34,782 research outputs found
Light Field Blind Motion Deblurring
We study the problem of deblurring light fields of general 3D scenes captured
under 3D camera motion and present both theoretical and practical
contributions. By analyzing the motion-blurred light field in the primal and
Fourier domains, we develop intuition into the effects of camera motion on the
light field, show the advantages of capturing a 4D light field instead of a
conventional 2D image for motion deblurring, and derive simple methods of
motion deblurring in certain cases. We then present an algorithm to blindly
deblur light fields of general scenes without any estimation of scene geometry,
and demonstrate that we can recover both the sharp light field and the 3D
camera motion path of real and synthetically-blurred light fields.Comment: To be presented at CVPR 201
Seismic response trends evaluation and finite element model calibration of an instrumented RC building considering soil-structure interaction and non-structural components
Peer reviewedPostprin
PreSEIS: A Neural Network-Based Approach to Earthquake Early Warning for Finite Faults
The major challenge in the development of earthquake early warning (EEW) systems is the achievement of a robust performance at largest possible warning time. We have developed a new method for EEW—called PreSEIS (Pre-SEISmic)—that is as quick as methods that are based on single station observations and, at the same time, shows a higher robustness than most other approaches. At regular timesteps after the triggering of the first EEW sensor, PreSEIS estimates the most likely source parameters of an earthquake using the available information on ground motions at different sensors in a seismic network. The approach is based on two-layer feed-forward neural networks to estimate the earthquake hypocenter location, its moment magnitude, and the expansion of the evolving seismic rupture. When applied to the Istanbul Earthquake Rapid Response and Early Warning System (IERREWS), PreSEIS estimates the moment magnitudes of 280 simulated finite faults scenarios (4.5≤M≤7.5) with errors of less than ±0.8 units after 0.5 sec, ±0.5 units after 7.5 sec, and ±0.3 units after 15.0 sec. In the same time intervals, the mean location errors can be reduced from 10 km over 6 km to less than 5 km, respectively. Our analyses show that the uncertainties of the estimated parameters (and thus of the warnings) decrease with time. This reveals a trade-off between the reliability of the warning on the one hand, and the remaining warning time on the other hand. Moreover, the ongoing update of predictions with time allows PreSEIS to handle complex ruptures, in which the largest fault slips do not occur close to the point of rupture initiation. The estimated expansions of the seismic ruptures lead to a clear enhancement of alert maps, which visualize the level and distribution of likely ground shaking in the affected region seconds before seismic waves will arrive
Compensation of Magnetic Disturbances Improves Inertial and Magnetic Sensing of Human Body Segment Orientation
This paper describes a complementary Kalman filter design to estimate orientation of human body segments by fusing gyroscope, accelerometer, and magnetometer signals from miniature sensors. Ferromagnetic materials or other magnetic fields near the sensor module disturb the local earth magnetic field and, therefore, the orientation estimation, which impedes many (ambulatory) applications. In the filter, the gyroscope bias error, orientation error, and magnetic disturbance error are estimated. The filter was tested under quasi-static and dynamic conditions with ferromagnetic materials close to the sensor module. The quasi-static experiments implied static positions and rotations around the three axes. In the dynamic experiments, three-dimensional rotations were performed near a metal tool case. The orientation estimated by the filter was compared with the orientation obtained with an optical reference system Vicon. Results show accurate and drift-free orientation estimates. The compensation results in a significant difference (p<0.01) between the orientation estimates with compensation of magnetic disturbances in comparison to no compensation or only gyroscopes. The average static error was 1.4/spl deg/ (standard deviation 0.4) in the magnetically disturbed experiments. The dynamic error was 2.6/spl deg/ root means square
System Identification of Constructed Facilities: Challenges and Opportunities Across Hazards
The motivation, success and prevalence of full-scale monitoring of constructed buildings vary
considerably across the hazard of concern (earthquakes, strong winds, etc.), due in part to various
fiscal and life safety motivators. Yet while the challenges of successful deployment and
operation of large-scale monitoring initiatives are significant, they are perhaps dwarfed by the
challenges of data management, interrogation and ultimately system identification. Practical
constraints on everything from sensor density to the availability of measured input has driven the
development of a wide array of system identification and damage detection techniques, which in
many cases become hazard-specific. In this study, the authors share their experiences in fullscale monitoring of buildings across hazards and the associated challenges of system
identification. The study will conclude with a brief agenda for next generation research in the
area of system identification of constructed facilities
Pioneer Anomaly: Evaluating Newly Recovered Data
The Pioneer 10/11 spacecraft yielded the most precise navigation in deep
space to date. However, their radio-metric tracking data received from the
distances between 20--70 astronomical units from the Sun consistently indicated
the presence of a small, anomalous, Doppler frequency drift. The drift is a
blue frequency shift that can be interpreted as a sunward acceleration of a_P =
(8.74 +/- 1.33) x 10^(-10) m/s^2 for each particular spacecraft. This signal
has become known as the Pioneer anomaly; the nature of this anomaly remains
unexplained.
