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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Sci-Thur PM – Colourful Interactions: Highlights 01: Design to delivery of spatially fractionated mini-beam canine radiotherapy

Spatial fractionation of radiation using arrays of narrow parallel micro-planar beams (less than 1 mm), is a relatively new concept with many unknowns specifically within the underlying biology of cell death. A tungsten collimator has been designed to produce mini-beams with a Varian linear accelerator for translational animal research into the effectiveness of spatial fractionation mini-beam radiotherapy (MBRT). This work presents the treatment planning process and workflow for the application of MBRT treatments within a clinical study. For patient dose calculations, the MBRT collimator was incorporated into a Monte Carlo based treatment planning system called MMCTP. Treatment planning was split between Eclipse and MMCTP, as the field apertures were determined within Eclipse prior to being sent to MMCTP for dose calculations. The calculated plan was transferred back into Aria with updated MUs per field for patient treatment. Patients were positioned within a vac-lock bag lying prone with a bite block and a thermoplastic mask to immobilize the head. Prior to treatment, a delivery verification plan was created within MMCTP. DQA output measurements of the treatment fields agreed with the calculated dose to within 1.5%. We have presented a workflow for MBRT treatments that include the planning technique, dose calculation method, DQA process and data integration into a record and verify system. The clinical study following this workflow represent the first series of linac based MBRT patients and depending on the clinical outcome of the study, our technique could be applied to human MBRT treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Sci-Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques - 06: Patient-specific QA Procedure for Gated VMAT SABR Treatments using 10x Beam in Flattening-Filter Free Mode

Purpose: To develop a highly sensitive patient specific QA procedure for gated VMAT stereotactic ablative radiotherapy (SABR) treatments. Methods: A platform was constructed to attach the translational stage of a Quasar respiratory motion phantom to a pinpoint ion chamber insert and move the ion chamber inside the ArcCheck. The Quasar phantom controller uses a patient-specific breathing pattern to translate the ion chamber in a superior-inferior direction inside the ArcCheck. With this system the ion chamber is used to QA the correct phase of the gated delivery and the ArcCheck diodes are used to QA the overall dose distribution. This novel approach requires a single plan delivery for a complete QA of a gated plan. The sensitivity of the gating QA procedure was investigated with respect to the following parameters: PTV size, exhale duration, baseline drift, gating window size. Results: The difference between the measured dose to a point in the penumbra and the Eclipse calculated dose was under 2% for small residual motions. The QA procedure was independent of PTV size and duration of exhale. Baseline drift and gating window size, however, significantly affected the penumbral dose measurement, with differences of up to 30% compared to Eclipse. Conclusion: This study described a highly sensitive QA procedure for gated VMAT SABR treatments. The QA outcome was dependent on the gating window size and baseline drift. Analysis of additional patient breathing patterns is currently undergoing to determine a clinically relevant gating window size and an appropriate tolerance level for this procedure.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MULTIWAVELENGTH OBSERVATIONS OF THE REDBACK MILLISECOND PULSAR J1048+2339

We report on radio timing and multiwavelength observations of the 4.66 ms redback pulsar J1048+2339, which was discovered in an Arecibo search targeting the Fermi -Large Area Telescope source 3FGL J1048.6+2338. Two years of timing allowed us to derive precise astrometric and orbital parameters for the pulsar. PSR J1048+2339 is in a 6 hr binary and exhibits radio eclipses over half the orbital period and rapid orbital period variations. The companion has a minimum mass of 0.3 M {sub ⊙}, and we have identified a V ∼ 20 variable optical counterpart in data from several surveys. The phasing of its ∼1 mag modulation at the orbital period suggests highly efficient and asymmetric heating by the pulsar wind, which may be due to an intrabinary shock that is distorted near the companion, or to the companion’s magnetic field channeling the pulsar wind to specific locations on its surface. We also present gamma-ray spectral analysis of the source and preliminary results from searches for gamma-ray pulsations using the radio ephemeris.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Angular Momentum Evolution of Young Stars in the nearby Scorpius–Centaurus OB Association

