Nickel deposition on γ-Al2O3 model catalysts: An experimental and theoretical investigation

Recently, surface modifications on a commercial Ni/γ-Al₂O₃ catalyst during the production of methane from synthesis gas were investigated by quasi insitu X-ray photoelectron spectroscopy (XPS) [I. Czekaj, F. Loviat, F. Raimondi, J. Wambach, S. Biollaz, A. Wokaun, Appl. Catal. A: Gen. 329 (2007) 68]. The conclusion was that the reactivity and the observed reaction mechanisms on the different Ni particles are influenced directly by both the size and the composition of the particles on the γ-Al₂O₃ support.In this investigation, Ni deposition and cluster growth on model catalyst samples (10 nm thick, polycrystalline γ-Al₂O₃ on Si(100)) were investigated by XPS. Several steps in the binding energy during Ni deposition indicate changes in the cluster growth. The molecular structure of the catalyst was investigated using Density Functional Theory calculations (StoBe) with a cluster model and non-local functional (RPBE) approach. An Al₁₅O₄₀H₃₅ cluster was selected to represent the γ-Al₂O₃(100) surface. Ni clusters of different size were cut from a Ni(100) surface and deposited on the Al₁₅O₄₀H₃₅ cluster in order to validate the deposition model determined by XPS.     

CN− secondary ions form by recombination as demonstrated using multi-isotope mass spectrometry of 13C- and 15N-labeled polyglycine

We have studied the mechanism of formation CN- secondary ions under Cs+ primary ion bombardment. We have synthesized 13C and 15N labeled polyglycine samples with the distance between the two labels and the local atomic environment of the 13C label systematically varied. We have measured four masses in parallel: 12C, 13C, and two of 12C14N, 13C14N, 12C15N, and 13C15N. We have calculated the 13C/12C isotope ratio, and the different combinations of the CN isotope ratios (27CN/26CN, 28CN/27CN, and 28CN/26CN). We have measured a high 13C15N- secondary ion current from the 13C and 15N labeled polyglycines, even when the 13C and 15N labels are separated. By comparing the magnitude of the varied combinations of isotope ratios among the samples with different labeling positions, we conclude the following: CN- formation is in large fraction due to recombination of C and N; the CO double bond decreases the extent of CN- formation compared to the case where carbon is singly bonded to two hydrogen atoms; and double-labeling with 13C and 15N allows us to detect with high sensitivity the molecular ion 13C15N-.     

Commissioning of a multi‐beamline femtoslicing facility at SOLEIL

The investigation of ultrafast dynamics, taking place on the few to sub‐picosecond time scale, is today a very active research area pursued in a variety of scientific domains. With the recent advent of X‐ray free‐electron lasers (XFELs), providing very intense X‐ray pulses of duration as short as a few femtoseconds, this research field has gained further momentum. As a consequence, the demand for access strongly exceeds the capacity of the very few XFEL facilities existing worldwide. This situation motivates the development of alternative sub‐picosecond pulsed X‐ray sources among which femtoslicing facilities at synchrotron radiation storage rings are standing out due to their tunability over an extended photon energy range and their high stability. Following the success of the femtoslicing installations at ALS, BESSY‐II, SLS and UVSOR, SOLEIL decided to implement a femtoslicing facility. Several challenges were faced, including operation at the highest electron beam energy ever, and achievement of slice separation exclusively with the natural dispersion function of the storage ring. SOLEIL's setup also enables, for the first time, delivering sub‐picosecond pulses simultaneously to several beamlines. This last feature enlarges the experimental capabilities of the facility, which covers the soft and hard X‐ray photon energy range. In this paper, the commissioning of this original femtoslicing facility is reported. Furthermore, it is shown that the slicing‐induced THz signal can be used to derive a quantitative estimate for the degree of energy exchange between the femtosecond infrared laser pulse and the circulating electron bunch.     

