Materials Literature
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We study the slippage of a highly viscous polymer melt ( P monomers per chain) on a solid substrate grafted by a few smaller chains in the mushroom regime ( N monomers per chain, grafting density ν). The friction is provided by the sliding motion of the P chains of the “skin” (thickness R p = P 1/2 a ) which are entan…
The use of adjustable-speed drives requires transformers capable of withstanding high levels of harmonic currents under normal operating conditions. Experience has been that overheating problems are much more common with dry-type transformers than with liquid-filled transformers. Transformer insulation life is determi…
We report here a prototype material for the sustained catalytic decontamination of mustard analogues with the ultimate goal being the fabrication of self-decontaminating clothing. H 5 PV 2 Mo 10 O 40 ( 1 ) can be supported on carbon cloths as well as powders, with 1 /Ambersorb 572 being the best material (high catalyt…
We have examined the structural changes in the boron−oxygen network that result from chemical modification of glassy boron oxide by potassium oxide. By means of boron-11 dynamic angle spinning (DAS) NMR and Raman spectroscopies, we have identified changes in the structure resulting from conversion of three-coordinate…
Monovalent cations activate the pyridoxal phosphate-dependent reactions of tryptophan synthase and affect intersubunit communication in the alpha2beta2 complex. We report refined crystal structures of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium in the presence of K+ at 2.0 angstrom and of C…
We have investigated the structure of five disilicate glass compositions K 2 O·2SiO 2, (Na 0.25 K 0.75 ) 2 O·2SiO 2, (Na 0.50 K 0.50 ) 2 O·2SiO 2, (Na 0.75 K 0.25 ) 2 O·2SiO 2, and Na 2 O·2SiO 2 using 2D 17 O Dynamic Angle Spinning (DAS) Nuclear Magnetic Resonance (NMR). The nonbridging and bridging oxygen sites can b…
The synthesis, electrochemistry, spectroscopy, and structural characterization of two high-valent phenyl sigma-bonded cobalt corroles containing a central cobalt ion in formal +IV and +V oxidation states is presented. The characterized compounds are represented as phenyl sigma-bonded cobalt corroles, (OEC)Co(C(6)H(5))…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTAn Efficient Rhodium(I) Initiator for Stereospecific Living Polymerization of PhenylacetylenesYasuhisa Kishimoto, Tatsuya Miyatake, Takao Ikariya, and Ryoji NoyoriView Author Information ERATO Molecular Catalysis Project, Research D…
We use scaling arguments to determine the patterns that form when Y-shaped AB copolymers are grafted onto a flat surface. One “arm” of the Y is an A homopolymer, and the other arm is an incompatible B chain, and the short “stem” tethers the entire copolymer to the surface. We investigate the behavior of the brush form…
This study focuses on interfacial bonding between intergranular silicon carbide particles and an alumina matrix, to determine the creep inhibition mechanism of alumina/ silicon carbide nanocomposites. It is revealed that the silicon carbide/alumina interface possesses much stronger bonding than the alumina/alumina int…
An investigation of the surfaces of linear, segmented block copolymers of poly(dimethylsiloxane−urea−urethanes) by dynamic contact angle analysis is reported. The polymer films are immersed in water, the time-dependent advancing and receding contact angles are observed, and the contact angle hysteresis is reported. Th…
We have determined by forced Rayleigh scattering the diffusion coefficients D of several photochromic tracers with van der Waals radii between 0.38 and 8 nm (the largest ones being photolabeled polystyrene micronetworks) in 10 glass-forming liquids at temperatures between the glass temperature T g and ∼1.2 T g . The r…
A phenomenological theory for the cholesteric phase induced by a chiral solute in a nematic solvent is derived from (i) the continuum representation of twist deformation of the nematic solvent, and (ii) the surface anchoring energy approximation for the interactions between the solvent and a solute of given shape. Thi…
${\mathrm{KTaO}}_{3}$ was investigated using density functional methods. These local-density approximation calculations correctly show the absence of a ferroelectric instability in this compound. Phonon frequencies and bulk properties in good agreement with existing measurements are obtained. A highly anharmonic low-f…
The diameter containing a fraction of the current is used as the measure of the charged particle probe size. This has, particularly in the case of analytical microscopies, proven to be a more practical measure than those based on widths of the current density distribution. The diameter of current carrying beams of fin…
The structure of bovine liver cytochrome b(5), a soluble 93-residue proteolytic fragment of a 16 kDa membrane-bound hemoprotein, initially solved at 2.0 A resolution, has been refined at 1.5 A using data collected on a diffractometer. Refinement to 2.0 A resolution used the Hendrickson-Konnert procedure PROLSQ and was…
Structural, thermal, and optical studies on regioregular poly[3-oligo(oxyethylene)-4-methylthiophene] have revealed interesting thermochromic and ionochromic effects related to a planar/nonplanar transition of the conjugated backbone. This first-order-like conformational transition (formation of twistons) seems driven…
Photochemical and thermal surface modifications of diamond powders and (100), (110), and (111) oriented single crystals were achieved. Clean, hydrogen-terminated diamond was chlorinated by heating in Cl 2 (g) or by UV irradiation in Cl 2 (g). The surface chlorine titer was shown to correlate with the dangling bond den…
Transmission electron imaging and diffraction are used to probe the atomic-level structure of single-layer carbon nanotubes. The nanotubes bend, fold, kink, and radially deform. They have a tendency to form parallel bundles of tubes, and this bundling process has been observed in real time. In addition, the electron b…
Homogeneous precipitation from solution by hydrolysis of urea at elevated temperatures (T= 120 °C) yields novel ammonia-intercalated α-type hydroxide phases of the formula M(OH)x(NH3)0.4(H2O)y(NO3)2 –x where x= 2,y= 0.68 for M = Ni and x= 1.85, y= 0 for M = Co. These triple-layered hexagonal phases (a= 3.08 ± 0.01 Å,…