1,689 research outputs found
The Spectropolarimetric Evolution of V838 Monocerotis
I review photo-polarimetric and spectropolarimetric observations of V838 Mon,
which revealed that it had an asymmetrical inner circumstellar envelope
following its 2nd photometric outburst. Electron scattering, modified by pre-
or post-scattering H absorption, is the polarizing mechanism in V838 Mon's
envelope. The simplest geometry implied by these observations is that of a
spheroidal shell, flattened by at least 10% and having a projected position
angle on the sky of . Analysis of V838 Mon's polarized flux
reveals that this electron scattering shell lies interior to the envelope
region in which H and Ca II triplet emission originates. To date, none
of the theoretical models proposed for V838 Mon have demonstrated that they can
reproduce the evolution of V838 Mon's inner circumstellar environment, as
probed by spectropolarimetry.Comment: 8 pages, to appear in ASP Conf. Ser., The Nature of V838 Mon and Its
Light Echo, eds. R.L.M. Corradi and U. Munar
Model Reduction by Moment Matching for Linear Switched Systems
Two moment-matching methods for model reduction of linear switched systems
(LSSs) are presented. The methods are similar to the Krylov subspace methods
used for moment matching for linear systems. The more general one of the two
methods, is based on the so called "nice selection" of some vectors in the
reachability or observability space of the LSS. The underlying theory is
closely related to the (partial) realization theory of LSSs. In this paper, the
connection of the methods to the realization theory of LSSs is provided, and
algorithms are developed for the purpose of model reduction. Conditions for
applicability of the methods for model reduction are stated and finally the
results are illustrated on numerical examples.Comment: Sent for publication in IEEE TAC, on October 201
Stochastic Analysis of Synchronization in a Supermarket Refrigeration System
Display cases in supermarket systems often exhibit synchronization, in which
the expansion valves in the display cases turn on and off at exactly the same
time. The study of the influence of switching noise on synchronization in
supermarket refrigeration systems is the subject matter of this work. For this
purpose, we model it as a hybrid system, for which synchronization corresponds
to a periodic trajectory. Subsequently, we investigate the influence of
switching noise. We develop a statistical method for computing an intensity
function, which measures how often the refrigeration system stays synchronized.
By analyzing the intensity, we conclude that the increase in measurement
uncertainty yields the decrease at the prevalence of synchronization.Comment: In Proceedings HAS 2014, arXiv:1501.0540
Model Reduction of Linear Switched Systems by Restricting Discrete Dynamics
We present a procedure for reducing the number of continuous states of
discrete-time linear switched systems, such that the reduced system has the
same behavior as the original system for a subset of switching sequences. The
proposed method is expected to be useful for abstraction based control
synthesis methods for hybrid systems
The Spectropolarimetric Evolution of V838 Mon
I review photo-polarimetric and spectropolarimetric observations of V838 Mon, which revealed that it had an asymmetrical inner circumstellar envelope following its 2nd photometric outburst. Electron scattering, modified by preor post-scattering H absorption, is the polarizing mechanism in V838 Mon's envelope. The simplest geometry implied by these observations is that of a spheroidal shell, flattened by at least 20% and having a projected position angle on the sky of approx. 37 degrees. Analysis of V838 Mon's polarized flux reveals that this electron scattering shell lies interior to the envelope region in which Halpha and Ca II triplet emission originates. To date, none of the theoretical models proposed for V838 Mon have demonstrated that they can reproduce the evolution of V838 Mon's inner circumstellar environment, as probed by spectropolarimetry
Discovery of a New Dusty B[e] Star in the Small Magellanic Cloud
We present new optical spectroscopic and archival Spitzer IRAC photometric
observations of a B-type star in the SMC cluster NGC 346, NGC 346:KWBBe 200. We
detect numerous Fe II, [O I], and [Fe II] lines, as well as strong P-Cygni
profile H I emission lines in its optical spectrum. The star's near-IR color
and optical to IR SED clearly indicate the presence of an infrared excess,
consistent with the presence of gas and warm, T ~800 K, circumstellar dust.
Based on a crude estimate of the star's luminosity and the observed
spectroscopic line profile morphologies, we find that the star is likely to be
a B-type supergiant. We suggest that NGC 346:KWBBe 200 is a newly discovered
B[e] supergiant star, and represents the fifth such object to be identified in
the SMC.Comment: 12 pages, accepted by Ap
Moment Matching Based Model Reduction for LPV State-Space Models
We present a novel algorithm for reducing the state dimension, i.e. order, of
linear parameter varying (LPV) discrete-time state-space (SS) models with
affine dependence on the scheduling variable. The input-output behavior of the
reduced order model approximates that of the original model. In fact, for input
and scheduling sequences of a certain length, the input-output behaviors of the
reduced and original model coincide. The proposed method can also be
interpreted as a reachability and observability reduction (minimization)
procedure for LPV-SS representations with affine dependence
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