Materials Literature
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First-principles and tight-binding electronic-structure calculations of hypothetical tubule forms of hexagonal ${\mathrm{BC}}_{3}$ have been performed. According to the total-energy and force calculations, stable atomic geometries of the ${\mathrm{BC}}_{3}$ tubules can be obtained by rolling hexagonal ${\mathrm{BC}}_{…
For Part I see ibid., vol.27, pp.852-60 (1994). A theoretical treatment based on a partly interactive trap system (PITS) described in Part I is applied to peak 5 of LiF:Mg,Ti. The model assumes two types of thermoluminescence traps for the given glow peak: (i) those which produce a linear response with dose and (ii) t…
Fast-anion-conducting glasses in the system xPbF 2 :(1-x)B 2 O 3 have been synthesized and analysed by thermal, electrical and spectroscopic techniques. The ionic conductivity ( sigma ) of these glasses is measured as a function of temperature and chemical composition by the complex impedance method and the results in…
The work consists in a taxonomic survey and classification of genera of blue green algae from soil and paving, which were found in eight samplis and conducted in five stations in the Campus or Universidade Federal de Santa Maria. Twenty two genera were obtained and distributed in five families and three orders.
The quantitative analysis of the properties of domain walls in Hg 2 Br 2 and KSCN is performed using the Landau-Ginzburg phenomenological description. The domain walls in KSCN are thin and possess high internal stresses in comparison with Hg 2 Br 2 . The interactions between domain walls have opposite characters in th…
The variance of the pair correlation function, the triplet correlation function, g (3) (r,s,t), and the three-body contribution to the configurational entropy, S 3 , were studied as possible tools for distinguishing between three different models of amorphous silicon (a-Si) with (nearly) identical pair correlation fun…
We have combined a technique for the lift-off of thin diamond films from a bulk diamond with a technique for engraving diamond with a focused excimer laser to produce free-standing single-crystal diamond microstructures. One microcomponent that has been produced is a 12 tooth gear ∼400 μm in diameter and ∼13 μm thick.…
Nanocrystalline Co0.5Fe2.5O4 has been prepared by mechanical alloying and subsequent vacuum annealing. Significant increase of coercivity was observed after a postannealing at low temperatures in air. Magnetic annealing resulted in anisotropic sample with a coercivity of 2.8 kOe and a remanence of 81% of the saturatio…
It is demonstrated that controlled high-strain-rate plastic deformation of heterogeneous reactive porous materials (Nb+Si, Mo+Si+MoSi2) produces shear localization. Within the shear bands, having thicknesses 5–20 μm, the overall strains (γ≤100) and strain rates (γ̇≤107 s−1) result in changes in particle morphology, me…
We apply density-functional theory to study the expanded-FCC-to-condensed-FCC transition of a system of hard, spherical particles with a short-ranged attractive interaction, predicted recently by the simulations of Bolhuis and Frenkel (1994). Our approach is based on a non-perturbative treatment of the repulsive hard-…
Thin films of microphase separated symmetric diblock copolymers exhibit terraces. Atomic force microscopy is used to measure the free surface profile and transmission electron microscopy is used to elucidate the morphology within the film. Previous work has found the terraces to be composed of homeotropically aligned…
Abstract The rheological properties of the blend components are an important parameter in the formation of a blend morphology. The effect of viscosity ratio on the morphology of polyamide 66/polypropylene blends was studied, with primary attention to the phase‐inversion behavior and the average particle size of the di…
Abstract Dimroth and Reichardt polarity parameters E T (30) have been used, in a new approach, to quantitatively describe the swelling features due to polymer liquid interactions in binary and ternary systems. With the help of a polyurethaneimide (PUI) synthesized from polytetramethyleneglycol 650, sorption of pure li…
Abstract The morphology and the mechanical properties of polycarbonate (PC) blends with different acrylonitrile–butadiene–styrene (ABS) materials were investigated. PC/ABS blends based on a mass‐made ABS with 16% rubber and large (0.5–1μm) rubber particles are compared to blends based on an emulsion‐made ABS with 50%…
We present a theory of semiflexible polymers in inhomogeneous environments, which we use to analyze a symmetric interface between two immiscible, semiflexible polymers. Our theory reduces in the limit of small chain rigidity to the existing self-consistent-field theory of flexible polymers, but yields qualitatively di…
The size dependent electronic absorption spectra of CdSe nanocrystals have been measured in a diamond anvil cell. Under pressure, these nanocrystals are reversibly converted from a direct gap wurtzite structure to a rock salt structure which has an indirect gap in the bulk. It is thus possible to compare the influence…
Abstract Microbeads possessing amine functionality at the surface have been prepared by two methods: In the first method, poly(4‐vinylpridine/styrene) P(4VP/S) copolymer microbeads containing 13–69 mol % 4‐vinylpridine (4VP) were synthesized from the monomers. In the second method, animated polystyrene (PS) particles…
Abstract The reaction of poly(ethylene terephthalate) (PET) melts with ethylene glycol was examined in a pressure reactor at temperatures above 245°C. The reaction rate was found to depend on temperature and on the concentrations of liquid ethylene glycol and of ethylene diester groups in the polymer. A kinetic model…
Using density-functional theory we investigate several properties of Al(111), Al(100), Al(110), and stepped Al(111) surfaces. We report results of formation energies of surfaces, steps, adatoms, and vacancies. For the adsorption and diffusion of Al on flat regions of Al(111) surfaces we find the hcp site energetically…
Abstract The mechanical properties of composites of granular starch and low density polyethylene (PE) have been studied as functions of starch volume fraction ϕ, granule size, and presence of compatibilizer. Property–volume fraction relationships were interpreted using various theories of composite properties. The dep…