Entrapment of Humic Acid in a Sol-Gel Matrix—A New Tool for Sorption Studies

Humic substances are natural complexed mixtures of organic compounds originated from the decomposition of plant and animal residues. These compounds are ubiquitous in soils, sediments, surface waters and groundwaters. They contain both hydrophobic and hydrophilic moieties, able to interact with hydrophobic organic contaminants and with heavy metals. These sorption interactions play a crucial role in contaminants fate and transport and their understanding and quantification are essential for modeling and predictions. However, sorption analyses frequently suffer from experimental problems. A novel idea presented in this study is to use sol-gel as an inert matrix to immobilize (entrap) specific, well defined, humic molecules which then be used in sorption studies. We developed a successful procedure for the immobilization of humic acid (HA) in a sol-gel matrix. After gelation and drying, the doped gel was crushed and washed several times, yielding a very stable product. It was then used in a series of batch experiments, studying the sorption of several polycyclic aromatic hydrocarbons (PAHs) with Aldrich HA. The sorption coefficients (K _oc) obtained with the immobilized HA were highly correlated with the values expected based on the hydrophobicity of the contaminants. We concluded that the entrapped HA retained its original properties and that it was accessible to the external contaminants through the pore network.     

Improved Estimation of Parameter Matrices in a One-Sample and Two-Sample Problems

In this paper, the problems of estimating the covariance matrix in a Wishart distribution (refer as one-sample problem) and the scale matrix in a multi-variate F distribution (which arise naturally from a two-sample setting) are considered. A new class of estimators which shrink the eigenvalues towards their harmonic mean is proposed. It is shown that the new estimator dominates the best linear estimator under two scale invariant loss functions.     

A Modification of an Algorithm by Golub and Plemmons for Large Linear Least Squares in the Context of Doppler Positioning

This paper considers the solution of the geodetic Doppler multi-stationadjustment, i.e. the problem of computing the positions of severalstations observing the Doppler shift on radio frequencies emittedby several artificial satellites passing over the horizon. Amodification of an algorithm due to Golub and Plemmons, forsolving large linear least-squares problems where the observationmatrix has a block dual angular form, is proposed in this framework.This modification is shown to reduce substantially both datatransfer between the tracking stations and the main computingcentre, and the total computational effort required to obtainthe solution of the problem. Preliminary numerical results arediscussed and some further comments presented.     

Phonon dispersion relations in semiconductor superlattices in the adiabatic bond-charge model

The phonon dispersion in semiconductor superlattices is studied in the adiabatic bond-charge model. The complex phonon dispersion relations of the constituent bulk materials are obtained via the eigenvalue method in a zeroth-order calculation, which includes only short range forces and Coulomb interactions between ions and bond charges in the same and neighboring layers. The eigenmode displacements of the superlattice are obtained by matching the eigenvectors associated with complex phonon branches at the interfaces. The effect of the remaining Coulomb interactions are then included in the first-order approximation. The results for the superlattice phonon frequencies compare favorably with the existing experimental data.     

Fission yields at different fission-product kinetic energies for thermal-neutron-induced fission of 239Pu

At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of ²³⁹Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even-Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd-Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data ¹) for thermal-neutron-induced fission of ²³⁵U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for ²³⁵U and ²³⁹Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σ_z². for thermal-neutron fission of ²³⁵U and ²³⁹Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σ_z² is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.     

BaIr0,67Be0,33O3: Eine stabilisierte kubische Form von BaIrO3

Inhaltsübersicht. Es ist gelungen, ein durch BeO stabilisiertes Bariumoxoiridat der Zusammensetzung BaIr_0,67Be_0,33O₃ in der Kristallform eines kubischen Perowskits mit kleiner Elementarzelle erstmals darzustellen. Raumgruppe O¹_h–Pm3m, a = 4,1009 Å, Z = 1. Ir⁵⁺ und Be² + besetzen die Oktaederposition des Perowskits statistisch. BaIr_0,67Be_0,33O₃: A Stabilized Cubic Form of BaIrO₃ For the first time it was possible to prepare a new barium-oxoiridate of the formula BaIr_0,67Be_0,33O₃, stabilized by BeO. It crystallizes in a small cubic unit cell of the perovskite type. Space group O¹_h–Pm3m; a = 4.1009 Å; Z = 1. Ir⁵⁺ and Be²⁺ occupy the octahedra positions of the perovskite structure statistically.     

Energy distributions of CO produced in an acetone-containing discharge

Tunable infrared diode laser absorption (TDLAS) and Fourier transform infrared absorption spectroscopies (FTIR) have been utilized to characterize the translational, rotational and vibrational distributions of CO in an acetone/argon DC plasma at total pressures ranging from 4 to 5 Torr and currents of 0.1–0.3 A. A broad vibrational distribution of CO was observed with gradually decreasing intensities from the fundamental band to v=12←11. When nitrogen was added to the plasma, the distribution is narrower, due to the efficient energy transfer between CO and N₂ molecules. The measured translational temperature in such plasmas ranged from 400–550 K. The rotational distribution can generally be fitted to a Boltzmann distribution within each vibrational level although the rotational temperature is highest for the lowest vibrational quantum number.     

Iridium-promoted deoxyglycoside synthesis: stereoselectivity and mechanistic insight

Herein, we devised a method for stereoselective O-glycosylation using an Ir(i)-catalyst which enables both hydroalkoxylation and nucleophilic substitution of glycals with varying substituents at the C3 position. In this transformation, 2-deoxy-α-O-glycosides were acquired when glycals equipped with a notoriously poor leaving group at C3 were used; in contrast 2,3-unsaturated-α-O-glycosides were produced from glycals that bear a good leaving group at C3. Mechanistic studies indicate that both reactions proceed via the directing mechanism, through which the acceptor coordinates to the Ir(i) metal in the α-face-coordinated Ir(i)-glycal π-complex and then attacks the glycal that contains the O-glycosidic bond in a syn-addition manner. This protocol exhibits good functional group tolerance and is exemplified with the preparation of a library of oligosaccharides in moderate to high yields and with excellent stereoselectivities.

Ir(i)-catalyzed α-selective O-glycosylation of glycals provided an access to both 2-deoxyglycosides and 2,3-unsaturated glycosides with a broad substrate scope. The underlying rationale of α-selectivity has been illustrated by the DFT study.