Pore Characterization Methodology by Means of Capillary Sorption Tests

In this study, a methodology is proposed for obtaining information about the porous structure of materials by analysing data supplied by a hydric absorption test. A model of vertical cylindrical pores is used for studying the variation of absorbed mass versus time. The proposed methodology requires an estimation of the numerical interval in which the radius distribution must be calculated and a minimum amount of experimental data. The experimental tests are developed with a system, designed and built in our laboratory, that allows capture the amount of data necessary to use the calculus methodology proposed. This methodology is based on the derivative of normalized mass in relation to the square root of time of the capillary absorption tests. The simplicity and low cost, in many cases, of the capillary absorption tests compared to other experimental techniques such as mercury porosimetry or SEM, make it feasible to design a simple methodology to obtain valuable information about the structure of a porous material, pore size distribution, and tortuosity factor.     

Kinetics and dynamics study of the H + CCl4?��?HCl(v��, j��)?+?CCl3 reaction

Based on a previous potential energy surface describing the H?+?CCl₄ reaction, a new analytical surface named PES-2010 was developed modifying both the functional form to give it more flexibility, and the calibration process in which exclusively theoretical information was used. Thus, the surface is completely symmetric with respect to the permutation of the four methane chlorine atoms, and no experimental information is used in the process. For the kinetics, the thermal rate constants were calculated using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 300?C2,500?K. The theoretical results reproduce the experimental variation with temperature. The influence of the tunneling factor is small, since the abstraction reaction involves the motion of a heavy particle (a chlorine atom) that cannot easily tunnel through the reaction barrier. The coupling between the reaction coordinate and the vibrational modes shows qualitatively that the HCl stretching mode in the products appears vibrationally excited. The dynamics study was performed using quasi-classical trajectory calculations, including corrections to avoid the zero-point energy problem. First, we found that the HCl(????, j??) product mostly appears with small rotational energy and vibrational population inversion. Second, the state-specific scattering distributions show backward scattering, which becomes more noticeable as the HCl(????) vibrational state increases. Unfortunately, no experimental dynamics data are available for the title reaction, but the comparison with the kinematically similar and well-studied H?+?Cl₂ reaction shows good agreement, indicative of similar mechanisms. These kinetics and dynamics results seem to indicate that the potential energy surface is adequate to describe this reaction, and the reasonable agreement with experiment lends further confidence to this new surface.     

Uniform Estimates for the Fourier Transform of Surface Carried Measures in ?3 and an Application to Fourier Restriction

Let S be a hypersurface in \BbbR³{\Bbb{R}}^{3} which is the graph of a smooth, finite type function φ, and let μ=ρ  dσ be a surface carried measure on S, where dσ denotes the surface element on S and ρ a smooth density with sufficiently small support. We derive uniform estimates for the Fourier transform [^(m)]\hat{\mu} of μ, which are sharp except for the case where the principal face of the Newton polyhedron of φ, when expressed in adapted coordinates, is unbounded. As an application, we prove a sharp L ^p -L ² Fourier restriction theorem for S in the case where the original coordinates are adapted to φ. This improves on earlier joint work with M. Kempe.     

Determination of Chlorophenoxy Acid Herbicides in Water Samples by Suspended Liquid-Phase Microextraction�CLiquid Chromatography

In this study, directly suspended liquid-phase microextraction was investigated for the extraction and determination of five chlorophenoxy acid herbicides in water samples. The optimized parameters for extraction of chlorophenoxy acid herbicides were 1 M HCl concentration in sample solution, solution temperature 20 °C, 45-min extraction time, 1,000 rpm stirring rate, 25 ??L extracting solvent volume and without NaCl addition. Under the optimum conditions, the enrichment factor ranged from 192 to 390. Calibration curves yielded good linearity (R ² > 0.999) and the linear range was 5.0?C500.0 ??g L^?1, limit of detection was 0.3?C0.4 ??g L^?1 and limit of quantification was 1?C2 ??g L^?1 for analytes and the relative standard deviations were in the range of 3?C10% (n = 3). Finally, the proposed method was successfully applied to the quantification of five chlorophenoxy acid herbicides in water samples and recovery was in the range of 74?C110%.     

Proof complexity of propositional default logic

Default logic is one of the most popular and successful formalisms for non-monotonic reasoning. In 2002, Bonatti and Olivetti introduced several sequent calculi for credulous and skeptical reasoning in propositional default logic. In this paper we examine these calculi from a proof-complexity perspective. In particular, we show that the calculus for credulous reasoning obeys almost the same bounds on the proof size as Gentzen??s system LK. Hence proving lower bounds for credulous reasoning will be as hard as proving lower bounds for LK. On the other hand, we show an exponential lower bound to the proof size in Bonatti and Olivetti??s enhanced calculus for skeptical default reasoning.     

