An analysis of the distribution of boulders in the vicinity of small lunar craters     

Winifred Sawtell Cameron  George J. Coyle 《Earth, Moon, and Planets》1971,3(2):159-188

Nine Orbiter 3 high-resolution photographs were examined at three sites for distributions of boulders around craters 110 m in diameter; three kinds of distributions were noted. Some had boulders inside and far outside (designated), others had boulders only inside or on their ramparts (), and some had no detectable boulders (). Additionally, shapes or morphologies of craters were classified according to their resemblance to one of three Jaffe models (1965); a third classification involved the depth of particulate overlay (Jaffe, 1965). Crater morphologies were classified (A) if they were relatively shallow with sharp, raised rims, (B) if they were rimless and shallow, and (C) if they were relatively deep and had low, broad rims. The data suggested that there were strong relationships between crater types and boulder distributions in which, generally, A-type was related to the-distribution, B-type to-distribution, and C-type to-distribution. Plots of numbers of craters of each crater type and each kind of boulder distribution versus steps of overlay for each site and for the totality of craters considered indicated that neither boulder distribution nor crater type represented orderly progression of age or erosional evolution. The apparent overlays for the A's and C's and for the's and's were similar, implying similar ages or stages of erosion. It is suggested that they represent two kinds of primary craters and that the A's are of impact origin while the C's are of volcanic origin. The B's probably represent later stages of erosion of the C's and possibly of some A's.Now at the University of Maryland.Receipt delayed by postal strike in Great Britain.  相似文献   

Pre-main sequence stellar evolution with mass loss     

Dilhan Ezer  A. G. W. Cameron 《Astrophysics and Space Science》1971,10(1):52-70

A semi-empirical formulation is given of the rate of stellar mass loss by stellar winds. Evolutionary studies of stars in the pre-main sequence (T Tauri) stage are presented for a variety of rates of mass loss. It has been found that different mass loss rates produce only small changes in the positions of equal evolutionary time lines in HR diagrams. Thus it is concluded that the spread of points in HR diagrams of young clusters results from a spread in their times of formation. This is consistent with the initiation of star formation by violent hydrodynamic compression of a typical interstellar cloud.  相似文献   

Evidence for temporal variations of coronal emission line intensity and profile     

D. H. Liebenberg  R. J. Bessey  B. Watson 《Solar physics》1976,50(1):109-112

The time sequence of line profiles of Fe xiv emission obtained at the 1965 solar eclipse is examined for temporal variations of intensity and profile. Although no variations are found in some regions examined, two regions with intensity and profile line width variations are found. A simple temperature wave is consistent with observations.Work performed under the auspices of the U.S. Energy Research and Development Administration.Work accomplished at the Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming.  相似文献   

Rapid neutron capture in supernova explosions     

J. W. Truran  W. D. Arnett  S. Tsuruta  A. G. W. Cameron 《Astrophysics and Space Science》1968,1(1):129-146

The implications of recent studies of the dynamics of the cores of highly evolved massive stars are considered with regard to the general problems of nucleosynthesis. The typical conditions estimated for these models are shown to be very promising for the process of element synthesis by neutron capture on a fast time scale (ther-process ofBurbidge et al., 1957).  相似文献   

MAGNETISM OF METEORITES: A REVIEW OF RUSSIAN STUDIES     

J. M. Herndon  M. W. Rowe  E. E. Larson  D. E. Watson 《Meteoritics & planetary science》1972,7(3):263-284

We present here a summary review of the work of Russian scientists, primarily Gus'kova and Pochtarev, on the magnetism of meteorites. They have measured the initial natural remanent magnetization and the magnetic susceptibility in more than 900 meteorite samples from collections throughout the Soviet Union. More sophisticated studies, involving both thermal and alternating field demagnetization experiments, were also conducted on a few samples. Meteorites almost invariably retain evidence of ancient magnetic fields in their pre-terrestrial history  相似文献   

Alpha thermochronology of carbonates   总被引：1，自引：0，他引：1  

Peter Copeland  E. Bruce Watson  Desmond Patterson 《Geochimica et cosmochimica acta》2007,71(18):4488-4511

Step-heating experiments on 17 calcites from 11 different samples and 6 dolomites from 5 samples suggest a closure temperature of He in carbonates ∼70 ± 10 °C for a cooling rate of 10 °C/m.y. The bulk closure temperature in some samples may tend slightly higher due to the presence of diffusion domains larger (and therefore more retentive) than the sites in which the majority of He resides. The diffusivity of He in calcite is independent of the genesis of the mineral (igneous, sedimentary, metamorphic) or the source of the He (radiogenic, common, or laboratory induced) and in all samples analyzed the effective diffusion dimension for He is smaller than the size of the crystals investigated. Although calcite is a low-U mineral, this shortcoming can be overcome by analyzing large samples (>2 mm diameter) provided samples have a minimum of ∼0.3 ppm U; samples with smaller concentrations of alpha-producers are unlikely to produce enough radiogenic ⁴He sufficient to overwhelm He present in the crystals at the time they passed through their closure temperature.  相似文献   

Addressing Hurricane Intensity through Angular Momentum and Scale Energetics Approaches     

T. N. Krishnamurti  L. Stefanova  L. Watson  S. Pattnaik 《Pure and Applied Geophysics》2007,164(8-9):1429-1441

This paper addresses two avenues for gaining insight into the hurricane intensity issue—the angular momentum approach and the scale interaction approach. In the angular momentum framework, the torques acting on a parcel's angular momentum are considered along an inflowing trajectory in order to construct the angular momentum budget. These torques are separable into three components: The pressure torque, the surface friction torque, and the cloud torque. All torques are found to diminish the angular momentum of an inflowing parcel, with the cloud torques having the most important role. In the scale interaction approach, energy exchanges among different scales within a hurricane are considered as a means of understanding hurricane intensity. It is found that the majority of kinetic energy contribution to the hurricane scales originates from potential-to-kinetic in-scale energy conversions. The contribution of mean-wave interactions in the kinetic energy varies with distance from the center and with the life stage of a storm. In the early stages, as the disorganized convection becomes organized on the hurricane scales, upscale energy transfers (i.e., from small to large scale) are found to take place in the outer radii of the storm. In a mature storm, the kinetic energy transfers are downscale, except for the inner radii.  相似文献   

Infrared Observations of Comet Hale–Bopp (C/1995 O1) from Gurushikhar Observatory     

Chandrasekhar  T.  Ashok  N. M.  Tej  Anandamayee  Mondal  Soumen  Watson  P. V. 《Earth, Moon, and Planets》1998,81(2):111-121

During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J, H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain the unusual brightness of comet Hale—Bopp. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Stellar Tomography     

A. Collier Cameron 《Astrophysics and Space Science》1998,261(1-4):71-80

I review recent progress in the field of stellar surface imaging, with particular reference to advanced methods for mapping surface-brightness inhomogeneities and the surface vector magnetic field on magnetically active late-type stars. New signal enhancement techniques, utilising profile information from hundreds or thousands of photospheric lines simultaneously, allow images to be derived for stars several magnitudes fainter than was previously possible. For brighter stars, the same techniques make it possible to map features as small as two or three degrees in extent on the stellar surface. This opens up whole new areas of research, such as the ability to use starspot tracking to study surface differential rotation patterns on single and binary stars, and to follow the secular evolution of the magnetic field itself. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Detection of subsidence conditions by photogeology     

J.W. Norman  I. Watson   《Engineering Geology》1975,9(4):359-381

A variety of air-photo interpretation criteria need to be used for detecting areas of potential subsidence. An initial step is to search for past failures showing on air photographs, to establish the cause and to interpret the boundaries of the environment that might be affected. Causes detectable include karstic terrain, areas liable to piping, or containing concealed peat, old shafts, and stratiform or vein workings. Airborne imaging conditions can be selected to improve the possibility of detection in some situations.

The technique can indicate situations where risks are high, but cannot be used to map with certainty voids liable to collapse.  相似文献