Community patterns and adaptive strategies of the infaunal benthos of Long Island Sound

Nearshore communities of infaunal benthos on soft bottoms are characterized by a highly variable species composition. Some species undergo large spatial and temporal variations in local abundance; other members of the same community change only a little...

Polarimetry of the Type Ia Supernova SN 1996X

We present broad-band and spectropolarimetry of the Type Ia SN 1996X obtained on April 14, 1996 (UT), and broad-band polarimetry of SN 1996X on May 22,1996, when the supernova was about a week before and 4 weeks after optical maximum, respectively. The Stokes parameters derived from the broad-band polarimetry are consistent with zero polarization. The spectropolarimetry, however, shows broad spectral features which are due intrinsically to an asymmetric SN atmosphere. The spectral features in the flux spectrum and the polarization spectrum show correlations in the wavelength range from 4900 AA up to 5500 AA. The degree of this intrinsic component is low (<0.3 %). Theoretical polarization spectra have been calculated. It is shown that the polarization spectra are governed by line blending. Consequently, for similar geometrical distortions, the residual polarization is smaller by about a factor of 2 to 3 compared to the less blended Type II atmosphere, making it intrinsically harder to detect asphericities in SNIa. Comparison with theoretical model polarization spectra shows a resemblance to the observations. Taken literally, this implies an asphericity of about 11 % in the chemical distribution in the region of partial burning. This may not imperil the use of Type Ia supernovae as standard candles for distance determination, but nontheless poses a source of uncertainty. SN 1996X is the first Type Ia supernova for which spectropolarimetry revealed a polarized component intrinsic to the supernova and the first Type Ia with spectropolarimetry well prior to optical maximum.Comment: 7 pages, 5 figures, macros 'aas2pp4.sty,psfig.tex'. LaTeX Style. Astrophysical Journal Letters, submitted September 199

Spectropolarimetry of the Type IIb Supernova 2001ig

We present spectropolarimetric observations of the Type IIb SN 2001ig in NGC 7424; conducted with the ESO VLT FORS1 on 2001 Dec 16, 2002 Jan 3 and 2002 Aug 16 or 13, 31 and 256 days post-explosion. These observations are at three different stages of the SN evolution: (1) The hydrogen-rich photospheric phase, (2) the Type II to Type Ib transitional phase and (3) the nebular phase. At each of these stages, the observations show remarkably different polarization properties as a function of wavelength. We show that the degree of interstellar polarization is 0.17%. The low intrinsic polarization (~0.2%) at the first epoch is consistent with an almost spherical (<10% deviation from spherical symmetry) hydrogen dominated ejecta. Similar to SN 1987A and to Type IIP SNe, a sharp increase in the degree of the polarization (~1%) is observed when the outer hydrogen layer becomes optically thin by day 31; only at this epoch is the polarization well described by a ``dominant axis.'' The polarization angle of the data shows a rotation through ~40 degrees between the first and second epochs, indicating that the asymmetries of the first epoch were not directly coupled with those observed at the second epoch. For the most polarized lines, we observe wavelength-dependent loop structures in addition to the dominant axis on the Q-U plane. We show that the polarization properties of Type IIb SNe are roughly similar to one another, but with significant differences arising due to line blending effects especially with the high velocities observed for SN 2001ig. This suggests that the geometry of SN 2001ig is related to SN 1993J and that these events may have arisen from a similar binary progenitor system.Comment: 42 pages, 12 figures (figs. 11 and 12 are both composed of four subpanels, figs. 6,7,8,11 and 12 are in color, fig. 1 is low res and a high res version is available at http://www.as.utexas.edu/~jrm/), ApJ Accepte

Analysis of the Flux and Polarization Spectra of the Type Ia Supernova SN 2001el: Exploring the Geometry of the High-velocity Ejecta

SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic polarization signal. In addition, during the epochs prior to maximum light, the CaII IR triplet absorption is seen distinctly and separately at both normal photospheric velocities and at very high velocities. The high-velocity triplet absorption is highly polarized, with a different polarization angle than the rest of the spectrum. The unique observation allows us to construct a relatively detailed picture of the layered geometrical structure of the supernova ejecta: in our interpretation, the ejecta layers near the photosphere (v \approx 10,000 km/s) obey a near axial symmetry, while a detached, high-velocity structure (v \approx 18,000-25,000 km/s) with high CaII line opacity deviates from the photospheric axisymmetry. By partially obscuring the underlying photosphere, the high-velocity structure causes a more incomplete cancellation of the polarization of the photospheric light, and so gives rise to the polarization peak and rotated polarization angle of the high-velocity IR triplet feature. In an effort to constrain the ejecta geometry, we develop a technique for calculating 3-D synthetic polarization spectra and use it to generate polarization profiles for several parameterized configurations. In particular, we examine the case where the inner ejecta layers are ellipsoidal and the outer, high-velocity structure is one of four possibilities: a spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The synthetic spectra rule out the spherical shell model, disfavor a toroid, and find a best fit with the clumped shell. We show further that different geometries can be more clearly discriminated if observations are obtained from several different lines of sight.Comment: 14 pages (emulateapj5) plus 18 figures, accepted by The Astrophysical Journa

Effect of deposit feeders on migration of 137Cs in lake sediments

Illite clay particles with adsorbed 137Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (~10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (~5 x 104 m-2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 +/- 0.007 cm/day (20[deg]C). When labeled particles entered the feeding zone, 137Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (~1.6 x 104 m-2) uniform activity developed rapidly (~17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm2/yr (7[deg]C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of 137Cs indicated an effective molecular diffusion coefficient of 0.02 cm2/yr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23642/1/0000606.pd

Linking teachers' memory-relevant language and the development of children's memory skills.

