Showing papers by "Nanjing University published in 2000"

Raman scattering study on anatase TiO2 nanocrystals

Abstract: Titanium dioxide (TiO2 ) nanocrystals are prepared by a hydrolysis process of tetrabutyl titanate. Nanocrystal samples with various sizes of 6.8-27.9 nm are obtained after annealing from 100 to 650 °C. The crystal structures and the average particle sizes are examined using x-ray diffraction. Raman scattering was employed to investigate the evolution of the anatase phase in the nanocrystals during annealing. Phonon confinement and non-stoichiometry effects are responsible for the blueshift and broadening of the lowest-frequency Eg Raman mode. The influence of interfacial vibrations on the Raman linewidth is also discussed.

An Emerging Flux Trigger Mechanism for Coronal Mass Ejections

Abstract: Observations indicate that reconnection-favored emerging flux has a strong correlation with coronal mass ejectons (CMEs). Motivated by this observed correlation and based on the flux rope model, an emerging flux trigger mechanism is proposed for the onset of CMEs, using two-dimensional magnetohydrodynamic (MHD) numerical simulations: when such emerging flux emerges within the filament channel, it cancels the magnetic field below the flux rope, leading to the rise of the flux rope (owing to loss of equilibrium) and the formation of a current sheet below it. Similar global restructuring and a resulting rise motion of the flux rope occur also when reconnection-favored emerging flux appears on the outer edge of the filament channel. In either case, fast magnetic reconnection in the current sheet below the flux rope induces fast ejection of the flux rope (i.e., CME). It is also shown that the nonreconnecting emerging flux, either within the filament channel or on the outer edge of the channel, makes the flux rope move down, i.e., no CMEs can be triggered. Although the present two-dimensional model can not provide many details of the largely unknown three-dimensional processes associated with prominence eruptions, it shows some observational features such as the height-time profile of erupting prominences. Most importantly, our model can well explain the observed correlation between CMEs and the reconnection-favored emerging flux.

Sources of Work‐Family Conflict: A Sino‐U.S. Comparison of the Effects of Work and Family Demands

Abstract: Given differences in values about work and family time, we hypothesize that Americans will experience greater family demand, which will have greater impact on work‐family conflict, whereas the Chinese will experience greater work demand, which will have the greater impact on work‐family conflict. The results of a survey of working men and women in the two countries generally supported the hypotheses; however, work demand did not differ significantly between the two countries and did not have a greater effect than family demand on work‐family conflict in China.

Alternating Direction Method with Self-Adaptive Penalty Parameters for Monotone Variational Inequalities

Abstract: The alternating direction method is one of the attractive approaches for solving linearly constrained separate monotone variational inequalities. Experience on applications has shown that the number of iterations depends significantly on the penalty parameter for the system of linear constraint equations. While the penalty parameter is a constant in the original method, in this paper we present a modified alternating direction method that adjusts the penalty parameter per iteration based on the iterate message. Preliminary numerical tests show that the self-adaptive adjustment technique is effective in practice.

Photoluminescence in anatase titanium dioxide nanocrystals

Abstract: Titanium dioxide (TiO2) nanocrystals were prepared by a hydrolysis process of tetrabutyl titanate. X-ray diffraction and Raman scattering showed that the as-prepared TiO2 nanocrystals have anatase structure of TiO2, and that the monophase anatase nanocrystals can be achieved through a series of annealing treatments below 650 °C. We measured photoluminescence (PL) spectra of the TiO2 nanocrystals. Under 2.41–2.71 eV laser irradiation, the TiO2 nanocrystals displayed strong visible light emission with maxima of 2.15–2.29 eV even at excitation power as low as 0.06 W/cm2. To identify the PL mechanism in the TiO2 nanocrystals, the dependences of the PL intensity on excitation power and irradiation time were investigated. The experimental results indicated that the radiative recombination is mediated by localized levels related to surface defects residing in TiO2 nanocrystallites.

Overall Evolution of Jetted Gamma-ray Burst Ejecta

Abstract: Whether gamma-ray bursts are highly beamed or not is a very difficult but important problem that we are confronted with. Some theorists suggest that beaming effect usually leads to a sharp break in the afterglow light curve during the ultrarelativistic phase, with the breaking point determined by γ = 1/θ0, where γ is the Lorentz factor of the blast wave and θ0 is the initial half-opening angle of the ejecta, but numerical studies tend to reject the suggestion. We note that previous studies are uniformly based on dynamics that is not proper for nonrelativistic blast waves. Here we investigate the problem in more detail, paying special attention to the transition from the ultrarelativistic phase to the nonrelativistic phase. Due to some crucial refinements in the dynamics, we can follow the overall evolution of a realistic jet until its velocity is as small as βc ~ 10-3c. We find no obvious break in the optical light curve during the relativistic phase itself. However, an obvious break does appear at the transition from the relativistic phase to the Newtonian phase if the physical parameters involved are properly assumed. Generally speaking, the Newtonian phase is characterized by a sharp decay of optical afterglows, with the power-law timing index α ~ 1.8-2.1. This is due to the quick lateral expansion at this stage. The quick decay of optical afterglows from GRB 970228, 980326, and 980519 and the breaks in the optical light curves of GRB 990123 and 990510 may indicate the presence of highly collimated gamma-ray burst ejecta.

