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  • 1995-1999  (1,680)
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  • 1
    Electronic Resource
    Electronic Resource
    A 31P nuclear magnetic resonance study of phosphate levels in roots of ectomycorrhizal and nonmycorrhizal plants of Castanea sativa Mill. (1999)
    Springer
    Trees 13 (1999), S. 168-172 
    Details
    ISSN: 0931-1890
    Keywords: Key words Castanea sativa ; Pisolithus tinctorius ; Ectomycorrhiza ; Phosphate ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  31P-Nuclear Magnetic Resonance (NMR) was used to assess phosphate distribution in ectomycorrhizal and nonmycorrhizal roots of Castanea sativa Mill. as well as in the mycorrhizal fungus Pisolithus tinctorius in order to gain insight into phosphate trafficking in these systems. The fungus P. tinctorius accumulated high levels of polyphosphates during the rapid phase of growth. Mycorrhizal and nonmycorrhizal roots accumulate orthophosphate. Only mycorrhizal roots presented polyphosphates. The content in polyphosphates increased along the 3 months of mycorrhiza formation. In mycorrhizal roots of plants cultured under axenic conditions, the orthophosphate pool decreased along the culture time. In nonmycorrhizal roots the decrease in the orthophosphate content was less pronounced. The level of orthophosphate in mycorrhizal roots was significantly lower than in nonmycorrhizal ones, which indicates that this system relies upon the fungal polyphosphates as a major source of phosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009748
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  • 2
    Electronic Resource
    Electronic Resource
    Radial distribution functions for a multicomponent system of sticky hard spheres (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6814-6819 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method to obtain (approximate) analytical expressions for the radial distribution functions and structure factors in a multicomponent system of sticky hard spheres is introduced. In its simplest implementation, the method yields the Percus–Yevick approximation. In the next order, only contact values of the cavity functions and the isothermal compressibility are required. Some tentative strategies to determine the input values are discussed. Illustrative examples following these strategies, in which the radial distribution functions and structure factors are computed, are also presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477328
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of multi-component hard-sphere mixtures (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3683-3693 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method to obtain (approximate) analytical expressions for the radial distribution functions and structure factors in a multi-component mixture of additive hard spheres is introduced. In this method, only contact values of the radial distribution function and the isothermal compressibility are required and thermodynamic consistency is achieved. The approach is simpler than but yields equivalent results to the Generalized Mean Spherical Approximation. Calculations are presented for a binary and a ternary mixture at high density in which the BoublíkMansoori-Carnahan-Starling-Leland equation of state is used. The results are compared with the Percus-Yevick approximation and the most recent simulation data. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475762
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  • 4
    Electronic Resource
    Electronic Resource
    Xenon–neon gas proportional scintillation counters: Experimental and simulation results (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6303-6312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When gas proportional scintillation counters (GPSC) are used to detect very low energy x rays, the addition of the light noble gas neon to the usual xenon filling improves the collection of primary electrons that originate near the detector window. However, xenon–neon mixtures have lower electroluminescence yields than pure xenon. Increasing the scintillation electric field jeopardizes the energy resolution because of the additional fluctuations introduced by electron multiplication. In this work we investigate the effect of a limited amount of charge multiplication on the electroluminescence yield and the energy resolution R of a xenon–neon GPSC using both Monte Carlo simulation and experimental measurements. We consider xenon–neon mixtures with 5%, 10%, 20%, 30%, 40%, 50%, 70%, 90%, and 100% Xe at a total pressure of 800 Torr. Comparing the experimental and Monte Carlo data for 5.9 keV x rays, we conclude that optimum value of R is reached in a region of weak ionization with a charge gain of less than 2. By extrapolating the experimental results for R to infinite light yield we obtain the intrinsic energy resolution Rint for 5.9 keV x rays in all mixtures. From these results we can predict Fw values, where F is the relative variance in the number of primary electrons (the Fano factor) and w is the mean energy required to produce a primary electron. From a comparison between Monte Carlo and experimental electroluminescence yields, F and w values are estimated for 5.9 keV x rays in the various mixtures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370131
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  • 5
    Electronic Resource
    Electronic Resource
    Full-energy absorption of x-ray energies near the Xe L- and K-photoionization thresholds in xenon gas detectors: Simulation and experimental results (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2742-2753 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenon L- and K-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor, w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certain narrow ranges containing the edges. However, our simulation results permit a detailed analysis of observations in these regions. At the K-edge, the discontinuities in the calculated Fano factor and energy resolution were found to depend on the extent to which the K-fluorescence produced by the xenon atoms is allowed to escape. A discussion of the asymmetry of the calculated full-energy absorption peaks is made in terms of the distinction between the different decay branches initiated by photoionization of the Xe atoms, and K-fluorescence escape is found to influence strongly the skewness of the calculated distributions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366105
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  • 6
    Electronic Resource
    Electronic Resource
    Temperature evaluation of UF6 and cluster detection in nozzle expansion using low-resolution infrared absorption spectroscopy (1998)
    Springer
    Applied physics 67 (1998), S. 653-658 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 33.20.E; 36.40; 47.40.K
