Martin A. Crimp

Physical factors that trigger cholesterol crystallization leading to plaque rupture

BACKGROUND Triggers of plaque rupture have been elusive. Recently it was demonstrated that cholesterol expands when transforming from a liquid to a crystal state, disrupting overlying plaque. This study examined the effect of physical conditions including saturation, temperature, hydration, pH on cholesterol crystallization. METHODS Graduated cylinders were filled with varying amount of cholesterol powder (1, 2 and 3g) and dissolved in corn oil at 37 degrees C. Change in volume expansion (DeltaVE) and time to crystallization were measured for each saturation. The same was repeated while varying temperature (22-44 degrees C); hydration (1-3ml H(2)O); pH (5-8.4) and combination of saturation and temperature. Scanning electron microscopy was performed to evaluate crystal morphology and X-ray diffractometry to assess molecular structure of cholesterol. RESULTS Increasing saturation raised both DeltaVE (3g: 0.53+/-0.1ml vs. 1g: 0.14+/-0.02ml and 2g: 0.3+/-0.1ml; p<0.0001; p<0.01) and rate of change over 3min (3g: 60% vs. 1g: 14%). Crystal morphology was the same seen with crystals perforating human plaques. Temperature drop increased DeltaVE (44 degrees C: 0.05+/-0.01ml vs. 22 degrees C: 0.5+/-0.07ml; p<0.0001) and initiated earlier crystallization. Hydration resulted in greater DeltaVE (3ml: 0.7+/-0.07 vs. 0ml: 0.1+/-0.05; p<0.001) with corresponding changes in cholesterol molecular structure. Rising pH was associated with increased DeltaVE (1.3+/-0.03ml vs. 0.1+/-0.02ml; p<0.001). Combined increase in saturation and temperature had greater DeltaVE than expected from the sum of each alone. CONCLUSIONS Physical factors influenced both volume and rate of cholesterol crystallization. This suggests that local factors may play an important role in triggering plaque rupture. Combination of several factors may even be a more powerful trigger for acute cardiovascular events.

The locking of 〈110〉 edge dislocations on {001} in L12 ordered compounds: High-resolution electron-microscopy observations

Abstract In the 〈110〉{001} slip system in L12 ordered alloys, both screw and edge dislocations may become locked by dissociating into nonplanar structures. In this paper the structure of edge dislocations in the [110](001) primary cube system in Ni3Ga and Ni3(Al, Ti) single crystals has been observed with weak-beam and lattice-imaging microscopy. Near 600°C the edge superdislocations are locked in the double Lomer—Cottrell lock; near 700°C the edge dislocations are locked in nonplanar structures formed by climb dissociations. Both structures have been observed directly by high-resolution electron microscopy. The implications of the locking of the edge dislocations on the operation of 〈110〉{001} and 〈110〉{111} slip systems are discussed.

Nanopipes in Gallium Nitride Nanowires and Rods

Gallium nitride nanowires and rods synthesized by a catalyst-free vapor-solid growth method were analyzed with cross section high-resolution transmission electron microscopy. The cross section studies revealed hollow core screw dislocations, or nanopipes, in the nanowires and rods. The hollow cores were located at or near the center of the nanowires and rods, along the axis of a screw dislocation. The formation of the hollow cores is consistent with effect of screw dislocations with giant Burgers vector predicted by Frank.

Orientation determination and defect analysis in the near-cubic intermetallic γ-TiAl using SACP, ECCI, and EBSD

Abstract Crystal orientation and defect analysis for the commercially important γ-TiAl intermetallic compound is complicated by the near-cubic tetragonality of the L10 TiAl crystal structure. The selected area channeling pattern (SACP) method successfully reveals the γ-TiAl superlattice information, allowing accurate discrimination between the c and a directions that are commonly unattainable by the conventional electron backscattered diffraction (EBSD) method. Combination of this orientation information with crystal defect images obtained via the electron channeling contrast imaging (ECCI) method allows for rapid identification of active deformation systems in individual grains using a trace analysis scheme. Because SACP and ECCI are scanning electron microscopy (SEM) based techniques, analysis can be carried out on regularly shaped macroscopic samples, allowing association of the sample stress state and active defect systems. This has been shown in relation to defect analysis associated with strain transfer at grain boundaries. Additionally, the orientations determined via SACP have been used to correct EBSD data in order to reveal localized rotation due to retained strain within individual grains.

A factor to predict microcrack nucleation at γ-γ grain boundaries in TiAl

Abstract Grain boundary microcracking between γ-TiAl grains has been studied in a duplex TiAl alloy. Microcracking initiated at impinging deformation twins. A predictive factor has been developed which incorporates contributions from deformation twinning and deformation transfer, which correlates with grain boundary fracture.

The locking of 〈112〉/3 super-Shockley partials in L12 ordered γ′ single crystals deformed at 77K

Abstract Abstract The structure of dislocations in L12 ordered γ′ single crystals (Ni3Ga and Ni3Al) deformed at 77 K has been studied by high resolution transmission electron microscopes. 〈110〉 superdislocations have been observed to dissociate into 〈112〉/3 super-Shockley partials coupled by superlattice intrinsic stacking faults (SISF). The substructure is characterized predominantly by SISF ribbons and the SISF ribbons are enclosed by 〈112〉/3 super-Shockley partial loops which have been identified to be the trailing super-Shockley partial on expanding superdislocations. Most of the 〈112〉/3 super-Shockleys are lying along 30-degree 〈110〉 directions. The low mobility of 30-degree 〈112〉/3 partials has been interpreted as their having transformed into the non-planar structure of Giamei locks. The core structure of 30-degree 〈112〉/3 super-Shockleys has been observed with lattice imaging TEM and the results are consistent with the Giamei lock. The effect of the locking of 30-degree 〈112〉/3 super-Shockleys on ...

Electronic and Structural Characteristics of Zinc-Blende Wurtzite Biphasic Homostructure GaN Nanowires

We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.

Study of twinning in alpha-Ti by EBSD and Laue microdiffraction

Activity of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Analysis of slip activity and heterogeneous deformation in tension and tension-creep of Ti-5Al-2.5Sn (wt %) using in-situ SEM experiments

\{ 11\bar{2} 1\} \langle \bar{1} \bar{1} 26 \rangle