Despite the recognized importance of the in vivo fatigue properties of Nitinol, there is still limited understanding of how fatigue cracks propagate in this material. This study represents an initial approach to gain such understanding via a combination of fracture-mechanics testing and synchrotron x-ray (micro) diffraction, by providing insight into the role of transformational and local strain fields on the progression of fracture in a stent-like material structure. The results presented here compare the fracture-mechanics predicted transformation-zone size and shape with the actual zones measured by micro-diffraction. Tests were conducted with compact-tension specimens, laser-cut from Nitinol tube that was shape-set flat; this configuration mimics the microstructure and texture observed in Nitinol medical devices. Fatigue cracks were grown ex situ at near-threshold conditions (ΔK = 3 MPa√m) to a crack length to sample width ratio of a/W = 0.5. Specimens were then loaded in situ with a miniature straining rig to various stress intensities for multiple fatigue cycles. Thousands of local diffraction patterns (1 μm 2 spot area) spanning hundreds of micrometers surrounding the crack tips, were combined to produce contour maps of phase volume and local strain. The differences in monotonic and cyclic loading conditions can be deduced from these tests and can be used to differentiate in vivo single-event versus cumulative-damage fractures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The photogeneration of an active amine within a cationically curable polymer coating can be used to design a novel positive-tone resist material. The resist is based on a copolymer containing 4-hydroxystyrene as well as 4-acetoxymethylstyrene units; when heated in the presence of an acid, this copolymer crosslinks through an electrophilic aromatic substitution process. Therefore, a small amount of 2-nitrobenzyl toluene-p-sulphonate, that decomposes upon heating to produce toluene sulphonic acid, is added to the resist along with a thermally stable but photoactive carbamate that liberates an amine upon irradiation. Exposure of a film of the resist to 254 nm UV radiation results in the formation of a latent image consisting of amine molecules dispersed within the polymer film. The latent image is 'fixed' by heating; this liberates acid, which is neutralized where amine has been formed, but causes crosslinking of the polymer by a cationic process in those areas of the film where no amine has been produced. This resist, based on an image-reversal concept applicable to numerous cationically activated resists, can be developed in aqueous base and shows a good sensitivity of ca. 19 mJ cm–2.
: Fracture by the progressive growth of incipient flaws under cyclically varying loads, i.e., by fatigue, must now be considered as the principal cause of in-service failures of engineering structures and components, whether associated with mechanical sliding and friction (fretting fatigue), rolling contact, aggressive environments (corrosion fatigue), rolling contact, aggressive environments (corrosion fatigue), or elevated temperatures (creep-fatigue). Of particular importance are the early stages of fatigue damage, involving the initial extension of microcracks and their subsequent growth at very low velocities, as these processes tend to dominate overall lifetime. This has been reflected by trends in fatigue research over the past five years, which have focused largely on so-called 'small cracks,' of dimensions comparable with the scale of microstructure or local plasticity, and on crack growth in the near-threshold regime, i.e., at stress intensities approaching the fatigue threshold below which cracks are presumed dormant. In addition, associated mechanistic studies have highlighted the critical role of crack tip shielding in fatigue, which arises predominantly from crack closure and deflection, and this has proved to be important in modeling aspects of environmentally-assisted cracking and behavior under variable amplitude loads, and in rationalizing the classical stress/strain-life and defect-tolerant design approaches. The series of international conferences 'Fatigue '87' covered a wide range of diverse views of the fundamental and applied aspects of fatigue. This included questions of cyclic deformation, crack initiation and propagation, small cracks, crack closure, variable amplitude effects, and environmentally-influenced behavior.
In order to declare the accurate vitamin A effectiveness of foodstuffs and synthetic vitamin A preparations, the biological activity of the individual isomers has to be known. Total activity is expressed as all-trans vitamin A equivalents which are calculated by multiplication of analytical content of each isomer with the corresponding biopotency factor. The biological activity of four cis and three or four dicis isomers of vitamin A acetate and palmitate was determined by means of rat vaginal smear assays. The purity of the compounds, the content and isomerisation in stock solutions were checked by HPLC methods prior to their dilution and application to the experimental animals. Based on analytical contents the following activities were found for vitamin A acetate isomers: all-trans 1.00, 13-cis 0.76, 11-cis 0.31, 9-cis 0.19, 7-cis 0.18, 9,13-dicis 0.16, 11,13-dicis 0.18, 9,11-dicis approx. 0.03. The corresponding values for vitamin A palmitate were: all-trans 1.00, 13-cis 0.73, 11-cis 0.34, 9-cis 0.19, 7-cis 0.14, 9,13-dicis 0.21, 11,13-dicis 0.20, 9,11-dicis approx. 0.04, 7,11-dicis approx. 0.12. The vitamin A activity of the cis isomers ranged from about 0.75 for 13-cis to about 0.05 for 9,11-dicis. For the cis series, a biopotency relationship depending on the distance between the beta-ionone ring system and the cis configuration could be observed.
In this work, we propose a contour and region detector for video data that exploits motion cues and distinguishes occlusion boundaries from internal boundaries based on optical flow. This detector outperforms the state-of-the-art on the benchmark of Stein and Hebert, improving average precision from .58 to .72. Moreover, the optical flow on and near occlusion boundaries allows us to assign a depth ordering to the adjacent regions. To evaluate performance on this edge-based figure/ground labeling task, we introduce a new video dataset that we believe will support further research in the field by allowing quantitative comparison of computational models for occlusion boundary detection, depth ordering and segmentation in video sequences.
I briefly describe the Lick Observatory Supernova Search with the 0.76-m Katzman Automatic Imaging Telescope. I then present an overview of optical observations of Type II, IIb, Ib, and Ic supernovae (SNe), all of which are thought to arise from core collapse in massive progenitors that have previously experienced different amounts of mass loss. SNe IIn are distinguished by relatively narrow emission lines with little or no P-Cygni absorption component; they probably have unusually dense circumstellar gas with which the ejecta interact. Some SNe IIn, however, might actually be super-outbursts of luminous variable stars; rarely, they may even be SNe Ia in disguise. Plausible detections of the progenitors of a few SNe II have been made. Spectropolarimetry of core-collapse SNe reveals that asphericity increases toward the core.
