Competition increases binding errors in visual working memory

When faced with maintaining multiple objects in visual working memory, item information must be bound to the correct object in order to be correctly recalled. Sometimes, however, binding errors occur, and participants report the feature (e.g., color) of an unprobed, non-target item. In the present study, we examine whether the configuration of sample stimuli affects the proportion of these binding errors. The results demonstrate that participants mistakenly report the identity of the unprobed item (i.e., they make a non-target response) when sample items are presented close together in space, suggesting that binding errors can increase independent of increases in memory load. Moreover, the proportion of these non-target responses is linearly related to the distance between sample items, suggesting that these errors are spatially specific. Finally, presenting sample items sequentially decreases non-target responses, suggesting that reducing competition between sample stimuli reduces the number of binding errors. Importantly, these effects all occurred without increases in the amount of error in the memory representation. These results suggest that competition during encoding can account for some of the binding errors made during VWM recall

Uncertain voronoi cell computation based on space decomposition

LNCS v. 9239 entitled: Advances in Spatial and Temporal Databases: 14th International Symposium, SSTD 2015 ... ProceedingsThe problem of computing Voronoi cells for spatial objects whose locations are not certain has been recently studied. In this work, we propose a new approach to compute Voronoi cells for the case of objects having rectangular uncertainty regions. Since exact computation of Voronoi cells is hard, we propose an approximate solution. The main idea of this solution is to apply hierarchical access methods for both data and object space. Our space index is used to efficiently find spatial regions which must (not) be inside a Voronoi cell. Our object index is used to efficiently identify Delauny relations, i.e., data objects which affect the shape of a Voronoi cell. We develop three algorithms to explore index structures and show that the approach that descends both index structures in parallel yields fast query processing times. Our experiments show that we are able to approximate uncertain Voronoi cells much more effectively than the state-of-the-art, and at the same time, improve run-time performance.postprin

The SKA Particle Array Prototype: The First Particle Detector at the Murchison Radio-astronomy Observatory

We report on the design, deployment, and first results from a scintillation detector deployed at the Murchison Radio-astronomy Observatory (MRO). The detector is a prototype for a larger array -- the Square Kilometre Array Particle Array (SKAPA) -- planned to allow the radio-detection of cosmic rays with the Murchison Widefield Array and the low-frequency component of the Square Kilometre Array. The prototype design has been driven by stringent limits on radio emissions at the MRO, and to ensure survivability in a desert environment. Using data taken from Nov.\ 2018 to Feb.\ 2019, we characterize the detector response while accounting for the effects of temperature fluctuations, and calibrate the sensitivity of the prototype detector to through-going muons. This verifies the feasibility of cosmic ray detection at the MRO. We then estimate the required parameters of a planned array of eight such detectors to be used to trigger radio observations by the Murchison Widefield Array.Comment: 17 pages, 14 figures, 3 table

Interferometric imaging with the 32 element Murchison Wide-field Array

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.Comment: Accepted for publication in PASP. This is the draft before journal typesetting corrections and proofs so does contain formatting and journal style errors, also has with lower quality figures for space requirement

Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array

We apply two methods to estimate the 21~cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly-spaced triangles of antenna tiles, as well as an estimate based on data gridded to the $uv$-plane. The direct and gridded bispectrum estimators are applied to 21 hours of high-band (167--197~MHz; $z$=6.2--7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 hours, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21~cm bispectrum may be accessible in less time than the 21~cm power spectrum for some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS

Nuclear Cryogenic Propulsion Stage for Mars Exploration

The fundamental capability of Nuclear Thermal Propulsion (NTP) is game changing for space exploration. A first generation Nuclear Cryogenic Propulsion Stage (NCPS) based on NTP could provide high thrust at a specific impulse above 900 s, roughly double that of state of the art chemical engines. Characteristics of fission and NTP indicate that useful first generation systems will provide a foundation for future systems with extremely high performance. The role of the NCPS in the development of advanced nuclear propulsion systems could be analogous to the role of the DC-3 in the development of advanced aviation. Progress made under the NCPS project could help enable both advanced NTP and advanced Nuclear Electric Propulsion (NEP)

The Murchison Widefield Array

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.Comment: Accepted for publication in Proceedings of Science [PoS(RFI2010)016]. 6 pages and 3 figures. Presented at RFI2010, the Third Workshop on RFI Mitigation in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland

A new layout optimization technique for interferometric arrays, applied to the MWA

Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21 cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed---even at the remote Australian location of the MWA (Murchison Widefield Array) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhance the PSF sidelobes and reduce the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution, and snapshot PSF for this array choice.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in MNRA

WSClean : an implementation of a fast, generic wide-field imager for radio astronomy

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Astronomical widefield imaging of interferometric radio data is computationally expensive, especially for the large data volumes created by modern non-coplanar many-element arrays. We present a new widefield interferometric imager that uses the w-stacking algorithm and can make use of the w-snapshot algorithm. The performance dependencies of CASA's w-projection and our new imager are analysed and analytical functions are derived that describe the required computing cost for both imagers. On data from the Murchison Widefield Array, we find our new method to be an order of magnitude faster than w-projection, as well as being capable of full-sky imaging at full resolution and with correct polarisation correction. We predict the computing costs for several other arrays and estimate that our imager is a factor of 2-12 faster, depending on the array configuration. We estimate the computing cost for imaging the low-frequency Square-Kilometre Array observations to be 60 PetaFLOPS with current techniques. We find that combining w-stacking with the w-snapshot algorithm does not significantly improve computing requirements over pure w-stacking. The source code of our new imager is publicly released.Peer reviewedFinal Published versio