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  • 1
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    High strain rate metalworking with vaporizing foil actuator: Control of flyer velocity by varying input energy and foil thickness (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-07-02
    Description: Electrically driven rapid vaporization of thin metallic foils can generate a high pressure which can be used to launch flyers at high velocities. Recently, vaporizing foil actuators have been applied toward a variety of impulse-based metal working operations. In order to exercise control over this useful tool, it is imperative that an understanding of the effect of characteristics of the foil actuator on its ability for mechanical impulse generation is developed. Here, foil actuators made out of 0.0508 mm, 0.0762 mm, and 0.127 mm thick AA1145 were used for launching AA2024-T3 sheets of thickness 0.508 mm toward a photonic Doppler velocimeter probe. Launch velocities ranging between 300 m/s and 1100 m/s were observed. In situ measurement of velocity, current, and voltage assisted in understanding the effect of burst current density and deposited electrical energy on average pressure and velocity with foil actuators of various thicknesses. For the pulse generator, geometry, and flyer used here, the 0.0762 mm thick foil was found to be optimal for launching flyers to high velocities over short distances. Experimenting with annealed foil actuators resulted in no change in the temporal evolution of flyer velocity as compared to foil actuators of full hard temper. A physics-based analytical model was developed and found to have reasonable agreement with experiment.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Single-nutrient microbial competition: qualitative agreement between experimental and theoretically forecast outcomes (1980)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1980-03-28
    Description: When microbial strains compete for the same limiting nutrient in continuous culture, resource-based competition theory predicts that only one strain will survive and all others will die out. The surviving strain expected from theory will be the one with the smallest subsistence or "break-even" concentration of the limiting resource, a concentration defined by the J parameter. This prediction has been confirmed in the case of auxotrophic bacterial strains competing for limiting tryptophan. Because the value of J can be measured on the strains grown alone, the theory can predict the qualitative outcomes of mixed-growth competition in advance of actual competition.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hansen, S R -- Hubbell, S P -- New York, N.Y. -- Science. 1980 Mar 28;207(4438):1491-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/6767274" target="_blank"〉PubMed〈/a〉
    Keywords: Bacteria/*growth & development ; Culture Media ; Drug Resistance, Microbial ; Escherichia coli/growth & development ; Kinetics ; Models, Theoretical ; Nalidixic Acid/pharmacology ; Nutritional Physiological Phenomena ; Pseudomonas aeruginosa/growth & development ; Tryptophan/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    High strain rate metalworking with vaporizing foil actuator: Control of flyer velocity by varying input energy and foil thickness (2014)
    American Institute of Physics
    Details
    Publication Date: 2014-07-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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  • 4
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    Effect of asphericity in caustic mass estimates of galaxy clusters (2015)
    Oxford University Press
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    Publication Date: 2015-02-16
    Description: The caustic technique for measuring mass profiles of galaxy clusters relies on the assumption of spherical symmetry. When applied to aspherical galaxy clusters, the method yields mass estimates affected by the cluster orientation. Here, we employ mock redshift catalogues generated from cosmological simulations to study the effect of clusters intrinsic shape and surrounding filamentary structures on the caustic mass estimates. To this end, we develop a new method for removing perturbations from large-scale structures, modelled as the two-halo term, in a caustic analysis of stacked cluster data. We find that the cluster masses inferred from kinematical data of 10 14 M clusters observed along the major axis are larger than masses from those observed along the minor axis by a factor of 1.7 within the virial radius, increasing to 1.8 within three virial radii. This discrepancy increases by 20 per cent for the most massive clusters. In addition, a smaller but still significant mass discrepancy arises when filamentary structures are present near a galaxy cluster. We find that the mean cluster mass from random sight lines is unbiased at all radii and their scatter ranges from 0.14 to 0.17 within one and three virial radii, with a 40 per cent increase for the most massive clusters. We provide tables which estimate the caustic mass bias given observational constraints on the cluster orientation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Dynamical signatures of infall around galaxy clusters: a generalized Jeans equation (2013)
    Oxford University Press
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    Publication Date: 2013-11-17
