Showing papers by "Chinese Academy of Sciences published in 1990"

Mathematics achievement of children in China and the United States.

Abstract: First and fifth graders in Beijing and Chicago were given a battery of mathematics test. Whether tested with problems requiring solely computation or with ones requiring application of knowledge about mathematics, American children's performance was consistently inferior to that of Chinese children. Interviews with American children suggested that they like mathematics, believe they are doing well in mathematics, and do not perceive mathematics as a difficult subject. American children's poor performance appears to be attributable, in part, to low motivation for devoting more attention to mathematics. Low standards held by American parents for academic achievement and lower interest in teaching mathematics by American teachers appear to contribute to American children's poor performance.

The synaptic organization of the dopaminergic amacrine cell in the cat retina.

Abstract: The dopaminergic amacrine cells of the cat retina have been stained by immunocytochemistry using an antibody to tyrosine hydroxylase (Toh). The complete population of Toh+ cells has been studied by light microscopy of retinal wholemounts to evaluate morphological details of dendritic structure and branching patterns. Selected Toh+ amacrine cells have been studied by serial-section electron microscopy to analyse synaptic input and output relationships. The majority of Toh+ amacrine cells occur in the amacrine cell layer of the retina and have their dendrites ramifying and forming the characteristic rings in stratum 1 of the inner plexiform layer. A minority of Toh+ cells have cell bodies displaced to the ganglion cell layer but their dendrites also stratify in stratum 1. All Toh+ cells have some dendritic branches running in stratum 2 as well as in stratum 1, and frequently they have long 'axon-like' processes (500-1000 microns long) dipping down to run in stratum 5 before passing up to rejoin the major dendritic arbors in stratum 1. In addition Toh+ stained processes follow blood vessels in the inner plexiform layer and in the ganglion cell layer. A population of Toh+ cells found in the inferior retina appears to give rise to stained processes that pass to the outer plexiform layer and therein to run for as far as one millimeter. Electron microscopy reveals that Toh+ amacrine cells are postsynaptic to amacrine cells and a few bipolar cell terminals in stratum 1 of the inner plexiform layer and are primarily presynaptic to AII amacrine cell bodies and lobular appendages, and to another type of amacrine cell body and amacrine dendrites hypothesized to be the A17 amacrine cell. The Toh+ dendrites in stratum 2 are presynaptic to AII lobular appendages primarily. Stained 'axon-like' processes running in stratum 5 prove to be presynaptic to AII amacrine dendrites as they approach the rod bipolar axon terminals and they may also be presynaptic to the rod bipolar terminal itself. The Toh+ stained dendrites that have been followed in the outer plexiform layer run along the top of the B-type horizontal cell somata and may have small synapses upon them. The only clear synapses seen in the outer plexiform layer are from the Toh+ profiles upon vesicle filled amacrine-like profiles that are in turn presynaptic to bipolar cell dendrites in the outer plexiform layer. We presume the cells postsynaptic to the Toh+ dendrites in the outer plexiform layer are interplexiform cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Urban heat islands in China

Abstract: We used 1954–1983 surface temperature from 42 Chinese urban (average population 1.7*106) and rural (average population 1.5*105) station pairs to study the urban heat island effects. Despite the fact that the rural stations are not true rural stations, the magnitude of the heat islands was calculated to average 0.23 °C over the thirty-year period with a minimum value during the 1964–1973 decade and maximum during the most recent decade. The urban heat islands were found to have seasonal dependence which varied considerably across the country. The urban heat islands also had a strong regional dependence with the Northern Plains dominating the magnitude of the heat islands. The changes in heat island intensity over three decades studied suggest a general increase in heat island intensity of about 0.1°C, but this has not been constant in time. These results suggest that caution must be exercised when attributing causes to observed trends when stations are located in the vicinity of metropolitan areas.

Phase stability and electronic structure of ScAl3 and ZrAl3 and of Sc-stabilized cubic ZrAl3 precipitates.

Abstract: The structural stability and the electronic structure of ${\mathrm{ScAl}}_{3}$ were studied using an all-electron, total-energy, local-density approach. The calculated results show that ${\mathrm{ScAl}}_{3}$ in the L${1}_{2}$ structure is energetically favored compared with the D${0}_{22}$ structure by about 0.42 eV per formula unit. The calculated lattice constant (4.055 \AA{}) is in fairly good agreement with experiment (4.10 \AA{}). As a comparison, the calculated electronic and cohesive properties for ${\mathrm{ZrAl}}_{3}$ in its metastable L${1}_{2}$ and D${0}_{22}$ phases are also presented. It is argued, on the basis of density-of-states results, that a cubic ${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sc}}_{\mathit{x}}$${\mathrm{Al}}_{3}$ compound (and also ${\mathrm{Ti}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sc}}_{\mathit{x}}$${\mathrm{Al}}_{3}$) might be a good candidate as a dispersed phase in the aluminum alloys for elevated temperature applications. To test this prediction, we determined the electronic structure and the stability of Sc-stabilized cubic (${\mathrm{Zr}}_{0.5}$${\mathrm{Sc}}_{0.5}$)${\mathrm{Al}}_{3}$ using the same total-energy approach. The calculated total energy for (${\mathrm{Zr}}_{0.5}$${\mathrm{Sc}}_{0.5}$)${\mathrm{Al}}_{3}$, which is about 0.24 eV per unit cell lower than the sum of the total energies of ${\mathrm{ZrAl}}_{3}$ and ${\mathrm{ScAl}}_{3}$, clearly indicates that cubic (${\mathrm{Zr}}_{0.5}$${\mathrm{Sc}}_{0.5}$)${\mathrm{Al}}_{3}$ is energetically favored compared with a mixture of its constituents. Finally, an analysis of the results indicates that the stability of the aluminides appears to be understood in the rigid-band sense in terms of the band filling of the bonding states.

