The effect of neutrinos on the initial fireballs in gamma-ray bursts     

Hylke B. J. Koers  Ralph A. M. J. Wijers 《Monthly notices of the Royal Astronomical Society》2005,364(3):934-942

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The meteorite collection sites of Antarctica     

William Cassidy  Ralph Harvey  John Schutt  Georg Delisle  Keizo Yanai 《Meteoritics & planetary science》1992,27(5):490-525

Abstract— Antarctic meteorites have been and are being well studied but the potential for glaciological and climatological information in the sites where they are found is only beginning to be realized. To date, meteorite stranding surfaces have been identified only in East Antarctica: (1) The MacKay Glacier/David Glacier region contains the Allan Hills and the Reckling Moraine/Elephant Moraine stranding surfaces. Because the Allan Hills Main Icefield has a large proportion of meteorites with long terrestrial ages, these concentrations of meteorites must have had catchment areas extending well inland, in contrast to the present. Where known, bedrock topography is mesa-like in form and influences ice flow directions. Ice levels at the Allan Hills may have been higher by 50–100 m in the past. Reckling Moraine and Elephant Moraine are located on a long patch of ice running westward from Reckling Peak; the ice appears to be pouring over a bedrock escarpment. (2) In North Victoria Land, ice diverges around Frontier Mountain and flows into a site behind the barrier where ablation occurs extensively. It is proposed that meteorites and rocks were dumped by ice flow at the mouth of a valley in the lee of the mountain at the site where a meltwater pond existed, in a depression produced by ablation. Later, the pond migrated headward along the valley to a point where it is today, leaving a morainal deposit with the meteorites at a higher level. (3) Between the Beardmore and Law Glaciers, ice flows sluggishly into the southwestern margin of the Walcott Névé. Northeastern sections of the Walcott are virtually barren of meteorites. The entering Plateau ice is diverted northward to flow along the base of Lewis Cliff. This flow apparently terminates in an ice tongue protruding into a vast moraine, where a very large concentration of meteorites was found on the ice. This final segment of flowing ice is called the Lewis Cliff Ice Tongue. Meteorite Moraine, a subsidiary occurrence 2 km to the northeast, is also found against morainal deposits. The origin of the moraines and the history of meteorite concentration at this site is the subject of some debate. (4) The Transantarctic Mountains are submerged along one segment many hundreds of km in length by ice flowing off the Polar Plateau. The Thiel Mountains, Pecora Escarpment and Patuxent Range are the only surface indications of the underlying mountains along this interval, and meteorite stranding surfaces are found at each of these sites. Little is yet known about ice dynamics at these sites. (5) The immense Yamato Mountains meteorite stranding surface covers an area of about 4000 km². So far, most meteorites have been recovered in the upper reaches of this blue ice field, where ice flow is slowed by outlying subice barriers of the Yamato Mountains. Individual massifs in this range extend northward over 50 km, and the Yamato Meteorite Icefield loses 1100 m in elevation over this distance. (6) The Sør Rondane Mountains form a barrier to ice flow off the Polar Plateau. The major meteorite stranding surface associated with this barrier is the Nansenisen Icefield, a large ablation area about 50 km upstream of the mountains. The existence of a meteorite stranding surface at this site has not been explained so far. Most meteorite stranding surfaces have been functioning for a long time. They are sites where net ablation of the surface is occurring; the ice at these sites is stagnant or flowing only slowly, and the numbers of meteorites with great terrestrial ages decrease exponentially. Concentration mechanisms operating at these sites involve ablation, direct infall, time, low temperatures, moderate weathering and wind ablation. Detrimental to concentration are ice flow out of the area and extreme weathering. In spite of the fact that the Antarctic Ice Sheet is thought to be over 10 Ma old, we do not find stranding surfaces with meteorites having greater terrestrial ages than 1 Ma. This suggests that stranding surfaces are transient features, affected on a continental scale by possible extreme warming during late Pliocene and on a smaller scale by regional changes that produce differential effects between icefields. The latter effect is suggested by differences in the average terrestrial age of meteorites at different stranding surfaces. In either case, these sites seem to appear as a result of thinning near the edges of the ice sheet, and stratigraphic sequences may be exposed in the ice at stranding surfaces. We review five models for the production of meteorite stranding surfaces: (1) simple deflation of the ice sheet, in which ablation removes great thicknesses of overlying ice, exposing the contained meteorites while allowing direct falls to accumulate, (2) simple accumulation of direct falls on a bare ice surface that is not deflating, (3) ablation of ice trapped against a barrier, in which meteorites accumulate by direct infall while inflowing ice contributes meteorites by ablation discovery, (4) deceleration of ice by a subice barrier, which allows ablation discovery of meteorites in incoming ice and accumulation of other meteorites on the surface by direct infall and (5) stagnation of ice by encounter with an ice mass able to produce an opposing flow vector, in which ablation discovery and direct infall accumulation processes operate to build the meteorite concentration.  相似文献   

Second Worm Conference on Sampling and Blending     

Dr. Ralph J Holmes 《《幕》》2005,28(4):291-292

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The paleoecological development of a late holocene,tidal freshwater marsh of the Upper Delaware River estuary     

Richard A. Orson  Robert L. Simpson  Ralph E. Good 《Estuaries and Coasts》1992,15(2):130-146

Changes in groundwater tables brought about by sea level increases in the Delaware River Basin (near Philadelphia) about 2,500 years B.P., initiated wetland development at the Princeton-Jefferson Branch of the Woodbury Creek marshes. Continual increases in sea level pushed groundwater tables further upward, and by approximately 800 years B.P., groundwater tables had risen to the upper limits for woody vegetation at the site. By the time European settlers arrived in the late 1600s nontidal sedge marshes dominated the site. Upon arriving colonists began manipulating the hydrology of the Delaware River Basin by constructing dams and dikes for flood control. Soon many areas were cut off from direct contact with the river. During the next one and one-half centuries sea level continued to rise, and because of channelization of the Delaware River the tidal range doubled. During the early 1900s flood control structures began to fail allowing tidal waters to periodically inundate these protected sites. At that time the site was dominated by a Quercus-Castanea swamp forest with hummocks of Cyperaceae interspersed throughout. In 1940 the dike surrounding the Princeton-Jefferson marsh collapsed and the site was immediately inundated with tidal waters on a regular basis. Within a short period of time tidal freshwater marsh developed and has continued to the present day. It is clear from this investigation that changes in hydrology brought about by cultural modifications have been directly responsible for the ontogeny of this tidal marsh. The influence cultural impacts have had on wetland development at the Princeton-Jefferson marsh suggest that it may be necessary to reevaluate the extent humans have modified the development and structure of the present day upper Delaware River estuary. Although the ability to discern historic vegetation zonation patterns is limited, these marshes can record individual events that have shaped these wetlands through time. Due to differences in the structure of the plant community, rates of decomposition, and processes of accretion, Redfield’s model (1972) of tidal salt marsh development does not apply to the Princeton-Jefferson marsh. Along a submerging coast, the development of tidal freshwater marsh in many estuaries may be necessary for the establishment of brackish and salt marshes by creating and maintaining a suitable habitat for the eventual colonization of more salt-tolerant plant species. The roles these wetlands have played in the development of the estuaries has been underestimated in the past.  相似文献   

Magnetics in geoexploration     

William J. Hinze  Ralph R. B. Von Frese 《Journal of Earth System Science》1990,99(4):515-547

The magnetic method is the oldest and one of the most widely used geophysical techniques for exploring the earth’s subsurface. It is a relatively easy and inexpensive tool to employ, being applicable to a wide variety of subsurface exploration problems involving horizontal magnetic property variations occurring from near the base of the crust to within the uppermost meter of soil. Successful applications of the magnetic method require an in-depth understanding of its basic principles and careful field work, data reduction, and interpretation. Commonly, interpretations are limited to qualitative approaches which simply map the spatial location of anomalous subsurface conditions, but under favourable circumstances the technological status of the method will permit more quantitative interpretations involving specification of the nature of the anomalous sources. No other geophysical method provides critical input to such a wide variety of problems. However, seldom does the magnetic method provide the complete answer to an investigation problem. As a result, it is generally used in concert with other geophysical and geological data to limit its interpretational ambiguities.  相似文献   

Stable isotopes and cellulase activity as evidence for detritus as a food source for juvenile Gulf menhaden     

Linda A. Deegan  Bruce J. Peterson  Ralph Portier 《Estuaries and Coasts》1990,13(1):14-19

Menhaden are one of the most abundant components of fish communities in Gulf and Atlantic estuaries. Juvenile menhaden have been reported to have zooplankton, phytoplankton, andSpartina-derived detritus in their guts. However, there has been disagreement over the importance of the detritus as a food source. We show, using physiological and stable isotope evidence, that detritus can be used by juvenile Gulf menhaden. Their diet is very roughly 30% detritus- and 70% plankton-based.  相似文献   

Matrix isolation technique for the study of some factors affecting the partitioning of trace elements     

Joseph M. Grzybowski  Ralph O. Allen 《Chemical Geology》1974,14(3):209-222

Some of the factors that affect the preferred positions of cations in ionic-solid solutions were investigated utilizing vibrational spectroscopy. Solid solutions of the sulfate and chromate ions codoped with La³⁺ and Ca²⁺ in a KBr host lattice were examined as a function of the polyvalent-cation concentration. The cation—anion pairing process was found to be random for Ca²⁺ whereas the formation of La³⁺SO₄^2? ion-pairs with a C_2v bonding geometry is highly preferential to any type of La³⁺CrO₄^2? ion-pair formation. The relative populations of ion-pair site configurations are discussed in terms of an energy—entropy competition which can be applied to the partition of trace elements during magmatic processes.  相似文献   

The Original Members Of The Association Of American Geographers     

Preston E. James  Ralph Ehrenberg 《The Professional geographer》1975,27(3):327-335

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Ice-rafted volcanic ash in the South Atlantic sector of the Southern Ocean during the last 100,000 years     

David G Smith  Michael T Ledbetter  Paul F Ciesielski 《Marine Geology》1983,53(4):291-312

Eucampia antarctica (Castr.) Mangin abundance curves for two piston cores from the western Agulhas Basin (southeast Atlantic sector of the Southern Ocean) were used to place volcanic glass shard and ice-rafted debris abundance curves into a stratigraphic framework for the last 100,000 years. A direct correlation is shown between increased abundance of E. antarctica, tephra and ice-rafted debris; low abundances are often characterized by calcareous sediment in the northern core. Peaks in abundance of E. antarctica have been interpreted as an indication of glacial periods and the increased ice-rafted debris and tephra during glacial periods is evidence for an ice-rafted origin for the tephra.Microprobe geochemical analysis of volcanic glass shards provides no single distinct source for the ash. The geochemical data is consistent, but not definitive, with a primary source in the Scotia Arc and a minor source from Bouvet Island. Between core correlations of geochemically “fingerprinted” dispersed tephra zones were not successful due to variability of glass shard geochemistry and limited sample size.  相似文献   

THE PROPOSED TRANS ALASKA PIPELINE SYSTEM: POTENTIAL HIGHWAY TO THE NORTH AMERICAN ARCTIC*     

Ralph C. Brown 《The Professional geographer》1971,23(1):15-18

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