New luminescence measurement facilities in retrospective dosimetry

This paper gives a review of recent developments in luminescence measurement facilities on the Risø TL/OSL reader including radio-luminescence (RL), exo-electron and violet stimulation attachments, and a method for characterising and if necessary correcting for beta irradiation source non-uniformity.We first describe improvements to the existing RL option to allow near infra-red detection (NIR) during irradiation by the built-in ⁹⁰Sr/⁹⁰Y beta source. The RL optical signal is collected by a liquid light guide through an F34-901 interference filter and detection is based on a dedicated thermoelectrically cooled NIR sensitive PMT (detection window peak at 855 nm, FWHM 27 nm). Software and electronics have been modified to allow standard TL and OSL measurements in the same sequence as RL measurements. Together with a new bleaching source based on a high-power UV LED (395 nm; 700 mW/cm²), this facility has been used to measure natural doses in feldspar using the decaying NIR RL signal.Secondly, we present a method for mapping radiation field of the built-in ⁹⁰Sr/⁹⁰Y β-source and estimating grain-location specific dose-rates. This is important for the accuracy of single grain results, when radiation field is spatially non-uniform across the sample area. We document the effect of this correction method and further investigate on the effect of lifting the source to achieve a better dose-rate uniformity.Finally we summarise two recently-developed novel facilities to help investigate (i) the time scales involved in OSL processes (time-resolved exo-electron detection) and (ii) extending the age range (violet stimulated signals from deep quartz OSL traps).     

17O NMR and density functional theory study of the dynamics of the carboxylate groups in DOTA complexes of lanthanides in aqueous solution

The rotation of the carboxylate groups in DOTA (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) complexes of several lanthanide ions and Sc(3+) was investigated with density functional theory (DFT) calculations and with variable temperature (17)O NMR studies at 4.7-18.8 T. The data obtained show that the rotation is much slower than the other dynamic processes taking place in these complexes. The exchange between the bound and unbound carboxylate oxygen atoms for the largest Ln(3+) ions (La(3+)→Sm(3+)) follows a pathway via a transition state in which both oxygens of the carboxylate group are bound to the Ln(3+) ion, whereas for the smaller metal ions (Tm(3+), Lu(3+), Sc(3+)) the transition state has a fully decoordinated carboxylate group. The activation free energies show a steady increase from about 75 to 125-135 kJ·mol(-1) going from La(3+) to Lu(3+). This computed trend is consistent with the results of the (17)O NMR measurements. Fast exchange between bound and unbound carboxylate oxygen atoms was observed for the diamagnetic La-DOTA, whereas for Pr-, Sm-, Lu-, and Sc-DOTA the exchange was slow on the NMR time scale. The trends in the linewidths for the various metal ions as a function of the temperature agree with trends in the rates as predicted by the DFT calculations.     

Electron Detachment Dissociation of Underivatized Chloride-Adducted Oligosaccharides

Chloride anion attachment has previously been shown to aid determination of saccharide anomeric configuration and generation of linkage information in negative ion post-source decay MALDI tandem mass spectrometry. Here, we employ electron detachment dissociation (EDD) and collision activated dissociation (CAD) for the structural characterization of underivatized oligosaccharides bearing a chloride ion adduct. Both neutral and sialylated oligosaccharides are examined, including maltoheptaose, an asialo biantennary glycan (NA2), disialylacto-N-tetraose (DSLNT), and two LS tetrasaccharides (LSTa and LSTb). Gas-phase chloride-adducted species are generated by negative ion mode electrospray ionization. EDD and CAD spectra of chloride-adducted oligosaccharides are compared to the corresponding spectra for doubly deprotonated species not containing a chloride anion to assess the role of chloride adduction in the stimulation of alternative fragmentation pathways and altered charge locations allowing detection of additional product ions. In all cases, EDD of singly chloridated and singly deprotonated species resulted in an increase in observed cross-ring cleavages, which are essential to providing saccharide linkage information. Glycosidic cleavages also increased in EDD of chloride-adducted oligosaccharides to reveal complementary structural information compared to traditional (non-chloride-assisted) EDD and CAD. Results indicate that chloride adduction is of interest in alternative anion activation methods such as EDD for oligosaccharide structural characterization.     

A Synthetic Route Toward Tetrazoles: The Thermolysis of Geminal Diazides

A new synthetic route toward the tetrazole core is described, which is based on a general fragmentation pattern that was found in a range of compounds featuring geminal diazido units. Through a simple two-step procedure, the synthesis of structurally diverse target compounds containing a tetrazole, such as tetrazoloquinoxalinones, benzoylaryltetrazoles, tetrazolotriazinones, and tetrazoloazepinones, was easily accomplished, starting from broadly accessible substrates (i.e., oxindoles, diarylethanones, pyrazolones, and phenanthrols). The initial oxidative diazidation reaction with iodine and sodium azide under mild conditions is followed by the thermal fragmentation under microwave irradiation, leading to the tetrazole products. Noteworthy, an experimental solution is presented in which the potentially hazardous diazide intermediates are not isolated and the concentration of crude reaction mixtures containing diazides is not required to achieve the tetrazoles in good yields.     

Fluctuation Results for General Block Spin Ising Models

Journal of Statistical Physics - We study a block spin mean-field Ising model, i.e. a model of spins in which the vertices are divided into a finite number of blocks with each block having a fixed...     

The teaching of proof at the lower secondary level—a video study

Teaching mathematical proof is one of the most challenging topics for teachers. Several empirical studies revealed repeatedly different kinds of students’ problems in this area. The results give support that students’ abilities in proving are significantly influenced by their specific mathematics classrooms. In this paper we will present a method for evaluating proof instruction and some results of a video study that describe proving processes in mathematics classrooms at the lower secondary level from a mathematical perspective.     

A synthetic approach to 2,3,4-substituted pyridines useful as scaffolds for tripeptidomimetics

The synthesis of 2,3,4-substituted pyridine derivatives useful as scaffolds in the development of peptidomimetics is described. The use of a variety of electrophiles in a halogen-dance reaction to produce 3-alkyl-2-fluoro-4-iodo-pyridine derivatives as ‘functionalized scaffolds’ and the possibility to differentiate between the reactivities of the two halogen handles have been explored. Coupling of amino acid derivatives in the 4-position of the pyridine was found to proceed efficiently by conversion of iodo-pyridine to a Grignard derivative, which was allowed to react with a protected amino aldehyde. Substitution of fluorine in the 2-position of the pyridine was found to be facile with alkoxide nucleophiles, whereas amines were much less reactive.     

Square-free perfect graphs

We prove that square-free perfect graphs are bipartite graphs or line graphs of bipartite graphs or have a 2-join or a star cutset.     

3′-Keto-1-nitro-2-phenylspiro[cyclopropane-3,2′-quinuclidine]: Synthesis and reactions with nucleophiles

3′-Keto-1-nitro-2-phenylspiro[cyclopropane-3,2′-quinuclidine] was synthesized by a two-step procedure from 2-benzylidenequinuclidin-3-one. Ring-opening reactions of the cyclopropane ring using a variety of N-, O-, and C-nucleophiles (amines, methoxide, nitromethanate, cyanide anions, and lithium diphenylcopper) were studied, and a general mechanism for the transformations is proposed.