Detection of Temperature-Dependent Spectral Variation on the Asteroid Eros and New Evidence for the Presence of an Olivine-Rich Silicate Assemblage     

Paul G. LuceyJohn Hinrichs  Mary KellyDennis Wellnitz  Noam IzenbergScott Murchie  Mark RobinsonBeth E. Clark  James F. Bell III 《Icarus》2002,155(1):181-188

Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros.  相似文献   

Infrared Spectroscopy from San Fernando Observatory: He I 1083 nm, O I 1316 nm, and Fe I 1565 nm     

M.J. Penn  J.A. Ceja  E. Bell  G. Frye  R. Linck 《Solar physics》2002,205(1):53-61

Imaging spectroscopy of the Sun was carried out at the California State University Northridge San Fernando Observatory using an InGaAs near-IR video camera. Using the Sii 1082.71 nm and Hei 1083.03 nm lines the Evershed effect is measured simultaneously in the photosphere and the chromosphere for three sunspots; the speed of the Evershed flow is measured to be between 3 to 8 times greater in the Hei line than in the Sii line, and the direction is radially inward in the chromosphere and outward in the photosphere. Telluric absorption lines prevented a meaningful measurement of Oi 1128.7 nm limb emission, but an upper limit of 20×10^–3 B is measured for chromospheric limb emission at Oi 1316.3 nm. Zeeman splitting in Fei 1564.9 nm was observed in six sunspot umbrae, and a linear relationship between magnetic field and umbral continuum intensity is confirmed.  相似文献   

Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August, 1999 and 9 July, 1945     

C. J. Davis  M. Lockwood  S. A. Bell  J. A. Smith  E. M. Clarke 《Annales Geophysicae》2000,18(2):182-190

Swept-frequency (1/10 MHz) ionosonde measurements were made at Helston, Cornwall (50°06N, 5°18W) during the total solar eclipse on August 11, 1999. Soundings were made every three minutes. We present a method for estimating the percentage of the ionising solar radiation which remains unobscured at any time during the eclipse by comparing the variation of the ionospheric E-layer with the behaviour of the layer during a control day. Application to the ionosonde date for 11 August, 1999, shows that the flux of solar ionising radiation fell to a minimum of 25±2% of the value before and after the eclipse. For comparison, the same technique was also applied to measurements made during the total solar eclipse of 9 July, 1945, at Sörmjöle (63°68N, 20°20E) and yielded a corresponding minimum of 16 ± 2%. Therefore the method can detect variations in the fraction of solar emissions that originate from the unobscured corona and chromosphere. We discuss the differences between these two eclipses in terms of the nature of the eclipse, short-term fluctuations, the sunspot cycle and the recently-discovered long-term change in the coronal magnetic field.  相似文献   

Skolithos pipes as strain markers in mylonites     

P. Wilkinson  N.J. Soper  A.M. Bell 《Tectonophysics》1975,28(3):143-157

It is argued that mylonite zones result from translatory movements between rock masses and that the deformation mechanism is one of simple shear. Evidence is adduced to show that the mylonite zones in the Moine Thrust Belt of northwestern Scotland were developed in association with the inverted limbs of early Caledonian folds which trend parallel to the thrust front. On this basis a method is developed for the determination of shear strain from parameters which can be measured in mylonites which contain deformed Skolithos worm burrows. Very large strains are indicated (γ - 10). Some general implications are discussed.  相似文献   

Recent crustal movements in the Sierra Nevada—Walker lane region of California—Nevada: Part i, rate and style of deformation     

David B. Slemmons  Douglas Van Wormer  Elaine J. Bell  Miles L. Silberman 《Tectonophysics》1979,52(1-4)

