Mechanical properties of certain oriented crystalline polymers

The yield stress is a simple function of the deformation ratio in the direction of testing for specimens oriented by uniaxial or biaxial stretching or rolling. Unless the yield stress increases more rapidly than in proportion to the deformation ratio, there will be instability during tensile creep under high loads. The relative merit of various polymers differs for creep and stress relaxation. Fatigue and bend recovery are also related to the molecular structure.     

Incorporation of surface-modified UHMWPE powders and fibers in tough polyurethane composites

Ultrahigh molecular weight polyethylene (UHMWPE) powder (60 micron diameter) and chopped fiber (6.5 mm length) were surface treated with a blend of reactive gases (fluorine and oxygen.) These powders and fibers were then compounded into a thermoset polyurethane matrix. Surface-treated and control reinforcements are compared at a 10 vol.% loading level. Tensile testing indicates improved stress transfer with surface treatment. Stress transfer is also improved with fibers versus powders. Fracture toughness is characterized by measuring the essential work of fracture, w_e. Surface-treated fiber composites exhibit work of fracture values almost three times the unfilled polyurethane values. Abrasion resistance was also measured. Surface treatment was found to significantly lower wear rates of powder composites. Fiber composites had lower wear rates than powder composites, although surface treatment had little effect. An approximate inverse relationship was found between wear rate and essential work of fracture.     

Evaluation of chromic oxide,glycerol triether,and β-sitosterol as fecal flow markers in two species of nonhuman primates

Recovery of β-sitosterol, glycerol triether (1-hexadecyl-2,3,-didodecyl glycerol triether), and chromic oxide was studied in African green monkeys and stumptail macaques consuming diets containing 0.75 mg/Cal cholesterol and 38% of calories as safflower oil or butter. Following oral administration of these compounds, feces were collected daily for 9 days. For all animals, excretion of β-sitosterol and glycerol triether paralleled one another almost exactly. Except for two animlas, this was also true for chromic acid. Essentially 100% of the administered β-sitosterol and 90–95% of the glycerol triether were recovered; excretion of these markers virtually was complete by day 3. Ninety-two percent of the β-sitosterol was isolated in the nonsaponifiable lipid extract of the feces with less than 6% in the remaining aqueous phase. A maximum of 3.1% of the β-sitosterol and 1.8% of the glycerol triether were found in the blood. For stumptail macaques, the major excretory form of β-sitosterol was the 5β-derivative. African green monkeys were more variable; one animal excreted the bulk of the β-sitosterol unchanged while others excreted greater than 80% as the ring-saturated 5β-derivative. Animals consuming the safflower oil containing diet consistently excreted a greater percentage of the β-sitosterol unchanged, compared with those animals eating the butter containing diet. There was no evidence for steroid ring degradation in any of the animals used in this study.     

Super-resolution: a comprehensive survey

Super-resolution, the process of obtaining one or more high-resolution images from one or more low-resolution observations, has been a very attractive research topic over the last two decades. It has found practical applications in many real-world problems in different fields, from satellite and aerial imaging to medical image processing, to facial image analysis, text image analysis, sign and number plates reading, and biometrics recognition, to name a few. This has resulted in many research papers, each developing a new super-resolution algorithm for a specific purpose. The current comprehensive survey provides an overview of most of these published works by grouping them in a broad taxonomy. For each of the groups in the taxonomy, the basic concepts of the algorithms are first explained and then the paths through which each of these groups have evolved are given in detail, by mentioning the contributions of different authors to the basic concepts of each group. Furthermore, common issues in super-resolution algorithms, such as imaging models and registration algorithms, optimization of the cost functions employed, dealing with color information, improvement factors, assessment of super-resolution algorithms, and the most commonly employed databases are discussed.     

Structure formation during spinning of poly(p-phenylenebenzobisthiazole) fiber

The structure formed in the coagulation stage of the spinning process of poly(p-phenylene benzobisthiazole) fiber is studied by electron microscopy. An oriented network of microfibrils with typical fibril diameters of about 80-100Å is observed. We suggest that these microfibrils are the fundamental structural elements of the fiber. Thus, knowledge of the mechanism by which this initial structure is formed may allow for better control of final fiber properties. The relation of structure formation during coagulation to the phase diagram of a rigid polymer solution and to the kinetic mechanism of the phase transition is discussed.     