Genesis of Young Lithospheric Mantle in Southeastern China: an LAM–ICPMS Trace Element Study

Abstract: depleted compositions occur in the upper part of the lithospheric Geological and geophysical evidence indicates that at least 100 km mantle, which now is >100 km thick. Garnet peridotites are of Archaean to Proterozoic lithospheric mantle has been removed essentially undepleted, and Y–Ga–Zr relationships of the garnets from beneath large areas of eastern and southeastern China during are typical of Phanerozoic mantle. The overall highly fertile nature late Mesozoic to Cenozoic time. Mantle-derived xenoliths in Tertiary of the existing lithosphere requires that the Archaean and Proterozoic basalts from several localities across this region have been studied mantle that existed beneath the region in Palaeozoic times has been by X-ray fluorescence, electron microprobe and laser ablation microlargely or completely removed, and replaced by younger, hotter and probe–inductively coupled plasma-mass spectrometry to characterize more fertile material. This probably occurred by upwelling of this thinner lithosphere. Trace element patterns of clinopyroxenes in asthenospheric material during late Mesozoic to Cenozoic time, the peridotites from southeastern China can be divided into four underplating to form new lithosphere. The occurrence of rare depleted groups: fertile garnet lherzolites, fertile spinel (± garnet) lherzolites, xenoliths may show that some older mantle material is residual and and depleted and enriched peridotites. The addition of Nb, Sr, light coexists with younger material beneath southeastern China. rare earth elements, but not of Ti and Zr, suggests a metasomatizing agent containing both H2O and CO2. This study also demonstrates that the negative Ti anomaly commonly observed in clinopyroxene from mantle peridotites cannot be balanced by the Ti in coexisting orthopyroxene, but can be explained by small degrees of partial

KAM Tori for 1D Nonlinear Wave Equations with Periodic Boundary Conditions

Abstract: In this paper, one-dimensional (1D) nonlinear wave equations $$$$ with periodic boundary conditions are considered; V is a periodic smooth or analytic function and the nonlinearity f is an analytic function vanishing together with its derivative at u≡0. It is proved that for “most” potentials V(x), the above equation admits small-amplitude periodic or quasi-periodic solutions corresponding to finite dimensional invariant tori for an associated infinite dimensional dynamical system. The proof is based on an infinite dimensional KAM theorem which allows for multiple normal frequencies.

Sr and O isotopic characteristics of porphyries in the Qinling molybdenum deposit belt and their implication to genetic mechanism and type

Abstract: A great deal of Mesozoic hypobatholithic granites and hypabyssal porphyries develop in the Qinling Mountains. The former has long been regarded as transformation type (or S-type), and the latter associated with Mo-mineralization regarded as syntexis type (or l-type) granitoids. Statistics show that Sr, andδ18O of hypabyssal porphyries respectively range from 0.705 to 0.714, and from 7.2‰ to 12.1‰, agreeing with those of hypobatholithes (Sr1=0.705-0.710, δ18O = 6.1‰-10.4‰), which indicates that they share similar material sources and petrogenic mechanism. Based on analysis of lithological, mineralogical and geochemical characteristics of these granitoids and on study of their petrogenic tectonic background and regional geophysical data, we argue that both the shallow-seated porphyries and deep-seated batholithes were the products of Mesozoic collision between South China and North China paleocontinents. Subsequently, all these granti-toids should be attributed to collision type.

Evaluation of sensitivity and specificity of two crustacean biochemical biomarkers

