Beiträge zur Chemie der Si-N-Bindung,XI [1] polymere 1, 3-diaza-2-sila-cyclopentane

Linear polymers are built up by polycondensation of aminodimethylsilyl- or aminodiphenylsilyl-terminated monomeric or oligomeric 1,3-diaza-2-sila-cyclo-pentanes with bisphenols or disilanols. The thermal properties of the polymers are determined.     

Thermodynamische und strukturelle Untersuchungen an den Verbindungen der Systeme KCl/MCl2 (M  Ca,Cd, Co,Ni)

Thermodynamic and Structural Investigations on Compounds of the Systems KCl/Mcl₂ (M=Ca, Cd, Co, Ni) . The formation of ternary chlorides according to the equation nKCl + MCl₂ = K_nMCl_n+2 with M = Ca, Cd, Co, Ni was investigated with a galvanic cell for solid electrolytes. Additionally to the Gibbs energies for the solid reactions, ΔG_R, the entropies, ΔS_R, and enthalpies, ΔH_R were determined by the dependence of the e.m.f. on temperature. But the stability of the double chlorides is given by the free enthalpy of synproportionation from the neighboured compounds. In case of RbSrCl₃ and RbPbCl₃ (stable only at higher temperature) the synproportionation is endothermic; the loss of enthalpy is compensated by a gain of entropy. The same is valid for K₂CoCl₄. Lattice parameters were measured for the modifications of KCaCl₃; the structure of KCdCl₃ was refined by single crystal measurements.     

RandomlyH-coverable graphs

A graph israndomly matchable if every matching of the graph is contained in a perfect matching. We generalize this notion and say that a graphG israndomly H-coverable if every set of independent subgraphs, each isomorphic toH, that does not cover the vertices ofG can be extended to a larger set of independent copies ofH. Various problems are considered for the situation whereH is a path. In particular, we characterize the graphs that are randomlyP ₃ -coverable.     

Parallel synthesis and evaluation of 132 (+)-1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one (CBI) analogues of CC-1065 and the duocarmycins defining the contribution of the DNA-binding domain

The solution-phase, parallel synthesis and evaluation of a library of 132 (+)-1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-one (CBI) analogues of CC-1065 and the duocarmycins containing dimeric monocyclic, bicyclic, and tricyclic heteroaromatic replacements for the DNA-binding domain are described. This systematic study revealed clear trends in the structural requirements for observation of potent cytotoxic activity and DNA alkylation efficiency, the range of which spans a magnitude of > or =10 000-fold. Combined with related studies, these results highlight that the role of the DNA-binding domain goes beyond simply providing DNA-binding selectivity and affinity (10-100-fold enhancement in properties), consistent with the proposal that it contributes significantly to catalysis of the DNA alkylation reaction accounting for as much as an additional 1000-fold enhancement in properties.     

Limits of time-reversal focusing through multiple scattering: long-range correlation

Experimental results of time-reversal focusing in a high-order multiple scattering medium are presented and compared to theoretical predictions based on a statistical model. The medium consists of a random collection of parallel steel rods. An ultrasonic source (3.2 MHz) transmits a pulse that undergoes multiple scattering and is recorded on an array. The time-reversed waves are sent by the array back to the source through the scattering medium. The quality of temporal focusing is very well predicted by a simple statistical model. However, for thicker samples, persistent temporal side-lobes appear. We interpret these side-lobes as a consequence of the growing number of crossing paths in the sample due to high-order multiple scattering. As to spatial focusing, the resolution is practically independent from the array's aperture. With a 16-element array, the resolution was found to be 30 times finer than in a homogeneous medium. Resolutions of the order of the wavelength (0.5 mm) were attained. These results are discussed in relation with the statistical properties of time-reversal mirrors in a random medium.     

The spatial focusing of a leaky time reversal chaotic cavity

Elastic waves propagating inside a solid chaotic cavity create a diffusive random field that contains both longitudinal and shear waves. In the current paper, we are interested in the field radiated in a fluid in contact with such cavity. The goal of this paper is to predict the spatial focusing properties that can be obtained in the fluid using a time-reversal piezoelectric transducer in contact with the cavity. We present a statistical approach that supposes a fully diffused wavefield inside the cavity with an equipartition of energy between longitudinal and shear waves. We show that the critical angles of transmission in the solid-fluid interface generate a cut-off of the spatial frequencies and then a degradation in the spatial focusing. This limitation can be overcome using a rough surface. A set of experiments conducted in the MHz range confirm the theoretical model.     

Adsorption and thermal evolution of SO2 on Ru(0001)

Using high resolution S 2p and O 1s x-ray photoelectron spectroscopies, the adsorption of SO2 and its surface bound reaction products on Ru(0001) have been investigated simultaneously while dosing SO2 and while heating the adsorbed species. SO2 is found to adsorb on Ru(0001) at 100 K molecularly in two variants as well as dissociatively and to react to SO3, SO4, SO, and S with increasing coverage. After the monolayer has been saturated, SO2 adsorbs molecularly in multilayers. When heating adsorbed SO2 from 100 K, SO, SO2, and SO4 decompose in a wide temperature range up to 305 K. In contrast SO3 is found to be stable bound to Ru(0001) up to 300 K and to disappear from the surface to below 325 K. At 550 K the surface remains with a saturated atomic sulfur and oxygen layer and some sulfur species in a second layer. Our quantitative analysis of the sulfur amount bound to the surface supports a simple desorption process only for SO4. All other species mainly or partly decompose on the surface.     

Single and multiple photoionisation of H2S by 40-250 eV photons

Multi-electron coincidence measurements on photoionisation of H(2)S have been carried out at photon energies from 40 to 250 eV. They quantify molecular field effects on the Auger process in detail and are in good agreement with the existing theory. Spectra of core-valence double ionisation of H(2)S are presented and partially analysed. Auger decays from the core-valence states produce triply charged product spectra with unexplained and surprising intensity distributions. Triple ionisation by the double Auger process from 2p hole states shows little effect of the molecular field splitting, but includes a substantial contribution from cascade processes, some involving dissociation in intermediate states. The onset of triple ionisation at the molecular geometry is determined as 61 ± 0.5 eV.