999 research outputs found
Machine-Vision Aids for Improved Flight Operations
The development of machine vision based pilot aids to help reduce night approach and landing accidents is explored. The techniques developed are motivated by the desire to use the available information sources for navigation such as the airport lighting layout, attitude sensors and Global Positioning System to derive more precise aircraft position and orientation information. The fact that airport lighting geometry is known and that images of airport lighting can be acquired by the camera, has lead to the synthesis of machine vision based algorithms for runway relative aircraft position and orientation estimation. The main contribution of this research is the synthesis of seven navigation algorithms based on two broad families of solutions. The first family of solution methods consists of techniques that reconstruct the airport lighting layout from the camera image and then estimate the aircraft position components by comparing the reconstructed lighting layout geometry with the known model of the airport lighting layout geometry. The second family of methods comprises techniques that synthesize the image of the airport lighting layout using a camera model and estimate the aircraft position and orientation by comparing this image with the actual image of the airport lighting acquired by the camera. Algorithms 1 through 4 belong to the first family of solutions while Algorithms 5 through 7 belong to the second family of solutions. Algorithms 1 and 2 are parameter optimization methods, Algorithms 3 and 4 are feature correspondence methods and Algorithms 5 through 7 are Kalman filter centered algorithms. Results of computer simulation are presented to demonstrate the performance of all the seven algorithms developed
Hyperfine interaction and electronic spin fluctuation study on SrLaFeCoO (x = 0, 1, 2) by high-resolution back-scattering neutron spectroscopy
The study of hyperfine interaction by high-resolution inelastic neutron
scattering is not very well known compared to the other competing techniques
viz. NMR, M\"ossbauer, PACS etc. Also the study is limited mostly to
magnetically ordered systems. Here we report such study on
SrLaFeCoO (x = 0, 1, 2) of which first (SrFeCoO with x
= 0) has a canonical spin spin glass, the second (SrLaFeCoO with x = 1) has
a so-called magnetic glass and the third (LaFeCoO with x = 2) has a
magnetically ordered ground state. Our present study revealed clear inelastic
signal for SrLaFeCoO, possibly also inelastic signal for SrFeCoO
below the spin freezing temperatures but no inelastic signal at all
for for the magnetically ordered LaFeCoO in the neutron scattering
spectra. The broadened inelastic signals observed suggest hyperfine field
distribution in the two disordered magnetic glassy systems and no signal for
the third compound suggests no or very small hyperfine field at the Co nucleus
due to Co electronic moment. For the two magnetic glassy system apart from the
hyperfine signal due only to Co, we also observed electronic spin fluctuations
probably from both Fe and Co electronic moments. \end{abstract
Gravitational wave burst vetoes in the LIGO S2 and S3 data analyses
The LIGO detectors collected about 4 months of data in 2003-2004 during two
science runs, S2 and S3. Several environmental and auxiliary channels that
monitor the instruments' physical environment and overall interferometric
operation were analyzed in order to establish the quality of the data as well
as the presence of transients of non-astrophysical origin. This analysis
allowed better understanding of the noise character of the instruments and the
establishment of correlations between transients in these channels and the one
recording the gravitational wave strain. In this way vetoes for spurious burst
were identified. We present the methodology we followed in this analysis and
the results from the S2 and S3 veto analysis within the context of the search
for gravitational wave bursts.Comment: 9 pages, 4 figures, submitted to Classical and Quantum Gravity for
the special issue of the GWDAW9 Proceeding
Doping dependence of the exchange energies in bilayer manganites: Role of orbital degrees of freedom
Recently, an intriguing doping dependence of the exchange energies in the
bilayer manganites has been observed in the neutron
scattering experiments. The intra-layer exchange only weakly changed with
doping while the inter-layer one drastically decreased. Here we propose a
theory which accounts for these experimental findings. We argue, that the
observed striking doping dependence of the exchange energies can be attributed
to the evaluation of the orbital level splitting with doping. The latter is
handled by the interplay between Jahn-Teller effect (supporting an axial
orbital) and the orbital anisotropy of the electronic band in the bilayer
structure (promoting an in-plane orbital), which is monitored by the Coulomb
repulsion. The presented theory, while being a mean-field type, describes well
the experimental data and also gives the estimates of the several interesting
energy scales involved in the problem.Comment: Added references, corrected typos. To appear in Phys. Rev.
