A color atlas of meteorites in thin section,by Dante S. Lauretta and Marvin Killgore     

Harold C. Connolly 《Meteoritics & planetary science》2005,40(6):939-940

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Phase transitions in leucite,KAISi2O6     

Dorian M. Hatch  Subrata Ghose  Harold T. Stokes 《Physics and Chemistry of Minerals》1990,17(3):220-227

An order parameter treatment of the phase transitions in leucite, KAlSi₂O₆, at approximately 950 and 920 K: (cubic) I4₁ acd(tetragonal) I4₁ a(tetragonal) is presented in terms of Landau theory and induced representation theory. The Al-Si order with decreasing temperature is taken as the primary order parameter to which other distortions (K⁺ ion displacements, strain components, etc.) couple linearly. The expected Al-Si ordering behavior and the associated K⁺ ion displacements for both transitions are derived and the resulting twin domain orientations are listed. The sequence of phase transitions results from a coupling of ₃ ⁺ and ₄ ⁺ representations. The Landau free energy for the five-dimensional reducible representation has been simplified to two components resulting in a linearquadratic coupling of the components. Possible phase diagrams are derived by free energy minimization. The cubic tetragonal transition is first-order, whereas the tetragonal-tetragonal transition may be second order. A tricritical point exists at which the first-order transition changes to second-order.  相似文献   

Frequency domain electromagnetic and ground penetrating radar investigation of ephemeral streams: case study near the Southern High Plains,Texas     

Jeffrey Burrell  Harold Gurrola  Kevin Mickus 《Environmental Geology》2008,55(6):1169-1179

A frequency domain electromagnetic (FDEM) and ground penetrating radar (GPR) study was conducted on an ephemeral stream in north-central Texas to determine if FDEM and GPR measurements can be combined to determine the electrical characteristics of current and ancient stream channels. GPR data were collected at several frequencies to image sedimentary structures of different scale lengths, and to determine the formation porosity and water content of stream sediments. FDEM measurements were collected using Geonics EM31 and EM34 loop–loop instruments on a profile along the current stream channel and five profiles perpendicular to the channel. The results indicate that the greater spatial resolution of the EM31 mapped the current and possible ancient channels better than the EM34, however, the EM34 provided depth information on the formations underlying the channel sediments that the EM31 could not image. GPR measurements taken along a point bar deposit with 200, 100 and 25 MHz antennae indicated that the higher frequency antenna better resolved channel structures including laminar bedding, trough scours and cross-bedding, however, lower frequency antenna (25 MHz) imaged sedimentary structures within the underlying channel sediments. Common midpoint GPR measurements collected along the point bar deposit were used to estimate the sediment formation porosity (26%) and the water content, during a dry period, of the unsaturated (12%) and saturated (26 or 100% of the pore space) sediments. The combined results indicated that the FDEM data should be collected first because of the speed and ease of measurements. The FDEM data (especially the EM31) pointed to the locations of possible sedimentary structures, which can then be resolved by using different frequency GPR measurements.  相似文献   

Headless submarine canyons and fluid flow on the toe of the Cascadia accretionary complex   总被引：1，自引：0，他引：1  

Daniel L. Orange  Brian G. McAdoo  J. Casey Moore  Harold Tobin  Elizabeth Screaton  Hank Chezar  Homa Lee  Mark Reid  & Rick Vail 《Basin Research》1997,9(4):303-312

Headless submarine canyons with steep headwalls and shallowly sloping floors occur on both the second and third landward vergent anticlines on the toe of the Cascadia accretionary complex off central Oregon (45 °N, 125° 30′W). In September 1993, we carried out a series of nine deep tow camera sled runs and nine ALVIN dives to examine the relationship between fluid venting, structure and canyon formation. We studied four canyons on the second and third landward vergent anticlines, as well as the apparently unfailed intercanyon regions along strike. All evidence of fluid expulsion is associated with the canyons; we found no evidence of fluid flow between canyons. Even though all fluid seeps are related to canyons, we did not find seeps in all canyons, and the location of the seeps within the canyons differed. On the landward facing limb of the second landward vergent anticline a robust cold seep community occurs at the canyon’s inflection point. This seep is characterized by chemosynthetic vent clams, tube worms and extensive authigenic carbonate. Fluids for this seep may utilize high-permeability flow paths either parallel to bedding within the second thrust ridge or along the underlying thrust fault before leaking into the overriding section. Two seaward facing canyons on the third anticlinal ridge have vent clam communities near the canyon mouths at approximately the intersection between the anticlinal ridge and the adjacent forearc basin. No seeps were found along strike at the intersection of the slope basin and anticlinal ridge. We infer that the lack of seepage along strike and the presence of seeps in canyons may be related to fluid flow below the forearc basin/slope unconformity (overpressured by the impinging thrust fault to the west?) directed toward canyons at the surface.  相似文献   

Life histories of large,grazing copepods in a subarctic ocean gyre: Neocalanus plumchrus,Neocalanus cristatus, and Eucalanus bungii in the Northeast Pacific     

