Clays and clay minerals: What can Mössbauer spectroscopy do to help understand them?

Mössbauer spectroscopy is a powerful technique for the characterization of materials formed in the weathering environment. Mössbauer studies of clay-sized phyllosilicates, however, are burdened with several problems: the samples are rarely monomineralic, they may be poor in iron, and only few iron-rich species order magnetically above 4.2 K. Site occupancies are difficult to determine, and cis and trans octahedral-OH site assignments are normally not possible. Unequivocal information that can be gained from such work thus is often restricted to the determination of the oxidation state of iron and average structural site distortions. Mössbauer data on iron oxides are generally more straightforward to interpret because these can be studied in the magnetically ordered state. A further asset of Mössbauer spectroscopy when studying iron oxides lies in its high sensitivity for magnetically ordered phases. Adverse effects ensuing from small particle size, interparticle interactions, non-stoichiometry and foreign-element substitution that often affect the Mössbauer parameters of iron oxides occurring in clays and soils can be at least partly offset by taking spectra at low temperatures.     

Formative ceramics from the Andes and their production: A Mössbauer study

The potential of Mössbauer spectroscopy in the reconstruction of production techniques of early ceramics is demonstrated by the results of a study of a Formative kiln site at the Archaeological Park at Batán Grande, Perú, and of ceramics from the nearby settlement of Huaca Chólope.     

(1/α)-Self similar α-stable processes with stationary increments

In this note we settle a question posed by Kasahara, Maejima, and Vervaat. We show that the α-stable Lévy motion is the only (1/α)-self-similar α-stable process with stationary increments if 0 < α < 1. We also introduce new classes of (1/α)-self-similar α-stable processes with stationary increments for 1 < α < 2.     

Resonance Raman and infrared spectroscopic studies of high-output forms of human soluble guanylyl cyclase

The allosteric regulator BAY-41-2272 converts the CO adduct of soluble guanylyl cyclase (CO-sGC) enzyme from a low- to high-output form, with respect to production of cGMP. Resonance Raman (RR) and Fourier Transform Infrared (FTIR) spectroscopic techniques are used to show that the CO-sGC exists as major and minor conformers, both having nu(Fe-CO) and nu(C-O) modes characteristic of 6-coordinate species. It is further shown that addition of BAY-41-2272 to the CO adduct induces the transition of some fraction of the initial CO-heme adducts into two new CO-heme complexes, the fractional conversion being dependent on the temperature. One new complex displays vibrational modes characteristic of pentacoordinated CO-adduct, and its formation is not affected by temperature. The second complex, although slightly different from the original CO-adducts, is hexacoordinated, and its formation is facilitated by temperature. The production of substantial amounts of the 5-coordinate CO adduct upon addition of BAY-41-2272, reveals the fact that several out-of-plane heme deformation modes are simultaneously activated, an observation similar to that realized upon NO activation. While the precise nature of these modes will require elucidation by isotopic labeling experiments, by analogy with earlier studies of other heme proteins, several bands associated with modes attributable to peripheral substituent deformations and methine carbon movements are implicated. The documented formation of two new forms upon addition of Bay-41-2272 (a 5-coordinate and a new 6-coordinate form) is discussed with respect to the implications for enzyme activation.     

Vacancy ion-exclusion chromatography of haloacetic acids on a weakly acidic cation-exchange resin

A new and simple approach is described for the determination of the haloacetic acids (such as mono-, di- and trichloroacetic acids) usually found in drinking water as chlorination by-products after disinfection processes and acetic acid. The new approach, termed vacancy ion-exclusion chromatography, is based on an ion-exclusion mechanism but using the sample solution as the mobile phase, pure water as the injected sample, and a weakly acidic cation-exchange resin column (TSKgel OApak-A) as the stationary phase. The addition of sulfuric acid to the mobile phase results in highly sensitive conductivity detection with sharp and well-shaped peaks, leading to excellent and efficient separations. The elution order was sulfuric acid, dichloroacetic acid, monochloroacetic acid, trichloroacetic acid, and acetic acid. The separation of these acids depends on their pKa values. Acids with lower pKa values were eluted earlier than those with higher pKa, except for trichloroacetic acid due to a hydrophobic-adsorption effect occurring as a side-effect of vacancy ion-exclusion chromatography. The detection limits of these acids in the present study with conductivity detection were 3.4 microM for monochloroacetic acid, 0.86 microM for dichloroacetic acid and 0.15 microM for trichloroacetic acid.     

Biofunctional properties of Eruca sativa Miller (rocket salad) hydroalcoholic extract

Eruca sativa Miller is a worldwide common alimentary plant (rocket leaves). The aim of this study was to correlate the potential in vitro scavenging activity of the E. sativa hydroalcoholic extract (HAE) with its in vivo hypoglycaemic effect. In DDPH free radical (DFR) and ferric-reducing antioxidant power assays, HAE in a concentration dependent manner (25–100 μg/mL) displayed a strong scavenging activity with maximum effect of 88% and 75% at 100 μg/mL, respectively. Daily administration of HAE (50 mg/kg; p.o.) in the in vivo model of alloxan-induced diabetic rabbits for 28 days showed significant reduction in glycaemia, also supported by recovery of body weight. In conclusion, our results give preliminary information on the potential use of this plant as a nutraceutical, useful to control and/or prevent a hyperglycaemic status.     

