Mössbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia

The local environment of implanted ¹¹¹Ag (t _1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 10¹³ cm⁻²) ¹¹¹Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free S_Zn sites (ν _Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30% of the ¹¹¹Ag atoms, 7% of which were located in regions of high defects concentration.     

Detecting embedded pure network structures in LP problems

Recently, linear programming problems with special structures have assumed growing importance in mathematical programming. It is well known that exploiting network structures within linear programs can lead to considerable improvement of the computational solution of large-scale linear programming problems. A linear program is said to contain an embedded network structure provided that some subset of its constraints can be interpreted as specifying conservation of flow. If a column of the constraint matrix has at most two non-zeros, then it leads to embedded generalized network structure and if these non-zeros are unit elements and of opposite signs, then it leads to embedded pure network structure. In this paper, we are concerned with algorithms for detecting embedded pure network structures within linear programs. The network extraction methods are presented in two groups. The first group covers deletion and addition based algorithms and the second group covers GUB based algorithms. We have extended the GUB based algorithm appearing in the second group by introducing Markowitz merit count approach for exploiting matrix non zeros. A set of well known test problems has been used to carry out computational experiments which show that our extensions to the GUB based algorithms give better results than the algorithms reported earlier.     

The scavenging of the precursors of the solvated electron from the positron lifetime spectroscopy and the doppler broadening of annihilation line shape technique

The electron scavenging properties of aqueous solutions of two series of solutes are investigated, using the positron as a probe. For a better interpretation of the data, both lifetime spectroscopy and the Doppler broadening of annihilation line shape technique are used. All solutes inhibit the positronium (Ps) formation, by the scavenging of electrons. The first series consists of the halate ions, that should follow the Hunt linear relation between the rate constant for reaction with the solvated electrons, k_(e^?aq+S), and that for its precursor(s), 1/C₃₇. The Ps inhibition constants, k, are 0.14, 1.44 and 3.45 M^?1 for ClO^?₃, BrO^?₃ and IO^?₃, respectively. This sequence is quantitatively consistent with that of the respective k_(e^?eq+S). The second series includes the SeO⁼₄, Te(OH)₆ and BrO^?₄ species, and the Ps inhibition constants are 5.62, 10.5 and 14.3 M^?1 respectively. These values are much higher than expected from the k_(e^?aq+S) constants, on basis of the Hunt relation, in agreement with previous results from pulse radiolysis experimets.     

Untersuchungen an Metallkatalysatoren. Zur Dispersität von Pt-Ir-Katalysatoren

Ohne Zusammenfassung     

Speciation of strontium in human and bovine milk

The speciation of strontium in human and bovine milk has been computed using a chemical equilibrium model and the ECCLES program. The calculations show     

Freeze-out volume in multifragmentation --Dynamical simulations

Stochastic mean-field simulations for multifragmenting sources at the same excitation energy per nucleon have been performed. The freeze-out volume, a concept which needs to be precisely defined in this dynamical approach, was shown to increase as a function of three parameters: freeze-out instant, fragment multiplicity and system size.     

Experimental charge density of a potential DHO synthetase inhibitor: dimethyl-trans-2-oxohexahydro-pyrimidine-4,6-dicarboxylate

The experimental charge density distribution of dimethyl-trans-2-oxohexahydro-pyrimidine-4,6-dicarboxylate 1 has been determined using single-crystal X-ray diffraction data measured at 100 K, in terms of the rigid-pseudoatom formalism. Multipole refinement converged at R(F) = 0.034 for 7283 reflections with I > 3 sigma (I) and sin theta/lambda < or = 1.13 A(-1). Covalent and hydrogen bonding interactions are analyzed using a topological analysis of the Laplacian of the charge density. The experimentally derived electrostatic potential mapped onto the reactive surface of the molecule reveals the potential binding sites of 1.     

Evaluation of the lipophilicity of bile acids and their derivatives by thin-layer chromatography and principal component analysis

The lipophilic character of bile acids and their glyco- and tauro-conjugates was studied. The classical R(Mo) values were measured by means of reversed thin-layer chromatography using a mixture of methanol-water as the solvent system and compared with the factors scores obtained by principal component analysis based also onto the TLC-retention data. The reliability of the factor scores values as lipophilic indices are shown by their high correlation with the classical R(Mo) values. In addition, a better correlation was observed between scores corresponding to the first principal components and the partition coefficients (log P) of bile acids. Finally, the "lipophilicity chart" described by the first two components has the effect of separating compounds from each other most effectively from the congeneric aspect point of view.