This review of geological, seismological, geochronological and paleobotanical data is made to compare historic and geologic rates and styles of deformation of the Sierra Nevada and western Basin and Range Provinces. The main uplift of this region began about 17 m.y. ago, with slow uplift of the central Sierra Nevada summit region at rates estimated at about 0.012 mm/yr and of western Basin and Range Province at about 0.01 mm/yr. Many Mesozoic faults of the Foothills fault system were reactivated with normal slip in mid-Tertiary time and have continued to be active with slow slip rates. Sparse data indicate acceleration of rates of uplift and faulting during the Late Cenozoic. The Basin and Range faulting appears to have extended westward during this period with a reduction in width of the Sierra Nevada.The eastern boundary zone of the Sierra Nevada has an irregular en-echelon pattern of normal and right-oblique faults. The area between the Sierra Nevada and the Walker Lane is a complex zone of irregular patterns of hörst and graben blocks and conjugate normal-to right- and left-slip faults of NW and NE trend, respectively. The Walker Lane has at least five main strands near Walker Lake, with total right-slip separation estimated at 48 km. The NE-trending left-slip faults are much shorter than the Walker Lane fault zone and have maximum separations of no more than a few kilometers. Examples include the 1948 and 1966 fault zone northeast of Truckee, California, the Olinghouse fault (Part III) and possibly the almost 200-km-long Carson Lineament.Historic geologic evidence of faulting, seismologic evidence for focal mechanisms, geodetic measurements and strain measurements confirm continued regional uplift and tilting of the Sierra Nevada, with minor internal local faulting and deformation, smaller uplift of the western Basin and Range Province, conjugate focal mechanisms for faults of diverse orientations and types, and a NS to NE—SW compression axis (σ₁) and an EW to NW—SE extension axis (σ₃).  相似文献   

Recent crustal movements in the Central Sierra Nevada—Walker lane region of California—Nevada: Part ii, The pyramid lake right-slip fault zone segment of the Walker lane     

Elaine J. Bell  David B. Slemmons 《Tectonophysics》1979,52(1-4)

The Pyramid Lake fault zone is within the Honey Lake—Walker Lake segment of the Walker Lane, a NW-trending zone of right-slip transcurrent faulting, which extends for more than 600 km from Las Vegas, Nevada, to beyond Honey Lake, California. Multiscale, multiformat analysis of Landsat imagery and large-scale (1: 12,000) lowsun angle aerial photography, delineated both regional and site-specific evidence for faults in Late Cenozoic sedimentary deposits southwest of Pyramid Lake. The fault zone is coincident with a portion of a distinct NW-trending topographic discontinuity on the Landsat mosaic of Nevada. The zone exhibits numerous geomorphic features characteristic of strike-slip fault zones, including: recent scarps, offset stream channels, linear gullies, elongate troughs and depressions, sag ponds, vegetation alignments, transcurrent buckles, and rhombohedral and wedge-shaped enclosed depressions. These features are conspicuously developed in Late Pleistocene and Holocene sedimentary deposits and landforms.The Pyramid Lake shear zone has a maximum observable width of 5 km, defined by Riedel and conjugate Riedel shears with maximum observable lenghts of 10 and 3 km, respectively. P-shears have formed symmetrical to the Riedel shears and the principal displacement shears, or continuous horizontal shears, isolate elongate lenses of essentially passive material; most of the shears are inclined at an angle of approximately 4° to the principal direction of displacement. This suggests that the shear zone is in an early “PreResidual Structure” stage of evolution, with the principal deformation mechanism of direct shear replacing the kinematic restraints inherent in the strain field.Historic seismic activity includes microseismic events and may include the earthquake of about 1850 reported for the Pyramid Lake area with an estimated Richter magnitude of 7.0. Based on worldwide relations of earthquake magnitude to length of the zone of surface rupture, the Pyramid Lake fault zone is inferred to be capable of generating a 7.0–7.5-magnitude event for a maximum observable length of approximately 6 km and a 6.75–7.25-magnitude event for a half length of approximately 30 km.  相似文献   

