8,961 research outputs found
Histological and Gross Studies of Brain Tissue of Kittens Exhibiting Spastic Behavior
Histological and gross studies of brain tissue revealed lowered brain weight, lower brain weight to body weight ratios, and poor brain development in relation to the degree of spasticity exhibited in kittens but did not reveal any definite histological changes
UV Spectroscopy of AB Doradus with the Hubble Space Telescope. Impulsive flares and bimodal profiles of the CIV 1549 line in a young star
We observed AB Doradus, a young and active late type star (K0 - K2 IV-V, P=
0.514 d) with the Goddard High Resolution Spectrograph of the post-COSTAR
Hubble Space Telescope with the time and spectral resolutions of 27 s and 15
km, respectively. The wavelength band (1531 - 1565 A) included the strong CIV
doublet (1548.202 and 1550.774, formed in the transition region at 100 000 K).
The mean quiescent CIV flux state was close to the saturated value and 100
times the solar one. The line profile (after removing the rotational and
instrumental profiles) is bimodal consisting of two Gaussians, narrow (FWHM =
70 km/s) and broad (FWHM =330km/s). This bimodality is probably due to two
separate broadening mechanisms and velocity fields at the coronal base. It is
possible that TR transient events (random multiple velocities), with a large
surface coverage, give rise to the broadening of the narrow component,while
true microflaring is responsible for the broad one.
The transition region was observed to flare frequently on different time
scales and magnitudes. The largest impulsive flare seen in the CIV 1549
emission reached in less than one minute the peak differential emission measure
(10**51.2 cm-3) and returned exponentially in 5 minutes to the 7 times lower
quiescent level.The 3 min average line profile of the flare was blue-shifted
(-190 km/s) and broadened (FWHM = 800 km/s). This impulsive flare could have
been due to a chromospheric heating and subsequent evaporation by an electron
beam, accelerated (by reconnection) at the apex of a coronal loop.Comment: to be published in AJ (April 98), 3 tables and 7 figures as separate
PS-files, print Table 2 as a landscap
Electroencephalograms of Kittens Exhibiting Spastic Behavior
Examination and comparison of some basic reflex tests and of the electroencephalograms of five kittens showing spastic behavior with a control permitted the grouping of these animals into categories which were in accord with those previously determined on the basis of behavioral observation only
Coronal structure of the cTTS V2129 Oph
The nature of the magnetic coupling between T Tauri stars and their disks
determines not only the mass accretion process but possibly the spin evolution
of the central star. We have taken a recently-published surface magnetogram of
one moderately-accreting T Tauri star (V2129 Oph) and used it to extrapolate
the geometry of its large-scale field. We determine the structure of the open
(wind-bearing) field lines, the closed (X-ray bright) field lines and those
potentially accreting field lines that pass through the equatorial plane inside
the Keplerian co-rotation radius. We consider a series of models in which the
stellar magnetic field is opened up by the outward pressure of the hot coronal
gas at a range of radii. As this radius is increased, accretion takes place
along simpler field structures and impacts on fewer sites at the stellar
surface. This is consistent with the observed variation in the Ca II IRT and
HeI lines which suggests that accretion in the visible hemisphere is confined
to a single high-latitude spot. By determining the density and velocity of the
accretion flows, we find that in order to have most of the total mass accretion
rate impacting on a single high-latitude region we need disk material to
accrete from approximately 7R*, close to the Keplerian co-rotation radius at
6.8R*. We also calculate the coronal density and X-ray emission measure. We
find that both the magnitude and rotational modulation of the emission measure
increase as the source surface is increased. For the field structure of V2129
Oph which is dominantly octupolar, the emission forms a bright, high-latitude
ring that is always in view as the star rotates. Since the accretion funnels
are not dense enough to cause significant scattering of coronal X-ray photons,
they provide only a low rotational modulation of around 10% at most.Comment: 10 pages, 9 figure
Adaptive robust estimation in sparse vector model
For the sparse vector model, we consider estimation of the target vector, of its l2-norm and of the noise variance. We construct adaptive estimators and establish the optimal rates of adaptive estimation when adaptation is considered with respect to the triplet "noise level - noise distribution - sparsity". We consider classes of noise distributions with polynomially and exponentially decreasing tails as well as the case of Gaussian noise. The obtained rates turn out to be different from the minimax non-adaptive rates when the triplet is known. A crucial issue is the ignorance of the noise variance. Moreover, knowing or not knowing the noise distribution can also influence the rate. For example, the rates of estimation of the noise variance can differ depending on whether the noise is Gaussian or sub-Gaussian without a precise knowledge of the distribution. Estimation of noise variance in our setting can be viewed as an adaptive variant of robust estimation of scale in the contamination model, where instead of fixing the "nominal" distribution in advance, we assume that it belongs to some class of distributions
XMM-Newton Observation of Solar Wind Charge Exchange Emission
We present an XMM-Newton spectrum of diffuse X-ray emission from within the
solar system. The spectrum is dominated by probable C VI lines at 0.37 keV and
0.46 keV, an O VII line at 0.56 keV, O VIII lines at 0.65 keV and ~0.8 keV, Ne
IX lines at ~0.92 keV, and Mg XI lines at ~1.35 keV. This spectrum is
consistent with that expected from charge exchange emission between the highly
ionized solar wind and either interstellar neutrals in the heliosphere or
material from Earth's exosphere. The emission is clearly seen as a low-energy
(E<1.5 keV) spectral enhancement in one of a series of four observations of the
Hubble Deep Field North. The X-ray enhancement is concurrent with an
enhancement in the solar wind measured by ACE, Wind, and SoHO spacecraft. The
solar wind enhancement reaches a flux level an order of magnitude more intense
than typical fluxes at 1 AU, and has a significantly enhanced O^{+7}/O^{+6}
ratio. Besides being of interest in its own right for studies of the solar
system, this emission can have significant consequences for observations of
cosmological objects. It can provide emission lines at zero redshift which are
of particular interest in studies of diffuse thermal emission (e.g., O VII and
O VIII), and which can therefore act as contamination in the spectra of objects
which cover the entire detector field of view. We propose the use of solar wind
monitoring data as a diagnostic to screen for such possibilities.Comment: 26 pages, 6 figures, ApJ accepte
Low-Cost Air Quality Monitoring Tools: From Research to Practice (A Workshop Summary).
In May 2017, a two-day workshop was held in Los Angeles (California, U.S.A.) to gather practitioners who work with low-cost sensors used to make air quality measurements. The community of practice included individuals from academia, industry, non-profit groups, community-based organizations, and regulatory agencies. The group gathered to share knowledge developed from a variety of pilot projects in hopes of advancing the collective knowledge about how best to use low-cost air quality sensors. Panel discussion topics included: (1) best practices for deployment and calibration of low-cost sensor systems, (2) data standardization efforts and database design, (3) advances in sensor calibration, data management, and data analysis and visualization, and (4) lessons learned from research/community partnerships to encourage purposeful use of sensors and create change/action. Panel discussions summarized knowledge advances and project successes while also highlighting the questions, unresolved issues, and technological limitations that still remain within the low-cost air quality sensor arena
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