165 research outputs found
Structural Analysis Methods for the Roll-Out Solar Array Flight Experiment
The Roll-Out Solar Array (ROSA) flight experiment was launched to the International Space Station (ISS) on June 3rd, 2017. ROSA is an innovative, lightweight solar array with a flexible substrate that makes use of the stored strain energy in its composite structural members to provide deployment without the use of motors. This paper discusses the effort to model the structural dynamics of ROSA using finite element modeling. Two distinct and agnostic approaches were used by separate teams to assess the structural dynamics of the solar array prior to ground vibrational testing and flight testing. Results from each approach are compared to measured dynamics from accelerometers and photogrammetry data gathered on orbit. Advantages and disadvantages of each approach are discussed as are preliminary efforts to calibrate the models to the empirical data for the benefit of future modeling efforts on similar space structures
Cretaceous-Paleogene Dinoflagellate Biostratigraphy and the Age of the Clayton Formation, Southeastern Missouri, USA
Sedimentary deposits in Stoddard County, southeastern Missouri, reveal a K-Pg transition sequence represented by the uppermost Maastrichtian Owl Creek Formation and the Paleocene Clayton Formation. The Clayton Formation is characterized by a basal fossiliferous coquinite that contains reworked late Maastrichtian macrofossils. Dinoflagellate biostratigraphy is used to determine the age of the coquinite layer and specifically whether or not it is an end-K tsunamite deposit resulting from the Chicxulub impact event. Results indicate a mixed assemblage of late Maastrichtian and early Danian dinocysts within the basal coquinite of the Clayton Formation. Maastrichtian dinocyst taxa identified are Riculacysta amplexa, Pierceites pentagonus, Phelodinium tricuspe and Dinogymnium sp. and dinocysts utilized as global indicators of the basal Danian, also present in the coquinite, consist of Senoniasphaera inornata, Carpatella cornuta, Damassadinium californicum, and Lanternosphaeridium reinhardtii. A gray mud occurring above the coquinite in the middle of the Clayton Formation contains the mid-Danian dinoflagellate Senegalinium iterlaaense. Collectively, these data suggest that the coquinite was deposited well after the K-Pg event but before the middle Danian. The mixed assemblage of Late Cretaceous and Paleocene dinocysts preserved in the coquinite weakens the hypothesis that it is an end-K tsunamite deposit and suggests instead that it may result from a long-term transgressive lag. We also extend the stratigraphic range of the Paleocene Senegalinium simplex downward into the uppermost Maastrichtian
On-Orbit Structural Dynamics Performance of the Roll-Out Solar Array
The Roll-Out Solar Array (ROSA) flight experiment was launched to the International Space Station (ISS) on June 3rd, 2017. ROSA is an innovative, lightweight solar array with a flexible substrate that makes use of the stored strain energy in its composite structural members to provide deployment without the use of motors. This paper will discuss the results of various structural dynamics experiments conducted on the ISS during the weeks following launch. Data gathered from instrumentation on the solar array wing during the experiments are compared with pre-flight predictions from two different finite element modeling efforts. Two distinct methods were used to reconstruct the modal characteristics of ROSA from the data collected on orbit. Of particular interest in this effort are the first few system modes and mode shapes of the array, the amount of structural damping present, and degree of structural thermal interaction seen during eclipse exit. Discrepancies between the behavior predicted by the models and that observed on orbit are identified and discussed. The goal in this effort was to better understand the performance of ROSA and to improve modeling efforts for future designs of similar solar arrays
Extreme Variability in a Broad Absorption Line Quasar
CRTS J084133.15+200525.8 is an optically bright quasar at z=2.345 that has
shown extreme spectral variability over the past decade. Photometrically, the
source had a visual magnitude of V~17.3 between 2002 and 2008. Then, over the
following five years, the source slowly brightened by approximately one
magnitude, to V~16.2. Only ~1 in 10,000 quasars show such extreme variability,
as quantified by the extreme parameters derived for this quasar assuming a
damped random walk model. A combination of archival and newly acquired spectra
reveal the source to be an iron low-ionization broad absorption line (FeLoBAL)
quasar with extreme changes in its absorption spectrum. Some absorption
features completely disappear over the 9 years of optical spectra, while other
features remain essentially unchanged. We report the first definitive redshift
for this source, based on the detection of broad H-alpha in a Keck/MOSFIRE
spectrum. Absorption systems separated by several 1000 km/s in velocity show
coordinated weakening in the depths of their troughs as the continuum flux
increases. We interpret the broad absorption line variability to be due to
