Self-condensation experimental results

The preparation of stable silanetriols of the type RSi(OH)3 has proven to be difficult, compared to the other types of silanols, in view of their well known tendency to self-condense and result in siloxane rings and polymers [9]. However, in recent years, the use of very bulky R groups on silicon and carefully chosen experimental conditions has led to the isolation of many stable silanetriols. While silanetriols such as [Pg.377]

All the experimental data and most of the calculations would correspond to gas-phase results and examples of chiral self-recognition. Only exceptionally, condensed phase results of chiral self-recognition or gas-phase results of classical... 

Once again, the Ghadiri group used the peptide with the leucine zip. Starting from a racemic mixture of the peptide fragments E and N (with 15 and 17 amino acids respectively), homochiral products were preferentially formed in a homochiral selection process in the catalytic self-replication cycle. The initial mixture contained the two peptide fragments, which each consisted of d- and L-amino acids, i.e., a total of four competing molecular species (NL, N°, EL and E°). Thus, four different products could be formed in the condensation reaction TLL, TDD, TLD and TDL. As stated above, TLL and TDD were formed preferentially. The experimental results can be summarized as shown in Fig. 5.8. 

Self-condensation of the fundamental cubane cluster, [Fe4S4(SH)4] , in acetonitrile forms sulfide-bridged cubanes. The simplest process is the reversible reaction (47). However, unlike reaction (46) further condensations are possible. On the basis of NMR and mass spectroscopic-results, it was concluded that the prevalent species under the experimental conditions employed is [Fe4S4(SH)3]2[Fe4S4(SH)2](/i2-S)2 , a cluster of nuclearity 12 with proposed structure (37). This species was not isolated in substance ... 

The self-similar solution of an unsteady rarefaction wave in a gas-vapour mixture with condensation is investigated. If the onset of condensation occurs at the saturation point, the rarefaction wave is divided into two zones, separated by a uniform region. If condensation is delayed until a fixed critical saturation ratio Xc > 1 is reached, a condensation discontinuity of the expansion type is part of the solution. Numerical simulation, using a simple relaxation model, indicates that time has to proceed over more then two decades of characteristic times of condensation before the self-similar solution can be recognized. Experimental results on heterogeneous nucleation and condensation caused by an unsteady rarefaction wave in a mixture of water vapour, nitrogen gas and chromium-K)xide nuclei are presented. The results are fairly well described by the numerical rdaxation model. No plateau formation could be observed. 

A number of quite different techniques have been presented in the last few years for studying self-organisation phenomena in the bimolecular reactions in condensed matter. At present those are covered in the review article [49] and Proceedings of the conference [50] only we discuss their advantages and shortcomings, and the principal approximations involved (in particular, that by Kirkwood). Where possible, analytical results are compared with computer simulations, since very limited experimental data are known at present in this field. Those that do exist are also considered and the conditions for the experimental observation of cooperative effects under study are predicted theoretically. We hope that this book may stimulate new experimental studies in this very important field. 

A typical experiment is shown in Fig. 4. Pressure, temperature, vapour mass fraction and saturation ratio are compared with numerical calculation. The characteristic time r, required for numerical evaluation, is obtained by a fit of the experimental vapour mass fraction signal, resulting in r = 5 ms. The chosen values of critical saturation ratio and piston velocity are rather arbitrary. The experimental saturation ratio is calculated from pressure, temperature and vapour mass fraction. When no liquid mass can be detected, the vapour mass fraction is set to the initial value. Experiment and numerical simulation agree fairly well. The first part of the expansion of the gas-vapour mixture is isentropic and accounts for an increase of the saturation ratio. Condensation on the heterogeneous nuclei starts at a value of the measured saturation ratio of about three. After the onset of condensation a rise in temperature is observed due to the release of latent heat. The saturation ratio tends to unity as time increases. The plateau formed in the numerical solution is not observed in the experimental signal. Obviously, the experimental condition is far from self-similarity, and the expansion process is still in its early stage, where relaxation is dominant. The simple numerical model does not describe accurately the... 

The scaled probability densities are calculated using the data presented in Fig. 18 and plotted against t in Fig. 19. The scaled probability densities at all t fell nicely onto single master curves both for H and K, demonstrating that the dynamical scaling law holds for interfacial curvatures within experimental accuracy. The results shown in Fig. 19 stand out by the fact that they demonstrate that not only the global structure but also the local shape of the spinodal interface evolves with the dynamical self-similarity. In addition, the probability densities experimentally obtained in the present study are expected to be universal in a variety of condensed matter systems. 

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