9,561 research outputs found
Cable insulation cut-through tester
Device accurately measures cut-through load within specified time or time when cut-through occurs at specific load. Tests are performed at ambient conditions or in an environmental chamber
An intelligent tutoring system for space shuttle diagnosis
An Intelligent Tutoring System (ITS) transcends conventional computer-based instruction. An ITS is capable of monitoring and understanding student performance thereby providing feedback, explanation, and remediation. This is accomplished by including models of the student, the instructor, and the expert technician or operator in the domain of interest. The space shuttle fuel cell is the technical domain for the project described below. One system, Microcomputer Intelligence for Technical Training (MITT), demonstrates that ITS's can be developed and delivered, with a reasonable amount of effort and in a short period of time, on a microcomputer. The MITT system capitalizes on the diagnostic training approach called Framework for Aiding the Understanding of Logical Troubleshooting (FAULT) (Johnson, 1987). The system's embedded procedural expert was developed with NASA's C-Language Integrated Production (CLIP) expert system shell (Cubert, 1987)
Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar
We present results from a temporal analysis of the longest and the most
sensitive X-ray observations of TV Columbae--an intermediate polar. The
observations were carried out with the RXTE PCA, ROSAT PSPC, and ASCA. Data
were analyzed using a 1-dimensional CLEAN and Bayesian algorithms. The presence
of a nearly sinusoidal modulation due to the spin of the white dwarf is seen
clearly in all the data, confirming the previous reports based on the EXOSAT
data. An improved period of 1909.7+/-2.5s is derived for the spin from the RXTE
data.The binary period of 5.5hr is detected unambiguously in X-rays for the
first time. Several side-bands due to the interaction of these periods are
observed in the power spectra, thereby suggesting contributions from both the
disk-fed and the stream-fed accretion for TV Col. The accretion disk could
perhaps be precessing as side-bands due to the influence of 4 day period on the
orbital period are seen. The presence of a significant power at certain
side-bands of the spin frequency indicates that the emission poles are
asymmetrically located. The strong power at the orbital side-bands seen in both
the RXTE and ROSAT data gives an indication for an absorption site fixed in the
orbital frame. Both the spin and the binary modulation are found to be
energy-dependent. Increased hardness ratio during a broad dip in the intensity
at binary phase of 0.75--1.0 confirms the presence of a strong attenuation due
to additional absorbers probably from an impact site of the accretion stream
with the disk or magnetosphere. Hardness ratio variations and the energy
dependent modulation depth during the spin modulation can be explained by
partially covered absorbers in the path of X-ray emission region in the
accretion stream.Comment: 34 pages, including 12 figures, Accepted for publication in
Astronomical Journal, scheduled for January 2004 issue (vol. 127
Self-recording portable soil penetrometer
A lightweight portable penetrometer for testing soil characteristics is described. The penetrometer is composed of a handle, data recording, and probe components detachably joined together. The data recording component has an easily removed recording drum which rotates according to the downward force applied on the handle, and a stylus means for marking the drum along its height according to the penetration depth of probe into the soil
Stylet-Bearing Nematodes Associated with Plants in Iowa Prairies
Native Iowa prairies contained a plant parasitic nematode population which differed markedly in predominant species from populations in cultivated fields. Nematode species and their abundance varied among the five prairies sampled. Aorolaimus was common in most prairies, but is not known in Iowa cultivated soils. Tylenchorhynchus maximus was common in the Kalsow and Sheeder prairies, but was not found in the Cayler and Hayden prairies. Helicotylenchus was common in all prairies, but the species were unevenly distributed
On the Meaning of the Principle of General Covariance
We present a definite formulation of the Principle of General Covariance
(GCP) as a Principle of General Relativity with physical content and thus
susceptible of verification or contradiction. To that end it is useful to
introduce a kind of coordinates, that we call quasi-Minkowskian coordinates
(QMC), as an empirical extension of the Minkowskian coordinates employed by the
inertial observers in flat space-time to general observers in the curved
situations in presence of gravitation. The QMC are operationally defined by
some of the operational protocols through which the inertial observers
determine their Minkowskian coordinates and may be mathematically characterized
in a neighbourhood of the world-line of the corresponding observer. It is taken
care of the fact that the set of all the operational protocols which are
equivalent to measure a quantity in flat space-time split into inequivalent
subsets of operational prescriptions under the presence of a gravitational
field or when the observer is not inertial. We deal with the Hole Argument by
resorting to de idea of the QMC and show how it is the metric field that
supplies the physical meaning of coordinates and individuates point-events in
regions of space-time where no other fields exist. Because of that the GCP has
also value as a guiding principle supporting Einstein's appreciation of its
heuristic worth in his reply to Kretschmann in 1918
Evidence for polar jets as precursors of polar plume formation
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are
utilized to study polar coronal jets and plumes. The study focuses on the
temporal evolution of both structures and their relationship. The data sample,
spanning April 7-8 2007, shows that over 90% of the 28 observed jet events are
associated with polar plumes. EUV images (STEREO/SECCHI) show plume haze rising
from the location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
jets, with the plume haze appearing minutes to hours after the jet was
observed. The remaining jets occurred in areas where plume material previously
existed causing a brightness enhancement of the latter after the jet event.
Short-lived, jet-like events and small transient bright points are seen (one at
a time) at different locations within the base of pre-existing long-lived
plumes. X-ray images also show instances (at least two events) of
collimated-thin jets rapidly evolving into significantly wider plume-like
structures that are followed by the delayed appearance of plume haze in the
EUV. These observations provide evidence that X-ray jets are precursors of
polar plumes, and in some cases cause brightenings of plumes. Possible
mechanisms to explain the observed jet and plume relationship are discussed.Comment: 10 pages, 4 figures, accepted as APJ Lette
Cluster Cosmology Redux: A Compact Model of the Halo Mass Function
Massive halos hosting groups and clusters of galaxies imprint coherent,
arcminute-scale features across the spectrophotometric sky, especially
optical-IR clusters of galaxies, distortions in the sub-mm CMB, and extended
sources of X-ray emission. Statistical modeling of such features often rely
upon the evolving space-time density of dark matter halos -- the halo mass
function (HMF) -- as a common theoretical ground for cosmological,
astrophysical and fundamental physics studies. We propose a compact (eight
parameter) representation of the HMF with readily interpretable parameters that
stem from polynomial expansions, first in terms of log-mass, then expanding
those coefficients similarly in redshift. We demonstrate good ()
agreement of this form, referred to as the dual-quadratic (DQ-HMF), with
Mira-Titan N-body emulator estimates for halo masses above over the redshift range , present best-fit
parameters for a Planck 2018 cosmology, and present parameter variation in the
plane. Convolving with a minimal mass-observable
relation (MOR) yields closed-form expressions for counts, mean mass, and mass
variance of cluster samples characterized by some observable property.
Performing information-matrix forecasts of potential parameter constraints from
existing and future surveys under different levels of systematic uncertainties,
we demonstrate the potential for percent-level constraints on model parameters
by an LSST-like optical cluster survey of 300,000 clusters and a richness-mass
variance of . Even better constraints could potentially be achieved by a
survey with one-tenth the sample size but with a reduced selection property
variance of . Potential benefits and extensions to the basic MOR
parameterization are discussed.Comment: 18 pages, 9 figure
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