Showing papers by "Chinese Academy of Sciences published in 1989"

New nonlinear-optical crystal: LiB 3 O 5

Abstract: The boron–oxygen compound LiB3O5 is recognized as a new nonlinear-optical crystal. This follows theoretical calculations of the second-harmonic generation (SHG) coefficients using the anionic group theory and the complete neglect of differential overlap approximation to obtain the localized wave functions of component groups. An optically perfect single crystal with space group Pna21, grown at the Fujian Institute of Research on the Structure of Matter by the high-temperature flux method, is found to be transparent from 160 nm to 2.6 μm. It has a SHG coefficient comparable with that of β-BaB2O4 as well as two other outstanding advantages: a high damage threshold of 25 GW/cm2 (at 1.064 μm, 0.1 nsec) and a wide acceptance angle of 25 mrad for θ ≠ 90° and 95 mrad for θ = 90° with a 6-mm-long crystal.

Kinking of A Crack Out of AN Interface

Abstract: Kinking of a plane strain crack out of the interface between two dissimilar isotropic elastic solids is analyzed. The focus is on the initiation of kinking and thus the segment of the crack leaving the interface is imagined to be short compared to the segment in the interface. Accordingly, the analysis provides the stress intensity factors and energy release rate of the kinked crack in terms of the corresponding quantities for the interface crack prior to kinking. Roughly speaking, the energy release rate is enhanced if the crack heads into the more compliant material and is diminished if it kinks into the stiff material. The results suggest a tendency for a crack to be trapped in the interface irrespective of the loading when the compliant material is tough and the stiff material is at least as tough as the interface.

The anionic group theory of the non-linear optical effect and its applications in the development of new high-quality NLO crystals in the borate series

Abstract: Starting from a general quantum-mechanical perturbation theory on the nonlinear optical (NLO) effect in crystals, this review gives a systematic presentation of the basic concepts and calculation methods of the ‘anionic group theory for the NLO effect of crystals’ and a brief discussion of the approximations involved. Calculations have been made for the second harmonic generation (SHG) coefficients of a few typical NLO crystals. Comparisions between these theoretical values and the experimental values made both on powdered crystals and on single crystals suffice to show the feasibility of the theoretical treatment and calculation methods. On this basis, borate ions of various structure types are classified and systematic calculations are carried out for the NLO susceptibilities of some typical borate crystals with good prospects of applications in opto-electronics. Through these calculations, a series of structural criteria serving as useful guidelines for searching and developing new NLO crystal...

Electronic-structures of zero-dimensional quantum wells

Abstract: Les structures electroniques des puits quantiques de dimension nulle sont etudies a l'aide d'un modele spherique dans le cadre de la theorie de la masse effective L'effet de melange des trous lourds et legers est pris en compte, et on obtient la classification de la symetrie et les niveaux d'energie des etats de trou On calcule les energies des etats des donneurs et accepteurs

Mew nonlinear optical crystal LiB3O5

Abstract: As another new high quality nonlinear optical (NLO) crystal of the borate series, lithium triborate LBO has been characterized in our Fujian Institute. This follows theoretical calculations of the second harmonic generation (SHG) coefficients on the basis of the anionic group theory (which has been generalized into a general NLO active group theory) with the GNDO approximation. This leads to localized wave functions for the component active anionic group (B3O7)5− and the resultant anionic group (B3O5)−.

Electronic structures of superlattices under in-plane magnetic field

Abstract: The electronic structures of superlattices under an in-plane magnetic field are studied by the method of expansion with sine functions. The electronic and hole magnetic energy levels are obtained as functions of ${k}_{x}$,${k}_{y}$ and the intensity of the magnetic field. The density of states and the magnetic-optical transition matrix elements are discussed. The variations of the binding energy of the heavy- and light-hole magnetic excitons with the magnetic field and the well width are also obtained. Finally, the electronic energy levels in the magnetic field along an arbitrary direction in the yz plane are calculated.

Highly efficient ultraviolet generation at 355 nm in LiB(3)O(5).

Abstract: Highly efficient generation of UV radiation at 355 nm has been achieved in a LiB(3)O(5) crystal through the frequency mixing of the fundamental and second-harmonic radiation of a Nd:YAG laser. An energy conversion efficiency of 60% has been obtained under the experimental conditions described here. Thus the usefulness of LiB(3)O(5) for frequency-conversion applications is demonstrated.

