Showing papers by "Chinese Academy of Sciences published in 1991"

A 13,000-year climate record from western tibet

Abstract: ALTHOUGH the Tibetan plateau is important in influencing the atmospheric circulation of the Northern Hemisphere1–3, there are only a few continuous palaeoclimate records available, and these are limited to the plateau's northeastern margin4–6. Here we present a 13,000-yr record from Sumxi Co (western Tibet), constructed from both lake-core and shoreline studies, which shows that conditions in the early–middle Holocene were warmer and wetter than at present. These results confirm model predictions of an intensified monsoon over the region at ∼9,000 yr BP, owing to an orbitally induced increase in summer insolation7,8. We also find evidence for warm, humid pulses at ∼12,500 and ∼10,000 yr BP, in phase with the steps of the last deglaciation, and for a return to cold, dry conditions at ∼11-10,000 yr BP, none of which can be explained by orbital variations. The existence of the cold episode confirms that the cooling associated with the Younger Dry as event occurred in continental China6,9, and provides further evidence of the global nature of this event10

Background concentrations of elements in soils of China

Abstract: Mean concentrations of 62 elements, pH, organic matter and grain size have been computed for soil samples from 4,095 locations throughout mainland China The compositions of geochemical data between mainland China and the conterminous United States and between Tibet and Alaska show a close correspondence for most elements determined. These geochemical data may reveal evidence of regional variations in the abundance of elements in soils. In general, the sequence for metal content in samples of soil orders was: Lithosol>Cold-highland soils>Inceptisol> Aridisol = Mollisol>Ultisol>Alfisol>Oxisol. This trend was apparently a result of climatic influence on soil genesis, with the Oxisols (high rainfall areas with highly weathered and highly leached soils) yielding the lowest elemental mean values. However, the highest mean values of most trace elements in the Lithosols were a result of its relatively high indigenous elemental contents as well as chemical properties of the bedrock from which the soils were formed.

Theory of negative differential conductivity in a superlattice miniband.

Abstract: Bloch equation conductivity perpendicular to the layers of a superlattice (period d) is evaluated using an extension of the balance-equation approach [X. L. Lei and C. S. Ting, Phys. Rev. B 32, 1112 (1985)] to narrow-band transport. The perpendicular peak drift velocity ${\mathit{v}}_{\mathit{p}}$ and the critical field ${\mathit{E}}_{\mathit{c}}$, at which the drift velocity peaks, are analyzed as functions of miniband width. Our theoretical prediction that ${\mathit{E}}_{\mathit{c}}$d increases with decreasing miniband width agrees well with the data of Sibille et al. [Phys. Rev. Lett. 64, 52 (1990)], even for the samples of narrowest miniband width in their experiment.

Noncubic symmetry in garnet structures studied using extended x-ray-absorption fine-structure spectra

Abstract: The noncubic symmetry appearing in garnets that can be represented by A3B5O12 is investigated. Extended x-ray-absorption fine-structure (EXAFS) spectra about Fe, Ga, and Y K-edge and Gd and Er L(III)-edge absorptions of Y3Fe5O12, Gd3Ga5O12, Y3Ga5O12, Y3Al5O12, and Er3Al5O12, respectively, are measured and analyzed. It is first confirmed from the results that about 10% of the A atoms exchange their sites with about 5% of the B atoms. This means, in garnet structure, 10% of the A atoms enter the (a) sites, which should be occupied by B atoms according to the crystallographic data; at the same time, those 5% of B atoms replaced by A go into the (c) sites. It is estimated that about two A and two B atoms exchange their sites with each other in a unit cell. This site exchange can be interpreted as an intrinsic characteristic of the garnet structure. Combining EXAFS results with other experimental ones on noncubic symmetry in garnets, a heuristic structural model is proposed to explain the noncubic symmetry in garnet structure tentatively, in which the atomic positions of atoms at (a) sites in four-body diagonals are shifted by small displacements and two B atoms at (a) sites in the [111] axis are assumed to be replaced by A atoms in a unit cell. Calculations of the x-ray-diffraction relative intensity are carried out with this model. The calculated results on the relations of intensities between {222} diffraction peaks, which are forbidden in cubic symmetry, are in agreement with the experimental ones for Y3Fe5O12 and Gd3Ga5O12. It is recognized that the site exchange between A and B atoms and the small displacement of atomic positions are mainly responsible for the noncubic symmetry in garnets. This noncubic symmetry can be described in R3BAR; i.e., the lowering of space-group symmetry from Ia3BARd into R3BAR occurs for the garnet structure.

