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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2016

Visual-Attention-Based Background Modeling for Detecting Infrequently Moving Objects

Motion is one of the most important cues to separate foreground objects from the background in a video. Using a stationary camera, it is usually assumed that the background is static, while the foreground objects are moving most of the time. However, in practice, the foreground objects may show infrequent motions, such as abandoned objects and sleeping persons. Meanwhile, the background may contain frequent local motions, such as waving trees and/or grass. Such complexities may prevent the existing background subtraction algorithms from correctly identifying the foreground objects. We propose a new approach that can detect the foreground objects with frequent and/or infrequent motions. Specifically, we use a visual-attention mechanism to infer a complete background from a subset of frames and then propagate it to the other frames for accurate background subtraction. Furthermore, we develop a feature-matching-based local motion stabilization algorithm to identify frequent local motions in the background for reducing false positives in the detected foreground. The proposed approach is fully unsupervised, without using any supervised learning for object detection and tracking. Extensive experiments on a large number of videos have demonstrated that the proposed approach outperforms the state-of-the-art motion detection and background subtraction methods in comparison.

42 ENGINEERING↗

NASA NTRS1993

Volatile loss from accreting icy protoplanets

A large self-gravitating body does not easily lose significant mass because the escape velocity is much larger than the sound speed of atmosphere-forming species under ambient thermal conditions. The most significant exceptions to this are giant impacts or impact jetting by fast-moving projectiles. A very small object (e.g. a comet) also does not easily lose significant volatile mass upon formation because the energy release associated with its accretion is so small. (It can however lose a great deal of mass if it is subsequently moved closer to the Sun.) I argue that there is an intermediate mass range (corresponding to bodies with radii of approximately 300-800 km) for which the ambient steady-state mass loss is a maximum. By ambient, I mean those conditions pertaining to the formation region of the body. By steady state, I mean to exclude infrequent traumas (giant impacts). The existence of a preferred intermediate mass arises through the competition of growing gravitational containment and growing energy release by accretion; it corresponds typically to GM/(Rc(sub s)(exp 2)) approximately equals 2 to 4, where M is the protoplanet mass of radius R, and c(sub s) is the sound speed. Several factors determine the amount of volatile loss is this vulnerable zone during accretion but in general the loss is a substantial fraction of the volatiles, sometimes approaching 100 percent. The principal implication is that bodies larger than a few hundred kilometers in radius will not have a 'primitive' (i.e. cometary) composition. This is relevant for understanding Triton, Pluto, Charon, and perhaps Chiron.

Stevenson, D. J.↗

DOE OSTI2014

WE-G-BRF-08: Robust Characterization and Patient Experience of a Time-Resolved Ultrasound System for Prostate Tracking

Purpose: Characterization of a time resolved ultrasound device (4D-US), used for localization and motion monitoring of prostate radiotherapy. Methods: The 4D-US system accuracy to reproduce prostate motion was investigated and artifacts were determined under detailed experimental and ultimately clinical conditions. Two fields of view (FOV) of 30 and 60 degrees and two corresponding acquisition speeds were evaluated under experimental conditions with gradual increased complexity. The reconstruction ability and trajectory tracking depends on the relative speed between the ultrasound probe and the moving object. Two different types of phantoms were developed; one capable of following a predetermined trajectory with variable speeds, and a second one designed to test the US ability to a track dynamically-deformed prostate. Four hypo-prostate patients (10fx) were monitored during the treatment to detect intrafraction motion. Results: Prostate speeds up to 6mm/s and 3mm/s can be successfully tracked by the system when using the small and large FOV, respectively. The system response time, calculated based on the speedinduced volumetric distortion, is dependent on the FOV, with 1.1s for the small FOV and 1.4s for the large FOV. The response time was also found dependent on the size of target, increasing from 1.4s to 1.7s for target diameters of 4cm to 2.8cm. The deformable dynamic phantom has shown that the system is able to successfully follow a highly-deformed, slowmoving prostate with an error < 0.5mm. The overall range of patient intrafraction motion was (−2.4 to 2.2)mm, (−2.6 to 2.4)mm, (−3.0 to 4.3)mm in the RL, SI and AP directions, respectively. Conclusion: The 4DUS system using a large FOV is appropriate to monitor the prostate motion as well as the adjacent organs at risk. However, infrequent abrupt motion can be problematic and the small FOV system is preferred for such patients, particularly for future applications as online prostate monitoring employed for MLC tracking.

60 APPLIED LIFE SCIENCES↗