115,554 research outputs found
The CFEPS Kuiper Belt Survey: Strategy and Pre-survey Results
We present the data acquisition strategy and characterization procedures for
the Canada-France Ecliptic Plane Survey (CFEPS), a sub-component of the
Canada-France-Hawaii Telescope Legacy Survey. The survey began in early 2003
and as of summer 2005 has covered 430 square degrees of sky within a few
degrees of the ecliptic. Moving objects beyond the orbit of Uranus are detected
to a magnitude limit of =23 -- 24 (depending on the image quality). To
track as large a sample as possible and avoid introducing followup bias, we
have developed a multi-epoch observing strategy that is spread over several
years. We present the evolution of the uncertainties in ephemeris position and
orbital elements as the objects progress through the epochs. We then present a
small 10-object sample that was tracked in this manner as part of a preliminary
survey starting a year before the main CFEPS project.
We describe the CFEPS survey simulator, to be released in 2006, which allows
theoretical models of the Kuiper Belt to be compared with the survey
discoveries since CFEPS has a well-documented pointing history with
characterized detection efficiencies as a function of magnitude and rate of
motion on the sky. Using the pre-survey objects we illustrate the usage of the
simulator in modeling the classical Kuiper Belt.Comment: to be submitted to Icaru
Semi-Strong Form Market Hypothesis: Evidence from CNBC\u27s Jim Cramer\u27s Mad Money Stock Recommendations
Mad Money has become one of the most popular shows on CNBC. The host, Jim Cramer, has an outlandish style and personality that viewers find intoxicating. Cramer\u27s goal for the show is to make people money. Does he succeed? This paper finds that investors can expect to gain above-average, risk adjusted returns by following Cramer\u27s stock recommendations and trading accordingly. These findings challenge the semi-strong form market hypothesis. According to this hypothesis investors should not recognize gains trading on public information since it states that the market has already adjusted prices for that information. It also contributes to current literature by providing analysis on the different segments of the Mad Money program and serving as a jumping-off point for future research on a possible Jim-Cramer-Mad-Money hedge fund strategy
Locating and quantifying gas emission sources using remotely obtained concentration data
We describe a method for detecting, locating and quantifying sources of gas
emissions to the atmosphere using remotely obtained gas concentration data; the
method is applicable to gases of environmental concern. We demonstrate its
performance using methane data collected from aircraft. Atmospheric point
concentration measurements are modelled as the sum of a spatially and
temporally smooth atmospheric background concentration, augmented by
concentrations due to local sources. We model source emission rates with a
Gaussian mixture model and use a Markov random field to represent the
atmospheric background concentration component of the measurements. A Gaussian
plume atmospheric eddy dispersion model represents gas dispersion between
sources and measurement locations. Initial point estimates of background
concentrations and source emission rates are obtained using mixed L2-L1
optimisation over a discretised grid of potential source locations. Subsequent
reversible jump Markov chain Monte Carlo inference provides estimated values
and uncertainties for the number, emission rates and locations of sources
unconstrained by a grid. Source area, atmospheric background concentrations and
other model parameters are also estimated. We investigate the performance of
the approach first using a synthetic problem, then apply the method to real
data collected from an aircraft flying over: a 1600 km^2 area containing two
landfills, then a 225 km^2 area containing a gas flare stack
Evolution of the Milky Way in Semi-Analytic Models: Detecting Cold Gas at z=3 with ALMA and SKA
We forecast the abilities of the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Square Kilometer Array (SKA) to detect CO and HI emission lines
in galaxies at redshift z=3. A particular focus is set on Milky Way (MW)
progenitors at z=3 for their detection within 24 h constitutes a key science
goal of ALMA. The analysis relies on a semi-analytic model, which permits the
construction of a MW progenitor sample by backtracking the cosmic history of
all simulated present-day galaxies similar to the real MW. Results: (i) ALMA
can best observe a MW at z=3 by looking at CO(3-2) emission. The probability of
detecting a random model MW at 3-sigma in 24 h using 75 km/s channels is
roughly 50%, and these odds can be increased by co-adding the CO(3-2) and
CO(4-3) lines. These lines fall into ALMA band 3, which therefore represents
the optimal choice towards MW detections at z=3. (ii) Higher CO transitions
contained in the ALMA bands geq6 will be invisible, unless the considered MW
progenitor coincidentally hosts a major starburst or an active black hole.
