We present radio transient search algorithms, results, and statistics from the ongoing Arecibo Pulsar ALFA (PALFA) survey of the Galactic plane. We have discovered seven objects through a search for isolated dispersed pulses. All of these objects are Galactic and have measured periods between 0.4 and 4.7 s. One of the new discoveries has a duty cycle of 0.01%, smaller than that of any other radio pulsar. We discuss the impact of selection effects on the detectability and classification of intermittent sources, and compare the efficiencies of periodicity and single-pulse (SP) searches for various pulsar classes. For some cases we find that the apparent intermittency is likely to be caused by off-axis detection or a short time window that selects only a few bright pulses and favors detection with our SP algorithm. In other cases, the intermittency appears to be intrinsic to the source. No transients were found with DMs large enough to require that they originate from sources outside our Galaxy. Accounting for the on-axis gain of the ALFA system, as well as the low gain but large solid-angle coverage of far-out sidelobes, we use the results of the survey so far to place limits on the amplitudes and event rates of transients of arbitrary origin.

We used hydrologic models to explore the potential linkages between oil‐field brine reinjection and increases in earthquake frequency (up to Md 3.26) in southeastern New Mexico and to assess different injection management scenarios aimed at reducing the risk of triggered seismicity. Our analysis focuses on saline water reinjection into the basal Ellenburger Group beneath the Dagger Draw Oil field, Permian Basin. Increased seismic frequency (>Md 2) began in 2001, 5 years after peak injection, at an average depth of 11 km within the basement 15 km to the west of the reinjection wells. We considered several scenarios including assigning an effective or bulk permeability value to the crystalline basement, including a conductive fault zone surrounded by tighter crystalline basement rocks, and allowing permeability to decay with depth. We initially adopted a 7 m (0.07 MPa) head increase as the threshold for triggered seismicity. Only two scenarios produced excess heads of 7m five years after peak injection. In the first, a hydraulic diffusivity of 0.1 m2 s−1 was assigned to the crystalline basement. In the second, a hydraulic diffusivity of 0.3 m2 s−1 was assigned to a conductive fault zone. If we had considered a wider range of threshold excess heads to be between 1 and 60 m, then the range of acceptable hydraulic diffusivities would have increased (between 0.1–0.01 m2 s−1 and 1–0.1 m2 s−1 for the bulk and fault zone scenarios, respectively). A permeability–depth decay model would have also satisfied the 5‐year time lag criterion. We also tested several injection management scenarios including redistributing injection volumes between various wells and lowering the total volume of injected fluids. Scenarios that reduced computed excess heads by over 50% within the crystalline basement resulted from reducing the total volume of reinjected fluids by a factor of 2 or more.

Neutral hydrogen (HI) provides a very important fuel for star formation, but is difficult to detect at high redshift due to weak emission, limited sensitivity of modern instruments, and terrestrial radio frequency interference (RFI) at low frequencies. We report the first attempt to use gravitational lensing to detect HI line emission from three gravitationally lensed galaxies behind the cluster Abell 773, two at redshifts of 0.398 and one at z = 0.487, using the Green Bank Telescope. We find that a 3σ upper limit for a galaxy with a rotation velocity of 200 km s −1 is M H I = 6.58 × 10 9 and 1.5 × 10 10 M e at z = 0.398 and z = 0.487. The estimated HI masses of the sources at z = 0.398 and z = 0.487 are factors of 3.7 and ∼30 times lower than our detection limits at the respective redshifts. To facilitate these observations we have used sigma-clipping to remove both narrow-and wideband RFI but retain the signal from the source. We are able to reduce the noise of the spectrum by ∼25% using our routine instead of discarding observations with too much RFI. The routine is most effective when ∼10% of the integrations or fewer contain RFI. These techniques can be used to study HI in highly magnified distant galaxies that are otherwise too faint to detect.

Purpose : This work is in the context of Monte Carlo simulation in radiotherapy. The objective was to study the modelling of a Siemens OncorTM linear accelerator on the GATE (Geant4 Application for Tomographic Emission) platform. A dosimetric study on water phantom was used to evaluate the reliability and the accuracy of the simulation. Methods: The study had two different objectives: (a) the modelling of the accelerator on the GATE v6.0 platform, and (b) a preliminary dosimetric assessment. Computations were performed in a 70×70×70 cm3 water phantom, with a 100 cm source‐to‐axis distance. The acceleratorˈs components and their geometrical and physical characteristics were defined according to the constructor specifications. The output data were obtained for a dosel (dose scoring voxel, Sarrut & Guigues 2008) of size 2.5×2.5×2.5 mm3 leading to a sensitive volume of 0.015 cm3. A comparative study of the absorbed dose in water calculated by simulation and measured was performed for the following criteria : Photon beam quality TPR (20, 10), i.e the dose ratio at 20 cm and 10 cm in water for a 100 cm source‐detector distance. Depth dose and dose profiles. Output factors for different field sizes. Simulations were performed using a cluster of 26 nodes, 100 CPUs, 194 GB RAM in total. Results: The user interface, based on macros and graphics, facilitates the modelling of different parts of the accelerator. The simulations results obtained with GATE showed a good agreement with actual measurement in water. For example, the photon beam quality obtained by simulation was 0.6725 while the measured one was 0.673. Conclusions: These preliminary results showed good agreement with real measurements. They also are a relevant illustration of the usefulness of GATE v6.0 in the field of radiotherapy. More complex modelling involving the dynamic 160 MLC leaves movements are underway (IMRT).

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