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21.
Germane-propane and germane-propene gaseous mixtures were studied by ion trap mass spectrometry. Variations of ion abundances observed under different partial pressure ratios and mechanisms of ion-molecule reactions elucidated by multiple isolation steps are reported. In addition, the rate constants for the main reactions were experimentally determined and compared with the collisional rate constants to obtain the reaction efficiencies. The yield of ions containing both Ge and C atoms is higher in the germane-propene than in the germane-propane system. In the former mixture, chain propagation takes place starting from germane ions reacting with propene and proceeds with the formation of clusters such as Ge(2)C(4)H(n) (+) and Ge(3)CH(n) (+). 相似文献
22.
We propose a preconditioned variant of the modified HSS (MHSS) iteration method for solving a class of complex symmetric systems of linear equations. Under suitable conditions, we prove
the convergence of the preconditioned MHSS (PMHSS) iteration method and discuss the spectral properties of the PMHSS-preconditioned matrix. Numerical implementations show
that the resulting PMHSS preconditioner leads to fast convergence when it is used to precondition Krylov subspace iteration
methods such as GMRES and its restarted variants. In particular, both the stationary PMHSS iteration and PMHSS-preconditioned
GMRES show meshsize-independent and parameter-insensitive convergence behavior for the tested numerical examples. 相似文献
23.
Let A be a symmetric matrix and let f be a smooth function defined on an interval containing the spectrum of A. Generalizing a well-known result of Demko, Moss and Smith on the decay of the inverse we show that when A is banded, the entries of f(A)are bounded in an exponentially decaying manner away from the main diagonal. Bounds obtained by representing the entries of f(A)in terms of Riemann-Stieltjes integrals and by approximating such integrals by Gaussian quadrature rules are also considered. Applications of these bounds to preconditioning are suggested and illustrated by a few numerical examples. 相似文献
24.
Carlotto S Polimeno A Ferrante C Benzi C Barone V 《The journal of physical chemistry. B》2008,112(27):8106-8113
A stochastic model for the interpretation of the emission fluorescence of 4-( N, N-dimethylamino)benzonitrile (DMABN) is discussed. We proceed by reviewing the stochastic modeling approach ( Polimeno, A. ; Barbon, A. ; Nordio, P. L. ; Rettig, W. J. Phys. Chem. 1994, 98, 12158 ), in which internal degrees of freedom are coupled with an effective solvent relaxation variable. Potential energy surfaces are obtained using a reliable but computationally cost-effective quantum mechanical (QM) approach, and estimates of dissipative parameters are calculated on the basis of direct hydrodynamic arguments. Emission fluorescence is estimated by solving numerically a diffusion/sink/source equation for the stationary population of excited state and compared to emission fluorescence of DMABN measured experimentally. 相似文献
25.
L Benzi V Pezzino P Marchetti D Gullo P Cecchetti A Masoni R Vigneri R Navalesi 《Journal of chromatography. A》1986,378(2):337-347
Reversed-phase high-performance liquid chromatography (RP-HPLC) allows the rapid separation of A14-[125I]monoiodoinsulin directly from the iodination mixtures. It remains to be clarified, however, whether the RP-HPLC chromatographic conditions affect the properties of the purified tracer. In this study we prepared A14-[125I]insulin purified by polyacrylamide gel electrophoresis (PAGE) and by three different RP-HPLC mobile phases containing, respectively, ammonium acetate, sodium perchlorate and trifluoroacetic acid. The binding characteristics of all these tracers were examined using an insulin antiserum and insulin cell receptors. The specific radioactivity corresponded to the theoretical maximum for the RP-HPLC-purified tracers and was significantly lower for the PAGE-purified tracers. Significant differences were found in the binding of different tracers to the insulin antiserum: maximum binding ranged from 94 to 99% and was significantly lower for tracers purified by RP-HPLC eluents B and C; antiserum dilution giving 50% tracer binding was lower for tracers purified by RP-HPLC eluent B. The four insulin derivatives showed no difference in non-specific precipitation and in the affinity constant values calculated from the Scatchard analysis. No significant difference was found in the binding of the four insulin derivatives to the human-cultured IM-9 lymphocytes and to the human circulating monocytes. In conclusion, the present work demonstrates that the immunological properties of the A14-[125I]monoiodoinsulin purified by RP-HPLC may be partially affected by the composition of the mobile phase. In order to obtain a fully potent A14-[125I]insulin derivative and to have the possibility of comparing data from different laboratories, the chromatographic conditions must be taken into account. 相似文献
26.
A set of ligands loaded on various supports have been tested to remove radium from aqueous solutions. Crown ethers have demonstrated inefficiency in all cases, while open chain ligands (podands) have shown satisfactory distribution coefficients and uptake rates in particular conditions. Hypotheses to explain the phenomenon are briefly discussed. 相似文献
27.
Benzi R 《Physical review letters》2005,95(2):024502
In this Letter, we study a simple hydrodynamical model showing abrupt flow reversals at random times. For a suitable range of parameters, we show that the dynamics of flow reversal is accurately described by stochastic differential equations, where the noise represents the effect of turbulence. 相似文献
28.
Summary The evolution of the marine thermocline is studied by using some algebraic relations derived by Mellor and Durbin. In particular,
a simple algebraic way to compute various turbulent quantities from experimental data is illustrated.
Research sponsored by C.N.R. ?Progetti Finalizzati Oceanografia?. 相似文献
Riassunto Si studia l'evoluzione del termoclino marino partendo dal modello ottenuto da Mellor e Durbin chiudendo al secondo ordine le equazioni della turbolenza. In particolare, si mostra un metodo che fornisce informazioni riguardanti le grandezze turbolente tramite soluzione di equazioni algebriche tratte dal modello. Si applica infine tale metodo a due serie di dati sperimentali.
Резюме Исследуется эволюция морского термоклика, используя некоторые алгебраические соотношения выведенные Меллором и Дурбином. В частности, предлагается простой алгебраический способ для вычисления различных турбулентных из зкспериментальных данных.
Research sponsored by C.N.R. ?Progetti Finalizzati Oceanografia?. 相似文献
29.
R. Benzi M. H. Jensen D. R. Nelson P. Perlekar S. Pigolotti F. Toschi 《The European physical journal. Special topics》2012,204(1):57-73
Organisms often grow, migrate and compete in liquid environments, as well as on solid surfaces. However, relatively little
is known about what happens when competing species are mixed and compressed by fluid turbulence. In these lectures we review
our recent work on population dynamics and population genetics in compressible velocity fields of one and two dimensions.
We discuss why compressible turbulence is relevant for population dynamics in the ocean and we consider cases both where the
velocity field is turbulent and when it is static. Furthermore, we investigate populations in terms of a continuos density
field and when the populations are treated via discrete particles. In the last case we focus on the competition and fixation
of one species compared to another. 相似文献
30.
We study different variants of the augmented Lagrangian (AL)‐based block‐triangular preconditioner introduced by the first two authors in [SIAM J. Sci. Comput. 2006; 28 : 2095–2113]. The preconditioners are used to accelerate the convergence of the Generalized Minimal Residual method (GMRES) applied to various finite element and Marker‐and‐Cell discretizations of the Oseen problem in two and three space dimensions. Both steady and unsteady problems are considered. Numerical experiments show the effectiveness of the proposed preconditioners for a wide range of problem parameters. Implementation on parallel architectures is also considered. The AL‐based approach is further generalized to deal with linear systems from stabilized finite element discretizations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献