701 research outputs found
Intelligent Data Reduction (IDARE)
A description of the Intelligent Data Reduction (IDARE) expert system and an IDARE user's manual are given. IDARE is a data reduction system with the addition of a user profile infrastructure. The system was tested on a nickel-cadmium battery testbed. Information is given on installing, loading, maintaining the IDARE system
Automatic Detection of Electric Power Troubles (ADEPT)
Automatic Detection of Electric Power Troubles (A DEPT) is an expert system that integrates knowledge from three different suppliers to offer an advanced fault-detection system. It is designed for two modes of operation: real time fault isolation and simulated modeling. Real time fault isolation of components is accomplished on a power system breadboard through the Fault Isolation Expert System (FIES II) interface with a rule system developed in-house. Faults are quickly detected and displayed and the rules and chain of reasoning optionally provided on a laser printer. This system consists of a simulated space station power module using direct-current power supplies for solar arrays on three power buses. For tests of the system's ablilty to locate faults inserted via switches, loads are configured by an INTEL microcomputer and the Symbolics artificial intelligence development system. As these loads are resistive in nature, Ohm's Law is used as the basis for rules by which faults are located. The three-bus system can correct faults automatically where there is a surplus of power available on any of the three buses. Techniques developed and used can be applied readily to other control systems requiring rapid intelligent decisions. Simulated modeling, used for theoretical studies, is implemented using a modified version of Kennedy Space Center's KATE (Knowledge-Based Automatic Test Equipment), FIES II windowing, and an ADEPT knowledge base
Automatic Detection of Electric Power Troubles (ADEPT)
ADEPT is an expert system that integrates knowledge from three different suppliers to offer an advanced fault-detection system, and is designed for two modes of operation: real-time fault isolation and simulated modeling. Real time fault isolation of components is accomplished on a power system breadboard through the Fault Isolation Expert System (FIES II) interface with a rule system developed in-house. Faults are quickly detected and displayed and the rules and chain of reasoning optionally provided on a Laser printer. This system consists of a simulated Space Station power module using direct-current power supplies for Solar arrays on three power busses. For tests of the system's ability to locate faults inserted via switches, loads are configured by an INTEL microcomputer and the Symbolics artificial intelligence development system. As these loads are resistive in nature, Ohm's Law is used as the basis for rules by which faults are located. The three-bus system can correct faults automatically where there is a surplus of power available on any of the three busses. Techniques developed and used can be applied readily to other control systems requiring rapid intelligent decisions. Simulated modelling, used for theoretical studies, is implemented using a modified version of Kennedy Space Center's KATE (Knowledge-Based Automatic Test Equipment), FIES II windowing, and an ADEPT knowledge base. A load scheduler and a fault recovery system are currently under development to support both modes of operation
Return of the quantum cosmic censor
The influential theorems of Hawking and Penrose demonstrate that spacetime
singularities are ubiquitous features of general relativity, Einstein's theory
of gravity. The utility of classical general relativity in describing
gravitational phenomena is maintained by the cosmic censorship principle. This
conjecture, whose validity is still one of the most important open questions in
general relativity, asserts that the undesirable spacetime singularities are
always hidden inside of black holes. In this Letter we reanalyze extreme
situations which have been considered as counterexamples to the cosmic
censorship hypothesis. In particular, we consider the absorption of fermion
particles by a spinning black hole. Ignoring quantum effects may lead one to
conclude that an incident fermion wave may over spin the black hole, thereby
exposing its inner singularity to distant observers. However, we show that when
quantum effects are properly taken into account, the integrity of the
black-hole event horizon is irrefutable. This observation suggests that the
cosmic censorship principle is intrinsically a quantum phenomena.Comment: 5 page
The COS-Dwarfs Survey: The Carbon Reservoir Around sub-L* Galaxies
We report new observations of circumgalactic gas from the COS-Dwarfs survey,
a systematic investigation of the gaseous halos around 43 low-mass z 0.1
galaxies using background QSOs observed with the Cosmic Origins Spectrograph.
From the projected 1D and 2D distribution of C IV absorption, we find that C IV
absorption is detected out to ~ 0.5 R of the host galaxies. The C IV
absorption strength falls off radially as a power law and beyond 0.5 R,
no C IV absorption is detected above our sensitivity limit of ~ 50-100 m.
We find a tentative correlation between detected C IV absorption strength and
star formation, paralleling the strong correlation seen in highly ionized
oxygen for L~L* galaxies by the COS-Halos survey. The data imply a large carbon
reservoir in the CGM of these galaxies, corresponding to a minimum carbon mass
of 1.2 out to ~ 110 kpc. This mass is
comparable to the carbon mass in the ISM and more than the carbon mass
currently in stars of these galaxies. The C IV absorption seen around these
sub-L* galaxies can account for almost two-thirds of all > 100 m C IV
absorption detected at low z. Comparing the C IV covering fraction with
hydrodynamical simulations, we find that an energy-driven wind model is
consistent with the observations whereas a wind model of constant velocity
fails to reproduce the CGM or the galaxy properties.Comment: 18 Pages, 11 Figures, ApJ 796 13
Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high
density structures, likely to be representative of the initial conditions for
massive star and star cluster formation. CO emission from IRDCs has the
potential to be useful for tracing their dynamics, but may be affected by
depleted gas phase abundances due to freeze-out onto dust grains. Here we
analyze C18O J=1-0 and J=2-1 emission line data, taken with the IRAM 30m
telescope, of the highly filamentary IRDC G035.39.-0033. We derive the
excitation temperature as a function of position and velocity, with typical
values of ~7K, and thus derive total mass surface densities, Sigma_C18O,
assuming standard gas phase abundances and accounting for optical depth in the
line, which can reach values of ~1. The mass surface densities reach values of
~0.07 g/cm^2. We compare these results to the mass surface densities derived
from mid-infrared (MIR) extinction mapping, Sigma_SMF, by Butler & Tan, which
are expected to be insensitive to the dust temperatures in the cloud. With a
significance of >10sigma, we find Sigma_C18O/Sigma_SMF decreases by about a
factor of 5 as Sigma increases from ~0.02 to ~0.2 g/cm^2, which we interpret as
evidence for CO depletion. Several hundred solar masses are being affected,
making this one of the most massive clouds in which CO depletion has been
observed directly. We present a map of the depletion factor in the filament and
discuss implications for the formation of the IRDC.Comment: 9 pages, accepted to ApJ, Mac users: Figure 1 is best viewed with
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The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
We analyze the physical conditions of the cool, photoionized (T
K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density
measurements for 44 gaseous halos within 160 kpc of galaxies at . These data are well described by simple photoionization models, with
the gas highly ionized (n/n) by the
extragalactic ultraviolet background (EUVB). Scaling by estimates for the
virial radius, R, we show that the ionization state (tracked by the
dimensionless ionization parameter, U) increases with distance from the host
galaxy. The ionization parameters imply a decreasing volume density profile
n = (10)(R/R. Our derived
gas volume densities are several orders of magnitude lower than predictions
from standard two-phase models with a cool medium in pressure equilibrium with
a hot, coronal medium expected in virialized halos at this mass scale. Applying
the ionization corrections to the HI column densities, we estimate a lower
limit to the cool gas mass M
M for the volume within R R. Allowing for an
additional warm-hot, OVI-traced phase, the CGM accounts for at least half of
the baryons purported to be missing from dark matter halos at the 10
M scale.Comment: 19 pages, 12 Figures, and a 37-page Appendix with 36 additional
figures. Accepted to ApJ June 21 201
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