296 research outputs found
Finite-thrust transfer in the two and three body problems Final report
Computer program for optimal finite thrust transfer between two orbit
ALMA observations of the supergiant B[e] star Wd1-9
Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible – radiatively driven winds, impulsive ejection and/or binary interaction – remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (∼100 km s-1 ) ionized wind, with an extreme mass-loss rate ≳6.4 × 105(d/5 kpc)1.5 Mȯyr-1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they – and by extension the wider class of supergiant B[e] stars – may provide a unique window into the physics of a process that shapes the life-cycle of ∼70 per cent of massive stars found in binary systems
Expressive and receptive use of speech and graphic symbols by typically developing children: What skills contribute to performance on structured sentence-level tasks?
Purpose: To explore expressive and receptive use of speech and graphic symbols and relationships with linguistic and cognitive skills in children with typical development.
Method: Participants were 82 children with typical development (4 to 9 years). Measures of memory, visual analysis skills, and receptive language were used, along with five experimental tasks with speech or symbols as input (stimulus) or output (response), using single clause and compound clause stimuli. Cluster analysis grouped participants with similar performances patterns, who were then compared on linguistic and cognitive skill measures.
Result: The lowest performing group sometimes accurately interpreted graphic symbol utterances that were visible during responding. The mid-performing group was stronger on expressive than receptive symbol utterances when the model did not remain visible. The highest group was comparable on expressive and receptive symbol tasks, but nonetheless stronger with spoken utterances. Relationships of linguistic and cognitive skills with task performance differed across the clusters.
Conclusion: The findings help clarify the input-output modality asymmetry in graphic symbol communication. Spoken language proficiency does not directly transfer to sentence-level expressive and receptive graphic symbol use. Exploring potentially challenging sentence-level phenomena is important. Research is warranted to explore developmental progressions and potential clinical applications more systematically
Quasilinearization program for determining optimum finite-thrust transfers between inclined orbits
Quasi-linearization program for boundary value problem of minimum fuel orbital transfe
Automaticity of lexical access in deaf and hearing bilinguals: Cross-linguistic evidence from the color Stroop task across five languages
The well-known Stroop interference effect has been instrumental in revealing the highly automated nature of lexical processing as well as providing new insights to the underlying lexical organization of first and second languages within proficient bilinguals. The present cross-linguistic study had two goals: 1) to examine Stroop interference for dynamic signs and printed words in deaf ASL-English bilinguals who report no reliance on speech or audiological aids; 2) to compare Stroop interference effects in several groups of bilinguals whose two languages range from very distinct to very similar in their shared orthographic patterns: ASL-English bilinguals (very distinct), Chinese-English bilinguals (low similarity), Korean-English bilinguals (moderate similarity), and Spanish-English bilinguals (high similarity). Reaction time and accuracy were measured for the Stroop color naming and word reading tasks, for congruent and incongruent color font conditions. Results confirmed strong Stroop interference for both dynamic ASL stimuli and English printed words in deaf bilinguals, with stronger Stroop interference effects in ASL for deaf bilinguals who scored higher in a direct assessment of ASL proficiency. Comparison of the four groups of bilinguals revealed that the same-script bilinguals (Spanish-English bilinguals) exhibited significantly greater Stroop interference effects for color naming than the other three bilingual groups. The results support three conclusions. First, Stroop interference effects are found for both signed and spoken languages. Second, contrary to some claims in the literature about deaf signers who do not use speech being poor readers, deaf bilinguals’ lexical processing of both signs and written words is highly automated. Third, cross-language similarity is a critical factor shaping bilinguals’ experience of Stroop interference in their two languages. This study represents the first comparison of both deaf and hearing bilinguals on the Stroop task, offering a critical test of theories about bilingual lexical access and cognitive control
A model for uranium, rhenium, and molybdenum diagenesis in marine sediments based on results from coastal locations
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 73 (2009): 2938-2960, doi:10.1016/j.gca.2009.02.029.The purpose of this research is to characterize the mobilization and
immobilization processes that control the authigenic accumulation of uranium (U),
rhenium (Re) and molybdenum (Mo) in marine sediments. We analyzed these redox–
sensitive metals (RSM) in benthic chamber, pore water and solid phase samples at a site
in Buzzards Bay, Massachusetts, U.S.A., which has high bottom water oxygen
concentrations (230–300 mol/L) and high organic matter oxidation rates (390 mol
C/cm2/y). The oxygen penetration depth varies from 2–9 mm below the sediment–water
interface, but pore water sulfide is below detection (< 2M). The RSM pore water
profiles are modeled with a steady–state diagenetic model that includes irrigation, which
extends 10–20 cm below the sediment–water interface. To present a consistent
description of trace metal diagenesis in marine sediments, RSM results from sediments in
Buzzards Bay are compared with previous research from sulfidic sediments (Morford et
al., GCA 71).
Release of RSM to pore waters during the remineralization of solid phases occurs
near the sediment–water interface at depths above the zone of authigenic RSM formation.
