Showing papers by "Chinese Academy of Sciences published in 1996"

Large-Scale Synthesis of Aligned Carbon Nanotubes

Abstract: Large-scale synthesis of aligned carbon nanotubes was achieved by using a method based on chemical vapor deposition catalyzed by iron nanoparticles embedded in mesoporous silica. Scanning electron microscope images show that the nanotubes are approximately perpendicular to the surface of the silica and form an aligned array of isolated tubes with spacings between the tubes of about 100 nanometers. The tubes are up to about 50 micrometers long and well graphitized. The growth direction of the nanotubes may be controlled by the pores from which the nanotubes grow.

Nanocrystalline metals crystallized from amorphous solids: nanocrystallization, structure, and properties

Abstract: Polycrystalline materials with nanometer-sized grains, termed nanocrystalline materials, can be formed by crystallizing completely amorphous solids under proper heat treatment conditions. The crystallized nanocrystalline materials exhibit some unique structural characteristics and novel properties which are fundamentally different from those of the conventional coarse-grained polycrystalline materials. This article reviews the present state of the art in this field. The current status of research and developments on the nanocrystallization, microstructure and properties of the materials will be summarized. Comparisons of structural characteristics and properties are made between the crystallized nanocrystalline materials and those prepared by other methods. Further considerations of the development and applications of this new class of materials will also be presented.

Impact of El Niño on the East Asian Monsoon A Diagnostic Study of the '86/87 and '91/92 Events

Abstract: The East Asian monsoon circulation during the El Nino episodes of'86/87 and '91/92 is studied diagnostically. It is found that a southerly wind anomaly appeared in the lower troposphere along the coast of the East Asia during the mature phases of these two El Nino events. In the case of '86/87, the mature phase covered the boreal summer and the East Asian summer monsoon was intensified. On the other hand, in the case of '91/92, the northern winter was within the mature phase and the East Asian winter monsoon was weakened. Examination of the circulation features suggests that the effects of the El Nino events on the East Asian monsoon are felt through the variation of convective activities over the western equatorial Pacific. Convections in this area are strongly influenced by the evolution of sea surface temperature anomalies in the equatorial Pacific and are strongly suppressed during the mature phase, which exerts significant influences on the direct monsoonal circulation over the western tropical Pacific and the East Asia. The relationship between the East Asian monsoon and El Nino in its mature phase is also confirmed by a historical 850 hPa wind dataset that covers 6 events prior to the '86/87 event. The dataset also suggests that an inverse relationship does not hold during the La Nina periods.

Chinese remainder theorem: applications in computing, coding, cryptography

Abstract: Introduction and philosophy Chinese remainder algorithm in modular computations in algorithmics in bridging computations in coding theory in cryptography tutorial in information theory tutorial in algebra list of mathematical symbols.

The ball-bearing effect of diamond nanoparticles as an oil additive

Abstract: Diamond nanoparticles synthesized by the detonation of explosives were used as an additive in paraffin oil. The tribological properties of the two-phase lubricant of paraffin oil and diamond nanoparticles were investigated. The results show that, under boundary lubricating conditions, this kind of two-phase lubricant possesses excellent load-carrying capacity, anti-wear and friction-reduction properties. The ball-bearing effect of diamond nanoparticles existed between the rubbing faces, the surface polishing and the increase in surface hardness effects of the diamond nanoparticles are the main reasons for the reduction in wear and friction.

Comparative mapping of QTLs for agronomic traits of rice across environments by using a doubled-haploid population.

Abstract: We report here the RFLP mapping of quantitative trait loci (QTLs) which affect some important agronomic traits in cultivated rice. An anther culture-derived doubled-haploid (DH) population was established from a cross between indica and japonica rice varieties. A molecular linkage map comprising 137 markers was constructed based on this population which covered the rice genome at intervals of 14.8 cM on average. The linkage map was used to locate QTLs for such important agronomic traits as heading date, plant height, number of spikelets per panicle, number of grains per panicle, 1000-grain weight and the percentage of seed set, by interval mapping. Evidence of genotype-by-environment interaction was found by comparing QTL maps of the same population grown in three diverse environments. A total of 22 QTLs for six agronomic traits was detected which were significant in at least one environment, but only seven were significant in all three environments; seven were significant in two environments and eight could only be detected in a single environment. However, QTLs-by-environment interaction was trait dependent. QTLs for spikelets and grains per panicle were common across environments while traits like heading date and plant height were more sensitive to environment.

