9,263 research outputs found

    Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

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    The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems

    The implications of lung-regulated buoyancy control for dive depth and duration

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    Among air-breathing divers, control of buoyancy through lung volume regulation may be most highly developed in marine turtles. In short, the turtle lung may serve a dual role as both an oxygen store and in buoyancy control. A simple model is developed to show that, for turtles diving up to the maximum depth at which they can still use their lungs to attain neutral buoyancy, the total oxygen store will increase greatly with dive depth, and hence a corresponding increase in dive duration is predicted. Time–depth recorders attached to free-living green turtles (Chelonia mydas) at Ascension Island confirmed a marked increase in dive duration with depth, with the gradient of this relationship being >10 times that seen in diving birds and mammals. Consistent with the prediction that the lungs serve a dual role, we found that, when lead weights were added to some turtles to increase their specific gravity, the mean depth of dives decreased, but for dives to the same depth, weighted animals dived for longer. The depth distribution of green turtles seems to be generally constrained by the maximum depth at which they can still attain close to neutral buoyancy

    Observations of the 5‐day wave in the mesosphere and lower thermosphere

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94851/1/grl7954.pd

    Intercalibration of HRDI and WINDII wind measurements

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    Increasing Pregnancy Rate in Beef Cattle by Clitoral Massage During Artificial Insemination

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    Clitoral massage (stimulation) at the time of artificial insemination (AI) has been reported to increase pregnancy rate in lactating beef cows, but not to increase pregnancy rate in heifers. These reports have been limited to studies conducted at one location in the U.S. (Miles City, Montana), and the efficacy of clitoral massage on AI pregnancy rates of beef cattle at other geographic locations has not been reported. To our knowledge, there are no reports in the literature indicating a negative effect of clitoral stimulation on pregnancy rate of cows. The following experiment was conducted to test the effects of clitoral massage on pregnancy rate to artificial insemination in beef cattle and to define the effects of age, postpartum interval, and technician on pregnancy responses to clitoral massage performed at the time of artificial inseminatio
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