Interaction Between Pt(acac)2 and Alumina Surfaces Studied by XAS

The anchoring and decomposition mechanisms of platinum(II) bis-acetylacetonate on alumina surfaces are studied by X-ray absorption spectroscopy at the platinum L_III edge. A distinction is made between highly reactive surfaces which are partially dehydroxylated and exhibit coordinatively unsaturated surface sites, and deactivated surfaces which are covered by a monolayer of OH groups. The samples are studied after three stages of a wet impregnation synthesis: after drying at room temperature, drying at 120 °C and calcination at 350 °C. The XANES signal and the filtered EXAFS signals of the first and second coordination shells around platinum were analyzed. Two different mechanisms are discussed for the two types of supports.     

Structure of Pt–Co/Al2O3 and Pt–Co/NaY Bimetallic Catalysts: Characterization by In Situ EXAFS,TPR, XPS and by Activity in Co (Carbon Monoxide) Hydrogenation

Temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and in situ extended X-ray absorption fine structure (EXAFS) studies were performed to investigate Pt-Co/NaY and Pt-Co/Al₂O₃ bimetallic catalysts. The EXAFS experiments were carried out at the Pt L_III and Co K edges of the same sample. This particular approach allows a precise determination of the electronic and structural characteristics of the metallic part of the catalyst. For both systems in situ reduction under pure H₂ results in the formation of nanometer-scale metallic clusters. For both Co and Pt, nearest neighbors are Co atoms. The complete set of parameters implies the presence of two families of nanometer-scale metallic clusters: monometallic Co nanosized particles and Pt-Co bimetallic clusters, in which only Pt-Co bonds exist (no Pt-Pt bonds). TPR and XPS results indicating a reduction of Co²⁺ ions in Pt-Co/NaY to a greater extent than in Pt-Co/Al₂O₃ give evidence of a facilitated reduction. XRD also shows the presence of nanometer-scale particles with only a very small fraction of larger bimetallic particles. In subsequent mild oxidation of the reduced systems the Co nanoparticles are still present inside the supercage of NaY zeolite in bimetallic form and the oxidation of the metallic particles is slowed down. Catalytic behavior is in good agreement with the structure of the Pt-Co bimetallic system.     

Dynamics And Assessment of Some Control Strategies of a Simulated Industrial Rotary Dryer

Rotary dryers are widely used for the continuous drying of minerals and chemicals on a large scale. Hot gases are passed parallel to the flowing solid to achieve the desired product moisture content. Because these dryers are energy intensive, it is mandatory to operate them as efficiently as possible to respond to economic pressures. Using a dynamic rotary dryer simulator for mineral concentrate, five control strategies are evaluated and compared. Two control strategies are based on PI controllers and the others use neural network models. Results clearly show that a feedforward action, in conjunction with a PI controller or incorporated within the structure of a neural network model, led to the best performances provided an accurate measurement of the feed moisture content is available.     

A multiple object geometric deformable model for image segmentation

Deformable models are widely used for image segmentation, most commonly to find single objects within an image. Although several methods have been proposed to segment multiple objects using deformable models, substantial limitations in their utility remain. This paper presents a multiple object segmentation method using a novel and efficient object representation for both two and three dimensions. The new framework guarantees object relationships and topology, prevents overlaps and gaps, enables boundary-specific speeds, and has a computationally efficient evolution scheme that is largely independent of the number of objects. Maintaining object relationships and straightforward use of object-specific and boundary-specific smoothing and advection forces enables the segmentation of objects with multiple compartments, a critical capability in the parcellation of organs in medical imaging. Comparing the new framework with previous approaches shows its superior performance and scalability.     

Simple architecture low phase noise microwave cryogenic sapphire oscillators

The operation of a low phase noise 10.35 GHz microwave cryogenic sapphire resonator oscillator is demonstrated. Based on a very simple architecture, the oscillator presents phase noise performances of -104 dBrad²/Hz at f=10 Hz off the carrier (slope 1/f ³), lower than -152 dBrad²/Hz at f=1 kHz (slope 1/f), and of -160 dBrad²/Hz at fgsim10 kHz (white)     

Reconstruction of nuclear charged fragment trajectories from a large-gap sweeper magnet

A new method to reconstruct charged fragment four-momentum vectors from measured trajectories behind an open, large gap, magnetic dispersion element (a sweeper magnet) has been developed. In addition to the position and angle behind the magnet it includes the position measurement in the dispersive direction at the target. The method improves the energy and angle resolution of the reconstruction significantly for experiments with fast rare isotopes, where the beam size at the target position is large.     

Handling of Dynamic Sequences in Nuclear Medicine

Nuclear Medicine is one of the first domains in which the analysis of image sequences was introduced. The development of this analysis was achieved parallel to the one of the computer systems linked to the scintillation cameras. The number of works that were performed in the research laboratories and have received an application in clinical routine is however limited. The authors indicate what could be the flow chart of the processing of dynamic sequences in scintigraphy and the kind of material that would be necessary to implement it. The possibilities of using the factor and compartmental analyses in clinical routine are particularly emphasized. The authors indicate why the factors and their associated images obtained by means of the factor analysis can have a physiological meaning.