Special configuration of a very large Schmidt telescope for extensive astronomical spectroscopic observation

Abstract: A special reflecting Schmidt telescope is used to observe celestial objects The telescope has an aperture of 4m, f ratio of 5, and a 5° field of view Its optical axis is fixed and tilted 25° to the horizontal that runs from south to north The celestial objects were observed for 15 h as they passed through the meridian The shape of the reflecting Schmidt plate has to be changed with each different declination δ and in the tracking process This is achieved with active optics The sky area to be observed is -10° ≤ δ ≤ +90° There are plans to place ~4000 optical fibers on the telescope focal surface that will lead to a dozen spectrographs

Asymptotics for kernel estimate of sliced inverse regression

Abstract: To explore nonlinear structures hidden in high-dimensional data and to estimate the effective dimension reduction directions in multivariate nonparametric regression, Li and Duan proposed the sliced inverse regression (SIR) method which is simple to use. In this paper, the asymptotic properties of the kernel estimate of sliced inverse regression are investigated. It turns out that regardless of the kernel function, the asymptotic distribution remains the same for a wide range of smoothing parameters.

Comparative study of Nickel-based perovskite-like mixed oxide catalysts for direct decomposition of NO

Abstract: The mixed oxides LaNiO3, La0.1Sr0.9NiO3, La2NiO4 and LaSrNiO4 were prepared and used as catalysts for the direct decomposition of NO. The catalysts were characterized by means of XRD, XPS, O-2-TPD, NO-TPD and chemical analysis. By comparing the physico-chemical properties and catalytic activity for NO decomposition, a conclusion could be drawn as follows. The direct decomposition of NO over perovskite and related mixed oxide catalysts follows a redox mechanism. The lower valent metal ions Ni2+ and disordered oxygen vacancies seem to be the active sites in the redox process. The oxygen vacancy plays an important role favorable for the adsorption and activation of NO molecules on one hand and on the other hand for increasing the mobility of lattice oxygen which is beneficial to the reproduction of active sites. The presence of oxygen vacancies is one of the indispensable factors to give the mixed oxides a steady activity for NO decomposition.

Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium-modified microdisk array electrode.

Abstract: A palladium particle-modified carbon fiber microdisk array electrode was designed and employed in capillary electrophoresis for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid. The Pd-modified microdisk electrode had high catalytic ability for hydrazines and exhibited good reproducibility and stability. The response for hydrazine was linear over 3 orders of magnitude with a correlation coefficient of 0.993. The detection limits for hydrazine, methylhydrazine, and isoniazid were 1.2, 2.1, and 6.2 pg, respectively.

The magnetic susceptibility of modern soils in china and its use for paleoclimate reconstruction

Abstract: Magnetic susceptibility of more than 160 modern silty soil samples in China was measured to assess the relationship between the magnetic susceptibility and modern climatic parameters. Correlation between magnetic susceptibility and mean annual temperature (MAT) or mean annual precipitation (MAP), shows a complex picture and no single function can be found to fit all the data on the national scale. In East China, where East Asian monsoon plays an important role for the climate conditions, magnetic susceptibility increases with the increase of MAT or MAP in temperate semi-arid regions of the Loess Plateau and surrounding areas. This can be attributed to increasing intensity of pedogenesis which would favor the formation of strongly magnetic minerals and/or reduce depositional rate of eolian dust. Magnetic susceptibility tends to decrease with the increase of temperature and precipitation in the tropical and subtropical warm and humid regions of the vast areas south of the Yangtze River. This may be explained by pedogenic transformation of iron-bearing minerals to weakly magnetic minerals. Between these two different correlation patterns, 15°C of MAT and/or 1200 mm of MAP seem to be the thresholds. In West China, the correlation becomes quite complex in the great mountains and vast sedimentary basins in the north-west. This may be due to the prevailing continental climate in this region and topographic contrast within short distance. The correlation for the Qinghai-Xizang (Tibetan) Plateau is not clear because very few samples were collected. Fluctuations of paleo-temperature and paleo-precipitation at Luochuan for the last 130 ka were estimated using the climofunction obtained from this study.

