Showing papers by "Academia Sinica published in 1986"

Basic principles of mechanical theorem proving in elementary geometrics

Abstract: At the end of 1976 and the beginning of 1977, the author discovered a mechanical method for proving theorems in elementary geometries. This method can be applied to various unordered elementary geometries satisfying the Pascalian Axiom, or to theorems not involving the concept of ‘order’ (e.g., thatc is ‘between’a andb) in various elementary geometries. In Section 4 we give the detailed proofs of the basic principles underlying this method. In Sections 2 and 3 we present the theory of well-ordering of polynomials and a constructive theory of algebraic varieties. Our method is based on these theories, both of which are based on the work of J. F. Ritt. In Section 5 we use Morley's theorem and the Pascal-conic theorem discovered by the author to illustrate the computer implementation of the method.

Leaf carbon isotope and mineral composition in subtropical plants along an irradiance cline

Abstract: Leaf carbon isotope ratios and leaf mineral composition (Ca, K, Mg, Mn, N, and P) were measured on the dominant species along an irradiance cline in a subtropical monsoon forest of southern China. This irradiance cline resulted from disturbance caused by fuel-harvesting. Leaf carbon isotope ratios increased from undisturbed to disturbed sites for all species, indicating that leaf intercellular CO2 concentrations decreased and leaf water use efficiencies increased along this cline. Nitrogen and magnesium levels were lower in leaves of species on the disturbed sites, but there were no clear patterns for calcium, potassium, phosphorus or manganese.

On the Existence of Positive Entire Solutions of a Semilinear Elliptic Equation

Abstract: Under suitable hypotheses we obtain various theorems concerning the existence of positive solutions of the equation $$\Delta u{\text{ }} - {\text{ }}u{\text{ }} + {\text{ }}Q{\text{(}}x{\text{) }}u^p {\text{ = 0}}$$ in ℝn, where p>1 and Q(x) is a given potential. If Q is radially symmetric, our result is particularly simple and general. We also study symmetries of solutions of the above equation in a ball with the boundary condition u = 0.

Palaeoclimatic and sedimentary history from magnetic susceptibility of loess in China

Abstract: The magnetostratigraphic age of the oldest loess sediments in the central Chinese loess plateau investigated so far has recently been placed at ca. 2.4 million years B.P. Thus, glaciations in Central Asia, which are believed to provide the detritus for the formation of Chinese loess, commenced at the same time as the first ice-rafted debris sank into the ocean basins of the northern hemisphere [Shackleton et al., 1984], Lithologic, palaeontologic, geochemical and especially rock-magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition. The variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen-isotope record [Shackleton and Opdyke, 1976] and establish for the first time a continuous record of the Pleistocene glacial and interglacial stages in a continental section. Spectral analysis of the rock-magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils. Variable aeolic sediment influx as well as erosion and/or polygenetic soil formation may also strongly influence the sedimentary history.

Preliminary conclusions of the Royal Society and Academia Sinica 1985 geotraverse of Tibet

Abstract: The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region. Continuing northwards movement of the Indian plate over the past 38 Myr has given rise to severe folding and thrust faulting, causing crustal thickening by internal deformation. Previous collisions of microplate terranes derived from Gondwanaland occurred during Mesozoic times but the Kun Lun terrane of northern Tibet was already part of Laurasia by the Carboniferous

Uniform illumination of large targets using a lens array.

Abstract: Inserting an array of nearly 100 similar lenses into a common focal system, the uniformity of the illumination of a target can evidently be improved without being affected by the near-field distribution of laser beams. We report here geometrical- and physical-optics analyses of the lens array and compare them with the experimental results.

On a conformally invariant elliptic equation on R n

Abstract: Forn≧3, the equation Δu+|u|4/(n−2) u=0 on ℝ n has infinitely many distinct solutions with finite energy and which change sign.

Dinitrogen-fixing endogenous rhythm in Synechococcus RF-1

Abstract: Under continuous illumination this unicellular aerobic cyanobacterium fixes dinitrogen continuously at a variable and usually low rate. Exposure of the culture to diurnal light/dark cycles invariably results in the virtual restriction of nitrogenase activity to the dark periods. The rhythmic diurnal dinitrogen fixation pattern becomes a truely endogenous cycle which persists for at least 4 days with decreasing magnitude on exposing the culture to continuous illumination. The free running time of the rhythm appears to decrease from an initial 26 h to 22 h in the course of 4 days. This appears to be the first record of an endogenous rhythm in a prokaryote.

Characteristics of the Response of Sea Surface Temperature in the Central Pacific Associated with Warm Episodes of the Southern Oscillation

Abstract: The zonal distribution of sea surface temperature (SST) in the equatorial Pacific (4°N-4°S, 120°E-80°W) associated with El Nino/Southern Oscillation (ENSO) has been studied by using the seasonal mean file of the Comprehensive Ocean-Atmosphere Data Set (COADS) for the period 1940 to 1983. Although the warmest ocean area in the western central Pacific exhibits very little annual variation, it is very sensitive to the ENSO, displaying large variability during such episodes. The eastward migration of this warmest area (28.5°C isotherm is used here as a criterion related to strong tropical convection and heavy rainfall) is a common feature in the developing stage of almost all ENSO events since 1940, not only for the event of 1982. The extent of its eastward migration varies from event to event and represents a large contribution to the interannual variability of zonal SST distribution in the equatorial Pacific, comparable to the behavior of the equatorial cold tongue in the east The spread of the war...

