Competitive Hydrogenation of Alkyl‐Substituted Arenes by Transition‐Metal Nanoparticles: Correlation with the Alkyl‐Steric Effect

The influence of substituents on rate constants of the hydrogenation of monoalkylbenzenes by transition metal nanoparticles or by classical heterogeneous catalysts can be rationalized in terms of the Taft rule. A series of the initial reaction rate constants obtained from various competitive toluene/benzene and toluene/monoalkylbenzene hydrogenation experiments catalyzed by transition‐metal nanoparticles prepared in the presence of imidazolium ionic liquids or surfactants [Ir(0), Rh(0) and Ru(0)] or by classical heterogeneous catalysts (PtO₂, Rh/C, Rh/Al₂O₃, Ru/C, Ru/Al₂O₃ and Pd/C) have been correlated with the Taft equation . Satisfactory correlation coefficients (r) (between 0.96 and 0.99) and positive slopes (ρ) between 0.38 and 0.83 have been obtained. The results clearly show that the reaction constants for the alkyl‐substituents can be expressed by steric factors and are independent of any other non‐steric factors. It is suggested that bulky alkylbenzene substituents, for both transition metal nanoparticles and classical heterogeneous hydrogenation reactions, lower the overall hydrogenation rate, implying a more disturbed transition state compared to the initial state of the hydrogenation (in terms of the Horiuti–Polanyi mechanism). This competitive method is suitable for the estimation of the constant selectivity for couples of alkylbenzenes in which the difference in hydrogenation rates are very high and experimentally difficult to measure and also useful for the design of more selective “nano” and classical catalysts for hydrogenation reactions.     

Thermodynamic analyses of adsorption-enhanced steam reforming of glycerol for hydrogen production

A non-stoichiometric thermodynamic analysis is performed on the adsorption-enhanced steam reforming of glycerol for hydrogen production based on the principle of minimising the Gibbs free energy. The effects of temperature (600–1000 K), pressure (1–4 bar), water to glycerol feed ratio (3:1–12:1), percentage of CO₂ adsorption (0–99%) and molar ratio of carrier gas to feed reactants (1:1–5:1) on the reforming reactions and carbon formation are examined. The results show that the use of a CO₂ adsorbent enhances glycerol conversion to hydrogen and the maximum number of moles of hydrogen produced per mole of glycerol can be increased from 6 to 7 due to the CO₂ adsorption. The analyses suggest that the most favourable temperature for steam–glycerol reforming is between 800 and 850 K in the presence of a CO₂ adsorbent, which is about 100 K lower than that for reforming without CO₂ adsorption. Although high pressures are favourable for CO₂ adsorption, a lower operating pressure gives a higher overall hydrogen conversion. The most favourable water to glycerol feed ratio is found to be 9.0 above which the benefit becomes marginal. Carbon formation could occur at low water to glycerol feed ratios, and the use of a CO₂ adsorbent can suppress the formation reaction and substantially reduce the lower limit of the water to glycerol feed ratio for carbon formation.     

Imidazolium ionic liquids as electrolytes for manganese dioxide free Leclanché batteries

A set of four imidazolium ionic liquids (solid at room temperature) and one imidazolium ionic solid was screened for its potential as electrolytes in manganese dioxide free Leclanché batteries, equipped with a zinc anode and graphite cathode. Electrical impedance spectroscopy allowed to determine the room-temperature ionic solids (RTISs) ionic conductivities, which was the highest for carboxylic acid functionalized RTIS 3 [C₂O₂MIm][Cl]. The toxic manganese dioxide was substituted by benzoquinone. A systematic ionic conductivity optimization of RTIS 3–benzoquinone–ZnSO₄–H₂O mixtures at room temperature resulted in the identification of the following conditions for the Leclanché battery studies: 50 mg of a 50:50 RTIS:benzoquinone mixture and 96 mg of water. The chronopotentiometric experiments with a constant current of 5 μA showed a remarkable performance for the RTIS 3 based battery. The potential (1.47 V) and stability is comparable to that of the commercial Rayovac^® battery filling (model AA). Furthermore, linear potentiodynamic voltammetry (0.01 V/s) and chronoamperometric analysis at short-circuit conditions (0.0 V) validated the RTIS 3–benzoquinone–water battery as a promising alternative for manganese dioxide free Leclanché batteries.     

