High-temperature condensates in chondrites and the environment in which they formed     

L Grossman  S.P Clark 《Geochimica et cosmochimica acta》1973,37(3):635-649

Chemical compositions of melilitee and titaniferous pyroxenes in calcium- and aluminum-rich inclusions in carbonaceous chondrites are consistent with their origin as hightemperature condensates from a gas of solar composition. Thermodynamic calculations indicate that the highest temperature minerals equilibrated with the gas at temperatures in excess of 1400°K. The lack of evidence for direct condensation of gas to liquid enables us to set an upper limit to the pressure when the inclusions formed which may be as low as 2.2 × 10^?3atm. Glasses, which are commonly found in chondrules, are interpreted as quench products of liquids formed by secondary reheating of primary solid condensates. The high-temperature inclusions constitute evidence that accretion of grains to cm-sized objects occurred at a very early stage in the evolution of the solar nebula.  相似文献   

Bacterial Movement Through Fractured Bedrock   总被引：1，自引：0，他引：1  

Martin J. Allen  S. M. Morrison 《Ground water》1973,11(2):6-10

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Oil on Puget Sound: Supervised by Juris Vagners,coordinated by Paul Mar. Published by Washington Sea Grant. Distributed by University of Washington Press,Seattle, Washington,USA 98195 (1972). 648 pp. Price $10.00     

Robert C. Clark 《Marine pollution bulletin》1973,4(2):31

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Constructing the Coronal Magnetic Field By Correlating Parameterized Magnetic Field Lines With Observed Coronal Plasma Structures     

Gary  G. Allen  Alexander  David 《Solar physics》1999,186(1-2):123-139

A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (i) the normal component of the photospheric field remains unchanged, (ii) the field is given in the entire corona over an active region, (iii) the field remains divergence-free, and (iv) electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10^–5.5 g cm s^–2 resulting from an electric current density of 0.079 A m^–2. Calculations show that the plasma beta becomes larger than unity at a relatively low height of 0.25 r supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients to maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.  相似文献   

A need for incentivizing field hydrology,especially in an era of open data: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*     

Scott T. Allen  Wouter R. Berghuijs 《水文科学杂志》2020,65(Z2):1262-1265

ABSTRACT

The sharing of data and collection of new data are both essential, but they are not inherently complementary. When data are openly available, researchers may be motivated to use those data rather than collect more because field work has costs and risks. The competitive advantage to those who do not put resources towards fieldwork may discourage field hydrology. Allocating efforts towards generating field data, which benefits hydrological sciences, is not necessarily best for individual hydrologists, especially in an era of open data. The objective of this work is to open a conversation on whether individuals’ best interests may contrast with the community’s desire for new observations. If the community wants new field observations, there is a need to consider the shifting balance of incentives and disincentives for pursuing field studies in hydrology.  相似文献   

Studies of the solar chromosphere from millimetre and sub-millimetre observations     

J. E. Beckman  C. D. Clark 《Solar physics》1973,29(1):25-39

Spectroheliograms were obtained in bands centred at 1.2 mm, 0.8 mm and 0.4 mm wavelength during 1969 and 1971. In order to obtain photometrically valid data, a specialized set of reduction techniques was employed, obviating the effects of severe differential attenuation across the disc by atmospheric water vapour and of emission noise from the atmosphere, before taking out the instrumental spread functions of the telescope and detector.Comparison of our maps with those of other observers at 3 mm and 8.6 mm wavelength suggests that the chromospheric brightness temperature increments above active regions show a monotonic increase with increasing height above the photosphere over the normal increase in brightness temperature in the quiet chromosphere. Within the limit of angular resolution of 3 available, no evidence was recorded of normal limb brightening in our three passbands but the presence of isophotes at 50% of the central disc temperature consistently circumscribing the optical limb implies a narrow spike of sub-millimetre brightening close to the limb.  相似文献   

The location of exploding granules     

Marc S. Allen  Steven Musman 《Solar physics》1973,32(2):311-314

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Saturn's satellites: Nuar-infrared spectrophotometry (0.6–2.5 μm) of the leading and trailing sides and compositional implications     

Roger N. Clark  Robert H. Brown  Pamela D. Owensby  Alex Steele 《Icarus》1984,58(2):265-281

Near-infrared spectra, 0.65–2.5 μm, are presented for Tethys, Dione, Rhea, Iapetus, and Hyperion. Water ice absorptions at 2.0, 1.5, and 1.25 μm are seen in the spectra of all five objects (except the 1.25-μm band was not detected in spectra of Hyperion) and the weak 1.04-μm ice absorption is detected on the leading and trailing sides of Rhea, and the trailing side of Dione. Upper limits to the 1.04-μm ice band depth are <0.3% for the leading side of Dione; <0.7% for the leading side of Iapetus, and the trailing side of Tethys; <1% on the trailing side of Iapetus; and <5% on the leading side of Tethys. The leading-trailing side ice band depth differences on Saturn's satellites are similar to those for the Galilean satellites, indicating possible surface modification by magnetospheric charged particle bombardment. Limits are determined for the amount of particulates, trapped gases, and amonium hydroxide on the surface. The surfaces of Saturn's satellites (except the dark side of Iapetus) are nearly pure water ice, with probably less than about 1 wt% particulate minerals. The ice could be clathrates with as much as a few weight percent trapped gases. The upper limit of amonium hydroxide depends on the spectral data precision and varies from ～ 1 wt% NH₃ for the leading side of Rhea to ～ 10 wt% NH₃ for Dione.  相似文献   

Chromospheric magnetic fields associated with supergranulation     

Alfred Clark Jr. 《Solar physics》1968,4(4):386-400

Some theoretical models are given which illustrate the structure of chromospheric magnetic fields associated with supergranulation. It is found that the chromospheric fields depend critically on whether or not there are large-scale vertical motions at the level where the horizontal supergranule motions are observed. In the absence of such motions, the concentration of field produced in the photosphere does not persist more than a few scale heights into the chromosphere; however, the chromospheric mass density is increased above the supergranule boundaries in this case. Completely different results-such as a chromospheric potential field-may be obtained by the inclusion of vertical motions. It is concluded that a rather wide range of chromospheric-field structures is consistent with present observational knowledge of the supergranulation.  相似文献   

J, H, K photometry of 433 Eros and other asteroids     

Clark R. Chapman  David Morrison 《Icarus》1976,28(1):91-94

We report photometry for nine asteroids at wavelengths of 1.25, 1.65, and 2.22 μm. Three C-type objects (88, 129, and 511) seem slightly redder in H?K and J?H color indices than four S-type objects (5, 6, 7, and 116) and an E-type object (64). Eros has an unusually red J?H color index; its infrared spectral reflectance is consistent with an appreciable quantity of metallic iron plus some pyroxene and olivine on its surface. JHK photometry is less diagnostic of composition than either higher resolution spectrophotometry in the infrared or spectrophotometry at shorter wavelengths.  相似文献