Variations in temperature and precipitation in the past 2000 a on the Xizang (Tibet) Plateau——Guliya ice core record

Abstract: The past temperature and precipitation variations are recorded precisely and continuously in μ18O and glacial accumulation records in the Guliya ice core. Fight warm periods and seven cold periods can be distinguished in the past 2000 a. Of the four most intensive cold periods, three are in the Little Ice Age and one in the 11th - 12th century. The variation of precipitation is relatively small compared with that of temperature. Five humid periods and four dry periods occurred in the past 2 000 a. The long-term variation of temperature is positively correlated with that of precipitation according to the Guliya ice core record, but the variation of precipitation lags behind the variation of temperature.

Effective-mass theory for InAs/GaAs strained coupled quantum dots

Abstract: In the framework of effective-mass envelope-function theory, the optical transitions of InAs/GaAs strained coupled quantum dots grown on GaAs (100) oriented substrates are studied. At the Gamma point, the electron and hole energy levels, the distribution of electron and hole wave functions along the growth and parallel directions, the optical transition-matrix elements, the exciton states, and absorption spectra are calculated. In calculations, the effects due to the different effective masses of electrons and holes in different materials are included. Our theoretical results are in good agreement with the available experimental data.

Analysis of electric current helicity in active regions on the basis of vector magnetograms

Abstract: The problem of (dc) magnetic field energy build up in the solar atmosphere is addressed. Although large-scale current generation may be due to large-scale shearing motions in the photosphere, recently a new approach was proposed: under the assumption that the magnetic field evolves through a sequence of force-free states, Seehafer (1994) found that the energy of small-scale fluctuations may be transferred into energy of large-scale currents in an AR (the α-effect). The necessary condition for the α-effect is revealed by the presence of a predominant sign of current helicity over the volume under consideration. We studied how frequently such a condition may occur in ARs. On the basis of vector magnetic field measurements we calculated the current helicity B z · (▽ × B) z in the photosphere over the whole AR area for 40 active regions and obtained the following results: The method proposed can be applied to those ARs where the determination of the predominant sign of current helicity by traditional visual inspection of Hα-patterns is not reliable.

High frequency pulses of East Asian monsoon climate in the last two glaciations: link with the North Atlantic

Abstract: Three loess sections in the Loess Plateau of China have been studied to characterize the variations of the East Asian monsoon climate in the Late Quaternary period. Paleo-weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity (LW), in the last glacial and late penultimate glacial loess, indicating significantly cooler or/and drier conditions. Most of them are identified at or near the transitional boundaries between loess and soil units, suggesting that climatic conditions favorable for LW events tended to occur at or near major climatic boundaries. Twenty-eight radiocarbon and thermoluminescence measurements, combined with Kukla's magnetic susceptibility age model date these events at ∼14, ∼21, ∼29, ∼38, ∼52, ∼71, ∼135, and ∼145 ka BP, with ∼5–10 ka frequency inlaid within the orbitally induced ∼20-ka periodicity. The ages of the first six events in the last glacial period are therefore close to those of the coarse-grained Heinrich layers in the North Atlantic Ocean, which resulted from massive discharges of icebergs. The results indicate that the climate in the area affected by the East Asian monsoon has experienced high-frequency changes more or less synchronous with the Heinrich events. These high-frequency changes have been reported by Porter and An, based on the grain-size time series from the Luochuan loess section. Our data also reveal that similar events also occurred during the penultimate glaciation. The mechanisms linking the Heinrich events and the East Asian monsoon climate may be similar to that driving the Younger Dryas event which has been identified in a large number of records in China and in the surrounding oceans.