Physiological properties of neurons in the mouse superior olive: membrane characteristics and postsynaptic responses studied in vitro

Abstract: 1. The physiological properties of cells in the superior olivary complex (SOC) were studied in 400-microns brain slices taken through the mouse auditory brain stem. Coronal sections were prepared f...

Electronic structure of β- BaB 2 O 4 and LiB 3 O 5 nonlinear optical crystals

Abstract: The relationship between the anionic groups of \ensuremath{\beta}-barium borate and lithium borate nonlinear optical (NLO) crystals and their bonding, electronic structure, and transmission cutoffs has been studied using the discrete variational self-consistent multipolar X\ensuremath{\alpha} method [B Delley and D E Ellis, J Chem Phys 76, 1949 (1982)] for the electronic structure of the borate anionic groups, coupled with experimental studies of the band gap, absorption edge, and valence bands, using vacuum ultraviolet spectroscopy and valence-band x-ray photoemission spectroscopy The band gap of \ensuremath{\beta}-${\mathrm{BaB}}_{2}$${\mathrm{O}}_{4}$ (BBO) is 643 eV while ${\mathrm{LiB}}_{3}$${\mathrm{O}}_{5}$(LBO) has a larger band gap of 778 eV The structures of LBO and BBO differ principally in two aspects: the bonding in the borate anionic groups, and the isolation or linkage of the anionic groups in the crystal BBO consists of (${\mathrm{B}}_{3}$${\mathrm{O}}_{6}$${)}^{3\mathrm{\ensuremath{-}}}$ anionic groups, with boron trigonally coordinated by oxygen; these groups are isolated in the crystal structure LBO, however, is based on (${\mathrm{B}}_{3}$${\mathrm{O}}_{7}$${)}^{5\mathrm{\ensuremath{-}}}$ anionic groups, with boron either trigonally or tetrahedrally coordinated by oxygen, these groups are linked throughout the crystal These structural differences between BBO and LBO lead to a larger band-gap energy in LBO The linkage of LBO's anionic groups removes states from the top of the valence band which arise from the nonbonding terminal oxygen atoms present in BBO's unlinked anionic groups and also partially removes the \ensuremath{\pi}-conjugated orbitals associated with trigonally coordinated boron-oxygen bonding The relationship between the crystal structure and the electronic structure can be seen as an extension of the molecular-engineering approach to search for additional NLO crystals in the uv range

A simple proof of the inequality MFFD(L)≤71/60 OPT(L) + 1,L for the MFFD bin-packing algorithm

Abstract: In 1985, Johnson and Garey[4] devised an algorithm which they call MFFD. Compared with other modifications of the famous FFD algorithm, their is apparently simpler in practical applications and substantially improves the worst case behavior of FFD. In fact, they proved that the inequality MFFD(L)≤71/60OPT(L)+31/6 holds for all the listsL. Their proof requires 40 pages. In this paper we give a proof for the inequality MFFD(L)≤71/60OPT(L)+1, ∀L. The proof is much simpler than theirs.

Turbulence effects on dust explosions in the 20-liter spherical vessel

Abstract: The method of collecting a large amount of data and taking ensemble average over all measurement periods using computer is employed to determine the turbulence parameters during the transient dispersion process in the 20 liter spherical vessel. The system studied is typical for laboratory pneumatic dispersion systems in explosion test vessels. Measurements show that a decaying turbulence feature is generated by the dispersion system and characterized by a decay period of 150–300 ms with the integral scale of about 1 cm and initial intensity of about 3 m/s, which has no analogue with the expected natural conditions of accidental explosions in industry. Two kinds of dust-air mixtures (aluminum and cornstarch) and methane-air mixtures, three different sizes of aluminum dust particle (5, 15, 30 μm) and one average size of corntarch dust (15 μm) are tested in this sphere. The maximum burning velocity is used instead of Kst factor to characterize the highest combustion rate occurred during the explosion process in the closed vessel for both dust and gas-air mixtures. The present experimental results demonstrate that the maximum burning velocities determined as a linear function of the initial rms turbulence velocity produced by the pneumatic dispersion system in the aluminum- and cornstarch-air mixtures. The experimental results also demonstrate that the reduction of dust particle size will increase significantly the turbulent buring velocity in dust-air mixtures, but the kind of dust seems to have no significant influence on explosion data, if their particle sizes are the same. These suggest that the dispersion induced turbulence may play more important role in formation of dust-air mixtures than in direct effect dust combustion process, and that the influence of the above turbulence on the combustion characteristics mainly enters through the mechanisms of creating uniform suspension of dust clouds.

