4,867 research outputs found
SuperCam, a 64-pixel heterodyne imaging array for the 870 micron atmospheric window
We report on the development of SuperCam, a 64 pixel, superheterodyne camera
designed for operation in the astrophysically important 870 micron atmospheric
window. SuperCam will be used to answer fundamental questions about the physics
and chemistry of molecular clouds in the Galaxy and their direct relation to
star and planet formation. The advent of such a system will provide an order of
magnitude increase in mapping speed over what is now available and
revolutionize how observational astronomy is performed in this important
wavelength regime. Unlike the situation with bolometric detectors, heterodyne
receiver systems are coherent, retaining information about both the amplitude
and phase of the incident photon stream. From this information a high
resolution spectrum of the incident light can be obtained without multiplexing.
SuperCam will be constructed by stacking eight, 1x8 rows of fixed tuned, SIS
mixers. The IF output of each mixer will be connected to a low-noise, broadband
MMIC amplifier integrated into the mixer block. The instantaneous IF bandwidth
of each pixel will be ~2 GHz, with a center frequency of 5 GHz. A spectrum of
the central 500 MHz of each IF band will be provided by the array spectrometer.
Local oscillator power is provided by a frequency multiplier whose output is
divided between the pixels by using a matrix of waveguide power dividers. The
mixer array will be cooled to 4K by a closed-cycle refrigeration system.
SuperCam will reside at the Cassegrain focus of the 10m Heinrich Hertz
telescope (HHT). A prototype single row of the array will be tested on the HHT
in 2006, with the first engineering run of the full array in late 2007. The
array is designed and constructed so that it may be readily scaled to higher
frequencies.Comment: 12 pages, 14 figures, to be published in the Proceedings of SPIE Vol.
6275, "Astronomical Telescopes and Instrumentation, Millimeter and
Submillimeter Detectors and Instrumentation for Astronomy III
Stellar population and kinematics of NGC404
NGC404 is a nearly face-on nearby low-luminosity lenticular galaxy. Probing
its characteristics provides a wealth of information on the details of possible
evolution processes of dS0 galaxies which may not be possible in other, more
distant objects. In order to study its kinematics and star formation history,
we obtained long slit spectroscopy at the OHP 1m93 telescope along the major
and minor axes of NGC404. The spectra have a resolution R = 3600 covering a
wavelength range from 4600 to 5500 A. The data are fitted against the Pegase.HR
stellar population models to derive simultaneously the internal stellar
kinematics, ages and metallicities. Firstly, the global properties of the
galaxy are analyzed by fitting a single model and to the data and looking at
the kinematic variations and SSP equivalent age and metallicities as a function
of radius. Afterwards, the stellar populations are decomposed into 4 components
that are individually analyzed. NGC404 clearly shows two radial velocity
inversions along its major axis. The kinematically decoupled core rotates in
the same direction as the neutral hydrogen shell that surrounds the galaxy. We
resolved the star formation history in the core of the galaxy ino 4 events: A
very young (< 150 Myr, and [Fe/H] = 0.4) component with constant on-going star
formation, a second young (430 Myr) component with [Fe/H] = 0.1, an
intermediate population (1.7 Gyr) which has [Fe/H] = -0.05 and, finally, an old
(12 Gyr) component with [Fe/H] = -1.26. The two young components fade very
quickly with radius, leaving only the intermediate and old population at a
radius of 25" (370 pc) from the centre. We conclude that NGC404 had a spiral
morphology about 1 Gyr ago and that one or many merger events has triggered a
morphological transition.Comment: 8 pages, 8 figures, accepted for publication in A&
Multiframe Scene Flow with Piecewise Rigid Motion
We introduce a novel multiframe scene flow approach that jointly optimizes
the consistency of the patch appearances and their local rigid motions from
RGB-D image sequences. In contrast to the competing methods, we take advantage
of an oversegmentation of the reference frame and robust optimization
techniques. We formulate scene flow recovery as a global non-linear least
squares problem which is iteratively solved by a damped Gauss-Newton approach.
As a result, we obtain a qualitatively new level of accuracy in RGB-D based
scene flow estimation which can potentially run in real-time. Our method can
handle challenging cases with rigid, piecewise rigid, articulated and moderate
non-rigid motion, and does not rely on prior knowledge about the types of
motions and deformations. Extensive experiments on synthetic and real data show
that our method outperforms state-of-the-art.Comment: International Conference on 3D Vision (3DV), Qingdao, China, October
201
Multiframe Scene Flow with Piecewise Rigid Motion
We introduce a novel multiframe scene flow approach that jointly optimizes
the consistency of the patch appearances and their local rigid motions from
RGB-D image sequences. In contrast to the competing methods, we take advantage
of an oversegmentation of the reference frame and robust optimization
techniques. We formulate scene flow recovery as a global non-linear least
squares problem which is iteratively solved by a damped Gauss-Newton approach.
As a result, we obtain a qualitatively new level of accuracy in RGB-D based
scene flow estimation which can potentially run in real-time. Our method can
handle challenging cases with rigid, piecewise rigid, articulated and moderate
non-rigid motion, and does not rely on prior knowledge about the types of
motions and deformations. Extensive experiments on synthetic and real data show
that our method outperforms state-of-the-art.Comment: International Conference on 3D Vision (3DV), Qingdao, China, October
201
Interference Cancellation at the Relay for Multi-User Wireless Cooperative Networks
We study multi-user transmission and detection schemes for a multi-access
relay network (MARN) with linear constraints at all nodes. In a MARN, sources, each equipped with antennas, communicate to one
-antenna destination through one -antenna relay. A new protocol called
IC-Relay-TDMA is proposed which takes two phases. During the first phase,
symbols of different sources are transmitted concurrently to the relay. At the
relay, interference cancellation (IC) techniques, previously proposed for
systems with direct transmission, are applied to decouple the information of
different sources without decoding. During the second phase, symbols of
different sources are forwarded to the destination in a time division
multi-access (TDMA) fashion. At the destination, the maximum-likelihood (ML)
decoding is performed source-by-source. The protocol of IC-Relay-TDMA requires
the number of relay antennas no less than the number of sources, i.e., . Through outage analysis, the achievable diversity gain of the proposed
scheme is shown to be . When {\small}, the proposed scheme achieves the maximum
interference-free (int-free) diversity gain . Since concurrent
transmission is allowed during the first phase, compared to full TDMA
transmission, the proposed scheme achieves the same diversity, but with a
higher symbol rate.Comment: submitted to IEEE Transaction on Wireless Communicatio
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