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971.
We have undertaken a study of coronal features observed at meter-decameter wavelengths using the Clark Lake radioheliograph.
Among the coronal structures we have studied are the radio manifestations of coronal streamers on the solar disk and above
the solar limb. We have analyzed the radio data quantitatively, using ray-tracing models for comparison with the maps. Our
study provides information about the streamers' three-dimensional shapes, scales, and density profiles, for comparison with
related observations using white-light coronagraphs. 相似文献
972.
E. V. Derishev F. A. Aharonian V. V. Kocharovsky Vl. V. Kocharovsky 《Astrophysics and Space Science》2005,297(1-4):21-30
We discuss the properties of gamma-ray radiation accompanying the acceleration of cosmic rays via the converter mechanism.
The mechanism exploits multiple photon-induced conversions of high-energy particles from charged into neutral state (namely,
protons to neutrons and electrons to photons) and back. Because a particle in the neutral state can freely cross the magnetic
field lines, this allows to avoid both particle losses downstream and reduction in the energy gain factor, which normally
takes place due to highly collimated distribution of accelerated particles. The converter mechanism efficiently operates in
relativistic outflows under the conditions typical for Active Galactic Nuclei, Gamma-Ray Bursts, and microquasars, where it
outperforms the standard diffusive shock acceleration.
The accompanying radiation has a number of distinctive features, such as an increase of the maximum energy of synchrotron
photons and peculiar radiation beam-pattern, whose opening angle is much wider at larger photon energies. This provides an
opportunity to observe off-axis relativistic jets in GeV–TeV energy range. One of the implications is the possibility to explain
high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars. 相似文献
973.
E. Juvigné 《Quaternary Research》1975,5(1):121-123
The following note on a new method for extracting pollen from fossil pollen grains summarizes two articles in French, published in Annales de la Société Géologique de Belgique (Juvigné, 1973a; 1973b).The new method proposed has three important parts: (1) Elutriation of the sediment in water; (2) the specific gravity of the heavy liquid must be between 2.25 and 2.5; and (3) the dispersion of the sediment in the heavy liquid is made with a high-speed mixer. 相似文献
974.
A. Määttänen F. Montmessin F. Scholten F. González-Galindo A. Spiga E. Hauber J.-P. Bibring 《Icarus》2010,209(2):452-469
This study presents the latest results on the mesospheric CO2 clouds in the martian atmosphere based on observations by OMEGA and HRSC onboard Mars Express. We have mapped the mesospheric CO2 clouds during nearly three martian years of OMEGA data yielding a cloud dataset of ∼60 occurrences. The global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor, at seasons Ls = 0-60° and again at and after Ls = 90°. A recent observation shows that the equatorial CO2 cloud season may start as early as at Ls = 330°. Three cases of mesospheric midlatitude autumn clouds have been observed. Two cloud shadow observations enabled the mapping of the cloud optical depth (τ = 0.01-0.6 with median values of 0.13-0.2 at λ = 1 μm) and the effective radii (mainly 1-3 μm with median values of 2.0-2.3 μm) of the cloud crystals. The HRSC dataset of 28 high-altitude cloud observations shows that the observed clouds reside mainly in the altitude range ∼60-85 km and their east-west speeds range from 15 to 107 m/s. Two clouds at southern midlatitudes were observed at an altitude range of 53-62 km. The speed of one of these southern midlatitude clouds was measured, and it exhibited west-east oriented speeds between 5 and 42 m/s. The seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work. The LMD Mars Global Climate Model shows that at the cloud altitude range (65-85 km) the temperatures exhibit significant daily variability (caused by the thermal tides) with the coldest temperatures towards the end of the afternoon. The GCM predicts the coldest temperatures of this altitude range and the season Ls = 0-30° in the longitudinal corridor where most of the cloud observations have been made. However, the model does not predict supersaturation, but the GCM-predicted winds are in fair agreement with the HRSC-measured cloud speeds. The clouds exhibit variable morphologies, but mainly cirrus-type, filamented clouds are observed (nearly all HRSC observations and most of OMEGA observations). In ∼15% of OMEGA observations, clumpy, round cloud structures are observed, but very few clouds in the HRSC dataset show similar morphology. These observations of clumpy, cumuliform-type clouds raise questions on the possibility of mesospheric convection on Mars, and we discuss this hypothesis based on Convective Available Potential Energy calculations. 相似文献
975.
976.
Michael E. McCormick 《Ocean Engineering》1976,3(3):133-144
The analysis of a pneumatic-type wave-energy conversion buoy is developed assuming independence of the buoy heaving motion and the motion of the water column within the center pipe. Results of the analysis are then compared with experimental data in a study of the relative air velocity within the turbine passage. The results compare very well. The effect of the variation of the center pipe length is found to be significant for periods about the surge chamber resonance but is negligible in the neighborhood of the heaving resonance period. Further, the theory is applied to a prototype buoy study of the U.S. Coast Guard, and a dimensionless design curve is developed from the results of the prototype analysis. 相似文献
977.
Roughness lengths were determined from average current profiles in the logarithmic boundary layer at a site in the southern North Sea. Grab samples indicated that the bed configuration controlling the bed roughness was unlikely to change even at maximum spring tides, but the measured roughness lengths were found to decrease as the speed of the flow 10 m above the bed increased. This has been qualitatively interpreted in terms of the size of the turbulent eddies within the flow and their effectiveness at “feeling” the size of the elements forming the bed roughness. It is also shown that the dependence of the observed drag coefficient on the Rossby number follows closely the theoretical form when the roughness length decreases with increasing flow speed. 相似文献
978.
The performance of Salter's cam as an energy extractor from ocean waves is studied numerically on the basis of linear theory of surface waves and floating bodies. Quantities of engineering interest such as efficiency, induced motion and reaction forces are presented and discussed both for fixed and for partly constrained cam shafts. 相似文献
979.
980.