New adsorbents from oil shales: Preparation, characterization and U, Th isotope adsorption tests

New activated adsorbents for radionuclides have been produced from Moroccan oil shales by pyrolysis of the natural material at 550 °C flowed by a KMnO₄ activation. The texture and composition of the native rock and the adsorbents were studied before their use in tests for adsorption of radionuclides from standard solutions prepared from uranylnitrate and thorium nitrate in equilibrium with their daughters. The distribution coefficients between solutions containing U, Th and Ra and the adsorbents were evaluated by means of specific activities, measured by g-ray spectrometry. The adsorbents were observed to eliminate U, Th, Ra, Ac and Tl from aqueous solutions. This revised version was published online in August 2006 with corrections to the Cover Date.     

RECOVERY FROM DAMAGE INDUCED BY ACRIDINE PLUS NEAR-ULTRAVIOLET LIGHT IN ESCHERICHIA COLI

Abstract— Escherichia coli cells treated with sublethal doses of acridine plus near-UV light exhibit an effective split-dose recovery response that requires an incubation period of about 30–45 min. Studies of the metabolic requirements for split-dose recovery revealed the following: (a) DNA synthesis is not required for split-dose recovery; (b) inhibition of electron transport or protein synthesis reduces the efficiency of split-dose recovery by about one-half; (c) inhibition of phospholipid synthesis or cell wall synthesis completely eliminates the split-dose recovery response. These results suggest an involvement of membrane repair mechanisms in response to damage by acridine plus near-UV light. Additional evidence for such a process was provided by more direct assays for membrane recovery. It was found that cells treated with sublethal doses of acridine plus near-UV light are sensitive to low concentrations of detergents, and lose that sensitivity upon incubation. Likewise, treated cells are susceptible to lethal osmotic shock, but can recover from this susceptibility if incubated after treatment but prior to exposure to low osmotic conditions. Based on accumulating evidence, we propose that E. coli cells are capable of repairing membrane damage resulting from exposure to acridine plus near-UV light.     

The Influence of the Calcination and Water Washing Treatments on the Uranium Content in Sedimentary Phosphate Samples Using Solid State Nuclear Track Detectors and Gamma-Ray Spectrometry

The uranium and thorium contents were evaluated in the 100–400 µm granulometric fraction of different sedimentary phosphate samples by using a method based on determining the mean critical angles of etching of the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) for detecting -particles emitted by the nuclei of the uranium-238 and thorium-232 series. Data obtained were compared with the results of -ray spectrometry measurements performed on the same samples. The influence of the calcination and water washing treatments as well as the lithology and stratigraphy on the uranium concentration of the phosphate samples was investigated.     

An efficient heuristic approach to detecting graph isomorphism based on combinations of highly discriminating invariants

The search for an easily computable, finite, complete set of graph invariants remains a challenging research topic. All measures characterizing the topology of a graph that have been developed thus far exhibit some degree of degeneracy, i.e., an inability to distinguish between non-isomorphic graphs. In this paper, we show that certain graph invariants can be useful in substantially reducing the computational complexity of isomorphism testing. Our findings are underpinned by numerical results based on a large scale statistical analysis.     

Generalized graph entropies

This article deals with generalized entropies for graphs. These entropies result from applying information measures to a graph using various schemes for defining probability distributions over the elements (e.g., vertices) of the graph. We introduce a new class of generalized measures, develop their properties, compute the measures for selected graphs, and briefly discuss potential applications to classification and clustering problems. © 2011 Wiley Periodicals, Inc. Complexity, 17,45–50, 2011     

Comment on the positron reactions with pseudo-halides in water

Comments are made on the data reported by Mogensen, Pedersen and Andersen on positron reactions with pseudo-halide ions in water and on their interpretation. Although some of our previous experimental curves are in agreement with theirs, there is a major discrepancy with some of their semi-empirical data, pointing to internal inconsistencies in their results. The possibility of another interpretation of the data is suggested.     

The chemistry of positronium: III. Inhibition and quencing by sikver and cadmium salts

The inhibition ofpositronium formation and the quenching reactions of positronium in aqueous solutions of AgCIO₄, Cd(C10₄)₂ and AgOOC-CF₃ have been studied using the positron lifetime spectroscopy. The variations of the lifetimes of ortho-positronium (0-Ps) wiLls the concentration of the solute in water reveal peculiar features, attributed to the formation of complex ions.     

Inhibition and enhancement of positronium formation: A contribution to the study of localisation processes in liquids

The formation of positronium in various solvents and the inhibition and enhancement of positronium formation by a wide variety of solutes are discussed. The studies contribute to the investigation of localisation processes in liquids.     

Analysis of uranium using delayed neutron emission

Analyses of uranium and thorium by delayed neutron counting are described.The experimental system comprises an automatic pneumatic transfer system associatedwith a device made of twelve BF 3 neutron counters. Using homogeneous preparedsolutions of the samples, the analyses were based on a triple cycle each including60-second irradiation followed by 1-second cooling and 60-second counting.In these conditions, the limit of detection of uranium is about 0.3 µgwith a precision of measurement better than 10%. The contributions of possibleperturbations from 17 O(n,p)17 N reactions, followed by simultaneous –disintegration and neutron emission and from (n) reactions, have been studied.     

On the concentration of the number of solutions of random satisfiability formulas

Let Z(F) be the number of solutions of a random k‐satisfiability formula F with n variables and clause density α. Assume that the probability that F is unsatisfiable is for some . We show that (possibly excluding a countable set of “exceptional” α's) the number of solutions concentrates, i.e., there exists a non‐random function such that, for any , we have with high probability. In particular, the assumption holds for all , which proves the above concentration claim in the whole satisfiability regime of random 2‐SAT. We also extend these results to a broad class of constraint satisfaction problems. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 45, 362–382, 2014