Chemical reactivity of supported gold : III. Atomic binding and coordination of gold from X-ray absorption fine structure spectroscopy

Preparations of Au and Pt supported on Al2O3, MgO, and SiO2 were subjected to analysis by extended X-ray absorption fine structure spectroscopy (EXAFS). The samples contained 0.20, 5.00, and 8.00 wt% Au, and 5.00 wt% Pt. Metal dispersion ranged between 0.3 to 45%. Anisotropic growth was detected in the larger particles. The liii X-ray absorption coefficient was normalized to the same atom basis and Fourier transformed to yield the radial structure function for each preparation. From bond distance comparison with reference materials, assignments were made to specific peaks of the radial structure function. The analysis of the results showed that the metals were present in two distinct phases: metallic with coordination and metal-to-metal distance characteristic of bulk Au, and Pt (particulate phase), and a highly disperse one (dissolved phase). It was concluded that the latter consisted of metal atomically dispersed, or condensed in small, flat clusters of a few atoms. It was further estimated that the majority of Au and Pt was present in the highly disperse form, i.e., 60% for Au and 86% for Pt. Au atoms did not simply substitute Mg in the MgO matrix to form the dissolved Au-MgO phase and they carried an average charge +1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21796/1/0000195.pd

Simulation and analysis of solenoidal ion sources

We present a detailed analysis and simulation of solenoidal, magnetically confined electron bombardment ion sources, aimed at molecular beam detection. The aim is to achieve high efficiency for singly ionized species while minimizing multiple ionization. Electron space charge plays a major role and we apply combined ray tracing and finite element simulations to determine the properties of a realistic geometry. The factors controlling electron injection and ion extraction are discussed. The results from simulations are benchmarked against experimental measurements on a prototype source

On the precise connection between the GRW master-equation and master-equations for the description of decoherence

We point out that the celebrated GRW master-equation is invariant under translations, reflecting the homogeneity of space, thus providing a particular realization of a general class of translation-covariant Markovian master-equations. Such master-equations are typically used for the description of decoherence due to momentum transfers between system and environment. Building on this analogy we show the exact relationship between the GRW master-equation and decoherence master-equations, further providing a collisional decoherence model formally equivalent to the GRW master-equation. This allows for a direct comparison of order of magnitudes of relevant parameters. This formal analogy should not lead to confusion on the utterly different spirit of the two research fields, in particular it has to be stressed that the decoherence approach does not lead to a solution of the measurement problem. Building on this analogy however the feasibility of the extension of spontaneous localization models in order to avoid the infinite energy growth is discussed. Apart from a particular case considered in the paper, it appears that the amplification mechanism is generally spoiled by such modifications.Comment: 9 pages, latex, no figures, to appear on J. Phys.

Bound States for a Magnetic Impurity in a Superconductor

We discuss a solvable model describing an Anderson like impurity in a BCS superconductor. The model can be mapped onto an Ising field theory in a boundary magnetic field, with the Ising fermions being the quasi-particles of the Bogoliubov transformation in BCS theory. The reflection S-matrix exhibits Andreev scattering, and the existence of bound states of the quasi-particles with the impurity lying inside the superconducting gap.Comment: 7 pages, Plain Te

Making a journey in knowledge management strategy

This paper reports results from an ongoing project examining what managers think about knowledge management in the context of their organisation. This was done in a facilitated computerassisted group workshop environment. Here we compare the outcomes of workshops held for two relatively large UK organisations, one public sector and the other private. Our conclusions are that there are relatively few differences between the perceptions of these two groups of managers, and that these differences stem more from the stage of the knowledge management life cycle that the two organisations have reached, rather than from the difference in context between public and private sector. © iKMS & World Scientific Publishing Co

Strong Coupling Fixed Points of Current Interactions and Disordered Fermions in 2D

The all-orders beta function is used to study disordered Dirac fermions in 2D. The generic strong coupling fixed `points' of anisotropic current-current interactions at large distances are actually isotropic manifolds corresponding to subalgebras of the maximal current algebra at short distances. The IR theories are argued to be current algebra cosets. We illustrate this with the simple example of anisotropic su(2), which is the physics of Kosterlitz-Thouless transitions. We work out the phase diagram for the Chalker-Coddington network model which is in the universality class of the integer Quantum Hall transition. One massless phase is in the universality class of dense polymers.Comment: published version (Phys. Rev. B

