摘要:

The spectral reflectance properties (0.3–1.1 μ) of a number of lunar mare, upland, and bright crater areas were observed with the use of ground‐based telescopes. These new data are discussed in view of earlier studies in an attempt to provide a basis for more detailed interpretation. The spectral reflectivity curves (0.3–1.1 μ) for all lunar areas studied consist of a positive sloping continuum with a superimposed symmetric absorption band centered at 0.95 μ. Upland, mare, and bright crater materials can be identified by their spectral curves. The curves for upland and mare regions show a range of shapes from fresh, bright craters to progressively darker background material that correlates with the apparent age of the surface features. The observed upland material has uniform spectral properties, but the mare material shows some variety, probably due to Ti3+dispersed in lunar‐soil glass. Copernicus and Aristarchus appear to have exposed upland material from beneath the mare but Kepler has not. This observation suggests that the mare is no deeper than about 15 km in the Copernicus area and about 6 km deep in the Aristarchus area, but in the Kepler area the mare must be at least about

ISSN:0148-0227    

DOI:10.1029/JB077i008p01349

年代:1972

数据来源: WILEY

摘要:

Detailed sequential studies by photoelectron spectroscopy of the change in valence states of iron in Fe2O3, Fe3O4, FeO, and Fe foil samples show that chemical reduction does take place on the sample surface when argon ion bombardment occurs. These spectra give evidence that, after prolonged ion bombardment, the surface of all four samples consisted predominantly of iron in the metallic state. Argon ion sputtering of 15 silicate and oxide samples under similar experimental conditions produced surface darkening only in samples containing iron. Monitoring of the photoelectron peak of carbon during the experiment indicates that ion‐bombardment darkening is not due to the buildup of hydrocarbon surface contaminants in our oil‐free high‐vacuum system. On the basis of these studies, we conclude that solar‐wind bombardment should be included as one of the possible mechanisms for producing darkening of the lunar

ISSN:0148-0227    

DOI:10.1029/JB077i008p01360

年代:1972

数据来源: WILEY

摘要:

A model that suggests that the high‐albedo central region of the Descartes Formation was formed by Copernican‐age volcanism was developed from Orbiter photography, Apollo 12 multispectral photography, earth‐based spectrophotometry, and thermal IR and radar data. The bright surface either is abundant in centimeter‐sized rocks or in formed from an insulating debris layer overlying a surface with an abundance of rocks in the 1‐ to 20‐cm size range. On the basis of these data, the bright unit is thought to be a young pyroclastic deposit mantling older volcanic units of the Descartes Formation. Since the Apollo 16 target point is only 50 km NW of the central part of this unit, evidence for material associated with this unique highland formation should be searched for in returned soil and r

ISSN:0148-0227    

DOI:10.1029/JB077i008p01368

年代:1972

数据来源: WILEY

摘要:

Experiments on impact craters and impact ionization of dust particles have been performed using iron microparticles from a 2‐Mv Van de Graaff accelerator. The particle velocity υ ranged from 0.2 to 40 km/sec and the massmranged from 1 × 10−15g to 5 × 10−10g. The analysis and mass determination of iron microspheres on smooth targets and of iron layers of the projectile in the middle of impact craters have been done with an electron microprobe. The Kαradiation emitted by the iron layer in the crater has been measured as a function of mass and velocity of the projectile. The radiation measurement gives, in combination with the crater diameterD, a means for the determination of the projectile parametersmand υ. The targets used were Ag, Al, Cu, Cd, and W. Within an error of approximately 20% the total mass of the iron projectile has been found inside the craters in W, Cu, and Al targets at velocities of ≤13 km/sec. The impact ionization has been studied for impact velocities of up to 40 km/sec and projectile masses of down to 10−15g. The yield of either ions or electrons, normalized to the incident massm, can be described by an empirical relation of the formQ= const ƒ(θ, υ) · mα· υβ, where θ is the angle of incidence. Analysis of impact ionization has been applied to extremely sensitive detectors of cosmic dust particles. The impact cratering and ionization are discussed in terms of shock effects by applying the Rankine‐Hugoniot theory. The energy partition in the form of kinetic energy and internal energy (e.g., elastic compression and irreversible heating) is discussed as a function of the velocity of iron particles impacting the targets Al, Cu, W, and Au. As a result, W and Au are targets that transform a greater fraction of the primary energy into heating and ionizati

ISSN:0148-0227    

DOI:10.1029/JB077i008p01375

年代:1972

数据来源: WILEY

摘要:

The frequency shifts observed in the power spectra of truncated sinusoids, when the sinusoids are computed by using the periodogram, are obviated when the power spectra are determined by means of a maximum entropy algorithm.

