18,578 research outputs found
Central spar and module joint Patent
Design and development of module joint clamping device for application to solar array constructio
The opposites task: Using general rules to test cognitive flexibility in preschoolers
A brief narrative description of the journal article, document, or resource. Executive functions play an important role in cognitive development, and during the preschool years especially, children's performance is limited in tasks that demand flexibility in their behavior. We asked whether preschoolers would exhibit limitations when they are required to apply a general rule in the context of novel stimuli on every trial (the "opposites" task). Two types of inhibitory processing were measured: response interference (resistance to interference from a competing response) and proactive interference (resistance to interference from a previously relevant rule). Group data show 3-year-olds have difficulty inhibiting prepotent tendencies under these conditions, whereas 5-year-olds' accuracy is near ceiling in the task. (Contains 4 footnotes and 1 table.
A MERLIN Study of 6 GHz Excited-state OH & 6.7 GHz Methanol Masers in ON1
MERLIN observations of 6.668-GHz methanol and both 6.031- and 6.035-GHz
hydroxyl (OH) emission from the massive star-formation region ON1 are
presented. These are the first methanol observations made in full polarization
using 5 antennas of MERLIN, giving high resolution and sensitivity to extended
emission. Maser features are found to lie at the southern edge of the
ultra-compact HII region, following the known distribution of ground-state OH
masers. The masers cover a region ~1 arcsec in extent, lying perpendicular to
the H13CO+ bipolar outflow. Excited-state OH emission demonstrates consistent
polarization angles across the strongest linearly polarized features which are
parallel to the overall distribution. The linear polarizations vary between
10.0 and 18.5 per cent, with an average polarization angle of -60 deg +/- 28
deg. The strongest 6.668-GHz methanol features provide an upper limit to linear
polarization of ~1 per cent. Zeeman splitting of OH shows magnetic fields
between -1.1 to -5.8 mG, and a tentative methanol magnetic field strength of
-18 mG is measured.Comment: 10 Pages, 5 Figure
Influence of Pre-Training Predator Stress on the Expression of c-fos mRNA in the Hippocampus, Amygdala, and Striatum Following Long-Term Spatial Memory Retrieval
We have studied the influence of pre-training psychological stress on the expression of c-fos mRNA following long-term spatial memory retrieval. Rats were trained to learn the location of a hidden escape platform in the radial-arm water maze, and then their memory for the platform location was assessed 24 h later. Rat brains were extracted 30 min after the 24-h memory test trial for analysis of c-fos mRNA. Four groups were tested: (1) Rats given standard training (Standard); (2) Rats given cat exposure (Predator Stress) 30 min prior to training (Pre-Training Stress); (3) Rats given water exposure only (Water Yoked); and (4) Rats given no water exposure (Home Cage). The Standard trained group exhibited excellent 24 h memory which was accompanied by increased c-fos mRNA in the dorsal hippocampus and basolateral amygdala (BLA). The Water Yoked group exhibited no increase in c-fos mRNA in any brain region. Rats in the Pre-Training Stress group were classified into two subgroups: good and bad memory performers. Neither of the two Pre-Training Stress subgroups exhibited a significant change in c-fos mRNA expression in the dorsal hippocampus or BLA. Instead, stressed rats with good memory exhibited significantly greater c-fos mRNA expression in the dorsolateral striatum (DLS) compared to stressed rats with bad memory. This finding suggests that stressed rats with good memory used their DLS to generate a non-spatial (cue-based) strategy to learn and subsequently retrieve the memory of the platform location. Collectively, these findings provide evidence at a molecular level for the involvement of the hippocampus and BLA in the retrieval of spatial memory and contribute novel observations on the influence of pre-training stress in activating the DLS in response to long-term memory retrieval
On the Structure and Scale of Cosmic Ray Modified Shocks
Strong astrophysical shocks, diffusively accelerating cosmic rays (CR) ought
to develop CR precursors. The length of such precursor is believed to
be set by the ratio of the CR mean free path to the shock speed,
i.e., , which is formally
independent of the CR pressure . However, the X-ray observations of
supernova remnant shocks suggest that the precursor scale may be significantly
shorter than which would question the above estimate unless the
magnetic field is strongly amplified and the gyroradius is strongly
reduced over a short (unresolved) spatial scale. We argue that while the CR
pressure builds up ahead of the shock, the acceleration enters into a strongly
nonlinear phase in which an acoustic instability, driven by the CR pressure
gradient, dominates other instabilities (at least in the case of low
plasma). In this regime the precursor steepens into a strongly nonlinear front
whose size scales with \emph{the CR pressure}as , where is the scale of
the developed acoustic turbulence, and is the ratio of CR to gas
pressure. Since , the precursor scale reduction may be strong
in the case of even a moderate gas heating by the CRs through the acoustic and
(possibly also) the other instabilities driven by the CRs.Comment: EPS 2010 paper, to appear in PPC
Edge Shear Flows and Particle Transport near the Density Limit in the HL-2A Tokamak
Edge shear flow and its effect on regulating turbulent transport have long
been suspected to play an important role in plasmas operating near the
Greenwald density limit . In this study, equilibrium profiles as well as
the turbulent particle flux and Reynolds stress across the separatrix in the
HL-2A tokamak are examined as is approached in ohmic L-mode discharges.
As the normalized line-averaged density is raised, the
shearing rate of the mean poloidal flow drops, and the
turbulent drive for the low-frequency zonal flow (the Reynolds power ) collapses. Correspondingly, the turbulent particle
transport increases drastically with increasing collision rates. The geodesic
acoustic modes (GAMs) gain more energy from the ambient turbulence at higher
densities, but have smaller shearing rate than low-frequency zonal flows. The
increased density also introduces decreased adiabaticity which not only
enhances the particle transport but is also related to a reduction in the
eddy-tilting and the Reynolds power. Both effects may lead to the cooling of
edge plasmas and therefore the onset of MHD instabilities that limit the plasma
density
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