    Description: We study the internal kinematics of galaxy clusters in the region beyond the sphere of virialization. Galaxies around a virialized cluster are infalling towards the cluster centre with a non-zero mean radial velocity. We develop a new formalism for describing the dynamical state of clusters, by generalizing the standard Jeans formalism with the inclusion of the peculiar infall motions of galaxies and the Hubble expansion as well as the contributions due to background cosmology. Using empirical fits to the radial profiles of density, mean radial velocity and velocity anisotropy of both a stacked cluster-mass halo and two isolated haloes of a cosmological dark matter only simulation, we verify that our generalized Jeans equation correctly predicts the radial velocity dispersion out to 4 virial radii. We find that the radial velocity dispersion inferred from the standard Jeans equation is accurate up to 2 virial radii, but overestimated by 20 per cent for the stacked halo and by 40 per cent for the isolated haloes, in the range 2–3 virial radii. Our model depends on the logarithmic growth rate of the virial radius (function of halo mass or concentration), which we estimate in seven different ways, and on the departure from self-similarity of the evolution of the peculiar velocity profile in virial units.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Seismic array constraints on reach-scale bedload transport (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-03-08
    Description: Measurements and mechanical models of heterogeneous bedload transport in rivers remain basic challenges for studies of landscape evolution and watershed management. A 700 m reach of the Trinity River (northern California, USA), a large gravel-bed river, was instrumented with an array of 76 seismographs during a dam-controlled flood and gravel augmentation to investigate the potential for out-of-stream monitoring. The temporal response to gravel augmentation during constant discharge provides strong evidence of seismic sensitivity to bedload transport and aids in identification of the seismic frequencies most sensitive to bedload in the study area. Following gravel augmentations, the seismic array reveals a period of enhanced transport that spans most or all of the reach for ~7–10 h. Neither the duration nor the downstream extent of enhanced transport would have been constrained without the seismic array. Sensitivity to along-stream transport variations is further demonstrated by seismic amplitudes that decrease between the upper and lower halves of the reach consistent with decreased bedload flux constrained by time-lapse bathymetry. Insight into the magnitude of impact energy that reaches the bed is also gained from the seismic array. Observed peak seismic power is ~1%–5% of that predicted by a model of saltation over exposed bedrock. Our results suggest that dissipation of impact energy due to cover effects needs to be considered to seismically constrain bedload transport rates, and that noninvasive constraints from seismology can be used to test and refine mechanical models of bedload transport.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    Variable thermal loading and flexural uplift along the Transantarctic Mountains, Antarctica (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-04-12
    Description: The high elevations of the Transantarctic Mountains (TAMs) have been suggested to be flexural in origin, but to date, the thermal contribution to uplift has yet to be quantified. Here, we present new P- and S-wave tomography images of the upper-mantle seismic structure beneath the central to northern TAMs, which reveal two, focused low-velocity anomalies beneath Ross Island and Terra Nova Bay that laterally extend beneath the TAMs front and that are connected by a low-velocity region constrained offshore within the Victoria Land Basin. The focused low velocities are interpreted as shallow regions of partial melt, connected by a broad region of slow (warm) upper mantle associated with Cenozoic extension along the Terror Rift. Thermal loading constraints based on our tomographic results are used to update flexural uplift models for the TAMs. Our findings confirm that thermal buoyancy is a principal component leading to the uplift of the TAMs but suggest that the thermal loading is variable along the TAMs front.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Structural dynamics of the competing forces of light and matter (2005)
    International Union of Crystallography
    Details
    Publication Date: 2005-08-23
    Print ISSN: 0108-7673
    Electronic ISSN: 2053-2733
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 9
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    Structural optimization using synthetic functions (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An efficient method for solving the structural optimization problem of defining member properties and responses in terms of design variables and calculated direct responses is proposed. The present approach provides the user with a simple means of interfacing design analysis models, as well as imposing constraints on functions which are not otherwise directly available. Results are presented for the examples of a three-bar truss, a 25-bar truss, the matching of calculated responses to measured responses, and the design of a rectangular beam.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 89-1222 , AIAA, ASME, ASCE, AHS, and ASC, Structures, Structural Dynamics and Materials Conference; Apr 03, 1989 - Apr 05, 1989; Mobile, AL; United States
    Format: text
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