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301.
Jack Lorell George H. Born Edward J. Christensen Pasquale B. Esposito J. Frank Jordan Philip A. Laing William L. Sjogren Sun K. Wong Robert D. Reasenberg Irwin I. Shapiro Gary L. Slater 《Icarus》1973,18(2):304-316
Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the Earth or the Moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The best determined coefficients of the harmonic expansion of the gravitational potential are: J2 = (1.96 ± 10.01) × 10?3 ; C22 = ?(5.1 ± 0.2) × 10?5; and S22 = (3.4 ± 0.2) × 10?5. The other coefficients have not been well determined on an individual basis, but the ensemble yields a useful model for the gravity field for all longitudes in the vicinity of 23° South latitude which corresponds to the periapse position for the orbiter.The value obtained for the inverse mass of Mars (3 098 720 ± 70 M⊙?1) is in good agreement with prior determinations from Mariner flyby trajectories. The direction found for the rotational pole of Mars, referred to the mean equinox and equator of 1950.0, is characterized by α = 317°.3 ± 0°.2, δ = 52°.7 ± 0°.2. This result is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites, but differs by about 0°.5 from the previously accepted value. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (i) the dynamical flattening, f = (5.24 ± 0.02) × 10?3; (ii) the maximum principal moment of inertia, C = (0.375 ± 0.006) MR2; and (iii) the period of precession of Mars' pole, P ? (1.73 ± 0.03) × 105 yr, corresponding to a rate of 7.4 sec of arc per yr. 相似文献
302.
High-resolution seismic-reflection/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (Vs30), and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter-wavelength frequencies. In terms of Vs30, similar values were determined from the two methods. There is <15% difference at four of the six sites. The Vs30 values at the other two sites differ by 21% and 48%. The relative site amplification factors differ generally by less than 10% for both P- and S-wave velocities. We also found that S-wave reflections and first-arrival phase delays are essential for identifying velocity inversions. The results suggest that seismic reflection/refraction data are a fast, non-invasive, and less expensive alternative to downhole data for determining Vs30. In addition, we emphasize that some P- and S-wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances. A strong correlation between the simple S-wave first-arrival travel time/apparent velocity on the ground surface at 100 m offset from the seismic source and the Vs30 value for that site is an additional unique feature of the reflection/refraction data that could greatly simplify Vs30 determinations. 相似文献
303.
Hong Wang Keith C. Hackley Samuel V. Panno Dennis D. Coleman Jack Chao-li Liu Johnie Brown 《Quaternary Research》2003,60(3):348-355
Radiocarbon (14C) dating of total soil organic matter (SOM) often yields results inconsistent with the stratigraphic sequence. The onerous chemical extractions for SOM fractions do not always produce satisfactory 14C dates. In an effort to develop an alternative method, the pyrolysis-combustion technique was investigated to partition SOM into pyrolysis volatile (Py-V) and pyrolysis residue (Py-R) fractions. The Py-V fractions obtained from a thick glacigenic loess succession in Illinois yielded 14C dates much younger but more reasonable than the counterpart Py-R fractions for the soil residence time. Carbon isotopic composition (δ13C) was heavier in the Py-V fractions, suggesting a greater abundance of carbohydrate- and protein-related constituents, and δ13C was lighter in the Py-R fractions, suggesting more lignin- and lipid-related constituents. The combination of 14C dates and δ13C values indicates that the Py-V fractions are less biodegradation resistant and the Py-R fractions are more biodegradation resistant. The pyrolysis-combustion method provides a less cumbersome approach for 14C dating of SOM fractions. With further study, this method may become a useful tool for analyzing unlithified terrestrial sediments when macrofossils are absent. 相似文献
304.
Jack D. Ives Prof. Dr. 《GeoJournal》1992,27(1):127-129
During the two decades since the 1972 Stockholm Conference the concern for mountain environments coalesced under an institutional framework involving several organizations and many scholars and scientists. The evolution of the progress of these interested individuals, institutions, and their scholarly journal is outlined with benchmarks noted. An appraisal of the past two decades is given here in recognition of the UNCED-92 conference, the Earth Summit. 相似文献
305.
Dissipative and reflective beaches in a large lake and the physical effects of lake level regulation
Mark S. Lorang Jack A. Stanford F.Richard Hauer Jon H. Jourdonnais 《Ocean & Coastal Management》1993,19(3)
Nearshore environments in Flathead Lake, Montana, USA, were described as dissipative or reflective on the basis of: the surf similarity parameter , grain size, morphology, number of breaking waves and angle of wave incidence. The relative resistance to foreshore and backshore erosion caused by anthropogenic lake level regulation was compared between these two nearshore configurations. Reflective systems were characterized by dynamic gravel beach faces and steep inshore shelves armored by wave-washed cobble. In contrast, dissipative systems were characterized by sand-sized substratum, broad flat inshore shelves and the presence of multiple linear bars approximately 350 m offshore. Five decades of regulated lake levels have resulted in extensive shoreline erosion (970 ha on the north shore of the lake) and a general reshaping of both types of nearshore environments, although dissipative shorelines eroded faster (5.7 m/year maximum and 2.0 m/year average). The presence of docks and other man-made structures on reflective beaches accelerated erosion by intercepting longshore gravel transport. This analysis provided a physical basis for understanding the effects of lake level regulation on shoreline ecology and management. 相似文献
306.