On the accuracy of mode superposition analysis in structural dynamics     

Ole Edvard Hansteen  Kolbein Bell 《地震工程与结构动力学》1979,7(5):405-411

It is pointed out that the number of modes which should be included in a mode superposition dynamic response analysis depends on both the frequency content and the distribution of the loading. If the loading frequency is low the effect of the higher modes can be approximated by a static analysis. A technique is described for calculating this static contribution from the higher modes; the total response is then represented by the sum of the lower mode dynamic response and the higher mode static effects. The effectiveness of the procedure is demonstrated by a numerical example.  相似文献   

Ground-based FTIR Measurements with High Temporal Resolution     

W. Bell  C. Paton Walsh  P.T. Woods  T.D. Gardiner  M.P. Chipperfield  A.M. Lee 《Journal of Atmospheric Chemistry》1998,30(1):131-140

We outline how ground-based Fourier transform infrared (FTIR) measurements of stratospheric trace species, obtained with high temporal resolution, could be used to detect filaments of polar vortex air at mid-latitudes and therefore test high spatial resolution chemical transport models (CTMs). Vertical column abundances of HCl, ClONO2, HNO3, N2O and HF have been obtained from FTIR solar absorption measurements made throughout the day from Aberdeen, UK (57°N, 2°W) on several days during winter/spring 1993/94 and 1994/95. The short-timescale ( 2 hours) variability observed in the columns is attributed to real atmospheric variations and is often associated with the passage of high latitude air over Aberdeen. This is confirmed by 3D modelling studies which qualitatively reproduce and rationalise the observed changes in the column data on January 19 1994, January 20 1995 and February 26 1995. We describe the viewing geometry of ground-based FTIR measurements and we suggest a measurement strategy which should maximise the information retrieved on horizontal gradients in stratospheric trace species columns from FTIR measurements.  相似文献   

Vergence: an evaluation     

A.M. Bell 《Journal of Structural Geology》1981,3(3):197-202

Fold asymmetry is an independent concept distinct from facing. Fold vergence is a direction relating to the sense of asymmetry of folds. The complementary concept of cleavage vergence is defined allowing asymmetry to be used to locate major fold traces where no minor folds exist. Cleavage vergence is a valuable tool in complex structural terrains. Both concepts can be used singly or in combination to identify refolding. Vergence can define structural way-up where sedimentological or stratigraphic way-up cannot be recognised.  相似文献   

Rare earth element geochemistry of potassic lavas from the Birunga and Toro-Ankole regions of Uganda,Africa     

Roger H. Mitchell  Keith Bell 《Contributions to Mineralogy and Petrology》1976,58(3):293-303

Neutron activation determination of La, Ce, Sm, Eu, Tb, Yb, Lu, Ta, Hf, Sc, Co and Th in potassic lavas from the Birunga and Toro-Ankole regions show that the rocks are characterized by high rare earth element (REE) contents (161–754 ppm) and form two groups based upon differing La/Yb ratios. One group is made up of katungite, ugandite and mafurite with La/Yb =146–312, and the other of rocks of the leucitite and phonolitic tephrite series, La/Yb =30–56. The trace element content of the ugandite group is similar to that of kimberlites. The data do not indicate any trends of differentiation or simple relationships between the two groups of rocks, although katungite is unlikely to be parental to rocks of lower La/Yb ratios. It is unlikely that in terms of La/Yb ratios that partial melting of mica-garnet-lherzolite mantle can form katungite because of the very small amounts of partial melting required (0.2%), although the La/Yb ratios of 150–200 (ugandites, mafurites) and 30–60 (leucitites, phonolitic tephrites) can be accounted for by 0.3–1.5% and 1–9% melting respectively, if the REE are then concentrated without further La and Yb fractionation. Partial melting of mantle which has been metasomatized by alkaline earths and REE bearing fluids or mixing of carbonatite and nephelenite are also compatable with the observed geochemistry of the lavas. It is considered that gas transfer processes which selectively enrich the light REE may have obscured REE evidence pertaining to early partial melting and/or differentiation processes and therefore that REE geochemistry is of little use in determining the petrogenetic processes involved in the formation of potassic lavas.  相似文献