15,263 research outputs found
Materials and construction techniques for cryogenic wind tunnel facilities for instruction/research use
The results of the cryogenic wind tunnel program conducted at NASA Langley Research Center are presented to provide a starting point for the design of an instructional/research wind tunnel facility. The advantages of the cryogenic concept are discussed, and operating envelopes for a representative facility are presented to indicate the range and mode of operation. Special attention is given to the design, construction and materials problems peculiar to cryogenic wind tunnels. The control system for operation of a cryogenic tunnel is considered, and a portion of a linearized mathematical model is developed for determining the tunnel dynamic characteristics
A Hybrid Observer for a Distributed Linear System with a Changing Neighbor Graph
A hybrid observer is described for estimating the state of an channel,
-dimensional, continuous-time, distributed linear system of the form
. The system's state is
simultaneously estimated by agents assuming each agent senses and
receives appropriately defined data from each of its current neighbors.
Neighbor relations are characterized by a time-varying directed graph
whose vertices correspond to agents and whose arcs depict
neighbor relations. Agent updates its estimate of at "event
times" using a local observer and a local parameter
estimator. The local observer is a continuous time linear system whose input is
and whose output is an asymptotically correct estimate of
where a matrix with kernel equaling the unobservable space of .
The local parameter estimator is a recursive algorithm designed to estimate,
prior to each event time , a constant parameter which satisfies the
linear equations , where is a small
positive constant and is the state estimation error of local observer
. Agent accomplishes this by iterating its parameter estimator state
, times within the interval , and by making use of
the state of each of its neighbors' parameter estimators at each iteration. The
updated value of at event time is then . Subject to the assumptions that (i) the neighbor graph
is strongly connected for all time, (ii) the system whose state
is to be estimated is jointly observable, (iii) is sufficiently large, it
is shown that each estimate converges to exponentially fast as
at a rate which can be controlled.Comment: 7 pages, the 56th IEEE Conference on Decision and Contro
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Numerical modelling of microwave sintering of lunar simulants under near lunar atmospheric condition
Forestland type identification and analysis in Western Massachussetts: A linkage of a LANDSAT forest inventory to an optimization study
Digital land cover files derived from computer processing of LANDSAT and soil productivity data were linked and used by linear programming model to determine production of forested areas under different management strategies. Results of model include maps and data graphics for four-county region in Western Massachusetts
Ion Trap Mass Spectrometers for Identity, Abundance and Behavior of Volatiles on the Moon
NASA GSFC and The Open University (UK) are collaborating to deploy an Ion Trap Mass Spectrometer on the Moon to investigate the lunar water cycle. The ITMS is flight-proven throughthe Rosetta Philae comet lander mission. It is also being developed under ESA funding to analyse samples drilled from beneath the lunar surface on the Roscosmos Luna-27 lander (2025).Now, GSFC and OU will now develop a compact ITMS instrument to study the near-surface lunar exosphere on board a CLPS Astrobotic lander at Lacus Mortis in 2021
Comparing the performance of stellar variability filters for the detection of planetary transits
We have developed a new method to improve the transit detection of
Earth-sized planets in front of solar-like stars by fitting stellar
microvariability by means of a spot model. A large Monte Carlo numerical
experiment has been designed to test the performance of our approach in
comparison with other variability filters and fitting techniques for stars of
different magnitudes and planets of different radius and orbital period, as
observed by the space missions CoRoT and Kepler. Here we report on the results
of this experiment.Comment: 4 pages, 3 postscript figures, Transiting Planets Proceeding IAU
Symposium No.253, 200
The structure of trailing vortices generated by model rotor blades
Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described
Is entanglement entropy proportional to area?
It is known that the entanglement entropy of a scalar field, found by tracing
over its degrees of freedom inside a sphere of radius , is
proportional to the area of the sphere (and not its volume). This suggests that
the origin of black hole entropy, also proportional to its horizon area, may
lie in the entanglement between the degrees of freedom inside and outside the
horizon. We examine this proposal carefully by including excited states, to
check probable deviations from the area law.Comment: 6 pages. Based on talk by S. Das at Theory Canada 1, Vancouver, 3
June, 2005. To be published in a special edition of the Canadian Journal of
Physics. Minor changes to match published versio
On a Petrov-type D homogeneous solution
We present a new two-parameter family of solutions of Einstein gravity with
negative cosmological constant in 2+1 dimensions. These solutions are obtained
by squashing the anti-de Sitter geometry along one direction and posses four
Killing vectors. Global properties as well as the four dimensional
generalization are discussed, followed by the investigation of the geodesic
motion. A simple global embedding of these spaces as the intersection of four
quadratic surfaces in a seven dimensional space is obtained. We argue also that
these geometries describe the boundary of a four dimensional nutty-bubble
solution and are relevant in the context of AdS/CFT correspondence.Comment: 20 pages, TeX fil
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