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31.
Jos R. Ascenso Maria de Deus Carvalho Alberto R. Dias Carlos C. Romo Maria J. Calhorda Luis F. Veiros 《Journal of organometallic chemistry》1994,470(1-2):147-152
The metallocene thioether derivatives [Cp2M(MeSCH2CH2SMe)][PF6]2 (1, M = MO; 2, M = W), [Cp2Mo(SCH2CH2SMe)][PF6] (3) and [Cp2M(SCH2CH2S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 ± 2 kJ mol−1), 2 (51.2 ± 4.6 kJ mol−1) and 3 (30.0 ± 3.1 kJ mol−1). Extended Hückel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S---C---C---S chain, is responsible for the observed fluxional behaviour. 相似文献
32.
Ward Whitt 《Queueing Systems》1991,9(3):235-268
A fundamental principle of queueing theory isL=W (Little's law), which states that the time-average or expected time-stationary number of customers in a system is equal to the product of the arrival rate and the customer-average or expected customer-stationary time each customer spends in the system. This principle is now well known and frequently applied. However, in recent years there have been extensions, such as H=G and the continuous, distributional, ordinal and central-limit-theorem versions, which show that theL=W relation, when viewed properly, has much more power than was previously realized. Moreover, connections have been established between H=G and other fundamental relations, such as the rate conservation law and PASTA (Poisson arrivals see time averages), which show that there is a much greater unity in the overall theory than was previously realized. This paper provides a review.This paper is dedicated to the memory of our colleague Professor Peter Franken (1937–1989), who contributed greatly to the subject of this paper and to queueing theory more generally. 相似文献
33.
Sergey?P.?BabailovEmail author Lubov?D.?Nikulina 《Journal of inclusion phenomena and macrocyclic chemistry》2005,51(1-2):103-109
1H and 13C NMR measurements are reported for the CDCl3 and CD2Cl2 solutions of [La(NO3)3(18-crown-6)] (I), [Pr(NO3)3(18-crown-6)] (II) and [Ce(NO3)3(18-crown-6)] (III) complexes. Temperature dependencies of the 1H NMR spectra of II have been analyzed using the dynamic NMR methods for multi-site exchange. Two types of conformational dynamic processes in II were identified (the first one with activation enthalpy ΔH
‡=26 ± 4 kJ/mol is conditioned by interconversion of complex enantiomeric form and pseudorotation of macrocycle molecule upon the C
2 symmetry axis, the second one with ΔH
‡=46 ± 5 kJ/mol is conditioned by macrocycle molecule inversion). Studies of the values of the lanthanide-induced shifts revealed that the structure of complexes in solution is similar to that reported for the complex I in the crystal state.This revised version was published online in July 2005 with a corrected issue number. 相似文献
34.
The complex, bis[N‐6‐aminopyridyl‐N‐(1S)‐(+)‐10‐camphorsulfonylamino]palladium, Pd[(S)‐APCS]2, 1 , was prepared by reaction of 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine with PdCl2 in THF. Complex 1 has been characterized by spectroscopic methods and its structure has been determined by X‐ray crystallography. Crystal data: space group C2, a= 16.082 (2), b = 17.104 (2), c = 13.051 (2)Å, β = 99.95 (1)°, V = 3535.9 (8) Å3, Z = 2 with final residuals R1 = 0.0491 and wR2 = 0.0944. Two independent molecules, (S,S)‐Pd[(S)‐APCS]2, 1a , and (R,R)‐Pd[(S)‐APCS]2, 1b , were found in each asymmetric unit, which exchange to each other via a series of nitrogen inversion and C‐C bond rotation. The inversion energy (ΔGc1≠) and the energy barrier (δGc2≠) were 11.5 ± 0.1 Kcal mol?1 at 246 K and 9.8 ± 0.1 Kcal mol?1 at 199 K, respectively, calculated by dynamic NMR data. 相似文献
35.
Preferred conformations of some azaspiran systems substituted with large groups at the nitrogen atoms were established by UV absorption spectroscopy. These groups prohibit the inversion at nitrogen, as was deduced from the1H NMR spectra. 相似文献
36.
Danny K. Long Wolfgang Bangerth Derek R. Handwerk Christopher B. Whitehead Patrick D. Shipman Richard G. Finke 《Journal of computational chemistry》2022,43(1):43-56
In order to quantitatively predict nano- as well as other particle-size distributions, one needs to have both a mathematical model and estimates of the parameters that appear in these models. Here, we show how one can use Bayesian inversion to obtain statistical estimates for the parameters that appear in recently derived mechanism-enabled population balance models (ME-PBM) of nanoparticle growth. The Bayesian approach addresses the question of “how well do we know our parameters, along with their uncertainties?.” The results reveal that Bayesian inversion statistical analysis on an example, prototype nanoparticle formation system allows one to estimate not just the most likely rate constants and other parameter values, but also their SDs, confidence intervals, and other statistical information. Moreover, knowing the reliability of the mechanistic model's parameters in turn helps inform one about the reliability of the proposed mechanism, as well as the reliability of its predictions. The paper can also be seen as a tutorial with the additional goal of achieving a “Gold Standard” Bayesian inversion ME-PBM benchmark that others can use as a control to check their own use of this methodology for other systems of interest throughout nature. Overall, the results provide strong support for the hypothesis that there is substantial value in using a Bayesian inversion methodology for parameter estimation in particle formation systems. 相似文献
37.
《Comptes Rendus Chimie》2014,17(4):342-351
A systematic study of the design and characterization of silica-microemulsion templates is presented. The ternary phase diagrams in micro-heterogeneous systems, by using a non-ionic surfactant (Brij 30) and different silica precursors (MTEOS, TEOS, PTEOS), have been drawn. Based on Khalweit diagrams, the phase inversion temperature was estimated as close to 315 K, for both alchil (TEOS) and aril (PTEOS) types of alcoxides. By correlating the information obtained from phase diagrams at room temperature with that of size effects revealed by VIS absorption molecular probes (bromthymol blue dye), the phase inversion point, i.e. the transition point from water-in-oil to oil-in-water microemulsion, was also clearly established as corresponding to R ∼ 1. Besides technically attractive features such as a wide variety of inorganic and hybrid nanomaterials, high specific surface and highly efficient applicative properties of the final materials, the approach of silica-microemulsion-based templates can be seen as a route towards the Green Chemistry concept. 相似文献
38.
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40.
Benjamin Radel Edme H. Hardy Zorana Djuric Markus Mahlbacher Michael Haist Harald S. Müller 《Magnetic resonance in chemistry : MRC》2019,57(10):836-844
Not only in low-field nuclear magnetic resonance, Laplace inversion is a relevant and challenging topic. Considerable conceptual and technical progress has been made, especially for the inversion of data encoding two decay dimensions. Distortion of spectra by overfitting of even moderate noise is counteracted requiring a priori smooth spectra. In this contribution, we treat the case of simple and fast one-dimensional decay experiments that are repeated many times in a series in order to study the evolution of a sample or process. Incorporating the a priori knowledge that also in the series dimension evolution should be smooth, peak position can be stabilized and resolution improved in the decay dimension. It is explained how the standard one-dimensional regularized Laplace inversion can be extended quite simply in order to include regularization in the series dimension. Obvious improvements compared with series of one-dimensional inversions are presented for simulated as well as experimental data. For the latter, comparison with multiexponential fitting is performed. 相似文献