Structure of Ag ON Rh and its effect on the adsorption of D2 and CO

Ag vapor deposited on Rh(100) is investigated as a possible model for the corresponding bimetallic cluster catalyst. Ag overlayer growth follows the Frank-Van der Merwe mechanism at 300 K and the Stranski-Krastanov mechanism at 640 K. The first Ag overlayer grows epitaxially with the Rh(100) surface and forms two-dimensional islands. The second layer reconstructs forming a pseudohexagonal lattice structure with a 19% greater Ag atom density than the first layer. Neither alloy formation nor dissolution of Ag into the Rh crystal lattice is observed. The presence of Ag decreases the capacity of the Rh(100) surface for both D₂ and CO chemisorption. In both cases, loss of adsorption sites on the Rh surface is attributed to physical site blocking by islands of Ag. Very weakly bound CO adsorption sites are observed which are attributed to CO bonding to Ag atoms in the first Ag overlayer. The Ag/Rh(100) system is found to be very similar to the analogous SiO₂ supported catalyst.     

Comparison of NNLO DIS scheme splitting functionswith results from exact gluon kinematics at small x

We consider the effect of exact gluon kinematics in the virtual photon-gluon impact factor at small x. By comparing with fixed order DIS scheme splitting and coefficient functions, we show that the exact kinematics results match the fixed order results well at each order, which suggests that they allow for an accurate NLL analysis of proton structure functions. We also present, available for the first time, x-space parameterisations of the NNLO DGLAP splitting functions in the DIS scheme, and also the longitudinal coefficients for neutral current scattering. Received: 21 July 2005, Revised: 14 September 2005, Published online: 25 November 2005     

Regioselective,intramolecular oxyselenation as a route to the tetrahydrofuran units of boromycin and aplasmomycin

A substance possessing the functionality and absolute configuration of the C(1′)-C(17′) half of boromycin has bean synthesized, employing an intra-molecular oxyselenation for construction of the tetrahydrofuran moiety from an olefinic diol.     

On the suitability of the virial equation for modeling the solubility of solids in supercritical fluids

Five model systems, the van der Waals fluid, the Soave-Redlich-Kwong fluid, the Peng-Robinson fluid, the hard-sphere fluid, and the square-well fluid, are used to examine the performance of the truncated virial expansion in describing the fugacity of a solute at infinite dilution in a solvent. It is demonstrated that the virial fugacity results deteriorate at significantly lower densities as the solute becomes larger. This has consequences for attempts to describe the solubility of solids in supercritical fluids, where the virial expansion, truncated after the third virial coefficient, has been considered as a modeling option. The results of this work suggest that, for the densities and solute-to-solvent size ratios commonly encountered in supercritical extraction, the truncated virial expansion should not be expected to describe correctly the solute fugacity, and therefore any success it has in fitting solubility data should be viewed with caution.     

Beliefs and Attitudes Toward Mathematics Among Third- and Fifth-Grade Students: A Descriptive Study

A survey on attitudes toward mathematics of third- and fifth-grade students enrolled in a large urban school district was conducted in the spring of 1994 as part of a review of the mathematics program. Student responses to survey items were analyzed with respect to gender and grade level. Although girls and boys were equally likely to indicate that they like mathematics, in both Grades 3 and 5, boys were more likely than girls to report being good at mathematics. This result has often been reported for older students but has rarely been explored in younger children. Some gender and grade differences were observed in students' attitudes towards the specific strands of mathematics. Both girls and boys in Grade 5 were more likely than students in Grade 3 to believe that mathematics was relevant to their lives. Virtually all children thought that both girls and boys needed to study mathematics. No gender or grade differences in students' beliefs regarding the process of learning mathematics were observed. The results support the need for further research to identify variables that influence the development of student perceptions and attitudes toward mathematics during elementary school.     

The Uses of Polynuclear Metal Complexes to Develop Designed Dispersions of Supported Metal Oxides: Part I. Synthesis and Characterization

One way to design a catalyst begins with a consideration of thereaction mechanism to the desired product so that only the chemistryrequired of that mechanism will be present on the surface. The reactionmechanism will suggest the structure(s) to be developed on the surface whichshould be stabilized against changes during operation. We believe that thisideal may be approached by decorating surfaces or porous powders with amonolayer of metal complexes having the desired structures. These complexesmay be partially decomposed to develop a high dispersion of the supportedmetal oxide.     

A survey of solution techniques for the partially observed Markov decision process

We survey several computational procedures for the partially observed Markov decision process (POMDP) that have been developed since the Monahan survey was published in 1982. The POMDP generalizes the standard, completely observed Markov decision process by permitting the possibility that state observations may be noise-corrupted and/or costly. Several computational procedures presented are convergence accelerating variants of, or approximations to, the Smallwood-Sondik algorithm. Finite-memory suboptimal design results are reported, and new research directions involving heuristic search are discussed.This research was supported by NSF Grant ECS-8708183 and ARO Contract DAAG-29-85-K0089.