We report the results of a study of archival SuperWASP light curves for stars in Scorpius–Centaurus (Sco–Cen), the nearest OB association. We use SuperWASP time-series photometry to extract rotation periods for 189 candidate members of the Sco–Cen complex and verify that 162 of those are members of the classic Sco–Cen subgroups of Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC). This study provides the first measurements of rotation periods explicitly for large samples of pre-main-sequence (pre-MS) stars spanning the UCL and LCC subgroups. Our final sample of 157 well-characterized pre-MS stars spans ages of ∼10–20 Myr, spectral types of ∼F3–M0, and masses of M ≃ 0.3–1.5 M{sub ⊙}{sup N}. For this sample, we find a distribution of stellar rotation periods with a median of P {sub rot} ≃ 2.4 days, an overall range of 0.2 < P {sub rot} < 8 days, and a fairly well-defined mass-dependent upper envelope of rotation periods. This distribution of periods is consistent with recently developed stellar angular momentum evolution models. These data are significant because they represent an undersampled age range and the number of measurable rotation periods is large compared to recent studies of other regions. We also search for new examples of eclipsing disk or ring systems analogous to 1SWASP J140747.93-394542.6 (J1407), but find none. Our survey yielded five eclipsing binaries, but only one appears to be physically associated with the Sco–Cen complex. V2394 Oph is a heavily reddened (A {sub V} ≃ 5 mag) massive contact binary in the LDN 1689 cloud whose Gaia astrometry is clearly consistent with kinematic membership with the Ophiuchus star-forming region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

DMTN-221: Periodicity Analysis in Alert Production

The baselined timeseries features to be computed in Alert Production include a Lomb-Scargle periodogram ran on two classes of variable systems: RR Lyrae and Eclipsing Binaries. Based on a simulated LSST-like cadence light curves taken from the Extended LSST Astronomical Time-series Classification Challenge (ELAsTiCC) we perform an end-to-end test to characterize the periodicity recovery on the Alert Production multi-band light curves. In both variable classes, we found that a single-band Lomb-Scargle implementation yields to a low fraction of recovered periods, with a significant preference on the simple periodic phenomena such as RR Lyrae. We also investigated the results from a multi-band Lomb-Scargle and found an increased fraction of recovered periodicities above 15% for the eclipsing binaries, and over 80$\%$ for the RR Lyrae stars. Our findings suggest that a multi-band Lomb-Scargle should be implemented for searching periodic phenomena through AP. We also asses the computational and scientific performance of several configurations on simulated alert data and find that our current configuration scales linearly with the number of detections while assuming an heuristic frequency grid.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Plasma-sheet ions at lunar distance preceding substorm onset.

During the partial lunar eclipse of August 17, 1970, four intense, transient bursts of kV-energy positive ions were detected at the lunar surface by the Rice University ALSEP Suprathermal Ion Detector Experiment. The eclipse happened to occur during a main-phase geomagnetic storm while the moon was within a few earth radii of the calculated position of the neutral sheet. The two most intense ion bursts were each followed roughly one-half hour later by the sudden onset of a several thousand gamma polar magnetic substorm at the earth's surface. Two smaller ion enhancements were also followed by smaller magnetic disturbances. This observation is interpreted in terms of a downstream escape of plasma-sheet particles associated with the substorm growth phase.

Garrett, H. B.↗
NASA NTRS1972

Current Sheet Magnetic Model for the Solar Corona

A new magnetic model is developed and compared with previous models and the observed solar corona. An attempt is made to more accurately compute the three-dimensional currents flowing in the solar corona. Physical reasons are given that require most of the large scale currents flowing in the solar corona to lie near thin sheets. The current sheets are not constrained into any particular geometry or symmetry as in the previous models of Altschuler and Newkirk (1969) and Schatten et al. (1969). A comparison with the axisymmetric, isothermal MHD solution of Pneuman and Kopp (1970) suggests that the model is able to simulate to high accuracy an isothermal corona. A comparison of the model with the May 30, 1965, solar eclipse and the November 12, 1966, solar eclipse shows the model is capable of computing many features including the polar plume orientations as well as radial and nonradial streamers in the solar corona.

Schatten, K. H.↗
NASA NTRS1972

On the mass-luminosity relation.

