We report on an effort to extract and monitor interstellar scintillation parameters in regular timing observations collected for the NANOGrav pulsar timing array. Scattering delays are measured by ...creating dynamic spectra for each pulsar and observing epoch of wide-band observations centered near 1500 MHz and carried out at the Green Bank Telescope and the Arecibo Observatory. The ~800-MHz wide frequency bands imply dramatic changes in scintillation bandwidth across the bandpass, and a stretching routine has been included to account for this scaling. For most of the 10 pulsars for which the scaling has been measured, the bandwidths scale with frequency less steeply than expected for a Kolmogorov medium. We find estimated scattering delay values that vary with time by up to an order of magnitude. The mean measured scattering delays are similar to previously published values and slightly higher than predicted by interstellar medium models. We investigate the possibility of increasing the timing precision by mitigating timing errors introduced by the scattering delays. For most of the pulsars, the uncertainty in the time of arrival of a single timing point is much larger than the maximum variation of the scattering delay, suggesting that diffractive scintillation remains only a negligible part of their noise budget.
We present time-of-arrival measurements and timing models of 47 millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American ...Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of time-of-arrival (TOA) measurements, based on "narrowband" analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. A separate set of "wideband" TOAs will be presented in a companion paper. We detail a number of methodological changes compared to our previous work which yield a cleaner and more uniformly processed data set. Our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of PSRs J1832-0836 and J2322+2057, the secular derivatives of the projected semi-major orbital axes of PSRs J0613-0200 and J2229+2643, and the first detection of the Shapiro delay in PSR J2145-0750. We report detectable levels of red noise in the time series for fourteen pulsars. As a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. We report flux density measurements for all pulsars observed. Searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications.
A cohort study with initial and 4-year follow-up evaluations was performed in 78 post-polio volunteers aged 34-65 years at the time of enrolment in the study, which was made to compare post-polio ...individuals living in Sweden and the United States, to determine whether lower limb musculature becomes weaker over time, and to determine whether individuals with complaints of post-polio syndrome, new weakness, fatigue, walking or stair climbing difficulty were weaker or lost more strength over a 4-year interval than those individuals without such complaints. Dynametrically-measured knee extensor and flexor strength and questionnaire data were obtained initially and 4 years later. The two cohorts were fairly similar, though they differed in weight gain. The Americans gained significantly (p < 0.05) more weight than the Swedish subjects. Both groups lost significant (p < 0.05) knee extensor strength (approximately 8%), but the loss was not significantly (p < 0.05) different between the groups. Knee flexor strength did not change significantly (p < 0.05) over time. Subjects acknowledging new strength loss were not significantly (p < 0.05) weaker than those denying strength loss; however, they lost significantly (p < 0.05) more isometric knee extensor strength than the other individuals. Subjects acknowledging new fatigue, walking or stair climbing difficulty were significantly (p < 0.05) weaker in both muscle groups than those without such complaints. Subjects acknowledging post-polio syndrome were significantly (p < 0.05) weaker than those denying this symptom, but the amount of loss of strength over time was not significantly (p < 0.05) different. We conclude that the two cohorts were quite similar. Knee extensor strength decreased during the study interval. Individuals acknowledging post-polio syndrome had weaker knee extensor musculature. Subjects with new fatigue, walking difficulty, or stair climbing difficulty were weaker in both the knee extensors and the knee flexors than the other subjects. Subjects reporting new muscle weakness also had a greater decline in isometric knee extensor strength during the study interval than those without such complaint.
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