ISSN:0148-0227    

DOI:10.1029/JB077i008p01396

年代:1972

数据来源: WILEY

摘要:

A stability indexSis defined for comparison of two vectorsJ1andJ2by the equationS1–2= 1 − |J1−J2|/J1. For example, two identical vectors haveSequal to 1.0, but two equal antiparallel vectors haveSequal to −1.0.Ssuccessfully indicates an objective distinction between different NRM components in a variety of common paleomagnetic situations. If this index is to be used in finding optimum fields for magnetic cleaning of NRM, an adequate number of partial demagnetization stages must be measured to justify linear interpolation of the NRM vector between successive measurements.Sis then expressed for successive equal increments of alternating field. Increments of 100 oe are proposed as standard. The index can also be used to choose optimum temperatures for thermal cleaning. Increments of 50°C are proposed as standard. Other potential applications include relating stability to coercivity or critical blocking temperature spectrums, to magnetic mineralogy, or to mode of origi

ISSN:0148-0227    

DOI:10.1029/JB077i008p01401

年代:1972

数据来源: WILEY

摘要:

The time‐dependent growth of an axial crack in single‐crystal quartz tested in uniaxial compression with a constant load was studied as a function of temperature,Tstress σ and partial pressure of waterP. The time‐dependent growth can be approximated by an equation of the formC−C0=Atn, whereCis crack length. Typically, as any one of the three variables was increased, the rate of crack growth increased. The data were analyzed by comparing the relative times required for two cracks, with the same initial length, to extend an arbitrarily selected increment of 0.20 mm as one of the parameters was varied. The experimental results indicate that the changes in the rate of crack growth due to a variation in any of three variables could be treated independently over the range studied and expressed bywheret1andt2are the times required for a crack to extend 0.20 mm. The relation between environment‐sensitive time‐dependent crack growth and creep in brittle rocks is discussed. The increase in the rate of creep strain in rocks due to an increase in temperature or stress is consistent with the explanation of creep in terms of crack growth. The static fatigue of glasses, brittle rocks, and quartz is shown to obey a dependence on stress, temperature, and moisture similar to the time‐dependent crack gr

ISSN:0148-0227    

DOI:10.1029/JB077i008p01406

年代:1972

数据来源: WILEY

摘要:

The effect of temperature changes ranging from −200° to +600°C on the internal friction of several kinds of rocks was measured by Forster's method. Most, but not all, rocks showed what appeared to be a prominent loss peak near room temperature. This peak was associated with the presence of tiny quantities of moisture in the rock. If the rock was heated sufficiently and allowed to cool, the peak was reduced or elimina

ISSN:0148-0227    

DOI:10.1029/JB077i008p01420

年代:1972

数据来源: WILEY

摘要:

In situ measurements of the electrical resistivity of Icelandic basalts using Schlumberger and dipole‐dipole sounding techniques agree well with laboratory measurements on water‐saturated specimens from the same area. A small volume‐compression coefficient at low pressures is indicated for the samples from one region even though the total porosity is quite large (8%). This small coefficient suggests that total porosity consists of a high ratio of circular pores to thin cracks. Furthermore, surface conduction along pore walls apparently outweighs conduction through the pore fluid itself for pore fluid resistivities of the order of 90

ISSN:0148-0227    

DOI:10.1029/JB077i008p01424

年代:1972

数据来源: WILEY

摘要:

Extensive lava flows, like those of the Columbia plateau of Washington state, require thicknesses only of the order of meters and temperatures only slightly above the melting point to spread over distances of the order of hundreds of kilometers. Other things being equal, the spreading distance is proportional to the cube of the thickness of the flow.

ISSN:0148-0227    

DOI:10.1029/JB077i008p01430

年代:1972

数据来源: WILEY