Sorption of Cadmium from Aqueous Solutions at Different Temperatures by Mexican HEU-type Zeolite Rich Tuff

Many factors may affect the heavy metals sorption on natural zeolites among them the temperature, for this reason in this paper the cadmium retention behavior on Mexican zeolitic rich tuff as a function of temperature is considered. The kinetic and the isotherms were determined at 303, 318, and 333 K, the remaining cadmium in the solution samples was analyzed by atomic absorption spectrometry. The pseudo-second order rate constant, k, as well as the apparent diffusion coefficients were calculated from the cadmium uptake by the zeolitic rock as a function of the contact time and temperature, the highest amounts were found for the experiments done at 333 K. The maximum cadmium adsorption capacity by the zeolitic material was 12.2 mg Cd²⁺/g at 318 K corresponding to 20% of the effective ion exchange capacity of the Chihuahua zeolitic rock. In order to explain the cadmium sorption behavior different kinetics and isotherm models were considered.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Kinetic equations and brownian motion for a solid in a stationary temperature gradient

A kinetic equation for the distribution function for a subsystem s interacting with a bath b maintained in a stationary non-isothermal state by reservoirs is derived by using a projection operator formalism and a perturbation expansion parameter λ appropriate to some brownian motion problems. Thus, when s is a heavy particle of mass m ₀ and b a lattice of light particles of mass m then λ = (m m ₀)^1/2. By means of an assumption about the decay of correlations of b variables in the field of s, the terms are classified as destruction terms which vanish to arbitrary order in λ for long enough times and collision terms which give well-defined integrals for long times. For the heavy particle in a lattice the leading collision terms, after linearization in the temperature gradient, lead to an equation equivalent to the generalized nonisothermal Fokker-Planck equation of Nicolis.     

Interdiffusion in strongly ionic insulating compounds: The Nernst–Planck equation

In strongly ionic insulating materials, the Nernst–Planck Equation relates the interdiffusion coefficient of the cations (having the same charge) with the corresponding tracer diffusivities and the thermodynamic factor. In this paper, we explore the Nernst–Planck Equation for ionic ternary (quasi-binary) and ionic quaternary (quasi-ternary) systems using the diffusion kinetics formalisms of Darken [Trans. Am. Inst. Min. (Metall.) Eng. 175 184 (1948)], Manning [Phys. Rev. B 4 1111 (1971)] and Moleko, Allnatt and Allnatt [Phil. Mag. A 59 141 (1989)]. It is shown that for the binary system, the Darken and Manning formalisms both give the usual form of the Nernst–Planck Equation. However, the almost exact Moleko, Allnatt and Allnatt formalism (for randomly mixed systems) provides an additional correction factor analogous to the vacancy-wind factor in the well-known Darken–Manning Equation used in binary alloy systems. Nernst–Planck-type equations are also derived for strongly ionic insulating ternary systems and are found to behave similar to the binary case.     

Formulae which relate pressure,activity and potentials of mean force to sums of integrals over Ursell-Mayer correlation functions of the distribution functions

The pure rotational spectrum in the far-infrared between 30 and 170 cm^-1 and its absolute intensity has been measured for CH₂D₂ in the vibrational ground state by high-resolution interferometric Fourier transform techniques. The analysis of the integrated cross-sections in the essentially water-free spectrum results in an accurate value for the permanent, vibrationally induced ground state electric dipole moment of CH₂D₂|μ₀| = (6·40±0·33) x 10^-3D.The influence of centrifugal effects on intensities and on the determination of the permanent dipole moment was investigated. Although centrifugal effects are important for the explanation of single band profiles, they appear to be of little relevance for the resulting permanent dipole moment. A new, more general 9- dimensional dipole moment function for methane is derived from ab initio calculations and experimental band strength information of CHD₃. Quantum Monte Carlo calculations using this function and a new, more general 9- dimensional analytical, anharmonic potential function for methane yield a semi-theoretical estimate μ₀ ^z = – (7·8±0·5)x10^-3D for CH₂D₂.     

