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151.
A mutant of aristolochene synthase, in which Phe 178 was replaced by Val, produced significant amounts of alpha-and beta-farnesene as well as alpha and beta-selinene and selina-4,11-diene, suggesting that Phe 178 is involved in the stabilisation of transition states preceding germacrene A and following eudesmane cation. 相似文献
152.
Szimtenings M Olt S Haase A 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,161(1):70-76
An NMR flow quantification technique applicable to metabolite flow in plants is presented. It combines flow sensitive magnetization preparation with slice selective spectroscopy. Flow encoded NMR spectroscopy is described to quantify, for the first time, flow velocities of metabolites in plants non-invasively. Flow sensitivity is introduced by magnetization preparation based on a stimulated echo experiment, prior to slice selective spectroscopy. For flow quantification eight different flow-weighted spectra are collected. With this flow preparation very slow flow velocities down to 0.1mm/s can be detected and small amounts of flowing metabolites can be observed despite the large background signal of stationary and flowing water. Important sequence optimization steps include appropriate choice of experimental parameters used for flow encoding as well as complete balancing of eddy currents from the flow encoding gradients. The method was validated in phantom experiments and applied in vivo. Examples of quantitative flow measurements of water and metabolites in phantoms and plants are provided to demonstrate the reliability and the performance of flow encoded spectroscopy. 相似文献
153.
154.
The study of the transport mechanisms connected to solid-liquid interactions is fundamental in the determination of the extension of the pollution of a site and in the evaluation of the best remediation process to be applied. The sorption of hydrophobic ionizable organic contaminants from the groundwaters is supervised not only by the physico-chemical properties of soil and pollutants, but also by the groundwaters pH, which deeply influences their solubility in the aqueous media, and consequently their transport mechanisms in the aquifer. In this work an experimental study of the sorption of phenol and 2-nitrophenol on two soils, different in particle-size distribution, CEC and organic carbon content, was realized. The sorption potential of the soils was evaluated by means of a physical, mineralogical and chemical characterization. The experimental data coming from some batch tests, performed at pH values equal to 4, 7 and 10 were fitted by means of linear, Freundlich and Langmuir isotherms models. The soil-contaminants interaction mechanisms that influence the isotherms shapes were then analyzed and discussed, and a comparison between the theoretical and experimental values of the partitioning coefficient KD was performed. 相似文献
155.
Building Wavelets on ]0,1[ at
Large Scales 总被引:1,自引:0,他引:1
Silvia?BertoluzzaEmail author Silvia?FallettaEmail author 《Journal of Fourier Analysis and Applications》2003,9(3):261-288
We present a new approach to the construction of orthonormal wavelets on the
interval which allows to overcome the non interacting boundaries restriction of existing constructions,
and therefore to construct wavelets for U0; 1T also at large scales in such a way that, in
the range of validity of the existing constructions, the two approaches give the same result. 相似文献
156.
Traversa Enrico Di Vona Maria Luisa Licoccia Silvia Sacerdoti Michele Carotta Maria Cristina Gallana Massimiliano Martinelli Giuliano 《Journal of Sol-Gel Science and Technology》2000,19(1-3):193-196
Pure, 5 at%, and 10 at% Ta- or Nb-doped TiO2 nanosized powders were prepared by the sol-gel method. The powders heated to 400°C have the crystalline anatase structure. While the pure TiO2 powder heated to 850°C has the rutile structure, the addition of Ta and Nb inhibited the anatase-to-rutile phase transformation at this temperature. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired at 650°C and 850°C for 1 h. SEM observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at the nanometric level even at 850°C. Conductance measurements showed that a good gas response is observed only for the nanostructured titania-based films. The CO response of these materials is only slightly affected by humidity. 相似文献
157.
The aim of this paper is to propose a stabilization technique in order to circumvent the two infsup conditions neededfor stability of the discretization of the three fields formulationfor domain decomposition methods (following the work of Brezzi& Marini (1993) Optimisation et Controle 8996). Realization of this technique in terms of wavelets is presented. Furthermore, the resulting discrete problem is shown to admitan asymptotically optimal preconditioner also based on wavelets.
Received 24 February, 1999. Revised 7 October, 1999.
* aivlis@ian.pv.cnr.it; http://www.ian.pv.cnr.it/~aivlis
kunoth@iam.un-bonn.de; http://www.iam.uni-bonn.de/~kunoth 相似文献
158.
A new general-relativistic theory of cosmology, the dynamical variables of whichare those of Hubble's, namely distances and redshifts, is presented. The theorydescribes the universe as having a three-phase evolution with a deceleratingexpansion followed by a constant and an accelerating expansion, and it predictsthat the universe is now in the latter phase. The theory is actually a generalizationof Hubble's law taking gravity into account by means of Einstein's theory ofgeneral relativity. The equations obtained for the universe expansion are elegantand very simple. It is shown, assuming 0 = 0.24, that the time at which theuniverse goes over from a decelerating to an accelerating expansion, i.e., theconstant expansion phase, occurs at 0.03 from the big bang, where is theHubble time in vacuum. Also, at that time the cosmic radiation temperature was11 K. Recent observations of distant supernovae imply, in defiance of expectations,that the universe's growth is accelerating, contrary to what has always beenassumed, that the expansion is slowing down due to gravity. Our theory confirmsthese recent experimental results by showing that the universe now is definitelyin a stage of accelerating expansion. 相似文献
159.
The water-silicas interfacial interaction energies were calculated for samples of quartz, silicas and silicas outgassed at high temperatures using own and published data of the spreading pressure of water, its surface tension, its contact angle and using formulas obtained by the combination of the Young equation with a general equation of pair interaction. The values obtained for 18 different samples were in the range 7.80-6.92 kJ mol−1. Lower values of energies are for samples that contain relatively less amounts of water at P/P0 = 0.25 and are characterized also by relatively low values of surface pressures. 相似文献
160.
Mariano Escobar M. Sergio Moreno Roberto J. Candal M. Claudia Marchi Pablo I. Polosecki Silvia Goyanes 《Applied Surface Science》2007,254(1):251-256
The effect of acetylene partial pressure on the structural and morphological properties of multi-walled carbon nanotubes (MWCNTs) synthesized by CVD on iron nanoparticles dispersed in a SiO2 matrix as catalyst was investigated. The general growing conditions were: 110 cm3/min flow rate, 690 °C synthesis temperature, 180 Torr over pressure and two gas compositions: 2.5% and 10% C2H2/N2. The catalyst and nanotubes were characterized by HR-TEM, SEM and DRX. TGA and DTA were also carried out to study degradation stages of synthesized CNTs. MWCNTs synthesized with low acetylene concentration are more regular and with a lower amount of amorphous carbon than those synthesized with a high concentration. During the synthesis of CNTs, amorphous carbon nanoparticles nucleate on the external wall of the nanotubes. At high acetylene concentration carbon nanoparticles grow, covering all CNTs’ surface, forming a compact coating. The combination of CNTs with this coating of amorphous carbon nanoparticles lead to a material with high decomposition temperature. 相似文献