25,670 research outputs found
The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees
We describe the BOOMERANG North America (BNA) instrument, a balloon-borne
bolometric radiometer designed to map the Cosmic Microwave Background (CMB)
radiation with 0.3 deg resolution over a significant portion of the sky. This
receiver employs new technologies in bolometers, readout electronics,
millimeter-wave optics and filters, cryogenics, scan and attitude
reconstruction. All these subsystems are described in detail in this paper. The
system has been fully calibrated in flight using a variety of techniques which
are described and compared. It has been able to obtain a measurement of the
first peak in the CMB angular power spectrum in a single balloon flight, few
hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB)
experiment.Comment: 40 pages, 22 figures, submitted to Ap
Loss-resilient Coding of Texture and Depth for Free-viewpoint Video Conferencing
Free-viewpoint video conferencing allows a participant to observe the remote
3D scene from any freely chosen viewpoint. An intermediate virtual viewpoint
image is commonly synthesized using two pairs of transmitted texture and depth
maps from two neighboring captured viewpoints via depth-image-based rendering
(DIBR). To maintain high quality of synthesized images, it is imperative to
contain the adverse effects of network packet losses that may arise during
texture and depth video transmission. Towards this end, we develop an
integrated approach that exploits the representation redundancy inherent in the
multiple streamed videos a voxel in the 3D scene visible to two captured views
is sampled and coded twice in the two views. In particular, at the receiver we
first develop an error concealment strategy that adaptively blends
corresponding pixels in the two captured views during DIBR, so that pixels from
the more reliable transmitted view are weighted more heavily. We then couple it
with a sender-side optimization of reference picture selection (RPS) during
real-time video coding, so that blocks containing samples of voxels that are
visible in both views are more error-resiliently coded in one view only, given
adaptive blending will erase errors in the other view. Further, synthesized
view distortion sensitivities to texture versus depth errors are analyzed, so
that relative importance of texture and depth code blocks can be computed for
system-wide RPS optimization. Experimental results show that the proposed
scheme can outperform the use of a traditional feedback channel by up to 0.82
dB on average at 8% packet loss rate, and by as much as 3 dB for particular
frames
HARP/ACSIS: A submillimetre spectral imaging system on the James Clerk Maxwell Telescope
This paper describes a new Heterodyne Array Receiver Programme (HARP) and
Auto-Correlation Spectral Imaging System (ACSIS) that have recently been
installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The
16-element focal-plane array receiver, operating in the submillimetre from 325
to 375 GHz, offers high (three-dimensional) mapping speeds, along with
significant improvements over single-detector counterparts in calibration and
image quality. Receiver temperatures are 120 K across the whole band and
system temperatures of 300K are reached routinely under good weather
conditions. The system includes a single-sideband filter so these are SSB
figures. Used in conjunction with ACSIS, the system can produce large-scale
maps rapidly, in one or more frequency settings, at high spatial and spectral
resolution. Fully-sampled maps of size 1 square degree can be observed in under
1 hour.
The scientific need for array receivers arises from the requirement for
programmes to study samples of objects of statistically significant size, in
large-scale unbiased surveys of galactic and extra-galactic regions. Along with
morphological information, the new spectral imaging system can be used to study
the physical and chemical properties of regions of interest. Its
three-dimensional imaging capabilities are critical for research into
turbulence and dynamics. In addition, HARP/ACSIS will provide highly
complementary science programmes to wide-field continuum studies, and produce
the essential preparatory work for submillimetre interferometers such as the
SMA and ALMA.Comment: MNRAS Accepted 2009 July 2. 18 pages, 25 figures and 6 table
SARAS: a precision system for measurement of the Cosmic Radio Background and signatures from the Epoch of Reionization
SARAS is a correlation spectrometer purpose designed for precision
measurements of the cosmic radio background and faint features in the sky
spectrum at long wavelengths that arise from redshifted 21-cm from gas in the
reionization epoch. SARAS operates in the octave band 87.5-175 MHz. We present
herein the system design arguing for a complex correlation spectrometer
concept. The SARAS design concept provides a differential measurement between
the antenna temperature and that of an internal reference termination, with
measurements in switched system states allowing for cancellation of additive
contaminants from a large part of the signal flow path including the digital
spectrometer. A switched noise injection scheme provides absolute spectral
calibration. Additionally, we argue for an electrically small
frequency-independent antenna over an absorber ground. Various critical design
features that aid in avoidance of systematics and in providing calibration
products for the parametrization of other unavoidable systematics are described
and the rationale discussed. The signal flow and processing is analyzed and the
response to noise temperatures of the antenna, reference termination and
amplifiers is computed. Multi-path propagation arising from internal
reflections are considered in the analysis, which includes a harmonic series of
internal reflections. We opine that the SARAS design concept is advantageous
for precision measurement of the absolute cosmic radio background spectrum;
therefore, the design features and analysis methods presented here are expected
to serve as a basis for implementations tailored to measurements of a
multiplicity of features in the background sky at long wavelengths, which may
arise from events in the dark ages and subsequent reionization era.Comment: 49 pages, 17 figure
Study and simulation of low rate video coding schemes
The semiannual report is included. Topics covered include communication, information science, data compression, remote sensing, color mapped images, robust coding scheme for packet video, recursively indexed differential pulse code modulation, image compression technique for use on token ring networks, and joint source/channel coder design
ACBAR: The Arcminute Cosmology Bolometer Array Receiver
We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a
multifrequency millimeter-wave receiver designed for observations of the Cosmic
Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of
galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240
mK bolometer array that can be configured to observe simultaneously at 150,
220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree
azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was
installed on the 2 m Viper telescope at the South Pole in January 2001. We
describe the design of the instrument and its performance during the 2001 and
2002 observing seasons.Comment: 59 pages, 16 figures -- updated to reflect version published in ApJ
A chaotic spread spectrum system for underwater acoustic communication
The work is supported in part by NSFC (Grant no. 61172070), IRT of Shaanxi Province (2013KCT-04), EPSRC (Grant no.Ep/1032606/1).Peer reviewedPostprin
The Sunyaev-Zel'dovich Infrared Experiment: A Millimeter-wave Receiver for Cluster Cosmology
Measurements of the Sunyaev-Zel'dovich (S-Z) effect towards distant clusters
of galaxies can be used to determine the Hubble constant and the radial
component of cluster peculiar velocities. Determination of the cluster peculiar
velocity requires the separation of the two components of the S-Z effect, which
are due to the thermal and bulk velocities of the intracluster plasma. The two
components can be separated practically only at millimeter (mm) wavelengths.
Measurements of the S-Z effect at mm wavelengths are subject to minimal
astrophysical confusion and, therefore, provide an important test of results
obtained at longer wavelengths. We describe the instrument used to make the
first significant detections of the S-Z effect at millimeter wavelengths. This
instrument employs new filter, detector, and readout technologies to produce
sensitive measurements of differential sky brightness stable on long time
scales. These advances allow drift scan observations which achieve high
sensitivity while minimizing common sources of systematic error.Comment: 19 pages, 15 postscript figures, LaTeX(aaspptwo.sty), ApJ(in press
- …