We report on the MIT Epoch of Reionization (MITEoR) experiment, a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce ...the cost of the high-sensitivity 3D mapping required for 21 cm cosmology. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction. We demonstrate and quantify the power and robustness of redundancy for scalability and precision. We find that the calibration parameters precisely describe the effect of the instrument upon our measurements, allowing us to form a model that is consistent with X2 per degree of freedom <1.2 for as much as 80 per cent of the observations. We use these results to develop an optimal estimator of calibration parameters using Wiener filtering, and explore the question of how often and how finely in frequency visibilities must be reliably measured to solve for calibration coefficients. The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious Hydrogen Epoch of Reionization Array project and other next-generation instruments, which would incorporate many identical or similar technologies.
The Murchison Widefield Array is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations but ...is initially focused on three key science projects: detection and characterization of three-dimensional brightness temperature fluctuations in the 21 cm line of neutral hydrogen during the epoch of reionization (EoR) at redshifts from six to ten; solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources; and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broadband active dipoles, arranged into 512 ldquotilesrdquo comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5 km in diameter, with a small number of outliers extending to 3 km. All tile-tile baselines are correlated in custom field-programmable gate array based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment, allowing full exploitation of the instrumental capabilities.
The study was aimed at evaluating the effects of music on selected physiological responses of 100 in-patients (72 men and 28 women), aged 20 to 60 years, awaiting non-orthopedic surgery. Patients ...were randomly assigned to two groups (50 patients per group); control (C) and music listening (M). In the morning of the day preceding surgery, the first measures (arterial pressure, heart rate, cardiac output, skin temperature, and glucose count) and blood samples were taken. The patient was then told about the surgical procedure. Subsequent measures and blood samples were taken every 20 minutes for a total period of 1 hr. During this time, patients in Group M listened to individually composed music programs from Walkman-type tape players. Information about surgical procedure proved to be a potent stressor as evidenced by highly significant (p < 0.001) percent changes in arterial pressure (systolic—by 6.6%, diastolic— 5.7%, and mean pressure—6.2%), heart rate (15.7%), cardiac output (14.0%), skin temperature (2.3%), and glucose (24.2%). At the end of the 1 hr period, mean values for all variables returned to initial values for patients in the music listening group, while values for the control group remained at about the stressor-induced levels. The total non-invasiveness of music listening makes this method of reducing pre-operative stress particularly attractive.
This paper summarizes modifications made to the Salem Generating Station’s (Salem) Circulating Water Traveling Screens (CWTS) as required by Salem’s New Jersey Pollutant Discharge Elimination System ...Permit (NJPDES Permit). The modifications incorporated newly designed CWTS baskets with hydrodynamically improved fish buckets (greatly reduced turbulence in the bucket); smooth woven mesh screens with 0.250×0.500 inch rectangular mesh openings (formerly 0.375 inch square mesh openings); lighter composite basket frame material allowing increased screen rotation speed; improved low and high pressure spray wash patterns; improved screen to sluice trough flap seal design and miscellaneous reliability improvements. In order to address the overall effects of the CWTS modifications on fish losses, the effect of both entrainment and impingement by fish size was addressed in a comparison study between modified and unmodified units. The results of the assessment indicate a 51% reduction in overall weakfish (
Cynoscion regalis) losses expressed as equivalent adults (larger than 187 mm total length individuals). These modifications also enhanced debris removal capability of the CWTS.
The therapeutic influence of Budesonide in 51 patients with pollen allergy were described. The preparation improved the symptoms after 2 weeks of therapy. The side effects were absent.
The Murchison Wide-field Array (MWA) is a low frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of re-ionisation (EOR) and to probe ...the structure of the solar corona. Sited in Western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles, and be capable of imaging the sky south of 40 degree declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32-station prototype of the MWA has been recently commissioned and a set of observations taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hour integrations of a field 20 degrees wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide field imaging distortions.
The Murchison Widefield Array Mitchell, Daniel A; Greenhill, Lincoln J; Ord, Stephen M ...
arXiv (Cornell University),
08/2010
Paper, Journal Article
Odprti dostop
It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images ...in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky.
In typical astrophysical environments, the abundance of heavy elements ranges from 0.001 to 2 times the solar value. Lower abundances have been seen in selected stars in the Milky Way's halo and in ...two quasar absorption systems at redshift z = 3 (ref. 4). These are widely interpreted as relics from the early Universe, when all gas possessed a primordial chemistry. Before now there have been no direct abundance measurements from the first billion years after the Big Bang, when the earliest stars began synthesizing elements. Here we report observations of hydrogen and heavy-element absorption in a spectrum of a quasar at z = 7.04, when the Universe was just 772 million years old (5.6 per cent of its present age). We detect a large column of neutral hydrogen but no corresponding metals (defined as elements heavier than helium), limiting the chemical abundance to less than 1/10,000 times the solar level if the gas is in a gravitationally bound proto-galaxy, or to less than 1/1,000 times the solar value if it is diffuse and unbound. If the absorption is truly intergalactic, it would imply that the Universe was neither ionized by starlight nor chemically enriched in this neighbourhood at z ≈ 7. If it is gravitationally bound, the inferred abundance is too low to promote efficient cooling, and the system would be a viable site to form the predicted but as yet unobserved massive population III stars.
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