changes in photoionization, rather than due to motion of material along our
line of sight. This source highlights one sort of rare transition object that
astronomy will now be finding through dedicated time-domain surveys.Comment: 6 pages, 4 figures; accepted for publication in Ap
Impacts of ocean wave‐dependent momentum flux on global ocean climate
Accurate knowledge of air‐sea fluxes of momentum, heat, and carbon are central to fully understanding the evolution of the climate system. The role of ocean surface waves has been largely overlooked in global climate models despite the growing body of work elucidating the influence of ocean wave state on air‐sea fluxes. Here we account for the impact of ocean surface waves on global ocean climate using a global ocean model through implementation of wave‐dependent momentum fluxes. Wave‐dependent momentum fluxes improve the simulation of observed ocean heat content (OHC) through increasing the trend in OHC over the last three decades. Specifically, the larger increase in OHC is attributable to increased net heat flux in the Southern Hemisphere (SH). These results highlight the important role of accounting for wave‐dependent momentum transfer in terms of both simulating future climate and understanding changes over the recent historical period
National health and medical research council statement on electronic cigarettes: 2022 update
Introduction: Electronic cigarette (e-cigarette) use in Australia has rapidly increased since the 2017 National Health and Medical Research Council (NHMRC) Chief Executive Officer (CEO) statement on e-cigarettes. The type of products available and the demographic characteristics of people using these products have changed. New evidence has been published and there is growing concern among public health professionals about the increased use, particularly among young people who do not currently smoke combustible cigarettes. The combination of these issues led NHMRC to review the current evidence and provide an updated statement on e-cigarettes. In this article, we describe the comprehensive process used to review the evidence and develop the 2022 NHMRC CEO statement on electronic cigarettes. Main recommendations: E-cigarettes can be harmful; all e-cigarette users are exposed to chemicals and toxins that have the potential to cause adverse health effects. There are no health benefits of using e-cigarettes if you do not currently smoke tobacco cigarettes. Adolescents are more likely to try e-cigarettes if they are exposed to e-cigarettes on social media. Short term e-cigarette use may help some smokers to quit who have been previously unsuccessful with other smoking cessation aids. There are other proven safe and effective options available to help smokers to quit. Changes in management as a result of this statement: The evidence base for the harms of e-cigarette use has strengthened since the previous NHMRC statement. Significant gaps in the evidence base remain, especially about the longer term health harms of using e-cigarettes and the toxicity of many chemicals in e-cigarettes inhaled as an aerosol
Effects of receptor clustering on ligand dissociation: Theory and simulations
Receptor-ligand binding is a critical first step in signal transduction and
the duration of the interaction can impact signal generation. In mammalian
cells, clustering of receptors may be facilitated by heterogeneous zones of
lipids, known as lipid rafts. In vitro experiments show that disruption of
rafts significantly alters the dissociation of fibroblast growth factor-2
(FGF-2) from heparan sulfate proteoglycans, co-receptors for FGF-2. In this
paper, we develop a continuum stochastic formalism in order to (i) study how
rebinding affects the dissociation of ligands from a planar substrate, and (ii)
address the question of how receptor clustering influences ligand rebinding. We
find that clusters reduce the effective dissociation rate dramatically when the
clusters are dense and the overall surface density of receptors is low. The
effect is much less pronounced in the case of high receptor density and shows
non-monotonic behavior with time. These predictions are verified via lattice
Monte Carlo simulations. Comparison with experimental results suggests that the
theory does not capture the complete biological system. We speculate that
additional co-operative mechanisms might be present in order to increase ligand
retention, and present one possible ``internal diffusion'' model.Comment: Expanded text and added figures, revised version to appear in
Biophys.
The Effects of Mothers' Depression on the Behavioral Assessment of Disruptive Child Behavior
This study uses a group design to compare depressed and non-depressed mothers and their disruptive children. It controls for broad environmental stress factors to examine whether specific differences between groups can be linked with mothers’ depression. It aims to build a more comprehensive picture of depressed mothers’ interactions with their disruptive children by comparing these interactions with those of similar, but non-maternally depressed mother-child dyads, and a non-clinic control group
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