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Wilber D.H.,Bowhead Science and Technology | Clarke D.G.,HDR | Gallo J.,U.S. Army | Alcoba C.J.,U.S. Army | And 2 more authors.
Estuaries and Coasts | Year: 2013

A long-term (2002-2011), spatially robust, ichthyoplankton sampling program conducted in the New York/New Jersey Harbor produced 3,033 epibenthic samples from which the relationships between winter flounder egg and larval distributions and environmental parameters were examined. Variations in water temperature, sediment characteristics, and tidal phase were all significantly associated with egg distributions. Inferences about spawning habitats were based on the presence of early-stage eggs (ES1 and ES2). In the Lower Bay (LB), these habitats were primarily non-channel and characterized by more sandy substrates, averaging 96.5 % sand, 2.3 % silt/clay, 0.2 % total organic carbon (TOC), and shallower water (average depths of 5.3 m) compared to LB non-channel stations without ES1 and ES2 eggs (50.2 % sand, 42.0 % silt/clay, 2.1 % TOC, and 7.9 m depths). Occurrences of all stages of eggs in channels were associated with strong tides and severe cold winter water temperatures. These conditions increase the probability of egg transport from shallow spawning sites through increased vertical mixing (strong tides) and delayed development that prolongs the risk of displacement (cold temperatures). Yolk-sac (YS) and Stage-2 larvae were smaller in 2010 when spring water temperatures were highest. Overall, YS larval size decreased with warmer winters (cumulative degree-days for the month preceding peak YS larval collections, r2 = 0.82, p < 0.05). In all years, YS larvae collected in LB were smaller and Stage-3 larvae collected in channels were larger and possibly older than those from non-channel habitat. Because estuarine winter flounder populations are highly localized, adverse effects experienced during egg and larval stages are likely to propagate resulting in detrimental consequences for the year class in the natal estuary. © 2013 Coastal and Estuarine Research Federation. Source

Kellogg F.,Bowhead Science and Technology | Zhou L.,University of Central Florida | Hofmeister C.,University of Central Florida | Giri A.,TKC Global | And 2 more authors.
Advances in Powder Metallurgy and Particulate Materials - Proceedings of the 2015 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2015 | Year: 2015

Previous research has shown that nanostructuring tungsten grains can significantly lower the ductile-tobrittle transition temperature of tungsten, improving low (near room) temperature ductility. Cryogenic attrition of coarse grained tungsten powders is an attractive technique for nanostructuring due to its capabilities for preventing oxidation, easing scalability, and possibly introducing grain-stabilizing nanoscale dispersoids. In this work, the feasibility of applying cryogenic attrition to the nanostructuring of coarse grain tungsten powders was explored through the examination of the morphology and grain size of the powder via transmission electron microscopy, scanning electron microscopy, and powder x-ray diffraction. Gas fusion chemical analysis was used to determine if there were any increases in the oxygen, hydrogen, or nitrogen concentration of the powder after cryogenic attrition. Source

Zhang T.G.,Bowhead Science and Technology | Satapathy S.S.,U.S. Army | Dagro A.M.,U.S. Army | McKee P.J.,Dynamic Science Inc.
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2013

Recent wars have heightened the need to better protect dismounted soldiers against emerging blast and ballistic threats. Traumatic Brain Injury (TBI) due to blast and ballistic loading has been a subject of many recent studies. In this paper, we report a numerical study to understand the effects of load transmitted through a combat helmet and pad system to the head and eventually to the brain during a blast event. The ALE module in LS-DYNA was used to model the interactions between fluid (air) and the structure (helmet/head assembly). The geometry model for the head was generated from the MRI scan of a human head. For computational simplicity, four major components of the head are modeled: skin, bone, cerebrospinal fluid (CSF) and brain. A spherical shape blast wave was generated by using a spherical shell air zone surrounding the helmet/head structure. A numerical evaluation of boundary conditions and numerical algorithm to capture the wave transmission was carried out first in a simpler geometry. The ConWep function was used to apply blast pressure to the 3D model. The blast pressure amplitude was found to reduce as it propagated through the foam pads, indicating the latter's utility in mitigating blast effects. It is also shown that the blast loads are only partially transmitted to the head. In the calculation where foam pads were not used, the pressure in the skin was found to be higher due to the underwash effect in the gap between the helmet and skin, which amplified the blast pressure. Copyright © 2013 by ASME. Source

Emerson R.,U.S. Army | Lawrence B.,Bowhead Science and Technology | Montgomery A.,Science and Mathematics Academy | Safriet S.,Air Force Research Lab
28th Annual Technical Conference of the American Society for Composites 2013, ASC 2013 | Year: 2013

In the present investigation novel needle-processed S2-glass laminates are fabricated and several key failure modes are characterized. Double cantilever beam testing shows that mode I fracture toughness improves up to 270% compared to non-needled baseline material. In-plane compressive strength of needled material improves by up to 475%. In plane tensile strength shows mixed results, improving by 6% for moderate volume fractions of through-thickness reinforcement (TTR) and decreasing by 6% at larger volume fractions. Double lap shear tests show that interlaminar shear strength improves as much as 17% for TTR inserted at ±45°; relative to the laminate plane. X-ray micro-computed tomography (micro-CT) is used to investigate the unique 3D microstructure resulting from the needling process for 90° TTR samples. The micro-CT reconstructions show that the dimensions of the disturbances of the inplane fabric are significantly smaller than those imparted by the conventional tufting or stitching processes at each penetration site. Micro-CT reveals that some penetration sites are aggregates of closely spaced neighbors, resulting from the lack of precise spatial control with the needling process used in the present research. At these aggregate locations the in-plane disturbances are roughly equal in size to those from tufting/stitching. Modifications to the automated processing equipment are shown and discussed. The modifications allow better spatial control at the penetration sites and the ability to insert TTR at ±45° relative to the laminate plane. Source

Sliozberg Y.R.,Bowhead Science and Technology | Sliozberg Y.R.,U.S. Army | Chantawansri T.L.,U.S. Army
Journal of Chemical Physics | Year: 2013

The structural and mechanical properties of imperfect entangled polymer networks with various fractions of elastically active chains are studied using a generic coarse-grained model. Network topology is analyzed at various degrees of cross-linking and correlated with the mechanical response under uniaxial deformation at various strain rates. We found excellent agreement between results obtained from the structural analysis and from fitting to stress relaxation data. The relaxation tensile modulus at various engineering strains was also calculated as a function of the fraction of active strands. Results indicate that the mechanical and viscoelastic properties of entangled polymer networks are susceptible to variation in the network structure, where defects can affect the mechanical response especially at low strain rates and the relaxation behavior at long times. © 2013 AIP Publishing LLC. Source

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