16 research outputs found
The Hydrogen Epoch of Reionization Array Dish II: Characterization of Spectral Structure with Electromagnetic Simulations and its science Implications
We use time-domain electromagnetic simulations to determine the spectral
characteristics of the Hydrogen Epoch of Reionization Arrays (HERA) antenna.
These simulations are part of a multi-faceted campaign to determine the
effectiveness of the dish's design for obtaining a detection of redshifted 21
cm emission from the epoch of reionization. Our simulations show the existence
of reflections between HERA's suspended feed and its parabolic dish reflector
that fall below -40 dB at 150 ns and, for reasonable impedance matches, have a
negligible impact on HERA's ability to constrain EoR parameters. It follows
that despite the reflections they introduce, dishes are effective for
increasing the sensitivity of EoR experiments at relatively low cost. We find
that electromagnetic resonances in the HERA feed's cylindrical skirt, which is
intended to reduce cross coupling and beam ellipticity, introduces significant
power at large delays ( dB at 200 ns) which can lead to some loss of
measurable Fourier modes and a modest reduction in sensitivity. Even in the
presence of this structure, we find that the spectral response of the antenna
is sufficiently smooth for delay filtering to contain foreground emission at
line-of-sight wave numbers below Mpc, in
the region where the current PAPER experiment operates. Incorporating these
results into a Fisher Matrix analysis, we find that the spectral structure
observed in our simulations has only a small effect on the tight constraints
HERA can achieve on parameters associated with the astrophysics of
reionization.Comment: Accepted to ApJ, 18 pages, 17 Figures. Replacement matches accepted
manuscrip
The Hydrogen Epoch of Reionization Array Dish I: Beam Pattern Measurements and Science Implications
The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer
aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen
from the Epoch of Reionization (EOR). Drawing on lessons from the Murchison
Widefield Array (MWA) and the Precision Array for Probing the Epoch of
Reionization (PAPER), HERA is a hexagonal array of large (14 m diameter) dishes
with suspended dipole feeds. Not only does the dish determine overall
sensitivity, it affects the observed frequency structure of foregrounds in the
interferometer. This is the first of a series of four papers characterizing the
frequency and angular response of the dish with simulations and measurements.
We focus in this paper on the angular response (i.e., power pattern), which
sets the relative weighting between sky regions of high and low delay, and
thus, apparent source frequency structure. We measure the angular response at
137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a
collecting area of 93 m^2 in the optimal dish/feed configuration, implying
HERA-320 should detect the EOR power spectrum at z~9 with a signal-to-noise
ratio of 12.7 using a foreground avoidance approach with a single season of
observations, and 74.3 using a foreground subtraction approach. Lastly we study
the impact of these beam measurements on the distribution of foregrounds in
Fourier space.Comment: 13 pages, 9 figures. Replaced to match accepted ApJ versio
Prediction of crossover in the molecular weight dependence of polyethylene viscosity using a polymer free volume theory
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THE HYDROGEN EPOCH OF REIONIZATION ARRAY DISH. II. CHARACTERIZATION OF SPECTRAL STRUCTURE WITH ELECTROMAGNETIC SIMULATIONS AND ITS SCIENCE IMPLICATIONS
Molecular Dynamics Study of the Adsorption Behavior of Normal Alkanes on a Relaxed α-Al 2
Proteome Databases
The awareness that protein and DNA sequence data are essential to the understanding of biological systems is now well established in the life science community. This community is progressively becoming conscious that this is also true of additional information about protein expression, post-translational modifications, tertiary structure and, of course, function. All of this knowledge needs to be encapsulated in various databases. The goal of this chapter is to describe the data resources that are available to researchers working in the field of proteome studies. We will not attempt here to survey all the different databases that are relevant to this field. Such an exercise would be tedious due to the large number of relevant databases and would only be valid for a very short period of time due to the extreme speed with which new databases are appearing and/or disappearing. It is also for this reason that you will find a table at the end of this chapter (Table 5.l) listing the World-Wide Web (WWW) addresses of the databases described in the following sections. The most important component of this table is the Internet address that allows you to download an upto- date version of the table! We will successively describe the type of information found in the following types of databases: protein sequence, nucleotide sequence, pattern/profile, 2-D PAGE, 3-D structure, post-translational modification, genomic and metabolic. The last section of this chapter will try to predict future trends in the evolution of protein information resources