Isolation and characterization of beta-actin gene of carp (Cyprinus carpio).

Abstract: A beta-actin gene of carp (Cyprinus carpio) was isolated from a genomic EMBL3 library. The nucleotide sequence of the gene indicates six exons spanning 3.6 kb. Southern blot hybridization of restriction endonuclease digests of carp genomic DNA indicate that there are two copies of the beta-actin isotype and several other species of actin genes. The transcriptional start site is 85 bp and 24 bp downstream respectively from consensus CCAAT and TATA promoter elements. The organization of the carp beta-actin gene is identical to that of chicken, human, and rat genes in terms of size, exon/intron locations and junctions and in having a translationally silent first exon. The fish gene is 90% and 99% conserved at the nucleotide and amino acid levels, respectively, with land vertebrate beta-actin genes. Northern blot analysis of beta-actin gene expression indicated that the gene is highly expressed in brain, less so in muscle, and much less so in liver cells. The putative beta-actin proximal promoter of carp, identified by the conservation of known actin regulatory sequences, is transcriptionally active in both mammalian and piscine cells.

Giant Al-M (M=transitional metal) crystals as Penrose-tiling approximants of the decagonal quasicrystal

Abstract: The two-dimensional decagonal quasicrystal has been found in many Al-M (M=transitional metal) alloys, very often coexisting with a large-unit-cell phase of similar composition and local structure. By introducing phasons in two orthogonal directions in the quasiperiodic plane perpendicular to the periodic tenfold axis, i.e., approximating the irrational golden mean \ensuremath{\tau} with rational ratios of two consecutive Fibonacci numbers ${\mathit{F}}_{\mathit{n}+1}$/${\mathit{F}}_{\mathit{n}}$, the Penrose pattern in this plane gradually becomes periodic with fairly large unit-cell parameters (1--3 nm). Some giant Al-M crystals with cubic, orthorhombic, and monoclinic symmetries have thus been derived as Penrose-tiling approximants of the decagonal quasicrystal, and their simulated electron diffraction patterns agreed fairly well with experiments.

Phase stability and magnetism of Ni3Al.

Abstract: The structural phase stability of ${\mathrm{Ni}}_{3}$Al is investigated for its cubic (L${1}_{2}$), tetragonal (D${0}_{22}$), and hexagonal (D${0}_{19}$) crystal structures with use of an all-electron total-energy local-density-functional approach. In agreement with experiment, the (weakly) ferromagnetic L${1}_{2}$ structure is found to be the most stable phase. The calculated lattice constant (3.55 \AA{}), the bulk modulus (2.1 Mbar), and the heat of formation (44.8 kcal/mol) are in fairly good agreement with experiment. The second-nearest-neighbor coupling between Ni d and Ni d states and the (higher-order) nearest-neighbor coupling between Ni d and Al p states may play an important role in accounting for the structural stability of ${\mathrm{Ni}}_{3}$Al. The inclusion of spin-orbit coupling is found to reduce the exchange-energy splitting and magnetic moment by \ensuremath{\sim}40%.

Five-dimensional structure refinement of decagonal Al65 Cu20 Co15

Abstract: A single-crystal X-ray structure analysis of decagonal Al65 Cu20Co15 has been performed using the n-dimensional approach. The structure has been solved by Patterson analysis and subsequent least-squares refinement, both in the five-dimensional description. A final value of wR=0.097 for 259 independent reflections was achieved with I≥2σ(1) and 12 variables. There are three atoms in the asymmetric unit. The calculated density of the refined, structure model is ρc = 4.8 M gm −3. The three-dimensional decagonal structure consists of two planar quasiperiodic layers, related by the tenfold screw axis, stacked periodically one upon the other. Characteristic large elements of the crystalline Al13 Fe4 structure type can be found in new combinations in the quasiperiodic layers. It is remarkable that pentagonal channels appear which are empty or occupied statistically.

Beta-globin locus activation regions: conservation of organization, structure, and function.

Abstract: The human beta-globin locus activation region (LAR) comprises four erythroid-specific DNase I hypersensitive sites (I-IV) thought to be largely responsible for activating the beta-globin domain and facilitating high-level erythroid-specific globin gene expression. We identified the goat beta-globin LAR, determined 10.2 kilobases of its sequence, and demonstrated its function in transgenic mice. The human and goat LARs share 6.5 kilobases of homologous sequences that are as highly conserved as the epsilon-globin gene promoters. Furthermore, the overall spatial organization of the two LARs has been conserved. These results suggest that the functionally relevant regions of the LAR are large and that in addition to their primary structure, the spatial relationship of the conserved elements is important for LAR function.

