16,207 research outputs found
F-region drift velocities from incoherent-scatter measurements at Millstone Hill
F-region drift velocities measured at Millstone Hill from 1968 to 1974 are presented in tabular form. A brief description of the measurement procedures is also given
Calculation of conductivities and currents in the ionosphere
Formulas and procedures to calculate ionospheric conductivities are summarized. Ionospheric currents are calculated using a semidiurnal E-region neutral wind model and electric fields from measurements at Millstone Hill. The results agree well with ground based magnetogram records for magnetic quiet days
Lunar surface exploration by satellite. An integrated experiment package to perform measurements of the composition of the lunar surface Final report
Integrated experiment package to measure lunar surface composition - gamma ray, alpha particle, X ray fluorescence, and neutron albedo experiment
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Iron Oxide Grains in Stardust Track 121 Grains as Evidence of Comet Wild 2 Hydrothermal Alteration
Stardust Track 121 terminal grains contain Fe-oxide. These are consistent with the presence of hydrothermal alteration on the Comet Wild 2 parent body
Recognition of 3-D Objects from Multiple 2-D Views by a Self-Organizing Neural Architecture
The recognition of 3-D objects from sequences of their 2-D views is modeled by a neural architecture, called VIEWNET that uses View Information Encoded With NETworks. VIEWNET illustrates how several types of noise and varialbility in image data can be progressively removed while incornplcte image features are restored and invariant features are discovered using an appropriately designed cascade of processing stages. VIEWNET first processes 2-D views of 3-D objects using the CORT-X 2 filter, which discounts the illuminant, regularizes and completes figural boundaries, and removes noise from the images. Boundary regularization and cornpletion are achieved by the same mechanisms that suppress image noise. A log-polar transform is taken with respect to the centroid of the resulting figure and then re-centered to achieve 2-D scale and rotation invariance. The invariant images are coarse coded to further reduce noise, reduce foreshortening effects, and increase generalization. These compressed codes are input into a supervised learning system based on the fuzzy ARTMAP algorithm. Recognition categories of 2-D views are learned before evidence from sequences of 2-D view categories is accumulated to improve object recognition. Recognition is studied with noisy and clean images using slow and fast learning. VIEWNET is demonstrated on an MIT Lincoln Laboratory database of 2-D views of jet aircraft with and without additive noise. A recognition rate of 90% is achieved with one 2-D view category and of 98.5% correct with three 2-D view categories.National Science Foundation (IRI 90-24877); Office of Naval Research (N00014-91-J-1309, N00014-91-J-4100, N00014-92-J-0499); Air Force Office of Scientific Research (F9620-92-J-0499, 90-0083
Supersonic combustor modeling
The physical phenomena involved when a supersonic flow undergoes chemical reaction are discussed. Detailed physical models of convective and diffusive mixing, and finite rate chemical reaction in supersonic flow are presented. Numerical algorithms used to solve the equations governing these processes are introduced. Computer programs using these algorithms are used to analyze the structure of the reacting mixing layer. It is concluded that, as in subsonic flow, exothermic heat release in unconfined supersonic flows retards fuel/air mixing. Non mixing is shown to be a potential problem in reducing the efficiency of supersonic as well as subsonic combustion. Techniques for enhancing fuel/air mixing and combustion are described
An application of multiattribute decision analysis to the Space Station Freedom program. Case study: Automation and robotics technology evaluation
The results are described of an application of multiattribute analysis to the evaluation of high leverage prototyping technologies in the automation and robotics (A and R) areas that might contribute to the Space Station (SS) Freedom baseline design. An implication is that high leverage prototyping is beneficial to the SS Freedom Program as a means for transferring technology from the advanced development program to the baseline program. The process also highlights the tradeoffs to be made between subsidizing high value, low risk technology development versus high value, high risk technology developments. Twenty one A and R Technology tasks spanning a diverse array of technical concepts were evaluated using multiattribute decision analysis. Because of large uncertainties associated with characterizing the technologies, the methodology was modified to incorporate uncertainty. Eight attributes affected the rankings: initial cost, operation cost, crew productivity, safety, resource requirements, growth potential, and spinoff potential. The four attributes of initial cost, operations cost, crew productivity, and safety affected the rankings the most
Studies at Oyster Bay in Jamaica, West Indies. II. Effacts of flow patterns and exchange on bioluminescent distributions
From July 1966 to July 1967, regular observations and some experiments were carried out in Oyster Bay at the eastern end of Falmouth Harbor, Jamaica, W. I. This paper gives a general description of the area; it reports observations on the tidal movement, the density currents, the wind force and direction, and the water discharge by the Martha Brae River; and it correlates the flow patterns in Oyster Bay with observed bioluminescent distribution
Dynamic Radio-Frequency Transverse Susceptibility in Magnetic Nanoparticle Systems
A novel resonant method based on a tunnel-diode oscillator (TDO) is used to
study the dynamic transverse susceptibility in a Fe nanoparticle system. The
magnetic system consists of an aggregate of nanometer-size core (Au)-shell (Fe)
structure, synthesized by reverse micelle methods. Static and dynamic
magnetization measurements carried out in order to characterize the system
reveal a superparamagnetic behavior at high temperature. The field-dependent
transverse susceptibility at radio-frequencies (RF), for different temperatures
reveals distinct peak structure at characteristics fields (H_k, H_c) which
changes with temperature. It is proposed that relaxation processes could
explain the influence of the temperature on the field dependence of the
transverse susceptibility on the MI.Comment: 3 pages, 2-column, 3 figures, To be published in J. Appl. Phys. 2000
(44th Annual MMM proceedings
Growth mechanisms of perturbations in boundary layers over a compliant wall
The temporal modal and nonmodal growth of three-dimensional perturbations in
the boundary-layer flow over an infinite compliant flat wall is considered.
Using a wall-normal velocity/wall-normal vorticity formalism, the dynamic
boundary condition at the compliant wall admits a linear dependence on the
eigenvalue parameter, as compared to a quadratic one in the canonical
formulation of the problem. This greatly simplifies the accurate calculation of
the continuous spectrum by means of a spectral method, thereby yielding a very
effective filtering of the pseudospectra as well as a clear identification of
instability regions. The regime of global instability is found to be matching
the regime of the favorable phase of the forcing by the flow on the compliant
wall so as to enhance the amplitude of the wall. An energy-budget analysis for
the least-decaying hydroelastic (static-divergence, traveling-wave-flutter and
near-stationary transitional) and Tollmien--Schlichting modes in the parameter
space reveals the primary routes of energy flow. Moreover, the flow exhibits a
slower transient growth for the maximum growth rate of a superposition of
streamwise-independent modes due to a complex dependence of the wall-boundary
condition with the Reynolds number. The initial and optimal perturbations are
compared with the boundary-layer flow over a solid wall; differences and
similarities are discussed. Unlike the solid-wall case, viscosity plays a
pivotal role in the transient growth. A slowdown of the maximum growth rate
with the Reynolds number is uncovered and found to originate in the transition
of the fluid-solid interaction from a two-way to a one-way coupling. Finally, a
term-by-term energy budget analysis is performed to identify the key
contributors to the transient growth mechanism
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