2,486 research outputs found
A Model for Patchy Reconnection in Three Dimensions
We show, theoretically and via MHD simulations, how a short burst of
reconnection localized in three dimensions on a one-dimensional current sheet
creates a pair of reconnected flux tubes. We focus on the post-reconnection
evolution of these flux tubes, studying their velocities and shapes. We find
that slow-mode shocks propagate along these reconnected flux tubes, releasing
magnetic energy as in steady-state Petschek reconnection. The geometry of these
three-dimensional shocks, however, differs dramatically from the classical
two-dimensional geometry. They propagate along the flux tube legs in four
isolated fronts, whereas in the two-dimensional Petschek model, they form a
continuous, stationary pair of V-shaped fronts.
We find that the cross sections of these reconnected flux tubes appear as
teardrop shaped bundles of flux propagating away from the reconnection site.
Based on this, we argue that the descending coronal voids seen by Yohkoh SXT,
LASCO, and TRACE are reconnected flux tubes descending from a flare site in the
high corona, for example after a coronal mass ejection. In this model, these
flux tubes would then settle into equilibrium in the low corona, forming an
arcade of post-flare coronal loops.Comment: 27 pages plus 16 figure
Patchy Reconnection in a Y-Type Current Sheet
We study the evolution of the magnetic field in a Y-type current sheet
subject to a brief, localized magnetic reconnection event. The reconnection
produces up- and down-flowing reconnected flux tubes which rapidly decelerate
when they hit the Y-lines and underlying magnetic arcade loops at the ends of
the current sheet. This localized reconnection outflow followed by a rapid
deceleration reproduces the observed behavior of post-CME downflowing coronal
voids. These simulations support the hypothesis that these observed coronal
downflows are the retraction of magnetic fields reconnected in localized
patches in the high corona.Comment: 4 pages, 3 figure
Field techniques for rearing and marking mountain pine beetle for use in dispersal studies
Mountain pine beetles, Dendroctonus ponderosae, were marked with fluorescent (DayGlo) powders in vacuum chambers and on powder-covered brood trees in the field for use in release-recapture studies of dispersal behaviour. A large wall tent was used as a field insectary to accelerate late stages of development of large numbers of beetles in naturally infested bolts of lodgepole pine. Up to 28% of the marked beetles which flew were recovered from lethal trap trees. Beetles self-marked on powdered brood trees were captured in barrier traps in predicted proportions
Macrophage Mal1 Deficiency Suppresses Atherosclerosis in Low-Density Lipoprotein Receptor -Null Mice by Activating Peroxisome Proliferator-Activated Receptor-g-Regulated Genes
Cataloged from PDF version of article.Objective-The adipocyte/macrophage fatty acid-binding proteins aP2 (FABP4) and Mal1 (FABP5) are intracellular lipid chaperones that modulate systemic glucose metabolism, insulin sensitivity, and atherosclerosis. Combined deficiency of aP2 and Mal1 has been shown to reduce the development of atherosclerosis, but the independent role of macrophage Mal1 expression in atherogenesis remains unclear.
Methods and Results-We transplanted wild-type (WT), Mal1(-/-), or aP2(-/-) bone marrow into low-density lipoprotein receptor-null (LDLR(-/-)) mice and fed them a Western diet for 8 weeks. Mal1(-/-)-> LDLR(-/-) mice had significantly reduced (36%) atherosclerosis in the proximal aorta compared with control WT -> LDLR(-/-) mice. Interestingly, peritoneal macrophages isolated from Mal1-deficient mice displayed increased peroxisome proliferator-activated receptor-gamma (PPAR gamma) activity and upregulation of a PPAR gamma-related cholesterol trafficking gene, CD36. Mal1(-/-) macrophages showed suppression of inflammatory genes, such as COX2 and interleukin 6. Mal1(-/-)-> LDLR(-/-) mice had significantly decreased macrophage numbers in the aortic atherosclerotic lesions compared with WT -> LDLR(-/-) mice, suggesting that monocyte recruitment may be impaired. Indeed, blood monocytes isolated from Mal1(-/-)-> LDLR(-/-) mice on a high-fat diet had decreased CC chemokine receptor 2 gene and protein expression levels compared with WT monocytes.
Conclusion-Taken together, our results demonstrate that Mal1 plays a proatherogenic role by suppressing PPAR gamma activity, which increases expression of CC chemokine receptor 2 by monocytes, promoting their recruitment to atherosclerotic lesions. (Arterioscler Thromb Vasc Biol. 2011;31:1283-1290.
Comments on a class of orthogonality relations relevant to fluid-structure interaction
Copyright @ 2011 Springer Science+Business Media B.V
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Efficient Estimation of a Semiparametric Characteristic-Based Factor Model of Security Returns
Point defect formation in optical materials expos ed to the space environment
Point defect formation associated with early stages of optical damage was observed unexpectedly in two, and possibly three, different optical materials subjected to short-duration space exposure. Three calcium fluoride, two lithium fluoride, and three magnesium fluoride samples were flown on Space Shuttle flight STS-46 as part of the Evaluation of Oxygen Interactions with Materials - Third Phase experiment. One each of the calcium and magnesium fluoride samples was held at a fixed temperature of 60 C during the space exposure, while the temperatures of the other samples were allowed to vary with the ambient temperature of the shuttle cargo bay. Pre-flight and post-flight optical absorption measurements were performed on all of the samples. With the possible exception of the magnesium fluoride samples, every sample clearly showed the formation of F-centers in that section of the sample that was exposed to the low earth orbit environment. Solar vacuum ultraviolet radiation is the most probable primary cause of the defect formation; however, the resulting surface metallization may be synergistically altered by the atomic oxygen environment
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