Charles B. Miller  Bruce W. Frost  Harold P. Batchelder  Martha J. Clemons  Richard E. Conway 《Progress in Oceanography》1984,13(2):201-243

Life histories for the dominant, larger copepods of the subartic Pacific have been constructed by sampling from weatherships patrolling Ocean Station P (50°N, 145°W) during 1980 and 1981. Neocalanus plumchrus reproduced at depths below 250 m from July through February. Copepodite stages were present in surface layers from October through August with a large peak in numbers and biomass in spring. Fifth copepodites prepared for diapuse in 38 days during spring and descended to depths below 250 m. They commenced immediately to mature, and the females reproduced without renewed feeding. This schedule contrasts with that of the population in the Strait of Georgia, which remains in diapause from July to January and matures exclusively in January and February. There appears to be a difference between the coastal and oceanic habitats in preparing the diapausing individuals for maturation.Maturation of the diapausing stock of N. plumchrus maintained constant adult populations, averaging 714 males m^?2 from June through October and 1,434 females m^?2 from August through January. This constancy, together with the exponential pattern of decline in the diapause stock from September through February, suggests that density of adults may regulate maturation of fifth copepodites. Offspring of individuals delaying maturation and, thus, reproduction would benefit from the resulting moderation of intraspecific competition, probably that among copepodites.Reproduction of Neocalanus cristatus also occurred below 250 m, and, while spawning was continuous through the year, there was a substantial peak in November. That resulted in a peak of abundance for early copepodite stages in mid-winter, and a peak for the fifth copepodite stage in June. Stocking of the population of fifth copepodites in diapause below 250 m occurred from July through October. Some fifth copepodites were present in surface layers through the entire summer, and some younger copepodites persisted through the summer in progressively declining abundance just below the mixed layer. In autumn 1980 resurgence of early copepodite populations was rapid, occurring during the course of a prolonged October storm. The storm may have improved the habitat either by cooling the mixed layer or by resupplying nutrients to the euphotic zone.Eucalanus bungii reproduced in the mixed layer in early May and in early July. The first event was a spawning by females that had previously spawned in 1979 and then had returned to diapause. The second, heavier spawning (more females, more eggs per female) was by newly matured females from stocks that had overwintered as fifth copepodites. Nauplii peaked sharply in abundance on 19 July, one week after the peak in spawning. First and second copepodites peaked on 1 August, and all had advanced to the third copepodite stage by September. The diapause stock was established by September, principally between 250 and 500 m, and consisted of copepodite stages from third to sixth. Duration of the E. bungii life cycle appears to be typically two years. New nauplii develop as far as the third or fourth copepodite stage during their first summer, then enter diapause. The second summer they advance to the fifth copepodite stage and reenter diapause. Fifth copepodites mature in their third summer at two years of age. The males remain at depth and mate without subsequent feeding. Females migrate at night to the mixed layer where spawning occurs. About 20% of females that had already spawned in 1980 reentered diapause. They would reproduce again in their fourth summer at three years of age. All aspects of the life cycle suggest low mortality rates for copepodite stages, particularly at depth in the habitat occupied during diapuse. There can be no premium on rapid reproduction for E. bungii in the subartic Pacific, and there must even be benefit from spreading reproduction between years. This iteroparity may amount to a “bet-hedging” tactic, the young from a given mother having more than one chance to find sustaining conditions. It also produces gene flow between the year classes of the biennial life cycle.  相似文献   

Study of the feasibility of immunochemical methods for identification of pleuronectid eggs     

Johnson  Allyn G.; Utter  Fred M.; Hodgins  Harold O. 《ICES Journal of Marine Science》1975,36(2):158-161

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Dilute-acid trace-metal fraction in northeastern Gulf of Mexico sediments     

Peter H. Feldhausen  Harold D. Palmer  David Johnson 《Geo-Marine Letters》1982,2(1-2):95-100

Variations in dilute-acid (partial digest) metal concentrations in bottom sediments from 49 stations on the Mississippi, Alabama and Florida continental margin are investigated with the aid of ordination and other multivariate statistical techniques. Total iron, carbonate content, clay fraction and water depth correlate well with the overall leachable sediment metal values for pooled station replicates over four sampling periods. Individual metal concentrations also are correlated with these and other environmental parameters using stepwise multiple linear regression techniques. A weak positive association between Ba, Cu, Cr, Ni, Pb, and V burdens in the demersal fishSyacium papillosum and the dilute-acid leachable sediment metal TOC and carbonate concentrations is demonstrated.  相似文献   

Video image selection studies of granules,pores, and penumbral flows near a large sunspot     

Harold Zirin  Haimin Wang 《Solar physics》1989,119(2):245-255

An excellent high-resolution movie in the green continuum was produced by shift-and-add treatment of two 60-min videotapes obtained at the Big Bear Solar Observatory. We have studied the digitized images by direct measurement, cross-correlation techniques, and correlation tracking. The seeing-limited resolution was about 0.3 arc sec.While the cross-correlation lifetime for granules is about five minutes, we find that actually tracking the growth and decay of a granule gives lifetimes from 10 to 22 minutes, the longest lifetimes pertaining to the largest granules. The longer lifetime comes from tracking the granule while it undergoes large changes in size and shape, while the cross-correlation lifetime is just the time in which it grows by a factor two. All the granules followed began as small elements, grew to some size, and either faded (88%), exploded (2%) or were hit by an exploding granule (10%). The major variation in granule structure appears to be due to substantial variations in the dark lanes, which often double in width.The granulation shows the typical exploding granule behavior; we find the probability that any granule will be affected by an exploding granule during its lifetime to be 10%. We also observed a larger scale explosion covering about 10 granules. This explosion was marked by rapid (1 km s^–1) outward flux of the granules.We tracked the development of six small pores, one of which could be followed for two hours. The latter showed four maxima of absorption separated by about 30 min each, virtually disappearing in between. Another was observed to form in about 20 min, but no changes occur in less than granule lifetime.We confirm the inflow in penumbral fibrils observed by Muller. The inflow velocity is about 0.5 km s^–1, and all bright spots disappear into the umbra. The inflow which affects bright and dark features in the penumbral fibrils, is also observed in the smaller spots. We surmise that the Evershed flow is limited to the areas between the bright fibrils. We confirm granular outflow outside the penumbra.  相似文献   

Evidence for rapid ice flow and proglacial lake evolution around the central Strait of Magellan region,southernmost Patagonia     

Harold Lovell  Chris R. Stokes  Michael J. Bentley  Douglas I. Benn 《第四纪科学杂志》2012,27(6):625-638

This paper presents a detailed palaeoglaciological reconstruction of ice sheet dynamics in the Seno Skyring, Seno Otway and Strait of Magellan region of the former Patagonian Ice Sheet, with a particular focus on previously hypothesised zones of rapid ice flow and the evolution of proglacial lakes. Geomorphological mapping from a combination of satellite imagery and oblique and vertical aerial photographs reveals a variety of glacial landforms that are grouped into several discrete flow‐sets and associated ice margin positions. The most distinct features are represented by flow‐sets of highly elongate streamlined glacial lineations on both sides of the Strait of Magellan. Based on the shape and dimensions of the flow‐sets and their abrupt lateral margins, a transverse and longitudinal variation in glacial lineation length and elongation ratio, and the reported presence of a potentially deformable bed and thrust moraines, the flow‐sets are interpreted as zones of rapid ice flow within the Otway and Magellan lobes. We hypothesise that this provides evidence for contemporaneous surge‐like advances within the lobes, which may explain the asymmetry in the lobate margin positions on either side of the strait. The mechanisms that initiated rapid flow are unclear, but are likely to have been influenced by internal factors such as a change in thermal/hydrological conditions at the bed. The topography of the region suggests ice‐dammed lakes would have formed as the ice lobes retreated. The westernmost of the former lakes, Lake Skyring, is delimited by a series of palaeo‐shorelines surrounding the present‐day lake Laguna Blanca and we reconstruct lake evolution based on manipulation of a digital elevation model. The size and orientation of meltwater channels and a large outwash plain indicate that Lake Skyring drained eastwards towards the Strait of Magellan, probably quite rapidly. We conclude that the potential for quasi‐independent surge‐like behaviour within adjacent lobes raises the possibility that, during climate‐driven ice expansion, some advances in this region may have been partly controlled by secondary internal feedback mechanisms. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Simulations of planet migration driven by planetesimal scattering     

David R. Kirsh  Martin Duncan  Harold F. Levison 《Icarus》2009,199(1):197-209

Evidence has mounted for some time that planet migration is an important part of the formation of planetary systems, both in the Solar System [Malhotra, R., 1993. Nature 365, 819-821] and in extrasolar systems [Mayor, M., Queloz, D., 1995. Nature 378, 355-359; Lin, D.N.C., Bodenheimer, P., Richardson, D.C., 1996. Nature 380, 606-607]. One mechanism that produces migration (the change in a planet's semi-major axis a over time) is the scattering of comet- and asteroid-size bodies called planetesimals [Fernandez, J.A., Ip, W.-H., 1984. Icarus 58, 109-120]. Significant angular momentum exchange can occur between the planets and the planetesimals during local scattering, enough to cause a rapid, self-sustained migration of the planet [Ida, S., Bryden, G., Lin, D.N.C., Tanaka, H., 2000. Astrophys. J. 534, 428-445]. This migration has been studied for the particular case of the four outer planets of the Solar System (as in Gomes et al. [Gomes, R.S., Morbidelli, A., Levison, H.F., 2004. Icarus 170, 492-507]), but is not well understood in general. We have used the Miranda [McNeil, D., Duncan, M., Levison, H.F., 2005. Astron. J. 130, 2884-2899] computer simulation code to perform a broad parameter-space survey of the physical variables that determine the migration of a single planet in a planetesimal disk. Migration is found to be predominantly inwards, and the migration rate is found to be independent of planet mass for low-mass planets in relatively high-mass disks. Indeed, a simple scaling relation from Ida et al. [Ida, S., Bryden, G., Lin, D.N.C., Tanaka, H., 2000. Astrophys. J. 534, 428-445] matches well with the dependencies of the migration rate: