Materials Literature
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The objective of this study is to establish a comprehensive set of backscatter factors for mammography based on the exposure model proposed by the European Protocol on Dosimetry in Mammography. The Monte Carlo calculated backscatter factors (BSFs) presented in this study are for various exposure conditions encountered…
A recent rigorous analysis of the broad thermoluminescence (TL) peak of a Brown microcline has shown it to be due to an exponential distribution of traps. Incidentally, from the statistical point of view one expects the traps to follow a Gaussian distribution. In order to elucidate the origin of the exponential trap d…
The effect of impurity on the two-dimensional (2D) nucleation rate, J, was investigated by estimating the edge free energy, γ, on the (0001) face of a hydroxyapatite crystal in the presence of magnesium and zinc as impurities. It was found that edge free energies, γ, at 0.06 mM magnesium and 0.75 μM zinc concentration…
Appreciable oxygen permeability at elevated temperatures (650–850°C) allows the well-known high-temperature superconductor YBa2Cu3O6+δ to be used as an oxygen separation membrane. Permeation of air through a YBa2Cu3O6+δ disk 1.2 mm thick gave an O2 stream in which N2 was barely detectable by gas chromatography. This t…
Constant-pressure molecular dynamics simulations and a systematic analysis of the local atomic structures have been performed to study the structural evolution of aluminium on different cooling runs. The regular and defective icosahedral atomic configurations depend strongly on the cooling rate, which is responsible f…
Mn–O and Mn–Mn interatomic distances were determined in LaxCa1−xMnO3 films grown heteroepitaxially on single crystal SrTiO3 and LaAlO3 substrates by molecular beam epitaxy. Mn–O bond lengths were found to be fixed at ∼1.975 Å for both types of substrates, while the Mn–Mn distance was detected to be larger for films gr…
We report 27 Al and 29 Si Nuclear Magnetic Resonance (NMR) spectra, collected at magnetic fields of 14.1 and 18.8 Tesla on samples as small as 1 mg, for Al‐bearing MgSiO 3 perovskite synthesized at 26–28 GPa. For Al, we find a 1∶1 ratio of two types of sites: a symmetrical, octahedral site and a low symmetry, distorte…
The thermal oxidation of polypropylene was probed, in situ, by a novel technique that simultaneously monitors chemically induced light emission (chemiluminescence) and changes in FTIR emission spectra of an oxidizing sample. The results obtained from this technique demonstrated that the chemiluminescence intensity ( I…
Relaxation dynamics of electrons in gold nanocrystals with diameters of 3.0--17.5 nm embedded in ${\mathrm{SiO}}_{2},$ ${\mathrm{Al}}_{2}{\mathrm{O}}_{3},$ and ${\mathrm{TiO}}_{2}$ matrices have been investigated by means of femtosecond pump and probe spectroscopy. The experiments show that the energy relaxation rates…
Shell-core structures of Fe(C), Co(C) and Fe-Co(C) nanocapsules, prepared by an arc discharge process in a mixture of methane and helium, have been demonstrated by means of high-resolution transmission electron microscopy (HRTEM). These nanoscale magnetic cores are protected by graphite shells. It has been found that…
The mechanical stability of amorphous carbon (a-C) films deposited on ultrasmooth Si(100) substrates by radio-frequency sputtering under different energetic ion bombardment conditions was investigated in light of results obtained from aging and annealing experiments. The a-C films were annealed at 495 °C in the high-v…
The mechanism for the pressure-induced transformation of cristobalite to stishovite and post-stishovite phases has been obtained from constant pressure ab initio molecular dynamics simulations. The cristobalite to stishovite transformation is found to be a two step process where ${\mathrm{SiO}}_{4}$ tetrahedra first r…
A density-functional theory of the isotropic–nematic phase transition in both rigid and semiflexible hard-sphere chain fluids is described. The theory is based on an exact analytical evaluation of the excluded volume and second virial coefficient B2 for rigid chain molecules, which demonstrates that B2 in these cases…
We present the first results on (0001) ZnO/(0001) epi-GaN/(0001) α-Al 2 O 3 heterostructure fabrication combining metal-organic vapour phase epitaxy and low-pressure chemical vapour deposition methods. The surface morphologies of the films were studied, and x-ray and reflection high-energy electron diffraction measure…
Fully saturated hydrocarbon polymers often exhibit superior stability toward thermal, oxidative, and radiation-induced degradation. Recent improvements in catalyst technology allow for the convenient synthesis of the saturated hydrocarbon poly(cyclohexylethylene) (PCHE) from polystyrene (PS) by heterogeneous catalytic…
Fluorinated surfaces are sought for a number of technologies requiring low surface energy, low adhesion, chemical robustness, among other desired properties. Bulk fluorinated materials (e.g., polymers) can be used, but their relative expense and difficult processing problems preclude widespread application. Small mole…
The structures of PrAlO 3 have been studied from room temperature to 10 K, using a combination of high resolution neutron and synchrotron powder diffraction data. At room temperature, PrAlO 3 has a rhombohedral structure in space group R c which transforms to an orthorhombic structure in Imma on lowering the temperatu…
We report on ${}^{13}\mathrm{C}$ nuclear magnetic resonance from $10$ up to $350$ K on single wall carbon nanotubes. The magic angle spinning NMR spectrum shows one isotropic line at $126$ ppm and the static spectrum a powder pattern typical for a curved graphene sheet. The T dependence of the spin-lattice relaxation…
Nanocomposite (Pr,Dy)2Fe14B/α-Fe magnets with compositions Pr8−xDyxFe86B6 (x=0, 0.5, 1, 1.5, and 2) have been synthesized by melt spinning using low wheel speeds in the range from 18 to 21.7 m/s. It has been found that the coercivity is significantly increased by Dy substitution. An optimum coercivity of 6.6 kOe is ob…
High-speed experimentation techniques have been applied in the synthesis and testing of silsesquioxane-based titanium catalysts (see picture) for the epoxidation of alkenes. Different solvents and organotrichlorosilanes were employed in the optimization of the hydrolytic condensation of silanes to open silsesquioxane…