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 6 and mixtures of UF6 with argon and nitrogen through a bidimensional nozzle was studied using low-resolution infrared spectroscopy in the ν3 absorption band region. The experiments were carried out in order to calculate the molecular temperature of the beam and also to verify cluster formation in the expansion. The molecular beam temperature evaluation was based on the measurements of the low-resolution bandwidth, which were compared to simulated spectra results. The temperatures were also evaluated using the measured pressure at the end of the nozzle by a pitot tube. In the conditions where no cluster formation was observed the calculated theoretical temperatures using an equilibrium expansion model are in good agreement with the data obtained through the analysis of the experimental spectra and through the pitot tube pressure measurement. Cluster formation was observed for temperatures below about 120 K. In these conditions the infrared spectra showed shoulders in the region above 630 cm-1 and a shoulder or band between 616 and 600 cm-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050561
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  • 7
    Electronic Resource
    Electronic Resource
    The role of phototrophic sulfur bacteria as food for meiobenthic harpacticoid copepods inhabiting eutrophic coastal lagoons (1996)
    Springer
    Hydrobiologia 329 (1996), S. 79-89 
    Details
    ISSN: 1573-5117
    Keywords: Feeding ecology ; meiofauna ; harpacticoid copepods ; coastal lagoons ; phototrophic bacteria ; microalgae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Laboratory experiments were undertaken using Amonardia normani and Schizopera cf. compacta, two meiobenthic harpacticoid copepods commonly found in coastal lagoons. The first experiments were designed to determine if the phototrophic sulfur bacteria Chromatium gracile can be ingested by these copepods and at what concentrations. Egestion rate was used as an index of feeding rate. The response of the egestion rate, expressed in numbers of faecal pellets produced by copepod per day, as a function of bacterial concentration followed the functional model. A. normani attained constant feeding rates from the bacterial concentration of 1 × 107 cells ml−1 (5 µg C ml−1) onwards, S. cf. compacta attained constant feeding rates from 2.6 × 107 cells ml−1 (13 µg C ml−1) onwards. The faecal pellet volume changed significantly (p〈0.05) between food concentrations for A. normani but not for S. cf. compacta (p〉0.05). In order to investigate the effect of the phototrophic bacterial diet on the population dynamics of A. normani three groups of nauplii were maintained at 2 × 107 cells ml−1 and observed every day. The mortality of these nauplii was very high compared to those maintained on a diatom diet (Nitzschia constricta); only in one of the groups did some copepodites develop but no adults were ever observed. Adults fed on bacteria did not have different (p〉0.05) survival rates compared to those fed on diatoms, nevertheless, the number of nauplii produced was significantly less (p〈0.05) on the bacterial diet. These results lead us to suggest that although the phototrophic sulfur bacteria (Chromatium gracile) can be ingested by both copepod species it cannot sustain the full development of the A. normani population. Thus, a bloom of phototrophic sulfur bacteria does not seem to be a favourable situation for opportunistic benthic copepods to colonize eutrophic coastal lagoons after a dystrophic crisis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00034549
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  • 8
    Electronic Resource
    Electronic Resource
    Phytotoxic effect of culture filtrate from Fusarium subglutinans the causal agent of fusariose of pineapple (Ananas comosus (L.) Merr (1998)
    Springer
    Euphytica 104 (1998), S. 73-77 
    Details
    ISSN: 1573-5060
    Keywords: Fusarium subglutinans ; callus ; tissue culture ; culture filtrate ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two pineapple varieties differing in resistance to fusariose were examined for the phytotoxic effect of Fusarium subglutinans culture filtrate. The cultivars were Perolera (more resistant to pathovars of Fusarium subglutinans) and Smooth Cayenne (more susceptible). The phytotoxic effect of culture filtrate was assessed in tissue culture pineapple plantlets (by electrolyte leakage and placing the culture filtrate on wound leaf segments) and callus (inhibition of growth). Smooth Cayenne proved to be the most sensitive cultivar in each test, whereas Perolera showed resistance to the culture filtrate and its callus grew in the presence of high concentrations of culture filtrate that were completely toxic to Smooth Cayenne. These results show that plants can display cellular resistance to the culture filtrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018387210157
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  • 9
    Electronic Resource
    Electronic Resource
    Application of High Temperature High Resolution Gas Chromatography to Crude Extracts of Propolis (1998)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 21 (1998), S. 396-400 
    Details
    ISSN: 0935-6304
    Keywords: high temperature gas chromatography ; flavonoids ; propolis ; high molecular weight compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The underivatized acetone and hexane fractions from propolis samples (predominant flora Citrus spp. and Vernonia polyanthes) were analyzed by HT-HRGC (high temperature high resolution gas chromatography) and HT-HRGC coupled to mass spectrometry (HT-HRGC-MS). Several compounds, including flavonoid aglycones, phenolic acids, and high molecular weight compounds were characterized in crude extracts by HT-HRGC-MS. HT-HRGC and HT-HRGC-MS were shown to be quick and informative tools for rapid analysis of crude extracts without need for prior derivatization and purification.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis of the model macroinitiators of free radical polymerization and their application for the preparation of block copolymers (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 1055-1066 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A series of polystyrenes having low molecular weight (4600-23,100) and narrow molecular weight distribution and functionalized with a benzophenone group at one or both ends of the chain have been prepared through anionic polymerization. Then the terminal benzophenone groups have been transformed into 1,2-bis(trimethylsilyloxy)tetraphenylethane (or benzopinacolate) groups by the duplication reaction with free benzophenone in the presence of chlorotrimethylsilane and hexamethylphosphorous triamide (HMPT) or hexamethylphosphoramide (HMPA), producing model thermal macroinitiators of free radical polymerization with well-defined structure. Polymerization of MMA initiated by these macroinitiators was carried out yielding poly(styrene-b-methyl-methacrylate) (PS-b-PMMA). © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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