Maximizing synthetic efficiency: multi-component transformations lead the way

With the emergence of high-throughput screening in the pharmaceutical industry in the early 1990's, organic chemists were faced with a new challenge: how to prepare large collections of molecules (the libraries) to "feed" the high-throughput screen? The unique exploratory power of some reactions (such as the 40 year-old Ugi four-component condensation) was soon recognized to be extremely valuable to produce libraries in a time- and cost-effective manner. Over the last five years, industrial and academic researchers have made these powerful transformations into one of the most efficient and cost-effective tools for combinatorial and parallel synthesis.     

In situ determination of glass transition temperatures in thin polymer films

A method for determining the glass transition temperature T_g of waveguiding NLO-films is presented. This enables for the first time monitoring of the T_g of NLO-films on device substrates in situ. T_g is shown to follow from the temperature dependencies of the refractive index n(T) or the thickness d_f(T) of thin films.     

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An experimental study of the antineutron-light nucleus annihilation at 1.4 GeV/c

The heavy liquid bubble chamber, Gargamelle, has been used to investigate the gross features of the annihilation of antineutrons in light nuclei (mainly Carbon). Results are presented on the distributions of multiplicity, momentum and emission angle for charged pions and protons together with a simple model to describe them.     

A study of diffusion phenomena in the rare earth region: The reaction 159Tb + 620 MeV 86Kr

Kinetic energy spectra, charge and angular distributions have been measured with ΔE-E telescopes for over twenty-five identified elements from the reaction ${}^{159}\text{Tb}\text{+ 620}\text{MeV}{}^{86}\text{Kr}$. At all angles and for all observed atomic numbers, the energy spectra indicate the presence of energetically relaxed products in the vicinity of the Coulomb barrier. Elements near the projectile also show a sizable contribution from incompletely damped events at angles close to the grazing angle. The charge distributions are peaked near the projectile Z and demonstrate a strong shape dependence on the angle of observation. The angular distributions show a weakening of the side peaking with increasing proton transfer to or from the projectile. Angular distributions and angle-integrated charge distributions have been calculated with a diffusion model which assumes the formation of a rotating intermediate complex with an l-dependent lifetime. The mass exchange between the two segments of the intermediate complex is treated as a diffusive process which is described by the master equation. Values for the diffusion constant, the overlap of the two density distributions, the mean lifetime of the intermediate complex and the spread in the average lifetime were used which semiquantitatively reproduced data from the 620 MeV ⁸⁶Kr reaction on ¹⁸¹Ta and ¹⁹⁷Au targets. Satisfactory agreement was obtained between these calculations and the data from the ¹⁵⁹Tb target. In addition, by increasing the lifetime of the complex by 30 %, the previously measured data for the ^{107, 109}Ag + 620 MeV ⁸⁶Kr reaction was semiquantitatively reproduced.