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101.
Solid state 1H, 29Si and 31P MAS NMR have been used to investigate the microstructure of phosphosilicate gels prepared by a modified sol-gel method involving hydrolysis of silicon precursors in a solely aqueous environment at 50 °C. Gels with molar compositions 5, 10, 20 and 30 mol% P2O5 in P2O5-SiO2 were studied. After drying to 400 °C the gels have very similar structures formed by a siloxane framework containing silanol groups and trapped molecules of orthophosphoric acid together with a very small amount, of pyrophosphoric acid. Unlike the gel samples previously synthesized by the hydrolysis of the silicon precursor in alcoholic solution at room temperature, the co-polymerization of phosphorus and silicon is much reduced. Although co-polymerization increases with phosphorus content, it still represents less than 50% of the phosphorus in the 30 mol% P2O5 gel. Furthermore there is no evidence for six-coordinated silicon in the glassy matrix. 相似文献
102.
A new asymmetric approach to the erythrinan alkaloid system is described, which involves chiral base desymmetrisation of a ring fused imide and a 6-exo-trig radical cyclisation as the key steps. 相似文献
103.
Nigel Boston 《Inventiones Mathematicae》1991,103(1):181-196
104.
Nigel Ribeiro Denis Heissler Anne Marie Albrecht-Gary Mari Gotoh Yoichi Nakatani Guy Ourisson 《Tetrahedron》2007,63(16):3395-3407
Cholesterol plays the role of membrane reinforcer in eukaryotes, whereas hopanoids play the same role in bacteria. Which components could have reinforced ‘primitive’ membranes? We describe here an efficient biomimetic synthesis of bi- and tri-cyclopolyprenols and demonstrate that these compounds reinforce the membranes of polyprenyl phosphate, which we speculated as ‘primitive’ membranes. 相似文献
105.
A potentially biomimetic synthesis of the guanidine-containing marine natural product crambescidin 359 via a double Michael addition of guanidine to a suitably functionalised bis-enone is reported. 相似文献
106.
Nigel J. Newton 《Journal of statistical physics》2008,133(4):711-737
This paper connects non-equilibrium statistical mechanics and optimal nonlinear filtering. The latter concerns the observation-conditional
behaviour of Markov signal processes, and thus provides a tool for investigating statistical mechanics with partial observations. These allow entropy
reduction, illustrating Landauer’s Principle in a quantitative way.
The joint process comprising a signal and its nonlinear filter is irreversible in its invariant distribution, which therefore
corresponds to a non-equilibrium stationary state of the associated joint system. Macroscopic entropy and energy flows are identified for this state. Since these are driven by observations internal to the system, they do not cause entropy increase, and so the joint system makes statistical mechanical sense in reverse
time.
Time reversal yields a dual system in which the signal and filter exchange roles. Despite the structural similarity of the original and dual systems,
there is a substantial asymmetry in their complexities. This reveals the direction of time, despite the systems being in stationary
states that do not produce entropy.
This work was partially supported by Leverhulme Trust Research Fellowship 2003/0426, by MURI Grant F49620-02-1-0325 (Complex
Adaptive Networks for Co-operative Control), by ARO-MURI Grant DAAD19-00-1-0466 (Data Fusion in Large Arrays of Microsensors
(sensor web)) and by NSF-ITR Grant CCR-0325774 Collaborative Research: New Approaches to Experimental Design and Statistical
Analysis of Genomic and Structural Biological Data from Multiple Sources. 相似文献
107.
Nigel Howard 《The Journal of the Operational Research Society》1993,44(6):613-623
This paper addresses two questions. (i) What is the role of emotions in decision-making? (ii) Can emotions be attributed to organizations, and is their role in decisions made between organizations the same as in decisions made between individual people? The answers given to question (ii) are yes and yes. The proposed answer to question (i) is based upon a game-theoretic approach, which considers how emotions may be of strategic benefit to game players. 相似文献
108.
Cheng F Kelly SM Young NA Clark S Francesconi MG Lefebvre F Bradley JS 《Chemical communications (Cambridge, England)》2005,(45):5662-5664
We report a general method for the preparation of transition-metal silicon nitride nanocomposites; for example, mesoporous Pd-Si3N4 nanocomposite materials with high surface area were prepared by pyrolysis of a silicon palladium imide-chloride complex which was synthesized by reaction of silicon diimide gel with palladium chloride. These porous nanocomposites catalyse organic reactions. 相似文献
109.
110.
I.Ralph C. Bick Mohammad A. Hai Nigel W. Preston Rex T. Gallagher 《Tetrahedron letters》1980,21(6):545-546
Aristotelinone and serratoline, two new Aristotelia alkaloids, are shown to have indole and indolenine structures respectively from their spectra and reduction products. 相似文献