Beta-crystalline form of isotactic polypropylene and method for forming the same

Abstract: This invention relates to obtaining beta crystalline Phase isotactic polypropylene with high purity and thermal stability simply by melt-crystallization in the presence of a two component beta nucleating agent. The two component beta-nucleating agent is formed by mixing 0.0001-1 weight % of dibasic acid with 0.001-1 weight % oxide, hydroxide or acid salt of a Group IIA metal. Such beta phase polypropylene can be used for the production of high impact strength molding extrusion shapes, microporous film and microporous hollow fiber.

The Perturbation Method in Elastic Wave Scattering

Abstract: Methods of theoretical study in seismic wave scattering are reviewed with the emphasis on the perturbation method. Detailed analysis for weak scattering using Born approximation is given. For elastic random media, the mean square amplitudes of scattered waves are derived using a new approach by working directly in the spectrum domain. The conditions for the scalar wave approximation are obtained. The problem of sensitivity of fore- and backscattering to heterogeneities with different scales and properties (velocity or impedance) is discussed.

Location of double bonds in fatty acids of fish oil and rat testis lipids. Gas chromatography-mass spectrometry of the oxazoline derivatives.

Abstract: A new approach to the derivatization and analysis of long chain polyunsaturated fatty acids is described. The method is based on the formation of 2-alkenyl-4,4-dimethyloxazolines by condensation of the starting material with 2-amino-2-methylpropanol. The derivatization method is rapid, efficient and specific with respect to the chain feature of the parent acids. Volatility, comparable with that of the corresponding simple esters, and improved gas chromatographic separation are achieved without difficulty. The derivatives exhibit clear and regular fragmentation patterns that allow easy discrimination of positional isomers and assignment of double bond location in the chain.

Two-dimensional riemann problem for a single conservation law

Abstract: On construit les solutions d'entropie pour l'equation aux derivees partielles (∂/∂t)u(t,x,y)+(∂/∂x)f(u(t,x,y))+(∂/∂y)g(u(t,x,y))=0 avec donnees initiales constantes dans chaque quadrant du plan (x,y). Ces solutions sont lisses par morceaux sous la condition f″(u)¬=0, g″(u)¬=0 (f″(u)/g″(u))'¬=0

Self-focusing and self-trapping in new types of Kerr media with large nonlinearities.

Abstract: Self-focusing and self-trapping of light in common liquid media such as Chinese tea, Chinese herbal medicine, and solutions of chlorophyll have been observed. These materials are found to be new types of natural Kerr media, and their nonlinear coefficients have been determined. Laser-heating-induced self-phase modulation in these materials has also been observed.

The vegetation of post-logged black spruce lowlands in central canada. ii. understorey vegetation

Abstract: SUMMARY (1) Logged Picea mariana-dominant stands in lowland north-eastern Ontario, Canada, were surveyed to examine patterns of vegetation recolonization and to assess the extent of successional return towards the pre-logged condition. (2) A data table of 244 plant species in 122 stands, incorporating a chronosequence spanning 56 years, was analysed by two-way indicator species analysis (TWINSPAN). This yielded four stand classes; two primary groups representing stands of nutrient-rich and nutrient-poor sites and two subgroups where stands had been logged either using horseskidding methods or by mechanical wheel skidding. (3) Ordination by detrended correspondence analysis (DCA) of the same data supported the TWINSPAN results. Separate ordinations of data from the horse and wheelskidded stands showed little relationship between variation in vegetation composition and time since logging, indicating that the nature of the disturbance was important in determining subsequent vegetation cover. However, successional trends could not be ruled out because stand age and skidding were confounded. (4) Comparison of the four logged stand groups with five groups (sixty-nine stands) of unlogged wetland forest vegetation from the same region yielded a strong two-gradient model related to site nutrient regime and intensity of disturbance and/or time elapsed since disturbance. This is interpreted in terms of site nutrient status, skidding method and nonconvergent successional pathways. (5) Although firstly, compositional change with time was ascribed primarily to the moss species in earlier postfire studies, post-logging tree recruitment was low in all stands, which will have inhibited moss establishment. However, the understorey rhizomatous perennial vascular plants of the pre-logged forest had resprouted and persisted in the open for many years. (6) Secondly, competitive broadleaved shrub species had invaded and dominated for a long period on the mechanically-skidded, nutrient-rich sites. (7) Thirdly, exposed peat remained uncolonized for several years on the mechanicallyskidded, nutrient-poor sites, because only slow growing, nutrient stress-tolerant plants can survive in such habitats. (8) A graphical model, predicting the recolonization patterns of the major plant groups of logged, boreal wetland forest sites in central Canada, is proposed.

