Hydrogen production by absorption enhanced water gas shift (AEWGS)

AEWGS is a reaction that combines the WGS reaction and CO₂ capture by a solid absorbent to produce high purity H₂ from synthesis gas in one single step at 600–800 °C. This reactor system, if homogeneous, would not require a catalyst. However, previous research on this concept was not conclusive, since a steel reactor was used and reactor walls were suspected to act as catalyst. Therefore, there is a need to address this issue and to select and evaluate suitable CO₂ absorbents for this concept. AEWGS was studied using a quartz-made fixed-bed reactor at; SV = 3000 h⁻¹, feed; 5% CO, 15% H₂O, balance He–N₂ at 600 °C, 1 atm. CO₂ absorbents tested were CaO*MgO, and Na₂ZrO₃. Empty quartz-reactor tests leaded to conclude that a catalyst is needed for the WGS at temperatures of interest. A 97% H₂ product was obtained with calcined dolomite suggesting this last to act as a WGS catalyst.     

ZnO crystals obtained by electrodeposition: Statistical analysis of most important process variables

In this paper a comparative study by means of a statistical analysis of the main process variables affecting ZnO crystal electrodeposition is presented. ZnO crystals were deposited on two different substrates, silicon wafer and indium tin oxide. The control variables were substrate types, electrolyte concentration, temperature, exposition time and current density. The morphologies of the different substrates were observed using scanning electron microscopy. The percentage of substrate area covered by ZnO deposit was calculated by computational image analysis. The design of the applied experiments was based on a two-level factorial analysis involving a series of 32 experiments and an analysis of variance. Statistical results reveal that variables exerting a significant influence on the area covered by ZnO deposit are electrolyte concentration, substrate type and time of deposition, together with a combined two-factor interaction between temperature and current density. However, morphology is also influenced by surface roughness of the substrates.     

A Cost-Effective Architecture for Vectorizable Numerical and Multimedia Applications

This paper analyzes the performance of vector-dominated regions of code in numerical and multimedia applications in a superscalar + vector architecture and compares it with an eight-way superscalar processor. The ability to split a program’s execution into scalar and vector regions allows us to show that (1) as expected, the vector unit is much better than the wide-issue superscalar at executing the vector-dominated regions of the code; (2) on the scalar regions, the eight-way superscalar, although better than a four-way superscalar, is clearly not worth the extra complexity in terms of extra transistors and potential cycle-time limitations. Overall, the vector-enhanced superscalar is from 6% to 303% better than an eight-way superscalar. We also present detailed data on the performance of the memory system, which is usually the key limiting factor when running numerical and multi-\break media applications. We evaluate two additional cache designs that try to alleviate problems created by non-unit stride memory references.     

Microbial quality of ostrich carcasses produced at an export-approved South African abattoir

The aim of this study was to evaluate the microbial quality of ostrich carcasses produced in a South African export-approved ostrich abattoir. Ninety surface samples were collected from 30 ostrich carcasses at three processing points in the abattoir: after skinning, after evisceration, and after chilling. Samples were evaluated for aerobic plate counts, for levels of Pseudomonas spp., Enterobacteriaceae, and Staphylococcus aureus, and for the presence of Escherichia coli. Surface counts (means +/- standard deviations) at postskinning, postevisceration, and postchilling processing points were, respectively, 4.32 +/- 0.62, 4.21 +/- 0.63, and 4.57 +/- 0.48 log CFU/cm2 for total aerobes; 2.82 +/- 1.65, 2.86 +/- 1.53, and 3.75 +/- 0.94 log CFU/ cm2 for Pseudomonas spp.; 2.89 +/- 0.78, 2.90 +/- 0.53, and 2.38 +/- 0.67 log CFU/cm2 for S. aureus; and 2.55 +/- 1.53, 2.78 +/- 1.31, and 2.73 +/- 1.46 log CFU/cm2 for Enterobacteriaceae. Statistically significant differences were detected between the counts for the postskinning and postchilling processing points and between the counts for the postevisceration and postchilling processing points for total aerobes, Pseudomonas spp., and S. aureus. Of practical significance was the increase in Pseudomonas spp. counts on samples collected after chilling. Seventeen of 90 samples (18.8%) tested positive for E. coli. Counts for E. coli-positive samples ranged from 1.0 to 3.79 log CFU/cm2, with a mean count of 2.15 +/- 0.94 log CFU/cm2. The majority of the samples testing positive for E. coli were collected after evisceration.     