The results of a least-squares study of the mass-luminosity relation for eclipsing and visual binary stars consisting of main sequence components are presented. Two methods are discussed. First, the values of the coefficients A and B in the relation log M = A + BM sub BOL are determined. Then a technique which permits the determination of alpha and beta in the relation M = alpha L beta, when only the sum of the masses, and not the individual masses of each component, is known. The results and a comparison of the two methods are discussed. It is found that the following mass-luminosity relation represents the observational data satisfactorily: log M = 0.504 - 0.103 M sub BOL, -8 less than or equal to M sub BOL less than or equal to +10.5. A discussion of the data and of the possibility that separate mass-luminosity relations may exist for visual and eclipsing binaries is given. The possibility that more than one mass-luminosity relation is required in the range -8 less than or equal to M sub BOL less than or equal to +13 is also discussed.

Mccluskey, G. E., Jr.↗
NASA NTRS1973

The solar wind cycle, the sunspot cycle, and the corona.

Recent theories of the solar cycle and of coronal heating strongly suggest that solar cycle variations of different quantities (i.e., sunspots, coronal green line, etc.) ought not to be expected to be in phase with one another. In agreement with this notion it is noted that the shape of the corona typical of a 'maximum' eclipse occurs 1.5 yr before sunspot maximum, compared with 2 yr as might be expected from Leighton's 'standard' model. Further, it is argued that the phase of the solar wind cycle can be determined from geomagnetic observations. Using this phase, a solar cycle variation of 100 km/sec in the solar wind velocity and 1 gamma in the magnetic field intensity becomes apparent. In general, the solar wind cycle lags behind the coronal-eclipse-form cycle by 3 yr, compared with the 2 yr that might be expected from model calculations.

Hirshberg, J.↗
NASA NTRS1973

Optical observations of Sanduleak 160.

The variability of Sanduleak 160, the proposed optical counterpart of SMC X-1, has been confirmed. It shows a double-peaked optical variation with the minimum at X-ray eclipse being the deeper. The cos 2 theta variation has a semiamplitude of 0.050 mag in the B filter, the cos theta variation has a semiamplitude of 0.025 mag, and there is a cos 3 theta variation of 0.012 mag semiamplitude. From an analysis of the optical photometry and X-ray eclipse duration the mass ratio is found to be 0.28, i = 79 deg, and P = 3.89206 days. On the assumption that the mass of Sk 160 is 20 solar masses, the mass of SMC X-1 is 5.6 solar masses.

Petro, L.↗
NASA NTRS1974

Photoelectric observations of Krzeminski's star, the companion of Cen X-3

Centaurus X-3 was the first discovered X-ray source whose intensity is pulsed and eclipsed. Though the X-ray properties of the Cen X-3 system have been intensively studied, the optical properties remained unstudied until Krzeminski's identification of the optical counterpart of Cen X-3. Observations of the X-ray eclipse duration, pulsation frequency variation, and pulse arrival time variation have been used to place limits on the nature of the system and to predict the nature of the optical companion and X-ray sources. An observational determination is presented of the several system parameters based on a preliminary interpretation of the light curve of Krzeminski's star.

Petro, L. D.↗
NASA NTRS1973

Accuracy analysis of the ephemerides of the Galilean satellites

Known discrepancies between Sampson's Theory and observations of the Galilean satellites produce in plane errors of about 1200 km. Since the mean longitude is responsible for most of the discrepancy a simple time correction may be used to significantly reduce these errors. An analysis of the time corrections derived for Sampson's Theory, concludes that the dominant error in the mean longitudes results from Sampson's definition of time, which was determined by the observations which he used in constructing the theory. Imposition of the libration constraint results in changes to the time corrections which are less than the standard deviation of those quantities. The individual eclipse observational errors are shown to be proportional to the square root of the period. With improved star catalogs, the attainable accuracy of the ephemerides of the Galilean satellites is about 100 km from photographic plates versus about 200 km for eclipse observations.-

Peters, C. F.↗
NASA NTRS1973

Does Io have an ammonia atmosphere

A number of anomalous or discordant observations of Io can be explained if this Jovian satellite has an atmosphere containing ammonia. Such an atmosphere will be frozen at the unilluminated pole during the solstices, but will evaporate at the equinoctial seasons. The ammonia atmosphere will explain (1) the posteclipse brightenings and their observed times of occurrence and nonoccurrence; (2) the observed departure from a two-layer model heating curve upon emergency from the eclipse; (3) the discordant temperatures obtained at 10 and 20 micrometers; and (4) discordant temperatures obtained at 10 and 20 micrometers during the total phase of an eclipse by Jupiter.

