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)

Dissecting the Red Sequence - III. Mass-to-Light Variations in 3D Fundamental Plane Space

The Fundamental Plane has finite thickness and is tilted from the virial relation, indicating that dynamical mass-to-light ratios (Mdyn/L) vary among early type galaxies. We use a sample of 16,000 quiescent galaxies from the Sloan Digital Sky Survey to map out variations in Mdyn/L through the 3D Fundamental Plane space defined by velocity dispersion (sigma), effective radius (R_e), and effective surface brightness. We consider contributions to Mdyn/L variation due to stellar population effects, IMF variations, and variations in the dark matter fraction within one R_e. Along the FP, we find that the stellar population contribution scales as M*/L ~ f(sigma), while the dark matter and/or IMF contribution scales as Mdyn/M* ~ g(Mdyn). The two contributions to the tilt of the FP rotate the plane around different axes in the 3D space, with dark matter/IMF variations likely dominating. Through the thickness of the FP, we find that Mdyn/L variations must be dominated either by IMF variations or by real differences in dark matter fraction with R_e. Thus the finite thickness of the FP is due to variations in the stellar mass surface density within R_e, not the fading of passive stellar populations. These structural variations are correlated with galaxy star formation histories such that galaxies with higher Mdyn/M* at a given sigma have higher [Mg/Fe], lower metallicities, and older mean stellar ages. It is difficult to explain the observed correlations by allowing the IMF to vary, suggesting difference in dark matter fraction dominate. These can be produced by variations in the "conversion efficiency" of baryons into stars or by the redistribution of stars and dark matter through dissipational merging. A model in which some galaxies experience low conversion efficiencies due to premature truncation of star formation provides a natural explanation for the observed trends.Comment: 26 pages, 15 figures, resubmitted to ApJ after incorporating referee's comments

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

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

Dissecting the Red Sequence. IV. The Role of Truncation in the Two-Dimensional Family of Early-Type Galaxy Star Formation Histories

In the three-dimensional parameter space defined by velocity dispersion, effective radius (R_e), and effective surface brightness (I_e), early-type galaxies are observed to populate a two-dimensional fundamental plane (FP) with finite thickness. In Paper III of this series, we showed that the thickness of the FP is predominantly due to variations in the stellar mass surface density (Sigma_*) inside the effective radius R_e. These variations represent differences in the dark matter fraction inside R_e (or possibly differences in the initial mass function) from galaxy to galaxy. This means that galaxies do not wind up below the FP at lower surface brightness due to the passive fading of their stellar populations; they are structurally different. Here, we show that these variations in Sigma_* at fixed dynamical mass (M_dyn) are linked to differences in the galaxy stellar populations, and therefore to differences in their star formation histories. We demonstrate that the ensemble of stellar population and Sigma_* variations through the FP thickness can be explained by a model in which early-type galaxies at fixed M_dyn have their star formation truncated at different times. The thickness of the FP can therefore be interpreted as a sequence of truncation times. Galaxies below the FP have earlier truncation times for a given M_dyn, resulting in lower Sigma_*, older ages, lower metallicities in both [Fe/H] and [Mg/H], and higher [Mg/Fe]. We show that this model is quantitatively consistent with simple expectations for chemical enrichment in galaxies. We also present fitting functions for luminosity-weighted age, [Fe/H], [Mg/H], and [Mg/Fe] as functions of the FP parameters velocity dispersion, R_e, and I_e. These provide a new tool for estimating the stellar population properties of quiescent early-type galaxies for which high-quality spectra are not available.Comment: 21 pages, 9 figures. Accepted to Ap

Dissecting the Red Sequence--II. Star Formation Histories of Early-Type Galaxies Throughout the Fundamental Plane

This analysis uses spectra of ~16,000 nearby SDSS quiescent galaxies to track variations in galaxy star formation histories along and perpendicular to the Fundamental Plane (FP). We sort galaxies by their FP properties (sigma, R_e, and I_e) and construct high S/N mean galaxy spectra that span the breadth and thickness of the FP. From these spectra, we determine mean luminosity-weighted ages, [Fe/H], [Mg/H], and [Mg/Fe] based on single stellar population models using the method described in Graves & Schiavon (2008). In agreement with previous work, the star formation histories of early-type galaxies are found to form a two-parameter family. The major trend is that mean age, [Fe/H], [Mg/H], and [Mg/Fe] all increase with sigma. However, no stellar population property shows any dependence on R_e at fixed sigma, suggesting that sigma and not dynamical mass (M_dyn ~ sigma^2 R_e) is the better predictor of past star formation history. In addition to the main trend with sigma, galaxies also show a range of population properties at fixed sigma that are strongly correlated with surface brightness residuals from the FP, such that higher surface brightness galaxies have younger mean ages, higher [Fe/H], higher [Mg/H], and lower [Mg/Fe] than lower-surface brightness galaxies. These latter trends are a major new constraint on star-formation histories.Comment: 23 pages, 14 figures. Accepted to Ap