New Pioneer 10 and 11 radio-metric Doppler data recently became available.
The much extended set of Pioneer Doppler data is the primary source for new
upcoming investigation of the anomaly. We also have almost entire records of
flight telemetry files received from the the Pioneers. Together with original
project documentation and newly developed software tools, this additional
information is now used to reconstruct the engineering history of both
spacecraft. To that extent, a thermal model of the Pioneer vehicles is being
developed to study possible contribution of thermal recoil force acting on the
two spacecraft. In addition, to improve the accuracy of orbital reconstruction,
we developed a new approach that uses actual flight telemetry data during
trajectory analysis of radio-metric Doppler files. The ultimate goal of these
efforts is to investigate possible contributions of the thermal recoil force to
the detected anomalous acceleration.Comment: 12 pages, 15 figures, invited talk at the "III Mexican Meeting on
Mathematical and Experimental Physics," Mexico City, Mexico, 10-14 September
200
Robustness of the Thirty Meter Telescope Primary Mirror Control System
The primary mirror control system for the Thirty Meter Telescope (TMT) maintains the alignment of the 492 segments in the presence of both quasi-static (gravity and thermal) and dynamic disturbances due to unsteady wind loads. The latter results in a desired control bandwidth of 1Hz at high spatial frequencies. The achievable bandwidth is limited by robustness to (i) uncertain telescope structural dynamics (control-structure interaction) and (ii) small perturbations in the ill-conditioned influence matrix that relates segment edge sensor response to actuator commands. Both of these effects are considered herein using models of TMT. The former is explored through multivariable sensitivity analysis on a reduced-order Zernike-basis representation of the structural dynamics. The interaction matrix ("A-matrix") uncertainty has been analyzed theoretically elsewhere, and is examined here for realistic amplitude perturbations due to segment and sensor installation errors, and gravity and thermal induced segment motion. The primary influence of A-matrix uncertainty is on the control of "focusmode"; this is the least observable mode, measurable only through the edge-sensor (gap-dependent) sensitivity to the dihedral angle between segments. Accurately estimating focus-mode will require updating the A-matrix as a function of the measured gap. A-matrix uncertainty also results in a higher gain-margin requirement for focus-mode, and hence the A-matrix and CSI robustness need to be understood simultaneously. Based on the robustness analysis, the desired 1 Hz bandwidth is achievable in the presence of uncertainty for all except the lowest spatial-frequency response patterns of the primary mirror
Adaptive identification and control of structural dynamics systems using recursive lattice filters
A new approach for adaptive identification and control of structural dynamic systems by using least squares lattice filters thar are widely used in the signal processing area is presented. Testing procedures for interfacing the lattice filter identification methods and modal control method for stable closed loop adaptive control are presented. The methods are illustrated for a free-free beam and for a complex flexible grid, with the basic control objective being vibration suppression. The approach is validated by using both simulations and experimental facilities available at the Langley Research Center
Aeronautical Engineering: A continuing bibliography, supplement 120
This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980
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