Methods for Reducing False Alarms in Searches for Compact Binary Coalescences in LIGO Data
The LIGO detectors are sensitive to a variety of noise transients of
non-astrophysical origin. Instrumental glitches and environmental disturbances
increase the false alarm rate in the searches for gravitational waves. Using
times already identified when the interferometers produced data of questionable
quality, or when the channels that monitor the interferometer indicated
non-stationarity, we have developed techniques to safely and effectively veto
false triggers from the compact binary coalescences (CBCs) search pipeline
Property (RD) for Hecke pairs
As the first step towards developing noncommutative geometry over Hecke
C*-algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the
subgroup H in a Hecke pair (G,H) is finite, we show that the Hecke pair (G,H)
has (RD) if and only if G has (RD). This provides us with a family of examples
of Hecke pairs with property (RD). We also adapt Paul Jolissant's works in 1989
to the setting of Hecke C*-algebras and show that when a Hecke pair (G,H) has
property (RD), the algebra of rapidly decreasing functions on the set of double
cosets is closed under holomorphic functional calculus of the associated
(reduced) Hecke C*-algebra. Hence they have the same K_0-groups.Comment: A short note added explaining other methods to prove that the
subalgebra of rapidly decreasing functions is smooth. This is the final
version as published. The published version is available at: springer.co
LOOC UP: Locating and observing optical counterparts to gravitational wave bursts
Gravitational wave (GW) bursts (short duration signals) are expected to be
associated with highly energetic astrophysical processes. With such high
energies present, it is likely these astrophysical events will have signatures
in the EM spectrum as well as in gravitational radiation. We have initiated a
program, "Locating and Observing Optical Counterparts to Unmodeled Pulses in
Gravitational Waves" (LOOC UP) to promptly search for counterparts to GW burst
candidates. The proposed method analyzes near real-time data from the
LIGO-Virgo network, and then uses a telescope network to seek optical-transient
counterparts to candidate GW signals. We carried out a pilot study using
S5/VSR1 data from the LIGO-Virgo network to develop methods and software tools
for such a search. We will present the method, with an emphasis on the
potential for such a search to be carried out during the next science run of
LIGO and Virgo, expected to begin in 2009.Comment: 11 pages, 2 figures; v2) added acknowledgments, additional
references, and minor text changes v3) added 1 figure, additional references,
and minor text changes. v4) Updated references and acknowledgments. To be
published in the GWDAW 12 Conf. Proc. by Classical and Quantum Gravit
Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector
The upcoming European design study `Einstein gravitational-wave Telescope'
represents the first step towards a substantial, international effort for the
design of a third-generation interferometric gravitational wave detector. It is
generally believed that third-generation instruments might not be installed
into existing infrastructures but will provoke a new search for optimal
detector sites. Consequently, the detector design could be subject to fewer
constraints than the on-going design of the second generation instruments. In
particular, it will be prudent to investigate alternatives to the traditional
L-shaped Michelson interferometer. In this article, we review an old proposal
to use three Michelson interferometers in a triangular configuration. We use
this example of a triple Michelson interferometer to clarify the terminology
and will put this idea into the context of more recent research on
interferometer technologies. Furthermore the benefits of a triangular detector
will be used to motivate this design as a good starting point for a more
detailed research effort towards a third-generation gravitational wave
detector.Comment: Minor corrections to the main text and two additional appendices. 14
pages, 6 figure
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