Laser spectroscopy of the 1s22s2p 3P2-3P1 transition in beryllium-like argon using the Oxford EBIT

A study of the 1s²2s2p ³P₂-³P₁ fine-structure transition in beryllium-like argon is planned on the Oxford electron beam ion trap (EBIT), using laser-induced resonance. This transition wavelength was measured previously as 594.373(4) nm, which is accessible using a dye laser. The ions are produced and excited in the EBIT and are confined during laser irradiation using the magnetic trapping mode. The ³P₂ level population is depleted by the laser and by subsequently monitoring the emitted fluorescence a laser resonance signal can be obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

New gravitational instantons and universal spin structures

An infinite class of new gravitational instantons for the axial anomaly is found. It consists entirely of algebraic spin- manifolds. In theories that allow manifolds without ordinary spin structure we find the presence of spinorial matter fields to require the existence of a “universal” gauged SU(2) or higher internal symmetry (e.g., SU(2) × SU(2) × G) and of an “internal-spin” -statistics connection. The possible relation of this to the gauge theory of weak and electromagnetic interactions is explored.     

Anomalous gamma-ray multiplicity distributions-evidence for pre-equilibrium neutron emission

Multiplicity distributions and 〈E_γ〉 have been measured for the ${}^{124}\text{Sn}\text{(}{}^{40}\text{Ar}\text{, x}\text{n}\text{)}{}^{\mathrm{164?x}}\text{Er}$ reaction at E(Ar) = 161, 182, 189, 209, and 236 MeV. The data at E(Ar) = 236 MeV indicate that pre-equilibrium neutrons are emitted. These data, together with other reactions leading to Er final systems, are discussed in terms of pre-equilibrium mechanisms.     

Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C₂H₆ and N₂, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C₃H₈ (3.5 × 10^?3), C₂H₄ (3.2 × 10^?4), CH₄ (3 × 10^?3), and n-C₄H₁₀ (trace). Quantum yields of H₂ of 4 × 10^?5 and 2 × 10^?5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively. The minor hydrocarbon products can be accounted for by reactions of CH₃ and C₂H₅ radicals following hydrogen abstraction from azomethane by CH₃. The H₂ product observed represents an upper limit for the H₂ elimination from vibrationally excited C₂H₆ formed by CH₃ combination in the system, corresponding to a rate of elimination ca. 5 × 10^?5 times the competing rate of dissociation to 2CH₃. Assuming a frequency factor of 10¹³ s^?1 for the H₂ elimination, a lower limit of about 90 kcal mol^?1 was estimated for the energy barrier.     

Cyclic seleninate esters as catalysts for the oxidation of sulfides to sulfoxides, epoxidation of alkenes, and conversion of enamines to α-hydroxyketones

Cyclic seleninate esters serve as catalysts for the rapid oxidation of sulfides to sulfoxides, alkenes to epoxides, and enamines to α-hydroxyketones. Optimal conditions were found that minimize the overoxidation of the product sulfoxides to sulfones and the hydrolysis of epoxides to diols. In some examples such as styrene derivatives, oxidative cleavage was observed instead of epoxidation. The enamine oxidations proceed via the initial formation of dimeric 2,5-diamino-1,4-dioxane species, which were hydrolyzed in situ to the final products. The structure of one such dimer was confirmed by X-ray crystallography.     

Application of Copper(I) Iodide/Diorganoyl Dichalcogenides to the Synthesis of 4‐Organochalcogen Isoquinolines by Regioselective C?N and C?Chalcogen Bond Formation

A copper‐catalyzed cyclization of (ortho‐alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4‐organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4‐position. The cyclization reaction was carried out by using CuI (20 %) as a catalyst with diorganoyl dichalcogenides (1.5 equiv) in the presence of DMF at 100 °C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho‐alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six‐membered heterocyclic ring exclusively through a 6‐endo‐dig cyclization process. The organochalcogen group present at the 4‐position of the isoquinoline ring was further subjected to a selective chalcogen–lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C? C bond formation.     

Spaces to discuss mathematics: communities of practice on an online discussion board

In theories of learning that adopt a situated stance to knowledge the notion of identity is vital; how learners position themselves in relation to, and are mutually positioned by, the situation within which they are learning will have a strong bearing on the learning outcomes. One of the challenges for learning mathematics in school is that learners position themselves, and are positioned, as pupils rather than as mathematicians. This paper focuses on discussion boards designed for secondary school mathematics students, and we use Wenger's (1998) model of communities of practice, building on earlier work by the authors (Back and Pratt 2007; Pratt and Kelly 2007) in which ‘idealised communities’ are constructed and used, to consider a case study of one participant who engages in developing his identity as a mathematician doing mathematics, as well his identity as a learner and a teacher of mathematics.