The thermodynamics of the A–B transition in superfluid He as a probe of the A-phase gap node geometry

We have used a magnetic field gradient to stabilise the phase boundary between the A- and B-phases of superfluid ³He inside a quasiparticle black body radiator down to 146 μK. The radiator technique enables us to measure very accurately the density of quasiparticle excitations and therefore the temperature of the B-phase inside the radiator. As we ramp the field through the transition we can observe the cooling (warming) effect when the volume of A-phase is increased (decreased). From these measurements we deduce the temperature dependence of the latent heat, which provides the lowest temperature verification yet of the existence of nodes in the A-phase order parameter.     

Prediction of high T(c) superconductivity in hole-doped LiBC

The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs B2). We show that hole doping of LiBC results in Fermi surfaces of B-C p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at T(c) approximately equal to 40 K in MgB2. Comparison of Li(0.5)BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2.     

Bridging Engineering and Science Teaching: A Collaborative Effort to Design Instruction for College Students

Reformers seeking to increase student understanding and interest are looking to collaborative partnerships to support improved science, technology, engineering, and mathematics (STEM) teaching. At the college level, partnerships across colleges are encouraged by reformers in order to provide all students with strong content understanding, model recommended practices for future teachers, and increase participation by underrepresented groups in STEM careers. Collaborative curriculum development, however, is not a trivial undertaking and success is not guaranteed. A better understanding of how partners with different backgrounds interact and what types of instructional changes can be expected from initial attempts will facilitate this potentially powerful approach to instructional change. In this project, 2 engineers and 2 science educators worked jointly to develop a design‐based core engineering course to meet the needs and interests of future engineers and science educators. Interaction among planners and development progress were documented by written meeting records and reflections, emails, and records of planning stages and products. Analysis characterized interactions between engineers and educators and the resulting instructional changes. In spite of a strong interest in partners' topics and mutual goals, specialized language and professional cultural differences presented obstacles to understanding and development progress. Also described are the types of instructional changes reasonable to expect in initial development efforts.     

Autoradiography using storage phosphor technology

We describe the application of photostimulable storage phosphor imaging plates to autoradiography of samples labeled with 32P, 14C and 35S. Imaging plates can detect a 32P-labeled sample at an exposure level of 1 disintegration/mm2, and 14C and 35S at 25 disintegrations/mm2. Compared to X-ray film, imaging plates offer increased sensitivity of 15- to 250-fold for 32P and 20- to 100-fold for 14C and 35S. Resolution is in the 0.3 mm range and is therefore suitable for any gel or blot application.     

Electron transfer at a dithiolate-bridged diiron assembly: electrocatalytic hydrogen evolution

Electrochemical reduction of Fe(2)(mu-pdt)(CO)(6) 1 (pdt = propane-1,3-dithiolate) leads initially to a short-lived species, 1-, then subsequently to two-electron reduced products, including a CO-bridged diiron compound, 1B. The assignment of the redox level of 1- is based on EPR and UV-vis spectra together with the observation that a CO-saturated solution of 1- decays to give 1 and 1B. Hydride reduction of 1 also results in formation of 1B via a relatively long-lived formyl species, 1(formyl). Despite its involvement in hydride transfer reactions, 1B is formulated as [Fe(2)(mu-S(CH(2))(3)SH)(mu-CO)(CO)(6)](-) based on a range of spectroscopic measurements together with the Fe-Fe separation of 2.527 A (EXAFS). Electrocatalytic proton reduction in the presence of 1 in moderately strong acids has been examined by electrochemical and spectroelectrochemical techniques. The acid concentration dependence of the voltammetry is modeled by a mechanism with two electron/proton additions leading to 1H(2), where dissociation of dihydrogen leads to recovery of 1. Further reduction processes are evident at higher acid concentrations. Whereas free CO improves the reversibility of the electrochemistry of 1, CO inhibits electrocatalytic proton reduction, and this occurs through side reactions involving a dimeric species formed from 1-.     

First-order isostructural Mott transition in highly compressed MnO

We present evidence for an isostructural, first-order Mott transition in MnO at 105+/-5 GPa, based on high-resolution x-ray emission spectroscopy and angle-resolved x-ray diffraction data. The pressure-induced structural and spectral changes provide a coherent picture of MnO phase transitions from paramagnetic B1 to antiferromagnetic distorted B1 at 30 GPa, to paramagnetic B8 at 90 GPa, and to diamagnetic B8 at 105+/-5 GPa. The last is the Mott transition, accompanied by a significant loss of magnetic moment, an approximately 6.6% volume collapse and the insulator-metal transition as demonstrated by recent resistance measurements.     

Quantum dot-labelled polymer beads by suspension polymerisation

CdSe quantum dots with polymerisable ligands have been incorporated into polystyrene beads, via a suspension polymerisation reaction, as a first step towards the optical encoding of solid supports for application in solid phase organic chemistry.     

Optical properties of Nb3Sn: A probe of the electronic density of states

An expression for the conductivity of an impure metal is derived in a simple manner in terms of a frequency dependent relaxation time τ. This method involves perturbation theory and an (ωτ)^?1 expansion but is shown to agree with a rigorous treatment. The infrared absorptivity of the A-15 material Nb₃Sn is calculated and it is found that optical properties will give direct information about the electronic density of states.