Interfacial energy of the superfluid 3He a-B phase interface in the zero-temperature limit

We have measured the surface energy of the interface between the A and B phases of superfluid 3He in the low temperature limit at zero pressure. Using a shaped magnetic field, we control the passage of the phase boundary through a small aperture. We obtain the interphase surface energy from the over- or undermagnetization required to force the interface through the aperture in both directions, yielding values of the surface tension and the interfacial contact angle. This is the first measurement of the interfacial energy in high magnetic fields and in the zero-temperature limit.     

Superconductivity in boron-doped diamond

Superconductivity of boron-doped diamond, reported recently at T(c)=4 K, is investigated exploiting its electronic and vibrational analogies to MgB2. The deformation potential of the hole states arising from the C-C bond-stretch mode is 60% larger than the corresponding quantity in MgB2 that drives its high T(c), leading to very large electron-phonon matrix elements. The calculated coupling strength lambda approximately 0.5 leads to T(c) in the 5-10 K range and makes phonon coupling the likely mechanism. Higher doping should increase T(c) somewhat, but the effects of three dimensionality primarily on the density of states keep doped diamond from having a T(c) closer to that of MgB2.     

A novel {FeI-FeII-FeII-FeI} iron thiolate carbonyl assembly which electrocatalyses hydrogen evolution

A novel tetra-iron thiolate carbonyl assembly is described in which two dithiolate tetracarbonyl di-iron centres with a 'butterfly' configuration of the {2Fe3S}-cores are fused by two bridging thiolates which form a central planar 2Fe2S unit and comprise the first example of a chain of four metal-metal bonded iron atoms supported by a bridging sulfur framework; the assembly electrocatalyses hydrogen evolution.     

Generation and detection of quantum turbulence in superfluid 3He-B

We describe the first direct observations of turbulence in superfluid 3He-B. The turbulence is generated by a vibrating-wire resonator driven at velocities exceeding the pair-breaking critical velocity. It is detected by the resulting decrease in the thermal damping on a neighboring "detector" vibrating-wire resonator. The superfluid flow field associated with the turbulence Andreev reflects thermal quasiparticle excitations, effectively screening the detector wire, resulting in a decrease in the thermal damping.     

Primary and secondary nucleation of the transition between the A and B phases of superfluid 3He

We have studied nucleation in superfluid 3He across the A-B phase transition driven by a magnetic field, in a controllable environment at very low temperatures. Both B-->A and A-->B secondary nucleation appear to be governed by the survival of pockets of the new phase trapped at surfaces. We find that, at fields near B(AB), primary A-->B nucleation cannot be triggered by ionizing or neutron irradiation even at very high intensities. In our cell primary A-->B nucleation can only be triggered externally by mild mechanical shock.     

Metabolism of trimethylarsine oxide

Trimethylarsine oxide [(CH₃)₃AsO] has been shown to be easily reducible by various biological species, including both aerobic and anaerobic micro-organisms, some skin organisms, soil bacteria, sludge and rumen fluid. The results suggest an enhanced mobility for arsenic owing to facile production of the volatile (CH₃)₃As species.     

Electronic structure of the ideal silicon vacancy by the muffin-tin green's function method

The muffin-tin Green's function method is applied to the ideal vacancy in silicon in the extended-charge single site approximation. The characteristics of the partially occupied gap state are found to be strongly dependent on the extent of the charge perturbation outside of the vacancy muffin-tin.     

Density of states of Nb and Mo using Slater-Koster interpolation

Slater-Koster parameters are given which have been fit to APW band calculations for Nb and Mo. The density of states at the Fermi surface of the 4d bcc alloys agrees well with a rigid band interpretation of the calculated density of states.     

The rotation-inversion spectra and vibration-rotation interaction in NH2D

An additional 86 lines of the NH₂D rotation-inversion spectrum were measured between 7.5 and 850 GHz. These data and the existing NH₂D and ND₂H data are fitted to a Hamiltonian in which the vibration-rotation interaction is included in the form of an offdiagonal inertial tensor term. For comparison with the symmetric ammonias an oblate basis and a Watson-type reduced “S” set of distortion constants are used. A theory for the interaction term is given which is in excellent agreement with experiment. Structural parameters are derived. The magnitude and relative sign of the two dipole moment components of NH₂D are determined and previously measured nitrogen hyperfine structure for both species is reexamined using improved rotational wavefunctions.     

The microwave spectrum,structure, and dipole moment of amino acetonitrile

The microwave spectra of three isotopic species of amino acetonitrile (NH₂CH₂CN, NHDCH₂CN, and ND₂CH₂CN) have been investigated to learn something about the structure and bonding in this and similar compounds. The only rotamer observed is the form in which both NH bonds are gauche to the CN group and the structure is quite rigid. From the available data only the bond angles are well determined. The amino NCC angle is 114.5(3)°, the HCH angle is 103(2)°, the HNC angle is 109.6(4)°, and the HNH angle is 107(1)°. The dipole moment components are μ_a = 2.577(7) D and μ_b = 0.5754(10) D; these agree quite well in magnitude and direction with the sum of the acetonitrile and methyl amine dipoles. The rigidity of the molecule and its preference for the form in which the amino protons are closest to the triple bond confirms a suggestion based on earlier studies on similar molecules that there is a strong hydrogen bonding interaction between the amino group and the nitrile group, although in this molecule dipole-dipole forces also probably play a significant role in determining the structure and its rigidity.