TS-1 zeolite microengineered reactors for 1-pentene epoxidation

A zeolite-based microengineered reactor was fabricated and tested for 1-pentene epoxidation over titanium silicalite-1 (TS-1) catalyst, which has been selectively incorporated within the microreactor channel using a new synthesis procedure.     

A Geometric Invariant for Metabelian Pro-p Groups

In [2] Bieri and Strebel introduced a geometric invariant forfinitely generated abstract metabelian groups that determineswhich groups are finitely presented. For a valuable survey oftheir results, see [6]; we recall the definition briefly inSection 4. We shall introduce a similar invariant for pro-pgroups. Let F be the algebraic closure of F_p and U be the formal powerseries algebra F[T], with group of units U^x. Let Q be a finitelygenerated abelian pro-p group. We write Z_p[Q] for the completedgroup algebra of Q over Z_p. Let T(Q) be the abelian group Hom(Q,U^x) of continuous homomorphisms from Q to U^x. We write 1 forthe trivial homomorphism. Each vT(Q) extends to a unique continuousalgebra homomorphism from Z_p[Q]to U.     

A finite element method for interface problems in domains with smooth boundaries and interfaces

This paper is concerned with the analysis of a finite element method for nonhomogeneous second order elliptic interface problems on smooth domains. The method consists in approximating the domains by polygonal domains, transferring the boundary data in a natural way, and then applying a finite element method to the perturbed problem on the approximate polygonal domains. It is shown that the error in the finite element approximation is of optimal order for linear elements on a quasiuniform triangulation. As such the method is robust in the regularity of the data in the original problem.     

Density of states and charge distribution in hydrogenated amorphous silicon

The local density of states and the charge distribution in a cluster model of hydrogenated amorphous silicon is calculated using the recursion method. The results indicate an average charge transfer of 0.3 electrons from silicon to hydrogen. In addition Si-H dipoles carry small negative charges, which are neutralized by a positively charged bulk of silicon atoms. There are also static spatial charge fluctuations, which are due to the topological disorder.     

Cross section and stellar reaction rates for the 42Ca(p, γ) reaction

The cross section for the ⁴²Ca(p, γ)⁴³Sc reaction has been measured over the lab energy range from 0.7 to 5.5 MeV using a positron spectrometer to measure the annihilation radiation from the decay of 3.9 h ⁴³Sc. Stellar reaction rates N_A〈σv〉 have been calculated from the experimental cross section curve for a series of three temperatures of interest for explosive oxygen and silicon burning in stars. The calculated rates are compared with the theoretical predictions of Woosley et al. and found to be in agreement within the experimental errors and the quoted validity of the theoretical calculation     

The use of electron impact dissociation and the photon-photon cascade technique to measure the lifetime of the B2Σ+ state of CN

The lifetime of the (B³Σ⁺_{υ= 0, 1} state of the CN radical has been measured by the photon-photon delayed coincidence technique, the CN radical being produced by electron impact dissociation of acetonitrile. This is the first lifetime measurement in a free radical by this method. The optical cascade in the band spectrum of CN used for the present measurement is H²Π_r - B²Σ⁺ - X²Σ⁺. The lifetime of the (B²Σ⁺)_{υ=0, 1} state in CN has been found to be 61.1 ± 7.6 ns.     

Chemisorption of carbon monoxide on platinum {111}: Reflection-absorption infrared spectroscopy

Reflection-adsorption infrared spectroscopy has been combined with thermal desorption and surface stoichiometry measurements to study the structure of CO chemisorbed on a {111}- oriented platinum ribbon under uhv conditions. Desorption spectra show a single peak at coverages > 10¹⁴ molecules cm^?2, with the desorption energy decreasing with increasing coverage up to 0.4 of a monolayer, and then remaining constant at ≈135 kJ mol^?1 until saturation. The “saturation” coverage at 300 K is 7 × 10¹⁴ molecules cm^?2, and no new low temperatures state is formed after adsorption at 120 K. Infrared spectra show a single very intense, sharp band over the spectral range investigated (1500 to 2100 cm^?1), which first appears at low coverages at 2065 cm^?1 and shifts continuously with increasing coverage to 2101 cm^?1 at 7 × 10¹⁴ molecules cm^?2. The halfwidth of the band at 2101 cm^?1 is 9.0 cm^?1, independent of temperature and only slightly dependent on coverage. The band intensity does not increase uniformly with increasing coverage, and hysteresis is observed between adsorption and desorption sequences in the variation of both the band intensity and frequency as a function of coverage. The frequency shift and the virtual invariance of the absorption band halfwidt with increasing coverage (Jespite recent LEED evidence for overlayer compression in this system) are attributed to strong dipole-dipole coupling in the overlayer.