Mechanical and rheological properties of styrene/acrylic gradient polymers

A butyl acrylate monomer with a small amount of photosensitizer was diffused into a slightly crosslinked polystyrene matrix. After a certain swelling time, the diffusion gradient was either fixed (by rapid photopolymerization in situ) to form a gradient polymer or changed to form an interpenetrating polymer network (IPN), once thermodynamic equilibrium was achieved. Chemical compositions were determined by FTIR. Mechanical and rheological measurements were performed using a universal testing machine and dynamic rheometer, respectively. Impact properties were evaluated with a Falling Dart Impact Tester. Compared to the IPN materials, the gradient polymers exhibit higher moduli, considerable strain, and similar impact resistance. They are also able to retain plastic properties at higher temperatures. Differences in chemical structure of equivalent layers for gradient and IPN polymers yield such differences in properties. © 1995 John Wiley & Sons, Inc.     

M-subshell ionization of U by light-ion bombardment

M X-rays of U were produced by proton, deuteron and alpha-particle bombardment in the energy range of 0.20–1.00 MeV/u. N_6,7 → M₅ (M), N₆ → M₄ (M_β), N₅ → M₃ (M_γ), N₄ → M₂ and N₂ → M₁ line yields were obtained from a least-squares fit to the spectra and used to convert M X-ray production into M-subshell ionization cross sections. The uncertainty induced by the atomic parameters (X-ray fluorescence yields, Coster-Kronig and radiative transition rates) used in the conversion is discussed. The subshell ionization cross sections are then compared to PWBA values corrected for Coulomb deflection and energy loss according to Brandt and Lapicki, to the semiclassical theoretical values of Kocbach and to relativistic PWBA results, corrected for Coulomb and binding effects, of Chen et al. Intrashell transitions induced by the projectile and multiple ionization are suggested as causes of disagreement between theory and experiment, especially for alpha-particles. It is concluded that theory must go beyond the simple picture of the first-order perturbation approximation to explain M-subshell results and that care must be taken in the choice of wave functions.     

Measuring the understanding between two agents through concept similarity

Two agents previously unknown to each other cannot communicate by exchanging concepts (nodes of their own ontology): they need to use a common communication language. If they do not use a standard protocol, most likely they use a natural language. The ambiguities of it, and the different concepts the agents possess, give rise to imperfect understanding among them: How closely concepts in ontology O_A map¹ to which of O_B? Can we measure these mismatches?Given a concept from ontology O_A, a method is provided to find the most similar concept in O_B, and to measure the similarity between both concepts. The paper also gives an algorithm to gauge du(A, B), the degree of understanding that agent A has about the ontology of B. The procedures use word comparison, since no agent (except the Very Wise Creature, VWC) can measure du directly. Examples are given.     

Short-Term Wind Power Forecast Based on ARX Models

Among distributed energy resources, wind power has recently showed great potential and it is being promoted in many countries. The wind power penetration increase and the trend of the wind farms to enter the market, makes necessary the development of new prediction tools. Prediction tools have been fully verified and used for demand forecast and, more recently, to predict the market prices. Among the different prediction methods proposed, the initial and more deeply verified were the statistical ones. In the present work, time series statistical methods are used to explore and assess the achievable improvement over a persistent model. Both autoregressive (AR) models that consider wind power time series and autoregressive with exogenous variable (ARX) models which include wind speed time series are used to carry out the prediction. An analysis of the appropriate parameters for the models is carried out and shows, for different wind farms, comparative results for persistent, AR, and ARX models with 6, 12, and 24?h forecast which can be useful for the day-ahead and hour-ahead electricity markets. The study also includes a comparative analysis of the different wind farms considered both independently and in an aggregated manner. The forecast improvement due to the use of ARX models and to the wind farm aggregation is fully assessed.     

Parametric study of solidification of PCM around a cylinder for ice-bank applications

This paper presents the results of a numerical parametric study of the solidification of a phase change material (PCM) around a cylinder carrying a heat-transfer fluid (HTF) inside. A pure conduction model is used for the PCM and tube wall, the finite volume method is used together with the interface immobilization technique for treating the phase-change process. The convection problem inside the tube is solved by an energy balance with a Nusselt number value, obtained from the steady-state values for constant wall heat-flux conditions. The effects of the HTF entry temperature, the initial PCM temperature and the thermal conductivity of the tube material on the evolution of the solidification front are studied. Results for the temperature distribution during the process, phase-change interface velocity and thermal energy stored in the system are also presented.