Removal of Pyridine from Aqueous Solution by Adsorption on an Activated Carbon Cloth

Pyridine is a very toxic pollutant that has to be removed from wastewater. In this work, adsorption of pyridine on activated carbon cloth (ACC) is studied as a possible alternative for eliminating pyridine from aqueous solution. The ACC was produced from polyacrylonitrile. The adsorption equilibrium data of pyridine on ACC was obtained in a batch adsorber. The experimental data was interpreted with the isotherms of Langmuir, Freundlich, and Prausnitz‐Radke (PR), and the PR isotherm better represented the experimental data. The capacity of ACC for adsorbing pyridine was favored increasing the solution pH from 3 to 6, and this effect was due to the π–π dispersive and electrostatic interactions between the pyridine species in solution and the surface complexes of ACC. The modified Langmuir model fitted reasonably well the influence of pH on the adsorption capacity. In this model was assumed that both neutral pyridine and pyridinium were simultaneously adsorbed on ACC accordingly to the experimental results. The adsorption capacity was almost independent of temperature. The reversibility study revealed that 75% of the pyridine can be desorbed from ACC indicating that part of the pyridine was irreversibly adsorbed, and possibly chemisorbed.     

Evolution of density perturbations in double exponential quintessence models

In this work we investigate the evolution of matter (linear) density perturbations for quintessence models with a self-interaction potential that is a combination of exponentials. One of the models is based on the Einstein theory of gravity, while the other is based on the Brans-Dicke scalar tensor theory. We constrained the parameter space of the models by using the determinations of the growth rate of perturbations derived from data of the 2-degree Field Galaxy Redshift Survey.      

Asymptotic behavior of a scalar field with an arbitrary potential trapped on a Randall-Sundrum’s braneworld: the effect of a negative dark radiation term on a Bianchi I brane

In this work we present a phase space analysis of a quintessence field and a perfect fluid trapped in a Randall-Sundrum’s Braneworld of type 2. We consider a homogeneous but anisotropic Bianchi I brane geometry. Moreover, we consider the effect of the projection of the five-dimensional Weyl tensor onto the three-brane in the form of a negative Dark Radiation term. For the treatment of the potential we use the “Method of f-devisers” that allows investigating arbitrary potentials in a phase space. We present general conditions on the potential in order to obtain the stability of standard 4D and non-standard 5D de Sitter solutions, and we provide the stability conditions for both scalar field-matter scaling solutions, scalar field-dark radiation solutions and scalar field-dominated solutions. We find that the shear-dominated solutions are unstable (particularly, contracting shear-dominated solutions are of saddle type). As a main difference with our previous work, the traditionally ever-expanding models could potentially re-collapse due to the negativity of the dark radiation. Additionally, our system admits a large class of static solutions that are of saddle type. These kinds of solutions are important at intermediate stages in the evolution of the universe, since they allow the transition from contracting to expanding models and viceversa. New features of our scenario are the existence of a bounce and a turnaround, which lead to cyclic behavior, that are not allowed in Bianchi I branes with positive dark radiation term. Finally, as specific examples we consider the potentials V∝sinh^?α (β?) and V∝[cosh(ξ?)?1] which have simple f-devisers.     

Quinstant dark energy predictions for structure formation

We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the non-linear one, for redshifts larger than one.     

Torsional response of symmetric buildings to incoherent and phase‐delayed earthquake ground motion

This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three‐dimensional, multi‐storey, multi‐span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase‐delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd.