55,789 research outputs found
High frequency, high power capacitor development
A program to develop a special high energy density, high power transfer capacitor to operate at frequency of 40 kHz, 600 V rms at 125 A rms plus 600 V dc bias for space operation. The program included material evaluation and selection, a capacitor design was prepared, a thermal analysis performed on the design. Fifty capacitors were manufactured for testing at 10 kHz and 40 kHz for 50 hours at Industrial Electric Heating Co. of Columbus, Ohio. The vacuum endurance test used on environmental chamber and temperature plate furnished by Maxwell. The capacitors were energized with a special power conditioning apparatus developed by Industrial Electric Heating Co. Temperature conditions of the capacitors were monitored by IEHCo test equipment. Successful completion of the vacuum endurance test series confirmed achievement of the main goal of producing a capacitor or reliable operation at high frequency in an environment normally not hospitable to electrical and electronic components. The capacitor developed compared to a typical commercial capacitor at the 40 kHz level represents a decrease in size and weight by a factor of seven
Evaluating implicit feedback models using searcher simulations
In this article we describe an evaluation of relevance feedback (RF) algorithms using searcher simulations. Since these algorithms select additional terms for query modification based on inferences made from searcher interaction, not on relevance information searchers explicitly provide (as in traditional RF), we refer to them as implicit feedback models. We introduce six different models that base their decisions on the interactions of searchers and use different approaches to rank query modification terms. The aim of this article is to determine which of these models should be used to assist searchers in the systems we develop. To evaluate these models we used searcher simulations that afforded us more control over the experimental conditions than experiments with human subjects and allowed complex interaction to be modeled without the need for costly human experimentation. The simulation-based evaluation methodology measures how well the models learn the distribution of terms across relevant documents (i.e., learn what information is relevant) and how well they improve search effectiveness (i.e., create effective search queries). Our findings show that an implicit feedback model based on Jeffrey's rule of conditioning outperformed other models under investigation
Increasing resilience of ATM networks using traffic monitoring and automated anomaly analysis
Systematic network monitoring can be the cornerstone for
the dependable operation of safety-critical distributed
systems. In this paper, we present our vision for informed
anomaly detection through network monitoring and
resilience measurements to increase the operators'
visibility of ATM communication networks. We raise the
question of how to determine the optimal level of
automation in this safety-critical context, and we present a
novel passive network monitoring system that can reveal
network utilisation trends and traffic patterns in diverse
timescales. Using network measurements, we derive
resilience metrics and visualisations to enhance the
operators' knowledge of the network and traffic behaviour,
and allow for network planning and provisioning based on
informed what-if analysis
Principles for increased resilience in critical networked infrastructures
We propose a framework for deploying stronger, intelligent resilience mechanisms in mission-critical ATM networks over and above that offered by physical n-fold redundancy. We
compare the challenges facing power and data network resilience and discuss disruptive threats to real-world operations. Using recorded live data from an ATM data network we argue our proposed architecture with deployable, distributed on-demand anomaly detection and monitoring modules provides enhanced fail-secure versus current fail-safe resilience
Preliminary measurements of aircraft airframe noise with the NASA CV-990 aircraft
Flight tests were conducted in a CV-990 jet transport with engines at idle power to investigate aircraft airframe noise. Test results showed that airframe noise was measured for the aircraft in the landing configuration. The results agreed well with the expected variation with the fifth power of velocity. For the aircraft in the clean configuraton, it was concluded that airframe noise was measured only at higher airspeeds with engine idle noise present at lower speeds. The data show that landing gear and flaps make a significant contribution to airframe noise
Is Cosmology Solved?
We have fossil evidence from the thermal background radiation that our
universe expanded from a considerably hotter denser state. We have a well
defined and testable description of the expansion, the relativistic
Friedmann-Lemaitre model. Its observational successes are impressive but I
think hardly enough for a convincing scientific case. The lists of
observational constraints and free hypotheses within the model have similar
lengths. The scorecard on the search for concordant measures of the mass
density parameter and the cosmological constant shows that the high density
Einstein-de Sitter model is challenged, but that we cannot choose between low
density models with and without a cosmological constant. That is, the
relativistic model is not strongly overconstrained, the usual test of a mature
theory. Work in progress will greatly improve the situation and may at last
yield a compelling test. If so, and the relativistic model survives, it will
close one line of research in cosmology: we will know the outlines of what
happened as our universe expanded and cooled from high density. It will not end
research: some of us will occupy ourselves with the details of how galaxies and
other large-scale structures came to be the way they are, others with the issue
of what our universe was doing before it was expanding. The former is being
driven by rapid observational advances. The latter is being driven mainly by
theory, but there are hints of observational guidance.Comment: 13 pages, 3 figures. To be published in PASP as part of the
proceedings of the Smithsonian debate, Is Cosmology Solved
Fluctuation Spectrum from a Scalar-Tensor Bimetric Gravity Theory
Predictions of the CMB spectrum from a bimetric gravity theory
(gr-qc/0101126) are presented. The initial inflationary period in BGT is driven
by a vanishingly small speed of gravitational waves v_g in the very early
universe. This initial inflationary period is insensitive to the choice of
scalar field potential and initial values of the scalar field. After this
initial period of inflation, v_g will increase rapidly and the effects of a
potential will become important. We show that a quadratic potential introduced
into BGT yields an approximately flat spectrum with inflation parameters:
n_s=0.98, n_t=-0.027, alpha_s=-3.2e-4 and alpha_t=-5.0e-4, with r >= 0.014.Comment: 14 pages, uses amsmath, amssym
As-built specification for CCIT7 processor program
There are no author-identified significant results in this report
SkyDOT (Sky Database for Objects in the Time Domain): A Virtual Observatory for Variability Studies at LANL
The mining of Virtual Observatories (VOs) is becoming a powerful new method
for discovery in astronomy. Here we report on the development of SkyDOT (Sky
Database for Objects in the Time domain), a new Virtual Observatory, which is
dedicated to the study of sky variability. The site will confederate a number
of massive variability surveys and enable exploration of the time domain in
astronomy. We discuss the architecture of the database and the functionality of
the user interface. An important aspect of SkyDOT is that it is continuously
updated in near real time so that users can access new observations in a timely
manner. The site will also utilize high level machine learning tools that will
allow sophisticated mining of the archive. Another key feature is the real time
data stream provided by RAPTOR (RAPid Telescopes for Optical Response), a new
sky monitoring experiment under construction at Los Alamos National Laboratory
(LANL).Comment: to appear in SPIE proceedings vol. 4846, 11 pages, 5 figure
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