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991.
At high magnetic fields the 128.8 MHz (195)Pt NMR of all the species in the series [PtCl(n)(H(2)O)(6-n)](4-n) (n = 2-6) display unique (35/37)Cl isotope effects resulting in a unique 'fine-structure' of each individual resonance, which constitutes an unambiguous spectroscopic 'fingerprint' characteristic of the structure of the octahedral platinum(iv) complex, provided (195)Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed (195)Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic (18)O enrichment of the coordinated water molecules in the series [Pt(35/37)Cl(n)(H(2)(16/18)O)(6-n)](n-2) (n = 2-6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(iv) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of (195)Pt NMR shielding to very small and subtle Pt-(35/37)Cl and Pt-(16/18)OH(2) bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes. 相似文献
992.
L Wu V Degirmenci PC Magusin BM Szyja EJ Hensen 《Chemical communications (Cambridge, England)》2012,48(76):9492-9494
The dual template synthesis of zeolite SSZ-13 by use of trimethyl-adamantanammonium hydroxide and a diquaternary-ammonium mesoporogen induces considerable mesoporosity without impeding zeolite microporosity. The strongly improved accessibility of Br?nsted sites in mesoporous SSZ-13 increases its stability during application as an acid catalyst in the methanol-to-olefins reaction. 相似文献
993.
Banerjee S Mulder P Kleijn JM Cohen Stuart MA 《The journal of physical chemistry. A》2012,116(25):6481-6488
The roughness and softness of interacting surfaces are both important parameters affecting the capillary condensation of water in apolar media, yet are poorly understood at present. We studied the water capillary adhesion between a cellulose surface and a silica colloidal probe in hexane by AFM force measurements. Nanomechanical measurements show that the Young's modulus of the cellulose layer in water is significantly less (~7 MPa) than in hexane (~7 GPa). In addition, the cellulose surface in both water and hexane is rather rough (6-10 nm) and the silica probe has a comparable roughness. The adhesion force between cellulose and silica in water-saturated hexane shows a time-dependent increase up to a waiting time of 200 s and is much (2 orders of magnitude) lower than that expected for a capillary bridge spanning the whole silica probe surface. This suggests the formation of one or more smaller bridges between asperities on both surfaces, which is confirmed by a theoretical analysis. The overall growth rate of the condensate cannot be explained from diffusion mediated capillary condensation alone; thin film flow due to the presence of a wetting layer of water at both the surfaces seems to be the dominant contribution. The logarithmic time dependence of the force can also be explained from the model of the formation of multiple capillary bridges with a distribution of activation times. Finally, the force-distance curves upon retraction show oscillations. Capillary condensation between an atomically smooth mica surface and the silica particle show less significant oscillations and the adhesion force is independent of waiting time. The oscillations in the force-distance curves between cellulose and silica may stem from multiple bridge formation between the asperities present on both surfaces. The softness of the cellulose surface can bring in additional complexities during retraction of the silica particle, also resulting in oscillations in the force-distance curves. 相似文献
994.
We present a method, Non-Stationary Forward Flux Sampling, that allows efficient simulation of rare events in both stationary and non-stationary stochastic systems. The method uses stochastic branching and pruning to achieve uniform sampling of trajectories in phase space and time, leading to accurate estimates for time-dependent switching propensities and time-dependent phase space probability densities. It is suitable for equilibrium or non-equilibrium systems, in or out of stationary state, including non-Markovian or externally driven systems. We demonstrate the validity of the technique by applying it to a one-dimensional barrier crossing problem that can be solved exactly, and show its usefulness by applying it to the time-dependent switching of a genetic toggle switch. 相似文献
995.
Lionel Petton Andrs E. Ciolino Milan M. Stamenovi Pieter Espeel Filip E. Du Prez 《Macromolecular rapid communications》2012,33(15):1310-1315
A straightforward, novel strategy based on the in situ functionalization of polymers prepared by nitroxide‐mediated polymerization (NMP), for the use as an extension toward block copolymers and post‐polymerization modifications, has been investigated. The nitroxide end group is exchanged for a thiocarbonylthio end group by a rapid transfer reaction with bis(thiobenzoyl) disulfide to generate in situ reversible addition–fragmentation chain transfer (RAFT) macroinitiators. Moreover, not only have these macroinitiators been used in chain extension and block copolymerization experiments by the RAFT process but also a thiol‐terminated polymer is synthesized by aminolysis of the RAFT end group and subsequently reacted with dodecyl vinyl ether by thiol‐ene chemistry. 相似文献
996.