Thermodynamic stability and statistical significance of potential stem-loop structures situated at the frameshift sites of retroviruses

Abstract: RNA stem-loop structures situated just 3' to the frameshift sites of the retroviral gag-pol or gag-pro and pro-pol regions may make important contributions to frame-shifting in retroviruses. In this study, the thermodynamic stability and statistical significance of such secondary structural features relative to others in the sequence have been assessed using a newly developed method that combines calculations of the lowest free energy of formation of RNA secondary structures and the Monte Carlo simulations. Our results show that stem-loop structures situated just 3' to the frameshift sites are both highly stable and statistically significant relative to others in the gag-pol or gag-pro and pro-pol junction domains (both 300 nucleotides upstream and downstream from the possible frameshift sites are included) of Rous sarcoma virus (RSV), human immunodeficiency virus (HIV-1), bovine leukemia virus (BLV), human T-cell leukemia virus type II (HTLV-II), and mouse mammary tumor virus (MMTV). No other more stable, or significant folding regions are predicted in these domains.

Impact of tillage practices on microbial biomass carbon in top layer of black soils

Abstract: A study was conducted on a long-term (13 years) tillage and rotation experiment on black soil in northeast China to determine the effects of tillage, time and soil depth on soil microbial biomass carbon (MBC). Tillage systems included no tillage (NT), ridge tillage (RT) and mould-board plough (MP). Soil sampling was done at 0-5, 5-10 and 10-20 cm depths in June, August and September, 2013, and April, 2014 in the corn phase of corn-soybean rotation plots. MBC content was measured by the chloroform fumigation extraction (CFE) method. The results showed that the MBC content varied with sampling time and soil depth. Soil MBC content was the lowest in April for all three tillage systems, and was highest in June for MP, and highest in August for NT and RT. At each sampling time, tillage system had a significant effect on soil MBC content only in the top 0-5 cm layer. The MBC content showed obvious stratification under NT and RT with a higher MBC content in the top 0-5 cm layer than under MP. The stratification ratios under NT and RT were greatest in September when they were respectively 67.8% and 95.5% greater than under MP. Our results showed that soil MBC contents were greatly affected by the time and soil depth, and were more apparently accumulated in the top layer under NT and RT.

Acid‐base balance in aerosol components of the Asia‐Pacific region

Abstract: We have estimated for remote areas the potential extent of neutralization and solubilization of alkaline aerosol by sulfuric acid through atmospheric uptake of acidic sulfur gases by dust particles. Aerosol components were resolved from time sequence measurements of elemental composition in Nuclepore filter samples from 5 locations in the Asia-Pacific region, using factor analysis and multiple linear regression applied to data sets of 66–229 steps of 2.4–4.0 hours each, representing 526 analyses for 7–12 elements. Each component was evaluated for chemical equivalent concentrations of sulfur and alkaline mineral elements. Two or three factors accounted for 87–97% of the variance of each set, consistent with a model of linear mixing of components for most observed variability and resulting in 12 components that may represent a broad range of aging, from recently generated soil dust to particles exposed to trace SO 2 or other sulfur gases for a week or longer. Virtually no aerosol sulfur was found without being associated with soil elements. All 12 components contained statistically significant amounts of both sulfur and alkaline elements in relative proportions that suggest two rate limitations on acidic gas uptake: neutralization of rapidly reacting bases, mainly CaCO 3 , and gradual neutralization of slowly reacting bases, mainly clay minerals, by H 2 SO 4 after SO 2 uptake. After each stage of titration in the atmosphere, further gas uptake may be inhibited by an acidic particle surface. The resolved aerosol components show cases approaching both stoichiometric limits, but no case of excess sulfur beyond the second limit, consistent with these being practical limits in the remote areas investigated. If mineral aerosols are solubilized by strongly acidic surface solutions at ambient relative humidities, as suggested by these results, subsequent deposition to ocean, fresh water, or land surfaces may be more important inputs of nutrient or toxic metal ions than deposition of insoluble mineral particles or of wet or dry deposition of acids followed by dissolution of particles in seawater or leaching of soils. DOI: 10.1111/j.1600-0889.1989.tb00311.x