1,797 research outputs found
Schwannomatosis of the tibial nerve
Schwannoma is the most common type of benign tumor arising from the sheaths of the peripheral nerves. It occurs as a solitary tumor in most cases, but when it appears in multiple forms, it is necessary to differentiate it from plexiform schwannoma, schwannomatosis, neurofibroma and malignant peripheral nerve tumors. The authors experienced schwannomatosis in the tibial nerve without the features of neurofibromatosis type 2, so here we present a case report and literature review
Automating Reinforcement Learning with Example-based Resets
Deep reinforcement learning has enabled robots to learn motor skills from
environmental interactions with minimal to no prior knowledge. However,
existing reinforcement learning algorithms assume an episodic setting, in which
the agent resets to a fixed initial state distribution at the end of each
episode, to successfully train the agents from repeated trials. Such reset
mechanism, while trivial for simulated tasks, can be challenging to provide for
real-world robotics tasks. Resets in robotic systems often require extensive
human supervision and task-specific workarounds, which contradicts the goal of
autonomous robot learning. In this paper, we propose an extension to
conventional reinforcement learning towards greater autonomy by introducing an
additional agent that learns to reset in a self-supervised manner. The reset
agent preemptively triggers a reset to prevent manual resets and implicitly
imposes a curriculum for the forward agent. We apply our method to learn from
scratch on a suite of simulated and real-world continuous control tasks and
demonstrate that the reset agent successfully learns to reduce manual resets
whilst also allowing the forward policy to improve gradually over time.Comment: 8 pages, 6 figures; accepted for publication in the IEEE Robotics and
Automation Letters (RA-L); source code available at
https://github.com/jigangkim/autoreset_rl ; supplementary video available at
https://youtu.be/himd0Z5b64
Retrieval of NO2 Column Amounts from Ground-Based Hyperspectral Imaging Sensor Measurements
Total column amounts of NO2 (TCN) were estimated from ground-based hyperspectral imaging sensor (HIS) measurements in a polluted urban area (Seoul, Korea) by applying the radiance ratio fitting method with five wavelength pairs from 400 to 460 nm. We quantified the uncertainty of the retrieved TCN based on several factors. The estimated TCN uncertainty was up to 0.09 Dobson unit (DU), equivalent to 2.687 ?? 1020 molecules m???2) given a 1?? error for the observation geometries, including the solar zenith angle, viewing zenith angle, and relative azimuth angle. About 0.1 DU (6.8%) was estimated for an aerosol optical depth (AOD) uncertainty of 0.01. In addition, the uncertainty due to the NO2 vertical profile was 14% to 22%. Compared with the co-located Pandora spectrophotometer measurements, the HIS captured the temporal variation of the TCN during the intensive observation period. The correlation between the TCN from the HIS and Pandora also showed good agreement, with a slight positive bias (bias: 0.6 DU, root mean square error: 0.7 DU)
COMPARISON OF ANGULAR KINEMATIC PATTERNS BETWEEN CARVING TURN AND SKIDDING TURN DURING ALPINE SKIING
The purpose of this study was to investigate the movement patterns between segments (lower spine, pelvis, thigh, shank) and ski using the relative angular displacement on anteroposterior and vertical axis. Fourteen alpine ski instructors were participated in this study. Eight inertial measurement units were used to measure kinematic variables. Each skier was asked to perform ten carving turns and ten skidding turns on the groomed 15°slope, respectively. On the vertical axis, relative angular displacement of lower spine-ski was significantly increased during carving turn, whereas relative angular displacement of shank-ski was significantly increased during skidding turn. On the anteroposterior axis, relative angular displacement of lower spine-ski, pelvis-ski and thigh-ski were significantly increased during carving turn
Experimental studies of strong dipolar interparticle interaction in monodisperse Fe3O4 nanoparticles
Interparticle interaction of monodisperse Fe3 O4 nanoparticles has been experimentally investigated by dispersing the nanoparticles in solvents. With increasing the interparticle distances to larger than 100 nm in a controlled manner, the authors found that the blocking temperature (TB) of the nanoparticles drops continuously and eventually gets saturated with a total drop in TB of 7-17 K observed for 3, 5, and 7 nm samples, compared with their respective nanopowder samples. By carefully studying the dependence of TB on the interparticle distance, the authors could demonstrate that the experimental dependence of TB follows the theoretical curve of the dipole-dipole interaction. © 2007 American Institute of Physics.open313
Acoustic metamaterial exhibiting four different sign combinations of density and modulus
We fabricated a double negative acoustic metamaterial which consisted of
Helmholtz resonators and membranes. Experimental data on the transmission and
dispersion relation are presented. The system exhibits three frequencies where
the acoustic state makes sharp transitions from density negative ({\rho} -NG)
to double negative (DNG), modulus negative (B-NG), and double positive (DPS) in
sequence with the frequency. We observed a wide range of negative refractive
index from -0.06 to -3.7 relative to air, which will allow for new acoustic
transformation techniques.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
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