines for biomedical research involving human subjects

Abstract: This is the third version in the series of biomedical-research ethical guidelines issued by CIOMS since 1982. The members of redrafting group come from Africa, Asia, Latin America, Europe and Latin America, the United States and the CIOMS secretariat. Its core consists of 21 guidelines with commentaries. Like those of 1982 and 1993, the 2002 CIOMS guidelines are designed to be of use to countries in defining national policies on the ethics of biomedical research involving human subjects, applying ethical standards in local circumstances, and establishing or improving ethical review mechanisms.

Re-Os Dating of Polymetallic Ni-Mo-PGE-Au Mineralization in Lower Cambrian Black Shales of South China and Its Geologic Significance

Abstract: Black shales of the basal Lower Cambrian Niutitang Formation, southeast China, host a regionally distributed concordant, several centimeter-thick, sulfide layer which displays extreme metal enrichment, i.e., Mo-NiSe-Re-Os-As-Hg-Sb >1,000 times enriched and Ag-Au-Pt-Pd >100 times enriched over bulk continental crust. Mineable portions have about 5.5 wt percent Mo, 3.5 wt percent Ni, and 1 g/t PGE + Au. A six-point 187 Os/ 188 Os versus 187 Re/ 188 Os isochron on molybdenum-nickel ore samples defines an age of 541 ± 16 Ma (2σ) with an initial 187 Os/ 188 Os ratio of 0.78 ± 0.19. This age is in agreement with the depositional age of the black shale host; the initial ratio is close to present-day seawater. The sulfide layer/average seawater metal ratio is on the order of 10 6 to 10 8 , about 10 to 100 times higher than that for the black shale host and for average metalliferous black shale. Synsedimentary metal enrichment from seawater under anoxic (sulfate-reducing) conditions appears likely but requires an unusually low sedimentation rate and/or high replenishment rate of fresh seawater to the marine basin. The paleogeographic setting of the Lower Cambrian continental margin of the Yangtze craton indicates local basins controlled by synsedimentary rifting. Stagnant water episodically replenished by upwelling oxidized seawater is thought to be responsible for the formation of the polymetallic sulfide layer and of phosphorite, barite, and sapropelic “stone coal” (combustible black shale) beds.

An Amperometric Biosensor Based on the Coimmobilization of Horseradish Peroxidase and Methylene Blue on a Carbon Nanotubes Modified Electrode

Abstract: A novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carbon nanotube. The multiwall carbon nanotube (MWNT) was used as a coimmobilization matrix to incorporate horseradish peroxidase (HRP) and electron transfer mediator methylene blue (MB) onto a glassy carbon electrode surface. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of methylene blue as an electron carrier between the immobilized peroxidase and the surface of glassy carbon electrode. The amperometric response of this resulting biosensor to H2O2 shows a linear relation in the range from 4 μM to 2 mM. The detection limit was 1 μM when the signal to noise ratio is 3. The presence of dopamine and ascorbic acid hardly affects the sensitive determination of H2O2. This biosensor also possesses very good stability and reproducibility.

Effects of ligand planarity on the interaction of polypyridyl Ru(II) complexes with DNA

Abstract: Two new polypyridyl ligands containing substituent Br at different positions in the phenyl ring, OBIP {OBIP = 2-(2-bromophenyl)imidazo[4,5-f]-1,10-phenanthroline}, PBIP {PBIP = 2-(4-bromophenyl)imidazo[4,5-f]-1,10-phenanthroline} and their Ru(II) complexes, [Ru(dmp)2(OBIP)]2+1 and [Ru(dmp)2(PBIP)]2+2 (dmp = 2,9-dimethyl-1,10-phenanthroline), have been synthesized and characterized. The binding of the two complexes to calf thymus DNA (CT DNA) has been investigated by spectrophotometric methods, viscosity measurements, as well as equilibrium dialysis and circular dichroism spectroscopy. Theoretical calculations for the two complexes were also carried out applying the density functional theory (DFT) method. The structure of complex 1 has been determined by single-crystal X-ray diffraction techniques. The imidazo[4,5-f]-1,10-phenanthroline moiety is not coplanar with the 2-bromophenyl ring, having a dihedral angle of 48.6° in the OBIP ligand. The twisted conformation has been further confirmed by theoretical calculations, in which this dihedral angle is 48.2°. The theoretical calculations also suggest that the PBIP ligand in complex 2 is essentially planar (dihedral angle is 0.4°). The experimental results show that while complex 1 binds to CT DNA via a semi-intercalative mode, complex 2 strongly binds to CT DNA through intercalation. Complex 2 is thus a much better candidate as an enantioselective binder to CT DNA than complex 1. Some experimental regularities or trends have been reasonably explained by the theoretical results. These suggest that the planarity of the intercalated ligand has significant effects on the spectral properties and the DNA-binding behavior of the complexes, and that the DFT method can be used effectively to explain and predict some regularities or trends in the interaction of polypyridyl Ru(II) complexes with DNA.

Reversible Anion Exchanges between the Layered Organic–Inorganic Hybridized Architectures: Syntheses and Structures of Manganese(II) and Copper(II) Complexes Containing Novel Tripodal Ligands

Abstract: Six noninterpenetrating or- ganic ± inorganic hybridized coordina- tion complexes, (Mn(3)2(H2O)2)- (ClO4)2 ¥2 H2 O( 5), (Mn(3)2(H2O)2)- (NO3)2 (6), (Mn(3)2(N3)2 )¥2 H2 O( 7), (Cu(3)2(H2O)2)(ClO4)2 (8), (Mn(4)2- (H2O)(SO4)) ¥ CH3OH ¥ 5 H2 O( 9) and (Mn(4)2)(ClO4)2 (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imida- zol-1-ylmethyl)benzene (4) with the cor- responding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. En- tirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assem- blies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchang- es between complexes 5 and 6 without destruction of the frameworks demon- strate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemen- tal analyses, and X-ray powder diffrac- tion.

A simple wet-chemical synthesis and characterization of CuO nanorods

Abstract: Using a simple wet-chemical route, we synthesized CuO nanorods with diameters of ca. 5–15 nm and lengths of up to 400 nm. The purity, crystallinity, morphology, structure features, and chemical composition of the as-prepared CuO nanorods were investigated by powder X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.

International ethical guidelines for the choice of control in clinical trials Extracted from CIOMS International Ethical Guidelines for Biomedical Research Involving Human Subjects

Abstract: As a general rule, research subjects in the control group of a biomedical research involving human subjects should receive an established effective intervention. In some circumstances, however, it may be ethically acceptable to use an alternative comparator, such as placebo, “no treatment” or other effective alternative. This article discusses these special circumstances in detail, and puts forward means of minimizing harm to placebo control subjects.

Defective development and function of Bcl10-deficient follicular, marginal zone and B1 B cells.

Abstract: Bcl10 is an intracellular protein essential for nuclear factor (NF)-kappaB activation after lymphocyte antigen receptor stimulation. Using knockout mice, we show that absence of Bcl10 impeded conversion from transitional type 2 to mature follicular B cells and caused substantial decreases in marginal zone and B1 B cells. Bcl10-deficient B cells showed no excessive apoptosis. However, both Bcl10-deficient follicular and marginal zone B cells failed to proliferate normally, although Bcl10-deficient marginal zone B cells uniquely failed to activate NF-kappaB efficiently after stimulation with lipopolysaccharide. Bcl10-deficient marginal zone B cells did not capture antigens, and Bcl10-deficient (Bcl10-/-) mice failed to initiate humoral responses, leading to an inability to clear blood-borne bacteria. Thus, Bcl10 is essential for the development of all mature B cell subsets.

Conversing across cultures: East-West communication styles in work and nonwork contexts.

Abstract: Four experiments provided evidence that East-West differences in attention to indirect meaning are more pronounced in work settings compared with nonwork settings as suggested by prior research on Protestant relational ideology. Study 1 compared errors in interpreting indirect messages in work and nonwork contexts across three cultures. Studies 2 and 3 examined differences in self-reported indirectness with coworkers versus nonwork acquaintances across three cultures controlling for variation in individualism--collectivism. Study 4 examined self-reported indirectness in bicultural managers and experimentally manipulated the salience of Western versus Eastern culture. The results showed that Americans, but not East Asians, were less attentive to indirect cues in work than nonwork settings and that East-West differences in indirectness were greater in work than nonwork settings.