Online scheduling and placement of hardware tasks with multiple variants on dynamically reconfigurable field-programmable gate arrays

Hardware task scheduling and placement at runtime plays a crucial role in achieving better system performance by exploring dynamically reconfigurable Field-Programmable Gate Arrays (FPGAs). Although a number of online algorithms have been proposed in the literature, no strategy has been engaged in efficient usage of reconfigurable resources by orchestrating multiple hardware versions of tasks. By exploring this flexibility, on one hand, the algorithms can be potentially stronger in performance; however, on the other hand, they can suffer much more runtime overhead in selecting dynamically the best suitable variant on-the-fly based on its runtime conditions imposed by its runtime constraints. In this work, we propose a fast efficient online task scheduling and placement algorithm by incorporating multiple selectable hardware implementations for each hardware request; the selections reflect trade-offs between the required reconfigurable resources and the task runtime performance. Experimental studies conclusively reveal the superiority of the proposed algorithm in terms of not only scheduling and placement quality but also faster runtime decisions over rigid approaches.     

Synthesis of transparent fluorocarbon elastomers: Effect of crosslinker type and electron beam irradiation level on physical and mechanical behavior

Saturated fluorocarbon elastomers are very resistant to chemical reactions, including those of a crosslinking nature. In order to study proper methods of preparing these materials, Viton GLT was mixed with various levels of trimethylol propane trimethacrylate, TMPTM, and triallyl isocyanurate, Diak #7. After molding, the materials were subjected to electron beam irradiation. The glass transition, rubbery modulus, viscoelastic behavior, and equilibrium swelling were used to characterize the materials as a function of crosslinker and irradiation level. In general, the modulus and gel fraction increased with both crosslinker content and irradiation level. Mixtures of both crosslinking monomers produced an unexpected synergism, yielding higher tensile strength, and earlier onset of gelation.     

Bark beetle olfaction. III. Antennal olfactory responsiveness ofDendroctonus frontalis Zimmerman andD. brevicomis Le Conte (Coleoptera: Scolytidae) to aggregation pheromones and host tree terpene hydrocarbons

Electroantennograms from males and females ofDendroctonus frontalis andD. brevicomis in response to serial dilutions of the pheromonesexo brevicomin and frontalin and the host terpene hydrocarbons 3-carene and α-pinene show no significant differences in the threshold concentration for response to the compounds for either sex or species. The intensity of response was greater to higher concentrations of the pheromones (10 to >10⁴ μg) than the terpene hydrocarbons, suggesting the presence of more receptors on the antennae for pheromones than terpene hydrocarbons. Antennal olfactory responses to the compounds did not correlate to published data on behavioral responses by the beetles to the compounds in both field and laboratory studies. Adaptation experiments indicated that forD. frontalis, both frontalin andexo brevicomin share the same receptors on the antennae. The results indicated that the terpene hydrocarbons share some, but not all, of the same receptors.     

Effect of lecithin on jejunal absorption of micellar lipids in man and on their monomer activity in vitro

The effect of lecithin on jejunal absorption of fatty acids and octadecenoylglycerol was studied in healthy volunteers with a jejunal perfusion system which excluded pancreatic and biliary secretions from the test segment. Lecithin significantly reduced the absorption of oleic acid (P<0.05) and octadecenoylglycerol (P<0.01), while it had no effect on the absorption of ricinoleic acid. In vitro, lecithin reduced monomer activities of all three lipids; the changes were greater for oleic acid and octadecenoylglycerol than for ricinoleic acid (P<0.02). From these data it is concluded that lecithin reduces monomer activity of fatty acids in mixed micellar solutions and that it can thereby reduce the absorption rates of micellar lipids. Intact lecithin is not absorbed under these conditions. Maldigestion of lecithin in pancreatic insufficiency may, therefore, aggravate the steatorrhea observed in this condition.