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Small-scale vegetation patterns are frequently the results of plant-plant interactions such as facilitation and competition. Facilitation should be particularly pronounced when both abiotic and biotic stresses are high, but few studies were conducted in such habitats. In heavily-grazed pastures on the eastern Tibetan Plateau, an area with both high abiotic stress and strong biotic disturbance, we made relevés of herb species both beneath and outside canopies of three shrub species (Spiraea alpina, Sibiraea angustata and Potentilla fruticosa) differing in palatability and canopy structure. Herb species richness (S), pooled cover (PC) of all species, number of flowering species (FS) and number of inflorescences of all species (IN) were greater outside than beneath the shrub canopies. Evenness (J), in contrast, was smaller outside, while Shannon’s diversity index (H) was the same. Differences in S and J between plots beneath and outside the shrub canopies were greater in the case of P. fruticosa than in the cases of S. angustata and S. alpina, but differences in PC, FS or IN did not depend on the shrub species. Among the common species (frequency ≥6), 47–85% were equally frequent beneath and outside the shrubs, 13–39% were more frequent outside and 3–13% were more frequent beneath the shrubs. For the rarest species (frequency < 6), however, more species occurred beneath than outside the shrubs. The ordination diagram showed a clear separation between the relevés outside and beneath the shrubs and a gradient from P. fruticosa via S. alpina to S. angustata, accompanied by a distinct decrease in the extent of the difference between the vegetation beneath and outside the shrub canopies. In conclusion, the three shrub species facilitated some species in the herb layer and each shrub species had a specific impact, related to its canopy structure and palatability but also to the grazing pressure, which was greater around the P. fruticosa shrubs than around S. alpina and S. angustata.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
L. Zhou
,
S. Wen
,
J. Zhao
,
B. Yu
,
B. Han
, and
Ch. Yang

Abstract  

The -ray spectra of188Re decay have been studied by using two Ge/Li/ spectrometers and a three parameters /E-E-T/ List coincidence system. The energies and relative intensities of 52 -rays and cascade relations of 14 -rays are determined. Ten new -rays: 155 /633–478/, 984, 1096, 1463, 1332, 1530, 1574, 1810, 1867, and 1937 keV have been identified. The 155 /633–478/ transition is confirmed and its relative intensity is estimated by means of coincidence experiment. 24 levels of188Re are assigned. Among those, 6 levels are first put into the decay scheme of188Re. In addition to 1443 keV and 1937 keV levels, 1685, 1729 and 1965 keV levels are also observed in the decay of188Ir and other reaction studies. The 1948 level is recently suggested in the190Os/p, t/188Os reaction. The 486 keV and 811 keV -transitions are also put into the level scheme of188Re. The decay branching ratio is deduced.

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Journal of Thermal Analysis and Calorimetry
Authors:
P. P. Fedorov
,
Yu. G. Sizganov
,
B. P. Sobolev
, and
M. Shvanner

A phase diagram of the system CaF2-GdF3 was studied by thermal and X-ray analysis. Two wide domains of solid solutions based on CaF2 and a high-temperature modification of α-GdF3 (LaF3-structural type) are present in this system. Two maxima were found on the melting curves of the Ca1−xGdxF2+x and α-(Gd1−yCayF3−y solid solutions, at 1428 ± 10‡ (5 mole % GdF3) and 1282 ± 5‡ (85 mole % GdF3), respectively. The coordinates of the eutectic are 60 mole % GdF3 and 1233 ± 5‡.

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Abstract  

It has been shown that gamma-activation significantly extends possibilities of activation autoradiography with respect to determination of platinum group elements (PGE) in silicate samples. All PGE may be activated by bremsstrahlung with forming radionuclides having convenient half-lives for autoradiography (hours-days). Digital methods for quantitative 2D-densitometry of autoradiograph images by means of documents scanners have been developed and discussed. Approaches for increasing selectivity of analysis by means of autoradiography have been proposed and tested on the real sample containing PGE inclusions (analysis of decay kinetics while cooling, combination with gamma-ray spectrometry).

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Abstract  

Information on the biokinetics of cerium can be obtained directly from humans by using stable isotopes as tracers. Neutron, photon and proton activation analysis have all been tested as analytical techniques able to quantify different isotopes of the same element in biological fluids. The experimental conditions were optimized for Ce analysis in blood plasma samples. The performances of the different techniques have been explored. The simultaneous determination of two Ce isotopes with the required sensitivity in the order of few ppb is difficult to obtain using a single technique, and, therefore, a combination of techniques can be envisaged.

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Résumé  

On a déterminé la composition élémentaire d'échantillons de régolite lunaire obtenus par Luna 16 dans la mer d'abondance par méthode radioactive à l'aide d'un générateur de neutrons ainsi qu'un spectromètre γ à scintillations et détecteur Ge(Li).

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
V. Frenkel
,
V. Chistyakov
,
Yu. Kulyako
,
E. Erin
,
I. Lebedev
,
G. Timofeev
, and
B. Myasoedov

Abstract  

During electrolysis of a248Cm/III/ solution in 2M K2CO3 at pH=13 partial oxidation of curium to a higher oxidation state, probably Cm/IV/, was observed. The absorption spectra of Cm/III/ and Cm/IV/ in K2CO3 solution were recorded and the molar extinction coefficients of main absorption bands of curium have been evaluated.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
V. Frenkel
,
Yu. Kulyako
,
V. Chistyakov
,
I. Lebedev
,
B. Myasoedov
,
G. Timofeev
, and
E. Erin

Abstract  

The electrolysis of trivalent californium, terbium and praseodimium in 2M K2CO3 solutions at pH 13.2 results in a partial oxidation of the trivalent ions to a higher oxidation state. Absorption spectra of Cf/III/ in 1M HCLO4 and in 2M K2O3 and that of oxidized californium in carbonate solution have been recorded. Incomplete oxidation is accounted to a reducing species generated at high anode potentials.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
A. Krivokhatsky
,
Yu. Dubasov
,
E. Smirnova
,
N. Skovorodkin
,
V. Savonenkov
,
B. Alexandrov
, and
E. Lebedev

Abstract  

Actinide elements concentrations in the products of near release from CNPP accident were estimated. The data on uranium,237Np,241Am and plutonium and curium isotopes content in fuel particles are given. Sums of -emitting radionuclides and plutonium isotopes in reactor graphite particles and of uranium,242Cm,239+240Pu isotopes in the soil and aerosol samples were also determined. By 1989 soil and dust contamination in near release of the accident is due to long-lived -emitting plutonium isotopes.

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Abstract  

The heat capacities of trans-(R)-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid in the temperature range from 78 to 389 K were measured with a precise automatic adiabatic calorimeter. The sample was prepared with the purity of 0.9874 mole fraction. A solid-liquid fusion phase transition was observed in the experimental temperature range. The melting point, T m, enthalpy and entropy of fusion, Δfus H m, Δfus S m, were determined to be 344.75±0.02 K, 13.75±0.07 kJ mol−1, 39.88±0.21 J K−1 mol−1, respectively. The thermodynamic functions of the sample, H (T)-H (298.15), S (T)-S (298.15) and G (T)-G (298.15), were reported with a temperature interval of 5 K. The thermal decomposition of the sample was studied by TG analysis, the thermal decomposition starts at ca. 421 K and terminates at ca. 535 K, the maximum decomposition rate was obtained at 525 K. The order of reaction, pre-exponential factor and activation energy, are n=0.14, A=1.15·108 min−1, E=66.27 kJ mol−1, respectively.

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