This longitudinal study was designed to (i) examine changes in children’s deliberate memory across the first grade; (ii) characterize the memory-relevant aspects of their classrooms; and (iii) explore linkages between the children’s performance and the language their teachers use in instruction. In order to explore contextual factors that may facilitate the development of skills for remembering, 107 first graders were assessed three times with a broad set of tasks, while extensive observations were made in the 14 classrooms from which these children were sampled. When the participating teachers were classified as high or low in terms of their “mnemonic orientation,” in part on the basis of their use of metacognitive information and requests for deliberate remembering during instruction in language arts and mathematics, differences were observed in the use of mnemonic techniques by the children in their classes. By the end of the year, the children drawn from these two groups of classrooms differed in their spontaneous use of simple behavioral strategies for remembering and in their response to training in more complex verbally-based mnemonic techniques

An Examination of Recent Transformations to the BV(RI)_C Photometric System from the Perspective of Stellar Models for Old Stars

Isochrones for ages > 4 Gyr and metallicities in the range -2.5 < [Fe/H] < +0.3 that take the diffusion of helium and recent advances in stellar physics into account are compared with observations in the Johnson-Cousins BV(RI)_C photometric system for several open and globular star clusters. The adopted color-Teff relations include those which we have derived from the latest MARCS model atmospheres and empirical transformations for dwarf and subgiant stars given by Casagrande et al (2010, A&A, 512, 54; CRMBA). Those reported by VandenBerg & Clem (2003, AJ, 126, 778) have also been considered, mainly to resolve some outstanding questions concerning them. Remarkably, when the subdwarfs in the CRMBA data set that have sigma_pi/pi < 0.15 are superimposed on a set of 12 Gyr isochrones spanning a wide range in [Fe/H], the inferred metallicities and effective temperatures agree, in the mean, with those given by CRMBA to within +/- 0.05 dex and +/- 10 K, respectively. Thus the hot Teff scale derived by CRMBA is nearly identical with that predicted by stellar models and consequently, there is excellent consistency between theory and observations on the H-R diagram and the different color-magnitude diagrams considered in this investigation. To obtain similar consistency, the colors obtained from the MARCS and VandenBerg & Clem B-V vs. Teff relations for metal-poor dwarf stars should be adjusted to the red by 0.02-0.03 mag. In general, isochrones that employ the CRMBA transformations provide reasonably good fits to our BV(RI)_C photometry for main-sequence stars in the globular clusters 47 Tuc, M3, M5, M92 and NGC 1851 - but not the cluster giants (when adopting the synthetic MARCS colors). We speculate that differences between the actual heavy-element mixtures and those assumed in the theoretical models may be the primary cause of this difficulty.Comment: To appear in 2010, AJ, 140, 102

Genome-wide variation and transcriptional changes in diverse developmental processes underlie the rapid evolution of seasonal adaptation

Many organisms enter a dormant state in their life cycle to deal with predictable changes in environments over the course of a year. The timing of dormancy is therefore a key seasonal adaptation, and it evolves rapidly with changing environments. We tested the hypothesis that differences in the timing of seasonal activity are driven by differences in the rate of development during diapause in Rhagoletis pomonella, a fly specialized to feed on fruits of seasonally limited host plants. Transcriptomes from the central nervous system across a time series during diapause show consistent and progressive changes in transcripts participating in diverse developmental processes, despite a lack of gross morphological change. Moreover, population genomic analyses suggested that many genes of small effect enriched in developmental functional categories underlie variation in dormancy timing and overlap with gene sets associated with development rate in Drosophila melanogaster. Our transcriptional data also suggested that a recent evolutionary shift from a seasonally late to a seasonally early host plant drove more rapid development during diapause in the early fly population. Moreover, genetic variants that diverged during the evolutionary shift were also enriched in putative cis regulatory regions of genes differentially expressed during diapause development. Overall, our data suggest polygenic variation in the rate of developmental progression during diapause contributes to the evolution of seasonality in R. pomonella. We further discuss patterns that suggest hourglass-like developmental divergence early and late in diapause development and an important role for hub genes in the evolution of transcriptional divergence

Spectrum and ionization rate of low energy Galactic cosmic rays

We consider the rate of ionization of diffuse and molecular clouds in the interstellar medium by Galactic cosmic rays (GCR) in order to constrain its low energy spectrum. We extrapolate the GCR spectrum obtained from PAMELA at high energies ($\ge 200$ GeV/ nucleon) and a recently derived GCR proton flux at $1\hbox{--}200$ GeV from observations of gamma rays from molecular clouds, and find that the observed average Galactic ionization rate can be reconciled with this GCR spectrum if there is a low energy cutoff for protons at $10\hbox{--}100$ MeV. We also identify the flattening below a few GeV as being due to (a) decrease of the diffusion coefficient and dominance of convective loss at low energy and (b) the expected break in energy spectrum for a constant spectral index in momentum. We show that the inferred CR proton spectrum of $\Phi \propto E_{kin}^{-1.7\pm0.2}$ for $E_{kin} \le$ few GeV, is consistent with a power-law spectrum in momentum $p^{-2.45\pm0.4}$, which we identify as the spectrum at source. Diffusion loss at higher energies then introduces a steepening by $E^{-\alpha}$ with $\alpha \sim 1/3$, making it consistent with high energy measurements.Comment: 5 pages, 3 figures, to appear in MNRAS Letter