Bin Li Chang Jun Yu Kok Lay Teo Guang Ren Duan 《Journal of Optimization Theory and Applications》2011,151(2):260-291
In this paper, we consider a class of optimal control problems subject to equality terminal state constraints and continuous
state and control inequality constraints. By using the control parametrization technique and a time scaling transformation,
the constrained optimal control problem is approximated by a sequence of optimal parameter selection problems with equality
terminal state constraints and continuous state inequality constraints. Each of these constrained optimal parameter selection
problems can be regarded as an optimization problem subject to equality constraints and continuous inequality constraints.
On this basis, an exact penalty function method is used to devise a computational method to solve these optimization problems
with equality constraints and continuous inequality constraints. The main idea is to augment the exact penalty function constructed
from the equality constraints and continuous inequality constraints to the objective function, forming a new one. This gives
rise to a sequence of unconstrained optimization problems. It is shown that, for sufficiently large penalty parameter value,
any local minimizer of the unconstrained optimization problem is a local minimizer of the optimization problem with equality
constraints and continuous inequality constraints. The convergent properties of the optimal parameter selection problems with
equality constraints and continuous inequality constraints to the original optimal control problem are also discussed. For
illustration, three examples are solved showing the effectiveness and applicability of the approach proposed. 相似文献
997.
Canghua Jiang Qun Lin Changjun Yu Kok Lay Teo Guang-Ren Duan 《Journal of Optimization Theory and Applications》2012,154(1):30-53
In this paper, we consider a class of optimal control problems with free terminal time and continuous inequality constraints. First, the problem is approximated by representing the control function as a piecewise-constant function. Then the continuous inequality constraints are transformed into terminal equality constraints for an auxiliary differential system. After these two steps, we transform the constrained optimization problem into a penalized problem with only box constraints on the decision variables using a novel exact penalty function. This penalized problem is then solved by a gradient-based optimization technique. Theoretical analysis proves that this penalty function has continuous derivatives, and for a sufficiently large and finite penalty parameter, its local minimizer is feasible in the sense that the continuous inequality constraints are satisfied. Furthermore, this local minimizer is also the local minimizer of the constrained problem. Numerical simulations on the range maximization for a hypersonic vehicle reentering the atmosphere subject to a heating constraint demonstrate the effectiveness of our method. 相似文献
998.
999.
1000.
Shu‐Hua Zhang Dr. Hong‐Wei Xi Prof. Dr. Kok Hwa Lim Qingyong Meng Prof. Dr. Ming‐Bao Huang Prof. Dr. Cheuk‐Wai So 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(14):4258-4263
The synthesis and characterization of a singlet delocalized 2,4‐diimino‐1,3‐disilacyclobutanediyl, [LSi(μ‐CNAr)2SiL] ( 2 , L: PhC(NtBu)2, Ar: 2,6‐iPr2C6H3), and a silylenylsilaimine, [LSi(?NAr)? SiL] ( 3 ), are described. The reaction of three equivalents of the disilylene [LSi? SiL] ( 1 ) with two equivalents of ArN?C?NAr in toluene at room temperature for 12 h afforded [LSi(μ‐CNAr)2SiL] ( 2 ) and [LSi(?NAr)? SiL] ( 3 ) in a ratio of 1:2. Compounds 2 and 3 have been characterized by NMR spectroscopy and X‐ray crystallography. Compound 2 was also investigated by theoretical studies. The results show that compound 2 possesses singlet biradicaloid character with an extensive electronic delocalization throughout the Si2C2 four‐membered ring and exocyclic C?N bonds. Compound 3 is the first example of a silylenylsilaimine, which contains a low‐valent silicon center and a silaimine substituent. A mechanism for the formation of 2 and 3 is also proposed. 相似文献