1,000 research outputs found
Linear regulator design for stochastic systems by a multiple time scales method
A hierarchically-structured, suboptimal controller for a linear stochastic system composed of fast and slow subsystems is considered. The controller is optimal in the limit as the separation of time scales of the subsystems becomes infinite. The methodology is illustrated by design of a controller to suppress the phugoid and short period modes of the longitudinal dynamics of the F-8 aircraft
A finite-state, finite-memory minimum principle, part 2
In part 1 of this paper, a minimum principle was found for the finite-state, finite-memory (FSFM) stochastic control problem. In part 2, conditions for the sufficiency of the minimum principle are stated in terms of the informational properties of the problem. This is accomplished by introducing the notion of a signaling strategy. Then a min-H algorithm based on the FSFM minimum principle is presented. This algorithm converges, after a finite number of steps, to a person - by - person extremal solution
Robustness results in LQG based multivariable control designs
The robustness of control systems with respect to model uncertainty is considered using simple frequency domain criteria. Results are derived under a common framework in which the minimum singular value of the return difference transfer matrix is the key quantity. In particular, the LQ and LQG robustness results are discussed
Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope
The Submillimetre Common User Bolometer Array (SCUBA) instrument has been
operating on the James Clerk Maxwell Telescope (JCMT) since 1997. The data
archive is now sufficiently large that it can be used to investigate
instrumental properties and the variability of astronomical sources. This paper
describes the automated calibration and reduction scheme used to process the
archive data with particular emphasis on `jiggle-map' observations of compact
sources. We demonstrate the validity of our automated approach at both 850- and
450-microns and apply it to several of the JCMT secondary flux calibrators. We
determine light curves for the variable sources IRC+10216 and OH231.8. This
automation is made possible by using the ORAC-DR data reduction pipeline, a
flexible and extensible data reduction pipeline that is used on UKIRT and the
JCMT.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
CH radio emission from heiles cloud 2 as a tracer of molecular cloud evolution
A mapping observation of the -type doubling transition (3.3
GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus
molecular cloud complex to reveal its molecular cloud-scale distribution. The
observations were carried out with the Effelsberg 100 m telescope. The CH
emission is found to be extended over the whole region of HCL2. It is brighter
in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in
the northwestern part. Its distribution extends continuously from the peak of
the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were
connecting the distributions of the [C I] and CO emissions. Since CH is
an intermediate in gas-phase chemical reactions from C to CO, its emission
should trace the transition region. The above distribution of the CH emission
is consistent with this chemical behavior. Since the CH abundance is subject to
the chemical evolutionary effect, the CH column density in HCL2 no longer
follows a linear correlation wit the H column density reported for diffuse
and translucent clouds. More importantly, the CH line profile is found to be
composed of the narrow and broad components. Although the broad component is
dominant around the CI peak, the narrow component appears in the TMC-1 ridge
and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a
narrowing of the line width during the formation of dense cores. These results
suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and
physical evolution of molecular clouds.Comment: 8 page
High Spatial Resolution Observations of Two Young Protostars in the R Corona Australis Region
We present multi-wavelength, high spatial resolution imaging of the IRS 7
region in the R Corona Australis molecular cloud. Our observations include 1.1
mm continuum and HCO^+ J = images from the SMA, ^{12}CO J =
outflow maps from the DesertStar heterodyne array receiver on the HHT, 450
m and 850 m continuum images from SCUBA, and archival Spitzer IRAC
and MIPS 24 \micron images. The accurate astrometry of the IRAC images allow us
to identify IRS 7 with the cm source VLA 10W (IRS 7A) and the X-ray source X_W.
The SMA 1.1 mm image reveals two compact continuum sources which are also
distinguishable at 450 m. SMA 1 coincides with X-ray source CXOU
J190156.4-365728 and VLA cm source 10E (IRS 7B) and is seen in the IRAC and
MIPS images. SMA 2 has no infrared counterpart but coincides with cm source VLA
9. Spectral energy distributions constructed from SMA, SCUBA and Spitzer data
yield bolometric temperatures of 83 K for SMA 1 and 70 K for SMA 2. These
temperatures along with the submillimeter to total luminosity ratios indicate
that SMA 2 is a Class 0 protostar, while SMA 1 is a Class 0/Class I
transitional object (L= \Lsun). The ^{12}CO J = outflow map
shows one major and possibly several smaller outflows centered on the IRS 7
region, with masses and energetics consistent with previous work. We identify
the Class 0 source SMA 2/VLA 9 as the main driver of this outflow. The complex
and clumpy spatial and velocity distribution of the HCO^+ J =
emission is not consistent with either bulk rotation, or any known molecular
outflow activity.Comment: 31 pages, 8 figures, Accepted to Ap
Early response to impact knee injury in genetic strains of mice reveals similarity in cartilage but differences in synovium
Investigation of the Multiple Method Adaptive Control (MMAC) method for flight control systems
The stochastic adaptive control of the NASA F-8C digital-fly-by-wire aircraft using the multiple model adaptive control (MMAC) method is presented. The selection of the performance criteria for the lateral and the longitudinal dynamics, the design of the Kalman filters for different operating conditions, the identification algorithm associated with the MMAC method, the control system design, and simulation results obtained using the real time simulator of the F-8 aircraft at the NASA Langley Research Center are discussed
The Hot Inner Disk of FU Ori
We have constructed a detailed radiative transfer disk model which reproduces
the main features of the spectrum of the outbursting young stellar object FU
Orionis from ~ 4000 angstrom, to ~ 8 micron. Using an estimated visual
extinction Av~1.5, a steady disk model with a central star mass ~0.3 Msun and a
mass accretion rate ~ 2e-4 Msun/yr, we can reproduce the spectral energy
distribution of FU Ori quite well. With the mid-infrared spectrum obtained by
the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope, we
estimate that the outer radius of the hot, rapidly accreting inner disk is ~ 1
AU using disk models truncated at this outer radius. Inclusion of radiation
from a cooler irradiated outer disk might reduce the outer limit of the hot
inner disk to ~ 0.5 AU. In either case, the radius is inconsistent with a pure
thermal instability model for the outburst. Our radiative transfer model
implies that the central disk temperature Tc > 1000 K out to ~ 0.5 - 1 AU,
suggesting that the magnetorotational instability (MRI) can be supported out to
that distance. Assuming that the ~ 100 yr decay timescale in brightness of FU
Ori represents the viscous timescale of the hot inner disk, we estimate the
viscosity parameter (alpha) to be ~ 0.2 - 0.02 in the outburst state,
consistent with numerical simulations of MRI in disks. The radial extent of the
high mass accretion region is inconsistent with the model of Bell & Lin, but
may be consistent with theories incorporating both gravitational instability
and MRI.Comment: 32 pages, 10 figures, to appear in the Astrophysical Journa
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