It has been observed that the unrestrained free surface of a container can create relatively large liquid movements for even very small motions of the container. This excessive movement may endanger the stability as well as the maneuvering quality of the transporting vehicle. Therefore, the effects of the dynamic coupling of a liquid-tank system are of great concern. This dynamic coupling problem is studied analytically for a two-dimensional, rectangular rigid tank with no baffles. The governing equations of the liquid motion are derived with reference to a moving coordinate system which is fixed to the moving container. With the liquid forces generated by the fluid motion as the external exciting force for the tank, the motions of the liquid-tank system can be described according to Newton's Second Law of Motion. By using the Laplace transformation technique, the dynamic responses of the coupled system can be examined in detail. Numerical results for various types of external excitations and the resultant motions of the fluid-tank system are presented and compared with the equivalent non-shifting cargo system. The results of the comparison indicate that the discrepancy of responses in the two systems can obviously be observed when the ratio of the natural frequency of the fluid and the natural frequency of the tank is close to unity. Also, the amount of fluid inside the tank is a very important factor in determining the responses. 相似文献
307.
An analysis of radar and photographic meteor data and of spacecraft meteoroid penetration data indicates that there probably has not been a large increase in meteoroid impact rates in the last 104 yr. The solar flare tracks observed in the glass linings of meteoroid impact pits on lunar rock 15205 are therefore reanalyzed assuming a meteoroid flux that is constant in time. Based on this assumption, the data suggest that the production rate of Fe-group solar flare tracks may have varied by as much as a factor of 50 on a time scale of about 104 yr. No independently obtained data are known to require conflict with this interpretation. Confidence in this conclusion is somewhat qualified by the experimental and analytical uncertainties involved, but the conclusion nevertheless remains the present “best” explanation for the observed data trends. 相似文献
308.
We simulate the random front solutions of a nonlinear solute transport equation with spatial random coefficients modeling inhomogeneous sorption sites in porous media. The nonlinear sorption function is chosen to be Langmuir type, and the random coefficients are two independent stationary processes with fast decay of correlations. The model equation is in conservation form, and the random fronts are similar to random viscous shocks. We find that the average front speed is given by an ensemble averaged explicit Rankine–Hugoniot relation, and the front position fluctuates about its mean. Our numerical calculations show that the standard deviation is of the order O( $\sqrt t $ ) for large time, and the front fluctuation scaled by $\sqrt t $ converges to a Gaussian random variable wih mean zero. We come up with a formal theory of front fluctuation, yielding an explicit expression of the root t normalized front standard deviation in terms of the random media statistics. The theory agrees remarkably with the numerically discovered empirical formula. 相似文献
309.
Dubey Anant Aishwarya Hooper-Lewis Jack Ravi K. Dhami Navdeep Kaur Mukherjee Abhijit 《Acta Geotechnica》2022,17(12):5391-5410
Acta Geotechnica - Increased frequency of extreme weather events has made the conservation of riverbanks and coastlines a global concern. Soil stabilisation via microbially induced calcite... 相似文献
310.
David L. Morse Edwin D. Waddington Hans-Peter Marshall Tomas A. Neumann Eric J. Steig Jack E. Dibb Dale P. Winebrenner & Robert J. Arthern 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):683-694
Accumulation rate measurements on the East Antarctic plateau are challenging due to both spatial and temporal variability. Annual stratigraphy is often not reliably or consistently preserved in the firn, and so accumulation cannot be determined from snow pit stratigraphy. We present a suite of accumulation rate measurements collected over several seasons at Taylor Dome, East Antarctica. We compare net accumulation results from direct burial rate measurements and β -activity firn cores along a 35 km traverse. The two methods are consistent and show that the net accumulation varies from greater than 10 cm a−1 to about 1 cm a−1 (ice equivalent) southwest to northeast across the dome. We map the depth of shallow radar layering to interpolate and extrapolate these point-location measurements and show that considerable variations occur over kilometer scales resulting from subtle surface topography. We also present accumulation rates estimated from concentration of the cosmogenic isotope 10 Be and from activity profiles of 210 Pb. Finally, satellite passive microwave data are used to estimate spatially averaged accumulation rates on the regional to continental scale to provide a context for these local observations. We show that robust mass balance measurements in this environment must rely on spatial and/or temporal averaging. 相似文献