Sol-gel polycondensation of methyltrimethoxysilane in ethanol studied by <Superscript>29</Superscript>Si NMR spectroscopy using a two-step acid/base procedure

Sol-gel polymerization of methyltrimethoxysilane (MTMS) in ethanol using a two-step acid/base catalyzed procedure (B2) is followed by ²⁹Si NMR spectroscopy. Analysis of the structural evolution of the B2 system shows that esterification of monomeric and end silicon species is rate-limited while that of linear and cyclic species is able to reach pseudoequilibrium in the second basic step. Condensation reactivity is reduced with increasing network connectivity, however, to a much less degree under B2 conditions than MTMS polymerization under acidic conditions. Steric effects as well as many other factors are attributed to this trend. The concentration of cyclic and polycyclic species of the B2 system is nearly 3 times lower compared to the acid-catalyzed system. The empirical degree of condensation at the gel point is determined to be 0.88. The effects of cyclization and phase separation on MTMS gelation are discussed for both B2 and acid-catalyzed systems. Based on these results it is believed that MTMS-based gels form for B2 and not acid-catalyzed conditions due to reduced cyclization, rapid hydrolysis and condensation, effective use of functional groups, and effective contribution of branched and polycyclic species as crosslinking points to connect polymeric chains in the B2 system.     

Experimental evidence for a light and broad scalar resonance in D(+) --> pi(-)pi(+)pi(+) decay

From a sample of 1172 +/- 61 D(+)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)-->pi(-)pi(+)pi(+))/gamma(D(+)-->K-pi(+)pi(+)) = 0.0311 +/- 0.0018(+0.0016)(-0.0026). Using a coherent amplitude analysis to fit the Dalitz plot of these decays, we find strong evidence that a scalar resonance of mass 478(+24)(-23) +/- 17 MeV/c(2) and width 324(+42)(-40) +/- 21 MeV/c(2) accounts for approximately half of all decays.     

A comparison of the drag-reducing benefits of riblets in internal and external flows

Equivalent drag-reducing performance is observed with 3 M riblets in fully developed internal (pipe) and developing external (flat plate) flows. Drag reduction begins around h ⁺ = 3, peaks between 6 and 9% at about h ⁺ = 12, and becomes zero for a value of h ⁺ between 20 and 30. In laminar pipe flow no significant change in drag is observed with the 3 M riblets present. At high Reynolds numbers, after exhibiting fully rough behaviour, friction factors for the 3 M riblets are observed to monotonically decrease with increasing Reynolds number.     

Search for an effect of the ionic charge on the Coulomb capture of muons in Cu,CuSCN and Cu(SCN)2

Muonic Lyman series intensities and Coulomb capture ratios have been measured for CuSCN and Cu(SCN)₂, and the Cu Lyman series intensities also for Cu metal. No effect due to the ionic charge was found.     

Dielectric behavior of triethoxyfluorosilane aerogels

Low dielectric constant aerogels are being considered by the semiconductor industry as interlayer dielectrics to overcome capacitance problems which limit device feature sizes. Using sol-gel methods and CO₂ supercritical drying, a triethoxyfluorosilane (TEFS) precursor has been used to prepare bulk aerogels. Effects of pH and water to precursor ratio were studied with respect to aerogel dielectric and chemical properties. Methods of analysis for this study include FTIR-ATR and dielectric constant determination by impedance. Si-F bonds were determined to be present in both acid- and base-catalyzed TEFS. Dielectric constants were determined to increase slightly with increasing water to precursor ratios.     

First direct observation of strong interaction spin-orbit effects in antiprotonic atoms

The strong ¯p-nucleus spin-orbit interaction was investigated in a measurement of the strong-interaction effects of the 9→8 transition in ¯p ¹⁷⁴Yb at the Low-Energy Antiproton Ring (LEAR) at CERN. This measurement was part of an experimental programme where, for the first time, the fine-structure components of the last observable X-ray transition in a ¯p atom, which carries information on the strong ¯p-nucleus interaction, were resolved and studied individually. The observed splitting ΔE _exp=2408±26 eV consists of the electromagnetic fine-structure splitting ΔE _FS=2350 eV and an additional splitting Δ?=58±26 eV. In addition, one finds a significant difference in the level widths of Δ=195±59 eV with the larger value_?=1216±41 eV for the lower fine-structure level. This experiment follows an earlier measurement on ¯p ¹³⁸Ba, where the transition 8→7 is influenced by the strong interaction. In this case, however, the fine-structure components could not be resolved. The results for¹⁷⁴Yb may be attributed to a spin-orbit (LS) term in the complex strong-interaction potential.