21,966 research outputs found
Dynamic stability and parametric resonance in cylindrical propellant tanks Final report
Dynamic stability and parametric resonance of longitudinally excited liquid propellant tank mode
Exhaust cloud rise and diffusion in the atmosphere
Analytical approach develops physical-mathematical model of rocket engine exhaust cloud rise, growth, and diffusion. Analytic derivations and resultant model apply to hot exhaust cloud study or industrial stack plumes, making work results applicable to air pollution. Model formulations apply to all exhaust cloud types and various atmospheric conditions
Perception of Lower Extremity Loads in Stroke Survivors
Objective: This study aimed to improve our understanding of static and dynamic lower extremity sensory perception and the impact of sensory impairments on the control of walking in stroke survivors.
Methods: Using a custom, real-time unloading system, we tested load perception at heel strike, mid stance and push off in 10 stroke survivors and compared their performance to 10 age-matched and 5 young adult control subjects. Dynamic load perception was based on a judgment of which leg was bearing more load, which was altered on a step by step basis. We also examined lower extremity static load perception, coordination, proprioception, balance, and gait symmetry.
Results: The stroke survivors performed significantly worse than the control subjects in dynamic load perception, coordination, proprioception, balance and gait symmetry. Gait symmetry correlated with static and dynamic load perception measures but not with age, proprioception, coordination, and balance.
Conclusions: Sensory deficits related to load detection in the impaired limb could result in an increased uncertainty of limb load and a gait strategy in which stroke survivors minimize loading of the impaired limb.
Significance: This new method of measuring lower extremity dynamic load perception provides a framework for understanding gait-related sensory impairments in stroke survivors
Rise and growth of space vehicle engine exhaust and associated diffusion models
Space vehicle plume rise and associated diffusion models at Cape Kennedy Launch Comple
Properties of Five Iowa Fine Sands
Today a major problem in the State of Iowa is the development of substitute materials which can be used in place of the rapidly diminishing supplies of readily available gravel and rock surfacing materials for roads and streets. The materials now available are not evenly distributed throughout the state, and the rate at which they are being used indicates that it will soon be necessary to turn to materials which are not now considered suitable. One such material is fine sand, commonly discarded by gravel plants as waste. Fine sand is readily available in almost every section of the state. It forms a portion of the flood plain deposits of many of the major rivers and streams and is found in a variety of occurrences related to the glacial drift sheets of the -state. The Iowa State Highway Commission has inaugurated a research program to find ways of utilizing fine sands as highway surfacing materials. The portion of this problem dealing with the determination of fundamental properties of the sands was assigned to the Iowa Engineering Experiment Station, Iowa State College. This report presents the results of the Station\u27s study of five samples of fine sand
Dispersion Relations for Thermally Excited Waves in Plasma Crystals
Thermally excited waves in a Plasma crystal were numerically simulated using
a Box_Tree code. The code is a Barnes_Hut tree code proven effective in
modeling systems composed of large numbers of particles. Interaction between
individual particles was assumed to conform to a Yukawa potential. Particle
charge, mass, density, Debye length and output data intervals are all
adjustable parameters in the code. Employing a Fourier transform on the output
data, dispersion relations for both longitudinal and transverse wave modes were
determined. These were compared with the dispersion relations obtained from
experiment as well as a theory based on a harmonic approximation to the
potential. They were found to agree over a range of 0.9<k<5, where k is the
shielding parameter, defined by the ratio between interparticle distance a and
dust Debye length lD. This is an improvement over experimental data as current
experiments can only verify the theory up to k = 1.5.Comment: 8 pages, Presented at COSPAR '0
Positivity of Quasilocal Mass
Motivated by the important work of Brown adn York on quasilocal energy, we
propose definitions of quasilocal energy and momentum surface energy of a
spacelike 2-surface with positive intrinsic curvature in a spacetime. We show
that the quasilocal energy of the boundary of a compact spacelike hypersurface
which satisfies the local energy condition is strictly positive unless the
spacetime is flat along the spacelike hypersurface.Comment: 4 pages; final published versio
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