ELENA: the extra low energy anti-proton facility at CERN

At the last LEAP conference in Vancouver 2011 the authors stated that a project ”ELENA”, as an abbreviation for Extra Low ENergy Antiproton ring and as first discussed in 1982 for LEAR by H. Herr et al., was freshly proposed with a substantial new design and revised layout and that it was under consideration to be built at CERN. ELENA is an upgrade of the Anti-proton Decelerator (AD) at CERN and is devoted to special experiments with physics using low energy anti-protons. The main topics are the anti-hydrogen production and consecutive studies of the features of this anti-matter atom as well as the anti-proton nucleon interaction by testing the QED to high precision. During the last years the project underwent several steps in presentations at different committees at CERN and was finally approved such that the construction has started. ELENA will increase the number of useful anti-protons by about two orders of magnitude and will allow to serve up to four experiments simultaneously. Very first and convincing results from the experiments at the AD have been published recently. For high precision physics, however, it appears to be cumbersome, time consuming and ineffective when collecting the needed large numbers and high densities of anti-proton clouds with the present AD. Both the effectiveness and the availability for additional experiments at this unique facility will drastically increase, when the anti-proton beam of presently 5 MeV kinetic energy is reduced by the additional decelerator ELENA to 100 keV.     

The Control of Photochromism of [3H]-Naphthopyran Derivatives with Intramolecular CH-π Bonds

The photochromism of [3H]-naphthopyran derivatives can be switched from T-type to inverse- or P-type through the manipulation of relative thermodynamic stabilities of open isomers with intramolecular CH-π bonds.     

Insights into the mechanism of reaction of [(C5Me5)2Sm(II)(thf)2] with CO2 and COS by DFT studies

Reaction mechanisms for the oxidative reactions of CO(2) and COS with [(C(5)Me(5))(2)Sm] have been investigated by means of DFT methods. The experimental formation of oxalate and dithiocarbonate complexes is explained. Their formation involve the samarium(III) bimetallic complexes [(C(5)Me(5))(2)Sm-CO(2)-Sm(C(5)Me(5))(2)] and [(C(5)Me(5))(2)Sm-COS-Sm(C(5)Me(5))(2)] as intermediates, respectively, ruling out radical coupling for the formation of the oxalate complex.     

Plastic behavior of some yield stress fluids: from creep to long-time yield

The yielding of several reversible yield stress fluids is studied during scissometric-like creep experiments. The temporal evolution of the apparent deformation is recorded for applied stresses close and below the usual yield stress. Similarly to solids, three main creep regimes are observed. First, a primary creep regime displaying a temporal power law evolution of the deformation rate occurs, followed by a temporal minimum, which leads to an apparent flow of the material. This local minimum, defined as the “transition time,” and the subsequent fluidization can be observed at long times. The evolution of this time as a function of the applied stress appears to follow a universal law reminiscent of fracture behavior in hard solids.     

Comparison of methods for calculating the shock hugoniot of mixtures

Various methods used to determine the shock Hugoniot of condensed phase multi-component mixtures are reviewed and compared to available experimental data. The assumptions inherent in the different models are presented in this overview and their implications are discussed. The comparisons of the various models demonstrate that the predicted shock Hugoniots are in good agreement with published data despite the simplifying assumptions that are associated with the models. Averaging models are shown to be among the simplest methods to implement and result in the closest agreement with experimental data.     

A closure approximation for nematic liquid crystals based on the canonical distribution subspace theory

 A closure approximation for nematic polymers is presented. It approximates the fourth rank order tensor in terms of lower rank tensors, and is derived in the framework of the canonical distribution subspace theory. This approach requires a choice of the class of distributions: Here the set of Bingham distributions is chosen, as already introduced by Chaubal and Leal (1998). The closure is written in a generic frame of reference, and in an explicit form, so that it can be easily implemented. Such formulation also permits studying the closure approximation with continuation tools, which rather completely describe the system dynamics. The predictions can then be compared with those obtained with the exact model. The shear flow is considered as a test, since this flow condition appears to be the most demanding for closure approximations for nematic polymers. Received: 30 November 1999/Accepted: 30 November 1999