9,163 research outputs found
Millstone Hill Thomson Scatter Results for 1972
During 1972, the vertically directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperatures, and vertical ion velocity in the F-region over periods of 24 hours, one or two times per month. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams.
For a number of the days, the spectra of the signals gathered at altitudes between 450 and 1125 km have been the subject of further analysis in an effort to determine the percentage of H[superscript +] ions present over Millstone. The results suggest that H[superscript +] ions are escaping from the F-region to the magnetosphere at a value close to the theoretical limiting flux during the daytime in all seasons. At night the flux becomes downward commencing near midnight in winter, but may remain upward throughout the night in summer
Millstone Hill Thomson Scatter Results for 1971
During 1971, the incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure the electron density, electron and ion temperatures, and the vertical velocity of the 0[superscript +] ions in the F-region over periods of 24 hours on 20 days. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents these results, after smoothing as a set of machine-drawn contour plots.
The report discusses the behavior observed in 1971 in light of that seen in previous years. A significant number of days appear to have been disturbed by large traveling ionospheric disturbances. Results for the average exospheric temperature, the mean meridional, and zonal winds for 1970and 1971 derived from these incoherent scatter measurements in a separate study by B.A. Emery are summarized here for completeness. The results appear to confirm the mean wind behavior that would be predicted by the recent Mass-Spectrometer, Incoherent-Scatter (MSIS) global model for the thermosphere and support the view that interhemispheric transport of light neutral constituents (e.g., atomic oxygen) gives rise to tie anomalous seasonal behavior of the ionosphere at midlatitudes
Millstone Hill Thomson Scatter Results for 1973
During 1973, the vertically-directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperature and vertical ion velocity in the F-region over periods of 24 hours one or two times per month. The observations spanned the height interval 200-900 km approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams.
For a number of the days, the results have been used to derive the diurnal variation of the temperature of the neutral atmosphere above 300 km (the exospheric temperature) as well as the speed of the neutral wind in the magnetic meridian plane at this altitude. These results were used to define a model for the pressure variation in the thermosphere over Millstone whose E-W variation is set by the observed temperature variation, and whose N-S variation was adjusted to reproduce the observed winds calculated by solving momentum equations for the neutral air. These results, together with similar results obtained using data gathered over the six-year period 1970-1975 have been used in a study of the seasonal and sunspot cycle variation of the mean meridional and zonal winds. Also reported are the results of a study of the effect of magnetic storms on the thermospheric winds observed over Millstone Hill
Measurement of tensor analyzing powers in deuteron photodisintegration
New accurate measurement of tensor analyzing powers T20, T21 and T22 in
deuteron photodisintegration has been performed. Wide-aperture non-magnetic
detectors allowed to cover broad kinematic ranges in a single setup: photon
energy = 25 to 600 MeV, proton emission angle in CM = 24 to 48 deg. and 70 to
102 deg. New data provide a significant improvement of a few existing
measurements. The angular dependency of the tensor asymmetries in deuteron
photodisintegration is extracted for the first time.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Evidence for Proportionate Partition Between the Magnetic Field and Hot Gas in Turbulent Cassiopeia A
We present a deep X-ray observation of the young Galactic supernova remnant
Cas A, acquired with the ROSAT High Resolution Imager. This high dynamic range
(232 ks) image reveals low-surface-brightness X-ray structure, which appears
qualitatively similar to corresponding radio features. We consider the
correlation between the X-ray and radio morphologies and its physical
implications. After correcting for the inhomogeneous absorption across the
remnant, we performed a point by point (4" resolution) surface brightness
comparison between the X-ray and radio images. We find a strong (r = 0.75)
log-log correlation, implying an overall relationship of . This is
consistent with proportionate partition (and possibly equipartition) between
the local magnetic field and the hot gas --- implying that Cas A's plasma is
fully turbulent and continuously amplifying the magnetic field.Comment: 8 pages with embedded bitmapped figures, Accepted by ApJ Letters
5/1/9
Differentiating between Hemorrhagic Infarct and Parenchymal Intracerebral Hemorrhage
Differentiating hemorrhagic infarct from parenchymal intracerebral hemorrhage can be difficult. The immediate and long-term management of the two conditions are different and hence the importance of accurate diagnosis. Using a series of intracerebral hemorrhage cases presented to our stroke unit, we aim to highlight the clues that may be helpful in distinguishing the two entities. The main clue to the presence of hemorrhagic infarct on computed tomography scan is the topographic distribution of the stroke. Additional imaging modalities such as computed tomography angiogram, perfusion, and magnetic resonance imaging may provide additional information in differentiating hemorrhagic infarct from primary hemorrhages
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