Convergence rate of least-squares identification and adaptive control for stochastic systems†

Abstract: The strong consistency and the convergence rate of least-squares identification for the multidimensional ARMAX model are established under some decaying excitation conditions which are satisfied if both input and output do not grow too fast and the attenuating excitation technique is applied. The parameter-identification results are applied to adaptive-control systems with a quadratic loss function. The rate of convergence of the loss function to its minimum is also obtained.

Allelopathic research of subtropical vegetation in Taiwan : III. Allelopathic exclusion of understory byLeucaena leucocephala (Lam.) de Wit.

Abstract: Leucaena leucocephala plantations in Kaoshu, southern Taiwan, exhibit, after several years of growth, a unique pattern of weed exclusion beneathLeucaena canopy. The pattern has been observed in manyLeucaena plantations in Taiwan and is particularly pronounced in the area where a substantial amount ofLeucaena litter has accumulated on the ground. Field data showed that the phenomenon was primarily not due to physical competition involving light, soil moisture, pH, and nutrients. Instead, aqueous extracts ofLeucaena fresh leaves, litter, soil, and seed exudate showed significantly phytotoxic effects on many test species, including rice, lettuce,Acacia confusa, Alnus formosana, Casuarina glauca, Liquidambar formosana, andMimosa pudica. However, the extracts were not toxic to the growth ofLeucaena seedlings. The decomposing leaves ofLeucaena also suppressed the growth of the aforementioned plants grown in pots but did not inhibit that ofLeucaena plants. By means of paper and thin-layer chromatography, UV-visible spectrophotometry, and high-performance liquid chromatography, 10 phytotoxins were identified. They included mimosine, quercetin, and gallic, protocatechuic,p-hydroxybenzoic,p-hydroxyphenylacetic, vanillic, ferulic, caffeic, andp-coumaric acids. The mature leaves ofLeucaena possess about 5% dry weight of mimosine, the amount varying with varieties. The seed germination and radicle growth of lettuce, rice, and rye grass were significantly inhibited by aqueous mimosine solution at a concentration of 20 ppm, while that of the forest species mentioned was suppressed by the mimosine solution at 50 ppm or above. However, the growth ofMiscanthus floridulus andPinus taiwanensis was not suppressed by the mimosine solution at 200 ppm. The seedlings ofAgeratum conzoides died in mimosine solution at 50 ppm within seven days and wilted at 300 ppm within three days. It was concluded that the exclusion of understory plants was evidently due to the allelopathic effect of compounds produced byLeucaena. The allelopathic pattern was clearly shown in the area with a heavy accumulation ofLeucaena leaf litter, which was a result of drought and heavy wind influence.

Asymptotic error expansion and richardson extrapolation for linear fine elements

Abstract: The elliptic Ritz projection with linear finite elements is shown to admit asymptotic error expansions on certain uniform meshes. This justifies the application of Richardson extrapolation for increasing the accuracy.

Tide and tidal current charts for the marginal seas adjacent to China

Abstract: The tide phenomena in the marginal seas have attracted many people's attention since ancient time. Systematical studies based on modern theories began early in the present century. In 1930's, Ogura published cotidal charts for the Eastern China Sea which were considered as standard for many decades. The sea level data for the South China Sea were quite poor at that time compared with the available data in the Eastern China Sea. The cotidal charts produced by Dietrich (1944, see Defant 1961) were not accurate. During 1950's and early 1960's the Chinese scientists made great effort to measure and analyse the tides on the China coast and tidal currents in the offshore area. These results were studied extensively and appeared in 1964 in an unpublished report. H. L/u, F. You and W. Zheng were in charge of this work, and Zheng and the author of the present paper were the principal writers of the report. From late 1950's to 1970's several numerical computations based on the boundary value method appeared in Russian journals (Sergeev 1964, Thuy 1969, Minh 1975). Extensive numerical computations based on initial value method have been made by the present author and his co--workers since 1970. Unfortunately, the results remained unpublished for many years due to the fact that the publication of Chinese scientific magazines had been stopped since 1967. In recent years, many papers on ocean tides for the Eastern China Sea and the South China Sea appeared (see References). But the cotidal charts, especially for the South China Sea, show some even great diversity. Furthermore, the charts for tidal currents are generally not well presented. In the present paper we synthesize our works and give the charts for tides and tidal currents. Some comments on the reliability of these charts will also be given.

Sodium arsenite potentiates the clastogenicity and mutagenicity of DNA crosslinking agents

Abstract: To see if sodium arsenite enhances the clastogenicity and the mutagenicity of DNA crosslinking agents, Chinese hamster ovary (CHO) cells and human skin fibroblasts were exposed to cis-diamminedichloroplatinum (II) (cis-Pt(II)) or 8-methoxypsoralen (8-MOP) plus long-wave ultraviolet light (UVA) and then to sodium arsenite. The results indicate that the clastogenicity of cis-Pt(II) and 8-MOP plus UVA are enhanced by the post-treatment with sodium arsenite. Chromatid breaks and exchanges are predominantly increased in doubly treated cells. Furthermore, the mutagenicity of cis-Pt(II) at the hypoxanthine-guanine phosphoribosyl transferase locus is also potentiated by sodium arsenite in CHO cells.

Nitrogen loss from ammonium bicarbonate and urea fertilizers applied to flooded rice

Abstract: Total nitrogen loss and ammonia volatilization from applications of ammonium bicarbonate and urea to flooded rice (Oryza sativa L.) grown on an acidic lacustrine clay in China were measured by15N balance and micrometeorological methods. Attempts were also made to reduce nitrogen loss by using different methods of applying the fertilizers.