Subsolidus Phase Relationships in Part of the System Si,Al,Y/N,O: The System Si3N4─AIN─YN─Al2O3─Y2O3

Abstract: The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty-nine compatibility tetrahedra were established in the region Si3N4─AIN─Al2O3─Y2O3. The subsolidus phase relationships in the region Si3N4─AIN─YN─Y2O3 have also been studied. Only one compound, 2YN:Si3N4, was confirmed in the binary system Si3N4─YN. The solubility limits of the α′─SiAION on the Si3N4─YN:3AIN join were determined to range from m= 1.3 to m= 2.4 in the formula Ym/3Si12-mAlmN16. No quinary compound was found. Seven compatibility tetrahedra were established in the region Si3N4─AIN─YN─Y2O3.

Antidotal effects of dimercaptosuccinic acid

Abstract: Dimercaptosuccinic acid (DMS), HOOC-CH(SH)-CH(SH)-COOH, was first developed in China as an effective antidote for poisoning from many heavy metals, such as Pb, Hg, As, Cd, Sb, TI, Au, Zn, Ni, Pt, Ag, Co and Sn DMS increases the excretion of Ce, Pm, Sr and Po from the body Hundreds of patients suffering from hepatolenticular degeneration (Wilson's disease) have been treated successfully with DMS Recently, DMS was found to be effective also in treating certain non-metallic intoxications, like some of the new non-phosphate pesticides and mushroom poisonings

A simple method for prediction of gas-permeability of polymers from their molecular-structure

Abstract: A method for the prediction of gas permeabilities (P) through polymers from their chemical structure has been developed on the basis of the ratio of molar free volume to molar cohesive energy, V(f)/E(coh) The permeation of small gas molecules through polymer membranes is dependent on the chain packing density measured by V(f) and segmental motion of polymer chains measured by E(coh) But no simple relationship between P and V(f) or E(coh) alone was found The permeability data of more than 60 polymers covering 7 orders of magnitude for six gases have been treated with linear regression analysis All plots of log P vs V(f)/E(coh) gave good straight lines It is also found that a linear relationship holds when plotting both the intercepts and slopes of log P vs V(f)/E(coh) lines against square of the diameters of gas molecules Therefore, the permeabilities of all the non-swelling gases through a great variety of polymers can be estimated using two correlations above Moreover, this method is more accurate than others in the literature and may found useful for the selection of gas separation or barrier membrane materials

Selenium in geo-ecosystem and its relation to endemic diseases in China

Abstract: In China, Se deficiency is associated with Keshan disease and Kaschin-Beck disease. This paper further demonstrates this relationship by studying the Se levels in the geo-ecosystem substances, including soil, plant, herbage, food grain, wool and human hair in disease affected areas and in control non-disease areas. Buteha Qi and Tailai counties in Northeast China were selected as the typical areas for these studies. The results show that in affected areas the average Se contents were: for soil, 0.125mg kg1, plants, 0.057 mg kg−1; herbage, 0.026 mg kg1; wheat, 0.012 mg kg−1; maize, 0.008 mg kg1; wool, 0.046 mg kg−; and human hair, 0.144 mg kg1. In the control area, the substances mentioned above all had higher Se contents compared with those in the affected area. Thus, it was shown that the geo-ecosystem of the affected area was low in Se, an important reason for the occurrence of Keshan disease and Kaschin-Beck disease. In recent years, some increase in the Se level of human hair was also found in the studied areas. This increase coincides with the decline, since the mid 1980's, of the incidence of the two diseases. An elevation in hair Se may, therefore, be a good indication of an improved Se intake of the subject population.

Preparation and immobilization of polymer-protected bimetallic colloids

Abstract: Co-reduction of mixed metal ions of platinum-rhodium or rhodium-gold by refluxing its alcohol ic solution in presence of a protective polymer results in a corresponding stable bimetallic sol, which in turn interacts with a suspension of silica gel, bearing thioether ligand, to give supported bimetallic catalysts. The TEM and XRD measurements indicate the formation of the bimetallic alloy clusters. The sols are used as catalysts for the selective partial hydrogenation of cis, cis-1.5-cyclooctadiene to cyclooctene. The bimetallic sol catalyst PVP-Pt-Rh shows an activity which is about twice as that of the monometallic sol PVP-Rh.

