Embedded cluster Δ-XANES modeling of adsorption processes on Pt

Full multiple scattering models of X-ray absorption near edge spectra of Pt Janin clusters, with atop and bridge bound oxygen, were systematically improved by increasing the number of cluster atoms contributing X-ray photoelectrons from unity (limited-absorber model), to all six Janin cluster Pt atoms, and finally embedding the Janin cluster into a larger Pt reservoir with photoelectron contributions from all atoms. The simulated XANES of the adsorbate modified clusters were subtractively normalized to their respective clean clusters to yield Δ-XANES signatures. The sequential analysis of previously published limited-absorber model, and the isolated and embedded all atoms models provide insights concerning the relative contribution of surface vs. subsurface atoms to adsorbate induced ligand effects and charge compensation provided by the bulk lattice. Limitations to the application of Δ-XANES signatures to interpretation of Δ-XANES data obtained from an air-breathing fuel cell are discussed.     

Numerical Simulation of Anisotropic Shrinkage in a 2D Compact of Elongated Particles

Microstructural evolution during simple solid-state sintering of two-dimensional compacts of elongated particles packed in different arrangements was simulated using a kinetic, Monte Carlo model. The model used simulates curvature-driven grain growth, pore migration by surface diffusion, vacancy formation, diffusion along grain boundaries, and annihilation. Only the shape of the particles was anisotropic; all other extensive thermodynamic and kinetic properties such as surface energies and diffusivities were isotropic. We verified our model by simulating sintering in the analytically tractable cases of simple-packed and close-packed, elongated particles and comparing the shrinkage rate anisotropies with those predicted analytically. Once our model was verified, we used it to simulate sintering in a powder compact of aligned, elongated particles of arbitrary size and shape to gain an understanding of differential shrinkage. Anisotropic shrinkage occurred in all compacts with aligned, elongated particles. However, the direction of higher shrinkage was in some cases along the direction of elongation and in other cases in the perpendicular direction, depending on the details of the powder compact. In compacts of simple-packed, mono-sized, elongated particles, shrinkage was higher in the direction of elongation. In compacts of close-packed, mono-sized, elongated particles and of elongated particles with a size and shape distribution, the shrinkage was lower in the direction of elongation. The results of these simulations are analyzed, and the implication of these results is discussed.     

Randomized single-subject experiments and statistical tests.

The importance of intensive study of the individual subject in counseling research and the importance of the development of appropriate designs and analytical procedures for single-subject research has been recognized. Single-subject experiments are not always possible or ethical, but when they can be performed, treatment times should be randomly assigned to treatments, as this randomization is essential to provide the basis for a statistical test. The assumption of random sampling is not met in single-subject experiments. However, the data from a randomized single-subject experiment can be analyzed by use of a randomization test because such tests do not require random sampling. Randomized single-subject experiments can be helpful in determining what is best for a particular client, and systematic replications of such experiments can help in generalizing to other subjects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Capillary array electrophoresis-MALDI mass spectrometry using a vacuum deposition interface.

We previously introduced a vacuum deposition interface for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF MS) on a moving surface (e.g., quartz wheel, Mylar tape, metal target). In our present work, the approach has been extended to demonstrate parallel analysis for multiple on-line infusion MALDI MS and capillary array electrophoresis (CAE)-MALDI MS. In the infusion mode, individual peptide samples were simultaneously deposited on a Mylar tape cartridge using an array of eight capillaries, yielding eight parallel traces. For CAE-MALDI/TOF MS, the same number of separation capillaries were coupled with an array of eight infusion capillaries using a common liquid junction, containing matrix solution. A fast-scanning mirror was employed to traverse the beam of the desorption laser across the Mylar tape to probe one trace at a time. The positions of the eight sample traces formed on the tape were automatically determined, and all samples were analyzed in rapid sequence using a kilohertz repetition rate laser and a high-throughput data acquisition system. The instrumentation was operated with CAE MS for high-throughput analysis without compromising data quality. The principles of parallel separation-vacuum deposition should be generally applicable to MALDI/TOF MS analysis for proteomics and other areas where separation and high throughput are required.