This release occurs consistently for Mo at both sites, but only in the winter for Re in
Buzzards Bay and intermittently for U. At the Buzzards Bay site, Re removal to the solid
phase extends to the bottom of the profile, while the zone of removal is restricted to ~2–9
cm for U and Mo. Authigenic Re formation is independent of the anoxic
remineralization rate, which is consistent with an abiotic removal mechanism. The rate
of authigenic U formation and its modeled removal rate constant increase with increasing
anoxic remineralization rates, and is consistent with U reduction being microbially
mediated. Authigenic Mo formation is related to the formation of sulfidic
microenvironments. The depth and extent of Mo removal from pore water is closely
associated with the balance between iron and sulfate reduction and the consumption of
pore water sulfide via iron sulfide formation. Pore water RSM reach constant asymptotic
concentrations in sulfidic sediments, but only pore water Re is constant at depth in
Buzzards Bay. The increases in pore water U at the Buzzards Bay site are consistent with
addition via irrigation and subsequent upward diffusion to the removal zone. Deep pore
water Mo concentrations exceed its bottom water concentration due to irrigation–induced
oxidation and remobilization from the solid phase. In sulfidic sediments, there is no
evidence for higher pore water U or Mo concentrations at depth due to the absence of
irrigation and/or the presence of more stable authigenic RSM phases.
There are good correlations between benthic fluxes and authigenic accumulation
rates for U and Mo in sulfidic sediments. However, results from Buzzards Bay suggest
irrigation ultimately results in the partial loss of U and Mo from the solid phase, with
accumulation rates that are 20–30% of the modeled flux. Irrigation can augment (Re,
possibly U) or compromise (U, Mo) authigenic accumulation in sediments, and is
important when determining burial rates in continental margin sediments.The authors also acknowledge financial support from the National Science Foundation
(JLM, WRM: OCE–0220892), Research Corporation (JLM, CMC), Franklin & Marshall
College, and the Hackman Summer Research Program at F&M
Uranium diagenesis in sediments underlying bottom waters with high oxygen content
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 73 (2009): 2920-2937, doi:10.1016/j.gca.2009.02.014.We measured U in sediments (both pore waters and solid phase) from three
locations on the middle Atlantic Bight (MAB) from the eastern margin of the United
States: a northern location on the continental shelf off Massachusetts (OC426, 75 m water
depth), and two southern locations off North Carolina (EN433-1, 647 m water depth and
EN433-2, 2648 m water depth). These sediments underlie high oxygen bottom waters
(250-270 μM), but become reducing below the sediment-water interface due to the
relatively high organic carbon oxidation rates in sediments (EN433-1: 212 μmol C/cm2/y;
OC426: 120±10 μmol C/cm2/y; EN433-2: 33 μmol C/cm2/y). Pore water oxygen goes to
zero by 1.4-1.5 cm at EN433-1 and OC426 and slightly deeper oxygen penetration depths
were measured at EN433-2 (~4 cm).
All of the pore water profiles show removal of U from pore waters. Calculated
pore water fluxes are greatest at EN433-1 (0.66±0.08 nmol/cm2/y) and less at EN433-2
and OC426 (0.24±0.05 and 0.13±0.05 nmol/cm2/y, respectively). Solid phase profiles
show authigenic U enrichment in sediments from all three locations. The average
authigenic U concentrations are greater at EN433-1 and OC426 (5.8±0.7 nmol/g and
5.4±0.2 nmol/g, respectively) relative to EN433-2 (4.1±0.8 nmol/g). This progression is
consistent with their relative ordering of ‘reduction intensity’, with greatest reducing
conditions in sediments from EN433-1, less at OC426 and least at EN433-2. The
authigenic U accumulation rate is largest at EN433-1 (0.47±0.05 nmol/cm2/y), but the
average among the three sites on the MAB is ~0.2 nmol/cm2/y. Pore water profiles
suggest diffusive fluxes across the sediment-water interface that are 1.4-1.7 times greater
than authigenic accumulation rates at EN433-1 and EN433-2. These differences are
consistent with oxidation and loss of U from the solid phase via irrigation and/or
bioturbation, which may compromise the sequestration of U in continental margin
sediments that underlie bottom waters with high oxygen concentrations.
Previous literature compilations that include data exclusively from locations
where [O2]bw < 150 μM suggest compelling correlations between authigenic U
accumulation and organic carbon flux to sediments or organic carbon burial rate.
Sediments that underlie waters with high [O2]bw have lower authigenic U accumulation
rates than would be predicted from relationships developed from results that include
locations where [O2]bw < 150 μM.The
authors appreciate the financial support from NSF (JLM, WRM: OCE-0220892; and
OCE-0526389 to WRM), Research Corporation (JLM, CMC), Franklin & Marshall
College, and the Hackman Summer Research Program (CMC) at F&M
The rp-process and new measurements of beta-delayed proton decay of light Ag and Cd isotopes
Recent network calculations suggest that a high temperature rp-process could
explain the abundances of light Mo and Ru isotopes, which have long challenged
models of p-process nuclide production. Important ingredients to network
calculations involving unstable nuclei near and at the proton drip line are
-halflives and decay modes, i.e., whether or not -delayed proton
decay takes place. Of particular importance to these network calculation are
the proton-rich isotopes Ag, Ag, Cd and Cd. We
report on recent measurements of -delayed proton branching ratios for
Ag, Ag, and Cd at the on-line mass separator at GSI.Comment: 4 pages, uses espcrc1.sty. Proceedings of the 4th International
Symposium Nuclei in the Cosmos, June 1996, Notre Dame/IN, USA, Ed. M.
Wiescher, to be published in Nucl.Phys.A. Also available at
ftp://ftp.physics.ohio-state.edu/pub/nucex/nic96-gs
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