Aerosol particle chemical characteristics measured from aircraft in the lower troposphere during ACE‐2     

Martina Schmeling  Lynn M. Russell  Carynelisa Erlick  Donald R. Collins  Haflidi Jonsson  Qing Wang  Peter Kregsamer  Christina Streli 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):185-200

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Upper mantle shear structure of North America   总被引：5，自引：0，他引：5  

Stephen P. Grand  Donald V. Helmberger 《Geophysical Journal International》1984,76(2):399-438

Summary. The waveforms and travel times of S and SS phases in the range 10°–60° have been used to derive upper mantle shear velocity structures for two distinct tectonic provinces in North America. Data from earthquakes on the East Pacific Rise recorded at stations in western North America were used to derive a tectonic upper mantle model. Events on the north-west coast of North America and earthquakes off the coast of Greenland provided the data to investigate the upper mantle under the Canadian shield. All branches from the triplications due to velocity jumps near 400 and 660 km were observed in both areas. Using synthetic seismograms to model these observations placed tight constraints on heterogeneity in the upper mantle and on the details of its structure. SS–S travel-time differences of 30 s along with consistent differences in waveforms between the two data sets require substantial heterogeneity to at least 350 km depth. Velocities in the upper 170 km of the shield are about 10 per cent higher than in the tectonic area. At 250 km depth the shield velocities are still greater by about 4.5 per cent and they gradually merge near 400 km. Below 400 km no evidence for heterogeneity was found. The two models both have first-order discontinuities of 4.5 per cent at 405 km and 7.5 per cent at 695 km. Both models also have lids with lower velocities beneath. In the western model the lid is very thin and of relatively low velocity. In the shield the lid is 170 km thick with very high elocity (4.78 km s^-1); below it the velocity decreases to about 4.65 km s^-1. Aside from these features the models are relatively smooth, the major difference between them being a larger gradient in the tectonic region from 200 to 400 km.  相似文献   

Estimating the yields of the Amchitka tests by waveform intercorrelation     

Thorne Lay  L. J. Burdick  Donald V. Helmberger 《Geophysical Journal International》1984,78(1):181-207

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Stability of Pluto's atmosphere     

Donald M. Hunten  Andrew J. Watson 《Icarus》1982,51(3):665-667

L. Trafton (1980, Icarus44, 53–61) has pointed out that a substantial methane atmosphere, observed on Pluto by U. Fink, B.A. Smith, D.C. Benner, J.R. Johnson, and H.J. Reitsema (1980, Icarus44, 62–71), appears to be unstable against blowoff. The difficulty is shown to disappear if the actual heat balance and thermal structure are considered, instead of the classic assumption that the upper atmosphere is isothermal. An energy-limited flux (referred to the surface area) of 3.9 × 10¹⁰ cm^?2 sec^?1 is found. The loss of methane ice over the age of the solar system is an acceptable 3 km.  相似文献   

Radar detection of near-Earth Asteroids 1915 Quetzalcoatl, 3199 Nefertiti, 3757 (1982 XB), and 4034 (1986 PA)     

Michael K. Shepard  Lance A.M. Benner  Donald B. Campbell  John F. Chandler 《Icarus》2004,172(1):170-178

We describe Arecibo (2380 MHz, 12.6 cm) Doppler-only radar detections of near-Earth Asteroids 1915 Quetzalcoatl, 3199 Nefertiti, 3757 (1982 XB), and 4034 (1986 PA) obtained between 1981 and 1989. Estimates of the echo spectral bandwidths, radar cross-sections, and circular polarization ratios of these objects constrain their sizes, radar albedos, surface roughnesses, taxonomic classes, rotation periods, and pole directions. Our radar constraints on the diameters of Quetzalcoatl and Nefertiti are most consistent with sizes determined using thermal-radiometry and the Fast Rotation Model (FRM); this consistency may indicate that these asteroids have surfaces of high thermal inertia (i.e., little or no regolith). Constraints on Quetzalcoatl's radar albedo rule out a “metallic M” classification. The radar constraints for Nefertiti are inconsistent with a rotation pole published by Kaasalainen et al. (2004, Icarus 167, 178). Our estimates of 1982 XB's size are consistent with previously published estimates. The radar bandwidth of 1986 PA places an upper bound of about 24 h on its rotation period.  相似文献   

Book reviews     

Regina Tempel  Jaak Daemen  Donald E. Myers 《Mathematical Geology》1996,28(6):819-826

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Advances in underwater technology, ocean science and underwater engineering, volume 8 exclusive economic zones, resource opportunities and the legal regime : Society for underwater technology Graham and Trotman, London, 1986, 187 pp, £30.00     

Donald Cameron Watt 《Marine Policy》1987,11(4)

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Discriminant trace-element analysis of strata in the Witwatersrand System     

Ronald I. Hutchison  Donald L. Skinner  Donald R. Bowes 《Mathematical Geology》1976,8(4):413-427

Powdered rock samples from strata of the Witwatersrand System's sedimentary succession have been analyzed by x-ray fluorescence and optical spectroscopy techniques for nineteen elements. Using discriminant analysis it is possible to identify strata based on their trace-element compositions.  相似文献   

IPEDA LAND-TAX DATA AS A SOURCE OF INFORMATION ON THE INDONESIAN CITY: THE CASE OF UJUNG PANDANG,SULAWESI     

W. Donald McTaggart 《The Professional geographer》1979,31(4):416-422

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Resonant attitude instabilities for a symmetric satellite in a circular orbit     

Donald L. Hitzl 《Celestial Mechanics and Dynamical Astronomy》1972,5(4):433-450

The roll-yaw attitude motion of a spinning symmetric satellite in a circular orbit is investigated with particular emphasis on the behavior near resonance. Resonance in circular orbit occurs if there is a low-order commensurability between the coupled roll-yaw attitude frequencies. For the so-called Delp region where the Hamiltonian describing the linearized attitude oscillations is not positive definite, there can exist, near resonance, a simultaneous growth or decay of the energy of the two normal modes. Two sections of the resonance line ₂=3 ₁ permitting the largest effects are determined and the equations of motion are integrated numerically as a check on the resonance theory. In particular, resonance-induced instabilities are confirmed.  相似文献