(iii) The high-frequency array of SKA, fitted with 28.8 GHz receivers, would be
a powerful instrument for observing CO(1-0) at z=3, able to detect nearly all
simulated MWs in 24 h. (iv) HI detections in MWs at z=3 using the low-frequency
array of SKA will be impossible in any reasonable observing time. (v) SKA will
nonetheless be a supreme ha survey instrument through its enormous
instantaneous field-of-view (FoV). A one year pointed HI survey with an assumed
FoV of 410 sqdeg would reveal at least 10^5 galaxies at z=2.95-3.05. (vi) If
the positions and redshifts of those galaxies are known from an
optical/infrared spectroscopic survey, stacking allows the detection of HI at
z=3 in less than 24 h.Comment: 14 pages, 5 figures, 5 table
Surveys of Galaxy Clusters with the Sunyaev Zel'dovich Effect
We have created mock Sunyaev-Zel'dovich effect (SZE) surveys of galaxy
clusters using high resolution N-body simulations. To the pure surveys we add
`noise' contributions appropriate to instrument and primary CMB anisotropies.
Applying various cluster finding strategies to these mock surveys we generate
catalogues which can be compared to the known positions and masses of the
clusters in the simulations. We thus show that the completeness and efficiency
that can be achieved depend strongly on the frequency coverage, noise and beam
characteristics of the instruments, as well as on the candidate threshold. We
study the effects of matched filtering techniques on completeness, and bias. We
suggest a gentler filtering method than matched filtering in single frequency
analyses. We summarize the complications that arise when analyzing the SZE
signal at a single frequency, and assess the limitations of such an analysis.
Our results suggest that some sophistication is required when searching for
`clusters' within an SZE map.Comment: 8 pages, 7 figure
BDGS: A Scalable Big Data Generator Suite in Big Data Benchmarking
Data generation is a key issue in big data benchmarking that aims to generate
application-specific data sets to meet the 4V requirements of big data.
Specifically, big data generators need to generate scalable data (Volume) of
different types (Variety) under controllable generation rates (Velocity) while
keeping the important characteristics of raw data (Veracity). This gives rise
to various new challenges about how we design generators efficiently and
successfully. To date, most existing techniques can only generate limited types
of data and support specific big data systems such as Hadoop. Hence we develop
a tool, called Big Data Generator Suite (BDGS), to efficiently generate
scalable big data while employing data models derived from real data to
preserve data veracity. The effectiveness of BDGS is demonstrated by developing
six data generators covering three representative data types (structured,
semi-structured and unstructured) and three data sources (text, graph, and
table data)
Astrophotonic micro-spectrographs in the era of ELTs
The next generation of Extremely Large Telescopes (ELT), with diameters up to
39 meters, will start opera- tion in the next decade and promises new
challenges in the development of instruments. The growing field of
astrophotonics (the use of photonic technologies in astronomy) can partly solve
this problem by allowing mass production of fully integrated and robust
instruments combining various optical functions, with the potential to reduce
the size, complexity and cost of instruments. In this paper, we focus on
developments in integrated micro-spectrographs and their potential for ELTs. We
take an inventory of the identified technologies currently in development, and
compare the performance of the different concepts. We show that in the current
context of single-mode instruments, integrated spectrographs making use of,
e.g., a photonic lantern can be a solution to reach the desired performance.
However, in the longer term, there is a clear need to develop multimode devices
to improve overall the throughput and sensitivity, while decreasing the
instrument complexity.Comment: 9 pages. 2 figures. Proceeding of SPIE 9147 "Ground-based and
Airborne Instrumentation for Astronomy V
High-Redshift Galaxies: Their Predicted Size and Surface Brightness Distributions and Their Gravitational Lensing Probability
Direct observations of the first generation of luminous objects will likely
become feasible over the next decade. The advent of the Next Generation Space
Telescope (NGST) will allow imaging of numerous galaxies and mini-quasars at
redshifts z>5. We apply semi-analytic models of structure formation to estimate
the rate of multiple imaging of these sources by intervening gravitational
lenses. Popular CDM models for galaxy formation yield a lensing optical depth
of about 1% for sources at redshift 10. The expected slope of the luminosity
function of the early sources implies an additional magnification bias of about
5, bringing the fraction of lensed sources at z=10 to about 5%. We estimate the
angular size distribution of high-redshift disk galaxies and find that most of
them are more extended than the resolution limit of NGST, roughly 0.06
arcseconds. We also show that there is only a modest redshift evolution in the
mean surface brightness of galaxies at z>2. The expected increase by 1-2 orders
of magnitude in the number of resolved sources on the sky, due to observations
with NGST, will dramatically improve upon the statistical significance of
existing weak lensing measurements. We show that, despite this increase in the
density of sources, confusion noise from z>2 galaxies is expected to be small
for NGST observations.Comment: 27 pages, 8 PostScript figures (of which two are new), revised
version accepted for Ap
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