9,005 research outputs found
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
Factoring and Fourier Transformation with a Mach-Zehnder Interferometer
The scheme of Clauser and Dowling (Phys. Rev. A 53, 4587 (1996)) for
factoring by means of an N-slit interference experiment is translated into
an experiment with a single Mach-Zehnder interferometer. With dispersive phase
shifters the ratio of the coherence length to wavelength limits the numbers
that can be factored. A conservative estimate permits . It is
furthermore shown, that sine and cosine Fourier coefficients of a real periodic
function can be obtained with such an interferometer.Comment: 5 pages, 2 postscript figures; to appear in Phys.Rev.A, Nov. 1997;
Figures contained only in replaced versio
Analytical and experimental study of the effects of wing-body aerodynamic interaction on space shuttle subsonic flutter
The effects on flutter of the aerodynamic interaction between the space shuttle bodies and wing, 1/80th-scale semispan models of the orbiter wing, the complete shuttle and intermediate component combinations were tested in the NASA Langley Research Center 26-inch Transonic Blowdown Wind Tunnel. Using the double lattice method combined with slender body theory to calculate unsteady aerodynamic forces, subsonic flutter speeds were computed for comparison. Using calculated complete vehicle modes, flutter speed trends were computed for the full scale vehicle at an altitude of 15,200 meters and a Mach number of 0.6. Consistent with findings of the model studies, analysis shows the shuttle to have the same flutter speed as an isolated cantilevered wing
Theory of minimum effort control
Optimum control theory formulations for solving problems in optimum guidance for interplanetary manned space flight mission
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
Di-boson Production beyond NLO QCD and Anomalous Couplings
In these proceedings, we review results for several di-boson production
processes beyond NLO QCD at high transverse momenta using the VBFNLO
Monte-Carlo program together with the LOOPSIM method. Additionally, we show for
the WZ production process how higher order QCD corrections can resemble
anomalous coupling effects.Comment: Conference Proceedings:C15-05-25.
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
Investigations in space communications theory, including topics related to random processes, filtering, telemetry Semiannual status report, 1 Oct. 1966 - 31 Mar. 1967
Random processes, filtering, and telemetry problems in space communications theor
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