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81.
82.
LL Handley R Azcón Ruiz Lozano JM CM Scrimgeour 《Rapid communications in mass spectrometry : RCM》1999,13(13):1320-1324
It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
83.
84.
Error growth in the numerical integration of periodic orbits by multistep methods, with application to reversible systems 总被引:4,自引:0,他引:4
We study the growth with time of (the coefficients of the asymptoticexpansion of) the error in the numerical integration with linearmultistep methods of periodic solutions of systems of ordinarydifferential equations. Particular attention is devoted to reversiblesystems. It turns out that symmetric linear multistep methodscannot be recommended in spite of the fact that they mimic thereversibility of the true flow. For reversible second-ordersystems, linear multistep methods without parasitic double rootsare useful. 相似文献
85.
We describe a simple method to measure the top quark mass in the
channel that may be useful in Run II of D? detector. The method is validated by applying it to the Run Ib eμ data. 相似文献
86.
JM Chatterjee M Saha Sarkar S Bhattacharya P Banerjee S Sarkar RP Singh S Murulithar RK Bhowmik 《Pramana》2001,57(1):165-169
High-spin states of 95,97Mo (Z=42, N=53,55) nuclei have been investigated through 82Se(18O, xn) reaction at Eb=60 MeV. The level scheme in 95Mo has been observed upto ≏ 10 MeV in the present experiment. The level structure shows mainly single particle character.
In 97Mo, the ground state level sequence has been extended to ≏ 4.5 MeV while the previous information had been up to 2.4 MeV.
A negative parity band built on 1437 keV (11/2−) excited state has been extended to 5.5 MeV. The structure seems to show a coexistence of single particle and collective
modes of excitation. Properties of both the nuclei have been compared with shell model calculations using OXBASH. 相似文献
87.
Background
Clinical spinal cord injury in domestic dogs provides a model population in which to test the efficacy of putative therapeutic interventions for human spinal cord injury. To achieve this potential a robust method of functional analysis is required so that statistical comparison of numerical data derived from treated and control animals can be achieved. 相似文献88.
Palacios L De La Torre AG Bruque S García-Muñoz JL García-Granda S Sheptyakov D Aranda MA 《Inorganic chemistry》2007,46(10):4167-4176
Mayenite inorganic electrides are antizeolite nanoporous materials with variable electron concentration [Ca12Al14O32]2+ square5-deltaO1-delta2-e2delta- (0 < delta < or = 1), where square stands for empty sites. The oxymayenite crystal structure contains positively charged cages where loosely bounded oxide anions are located. These oxygens can be removed to yield electron-loaded materials in which the electrons behave like anions (electrides). Here, a new preparation method, which allows synthesizing powder mayenite electrides easily, is reported. Accurate structural data for the white (delta = 0) and green electride (delta approximately 0.5) are reported from joint Rietveld refinements of neutron and synchrotron X-ray powder diffraction data and also from single-crystal diffraction. The electride formation at high temperature under vacuum has been followed in-situ by neutron powder diffraction. The evolution of mayenite crystal structure, including the changes in the key occupation factor of the intracage oxide anions, is reported. Furthermore, the stability of mayenite framework in very low oxygen partial pressure conditions is also studied. It has been found that C12A7 decomposes, at 1373 K in reducing conditions, to give Ca5Al6O14 (C5A3) and Ca3Al2O6 (C3A). The kinetics of this transformation has also been studied. The fit of the transformed fraction to the classic Avrami-Erofe'ev equation gave an "Avrami exponent", n = 2, which indicates that nucleation is fast and the two-dimensional linear growth of the new phases is likely to be the limiting factor. 相似文献
89.
One major goal in materials chemistry is to find inexpensive compounds with improved capabilities. Stable inorganic electrides, derived from nanoporous mayenite [Ca12Al14O32]O, are a new family that has very interesting properties such as electronic conductivity combined with transparency. However, an intriguing fundamental problem is to understand the structures of these cubic materials and to characterize their free-electron loadings. Here we report an accurate structural study for three members of the series [Ca12Al14O32]O(1-delta)e(2delta) (delta = 0, 0.15, and 0.45), from single-crystal low-temperature synchrotron X-ray diffraction. The complex structural disorder imposed by the presence of the oxide anions into the mayenite cages has been unravelled. Furthermore, the final electron density map for delta = 0.45 black mayenite has shown electron density localized into the center of the cages, which is the first experimental proof of their electride nature. The reported structural findings challenge theorists to improve predictive models in this new family of materials. 相似文献
90.
Labajos-Broncano L Antequera-Barroso JA González-Martín ML Bruque JM 《Journal of colloid and interface science》2006,301(1):323-328
The imbibition of aqueous solutions of Triton X-100 in calcium fluoride columns has been studied in order to determine the influence of the interfacial adsorption of the surfactant in the capillary rise of the solutions. This system has been chosen because this surfactant behaves as non-adsorbable at the surface of this solid when it is in aqueous solution. The experiments have consisted of the measurement of the increase in the weight of the porous columns caused by the capillary rise of the solutions. The analysis of the results has been made through a modified expression of Washburn's equation that takes into account that the experimental increase in the weight is caused by the imbibition as well as by the development of a liquid meniscus around the bottom base of the columns. From this analysis, it has been deduced that the surfactant concentration does not influence on the imbibition rate, it being equal to the observed for water. However, it has been also proved that the contact angle depends on the surfactant concentration, taking decreasing values as the surface tension of the solutions decreases. In order to justify these findings, a study about the influence of the interfacial adsorption on the imbibition has been carried out. By means of them, it has been proved that the absence of adsorption at the solid-liquid interface is the reason that explains both the independence of the imbibition rate from the surfactant concentration and the decrease of the contact angle. Moreover, this fact indicates that the depletion of the surfactant molecules from the advancing meniscus, which has been normally adduced as the phenomenon causing the observed behaviour, has to be ruled out as the physical cause that justifies the behaviour found from the analysis of the imbibition experiments. As a corollary, it has been also stated that only if the adsorption at the solid interfaces happened, the imbibition of aqueous solution of surfactant in hydrophilic media could be influenced by the surfactant concentration. 相似文献