28,379 research outputs found
The impulsive motion of a liquid resulting from a particle collision
When two particles collide in a liquid, the impulsive acceleration due to the rebound produces a pressure pulse that is transmitted through the fluid. Detailed measurements
were made of the pressure pulse and the motion of the particles by generating controlled collisions with an immersed dual pendulum. The experiments were performed for a range of impact velocities, angles of incidence, and distances between the wall and the pairs of particles. The radiated fluid pressure was measured using a high-frequency-response pressure transducer, and the motion of the particles was recorded using a high-speed digital camera. The magnitude of the impulse pressure was found to scale with the particle velocity, the particle diameter and the density of the fluid. Additionally, a model is proposed to predict the impulse field in the fluid based on the impulse pressure theory. The model agrees well with the experimental measurements
The Politics of Hydroelectric Power in Alaska: Rampart and Devil Canyon -- A Case Study
Originally published January 1978, revised October 1978. OWRT Agreement No. 14-34-0001-7003 Project No. A-060-ALAS. Completion Report.Hydroelectric power in Alaska has had a curious history--and an
instructive one. This study focuses on three separate projects:
Eklutna, Rampart, and Devil Canyon. The Eklutna project functions
today; Rampart was not constructed; and the Devil Canyon project is
still in the planning stage. Yet for all their differences in location,
goals, and fate, the projects were related; and, taken together, their
histories highlight all the essential political elements involved in
hydroelectric power construction. There is still a fourth project which
is functioning today--the Snettisham installation near Juneau which is
not considered in this paper.
A complex decision-making process determines the progress of such
large projects. In following these three Alaskan projects, we can gain
a better perspective on the roles of the several government agencies and
the public; thus we can assess some of the inherent complexities. Such
an assessment fully substantiates the conclusion that it takes more than
moving dirt to build a dam.The work upon which this completion report is based was supported
by funds provided by the U. S. Department of the Interior, Office of
Water Research and Technology as authorized under the Water Resources
Research Act of 1964, Public Law 88-379, as amended
Multiple Media Interfaces for Music Therapy
This article describes interfaces (and the supporting technological infrastructure) to create audiovisual instruments for use in music therapy. In considering how the multidimensional nature of sound requires multidimensional input control, we propose a model to help designers manage the complex mapping between input devices and multiple media software. We also itemize a research agenda
Comment on "Long Time Evolution of Phase Oscillator Systems" [Chaos 19,023117 (2009), arXiv:0902.2773]
A previous paper (arXiv:0902.2773, henceforth referred to as I) considered a
general class of problems involving the evolution of large systems of globally
coupled phase oscillators. It was shown there that, in an appropriate sense,
the solutions to these problems are time asymptotically attracted toward a
reduced manifold of system states (denoted M). This result has considerable
utility in the analysis of these systems, as has been amply demonstrated in
recent papers. In this note, we show that the analysis of I can be modified in
a simple way that establishes significant extensions of the range of validity
of our previous result. In particular, we generalize I in the following ways:
(1) attraction to M is now shown for a very general class of oscillator
frequency distribution functions g(\omega), and (2) a previous restriction on
the allowed class of initial conditions is now substantially relaxed
Granular Flow in a Vertically Vibrating Hopper
The behavior of the flow of glass spheres in a vertically vibrating hopper is examined. A two-dimensional hopper is mounted on a shaker that provides sinusoidal, vertical vibrations. Both the frequency and amplitude of the vibrations are adjustable. Hopper discharge rates and flow patterns are measured as the acceleration amplitude of the vibrations is increased from 0 to 4g's. Comparisons are made with unvibrated hopper flows and with a two-dimensional discrete element simulation model
Local measurements of velocity fluctuations and diffusion coefficients for a granular material flow
Measurements were made of two components of the average and fluctuating velocities, and of the local self-diffusion coefficients in a flow of granular material. The experiments were performed in a 1 m-high vertical channel with roughened sidewalls and with polished glass plates at the front and the back to create a two-dimensional flow. The particles used were glass spheres with a nominal diameter of 3 mm. The flows were high density and were characterized by the presence of long-duration frictional contacts between particles. The velocity measurements indicated that the flows consisted of a central uniform regime and a shear regime close to the walls. The fluctuating velocities in the transverse direction increased in magnitude from the centre towards the walls. A similar variation was not observed for the streamwise fluctuations. The self-diffusion coefficients showed a significant dependence on the fluctuating velocities and the shear rate. The velocity fluctuations were highly anistropic with the streamwise components being 2 to 2.5 times the transverse components. The self-diffusion coefficients for the streamwise direction were an order-of-magnitude higher than those for the transverse direction. The surface roughness of the particles led to a decrease in the self-diffusion coefficients
Solid metabolic waste transport and stowage investigation
The basic Waste Collection System (WCS) design under consideration utilized air flow to separate the stool from the WCS user and to transport the fecal material to a slinger device for subsequent deposition on a storage bowel. The major parameters governing stool separation and transport were found to be the area of the air inlet orifices, the configuration of the air inlet orifice and the transport air flow. Separation force and transport velocity of the stool were studied. The developed inlet orifice configuration was found to be an effective design for providing fecal separation and transport. Simulated urine tests and female user tests in zero gravity established air flow rates between 0.08 and 0.25 cu sm/min (3 and 9 scfm) as satisfactory for entrapment, containment and transport of urine using an urinal. The investigation of air drying of fecal material as a substitute for vacuum drying in a WCS breadboard system showed that using baseline conditions anticipated for the shuttle cabin ambient atmosphere, flow rates of 0.14 cu sm/min (5 cfm) were adequate for drying and maintaining biological stability of the fecal material
Revisiting the 1954 Suspension Experiments of R. A.Bagnold
In 1954 R. A. Bagnold published his seminal findings on the rheological properties of a liquid-solid suspension. Although this work has been cited extensively over the last
fifty years, there has not been a critical review of the experiments. The purpose of this study is to examine the work and to suggest an alternative reason for the experimental findings. The concentric cylinder rheometer was designed to measure simultaneously the shear and normal forces for a wide range of solid concentrations, fluid viscosities and shear rates. As presented by Bagnold, the analysis and experiments demonstrated that the shear and normal forces depended linearly on the shear rate in the 'macroviscous' regime; as the grain-to-grain interactions increased in the 'grain-inertia' regime, the stresses depended on the square of the shear rate and were independent of the fluid viscosity. These results, however, appear to be dictated by the design of the experimental facility. In Bagnold's experiments, the height (h) of the rheometer was relatively short compared to the spacing (t) between the rotating outer and stationary inner cylinder (h/t=4.6). Since the top and bottom end plates rotated with the outer cylinder, the flow contained two axisymmetric counter-rotating cells in which flow moved outward along the end plates and inward through the central region of the annulus. At higher Reynolds numbers, these cells contributed significantly to the measured torque, as demonstrated by comparing Bagnold's pure-fluid measurements with studies on laminar-to-turbulent transitions that pre-date the 1954 study. By accounting for the torque along the end walls, Bagnold's shear stress measurements can be estimated by modelling the liquid-solid mixture as a Newtonian fluid with
a corrected viscosity that depends on the solids concentration. An analysis of the normal stress measurements was problematic because the gross measurements were not reported and could not be obtained
Approximating the largest eigenvalue of network adjacency matrices
The largest eigenvalue of the adjacency matrix of a network plays an
important role in several network processes (e.g., synchronization of
oscillators, percolation on directed networks, linear stability of equilibria
of network coupled systems, etc.). In this paper we develop approximations to
the largest eigenvalue of adjacency matrices and discuss the relationships
between these approximations. Numerical experiments on simulated networks are
used to test our results.Comment: 7 pages, 4 figure
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