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131.
Boeckx P Paulino L Oyarzún C van Cleemput O Godoy R 《Isotopes in environmental and health studies》2005,41(3):249-259
Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted delta15N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances (e.g. fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that delta15N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these delta15N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in 15N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil delta15N signal in the upper 20 cm. 相似文献
132.
Nonlinear resonant ultrasound spectroscopy (NRUS) applied to damage assessment in bone 总被引:1,自引:0,他引:1
Muller M Sutin A Guyer R Talmant M Laugier P Johnson PA 《The Journal of the Acoustical Society of America》2005,118(6):3946-3952
Nonlinear resonant ultrasound spectroscopy (NRUS) is a resonance-based technique exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency(ies) of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. This study shows the feasibility of this technique for application to damage assessment in bone. Two samples of bovine cortical bone were subjected to progressive damage induced by application of mechanical cycling. Before cycling commenced, and at each step in the cycling process, NRUS was applied for damage assessment. For independent assessment of damage, high-energy x-ray computed tomography imaging was performed but was only useful in identifying the prominent cracks. As the integral quantity of damage increased, NRUS revealed a corresponding increase in the nonlinear response. The measured change in nonlinear response is much more sensitive than the change in linear modulus. The results suggest that NRUS could be a potential tool for micro-damage assessment in bone. Further work must be carried out for a better understanding of the physical nature of damaged bone and for the ultimate goal of the challenging in vivo implementation of the technique. 相似文献
133.
134.
Nitrosation of thiols and thioethers in the gas phase: A combined theoretical and experimental study
Gerbaux P Wantier P Flammang R 《Journal of the American Society for Mass Spectrometry》2004,15(3):344-355
Recent studies have demonstrated the biological importance of the interaction of nitric oxide with proteins such as cytochrome-c or hemoglobin. In particular, the possibility that the nitrosonium cation, NO(+), could reversibly bind to sulfide atom type was proposed. At pH values of biological relevance, nitrosation was proposed to occur through the action of NO(+) carriers such as nitrosothiols or nitrosamines. In this context, the gas phase chemistry of protonated nitrosothiols is studied in the present work by a combination of mass spectrometry and computational methods. 相似文献
135.
136.
Bond lengths and bond strengths in weak and strong chemisorption: N2, CO,and CO/H on nickel surfaces
Sayago DI Hoeft JT Polcik M Kittel M Toomes RL Robinson J Woodruff DP Pascal M Lamont CL Nisbet G 《Physical review letters》2003,90(11):116104
New chemical-state-specific scanned-energy mode photoelectron diffraction experiments and density functional theory calculations, applied to CO, CO/H, and N2 adsorption on Ni(100), show that chemisorption bond length changes associated with large changes in bond strength are small, but those associated with changes in bond order are much larger, and are similar to those found in molecular systems. Specifically, halving the bond strength of atop CO to Ni increases the Ni-C distance by 0.06 A, but halving the bond order (atop to bridge site) at fixed bond strength causes an increase of 0.16 A. 相似文献
137.
Moores A Mézailles N Ricard L Mathey F Le Floch P 《Chemical communications (Cambridge, England)》2003,(15):1914-1915
Reaction of a tetraphenyl-1,2-diphosphinyl dianion with [FeCl2(THF)1.5] or [Ru(COD)(acac)2] yields dianionic complexes which further react with Ph3SnCl to afford the corresponding bis(1,4-diphosphabutadiene) complexes. 相似文献
138.
Rosa P Mézailles N Ricard L Mathey F Le Floch P 《Angewandte Chemie (International ed. in English)》2001,40(23):4476-4479
139.
Rosa P Mézailles N Ricard L Mathey F Le Floch P Jean Y 《Angewandte Chemie (International ed. in English)》2001,40(7):1251-1253
140.
Trong Phu Do Pascal Ziegler 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(4):359-388
Gear drives are key components for all kinds of machines as well as of industrial equipment. Therein, beveloid gears and cycloid gears are increasingly used in industry. Gaining a more comprehensive understanding of those types of gears is essential. However, the measurement of the dynamic response of these gears is not an option due to the high cost of the required experiments. Along with the development of computer technology, several numerical tools and methods to study gears with standard and non-standard flank profiles have been introduced. Various works related to standard gears or beveloid and cycloid gears have been published. In this study, a contemporary review about the modelling and contact simulation of beveloid and cycloid gear drives will be given. Some studies will also be introduced to present an efficient approach to simulate contact forces and contact characteristics of gear wheels with standard and non-standard tooth profiles considering deformations too. 相似文献