Abstract: Biochemical biomarkers are increasingly used for environmental assessment. Although the emphasis has been on vertebrate biomarkers, invertebrates biomarkers have been developed as well. This study evaluated the usefulness of biomarker responses of freshwater invertebrates by comparing the sensitivity and specificity of endpoints at three levels of biological organization: biochemical, physiological, and individual. The study focused on the epibenthic amphipod Gammarus pulex L., and the end points were cholinesterase (ChE) and glutathione-S-transferase (GST) activity, feeding inhibition, and mortality. Chemicals representing five major classes of toxic chemicals were assessed, including zinc, linear alkylbenzene sulphonate (LAS; surfactant), lindane (organochlorine), pirimiphos-methyl (organophosphorus), and permethrin (pyrethroid). Lethality was the least sensitive endpoint, with 96-h LC50 values ranging from 2.78 μg/L for permethrin to 6.31 mg/L for LAS. Comparison of the biochemical biomarkers and the sublethal feeding rate assay indicated that whereas ChE inhibition was a specific indicator of organophosphate exposure, the biochemical assay was more than 13-fold less sensitive than the feeding rate assay. The GST biomarker performed with greater sensitivity but with lower specificity compared with the ChE biomarker. However, only on exposure to lindane did the GST biomarker marginally outperform the feeding rate assay in terms of sensitivity. Feeding inhibition is both a general and a sensitive (LC50, <3%) indicator for exposure to a range of chemicals. The Gammarus sp. ChE biomarker may have utility in providing a diagnostic and rapid indicator of organophosphate exposure, but evidence from this and other studies questions the sensitivity of this biomarker in predicting sublethal, higher-order effects. The GST biomarker may provide a rapid and sensitive indicator for toxicant exposure, but it has limited use as a diagnostic tool and provides only limited improvement in sensitivity over more ecologically relevant sublethal end points (e.g., feeding rate, growth rate).

A simple copper(II)-L-histidine system for efficient hydrolytic cleavage of DNA.

Abstract: Copper(II)−l-histidine complexes effectively promote the cleavage of plasmid DNA and dideoxynucleotide dApdA at physiological pH and temperature. Studies of the mechanism of plasmid DNA cleavage by added radical scavengers, using rigorously anaerobic experiments, analyses for malondialdehyde-like products, religation assays, and HPLC analyses, indicate that DNA cleavage mediated by Cu(l-His) occurs via a hydrolytic path. The hydrolytic cleavage rate constants at 37 °C are estimated to be 0.76 h-1 for the decrease of form I and 0.25 h-1 for the increase of form III. The phosphoimager picture reveals that Cu(l-His) cleaves DNA with a certain sequence specificity (preferentially at 5‘-GT-3‘). The dinucleotide hydrolysis shows, with [Cu(l-His)] = 0.8 mM, rate enhancement factors of >108. Interestingly, histidine−metal ion interactions (with Cu(II), Ni(II), Zn(II), etc.) have been used for various applications, e.g., protein purification, cross-linking, and targeting proteins to lipid bilayers. Our findings ma...

Pose invariant face recognition

Abstract: We describe a novel neural network architecture, which can recognize human faces with any view in a certain viewing angle range (from left 30 degrees to right 30 degrees out of plane rotation). View-specific eigenface analysis is used as the front-end of the system to extract features, and the neural network ensemble is used for recognition. Experimental results show that the recognition accuracy of our network ensemble is higher than conventional methods such as using a single neural network to recognize faces of a specific view.

Inhibition of xanthine oxidase by liquiritigenin and isoliquiritigenin isolated from Sinofranchetia chinensis

Abstract: The methanol extract of the stem of Sinofranchetia chinensis inhibited the activity of xanthine oxidase in vitro. Bioassay-guided purification led to the isolation of liquiritigenin and isoliquiritigenin as the main xanthine oxidase inhibitors. This inhibition of enzyme activity was found to be dose dependent, with an IC50 value of approximately 49.3 μM for liquiritigenin and 55.8 μM for isoliquiritigenin. Lineweaver-Burk transformation of the inhibition data indicated that the inhibition was of a mixed type for both liquiritigenin and isoliquiritigenin. For liquiritigenin, the Ki and KI were determined to be 14.0 μM and 151.6 μM, respectively. For isoliquiritigenin, the Ki and KI were determined to be 17.4 μM and 81.9 μM, respectively. These results suggest that these natural products could be used to treat conditions where the inhibition of xanthine oxidase is warranted.

Microwave assisted preparation of binary oxide nanoparticles

Abstract: A group of binary oxide nanophase materials were prepared using a microwave assisted soft-chemical route. BaTiO3, Ba6Ti17O40, BaZrO3 and PbTiO3 were prepared from BaCl2 hydrate, Pb(Ac)2, Ti(OPri)4 and ZrOCl2. All reactions were performed in ethylene glycol, which acted as both a solvent and a growth regulating agent, under atmospheric pressure in a microwave reactor. The products that were obtained were analyzed by using XRD, TEM, XPS, EDX and FT-IR.

Chandra Observations of the Crab-like Supernova Remnant G21.5-0.9

Abstract: Chandra observations of the Crab-like supernova remnant G21.5-0.9 reveal a compact central core and spectral variations indicative of synchrotron burn-off of higher energy electrons in the inner nebula. The central core is slightly extended, perhaps indicating the presence of an inner wind-shock nebula surrounding the pulsar. No pulsations are observed from the central region, yielding an upper limit of ~40% for the pulsed fraction. A faint outer shell may be the first evidence of the expanding ejecta and blast wave formed in the initial explosion, indicating a composite nature for G21.5-0.9.