Phonons from neutron powder diffraction

The spherically averaged structure function \soq obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of \soq to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off-center phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure (dynamics from powder diffraction(DPD)) has been successfully implemented for two systems, a simple metal, fcc Ni, and an ionic crystal, CaF$_{2}$. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from powder neutron diffraction

The polarizability model for ferroelectricity in perovskite oxides

This article reviews the polarizability model and its applications to ferroelectric perovskite oxides. The motivation for the introduction of the model is discussed and nonlinear oxygen ion polarizability effects and their lattice dynamical implementation outlined. While a large part of this work is dedicated to results obtained within the self-consistent-phonon approximation (SPA), also nonlinear solutions of the model are handled which are of interest to the physics of relaxor ferroelectrics, domain wall motions, incommensurate phase transitions. The main emphasis is to compare the results of the model with experimental data and to predict novel phenomena.Comment: 55 pages, 35 figure

A comparison of the physical and chemical differences between cancellous and cortical bovine bone mineral at two ages

To assess possible differences between the mineral phases of cortical and cancellous bone, the structure and composition of isolated bovine mineral crystals from young (1–3 months) and old (4–5 years) postnatal bovine animals were analyzed by a variety of complementary techniques: chemical analyses, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and 31P solid-state magic angle spinning nuclear magnetic resonance spectroscopy (NMR). This combination of methods represents the most complete physicochemical characterization of cancellous and cortical bone mineral completed thus far. Spectra obtained from XRD, FTIR, and 31P NMR all confirmed that the mineral was calcium phosphate in the form of carbonated apatite; however, a crystal maturation process was evident between the young and old and between cancellous and cortical mineral crystals. Two-way analyses of variance showed larger increases of crystal size and Ca/P ratio for the cortical vs. cancellous bone of 1–3 month than the 4–5 year animals. The Ca/(P + CO3) remained nearly constant within a given bone type and in both bone types at 4–5 years. The carbonate and phosphate FTIR band ratios revealed a decrease of labile ions with age and in cortical, relative to cancellous, bone. Overall, the same aging or maturation trends were observed for young vs. old and cancellous vs. cortical. Based on the larger proportion of newly formed bone in cancellous bone relative to cortical bone, the major differences between the cancellous and cortical mineral crystals must be ascribed to differences in average age of the crystals

Mechanistic model of fuel selection in the muscle

Fuel selection in human muscle is key to explaining insulin resistance. in obesity and type 2 diabetes mellitus, there is an increased content of lipid within and around muscle fibers. Changes in muscle fuel partitioning of lipid, between oxidation and storage of fat, contribute to the accumulation of intramuscular triglycerides and to the pathogenesis of both obesity and type 2 diabetes mellitus. A mathematical model of the aggregated metabolism in skeletal muscle was developed and the effects of fuel selection for lean and obese individuals under fasting conditions, insulin-stimulated conditions, and oscillating insulin conditions were examined. Model results were complementary to prior observations that elevated lipid oxidation during insulin-stimulated conditions is correlated with insulin resistance. The model also adequately simulated metabolic inflexibility between fat and glucose oxidation in the obese individual. A novel sensitivity analysis indicated the strong interaction effects of parameters of glucose and lipid oxidation pathways on the variables of each pathway. (c) 2006 Elsevier Ltd. All rights reserved