Implementation of a Coarse-Grained Reconfigurable Media Processor for AVC Decoder

Architecture for Dynamically Reconfigurable Embedded Systems (ADRES) is a templatized coarse-grained reconfigurable processor architecture. It targets at embedded applications which demand high-performance, low-power and high-level language programmability. Compared with typical very long instruction word-based digital signal processor, ADRES can exploit higher parallelism by using more scalable hardware with support of novel compilation techniques. We developed a complete tool-chain, including compiler, simulator and HDL generator. This paper describes the design case of a media processor targeting at H.264 decoder and other video tasks based on the ADRES template. The whole processor design, hardware implementaiton and application mapping are done in a relative short period. Yet we obtain C-programmed real-time H.264/AVC CIF decoding at 50 MHz. The die size, clock speed and the power consumption are also very competitive compared with other processors.

Decomposition of a Three-Dimensional Discrete Object Surface into Discrete Plane Pieces

This paper deals with the polyhedrization of discrete volumes. The aim is to do a reversible transformation from a discrete volume to a Euclidean polyhedron, i.e. such that the discretization of the Euclidean volume is exactly the initial discrete volume. We propose a new polynomial algorithm to split the surface of any discrete volume into pieces of naive discrete planes with well-defined shape properties, and present a study of the time complexity as well as a study of the influence of the voxel tracking order during the execution of this algorithm.     

Development of a biosensor immunoassay for the quantification of alphas1-casein in milk

An immunoassay to quantify alphas1-casein (alphas1-CN) in milk using an optical biosensor, based on surface plasmon resonance (SPR) measurement, has been developed. The assay consists of a two-step sandwich strategy, with two anti-alphas1-CN antibodies directed against each extremity of the molecule. This strategy permits only intact alphas1-CN to be quantified and not its degradation products. The calibration curve was obtained using a reference milk powder with a known alphas1-CN concentration. Analysis time per sample was less than ten minutes. The antibody-coated surface could be used for more than 150 determinations. Detection limit was established at 0.87 microg/ml and the intra- and inter-assay variation coefficients were 2.86 and 5.31%, respectively. The method was applied to raw milk to quantify intact alphas1-CN, with no pretreatment of the sample. An initial analysis of 48 milk samples permitted alphas1-CN concentrations ranging from 8.8 to 12.06 mg/ml to be obtained.     

Comparison between MAP and postprocessed ML for image reconstruction in emission tomography when anatomical knowledge is available

Previously, the noise characteristics obtained with penalized-likelihood reconstruction [or maximum a posteriori (MAP)] have been compared to those obtained with postsmoothed maximum-likelihood (ML) reconstruction, for emission tomography applications requiring uniform resolution. It was found that penalized-likelihood reconstruction was not superior to postsmoothed ML. In this paper, a similar comparison is made, but now for applications where the noise suppression is tuned with anatomical information. It is assumed that limited but exact anatomical information is available. Two methods were compared. In the first method, the anatomical information is incorporated in the prior of a MAP-algorithm and is, therefore, imposed during MAP-reconstruction. The second method starts from an unconstrained ML-reconstruction, and imposes the anatomical information in a postprocessing step. The theoretical analysis was verified with simulations: small lesions were inserted in two different objects, and noisy PET data were produced and reconstructed with both methods. The resulting images were analyzed with bias-noise curves, and by computing the detection performance of the nonprewhitening observer and a channelized Hotelling observer. Our analysis and simulations indicate that the postprocessing method is inferior, unless the noise correlations between neighboring pixels are taken into account. This can be done by applying a so-called prewhitening filter. However, because the prewhitening filter is shift variant and object dependent, it seems that MAP reconstruction is the more efficient method.     

Characterization of pinhole SPECT acquisition geometry

A method is presented to estimate the acquisition geometry of a pinhole single photon emission computed tomography (SPECT) camera with a circular detector orbit. This information is needed for the reconstruction of tomographic images. The calibration uses the point source projection locations of a tomographic acquisition of three point sources located at known distances from each other. It is shown that this simple phantom provides the necessary and sufficient information for the proposed calibration method. The knowledge of two of the distances between the point sources proves to be essential. The geometry is estimated by fitting analytically calculated projections to the measured ones, using a simple least squares Powell algorithm. Some mild a priori knowledge is used to constrain the solutions of the fit. Several of the geometrical parameters are however highly correlated. The effect of these correlations on the reconstructed images is evaluated in simulation studies and related to the estimation accuracy. The highly correlated detector tilt and electrical shift are shown to be the critical parameters for accurate image reconstruction. The performance of the algorithm is finally demonstrated by phantom measurements. The method is based on a single SPECT scan of a simple calibration phantom, executed immediately after the actual SPECT acquisition. The method is also applicable to cone-beam SPECT and X-ray CT.