Anisotropic thermal conductivity of the 2D single quasicrystals: Al65Ni20Co15 and Al62Si3Cu20Co15.

Abstract: The anisotropic thermal conductivity of Al65Ni20Co15 and Al62Si3Cu20Co15 single quasicrystals has been measured. While a nearly isotropic phonon contribution was observed, the electronic thermal conductivity is almost completely suppressed in the quasicrystalline plane in contrast to the periodic direction where the materials behave like the usual 3D alloy except for a markedly lower electronic contribution.

Simultaneous multiple wavelength laser action in various neodymium host crystals

Abstract: The oscillation condition of a simultaneous multiple wavelength laser has been established and used to analyze the possibility of simultaneous oscillation in various neodymium host crystals, such as Nd:YAG, Nd:YLF, Nd:BEL, and Nd:YAP crystals at the transitions from /sup 4/F/sub 3/2/-/sup 4/I/sub 13/2/ and /sup 4/F/sub 3/2/-/sup 4/I/sub 11/2/. It is shown that this kind of laser can be realized in all the described crystals in a pulsed state. In general, continuous wave (CW) operation, however, can only be achieved for Nd:YAP. On the basis of these results, CW simultaneous double wavelength lasing has been achieved in a Nd:YAP crystal for the first time at both 1.0795 mu m and 1.314 mu m. >

Sintering Behavior of Fully Agglomerated Zirconia Compacts

Abstract: Fully agglomerated superfine zirconia powders were prepared with the coprecipitation and spray-drying method. The compaction of such powders shows no fragmentation of the agglomerates. The sintering behavior of the compacts was studied and two sintering stages were identified: densification within agglomerates at temperatures not higher than 1250°C and the removal of interagglomerate pores at temperatures above 1600°C. The interagglomerate pores are difficult to remove, and sintering between agglomerates even at 1600°C is still insignificant. Heating of the compacts at temperatures above 1600°C leads only to grain growth and the entrapping of pores in large grains.

Immunomodulating Chinese herbal medicines

Abstract: Traditional Chinese medicine always pays close attention to the strengthening of the patient's general resistance against illness, there are many Chinese herbs used for thousands of years are considered as tonics. Animal experiments and modern clinical trails have shown that quite a number herbs are immunologically active, and most of the tonics are excellent immunomodulating agents, such as polysaccharides or saponins isolated from Astragalus mongholicus, Acanthopanax senticosus and Panax notoginseng, which stimulated macrophages, promoted antibody formation, activated complement and increased T lymphocyte proliferation. Moreover, some of them were proved to be anti-irradiative and protected animals from liver intoxications. On the other hand, some anti-inflammative or anti-pyretic herbs such as Tripterygium wilfordii, Aconitum and Artemisiae species were proved to have immunosuppressive principles, some of them were now used clinically for the treatment of rheumatoid arthritis, chronic nephritis, systemic lupus erythematosis and various skin disorders. Pharmacological studies revealed that they have depressant effect on most of the humoral-immunity but not on the cell-mediated immunity. Some of them stimulated adrenal cortex functions and prolonged the survival time of transplanted allograft tissues.

Characterization of LiB(3)O(5) crystal for second-harmonic generation.

Abstract: We present second-harmonic generation characteristics of LiB(3)O(5) (LBO) crystal with different phase-matching lengths and comparison with those of beta-BaB(2)O(4) crystal. A computer program of the numerical interaction method was adopted to make the theoretical calculation of second-harmonic generation conversion efficiencies of LBO with different phase-matching lengths and power densities of the fundamental beam of a Nd:YAG laser, and the calculated result was compared with the experimental one. It is seen from the calculated and experimental results that for certain power densities of the fundamental laser beam, so long as the length of the LBO crystal is selected appropriately, a high energy conversion efficiency could be obtained. For example, an optimal external energy conversion efficiency of LBO crystal of more than 70% has been attained for several 100-MW/cm(2) fundamental laser beams. Experiments also showed that the crystal could be used under high power densities without any damage to the surface and the interior.