On Bootstrapping M-Estimated Residual Processes in Multiple Linear-Regression Models

It is shown, under fairly general conditions, that Efron′s bootstrap procedure captures the limit distribution of weighted empirical processes based on M-estimated residuals in multiple linear regression models. As an application, we construct bootstrap confidence bands for the error distribution function F. The main result can also be used to design distribution-free goodness-of-fit tests for F without any recourse to the split-sample estimation of the regression parameters.     

Production of a tracer packet of heavier rare earth elements

The paper describes the production of a tracer packet of heavier rare earth elements containing carrier-free radionuclides of ^153,155Tb, ^153,155,157Dy, ¹⁵⁹Ho, ^159,161Er, ¹⁶¹Tm produced by medium energy ⁷Li and ¹²C irradiation on an europium oxide target and the subsequent separation of bulk europium from the carrier-free products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tracer packet: A new conception for the production of tracers

The concept of tracer packet, which can be defined as a group of carrier-free radioactive isotopes of few elements, which have been produced together with an objective to study some particular physical, chemical or biological systems has been introduced in this paper. The tracer packet can be produced with low projectile energy (5-7 MeV/u) contrary to the multitracer technique. A thick cobalt foil has been irradiated consecutively with ¹⁶O, ⁷Li and ¹²C beams to produce the tracer packet containing carrier free radiotracers of Mn, Cu, Zn, Ga, Ge, As and Se which after removal of bulk cobalt can be used for further studies of essential micro nutrient elements.     

2,5-Dioxido-1,4-benzoquinonediimine (H2L2-), a hydrogen-bonding noninnocent bridging ligand related to aminated topaquinone: different oxidation state distributions in complexes [{(bpy)2Ru}2(mu-H2L)]n (n=0,+,2+,3+,4+) and [{(acac)2Ru}2(mu-H2L)]m (m=2-,-,0,+,2+)

The symmetrically dinuclear title compounds were isolated as diamagnetic [(bpy)2Ru(mu-H2L)Ru(bpy)2](ClO4)2 (1-(ClO4)2) and as paramagnetic [(acac)2Ru(mu-H2L)Ru(acac)2] (2) complexes (bpy=2,2'-bipyridine; acac- = acetylacetonate = 2,4-pentanedionato; H2L = 2,5-dioxido-1,4-benzoquinonediimine). The crystal structure of 22 H2O reveals an intricate hydrogen-bonding network: Two symmetry-related molecules 2 are closely connected through two NH(H2L2-)O(acac-) interactions, while the oxygen atoms of H2L2- of two such pairs are bridged by an (H2O)8 cluster at half-occupancy. The cluster consists of cyclic (H2O)6 arrangements with the remaining two exo-H2O molecules connecting two opposite sides of the cyclo-(H2O)6 cluster, and oxido oxygen atoms forming hydrogen bonds with the molecules of 2. Weak antiferromagnetic coupling of the two ruthenium(III) centers in 2 was established by using SQUID magnetometry and EPR spectroscopy. Geometry optimization by means of DFT calculations was carried out for 1(2+) and 2 in their singlet and triplet ground states, respectively. The nature of low-energy electronic transitions was explored by using time-dependent DFT methods. Five redox states were reversibly accessible for each of the complexes; all odd-electron intermediates exhibit comproportionation constants K(c)>10(8). UV-visible-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. In general, the complexes 1n+ prefer the ruthenium(II) configuration with electron transfer occurring largely at the bridging ligand (mu-H2Ln-), as evident from radical-type EPR spectra for 13+ and (+. Higher metal oxidation states (iii, iv) appear to be favored by the complexes 2m; intense long-wavelength absorption bands and RuIII-type EPR signals suggest mixed-valent dimetal configurations of the paramagnetic intermediates 2+ and 2-.     

