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123.
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
124.
R. Wiesendanger I. V. Shvets D. Bürgler G. Tarrach H. -J. Güntherodt J. M. D. Coey 《Zeitschrift für Physik B Condensed Matter》1992,86(1):1-2
Magnetic contrast at the atomic level has been observed for the first time in scanning tunneling microscopy experiments on a magnetite (Fe3O4(001)) surface using in-situ prepared ferromagnetic Fe tips. A periodic corrugation with a 12 Å periodicity is clearly observed along the rows of FeB-sites which corresponds to the repeat period of Fe2+ and Fe3+ along these rows. This periodicity is not observed by using non-magneticW tips although the rows of FeB-sites can be resolved as well. The magnetic contrast observed with Fe tips is attributed to the different spin configurations of the magnetic ions Fe2+ and Fe3+ in Fe3O4. 相似文献
125.
Mössbauer spectra of 57Fe impurities in α NiS show an abrupt collapse of the hyperfine splitting at Tt = 260 K, the nonmetal-metal transition; the extrapolated Néel point is ~420 K. Below Tt, it appears that iron adjacent to a vacancy is low-spin. There us evidence of substantial d-electrons delocalisation above Tt. β NiS does not order magnetically down to 4 K. 相似文献
126.
J. D. Fabris Mauro Resende Jacqueline Allan J. M. D. Coey 《Hyperfine Interactions》1986,29(1-4):1093-1096
Three sets of Brazilian Oxisols have been analysed by Mössbauer spectroscopy at 290, 80 and 4.2 K. In most cases two resolved magnetic hyperfine patterns associated with aluminous goethite and hematite are resolved; their ratio is related to soil colour. Samples from a 3 m soil profile show that both oxides become decreasingly aluminium substituted and/or better crystallized with depth. Goethite from surface or deep layers is readily differentiated by its hyperfine parameters. As there is no significant alternate source of iron, the results suggest that both hematite and goethite undergo continuous neoformation throughout the profile in response to the changing pedogenic environment. 相似文献
127.
128.
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
129.
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
130.
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