Goal Change in the Situation Calculus

Although there has been much discussion of belief change (e.g.[4, 21]), goal change has not received much attention. In thispaper, we propose a method for goal change in the frameworkof Reiter's; [12] theory of action in the situation calculus[8, 10], and investigate its properties. We extend the frameworkdeveloped by Shapiro et al. [17] and Shapiro and Lespérance[16], where goals and goal expansion were modelled, but goalcontraction was not.     

Existence and uniqueness of minimal realizations of nonlinear systems

In the theory of finite dimensional linear systems, it is well known that every input-output map that can be realized by one such system can also be realized by a system which is minimal, i.e. both controllable and observable. Moreover, the minimal realization of a given map is unique up to isomorphism. It is shown here that similar results hold for the class of all systems whose state space is a real analytic manifold, whose dynamics is given by a family of complete real analytic vector fields, and whose output is an arbitrary real analytic function on the state space.Research partially supported by NSF Grant GP-37488.     

The effect of ionic liquids with imidazolium and pyridinium cations on the corrosion inhibition of mild steel in acidic environment

Ionic liquids with chemical formula 1,3-dioctadecylimidazolium bromide and N-Octadecylpyridinium bromide were synthesized by conventional and microwave-assisted reactions, respectively. Ionic liquids tested as corrosion inhibitors after polarization curves displayed corrosion protection efficiency within 82-88% at 100 ppm for mild steel in a 1 M aqueous solution of sulfuric acid. Standard free energy indicated that corrosion inhibition occurred by a chemical adsorption process. Surface analysis (SEM, EDX) completed by XRD and Mössbauer spectroscopy indicated the presence of carbon species pertaining to inhibitor and corrosion products, which was rationalized in an inhibition mechanism.     

Quantum-efficiency measurements in oxygen-containing gallium lanthanum sulphide glasses and fibers doped with Pr/sup 3+/

The production of competitive fiber amplifiers in the 1.3-/spl mu/m region requires both good quantum efficiency in the lasing ion and the capability to produce low-loss fibers. Oxygen-doped gallium lanthanum sulphide (GLS) doped with Pr/sup 3+/ may provide a route to both, We describe measurements of the quantum efficiency of Pr/sup 3+/ emission at 1.3 /spl mu/m from the /sup 1/G/sub 4/-/sup 3/H/sub 5/ transition in GLS glass and fiber containing varying quantities of lanthanum oxide. We show that oxide-containing GLS glasses, which are known to have considerably better thermal and glass-forming properties than pure GLS, can show quantum efficiencies of up to 84% of that of pure GLS, No degradation of quantum efficiency is seen when oxide-containing GLS glass is pulled into fiber form.     

Synthesis and electrochemical characterization of stabilized nickel nanoparticles

Nickel stabilized nanoparticles produced by an organometallic approach (Chaudret's method) starting from the complex Ni(1,5-COD)₂ were used as electrode materials for hydrogen evolution in NaOH at two temperatures (298 and 323 K). The synthesis of the nickel nanoparticles was performed in the presence of two different stabilizers, 1,3-diaminopropane (DAP) and anthranilic acid (AA), by varying the molar ratios (1:1, 1:2 and 1:5 metal:ligand) in order to evaluate their influence on the shape, dispersion, size and electrocatalytic activity of the metallic particles. The presence of an appropriate amount of stabilizer is an effective alternative to the synthesis of small monodispersed metal nanoparticles with diameters around 5 and 8 nm for DAP and AA, respectively. The results are discussed in terms of morphology and the surface state of the nanoparticles. The importance of developing a well-controlled synthetic method which results in higher performances of the resulting nanoparticles is highlighted. Herein we found that the performance with respect to the HER of the Ni electrodes dispersed on a carbon black Vulcan substrate is active and comparable to that reported in the literature for the state-of-the-art electrocatalysts. Appreciable cathodic current densities of ∼240 mA cm⁻² were measured with highly dispersed nickel particles (Ni-5_DAP). This work demonstrates that the aforementioned method can be extended to the preparation of highly active stabilized metal particles without inhibiting the electron transfer for the HER reaction, and it could also be applied to the synthesis of bimetallic nanoparticles.     

RECURSIVE GENERALIZED M ESTIMATES FOR AUTOREGRESSIVE MOVING-AVERAGE MODELS

Abstract. Outliers in time series seriously affect conventional parameter estimates. In this paper a robust recursive estimation procedure for the parameters of auto-regressve moving-average models with additive outliers is proposed. Using 'cleaned' residuals from an initial robust fit of an autoregression of high order as input, bounded influence regression is applied recursively. The proposal follows certain ideas of Hannan and Rissanen, who suggested a three-stage procedure for order and parameter estimation in a conventional setting.
A Monte Carlo study is performed to investigate the robustness properties of the proposed class of estimates and to compare them with various other suggestions, including least squares, M estimates, residual autocovariance and truncated residual autocovariance estimates. The results show that the recursive generalized M estimates compare favourably with them. Finally, possible modifications to master even vigourous situations are suggested.     

The catalytic activity of the Pr2Zr2−xFexO7±δ system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO₂, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr₂Zr_2−xFe_xO_7±δ (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO₂ sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.     

On the prediction of gas hold-up in two-phase flow systems using an Euler–Euler model

We quantify the ability of the two-fluid Euler–Euler model to predict the overall gas hold-up during two-phase flow in vertical columns using a combination of experiments and simulations. Gas hold-up in a bubble column and gas hold-up in the less-frequently studied co-current flow are investigated. For homogeneous flow characterized by nearly uniform bubble size, Euler–Euler model predictions are within 10% of the experimental values for both modes of operation, if the bubble diameter supplied as input to the model is the average bubble diameter in the physical system. This also holds true for heterogeneous flow in bubble columns despite the presence of a broad distribution of bubble sizes, if turbulence and bubble swarm effects on momentum exchange between phases are properly accounted for. Swarm corrections adequate for bubble columns, are less successful for co-current heterogeneous flow, for which gas hold-up predictions are least accurate (average error of 22%).     

Effect of cellulosic sugar degradation products (furfural and hydroxymethyl furfural) on acetone–butanol–ethanol (ABE) fermentation using Clostridium beijerinckii P260

Studies were performed to identify chemical compounds present in wheat straw hydrolysate (WSH) that enhance acetone butanol ethanol (ABE) productivity. These compounds were identified as furfural and hydroxymethyl furfural (HMF). Control experiment resulted in the production of 21.38 g L^?1 ABE with a productivity of 0.30 g L^?1 h^?1. WSH contained 0.04–0.34 g L^?1 furfural and 0.12–0.88 g L^?1 HMF. Addition of furfural to the fermentation medium at a concentration of 0.50 g L^?1 resulted in a productivity of 0.88 g L^?1 h^?1 which is 293% of the productivity obtained in control experiments. Supplementation with 1.00 g L^?1 HMF into the fermentation medium produced 25.27 g L^?1 ABE with a productivity of 0.68 g L^?1 h^?1. A combination of furfural (0.50 g L^?1) and HMF (0.50 g L^?1) also enhanced ABE production and productivity when added to the fermentation medium. Both furfural and HMF enhanced specific productivity (233–308%) of ABE. In brief, WSH contained an adequate concentration of furfural and HMF that enhanced ABE productivity, specific productivity, and product concentration.