Carbon doping of MgB2 by toluene and malic-acid-in-toluene

The decomposition of malic acid (C₄H₆O₅) in the presence of Mg and B was studied using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) which revealed that malic acid reacted with Mg but not B. Also, the addition of toluene (C₇H₈) to dissolve malic acid followed by subsequent drying resulted in no reaction with Mg, indicating that the malic acid had decomposed during the dissolution/drying stage. The total carbon contributed by toluene versus a toluene/5 wt.% malic acid mixture was measured using a LECO CS600 carbon analyzer. The toluene sample contained ～0.4 wt.% C while the toluene/malic acid mixture had ～1.5 wt.% C, demonstrating that the toluene contributed a significant amount of carbon to the final product. Resistivity measurements on powder-in-tube MgB₂ monofilamentary wires established that the toluene/malic acid doped sample had the highest B_c2. However, the toluene-only sample had the highest transport J_c over most of the magnetic field range (0–9 T), equaled only by that of toluene/malic-acid sample in fields above 9 T.     

NDDO quantum chemical calculations of molecules. A comparison between the modified version and the AM1 method

Advantages and disadvantages of two approaches to electronic structure calculations of molecules using the NDDO approximation are revealed.     

Ion bombardment-induced charge state effects CaO single crystals: F+ and F centers

The effects of heavy-and light-ion bombardment on defect formation in CaO have been investigated by UV-absorption spectroscopy and volume measurements. While 500 keV Ar or Ca implantation produces only F⁺ centers, 240 keVH produces both F⁺ and F centers at a F⁺ to F ratio of 5.6 to 1. On the other hand, when an argon implanted sample is subsequently bombarded with hydrogen, about 30% of the F⁺ centers anneal during 1 ×10¹⁴ H/cm²; at higher H fluences, new F⁺ and F centers are produced. An effect of energy partition between ionization and nuclear/atomic collision processes for the incident ions on the charge state of the resulting defect is thus clearly demonstrated.

The formation and annealing of these defects are accompanied by volume changes in the ion implanted surface layer which can be monitored in sltu with a cantilever beam technique. The measurements show volume expansion of the order of 1.5% following 10¹⁶ 500 keV Ar implantation; subsequent implantation of 10¹⁸ 240 keV H compacts the previously expanded material by 25 %. These results are in qualitative agreement with the optical data and seem to indicate that volume changes are associated with the formation and annealing of F⁺ centers.     

An Akaike information criterion for multiple event mixture cure models

We derive the proper form of the Akaike information criterion for variable selection for mixture cure models, which are often fit via the expectation–maximization algorithm. Separate covariate sets may be used in the mixture components. The selection criteria are applicable to survival models for right-censored data with multiple competing risks and allow for the presence of a non-susceptible group. The method is illustrated on credit loan data, with pre-payment and default as events and maturity as the non-susceptible case and is used in a simulation study.     

Nuclear Level Mixing: From a Curiosity to Applications in Nuclear Physics, Solid State Physics and Gamma Optics

The history of “Nuclear Level Mixing” is closely related to the research that Prof. Coussement performed during the last 25 years. In particular, the impact of this quantum mechanical concept on different research fields will be discussed. Without going in detail, we aim to give the reader an idea of how one single concept may lead to different discoveries. This revised version was published online in July 2006 with corrections to the Cover Date.     

Eine systematische Herleitung verbesserter Plattengleichungen

Übersicht Ausgehend von den Grundgleichungen der linearen dreidimensionalen Elastizitätstheorie werden durch Entwicklung der Verschiebungen und der Verzerrungen in Potenzreihen bezüglich der Dickenkoordinate Plattengleichungen aus dem Prinzip der virtuellen Verrückungen hergeleitet. Zur Vereinfachung dieser Gleichungen werden Hilfsgrößen eingeführt, die sich aus dem ebenen Vektorfeld der Verschiebungen U und V in der Plattenebene berechnen. Die Durchbiegung der Mittelfläche läßt sich in zwei Anteile aufspalten: einen, der sich aus der klassischen Plattengleichung bestimmen läßt und einen weiteren, der aus der Berücksichtigung der Normalspannung in Dickenrichtung entsteht. Vernachlässigt man diese letzte Teildurchbiegung und außerdem sehr rasche abklingende Randstörungen, so erhält man eine Näherungstheorie, welche die Erfüllung von drei Randbedingungen je Plattenrand erlaubt.

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A systematic development of corrected plate equations

Summary Starting from the basic equations of the linear three-dimensional elasticity theory, plate-equations are established by means of the principle of virtual displacements. The displacements and the strains are expanded into power series in terms of the thickness coordinate. To reduce the system of equations, auxiliary variables are introduced which are derived from the two-dimensional vector field of the displacements U and V in the middle surface. The deflection of the middle surface can be split into two parts. One can be determined with the classical plate equation and the other results from the consideration of normal-stress in thickness direction. Neglecting the last partial deflection and disregarding very quickly decaying boundary effects, an approximate theory is obtained. This theory allows to satisfy three boundary conditions on each boundary.

     

Fingerprinting postblast explosive residues by portable capillary electrophoresis with contactless conductivity detection

A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of postblast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual‐opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from postblast residues using an optimized separation electrolyte composed of 20 mM MES, 20 mM l ‐histidine, 30 μM CTAB and 2 mM 18‐crown‐6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive.