Discovering research value in the Campo del Cielo,Argentina, meteorite craters     

William A. CASSIDY  Marc L. RENARD 《Meteoritics & planetary science》1996,31(4):433-448

Abstract The Campo del Cielo meteorite crater field in Argentina contains at least 20 small meteorite craters, but a recent review of the field data and a remote sensing study suggest that there may be more. The fall occurred ～4000 years ago into a uniform loessy soil, and the craters are well enough preserved so that some of their parameters of impact can be determined after excavation. The craters were formed by multi-ton fragments of a type IA meteoroid with abundant silicate inclusions. Relative to the horizontal, the angle of infall was ～9°. Reflecting the low angle of infall, the crater field is elongated with apparent dimensions of 3 × 18.5 km. The largest craters are near the center of this ellipse. This suggests that when the parent meteoroid broke apart, the resulting fragments diverged from the original trajectory in inverse relation to their masses and did not undergo size sorting due to atmospheric deceleration. The major axis of the crater field as we know it extends along N63°E, but the azimuths of infall determined by excavation of Craters 9 and 10 are N83.5°E and N75.5°E, respectively. This suggests that the major axis of the crater field is not yet well determined. The three or four largest craters appear to have been formed by impacts that disrupted the projectiles, scattering fragments around the outsides of the craters and leaving no large masses within them; these are relatively symmetrical in shape. Other craters are elongated features with multi-ton masses preserved within them and no fragmentation products outside. There are two ways in which field research on the Campo del Cielo crater field is found to be useful. (1) Studies exist that have been used to interpret impact craters on planetary surfaces other than the Earth. This occurrence of a swarm of projectiles impacting at known angles and similar velocities into a uniform target material provides an excellent field site at which to test the applicability of those studies. (2) Individual craters at Campo del Cielo can yield the masses of the projectiles that formed them and their velocities, angles and azimuths of impact. From these data, there is a possibility to estimate parameters for the parent meteoroid at entry and, thus, learn enough about its orbit to judge whether or not it was compatible with an asteroidal origin. Preliminary indications are that it was. Campo del Cielo is a IA iron meteorite and Sikhote-Alin, an observed fall, is a IIB iron meteorite in Wasson's classification. The Sterlitamak iron, also an observed fall, is a medium octahedrite in the Prior-Hey classification. It would be interesting to compare their orbital parameters.  相似文献   

Thermal Infrared Spectra of Comet Hale-Bopp at Heliocentric Distances of 4 and 2.9 AU     

Davis  John K.  Geballe  Thomas R.  Hanner  Marthe S.  Weaver  H. A.  Crovisier  Jacques  Bockelée-Morvan  Dominique 《Earth, Moon, and Planets》1997,78(1-3):293-298

We present 10 and 20 μm spectra of comet Hale-Bopp taken at UKIRT on 1996 June 20 and 1996 September 29.The 10 μm spectra clearly show a strong silicate feature with peaks at 10.0 and 11.2 μm. The 20 μm spectrum on September 29 has strong excess flux relative to a blackbody and a peak near 19μm, in good agreement with the ISO SWS spectra obtained a week later. However, the 20 μm spectrum on June 20 has significantly lower flux than would be expected based on a blackbody extrapolation from the flux at 12.5 μm. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

CCD Observations of Comet Hale-Bopp at Shajn Telescope I. Coude spectra     

Korsun  P. P.  Davis  S. P.  Shavrina  A. V.  Vasiljeva  I. E.  Malanushenko  V. P.  Savanov  I. S. 《Earth, Moon, and Planets》1997,78(1-3):119-125

Spectroscopic observations of Comet Hale-Bopp were made at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory. Some spectra were obtained with high spectral resolution, FWHM = 0.18–0.4Å, in the coude focus on February 22 and 26, 1997. The observations were made in selected spectral windows (4805–4872 Å,6528–6595 Å, 7186–7253 Å, 8276–8408 Å).The spectrograph slit was centered on the nucleus and had dimensions of 25.2 × 0.6 arcsec² on the plane of the sky. The continuum spatial profiles were extremely asymmetrical toward the Sun. However, the continuum-subtracted spatial profiles of the molecular emissions were symmetrical relative to the nucleus, except for C₂. The shape of the spatial profiles of the C₂ emissions is similar to that one of continuum but is more flattened. So, there are evidences that dust can be an additional source of the C₂ radicals in the cometary coma. The main aim of our research was identification of the cometary emissions. Using recent laboratory spectroscopic data we identified newlines of C₂ associated with the transitions from high rotational levels in the 4805–4872 Å spectral region. We detected cometary H_α emission as well. Emissions of NH₂, H₂O⁺,and C₂ (Phillips system) were found in the red spectral windows. Some emission features are still unassigned.  相似文献   