Diffusion kinetics in dilute binary alloys with the h.c.p. crystal structure

In this paper, an extended version of the matrix method is derived in order to address diffusion kinetics for the full anisotropic three-dimensional h.c.p. structure. It is shown that the diffusion anisotropy can be properly addressed with a model of 13 atom-vacancy frequencies which is an extended version of the well-known 5-frequency model for the f.c.c. lattice. Both tracer and phenomenological diffusion coefficients are calculated using this new approach. Extended Monte Carlo simulations are performed in order to cross-check some of the results of the matrix method. Applications of the proposed model to experimental diffusion data are discussed.     

Probabilistic Inductive Classes of Graphs

A unifying framework—probabilistic inductive classes of graphs (PICGs)—is defined by imposing a probability space on the rules and their left elements from the standard notion of inductive class of graphs. The rules can model the processes creating real-world social networks, such as spread of knowledge, dynamics of acquaintanceships or sexual contacts, and emergence of clusters. We demonstrate the characteristics of PICGs by casting some well-known models of growing networks in this framework. Results regarding expected size and order are derived. For PICG models of connected and 2-connected graphs order, size and asymptotic degree distribution are presented. The approaches used represent analytic alternative to computer simulation, which is mostly used to obtain the properties of evolving graphs.     

A reliable single parameter interatomic potential for argon

A simple semiempirical approximation previously proposed for the isotropic intermolecular forces between two closed shell systems is tested in detail for the argon-argon interaction. The potential is based on the knowledge of the first-order coulomb interaction energy, a suitably damped three term long range asymptotic expansion of the second order coulomb energy, and a semiempirical representation of the exchange interaction energy which contains one adjustable parameter. The single adjustable parameter can be reliably determined by fitting the second virial coefficient for argon in the 130–773 K temperature range with the long range interaction coefficients being constrained within the theoretical bounds specified by Tang, Norbeck and Certain. The reliability of the potential is compared with that of several literature potentials by comparing the theoretical predictions obtained from the potentials with experimental results for the second virial coefficient, viscosity, thermal conductivity and thermal diffusion ratios for dilute argon gas, and with spectroscopic data for the dimer, and with SCF calculations of the Ar-Ar potential at small interatomic separations. Our best potential predicts these properties with a precision as good as or better than other recent potentials which generally contain more adjustable parameters and/or involve more input data. The results confirm earlier work that suggested that the scheme tested is capable of yielding reliable isotropic potentials for the interaction of closed shell systems for 0·3 ? R/R_m ? ∞ where R_m is the intermolecular distance at the van der Waals minimum. The scheme appears to offer a method for obtaining reliable potentials while avoiding problems associated with optimizing many parameters with respect to fitting experimental constraints.     

Atom transport in random two sublattice structures: analogue of the random alloy sum rule

A simple and often used model of atom transport by the vacancy mechanism on two physically distinct interpenetrating sublattices assumes that each atom–vacancy exchange frequency depends only on the species of the atom and the sublattice from which it jumps. In the kinetic theory of this model, the phenomenological coefficients can be expressed as sums of partial correlation functions, each labelled by the sublattices associated with the atoms making the first and last jumps in the sequence of correlated jumps which it represents. A sum rule, a set of exact relations among these partial correlation functions, is derived for the model, assuming arbitrary vacancy content and any number of chemical species. It reduces to a widely used sum rule for the random lattice gas [L.K. Moleko and A.R. Allnatt, Phil. Mag. A 58 677 (1988)] in the limit that atom jump frequencies are made independent of sublattice. For the two sublattice model at very low vacancy contents, a more powerful sum rule is also derived; it is essentially the same as that of Belova and Murch [Defect Diffus. Forum 194/199 547 (2001)]. The efficiencies of the three sum rules are briefly compared. The low vacancy concentration sum rule is illustrated by numerical simulations for a binary two sublattice system.