Separation and Preconcentration by Dispersive Liquid�CLiquid Microextraction Procedure: Recent Applications

Dispersive liquid?Cliquid microextraction (DLLME) is a relatively novel miniaturized sample pre-treatment technique. DLLME has been applied for the analysis of a large variety of organic compounds and metal ions in different samples. This paper reviews the more recent applications of this procedure for sample preparation.     

Cyclodextrins in innovative engineering tools for risk-based environmental management

Experimental results, which may serve as basis for innovative applications of cyclodextrins (CDs) in environmental technologies, are presented here. Some newly developed CD-aided tools are used in sampling, measuring the concentration or testing the effect of contaminants in water and soil. The innovative methods such as the bacterial bioassays with CD-increased sensitivity or the CD-filled absorptive samplers for air and water sampling are utilised in environmental exposure, hazard and risk assessment. Technological developments aim the reduction of the risk of chemical substances in waters and soils. CD-aided environmental remediation is introduced through examples for the elimination of organic contaminants from water by CD-filters, and for the enhancement of the mobility and availability of soil contaminants in this way increasing the efficiency of soil remediation by water extraction, chemical oxidation, biodegradation, etc.     

Influence of rhodium additive on hydrogen electrosorption in palladium-rich Pd�CRh alloys

Hydrogen electrosorption into Pd-rich (>80?at.% Pd in the bulk) Pd?CRh alloys has been studied in acidic solutions (0.5?M H₂SO₄) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328?K), electrode potential and alloy bulk composition on hydrogen electrosorption properties of Pd?CRh alloys is presented. It has been found that the additive of Rh to Pd?CRh alloys increases the maximum hydrogen solubility (for Rh bulk content below 10?at.%), decreases the potential of absorbed hydrogen oxidation peak and decreases the potential of the ???????? phase transition. Increasing temperature decreases the potential of absorbed hydrogen oxidation peak, the maximum hydrogen solubility, and the potential of the ???????? phase transition. The amounts of electrosorbed hydrogen for ??- and ??-phase boundaries, i.e., ??_max and ??_min, have been determined from the integration of the initial parts of current?Ctime responses in hydrogen absorption and desorption processes. The H/M ratio corresponding to ??_max increases with increasing Rh content, while for ??_min a maximum of H/M ratio is observed for the alloys containing ca. 95% Rh.     

The N- and C-terminal domains of parathyroid hormone-related protein affect differently the osteogenic and adipogenic potential of human mesenchymal stem cells

Parathyroid hormone-related protein (PTHrP) is synthesized by diverse tissues, and its processing produces several fragments, each with apparently distinct autocrine and paracrine bioactivities. In bone, PTHrP appears to modulate bone formation in part through promoting osteoblast differentiation. The putative effect of PTH-like and PTH-unrelated fragments of PTHrP on human mesenchymal stem cell (MSCs) is not well known. Human MSCs were treated with PTHrP (1-36) or PTHrP (107-139) or both (each at 10 nM) in osteogenic or adipogenic medium, from the start or after 6 days of exposure to the corresponding medium, and the expression of several osteoblastogenic and adipogenic markers was analyzed. PTHrP (1-36) inhibited adipogenesis in MSCs and favoured the expression of osteogenic early markers. The opposite was observed with treatment of MSCs with PTHrP (107-139). Moreover, inhibition of the adipogenic differentiation by PTHrP (1-36) prevailed in the presence of PTHrP (107-139). The PTH/PTHrP type 1 receptor (PTH1R) gene expression was maximum in the earlier and later stages of osteogenesis and adipogenesis, respectively. While PTHrP (107-139) did not modify the PTH1R overexpression during adipogenesis, PTHrP (1-36) did inhibit it; an effect which was partially affected by PTHrP (7-34), a PTH1R antagonist, at 1 µM. These findings demonstrate that both PTHrP domains can exert varying effects on human MSCs differentiation. PTHrP (107-139) showed a tendency to favor adipogenesis, while PTHrP (1-36) induced a mild osteogenic effect in these cells, and inhibited their adipocytic commitment. This further supports the potential anabolic action of the latter peptide in humans.     

An Algorithm to Find the Lineality Space of the Positive Hull of a Set of Vectors

The positive hull of a finite set of vectors, V{\cal V}, in d-dimensional space may or may not contain a lineality space L{\cal L}. This article presents an algorithm that identifies the vectors of V{\cal V} that belong to L{\cal L}. This is done by means of a sequence of supporting hyperplanes because every supporting hyperplane of the positive hull of V{\cal V} contains L{\cal L}. Computational results show the effectiveness of the algorithm, which is compared to the best procedure currently available (to the best knowledge of the author) that solves the same problem. The algorithm introduced here is especially efficient in the case of large problems, where cardinality and/or dimensions are large.