8,975 research outputs found
Adaptive Filtering for Large Space Structures: A Closed-Form Solution
In a previous paper Schaechter proposes using an extended Kalman filter to estimate adaptively the (slowly varying) frequencies and damping ratios of a large space structure. The time varying gains for estimating the frequencies and damping ratios can be determined in closed form so it is not necessary to integrate the matrix Riccati equations. After certain approximations, the time varying adaptive gain can be written as the product of a constant matrix times a matrix derived from the components of the estimated state vector. This is an important savings of computer resources and allows the adaptive filter to be implemented with approximately the same effort as the nonadaptive filter. The success of this new approach for adaptive filtering was demonstrated using synthetic data from a two mode system
Probing Sub-parsec Structure in the Lyman Alpha Forest with Gravitational Microlensing
We present the results of microlens ray-tracing simulations showing the
effect of absorbing material between a source quasar and a lensing galaxy in a
gravitational lens system. We find that, in addition to brightness fluctuations
due to microlensing, the strength of the absorption line relative to the
continuum varies with time, with the properties of the variations depending on
the structure of the absorbing material. We conclude that such variations will
be measurable via UV spectroscopy of image A of the gravitationally lensed
quasar Q2237+0305 if the Lyman Alpha clouds between the quasar and the lensing
galaxy possess structure on scales smaller than pc. The time scale
for the variations is on the order of order years to decades, although very
short term variability can occur. While the Lyman alpha lines may not be
accessible at all wavelengths, this approach is applicable to any absorption
system, including metal lines.Comment: 8 pages, 11 figures, to appear in MNRAS (note resolution of some
figures reduced due to size limitations
Penalty Methods for the Hyperbolic System Modelling the Wall-Plasma Interaction in a Tokamak
The penalization method is used to take account of obstacles in a tokamak,
such as the limiter. We study a non linear hyperbolic system modelling the
plasma transport in the area close to the wall. A penalization which cuts the
transport term of the momentum is studied. We show numerically that this
penalization creates a Dirac measure at the plasma-limiter interface which
prevents us from defining the transport term in the usual sense. Hence, a new
penalty method is proposed for this hyperbolic system and numerical tests
reveal an optimal convergence rate without any spurious boundary layer.Comment: 8 pages; International Symposium FVCA6, Prague : Czech Republic
(2011
3D Photoionisation Modelling of NGC 6302
We present a three-dimensional photoionisation and dust radiative transfer
model of NGC 6302, an extreme, high-excitation planetary nebula. We use the 3D
photoionisation code Mocassin} to model the emission from the gas and dust. We
have produced a good fit to the optical emission-line spectrum, from which we
derived a density distribution for the nebula. A fit to the infrared coronal
lines places strong constraints on the properties of the unseen ionising
source. We find the best fit comes from using a 220,000 K hydrogen-deficient
central star model atmosphere, indicating that the central star of this PN may
have undergone a late thermal pulse.
We have also fitted the overall shape of the ISO spectrum of NGC 6302 using a
dust model with a shallow power-law size distribution and grains up to 1.0
micron in size. To obtain a good fit to the infrared SED the dust must be
sufficiently recessed within the circumstellar disk to prevent large amounts of
hot dust at short wavelengths, a region where the ISO spectrum is particularly
lacking. These and other discoveries are helping to unveil many properties of
this extreme object and trace it's evolutionary history.Comment: 8 pages, 4 figures; for the proceedings of "Asymmetric Planetary
Nebuale IV," R. L. M. Corradi, A. Manchado, N. Soker ed
Minimal Uncertainty in Momentum: The Effects of IR Gravity on Quantum Mechanics
The effects of the IR aspects of gravity on quantum mechanics is
investigated. At large distances where due to gravity the space-time is curved,
there appears nonzero minimal uncertainty in the momentum of a
quantum mechanical particle. We apply the minimal uncertainty momentum to some
quantum mechanical interferometry examples and show that the phase shift
depends on the area surrounded by the path of the test particle . We also put
some limits on the related parameters. This prediction may be tested through
future experiments. The assumption of minimal uncertainty in momentum can also
explain the anomalous excess of the mass of the Cooper pair in a rotating thin
superconductor ring.Comment: 8 pages, revised version accepted by PR
Fractal geometry of critical Potts clusters
Numerical simulations on the total mass, the numbers of bonds on the hull,
external perimeter, singly connected bonds and gates into large fjords of the
Fortuin-Kasteleyn clusters for two-dimensional q-state Potts models at
criticality are presented. The data are found consistent with the recently
derived corrections-to-scaling theory. However, the approach to the asymptotic
region is slow, and the present range of the data does not allow a unique
identification of the exact correction exponentsComment: 7 pages, 8 figures, Late
Body-freedom flutter of a 1/2-scale forward-swept-wing model, an experimental and analytical study
The aeroelastic phenomenon known as body-freedom flutter (BFF), a dynamic instability involving aircraft-pitch and wing-bending motions which, though rarely experienced on conventional vehicles, is characteristic of forward swept wing (FSW) aircraft was investigated. Testing was conducted in the Langley transonic dynamics tunnel on a flying, cable-mounted, 1/2-scale model of a FSW configuration with and without relaxed static stability (RSS). The BFF instability boundaries were found to occur at significantly lower airspeeds than those associated with aeroelastic wing divergence on the same model. For those cases with RSS, a canard-based stability augmentation system (SAS) was incorporated in the model. This SAS was designed using aerodynamic data measured during a preliminary tunnel test in which the model was attached to a force balance. Data from the subsequent flutter test indicated that BFF speed was not dependent on open-loop static margin but, rather, on the equivalent closed-loop dynamics provided by the SAS. Servo-aeroelastic stability analyses of the flying model were performed using a computer code known as SEAL and predicted the onset of BFF reasonably well
Molekulare Karyotypisierung in der Diagnostik neurokognitiver Entwicklungsstörungen
Zusammenfassung: Die Ursache neurokognitiver Entwicklungsstörungen mit Intelligenzminderung stellt eine der häufigsten Fragestellungen in der genetischen Sprechstunde dar. Obwohl mehr als 400 krankheitsverursachende Einzelgendefekte bekannt sind, machen Chromosomenaberrationen derzeit den größten Anteil der bekannten Ursachen aus. Mittels hochauflösender Array-Techniken lassen sich nach Ausschluss des Down-Syndroms bei unselektionierten Patienten in 18% der Fälle relevante chromosomale Imbalancen nachweisen, wobei die Aberrationen nur in 4% der Fälle auch primär mikroskopisch sichtbar wären. Mit zunehmender Auflösung steigt jedoch auch die Rate an detektierten Kopienzahl-Normvarianten, welche die Beurteilung der Befunde erschweren können. Indikatoren für krankheitsrelevante Aberrationen sind Aberrationsgröße, Gengehalt und Segregation innerhalb der Familie. Eine Kausalität kann letztlich aber nur dann belegt werden, wenn Vergleichsfälle mit ähnlichem Genotyp und Phänotyp vorliege
The cool end of the DZ sequence in the SDSS
We report the discovery of cool DZ white dwarfs, which lie in the SDSS (u-g)
vs. (g-r) two-color diagram across and below the main sequence. These stars
represent the extension of the well-known DZ sequence towards cooler
temperatures.Comment: To appear in the proceedings of the "17th European Workshop on White
Dwarfs", Tuebingen, Germany, August 16-20, 201
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