Six factors which affect the condition number of matrices associated with kriging     

George J. Davis  Max D. Morris 《Mathematical Geology》1997,29(5):669-683

Determining kriging weights to estimate some variable of interest at a given point in the field involves solving a system of linear equations. The matrix of this linear system is subject to numerical instability, and this instability is measured by the matrix condition number. Six parameters in the kriging process have been identified which directly affect this condition number. Analysis of a series of 648 experiments gives some insight on these parameters, and how the condition number relates to kriging variance.  相似文献   

Hydrologic and hydraulic computations on small programmable calculators: Thomas E. Croley II,IOWA Institute of Hydraulic Research     

John Davis 《Advances in water resources》1978,1(4):247

  相似文献   

Book review     

Robert Ehrlich  John C. Davis 《Mathematical Geology》1985,17(5):587-590

  相似文献   

The numerical calculation of integrals of an isotropic variogram function on hypercubes     

Michael W. D. Davis  Michel David 《Mathematical Geology》1978,10(3):311-314

  相似文献   

Computer model of wind, waves, and longshore currents during a coastal storm     

William T. Fox  Richard A. Davis Jr. 《Mathematical Geology》1979,11(2):143-164

A mathematical model has been developed to forecast or hindcast wind, waves, and longshore currents during the passage of a coastal storm. Storm intensity is a function of the barometric pressure gradient which is modeled by rotating an inverted normal curve around the center of an ellipse. The length and orientation of the major and minor axes of the ellipse control the size and shape of the storm. The path of the storm is determined by a sequence of storm positions for the hindcast mode, and by interpolated positions assuming constant speed and direction for the forecast mode. The site location, shoreline orientation, and nearshore bottom slope provide input data for the shore position. The geostrophic wind speed and direction at the shore site are computed from the latitude and barometric pressure gradient. The geostrophic wind is converted into surface wind speed and direction by applying corrections for frictional effects over land and sea. The surface wind speed and direction, effective fetch, and wind duration are used to compute wave period, breaker height, and breaker angle at the shore site. The longshore current velocity is computed as a function of wave period, breaker height and angle, and nearshore slope. The model was tested by comparing observed data for several coastal locations with predicted values for wind speed, wave period and height, and longshore current velocity. Forecasts were made for actual storms and for hypothetical circular and elliptical storms.  相似文献   

Properties of coronal arches     

John M. Davis  Allen S. Krieger 《Solar physics》1982,80(2):295-307

The properties of coronal arches located on the peripheries of active regions, observed during a sounding rocket flight on March 8, 1973, are discussed. The arches are found to overlie filament channels and their footpoints are traced to locations on the perimeters of supergranulation cells. The arches have a wide range of lengths although their widths are well approximated by the value 2.2 × 10⁹ cm. Comparison of the size of the chromospheric footprint with the arch width indicates that arches do not always expand as they ascend into the corona. The electron temperatures and densities of the plasma contained in the arches were measured and the pressure calculated; typical values are 2 × 10⁶ K, 1 × 10⁹ cm^–3, and 2 × 10^–1 dyne cm^–2, respectively. The variation of these parameters with position along the length of the arch indicates that the arches are not in hydrostatic equilibrium.  相似文献   

Rapid shearing in a rate-type soil surrounding a cylindrical cavity     

G. Mullenger  R. F. Scott  R. O. Davis 《国际地质力学数值与分析法杂志》1984,8(2):141-155

The stress and deformation resulting from rapidly applied axial traction on the face of a cylindrical cavity in a saturated soil are analysed. A simple rate-type constitutive model is used for the effective stress response.  相似文献