Sinton, W. M.↗
NASA NTRS1974

A comparison of infrared, radar, and geologic mapping of lunar craters

Between 1000 and 2000 infrared (eclipse) and radar anomalies have been mapped on the nearside hemisphere of the moon. A study of 52 of these anomalies indicates that most are related to impact craters and that the nature of the infrared and radar responses is compatible with a previously developed geologic model of crater aging processes. The youngest craters are pronounced thermal and radar anomalies; that is, they have enhanced eclipse temperatures and are strong radar scatterers. With increasing crater age, the associated thermal and radar responses become progressively less noticeable until they assume values for the average lunar surface. The last type of anomaly to disappear is radar enhancement at longer wavelengths. A few craters, however, have infrared and radar behaviors not predicted by the aging model. One previously unknown feature - a field strewn with centimeter-sized rock fragments - has been identified by this technique of comparing maps at the infrared, radar, and visual wavelengths.

Thompson, T. W.↗
NASA NTRS1974

Interpretation of epsilon Aurigae. III

The light curve expected from the eclipse of a star by a companion possessing a semitransparent disk has been investigated. Two computational procedures for deriving the light curve based on the geometrically thin-disk model are given here. Using these procedures, we have calculated the light curves of epsilon Aur based on different sets of parameters including those given previously by Wilson. We have also studied the light curve of epsilon Aur based on a geometrically thick disk model, and have advanced two proposals in order to understand the change in the shape of the light curve from one eclipse to the next, namely, (1) the rapid evolution that occurs in the disk and (2) the density waves in the disk and/or individual condensations that are revolving around the secondary each in an independent way.

Huang, S.-S.↗
NASA NTRS1974

Recent results from satellite beacon measurements

A review is made of the techniques for measuring ionospheric electron content, the most important parameter in the study of transionospheric propagation. Data collected since 1964 have yielded a synoptic description of the behavior of the electron content in mid-latitudes. Empirical relationships between the level of solar activity and the electron content have been developed permitting the prognostication of the electron content values. Marked discrepancies between prognostication and observation which occur during ionospheric storms are being studied to identify their causes. Electron content bite-outs during solar eclipses fall off with distance from totality more rapidly than simple theory predicts suggesting the action of eclipse induced neutral winds. Gravity waves propagating in the thermosphere leave a signature in the electron content records. Studies of such records have allowed the identification of the position of the gravity wave source, and its radiation pattern.

Da Rosa, A. V.↗
NASA NTRS1975

Spacecraft charging control demonstration at geosynchronous altitude

ATS-6, which was launched on May 30, 1974, has now completed its first eclipse season. Potentials as great as 11,000 volts were observed between the spacecraft and ambient plasma. Both ATS-5 and 6 have ion engine experiments onboard. These experiments have been used to clamp the spacecraft potential slightly negative when emitting an ion beam and momentarily discharge the spacecraft when only operating the ion engine's neutralizing electron source. Descriptions of the neutralizer's operation and their effect on potential are presented. In addition, spacecraft charging data for ATS-5 and 6 are presented and correlated over the same eclipse season.

Bartlett, R. O.↗
NASA NTRS1976

The interpretation of optical light variations of Centaurus X-3

The interpretation of optical light variations of X-ray binaries is discussed for the case of negligible reflection effect. The limiting cases of synchronous rotation of the visible star (Roche configuration) and of no rotation (pure tidal deformation) are considered. The theoretical results are compared with the available light curves of Cen X-3. X-ray data of the Copernicus satellite are used to get an impression of the atmospheric structure of the outer layers of the visible component. It is shown, that the X-ray eclipse duration is in good agreement with the mass ration derived from the optical variations. The X-ray eclipse duration is discussed with respect to the extended low states, and a possible correlation of the extended lows with the appearance of the optical light curves is considered.

Mauder, H.↗