11,207 research outputs found
Aberration Corrected Emittance Exchange
Full exploitation of emittance exchange (EEX) requires aberration-free
performance of a complex imaging system including active radio-frequency (RF)
elements which can add temporal distortions. We investigate the performance of
an EEX line where the exchange occurs between two dimensions with normalized
emittances which differ by multiple orders of magnitude. The transverse
emittance is exchanged into the longitudinal dimension using a double dog-leg
emittance exchange setup with a five cell RF deflector cavity. Aberration
correction is performed on the four most dominant aberrations. These include
temporal aberrations that are corrected with higher order magnetic optical
elements located where longitudinal and transverse emittance are coupled. We
demonstrate aberration-free performance of an EEX line with emittances
differing by four orders of magnitude, \textit{i.e.} an initial transverse
emittance of 1~pm-rad is exchanged with a longitudinal emittance of 10~nm-rad
Repair techniques for celion/LARC-160 graphite/polyimide composite structures
The large stiffness-to-weight and strength-to-weight ratios of graphite composite in combination with the 600 F structural capability of the polyimide matrix can reduce the total structure/TPS weight of reusable space vehicles by 20-30 percent. It is inevitable that with planned usage of GR/PI structural components, damage will occur either in the form of intrinsic flaw growth or mechanical damage. Research and development programs were initiated to develop repair processes and techniques specific to Celion/LARC-160 GR/PI structure with emphasis on highly loaded and lightly loaded compression critical structures for factory type repair. Repair processes include cocure and secondary bonding techniques applied under vacuum plus positive autoclave pressure. Viable repair designs and processes are discussed for flat laminates, honeycomb sandwich panels, and hat-stiffened skin-stringer panels. The repair methodology was verified through structural element compression tests at room temperature and 315 C (600 F)
Graphite/Larc-160 technology demonstration segment test results
A structural test program was conducted on a Celion/LARC-160 graphite/polyimide technology demonstration segment (TDS) to verify the technology. The 137 x 152 cm (54 x 60 in.) TDS simulates a full-scale section of the orbiter composite body flap design incorporating three ribs and extending from the forward cove back to the rear spar. The TDS was successfully subjected to mechanical loads and thermal environments (-170 to 316 C) simulating 100 shuttle orbiter missions. Successful completion of the test program verified the design, analysis, and fabrication methodology for bonded Gr/PI honeycomb sandwich structure and demonstration that Gr/PI composite technology readiness is established
Nano-modulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation
We present a new method for generation of relativistic electron beams with
current modulation on the nanometer scale and below. The current modulation is
produced by diffracting relativistic electrons in single crystal Si,
accelerating the diffracted beam and imaging the crystal structure, then
transferring the image into the temporal dimension via emittance exchange. The
modulation period can be tuned by adjusting electron optics after diffraction.
This tunable longitudinal modulation can have a period as short as a few
angstroms, enabling production of coherent hard x-rays from a source based on
inverse Compton scattering with total accelerator length of approximately ten
meters. Electron beam simulations from cathode emission through diffraction,
acceleration and image formation with variable magnification are presented
along with estimates of the coherent x-ray output properties
ContextVP: Fully Context-Aware Video Prediction
Video prediction models based on convolutional networks, recurrent networks,
and their combinations often result in blurry predictions. We identify an
important contributing factor for imprecise predictions that has not been
studied adequately in the literature: blind spots, i.e., lack of access to all
relevant past information for accurately predicting the future. To address this
issue, we introduce a fully context-aware architecture that captures the entire
available past context for each pixel using Parallel Multi-Dimensional LSTM
units and aggregates it using blending units. Our model outperforms a strong
baseline network of 20 recurrent convolutional layers and yields
state-of-the-art performance for next step prediction on three challenging
real-world video datasets: Human 3.6M, Caltech Pedestrian, and UCF-101.
Moreover, it does so with fewer parameters than several recently proposed
models, and does not rely on deep convolutional networks, multi-scale
architectures, separation of background and foreground modeling, motion flow
learning, or adversarial training. These results highlight that full awareness
of past context is of crucial importance for video prediction.Comment: 19 pages. ECCV 2018 oral presentation. Project webpage is at
https://wonmin-byeon.github.io/publication/2018-ecc
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