Microarcsecond Radio Imaging using Earth Orbit Synthesis

The observed interstellar scintillation pattern of an intra-day variable radio source is influenced by its source structure. If the velocity of the interstellar medium responsible for the scattering is comparable to the earth's, the vector sum of these allows an observer to probe the scintillation pattern of a source in two dimensions and, in turn, to probe two-dimensional source structure on scales comparable to the angular scale of the scintillation pattern, typically $\sim 10 \mu$as for weak scattering. We review the theory on the extraction of an ``image'' from the scintillation properties of a source, and show how earth's orbital motion changes a source's observed scintillation properties during the course of a year. The imaging process, which we call Earth Orbit Synthesis, requires measurements of the statistical properties of the scintillations at epochs spread throughout the course of a year.Comment: ApJ in press. 25 pages, 7 fig

Primary Beam Shape Calibration from Mosaicked, Interferometric Observations

Image quality in mosaicked observations from interferometric radio telescopes is strongly dependent on the accuracy with which the antenna primary beam is calibrated. The next generation of radio telescope arrays such as the Allen Telescope Array (ATA) and the Square Kilometer Array (SKA) have key science goals that involve making large mosaicked observations filled with bright point sources. We present a new method for calibrating the shape of the telescope's mean primary beam that uses the multiple redundant observations of these bright sources in the mosaic. The method has an analytical solution for simple Gaussian beam shapes but can also be applied to more complex beam shapes through $\chi^2$ minimization. One major benefit of this simple, conceptually clean method is that it makes use of the science data for calibration purposes, thus saving telescope time and improving accuracy through simultaneous calibration and observation. We apply the method both to 1.43 GHz data taken during the ATA Twenty Centimeter Survey (ATATS) and to 3.14 GHz data taken during the ATA's Pi Gigahertz Sky Survey (PiGSS). We find that the beam's calculated full width at half maximum (FWHM) values are consistent with the theoretical values, the values measured by several independent methods, and the values from the simulation we use to demonstrate the effectiveness of our method on data from future telescopes such as the expanded ATA and the SKA. These results are preliminary, and can be expanded upon by fitting more complex beam shapes. We also investigate, by way of a simulation, the dependence of the accuracy of the telescope's FWHM on antenna number. We find that the uncertainty returned by our fitting method is inversely proportional to the number of antennas in the array.Comment: Accepted by PASP. 8 pages, 8 figure

The Precision Array for Probing the Epoch of Reionization: 8 Station Results

We are developing the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21cm emission from the early Universe, when the first stars and galaxies were forming. We describe the overall experiment strategy and architecture and summarize two PAPER deployments: a 4-antenna array in the low-RFI environment of Western Australia and an 8-antenna array at our prototyping site in Green Bank, WV. From these activities we report on system performance, including primary beam model verification, dependence of system gain on ambient temperature, measurements of receiver and overall system temperatures, and characterization of the RFI environment at each deployment site. We present an all-sky map synthesized between 139 MHz and 174 MHz using data from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5 steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that indicates what would be achievable with better foreground subtraction. We calculate angular power spectra ($C_\ell$) in a cold patch and determine them to be dominated by point sources, but with contributions from galactic synchrotron emission at lower radio frequencies and angular wavemodes. Although the cosmic variance of foregrounds dominates errors in these power spectra, we measure a thermal noise level of 310 mK at $\ell=100$ for a 1.46-MHz band centered at 164.5 MHz. This sensitivity level is approximately three orders of magnitude in temperature above the level of the fluctuations in 21cm emission associated with reionization.Comment: 13 pages, 14 figures, submitted to AJ. Revision 2 corrects a scaling error in the x axis of Fig. 12 that lowers the calculated power spectrum temperatur

Neoliberal Redistributive Policy: The U.S. Net Social Wage in the 21st Century

In this paper, I examine the trends of fiscal transfers between the state and workers during 1959 - 2012 to understand the net impact of redistributive policy in the United States. This paper presents original net social wage data from and analysis based on the replication and extension of Shaikh and Tonak (2002). The paper investigates the appearance of a post-2001 variation in the net social wage data. The positive net social wage in the 21st century is the result of a combination of factors including the growth of income support, healthcare inflation, neoliberal tax reforms, and macroeconomic instability. Growing economic inequality does not appear to alter the results of the net social wage methodology

Departures From Axisymmetric Morphology and Dynamics in Spiral Galaxies

New HI synthesis data have been obtained for six face-on galaxies with the Very Large Array. These data and reanalyses of three additional data sets make up a sample of nine face-on galaxies analyzed for deviations from axisymmetry in morphology and dynamics. This sample represents a subsample of galaxies already analyzed for morphological symmetry properties in the R-band. Four quantitative measures of dynamical nonaxisymmetry are compared to one another and to the quantitative measures of morphological asymmetry in HI and R-band to investigate the relationships between nonaxisymmetric morphology and dynamics. We find no significant relationship between asymmetric morphology and most of the dynamical measures in our sample. A possible relationship is found, however, between morphology and dynamical position angle differences between approaching and receding sides of the galaxy.Comment: 24 pages, 19 figures, AASTeX, accepted for publication in AJ, postscript figures available at ftp://culebra.tn.cornell.edu/pub/david/figures.tar.g

A Per-Baseline, Delay-Spectrum Technique for Accessing the 21cm Cosmic Reionization Signature

A critical challenge in measuring the power spectrum of 21cm emission from cosmic reionization is compensating for the frequency dependence of an interferometer's sampling pattern, which can cause smooth-spectrum foregrounds to appear unsmooth and degrade the separation between foregrounds and the target signal. In this paper, we present an approach to foreground removal that explicitly accounts for this frequency dependence. We apply the delay transformation introduced in Parsons & Backer (2009) to each baseline of an interferometer to concentrate smooth-spectrum foregrounds within the bounds of the maximum geometric delays physically realizable on that baseline. By focusing on delay-modes that correspond to image-domain regions beyond the horizon, we show that it is possible to avoid the bulk of smooth-spectrum foregrounds. We map the point-spread function of delay-modes to k-space, showing that delay-modes that are uncorrupted by foregrounds also represent samples of the three-dimensional power spectrum, and can be used to constrain cosmic reionization. Because it uses only spectral smoothness to differentiate foregrounds from the targeted 21cm signature, this per-baseline analysis approach relies on spectrally- and spatially-smooth instrumental responses for foreground removal. For sufficient levels of instrumental smoothness relative to interfering foregrounds, this technique substantially reduces the level of calibration previously thought necessary to detect 21cm reionization. As a result, this approach places fewer constraints on antenna configuration within an array, facilitating the adoption of configurations optimized for power-spectrum sensitivity. Under these assumptions, we demonstrate the potential for PAPER to detect 21cm reionization at an amplitude of 10 mK^2 near k~0.2h Mpc^-1 with 132 dipoles in 7 months of observing.Comment: 33 Pages, 11 figures, accepted to Ap

Implementation and engagement of the SMART Work & Life sitting reduction intervention: an exploratory analysis on intervention effectiveness

Background: To enhance the impact of interventions, it is important to understand how intervention engagement relates to study outcomes. We report on the level of implementation and engagement with the SMART Work & Life (SWAL) programme (delivered with (SWAL plus desk) and without a height-adjustable desk (SWAL)) and explore the effects of different levels of this on change in daily sitting time in comparison to the control group. Methods: The extent of intervention delivery by workplace champions and the extent of engagement by champions and participants (staff) with each intervention activity was assessed by training attendance logs, workplace champion withdrawal dates, intervention activities logs and questionnaires. These data were used to assess whether a cluster met defined criteria for low, medium, or high implementation and engagement or none of these. Mixed effects linear regression analyses tested whether change in sitting time varied by: (i) the number of intervention activities implemented and engaged with, and (ii) the percentage of implementation and engagement with all intervention strategies. Results: Workplace champions were recruited for all clusters, with 51/52 (98%) attending training. Overall, 12/27 (44.4%) SWAL and 9/25 (36.0%) SWAL plus desk clusters implemented all main intervention strategies. Across remaining clusters, the level of intervention implementation varied. Those in the SWAL (n = 8 (29.6%) clusters, 80 (32.1%) participants) and SWAL plus desk (n = 5 (20.0%) clusters, 41 (17.1%) participants) intervention groups who implemented and engaged with the most intervention strategies and had the highest percentage of cluster implementation and engagement with all intervention strategies sat for 30.9 (95% CI -53.9 to -7.9, p = 0.01) and 75.6 (95% CI -103.6 to -47.7, p < 0.001) fewer minutes/day respectively compared to the control group at 12 month follow up. These differences were larger than the complete case analysis. The differences in sitting time observed for the medium and low levels were similar to the complete case analysis. Conclusions: Most intervention strategies were delivered to some extent across the clusters although there was large variation. Superior effects for sitting reduction were seen for those intervention groups who implemented and engaged with the most intervention components and had the highest level of cluster implementation and engagement. Trial Registration: ISRCTN11618007. Registered on 24 January 2018. https://www.isrctn.com/ISRCTNISRCTN11618007