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We describe the successful design, implementation, and operation of a 12 GHz holography system installed on the Robert C. Byrd Green Bank Telescope (GBT). We have used a geostationary satellite beacon to construct high-resolution holographic images of the telescope mirror surface irregularities. These images have allowed us to infer and apply improved position offsets for the 2209 actuators which control the active surface of the primary mirror, thereby achieving a dramatic reduction in the total surface error (from 390 μm to∼240 μm ∼ 240     μ m , rms). We have also performed manual adjustments of the corner offsets for a few panels. The expected improvement in the radiometric aperture efficiency has been rigorously modeled and confirmed at 43 GHz and 90 GHz. The improvement in the telescope beam pattern has also been measured at 11.7 GHz with greater than 60 dB of dynamic range. Symmetric features in the beam pattern have emerged which are consistent with a repetitive pattern in the aperture due to systematic panel distortions. By computing average images for each tier of panels from the holography images, we confirm that the magnitude and direction of the panel distortions, in response to the combination of gravity and thermal gradients, are in general agreement with finite-element model predictions. The holography system is now fully integrated into the GBT control system, and by enabling the telescope staff to monitor the health of the individual actuators, it continues to be an essential tool to support high-frequency observations.

Wind-induced pointing errors are a serious concern for large-aperture high-frequency radio telescopes. In this paper, we describe the implementation of an optical quadrant detector instrument that can detect and provide a correction signal for wind-induced pointing errors on the 100 m diameter Green Bank Telescope (GBT). The instrument was calibrated using a combination of astronomical measurements and metrology. We find that the main wind-induced pointing errors on timescales of minutes are caused by the feed arm being blown along the direction of the wind vector. We also find that wind-induced structural excitation is virtually nonexistent. We have implemented offline software to apply pointing corrections to the data from imaging instruments such as the MUSTANG 3.3 mm bolometer array, which can recover∼70% ∼ 70 % of sensitivity lost due to wind-induced pointing errors. We have also performed preliminary tests that show great promise for correcting these pointing errors in real time using the telescope’s subreflector servo system in combination with the quadrant detector signal.

Radio Frequency Interference (RFI) greatly reduces sensitivity of radio observations to astrophysical signals and creates false positive candidates in searches for radio transients. Real signals are missed while considerable computational and human resources are needed to remove RFI candidates. In the context of transient astrophysics, this makes effective RFI removal vital to effective searches for fast radio bursts and pulsars. Radio telescopes typically sample at rates that are high enough for there to be tens to hundreds of samples along the transient's pulse. Mitigation techniques should excise RFI on this timescale to account for a changing radio frequency environment. We evaluate the effectiveness of three filters, as well as a composite of the three, that excises RFI at the cadence that the data are recorded. Each of these filters operates in a different domain and thus excises as a different RFI morphology. We analyze the performance of these four filters in three different situations: (I) synthetic pulses in Gaussian noise; (II) synthetic pulses injected into real data; (III) four pulsar observations. From these tests, we gain insight into how the filters affect both the pulse and the noise level. This allows use to outline which and how the filters should be used based on the RFI present and the characteristics of the source signal. We show by flagging a small percentage of the spectrum we can substantially improve the quality of transit observations.

We describe GBTrans, a real-time search system designed to find fast radio bursts (FRBs) using the 20-m radio telescope at the Green Bank Observatory. The telescope has been part of the Skynet educational program since 2015. We give details of the observing system and report on the non-detection of FRBs from a total observing time of 503 days. Single pulses from four known pulsars were detected as part of the commensal observing. The system is sensitive enough to detect approximately half of all currently known FRBs and we estimate that our survey probed redshifts out to about 0.3 corresponding to an effective survey volume of around 124,000~Mpc\\(^3\\). Modeling the FRB rate as a function of fluence, \\(F\\), as a power law with \\(F^{-\\alpha}\\), we constrain the index \\(\\alpha < 2.5\\) at the 90% confidence level. We discuss the implications of this result in the context of constraints from other FRB surveys.

The General Single-Dish Data format (GSDD) was developed in the mid-1980s as a data model to support centimeter, millimeter and submillimeter instrumentation at NRAO, JCMT, the University of Arizona and IRAM. We provide an overview of the GSDD requirements and associated data model, discuss the implementation of the resultant file formats, describe its usage in the observatories and provide a retrospective on the format.

The Graphics Processing Unit (GPU) has become an integral part of astronomical instrumentation, enabling high-performance online data reduction and accelerated online signal processing. In this paper, we describe a wide-band reconfigurable spectrometer built using an off-the-shelf GPU card. This spectrometer, when configured as a polyphase filter bank (PFB), supports a dual-polarization bandwidth of up to 1.1 GHz (or a single-polarization bandwidth of up to 2.2 GHz) on the latest generation of GPUs. On the other hand, when configured as a direct FFT, the spectrometer supports a dual-polarization bandwidth of up to 1.4 GHz (or a single-polarization bandwidth of up to 2.8 GHz).

Wind-induced pointing errors are a serious concern for large-aperture high-frequency radio telescopes. In this paper, we describe the implementation of an optical quadrant detector instrument that can detect and provide a correction signal for wind-induced pointing errors on the 100m diameter Green Bank Telescope (GBT). The instrument was calibrated using a combination of astronomical measurements and metrology. We find that the main wind-induced pointing errors on time scales of minutes are caused by the feedarm being blown along the direction of the wind vector. We also find that wind-induced structural excitation is virtually non-existent. We have implemented offline software to apply pointing corrections to the data from imaging instruments such as the MUSTANG 3.3 mm bolometer array, which can recover ~70% of sensitivity lost due to wind-induced pointing errors. We have also performed preliminary tests that show great promise for correcting these pointing errors in real-time using the telescope's subreflector servo system in combination with the quadrant detector signal.

We describe the successful design, implementation, and operation of a 12 GHz holography system installed on the Robert C. Byrd Green Bank Telescope (GBT). We have used a geostationary satellite beacon to construct high-resolution holographic images of the telescope mirror surface irregularities. These images have allowed us to infer and apply improved position offsets for the 2209 actuators which control the active surface of the primary mirror, thereby achieving a dramatic reduction in the total surface error (from 390 microns to ~240 microns, rms). We have also performed manual adjustments of the corner offsets for a few panels. The expected improvement in the radiometric aperture efficiency has been rigorously modeled and confirmed at 43 GHz and 90 GHz. The improvement in the telescope beam pattern has also been measured at 11.7 GHz with greater than 60 dB of dynamic range. Symmetric features in the beam pattern have emerged which are consistent with a repetitive pattern in the aperture due to systematic panel distortions. By computing average images for each tier of panels from the holography images, we confirm that the magnitude and direction of the panel distortions, in response to the combination of gravity and thermal gradients, are in general agreement with finite-element model predictions. The holography system is now fully integrated into the GBT control system, and by enabling the telescope staff to monitor the health of the individual actuators, it continues to be an essential tool to support high-frequency observations.

Determine the acceptability and epidemiological impact of increases in HIV testing in gay men in New South Wales (NSW), Australia- particularly pertinent when considering treatment as prevention and the need to reduce undiagnosed infections. We conducted an online survey and focus groups to assess whether increases in HIV testing would be acceptable to gay men in NSW. In parallel, we assessed the potential impact of increases in testing coverage and/or frequency using an individual-based model of HIV transmission. If sexual practices and the rate of initiating HIV treatment are unchanged then increasing HIV testing reduces infections. Increasing testing frequency has the largest impact, with a 13.8% reduction in HIV infections over 10 years if the ∼55-75% of men who test at least once per year increased their testing frequency to four times per year. If testing levels decrease from current levels then we expect an increase in HIV infections with a sharply rising trend over time. Increasing HIV testing would be acceptable if testing was more convenient. However, only ∼25% of men surveyed were 'very likely' to increase their level of HIV testing. Men delayed or avoided testing due to the slowness in obtaining results and if they believed they had not put themselves at risk. An increase in HIV testing alone is unlikely to reduce HIV incidence substantially in NSW gay men- however, the relatively high testing levels need to continue to prevent an increase in HIV infections. In jurisdictions with lower levels of HIV testing, increases in testing coverage and frequency are likely to have a larger impact. Successful treatment as prevention interventions will require increases in testing rates; such increases would be acceptable to gay men in NSW but only if more convenient testing and rapid communication of results were available.

Condoms continue to be used by many gay, bisexual, and other men who have sex with men (GBM) to reduce the risk of HIV transmission. However this is impacted by condom failure events, defined here as condom breakage and slippage. In a prospective, observational cohort study of 343 HIV serodiscordant male couples recruited through high HIV caseload clinics and hospitals between 2012 and 2016 in Australia, Brazil, and Thailand, condom failure rates and associated factors were analysed, including with the study partner versus other sexual partners. There were 717 reported instances of condom failure from an estimated total of 25,831 sex acts with condoms, from over 588.4 participant years of follow up. Of the HIV-negative partners (n = 343) in the study, more than a third (n = 117, 36.7%) reported at least one instance of condom failure with any partner type during study follow-up. Condom failure with their study partner was reported by 91/343 (26.5%) HIV-negative partners, compared with 43/343 (12.5%) who reported condom failure with other partners. In total, there were 86 events where the HIV-negative partner experienced ano-receptive condom failure with ejaculation, representing 12.0% of all failure events. In multivariable analysis, compared to Australia, HIV-negative men in Brazil reported a higher incidence risk rate of condom failure (IRR = 1.64, 95%CI 1.01–2.68, p = 0.046) and HIV-negative men who reported anal sex with other partners reported an increased risk of condom failure compared with men who only had sex with their study partner (IRR = 1.89, 95%CI 1.08–3.33, p = 0.025). Although at least one event of condom failure was reported by a significant proportion of participants, overall condom failure events represented a small proportion of the total condom protected sex acts.