32,717 research outputs found

    NASA information resources for the feedback process

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    NASA information resources for feedback proces

    The weathering of micrometeorites from the Transantarctic Mountains

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    Micrometeorites are cosmic dust particles recovered from the Earth's surface that dominate the influx of extraterrestrial material accreting to our planet. This paper provides the first in-depth study of the weathering of micrometeorites within the Antarctic environment that will allow primary and secondary features to be distinguished. It is based on the analysis of 366 particles from Larkman Nunatak and 25 from the Transantarctic Mountain collection. Several important morphological categories of weathering effects were identified: (1) irregular and faceted cavities, (2) surface etch pits, (3) infilled cavities, (4) replaced silicate phases, and (5) hydrated and replaced metal. These features indicate that congruent dissolution of silicate phases, in particular olivine, is important in generating new pore space within particles. Comparison of the preservation of glass and olivine also indicates preferential dissolution of olivine by acidic solutions during low temperature aqueous alteration. Precipitation of new hydrous phases within cavities, in particular ferrihydrite and jarosite, results in pseudomorph textures within heavily altered particles. Glass, in contrast, is altered to palagonite gels and shows a sequential replacement indicative of varying water to rock ratios. Metal is variably replaced by Fe-oxyhydroxides and results in decreases in Ni/Fe ratio. In contrast, sulphides within metal are largely preserved. Magnetite, an essential component of micrometeorites formed during atmospheric entry, is least altered by interaction with the terrestrial environment. The extent of weathering in the studied micrometeorites is sensitive to differences in their primary mineralogy and varies significantly with particle type. Despite these differences, we propose a weathering scale for micrometeorites based on both their degree of terrestrial alteration and the level of encrustation by secondary phases. The compositions and textures of weathering products, however, suggest open system behaviour and variable water to rock ratios that imply climatic variation over the lifetime of the micrometeorite deposits

    Extent and mechanism of sealing in transected giant axons of squid and earthworms

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    Transected axons are often assumed to seal at their cut ends by the formation of continuous membrane barriers that allow for the restoration of function in the axonal stumps. We have used several electrophysiological measures (membrane potential, input resistance, injury current density) and several morphological measures (phase-contrast, video-enhanced differential interference contrast, light, and electron microscopies) of living and fixed material to assess the extent and mechanism of sealing within hours after transecting giant axons of squid (Loligo pealeiand Sepioteuthis lessoniana) and earthworms (Lumbricus terrestris). Our electrophysiological data suggest that the proximal and distal ends of transected squid giant axons do not completely seal within 2.5 hr in physiological saline. In contrast, the same set of measures suggest that proximal and distal ends of transected earthworm giant axons seal within 1 hr in physiological saline. Our morphological data show that the cut ends of both squid and earthworm axons constrict, but that a 20- 70-am-diameter opening always remains at the cut end that is filled with vesicles. Axonal transection induces the formation of vesicles that are observed in the axoplasm within minutes in standard salines and that rapidly migrate to the cut ends. These injury-induced vesicles are loosely packed near the cut ends of squid giant axons, which do not functionally seal within 2.5 hr of transection. In contrast, vesicles formed a tightly packed plug at the cut ends of earthworm medial giant axons, which do functionally seal within 1 hr of transection in physiological saline. Since we detect no single continuous membrane that spans the cut end, sealing does not appear to occur by the fusion of constricted axolemmal membrane or the formation of a membranous partition at the cut end. Rather, our data are consistent with the hypothesis that a tightly packed vesicular plug is responsible for sealing of earthworm giant axons.This work was supported in part by NIH Grant NS31256 and ONR Grant N00014-90-J-1137 to H.M.F., an NIAAA fellowship to T.L.K., and an ATP grant to G.D.B.Neuroscienc

    Audiogenic reflex seizures in cats

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    This study aims at characterizing feline audiogenic reflex seizures (FARS). An online questionnaire was developed to capture information from owners with cats suffering FARS. This was collated with the medical records from the primary veterinarian. Ninety-six cats were included. Myoclonic seizures were one of the cardinal signs of this syndrome (90/96), frequently occurring prior to generalized tonic-clonic seizures (GTCS) in this population. Other features include a late-onset (median 15 years) and absence seizures (6/96), with most seizures triggered by high frequency sounds amid occasional spontaneous seizures (up to 20%). Half the population (48/96) had hearing impairment or were deaf. One third of cats (35/96) had concurrent diseases, most likely reflecting the age distribution. Birmans were strongly represented (30/96). Levetiracetam gave good seizure control. The course of the epilepsy was non-progressive in the majority (68/96) with an improvement over time in some (23/96). Only 33/96 and 11/90 owners respectively felt the GTCS and myoclonic seizures affected their cat’s quality of life (QoL). Despite this, many owners (50/96) reported a slow decline in their cat’s health becoming less responsive (43/50), not jumping (41/50), uncoordinated or weak in the pelvic limbs (24/50), and exhibiting dramatic weight loss (39/50). These signs were exclusively reported in cats experiencing seizures for >2 years with 42/50 owners stating these signs affected their cat’s QoL. In gathering data on audiogenic seizures in cats, we have identified a new epilepsy syndrome named FARS with a geriatric-onset. Further studies are warranted to investigate potential genetic predispositions to this condition

    MAGMO: Coherent magnetic fields in the star forming regions of the Carina-Sagittarius spiral arm tangent

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    We present the pilot results of the `MAGMO' project, targeted observations of ground-state hydroxyl masers towards sites of 6.7-GHz methanol maser emission in the Carina-Sagittarius spiral arm tangent, Galactic longitudes 280 degrees to 295 degrees. The `MAGMO' project aims to determine if Galactic magnetic fields can be traced with Zeeman splitting of masers associated with star formation. Pilot observations of 23 sites of methanol maser emission were made, with the detection of ground-state hydroxyl masers towards 11 of these and six additional offset sites. Of these 17 sites, nine are new detections of sites of 1665-MHz maser emission, three of them accompanied by 1667-MHz emission. More than 70% of the maser features have significant circular polarization, whilst only ~10% have significant linear polarization (although some features with up to 100% linear polarization are found). We find 11 Zeeman pairs across six sites of high-mass star formation with implied magnetic field strengths between -1.5 mG and +3.8 mG and a median field strength of +1.6 mG. Our measurements of Zeeman splitting imply that a coherent field orientation is experienced by the maser sites across a distance of 5.3+/-2.0 kpc within the Carina-Sagittarius spiral arm tangent.Comment: 19 pages, 13 figures, accepted for publication in MNRA

    Volume 1, Number 05, May, 1865

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    https://place.asburyseminary.edu/reposofholiness/1004/thumbnail.jp

    Volume 1, Number 06, June, 1865

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    https://place.asburyseminary.edu/reposofholiness/1005/thumbnail.jp

    Volume 1, Number 04, April, 1865

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    https://place.asburyseminary.edu/reposofholiness/1003/thumbnail.jp

    Explosive Events and the Evolution of the Photospheric Magnetic Field

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    Transition region explosive events have long been suggested as direct signatures of magnetic reconnection in the solar atmosphere. In seeking further observational evidence to support this interpretation, we study the relation between explosive events and the evolution of the solar magnetic field as seen in line-of-sight photospheric magnetograms. We find that about 38% of events show changes of the magnetic structure in the photosphere at the location of an explosive event over a time period of 1 h. We also discuss potential ambiguities in the analysis of high sensitivity magnetograms
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