Excitations of metastable superfluid 4He at pressures up to 40 bars

Neutron scattering measurements of the fundamental excitations of liquid 4He confined in 44 A pore diameter gelsil glass at pressures up to 40 bars in the wave vector range 0.41.6 A(-1), especially the rotons, are observed up to complete solidification of all the liquid at a pressure of approximately 40 bars where the roton vanishes. At and above a pressure of 35.1 bars, Bragg peaks are observed, indicating coexistence of liquid and solid in the pores at pressures 35 less than or approximately equal P less than or approximately equal 40 bars.     

Channel formation and intermediate range order in sodium silicate melts and glasses

We use inelastic neutron scattering and molecular dynamics simulation to investigate the interplay between the structure and the fast sodium ion diffusion in various sodium silicates. With increasing temperature and decreasing density the structure factors exhibit an emerging prepeak around 0.9 A(-1). We show that this prepeak has its origin in the formation of sodium rich channels in the static structure. The channels serve as preferential ion conducting pathways in the relative immobile Si-O matrix. On cooling below the glass transition this intermediate range order is frozen in.     

Direct access to 3-substituted 1,4-oxathiepino[5,6-b]pyridine-5-one through one-pot substitution cyclization reaction of 2-mercapto-3-nicotinic acid with α-bromo ketones

A direct, one-pot synthesis route to [1,4]oxathiepino[5,6-b]pyridin-5-one derivatives was optimized by reacting different α-bromo ketones with 2-mercaptonicotinic acid. The advantages of this method include high efficiency, regioselective, and multistep conversion in a single-pot protocol. These types of pyridine annulated[1,4]oxathiepin-5-one derivatives are described here for the first time and seem to be interesting candidates for screening purpose. The presented protocol is suitable for using rare chemicals for synthesis of such derivatives.     

Mach number dependence of turbulent magnetic field amplification: solenoidal versus compressive flows

We study the growth rate and saturation level of the turbulent dynamo in magnetohydrodynamical simulations of turbulence, driven with solenoidal (divergence-free) or compressive (curl-free) forcing. For models with Mach numbers ranging from 0.02 to 20, we find significantly different magnetic field geometries, amplification rates, and saturation levels, decreasing strongly at the transition from subsonic to supersonic flows, due to the development of shocks. Both extreme types of turbulent forcing drive the dynamo, but solenoidal forcing is more efficient, because it produces more vorticity.     

Optical response of relativistic electrons in the polar BiTeI semiconductor

The transitions between the spin-split bands by spin-orbit interaction are relevant to many novel phenomena such as the resonant dynamical magnetoelectric effect and the spin Hall effect. We perform optical spectroscopy measurements combined with first-principles calculations to study these transitions in the recently discovered giant bulk Rashba spin-splitting system BiTeI. Several novel features are observed in the optical spectra of the material including a sharp edge singularity due to the reduced dimensionality of the joint density of states and a systematic doping dependence of the intraband transitions between the Rashba-split branches. These confirm the bulk nature of the Rashba-type splitting in BiTeI and manifest the relativistic nature of the electron dynamics in a solid.     

Polystyrene-nylon 6 graft copolymers

The synthesis of well-defined polystyrene-g-Nylon 6 copolymers is described. The materials were prepared for study of their rheological behaviour and to compare it with the recent findings for 2-phase block copolymer systems.The anionic polymerization of ?-caprolactam in the presence of polystyrene-ethyl acrylate copolymer was chosen as the preparative route. The reasons for the choice were (1) the fact that ester groups are known to be good initiators for the lactam polymerization and (2) that it has been previously established that uniform copolymers can be obtained from styrene and acrylate esters. The present paper describes initial results on preparation and characterization of graft copolymers.It was found that cross-linked materials resulted when the polystyrene copolymer contained more than 1 per cent by weight of ethyl acrylate. At lower ester concentrations, soluble and thermoplastic materials were obtained. The cross-linking reaction was tentatively identified as arising from the presence of the tertiary hydrogen alpha to the ester group. In agreement with this postulate, methacrylate copolymers produced soluble, thermoplastic grafts at concentrations as high as 5 weight per cent.The mechanical properties and the modulus-temperature behaviour of the 2-phase graft copolymer systems are also presented.     

Estimates for inverse coefficients of univalent functions from integral means

The purpose of this note is to point out that sharp coefficient bounds for the inverses of univalent functions from certain families are fairly direct corollaries of results on integral means. As an example, in §1 the method is applied to the familiar schlicht classS. The resulting coefficient estimates for the inverses of functions inS were first obtained by K. Löwner. Following this prototype, in §2 we obtain corresponding results, which are new, for a classS(p) of meromorphic schlicht functions in |z|<1.