Nigranoic acid, a triterpenoid from Schisandra sphaerandra that inhibits HIV-1 reverse transcriptase

Abstract: An A ring-secocycloartene triterpenoid, nigranoic acid (3,4-secocycloarta-4(28),24-(Z)-diene-3,-26-dioic acid, (1) was isolated from the stems of Schisandra sphaerandra, a Chinese traditional medicinal plant. Its structure elucidation and unambiguous NMR spectral assignment were achieved by the combination of 1D- and 2D-NMR techniques with the aid of computer modeling. Nigranoic acid showed activity in several anti-HIV reverse transcriptase and polymerase assays.

Prevention of fish oil rancidity by phlorotannins from Sargassum kjellmanianum

Abstract: Known only in the Phaeophyceae, phlorotannins (brown algal polyphenols) are a class of natural products with potential uses in pharmacology This study reports that phlorotannins from Sargassum kjellmanianum can prevent fish oil from rancidification; the antioxidation activity was about 26 times higher than that of 002% BHT (tertbutyl-4-hydroxytoluene)

Grain size dependence of anatase-to-rutile structural transformation in gel-derived nanocrystalline titania powders

Abstract: Nanocrystalline materials, which are composed of ultrafine crystals with dimensions ranging from several to tens of nanometres, are currently receiving much attention by virtue of their special chemical, physical and mechanical properties, which are suited for various applications. For the past two decades, the sol-gel process has become one of the successful techniques for preparing nanocrystalline metallic oxide materials. Among these oxides, titania is a very useful material for its gas sensitivity [1, 2] and excellent dielectric properties [3], as well as having catalysis applications [4-7]. Titania has three naturally occurring polymorphs: brookite (orthorhombic, Pcab), anatase (tetragonal, I41/amd), and rutile (tetragonal, P42/mnm). Rutile is the only stable phase, whereas anatase and brookite are both metastable at all temperatures. It has been widely demonstrated that some properties of titania are very sensitive to its microstructure. For example, the anatase phase is fotmd to be a superior support of V205/TiO2 catalyst for the selective i~artial oxidation reaction relative to the rutile phase [5], while rutile phase has proved to be rauch efficient to catalyse the decomposition of H2S gas than anatase phase in nanocrystalline titania powders with approximately the same specific surface area [6]. Recently [7], it has also been found that a 70%/30% anatase/rutile mix makes the best photocatalyst for the oxidation of organics when titania was applied to the treatment of wastewater. Therefore, it is of importance to investigate, in detail, the structural transformation of the titania system. In our previous papers, we have found that the transformation behaviour of anatase-to-rutile (A ~ R) in gel-derived nanocrystalline titania powders can be affected by many factors, such as impurities [8, 9], preparation conditions [10, 11] and so on. In this letter, the grain size dependence of the A--+ R transformation is reported. Nanocrystalline titania powders were prepared by a sol-gel method [8]. Tetrabutyl titanate was used as the precursor, ethanol as the solvent and hydrochloric acid as the hydrolysis catalyst. The molar ratio of these reactants was: Ti(Osu)4:EtOH:HC1 :H20 = 1:15:0.3:1. The experimental procedure has been described in detail previously. The as-prepared dry gel was confirmed to be of amorphous structure, and then crystallized into an anatase structure after annealing at 523K for 2h. The A + R phase

Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences

Abstract: The masses of clusters of galaxies estimated by gravitational lensing exceed in many cases the mass estimates based on hydrostatic equilibrium. This may suggest the existence of nonthermal pressure. We ask if radio galaxies can heat and support the cluster gas with injected cosmic ray protons and magnetic field densities, which are permitted by Faraday rotation and gamma ray observations of clusters of galaxies. We conclude that they are powerful enough to do this within a cluster radius of roughly 1 Mpc. If present, nonthermal pressures could lead to a revised estimate of the ratio of baryonic mass to total mass, and the apparent baryonic overdensity in clusters would disappear. In consequence, $\Omega_{\rm cold}$, the clumping part of the cosmological density $\Omega_{o}$, would be larger than $0.4\,h_{50}^{-1/2}$.