Portal dose images. II: Patient dose estimation.

Abstract: Due to the many sources of uncertainties in radiotherapy, conventional treatment planning can only provide a nominal presentation of the dose delivered to the patient. Provided that large setup errors can be detected and corrected, we propose that measured and calculated portal dose images can be used to improve estimation of patient dose. The iterative approach described in this paper requires an accurate method of dose calculations, 3-dimensional CT data that closely represents the patient and the measured portal dose image. From the CT data, a portal dose image is calculated for comparison with the measured one. The differences are then used to modify the original CT data so that a new image can be calculated. The process is repeated until the calculated and measured images agree to satisfaction. At that point, the internal dose is calculated using the modified CT data. If the method is successful, daily portal dose images could be used to cumulatively estimate patient dose throughout the course of treatment. This manuscript describes 60Co simulation results to demonstrate the feasibility of the approach.

Transmission fluctuations across an array and heterogeneities in the crust and upper mantle

Abstract: Adopting the spectral approach, we derive the formulation of angular coherence and transverse coherence of transmission fluctuations. Our derivation and results provide new insight on transmission fluctuation analysis. A review of research work on fluctuation analysis using observations at large seismic arrays such as LASA and NORSAR-follows. We point out that the model of a single-layer Gaussian medium cannot explain the angular coherence of NORSAR data and a more general model of a non-Gaussian, multi-scale, vertically inhomogeneous random media is needed. The model of a two-layer power-law medium proposed by Flatte and Wu is among the simplest of such models.

A VLSI design for computing exponentiations in GF(2/sup m/) and its application to generate pseudorandom number sequences

Abstract: A VLSI design for computing exponentiation in finite fields is developed. An algorithm to generate a relatively long pseudorandom number sequence is presented. It is shown that the period of this sequence is significantly increased compared to that of the sequence generated by the most commonly used maximal length shift register scheme. >

Multi-stage symplectic schemes of two kinds of Hamiltonian systems for wave equations

Abstract: Multi-stage schemes for wave equation are constructed. Their stability conditions are discussed.

Crystal structure of melamine cyanuric acid complex (1:1) trihydrochloride, MCA·3HCl

Abstract: C 3 H 6 N 6 •C 3 H 3 N 3 O 3 •3HCl cristallise dans C2/c avec a=9,853, b=15,305 et c=10,082 A, β=81,28°, Z=4; affinement jusqu'a R=0,041•MCA•3HCl a une construction lamellaire, comme la plupart des lubrifiants solides

Measurement of the refractive index and thermal refractive index coefficients of Nd:YAP crystal.

Abstract: The principal refractive indices of yttrium aluminate crystal doping with 1-wt.% neodymium (Nd:YAP) have been measured by a minimum deviation method for the wavelengths 0.5398, 0.6328, and 1.0795 microm in the temperature range of 289-435 K. The thermal refractive index coefficients have been obtained at these wavelengths, and they are all positive and slightly decrease with increased wavelength. The constants of the single term Sellmeier equation are also given for the 273-420 K temperature range. These constants are in linear relationship with temperature in the 4 x 10(-3) error range.

An experimental study of complex response in river channel adjustment downstream from a reservoir

Abstract: An experimental study is described which attempts to reveal the complex response process of river channel adjustment downstream from a reservoir. A descriptive model has been established which identifies three adjustment stages. In stage I following the change of water and sediment input, the width-depth ratio of river channel (w/d) and the river channel gradient (s) both decrease, but the river channel sinuosity (r) increases. In stage II, because of feedback from the changing boundary conditions, w/d starts to increase, r decreases, and the rate of gradient decrease becomes very slow. In stage III, equilibrium is reestablished, w/d, r, and s tend to constant values, and the system recovers its stable state.

Anisotropic transport properties of a stable two-dimensional quasicrystal: Al62Si3Cu20Co15.

Abstract: The anisotropic nature of the transport properties in a two-dimensional quasicrystal has been observed for the first time. The resistivity depends linearly on temperature from 80 K up to 400 K for both the crystalline and quasicrystalline directions but with opposite temperature coefficients. The thermopower is positive in the crystalline direction and negative in the quasicrystalline plane. the results are discussed in connection with the anisotropy of band structure, scattering characteristics, and defects formation.

A note on the continuity of solutions of parametric linear programs

Abstract: This note shows that, if a parametric linear program, min{cx: Ax = b1θ+b2,x≥0}, has optimal solutions in an interval\(\left[ {\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{\theta } ,\bar \theta } \right]\) forθ, then, depending on degeneracy, the solutions(θ) is a continuous vector function or a continuous point-to-set mapping. In the latter case an algorithm is introduced to solve the problem and generate a continuous vector solution in\(\left[ {\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{\theta } ,\bar \theta } \right]\).