2,203 research outputs found
Electronic structure of the double perovskite Ba2Er(Nb,Sb)O 6
In this work, we present a detailed study of the structural and the electronic structure of the double perovskite Ba2Er(Nb,Sb)O 6. All calculations were performed with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) based on the Density Functional Theory (DFT). From the minimization of energy as a function of volume using the Murnaghan's state equation has been obtained the equilibrium lattice parameter and the bulk modulus of these compounds. The study of the electronic structure was based in the analysis of the electronic density of states (DOS), and the density of charge, showing that these compounds have a total magnetic moment of 3.0 ÎŒB per formula unit due to Er atoms.Fil: Gil Rebaza, Arles VĂctor. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; ArgentinaFil: Deluque Toro, Crispulo Enrique. Universidad Popular del Cesar; ColombiaFil: TĂ©llez LandĂnez, D. A. Universidad Nacional de Colombia; ColombiaFil: Roa Rojas, J.. Universidad Nacional de Colombia; Colombi
Guest charges in an electrolyte: renormalized charge, long- and short-distance behavior of the electric potential and density profile
We complement a recent exact study by L. Samaj on the properties of a guest
charge immersed in a two-dimensional electrolyte with charges . In
particular, we are interested in the behavior of the density profiles and
electric potential created by the charge and the electrolyte, and in the
determination of the renormalized charge which is obtained from the
long-distance asymptotics of the electric potential. In Samaj's previous work,
exact results for arbitrary coulombic coupling were obtained for a
system where all the charges are points, provided and .
Here, we first focus on the mean field situation which we believe describes
correctly the limit but large. In this limit we can
study the case when the guest charge is a hard disk and its charge is above the
collapse value . We compare our results for the renormalized charge
with the exact predictions and we test on a solid ground some conjectures of
the previous study. Our study shows that the exact formulas obtained by Samaj
for the renormalized charge are not valid for , contrary to a
hypothesis put forward by Samaj. We also determine the short-distance
asymptotics of the density profiles of the coions and counterions near the
guest charge, for arbitrary coulombic coupling. We show that the coion density
profile exhibit a change of behavior if the guest charge becomes large enough
(). This is interpreted as a first step of the counterion
condensation (for large coulombic coupling), the second step taking place at
the usual Manning--Oosawa threshold
Exact asymptotic expansions for the cylindrical Poisson-Boltzmann equation
The mathematical theory of integrable Painleve/Toda type systems sheds new
light on the behavior of solutions to the Poisson-Boltzmann equation for the
potential due to a long rod-like macroion. We investigate here the case of
symmetric electrolytes together with that of 1:2 and 2:1 salts. Short and large
scale features are analyzed, with a particular emphasis on the low salinity
regime. Analytical expansions are derived for several quantities relevant for
polyelectrolytes theory, such as the Manning radius. In addition, accurate and
practical expressions are worked out for the electrostatic potential, which
improve upon previous work and cover the full range of radial distances
Kinetics of Drying Medicinal Plants by Hybridization of Solar Technologies
Historically, medicinal plants have always had an important place in medicine. Medicinal plants processing represents a great challenge, due to their compounds sensitive to the environmental conditions that surround and degrade them. Mostly of these plants require to be dry to preserve its safety and medicinal properties; therefore, for proper drying, it is necessary to use sustainable devices that protect the desirable characteristics of plants from direct radiation. In this work, the kinetics of dehydration of three medicinal plants are presented in an indirect solar dryer. In addition, the experimental results were adjusted to nine mostly used models, to estimate the drying conditions required to achieve a desired final moisture content. Modified Page and Page were the models with better fit to experimental results. Furthermore, a computational simulation of temperature evolution and distribution inside the dryer is presented. These results agree with those obtained experimentally
Production of Transglutaminase by Streptoverticillium ladakanum NRRL-3191 Using Glycerol as Carbon Source
The enzyme transglutaminase (TG) catalyses the formation of covalent bonds between adjacent proteins, thereby improving the gel structure of proteins and has important applications for the food industry. The aims of this work were: (i) to elucidate the effect of agitation speed during the biotechnological production of TG by Streptoverticillium ladakanum NRRL-3191 using glycerol as carbon source; and (ii) to improve TG production by optimising the composition of media based on glycerol, xylose and casein. An agitation speed of 250 rpm and a fermentation time of 72 h resulted in the optimal enzymatic activity (0.628 U/mL) with a productivity of 0.087 U/(mL·h). The composition of media with glycerol, xylose and casein were optimised using an experimental design to improve TG production. The model predicts that the maximum TG activity (0.725 U/mL) can be obtained using glycerol 50.5 g/L and casein 20 g/L without the addition of xylose
Insight into the reversible structural crystalline-state transformation from MIL-53(Al) to MIL-68(Al)
The reversible crystalline transformation between MIL-53(Al) and MIL-68(Al) is described. This followed a uniform conversion model with cleavage and formation of metal-ligand bonds after exchange or removal of guest molecules. MIL-68(Al) materials produced during the transformations had higher thermal stability and crystallinity than the as-synthesized MIL-68(Al)
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