No abstract available

[en] The Digital Imaging Network (DIN) Project is a collaborative effort involving the Department of Defense, Public Health Service, Veterans Administration, MITRE Corporation, university medical centers, and private industry. The objectives are to install, operate, and evaluate two different prototype DIN/picture archiving and communication systems (PACS), and to develop guidelines and specifications for operational DIN/PACS in military and civilian settings. The evaluation emphasizes clinical acceptance and utility, technical and operational feasibility, and impact on radiology department function and the clinical care process. New imaging devices being developed for combat use are evaluated to ensure compatibility with future DIN/PACS

[en] The Center for Devices and Radiological Health of the Johns Hopkins University Hospital and Applied Physics Laboratory, several DOD components, and the Veterans Administration are developing and evaluating prototype low-cost radiology reporting systems that incorporate the latest in flat screen color graphics display, microprocessing controls, and speech recognition technology. Reports generated by the prototype systems are available immediately. Tri-Services Medical Information Systems (TRIMIS) participation promotes compatibility with radiology information systems. Starting in the fall of 1986, prototype systems will be evaluated clinically at Army and Navy hospitals (with Air Force participation) and the VA Hospital in the Washington, D.C., area and at Johns Hopkins Hospital

[en] We assess the detectability of a nanohertz gravitational wave (GW) background in a pulsar timing array (PTA) program by considering the shape and amplitude of the cross-correlation function summed over pulsar pairs. The distribution of correlation amplitudes is found to be non-Gaussian and highly skewed, which significantly influences detection and false-alarm probabilities. When only white noise combines with GWs in timing data, our detection results are consistent with those found by others. Contamination by red noise from spin variations and from any uncorrected interstellar plasma effects significantly increases the false-alarm probability. The number of arrival times (and thus the observing cadence) is important only as long as the residuals are dominated by white noise. When red noise and GWs dominate, the statistical significance of the correlation estimate can be improved only by increasing the number of pulsars. We characterize plausible detection regimes by evaluating the number of millisecond pulsars (MSPs) that must be monitored in a high-cadence, five-year timing program to detect a GW background spectrum h_c (f) = A(f/f₀)^–2/3 with f₀ = 1 yr^–1 and A = 10^–15. Our results indicate that a sample of 20 super-stable MSPs—those with rms timing residuals σ_r ∼< 20 ns(A/10^–15) from red-noise contributions over a five-year span—will allow detection of the GW background and study of its spectrum. However, a timing program on ∼> 50-100 MSPs is likely needed for a complete PTA program, particularly if red noise is generally present in MSPs.

[en] We report a numerical analysis of the scattered light from within the field of view of an eLISA-like full-duplex telescope and, by comparison to a nominal allowable scattered light specification, we place constraints on the permissible mirror surface roughness and contamination levels of the mirrors. Our analysis was performed with commercially available stray light software, typically used in non-interferometric imaging telescopes and we do not include polarization or coherent effects. This work therefore represents the early steps towards a more complete understanding of the scattered light budget. (paper)

[en] We have searched a sample of 151 young, energetic pulsars for periodic variation in pulse time-of-arrival arising from the influence of planetary companions. We are sensitive to objects with masses two orders of magnitude lower than those detectable with optical transit timing, but we find no compelling evidence for pulsar planets. For the older pulsars most likely to host planets, we can rule out Mercury analogs in one third of our sample and planets with masses >0.4 M_⨁ and periods $P_b<<!--\; <\; -->1$ year in all but 5% of such systems. If pulsar planets form primarily from supernova fallback disks, these limits imply that such disks do not form, are confined to <0.1 AU radii, are disrupted, or form planets more slowly (>2 Myr) than their protoplanetary counterparts.

[en] We have detected sporadic, bright, short-duration radio pulses from PSR J0901–4624. These pulses are emitted simultaneously with persistent, periodic emission that dominates the flux density when averaging over many periods of the pulsar. The bright pulses have energies that are consistent with a power-law distribution. The integrated profile of PSR J0901–4624 is highly polarized and shows four distinct components. The bright pulses appear to originate near the magnetic pole of the pulsar and have polarization properties unlike those of the underlying emission at the same pulse phase. We conclude that the bright pulses represent a secondary giant-micropulse emission process, possibly from a different region in the pulsar magnetosphere

[en] In this work, we document the first complete alignment of a subscale prototype telescope for the LISA mission. An optical wavefront error map, which meets current mission requirements, was attained using alignment techniques consistent with production of multiple identical copies of a telescope for flight. We find that the telescope wavefront error is dominated by the as-built surface figure error of the mirrors and not the residual design wavefront error of the telescope prescription. Furthermore, this work shows the ability to implement a wavefront error allocation specific to the LISA telescope, lending confidence to such allocations for future flight telescopes, and provides a verified reference point for ongoing research into many aspects of the LISA optical system. (paper)

[en] We have constructed timing solutions for 81 γ-ray pulsars covering more than five years of Fermi data. The sample includes 37 radio-quiet or radio-faint pulsars which cannot be timed with other telescopes. These timing solutions and the corresponding pulse times of arrival are prerequisites for further study, e.g., phase-resolved spectroscopy or searches for mode switches. Many γ-ray pulsars are strongly affected by timing noise (TN), and we present a new method for characterizing the noise process and mitigating its effects on other facets of the timing model. We present an analysis of TN over the population using a new metric for characterizing its strength and spectral shape, namely, its time-domain correlation. The dependence of the strength on ν and $\stackrel{\dot{}<!--\; ??\; -->}{\mathrm{\nu <!--\; ??\; -->}}$ is in good agreement with previous studies. We find that noise process power spectra S(f) for unrecycled pulsars are steep, with strong correlations over our entire data set and spectral indices $S(f)\propto <!--\; ???\; -->f^{-<!--\; ???\; -->\mathrm{\alpha <!--\; ??\; -->}}$ of α ∼ 5–9. One possible explanation for these results is the occurrence of unmodeled, episodic “microglitches.” Finally, we show that our treatment of TN results in robust parameter estimation, and in particular we measure a precise timing position for each pulsar. We extensively validate our results with multi-wavelength astrometry, and using our updated position, we firmly identify the X-ray counterpart of PSR J1418−6058.

[en] Fast radio bursts (FRB) are millisecond-duration radio pulses with apparent extragalactic origins. All but two of the FRBs have been discovered using the Parkes dish, which employs multiple beams formed by an array of feed horns on its focal plane. In this paper, we show that (i) the preponderance of multiple-beam detections and (ii) the detection rates for varying dish diameters can be used to infer the index α of the cumulative fluence distribution function (the log N –log F function: α = 1.5 for a non-evolving population in a Euclidean universe). If all detected FRBs arise from a single progenitor population, multiple-beam FRB detection rates from the Parkes telescope yield the constraint 0.52 < α < 1.0 with 90% confidence. Searches at other facilities with different dish sizes refine the constraint to 0.5 < α < 0.9. Our results favor FRB searches with smaller dishes, because for α < 1 the gain in field of view for a smaller dish is more important than the reduction in sensitivity. Further, our results suggest that (i) FRBs are not standard candles, and (ii) the distribution of distances to the detected FRBs is weighted toward larger distances. If FRBs are extragalactic, these results are consistent with a cosmological population, which would make FRBs excellent probes of the baryonic content and geometry of the universe.