12,426 research outputs found
Optical Properties of the Arctic Upper Water
Optical properties of the Arctic Upper Water have been measured from Fletcher's Ice Island, T-3, in the Arctic Ocean. Beam transmittance for various wave-lengths and the upwelling and downwelling irradiance have been measured to a depth of 120 metres. In the spectral region of maximum transmittance, the beam transmittance was found to be 93.1% per metre and the diffuse attenuation coefficient for irradiance was 0.0444 per metre. The data show that the Arctic Upper Water, in early May before the snow cover on the ice has cleared, is optically uniform and very clear
An underwater spectral irradiance collector
The design, testing, and evaluation of the accuracy of a collector for measuring underwater spectral irradiance is the subject of this paper. A successful underwater irradiance collector is described. Emphasis is placed on the experimental techniques employed in testing its collecting properties and in measuring the immersion effect so that its accuracy can be estimated...
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Issue Brief: European Americans and Native Americans
This issue brief examines the relationship between European/White Americans and Native Americans. Complicated even to the present day, the relationship between these two groups has historically been one of oppressor versus oppressed, a dichotomy that has since evolved but which serves to shed light on the intricacies of the contemporary Native American experience in comparison to that of white America
The Role of Diffusive Shock Acceleration on Nonequilibrium Ionization in Supernova Remnant Shocks II: Emitted Spectra
We present a grid of nonequilibrium ionization models for the X-ray spectra
from supernova remnants undergoing efficient diffusive shock acceleration. The
calculation follows the hydrodynamics of the blast wave as well as the
time-dependent ionization of the plasma behind the shock. The ionization state
is passed to a plasma emissivity code to compute the thermal X-ray emission,
which is combined with the emission from nonthermal synchrotron emission to
produce a self-consistent model for the thermal and nonthermal emission from
cosmic-ray dominated shocks. We show how plasma diagnostics such as the
G'-ratio of He-like ions, defined as the ratio of the sum of the
intercombination, forbidden, and satellite lines to the resonance line, can
vary with acceleration efficiency, and discuss how the thermal X-ray emission,
when the time-dependent ionization is not calculated self-consistently with the
hydrodynamics, can differ from the thermal X-ray emission from models which do
account for the hydrodynamics. Finally we compare the thermal X-ray emission
from models which show moderate acceleration (~ 35%) to the thermal X-ray
emission from test-particle models.Comment: 17 pages, 12 figures. accepted for publication in the Astrophysical
Journa
Trends in forest taxes in South Missouri
Cover title.Includes bibliographical references (page 26)
Sawmill efficiency in the eastern Ozark region
This bulletin reports on School of Forestry research project 450, Sawmill Efficiency--P. [2].Includes bibliographical references (page 31)
Laboratory studies in ultraviolet solar physics
The research activity comprised the measurement of basic atomic processes and parameters which relate directly to the interpretation of solar ultraviolet observations and to the development of comprehensive models of the component structures of the solar atmosphere. The research was specifically directed towards providing the relevant atomic data needed to perform and to improve solar diagnostic techniques which probe active and quiet portions of the solar chromosphere, the transition zone, the inner corona, and the solar wind acceleration regions of the extended corona. The accuracy with which the physical conditions in these structures can be determined depends directly on the accuracy and completeness of the atomic and molecular data. These laboratory data are used to support the analysis programs of past and current solar observations (e.g., the Orbiting solar Observatories, the Solar Maximum Mission, the Skylab Apollo Telescope Mount, and the Naval Research Laboratory's rocket-borne High Resolution Telescope and Spectrograph). In addition, we attempted to anticipate the needs of future space-borne solar studies such as from the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft. Our laboratory activities stressed two categories of study: (1) the measurement of absolute rate coefficients for dielectronic recombination and electron impact excitation; and (2) the measurement of atomic transition probabilities for solar density diagnostics. A brief summary of the research activity is provided
Shock Speed, Cosmic Ray Pressure, and Gas Temperature in the Cygnus Loop
Upper limits on the shock speeds in supernova remnants can be combined with
post-shock temperatures to obtain upper limits on the ratio of cosmic ray to
gas pressure (P_CR / P_G) behind the shocks. We constrain shock speeds from
proper motions and distance estimates, and we derive temperatures from X-ray
spectra. The shock waves are observed as faint H-alpha filaments stretching
around the Cygnus Loop supernova remnant in two epochs of the Palomar
Observatory Sky Survey (POSS) separated by 39.1 years. We measured proper
motions of 18 non-radiative filaments and derived shock velocity limits based
on a limit to the Cygnus Loop distance of 576 +/- 61 pc given by Blair et al.
for a background star. The PSPC instrument on-board ROSAT observed the X-ray
emission of the post-shock gas along the perimeter of the Cygnus Loop, and we
measure post-shock electron temperature from spectral fits. Proper motions
range from 2.7 arcseconds to 5.4 arcseconds over the POSS epochs and post-shock
temperatures range from kT ~ 100-200 eV. Our analysis suggests a cosmic ray to
post-shock gas pressure consistent with zero, and in some positions P_CR is
formally smaller than zero. We conclude that the distance to the Cygnus Loop is
close to the upper limit given by the distance to the background star and that
either the electron temperatures are lower than those measured from ROSAT PSPC
X-ray spectral fits or an additional heat input for the electrons, possibly due
to thermal conduction, is required.Comment: Submitted to ApJ, 7 color figure
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