172 research outputs found
MEMS practice, from the lab to the telescope
Micro-electro-mechanical systems (MEMS) technology can provide for deformable
mirrors (DMs) with excellent performance within a favorable economy of scale.
Large MEMS-based astronomical adaptive optics (AO) systems such as the Gemini
Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our
decade of practice with the micromirrors, from inspecting and characterizing
devices to evaluating their performance in the lab. We also show MEMS wavefront
correction on-sky with the "Villages" AO system on a 1-m telescope, including
open-loop control and visible-light imaging. Our work demonstrates the maturity
of MEMS technology for astronomical adaptive optics.Comment: 14 pages, 15 figures, Invited Paper, SPIE Photonics West 201
Automatic Detection of Reflective Thinking in Mathematical Problem Solving based on Unconstrained Bodily Exploration
For technology (like serious games) that aims to deliver interactive learning, it is important to address relevant mental experiences such as reflective thinking during problem solving. To facilitate research in this direction, we present the weDraw-1 Movement Dataset of body movement sensor data and reflective thinking labels for 26 children solving mathematical problems in unconstrained settings where the body (full or parts) was required to explore these problems. Further, we provide qualitative analysis of behaviours that observers used in identifying reflective thinking moments in these sessions. The body movement cues from our compilation informed features that lead to average F1 score of 0.73 for binary classification of problem-solving episodes by reflective thinking based on Long Short-Term Memory neural networks. We further obtained 0.79 average F1 score for end-to-end classification, i.e. based on raw sensor data. Finally, the algorithms resulted in 0.64 average F1 score for subsegments of these episodes as short as 4 seconds. Overall, our results show the possibility of detecting reflective thinking moments from body movement behaviours of a child exploring mathematical concepts bodily, such as within serious game play
What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization
A number of experiments are currently working towards a measurement of the 21
cm signal from the Epoch of Reionization. Whether or not these experiments
deliver a detection of cosmological emission, their limited sensitivity will
prevent them from providing detailed information about the astrophysics of
reionization. In this work, we consider what types of measurements will be
enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the
type of constraints that will be possible with such arrays, we use simple
models for the instrument, foreground emission, and the reionization history.
We focus primarily on an instrument modeled after the
collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and
parameterize the uncertainties with regard to foreground emission by
considering different limits to the recently described "wedge" footprint in
k-space. Uncertainties in the reionization history are accounted for using a
series of simulations which vary the ionizing efficiency and minimum virial
temperature of the galaxies responsible for reionization, as well as the mean
free path of ionizing photons through the IGM. Given various combinations of
models, we consider the significance of the possible power spectrum detections,
the ability to trace the power spectrum evolution versus redshift, the
detectability of salient power spectrum features, and the achievable level of
quantitative constraints on astrophysical parameters. Ultimately, we find that
of collecting area is enough to ensure a very high significance
() detection of the reionization power spectrum in even the
most pessimistic scenarios. This sensitivity should allow for meaningful
constraints on the reionization history and astrophysical parameters,
especially if foreground subtraction techniques can be improved and
successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi
Mapmaking for Precision 21 cm Cosmology
In order to study the "Cosmic Dawn" and the Epoch of Reionization with 21 cm
tomography, we need to statistically separate the cosmological signal from
foregrounds known to be orders of magnitude brighter. Over the last few years,
we have learned much about the role our telescopes play in creating a
putatively foreground-free region called the "EoR window." In this work, we
examine how an interferometer's effects can be taken into account in a way that
allows for the rigorous estimation of 21 cm power spectra from interferometric
maps while mitigating foreground contamination and thus increasing sensitivity.
This requires a precise understanding of the statistical relationship between
the maps we make and the underlying true sky. While some of these calculations
would be computationally infeasible if performed exactly, we explore several
well-controlled approximations that make mapmaking and the calculation of map
statistics much faster, especially for compact and highly redundant
interferometers designed specifically for 21 cm cosmology. We demonstrate the
utility of these methods and the parametrized trade-offs between accuracy and
speed using one such telescope, the upcoming Hydrogen Epoch of Reionization
Array, as a case study.Comment: 28 pages, 14 figures. Slightly revised to match published Physical
Review D versio
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
Mapping our Universe in 3D with MITEoR
Mapping our universe in 3D by imaging the redshifted 21 cm line from neutral
hydrogen has the potential to overtake the cosmic microwave background as our
most powerful cosmological probe, because it can map a much larger volume of
our Universe, shedding new light on the epoch of reionization, inflation, dark
matter, dark energy, and neutrino masses. We report on MITEoR, a pathfinder
low-frequency radio interferometer whose goal is to test technologies that
greatly reduce the cost of such 3D mapping for a given sensitivity. MITEoR
accomplishes this by using massive baseline redundancy both to enable automated
precision calibration and to cut the correlator cost scaling from N^2 to NlogN,
where N is the number of antennas. The success of MITEoR with its 64
dual-polarization elements bodes well for the more ambitious HERA project,
which would incorporate many identical or similar technologies using an order
of magnitude more antennas, each with dramatically larger collecting area.Comment: To be published in proceedings of 2013 IEEE International Symposium
on Phased Array Systems & Technolog
Mapmaking for precision 21 cm cosmology
In order to study the “Cosmic Dawn” and the Epoch of Reionization with 21 cm tomography, we need to statistically separate the cosmological signal from foregrounds known to be orders of magnitude brighter. Over the last few years, we have learned much about the role our telescopes play in creating a putatively foreground-free region called the “EoR window.” In this work, we examine how an interferometer’s effects can be taken into account in a way that allows for the rigorous estimation of 21 cm power spectra from interferometric maps while mitigating foreground contamination and thus increasing sensitivity. This requires a precise understanding of the statistical relationship between the maps we make and the underlying true sky. While some of these calculations would be computationally infeasible if performed exactly, we explore several well-controlled approximations that make mapmaking and the calculation of map statistics much faster, especially for compact and highly redundant interferometers designed specifically for 21 cm cosmology. We demonstrate the utility of these methods and the parametrized trade-offs between accuracy and speed using one such telescope, the upcoming Hydrogen Epoch of Reionization Array, as a case study.National Science Foundation (U.S.) (Grant AST-0457585)National Science Foundation (U.S.) (Grant AST-0821321)National Science Foundation (U.S.) (Grant AST-0804508)National Science Foundation (U.S.) (Grant AST-1105835)National Science Foundation (U.S.) (Grant AST-1125558)National Science Foundation (U.S.) (Grant AST-1129258)National Science Foundation (U.S.) (Grant AST-1410484)National Science Foundation (U.S.) (Grant AST-1411622)Mount Cuba Astronomical AssociationMIT School of ScienceMarble Astrophysics Fun
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