Observation of out-of-phase bilayer plasmons in YBa_2Cu_3O_7-delta

The temperature dependence of the c-axis optical conductivity \sigma(\omega) of optimally and overdoped YBa_2Cu_3O_x (x=6.93 and 7) is reported in the far- (FIR) and mid-infrared (MIR) range. Below T_c we observe a transfer of spectral weight from the FIR not only to the condensate at \omega = 0, but also to a new peak in the MIR. This peak is naturally explained as a transverse out-of-phase bilayer plasmon by a model for \sigma(\omega) which takes the layered crystal structure into account. With decreasing doping the plasmon shifts to lower frequencies and can be identified with the surprising and so far not understood FIR feature reported in underdoped bilayer cuprates.Comment: 7 pages, 3 eps figures, Revtex, epsfi

Star-forming Galaxies in the 'Redshift Desert'

We describe results of optical and near-IR observations of a large spectroscopic sample of star-forming galaxies photometrically-selected to lie in the redshift range 1.4 < z < 2.5, often called the ``redshift desert'' because of historical difficulty in obtaining spectroscopic redshifts in this range. We show that the former ``redshift desert'' is now very much open to observation.Comment: 10 pages, 6 figures, to appear in the Proceedings of the ESO/USM/MPE Workshop on "Multiwavelength Mapping of Galaxy Formation and Evolution", eds. R. Bender and A. Renzin

Rest-Frame Optical Spectra of Three Strongly Lensed Galaxies at z~2

We present Keck II NIRSPEC rest-frame optical spectra for three recently discovered lensed galaxies: the Cosmic Horseshoe (z = 2.38), the Clone (z = 2.00), and SDSS J090122.37+181432.3 (z = 2.26). The boost in signal-to-noise ratio (S/N) from gravitational lensing provides an unusually detailed view of the physical conditions in these objects. A full complement of high S/N rest-frame optical emission lines is measured, spanning from rest-frame 3600 to 6800AA, including robust detections of fainter lines such as H-gamma, [SII]6717,6732, and in one instance [NeII]3869. SDSS J090122.37+181432.3 shows evidence for AGN activity, and therefore we focus our analysis on star-forming regions in the Cosmic Horseshoe and the Clone. For these two objects, we estimate a wide range of physical properties, including star-formation rate (SFR), metallicity, dynamical mass, and dust extinction. In all respects, the lensed objects appear fairly typical of UV-selected star-forming galaxies at z~2. The Clone occupies a position on the emission-line diagnostic diagram of [OIII]/H-beta vs. [NII]/H-alpha that is offset from the locations of z~0 galaxies. Our new NIRSPEC measurements may provide quantitative insights into why high-redshift objects display such properties. From the [SII] line ratio, high electron densities (~1000 cm^(-3)) are inferred compared to local galaxies, and [OIII]/[OII] line ratios indicate higher ionization parameters compared to the local population. Building on previous similar results at z~2, these measurements provide further evidence (at high S/N) that star-forming regions are significantly different in high-redshift galaxies, compared to their local counterparts (abridged).Comment: 16 pages, 8 figures. Accepted for publication in the Astrophysical Journa

Total System Performance Assessment-License Application Design Selection (LADS) Phase 1 Analysis of Surface Modification Consisting of Addition of Alluvium (Feature 23a)

The objective of this report is to document the analysis that was conducted to evaluate the effect of a potential change to the TSPA-VA base case design that could improve long-term repository performance. The design feature evaluated in this report is a modification of the topographic surface of Yucca Mountain. The modification consists of covering the land surface immediately above the repository foot-print with a thick layer of unconsolidated material utilizing rip-rap and plants to mitigate erosion. This surface modification is designated as Feature 23a or simply abbreviated as F23a. The fundamental aim of F23a is to reduce the net infiltration into the unsaturated zone by enhancing the potential for evapotranspiratiration at the surface; such a change would, in turn, reduce the seepage flux and the rate of radionuclide releases from the repository. Field and modeling studies of water movement in the unsaturated zone have indicated that shallow infiltration at the surface is almost negligible in locations where the bedrock is covered by a sufficiently thick soil layer. In addition to providing storage for meteoric water, a thick soil layer would slow the downward movement of soil moisture to such an extent that evaporation and transpiration could easily transfer most of the soil-water back to the atmosphere. Generic requirements for the effectiveness of this design feature are two-fold. First, the soil layer above the repository foot-print must be thick enough to provide sufficient storage of meteoric water (from episodic precipitation events) and accommodate plant roots. Second, the added soil layer must be engineered so as to mitigate thinning by erosional processes and have sufficient thickness to accommodate the roots of common desert plants. Under these two conditions, it is reasonable to expect that modification would be effective for a significant time period and the net infiltration and deep percolation flux would be reduced by orders of magnitude lower than the present levels. Conceptually, the topographic surface above the repository foot-print would be re-contoured to make it more suitable for placement of unconsolidated materials (e.g., alluvium). Figure 1 shows the region of the surface modification in relation to the location of the repository foot-print. The surface contours in this region after modification are shown in the plot presented in Figure 2. Basically, the surface modification would be accomplished by applying cuts to the ridges slopes on the east flank of Yucca Mountain to produce a relatively uniform slope of about 10%. The alluvium would be covered with rock fragments (to imitate the desert pavement) to reduce erosion. This report documents the modeling assumptions and performance analysis conducted to estimate the long-term performance for Feature 23a. The performance measure for this evaluation is dose-rate. Results are presented that compare the dose-rate time histories for the new design feature to those of the TSPA-VA base case calculation (CRWMS M&amp;O 1998a)

Total System Performance Assessment- License Application Design Selection (LADS) Phase 1 Analysis for Higher Thermal Loa (Feature 26)

The objective of this report is to evaluate the effect of potential changes to the TSPA-VA base case design on long-term repository performance. The design feature that is evaluated in this report is a higher thermal load (Feature 26 or F26). The following paragraph briefly describes the motivation for evaluating higher thermal loading. Higher thermal load has been identified as a design feature that might have a beneficial effect on long-term repository performance. A higher thermal load will increase temperatures and decrease relative humidity on the waste package surface. The decrease in relative humidity may delay the onset of corrosion, thus delaying the failure of waste packages and the release of radionuclides from the engineered barrier system (EBS). For the current calculation a thermal load of 109 MTU/acre (metric tons of uranium per acre) is considered. Two cases are evaluated, one with the base case inventory and a higher thermal load and a second with an increased inventory that would cover the current repository footprint at the higher thermal load. This report documents the modeling assumptions and calculations conducted to evaluate the long-term performance of higher thermal loading. The performance measure for this evaluation is dose-rate. Results are presented that compare the dose-rate time histories with the new design feature to that for the TSPA-VA base case calculation (CRWMS M&amp;O, 1998a)

Linear graph convolutional networks

Many neural networks for graphs are based on the graph convolution operator, proposed more than a decade ago. Since then, many alternative definitions have been proposed, that tend to add complexity (and non-linearity) to the model. In this paper, we follow the opposite direction by proposing a linear graph convolution operator. Despite its simplicity, we show that our convolution operator is more theoretically grounded than many proposals in literature, and shows improved predictive performance