Experimental Simulation on Separation of Alpha-Particle Induced Rhenium Isotopes from Bulk Tantalum

Trace level tantalum and rhenium, ¹⁸²Ta and ^186,188Re, have been separated with liquid anion exchanger, TOA from HNO₃ medium. The feasibility of the separation process has also been verified for the separation of trace level rhenium from bulk or macro quantity of tantalum. The developed radiochemical scheme will be useful for the separation of carrier-free rhenium radionuclides produced in -particle activated matrix target.     

The triruthenium complex [[(acac)2Ru(II)]3(L)] containing a conjugated diquinoxaline[2,3-a:2',3'-c]phenazine (L) bridge and acetylacetonate (acac) as ancillary ligands. Synthesis, spectroelectrochemical and EPR investigation

The compound [[(acac)2Ru]3(L)] (1) undergoes three well-separated one-electron oxidation and reduction processes. The EPR results indicate electron removal from the ruthenium(II) centres on oxidation and the occupation of a largely L-based molecular orbital on reduction. In spite of well-separated (DeltaE > or = 340 mV) oxidation no obvious intervalence charge transfer bands were detected in the Vis, NIR or IR regions, suggesting very weak electronic coupling between the metal centres in the mixed-valent intermediates 1+ and 1(2+). The separated (DeltaE > or = 540 mV) stepwise reduction produces weak near-infrared features associated with partially occupied pi* orbitals of L, the unusually high g anisotropy in the EPR spectrum of 1- is attributed to the occupation of a degenerate MO by the unpaired electron.     

Boolean methods in interpolation and approximation

Book Reviews

Boolean methods in interpolation and approximationF.-J. Delvos and W Schempp: Longman Scientific and Technical, Harlow, Essex, U.K., 1989, 168 pp., £17.50, ISBN 0-582-06263-2     

Adsorption of <Superscript>125</Superscript>Sb on alumina and titania surfaces

Adsorption of long-lived ¹²⁵Sb radioisotope (T _1/2 = 2.75 y) on alumina (Al₂O₃) and titania (TiO₂) has been studied at different pH. Both the oxides have good adsorption capability for the ¹²⁵Sb radioisotopes but the TiO₂ is much superior. Adsorption kinetics of ¹²⁵Sb radioisotopes on TiO₂ surface and desorption of ¹²⁵Sb radioisotopes from TiO₂ surface in acidic and alkaline media have also been studied. The ¹²⁵Sb-TiO₂ phase has been subjected to γ-irradiation and found to be radiation stable against antimony release.     

Valence-state alternatives in diastereoisomeric complexes [(acac)2Ru(mu-QL)Ru(acac)2]n (QL2- = 1,4-dioxido-9,10-anthraquinone,n = +2, +1, 0, -1, -2)

The title complexes were obtained in neutral form (n = 0) as rac (1) and meso isomers (2). 2 was crystallized for X-ray diffraction and its temperature-dependent magnetism studied. It contains two antiferromagnetically coupled ruthenium(III) ions, bridged by the quinizarine dianion QL(2-) (quinizarine = 1,4-dihydroxy-9,10-anthraquinone). The potential of both the ligand (QLo --> QL4-) and the metal complex fragment combination [(acac)2RuII]2 --> ([(acac)2RuIV]2)4+ to exist in five different redox states creates a large variety of combinations, which was assessed for the electrochemically reversibly accessible 2+, 1+, 0, 1-, 2- forms using cyclic voltammetry as well as EPR and UV-vis-NIR spectroelectrochemistry. The results for the two isomers are similar: Oxidation to 1+ or 2+ causes the emergence of a near-infrared band (1390 nm), without revealing an EPR response even at 4 K. Reduction to 1- or 2- produces an EPR signal, signifying metal-centered spin but no near-infrared absorption. Tentatively, we assume metal-based oxidation of [(acac)2RuIII(mu-QL2-)RuIII(acac)2] to a mixed-valent intermediate [(acac)2RuIII(mu-QL2-)RuIV(acac)2]+ and ligand-centered reduction to a radical complex [(acac)2RuIII(mu-QL.3-)RuIII(acac)2 (-) with antiferromagnetic three-spin interaction.