Serous cystic neoplasm of the pancreas: A multinational study of 2622 patients under the auspices of the International Association of Pancreatology and European Pancreatic Club (European Study Group on Cystic Tumors of the Pancreas)

OBJECTIVES: Serous cystic neoplasm (SCN) is a cystic neoplasm of the pancreas whose natural history is poorly known. The purpose of the study was to attempt to describe the natural history of SCN, including the specific mortality. DESIGN: Retrospective multinational study including SCN diagnosed between 1990 and 2014. RESULTS: 2622 patients were included. Seventy-four per cent were women, and median age at diagnosis was 58\u2005years (16-99). Patients presented with non-specific abdominal pain (27%), pancreaticobiliary symptoms (9%), diabetes mellitus (5%), other symptoms (4%) and/or were asymptomatic (61%). Fifty-two per cent of patients were operated on during the first year after diagnosis (median size: 40\u2005mm (2-200)), 9% had resection beyond 1\u2005year of follow-up (3\u2005years (1-20), size at diagnosis: 25\u2005mm (4-140)) and 39% had no surgery (3.6\u2005years (1-23), 25.5\u2005mm (1-200)). Surgical indications were (not exclusive) uncertain diagnosis (60%), symptoms (23%), size increase (12%), large size (6%) and adjacent organ compression (5%). In patients followed beyond 1\u2005year (n=1271), size increased in 37% (growth rate: 4\u2005mm/year), was stable in 57% and decreased in 6%. Three serous cystadenocarcinomas were recorded. Postoperative mortality was 0.6% (n=10), and SCN's related mortality was 0.1% (n=1). CONCLUSIONS: After a 3-year follow-up, clinical relevant symptoms occurred in a very small proportion of patients and size slowly increased in less than half. Surgical treatment should be proposed only for diagnosis remaining uncertain after complete workup, significant and related symptoms or exceptionally when exists concern with malignancy. This study supports an initial conservative management in the majority of patients with SCN

Functional Lagrange formalism for time-non-local Lagrangians

We develop a time-non-local (TNL) formalism based on variational calculus, which allows for the analysis of TNL Lagrangians. We derive the generalized Euler-Lagrange equations starting from the Hamilton's principle and, by defining a generalized momentum, we introduce the corresponding Hamiltonian formalism. We apply the formalism to second order TNL Lagrangians and we show that it reproduces standard results in the time-local limit. An example will show how the formalism works, and will provide an interesting insight on the non-standard features of TNL equations.Comment: 13 pages, 2 figure

Bimetallic ruthenium-gold-on-magnesia catalysts: Chemicophysical properties and catalytic activity

Bimetallic Ru-Au catalysts supported on MgO were prepared, their atomic composition varying from 100% Ru to 100% Au. Samples were characterized after impregnation and drying at 110 [deg]C and after further reduction by hydrogen at 400 [deg]C. X-Ray line broadening analysis, small-angle X-ray scattering, transmission electron microscopy, gas chemisorption, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) analysis were used. Catalytic activity was measured for the oxygen transfer between CO and CO2. The Ru and Au precursor compounds appear to be modified, and have probably interacted in the bimetallic samples, already after impregnation and drying. Relevant amounts of metal oxides are found in some "reduced" catalysts; a metal-support interaction is proposed for Au/MgO. The amounts of the Ru and Au oxidized species found by EXAFS in the examined bimetallic sample are significantly different from those found in Ru/MgO and Au/MgO, respectively. The DR spectra of the bimetallic samples are not a simple combination of those of the monometallic catalysts. The Ru/Au atomic ratios measured by XPS are higher than the analytical ones. The fraction of surface Ru atoms, measured by hydrogen chemisorption, increases on decreasing the bulk Ru/Au atomic ratio. The Au/MgO sample has an activity which is two orders of magnitude higher than that of the remaining samples. All of this suggests the existence of a Ru surface enrichment and also an Ru-Au chemical interaction. These conclusions are also supported by an ir study of CO chemisorbed on the same samples.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23184/1/0000111.pd