2,442 research outputs found
The earth's trapped radiation belts
The near-earth charged particle environment is discussed in terms of spacecraft design criteria. Models are presented of the trapped radiation belts and based on in-situ data obtained from spacecraft
The chemistry of Antarctic ozone 1960-1987
The factors that influence Antarctic ozone are examined with a view to understanding the observed historical trend. Researchers show that reduced ambient temperatures can dramatically enhance the efficiency of chemical removal processes. Attention is focused on positive feedback between levels of ozone, temperature, and rates of heterogeneous chemical reactions. ClO and its dimer, and high levels of these gases are maintained until the clouds evaporate, on 15 September for the simulation shown here
Vortex avalanches in the non-centrosymmetric superconductor Li2Pt3B
We investigated the vortex dynamics in the non-centrosymmetric superconductor
Li_2Pt_3B in the temperature range 0.1 K - 2.8 K. Two different logarithmic
creep regimes in the decay of the remanent magnetization from the Bean critical
state have been observed. In the first regime, the creep rate is
extraordinarily small, indicating the existence of a new, very effective
pinning mechanism. At a certain time a vortex avalanche occurs that increases
the logarithmic creep rate by a factor of about 5 to 10 depending on the
temperature. This may indicate that certain barriers against flux motion are
present and they can be opened under increased pressure exerted by the
vortices. A possible mechanism based on the barrier effect of twin boundaries
is briefly discussed
Ultraviolet absorption: Experiment MA-059
A technique devised to permit the measurement of atmospheric species concentrations is described. This technique involves the application of atomic absorption spectroscopy and the quantitative observation of resonance fluorescence in which atomic or molecular species scatter resonance radiation from a light source into a detector. A beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation was sent from Apollo to Soyuz. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Results of postflight analysis of the resonance fluorescence data are discussed
Durable low surface-energy surfaces
A formulation for forming a low surface-energy surface on a substrate having (i) a fluoroalkyl silane having a low surface energy part, (ii) a liquid crystal silane operable for enhancing the orientation of the molecules of the fluoroalkyl silane and for crosslinking with the fluoroalkyl silane, and, (iii) a transport medium for applying the fluoroalkyl silane and the liquid crystal silane to the surface of a substrate. In one embodiment the formulation can includes a crosslinking agent for crosslinking the fluoroalkyl silane. In another embodiment the formulation has a condensation catalyst for enhancing chemical bonding of the fluoroalkyl silane to the substrate. The transport medium can be an alcohol such as methanol or ethanol
Agricultural Perturbations of the Nitrogen Cycle and Related Impact on Atmospheric N_2O and Ozone
The available data are employed to
identify the fate of agricultural nitrogen
in the environment. Best estimates
predict denitrification of nearly 50% of
fertilizer nitrogen in less than 10 years
after application. We also discuss in
detail the expected demand curve for agricultural N. If population growth
continues at projected levels, between 100
and 200 M tons/yr of agricultural N will
be needed by the year 2000. We estimate
that as a result, atmospheric N_2O could be
more than doubled by 2050, and that
perturbations of O_3 at that time could
range from 10 to more than 20%. Major
uncertainties remain however, and we
emphasize the importance of further
experimental research into the nitrogen
cycle
Balloon-borne radiometer measurement of Northern Hemisphere mid-latitude stratospheric HNO3 profiles spanning 12 years
Low-resolution atmospheric thermal emission spectra collected by balloon-borne radiometers over the time span of 1990–2002 are used to retrieve vertical profiles of HNO3, CFC-11 and CFC-12 volume mixing ratios between approximately 10 and 35 km altitude. All of the data analyzed have been collected from launches from a Northern Hemisphere mid-latitude site, during late summer, when stratospheric dynamic variability is at a minimum. The retrieval technique incorporates detailed forward modeling of the instrument and the radiative properties of the atmosphere, and obtains a best fit between modeled and measured spectra through a combination of onion-peeling and global optimization steps. The retrieved HNO3 profiles are consistent over the 12-year period, and are consistent with recent measurements by the Atmospheric Chemistry Experiment-Fourier transform spectrometer satellite instrument. This suggests that, to within the errors of the 1990 measurements, there has been no significant change in the HNO3 summer mid-latitude profile
Nitrous oxide in fresh water systems: An estimate for the yield of atmospheric N2O associated with disposal of human waste
The N2O content of waters in the Potomac and Merrimack Rivers was measured on a number of occasions over the period April to July 1977. The concentrations of dissolved N2O exceeded those which would apply in equilibrium with air by factors ranging from about 46 in the Potomac to 1.2 in the Merrimack. Highest concentrations of dissolved N2O were associated with sewage discharges from the vicinity of Washington, D. C., and analysis indicates a relatively high yield, 1.3 to 11%, for prompt conversion of waste nitrogen to N2O. Measurements of dissolved N2O in fresh water ponds near Boston demonstrated that aquatic systems provide both strong sources and sinks for atmospheric N2O
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