Microwave Synthesis of SAPO‐11 and AlPO‐11: Aspects of Reactor Engineering

AlPO‐11 and SAPO‐11 are synthesized using microwave heating. The effects of precursor volume, reaction temperature, reactor geometry, stirring, applicator type and frequency on the microwave synthesis of SAPO‐11 and AlPO‐11 are studied. The nucleation time and crystallization rate are determined from crystallization curves for SAPO‐11 (and/or AlPO‐11), for the various parameters investigated. Increasing volume of the reacting material decreases the reaction rate of SAPO‐11 at 160°C. In particular, the nucleation time increases with increase in the reaction volume. Increasing the reaction temperature increases the crystallization rate and decreases the nucleation time, however it decreases the particle size. Nucleation of SAPO‐11 and AlPO‐11 under microwave heating is strongly dependant on the reaction temperature. Using wider geometry vessel (33 mm compared to 11 mm diameter) enhances the reaction rate, producing larger crystals in the same reaction time, even though the crystallization rate is decreased. The crystallization rate is enhanced by applicator type in the following order CEM MARS‐5 oven>CEM Discover “focused” system>monomode waveguide. Stirring the reacting solution during heating affects primarily the nucleation time. The effect of microwave frequency on the nucleation and growth of SAPO‐11 shows a dependence on the applicator type more than the specific frequency, for the frequency range 2.45–10.5 GHz. The difference between the crystallization rate observed at higher frequencies and that at 2.45 GHz maybe due to the multimode nature of the waveguide at frequencies above 2.45 GHz. Sweeping the microwave frequency linearly between 8.7 and 10.5 GHz at rates of 10 min^?1 and 100 min^?1 shows an intermediate crystallization curve to that for fixed frequencies of 2.45 GHz and that for 5.8, 8.7 and 10.5 GHz.     

Neural field dynamics under variation of local and global connectivity and finite transmission speed

Spatially continuous networks with heterogeneous connections are ubiquitous in biological systems, in particular neural systems. To understand the mutual effects of locally homogeneous and globally heterogeneous connectivity, we investigate the stability of the steady state activity of a neural field as a function of its connectivity. The variation of the connectivity is implemented through manipulation of a heterogeneous two-point connection embedded into the otherwise homogeneous connectivity matrix and by variation of the connectivity strength and transmission speed. Detailed examples including the Ginzburg–Landau equation and various other local architectures are discussed. Our analysis shows that developmental changes such as the myelination of the cortical large-scale fiber system generally result in the stabilization of steady state activity independent of the local connectivity. Non-oscillatory instabilities are shown to be independent of any influences of time delay.     

A two-scale non-local model of swelling porous media incorporating ion size correlation effects

A new two-scale model is proposed for derivation of the macroscopic modified effective stress principle for swelling porous media saturated by an electrolyte solution containing finite size ions. A non-local pore-scale model is developed within the framework of Statistical Mechanics in conjunction with the thermodynamic approach based on Density Functional Theory leading to a nonlinear integral Fredholm equation of second kind for the ion/nanopore correlation function coupled with Poisson problem for the electric double layer potential. When combined with the fluid equilibrium condition such non-local electrochemical problem gives rise to a constitutive law for the fluid stress tensor in terms of the disjoining pressure which is decomposed into several components of different nature. The homogenization procedure based on formal asymptotic expansions is applied to up-scale the model to the macroscale leading to a two-scale constitutive law for the swelling pressure appearing in the modified effective stress principle with improved accuracy incorporating the deviations from the Gouy–Chapman Poisson–Boltzmann-based theory due to the finite size short-range ion–ion correlation effects. The integro-differential problem posed in a periodic cell is discretized by collocation schemes. Numerical results are obtained for a stratified arrangement of parallel macromolecules showing that the effects of ion–ion correlation forces give rise to anomalous attraction patterns between the particles for divalent ions.     

Numerical Computation of First-Passage Times of Increasing Lévy Processes

Let {D(s), s ≥ 0} be a non-decreasing Lévy process. The first-hitting time process {E(t), t ≥ 0} (which is sometimes referred to as an inverse subordinator) defined by $E(t) = \inf \{s: D(s) > t \}$E(t) = \inf \{s: D(s) > t \} is a process which has arisen in many applications. Of particular interest is the mean first-hitting time U(t)=\mathbbEE(t)U(t)=\mathbb{E}E(t). This function characterizes all finite-dimensional distributions of the process E. The function U can be calculated by inverting the Laplace transform of the function [(U)\tilde](l) = (lf(l))^-1\widetilde{U}(\lambda) = (\lambda \phi(\lambda))^{-1}, where ϕ is the Lévy exponent of the subordinator D. In this paper, we give two methods for computing numerically the inverse of this Laplace transform. The first is based on the Bromwich integral and the second is based on the Post-Widder inversion formula. The software written to support this work is available from the authors and we illustrate its use at the end of the paper.