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1.
Glacial conditions that contribute to the regeneration of Fountain Glacier proglacial icing,Bylot Island,Canada 下载免费PDF全文
Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro‐thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier‐related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Morita T Ohtsuka Y Fujimoto K Minamisako Y Iida R Nakamura M Kayama T 《Marine pollution bulletin》2010,60(12):2311-2322
The anthropogenic radionuclides, 137Cs, 90Sr, 108mAg, 239+240Pu, were measured in two Chionoecetes species, red queen crab (Chionoecetes japonicus) and snow crab (Chionoecetes opilio) collected around Japan during 1996–2007. There was no increase in the concentrations of these radionuclides and no large variation of the atom ratio of 240Pu/239Pu during this research period. These results indicated that the source of the radionuclides was not the radioactive wastes dumped by the former USSR and Russia and originated from past nuclear weapon tests. The higher atom ratio in the crab species than that from global fallout would be contributed by the Pacific Proving Grounds close-in fallout. The variability of the concentration of radionuclides in the crab species would result from the variability of the composition and quantity in the diet. However, the decrease in the concentration of radionuclides with sampling depth would depend on the concentration in the seawater and diet. 相似文献
4.
目前利用激光来冷却和囚禁中性原子的技术已取得激动人心的进展。通过使用廉价的二极管激光器和蒸汽室收集器,有效地降低了囚禁原子的复杂性和高成本,在零点几μK温度下,可得到1011个原子/cm3的原子密度。本文介绍了有关激光冷却与囚禁技术,讨论了其现实应用:频率标准一基本物理性质研究。 相似文献
5.
Hydrogeologic delineation of habitats for endangered species: the Comal Springs/River System 总被引:1,自引:0,他引:1
We delineate 18 distinct habitats for the endangered fountain darter in the Comal Springs/River system based upon a combination
of vegetative, geologic, and hydrologic criteria. Comal Springs are the largest natural discharge from the Edwards aquifer
of central Texas; they issue along faults which penetrate the confined portion of the aquifer. The springs are the head of
the Comal River which is an important economic and recreational resource to the local community. The spring/river system is
the home of the fountain darter, a federally listed endangered species. Previous studies of this system were on a large scale
and lacked detail necessary for characterization. The fountain darter and other fauna in the Comal Springs/River system are
threatened by the possibility of diminished flows and the concomitant habitat change. The 18 habitats are defined by the dominant
species of vegetation, the substrate, and the flow conditions. Human alterations and spring discharge control the morphology
of the river and the substrates. Stream velocities determined substrate conditions and, thus indirectly, the distribution
of vegetation and habitats. In this system, hydrochemical parameters were uniform as were the soils adjacent to the stream;
these factors were not important to the habitat delineation. The range of stream velocities necessary to maintain the habitats
can be estimated with the Hjulstrom diagram. The darters were associated with a number of these habitats. We surmise that
significant alteration of the system's habitats will occur if discharge conditions change.
Received: 22 January 1996 · Accepted: 4 March 1996 相似文献
6.
《Experimental Astronomy》2009,23(2):611-649
In response to ESA’s Call for proposals of 5 March 2007 of the COSMIC VISION 2015–2025 plan of the ESA science programme,
we propose a M-class satellite mission to test of the Equivalence Principle in the quantum domain by investigating the extended free fall of matter waves instead of macroscopic bodies as in the case of GAUGE, MICROSCOPE
or STEP. The satellite, called Matter Wave Explorer of Gravity, will carry an experiment to test gravity, namely the measurement of the equal rate of free fall with various isotopes
of distinct atomic species with precision cold atom interferometry in the vicinity of the earth. This will allow for a first
quantum test the Equivalence Principle with spin polarised particles and with pure fermionic and bosonic atomic ensembles. Due to the
space conditions, the free fall of Rubidium and Potassium isotopes will be compared with a maximum accelerational sensitivity
of 5·10 − 16 m/s2 corresponding to an accuracy of the test of the Equivalence Principle of 1 part in 1016. Besides the primary scientific goal, the quantum test of the Equivalence Principle, the mission can be extended to provide
additional information about the gravitational field of the earth or for testing theories of fundamental processes of decoherence
which are investigated by various theory groups in the context of quantum gravity phenomenology. In this proposal we present
in detail the mission objectives and the technical aspects of the proposed mission. 相似文献
7.
G. Amelino-Camelia K. Aplin M. Arndt J. D. Barrow R. J. Bingham C. Borde P. Bouyer M. Caldwell A. M. Cruise T. Damour P. D’Arrigo H. Dittus W. Ertmer B. Foulon P. Gill G. D. Hammond J. Hough C. Jentsch U. Johann P. Jetzer H. Klein A. Lambrecht B. Lamine C. Lämmerzahl N. Lockerbie F. Loeffler J. T. Mendonca J. Mester W.-T. Ni C. Pegrum A. Peters E. Rasel S. Reynaud D. Shaul T. J. Sumner S. Theil C. Torrie P. Touboul C. Trenkel S. Vitale W. Vodel C. Wang H. Ward A. Woodgate 《Experimental Astronomy》2009,23(2):549-572
The GAUGE (GrAnd Unification and Gravity Explorer) mission proposes to use a drag-free spacecraft platform onto which a number
of experiments are attached. They are designed to address a number of key issues at the interface between gravity and unification
with the other forces of nature. The equivalence principle is to be probed with both a high-precision test using classical
macroscopic test bodies, and, to lower precision, using microscopic test bodies via cold-atom interferometry. These two equivalence
principle tests will explore string-dilaton theories and the effect of space–time fluctuations respectively. The macroscopic
test bodies will also be used for intermediate-range inverse-square law and an axion-like spin-coupling search. The microscopic
test bodies offer the prospect of extending the range of tests to also include short-range inverse-square law and spin-coupling
measurements as well as looking for evidence of quantum decoherence due to space–time fluctuations at the Planck scale. 相似文献
8.
We compare eruptive dynamics, effects and deposits of the Bezymianny 1956 (BZ), Mount St Helens 1980 (MSH), and Soufrière
Hills volcano, Montserrat 1997 (SHV) eruptions, the key events of which included powerful directed blasts. Each blast subsequently
generated a high-energy stratified pyroclastic density current (PDC) with a high speed at onset. The blasts were triggered
by rapid unloading of an extruding or intruding shallow magma body (lava dome and/or cryptodome) of andesitic or dacitic composition.
The unloading was caused by sector failures of the volcanic edifices, with respective volumes for BZ, MSH, and SHV c. 0.5,
2.5, and 0.05 km3. The blasts devastated approximately elliptical areas, axial directions of which coincided with the directions of sector
failures. We separate the transient directed blast phenomenon into three main parts, the burst phase, the collapse phase,
and the PDC phase. In the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into
the atmosphere, with much of the expansion having an initially lateral component. The erupted material fails to mix with sufficient
air to form a buoyant column, but in the collapse phase, falls beyond the source as an inclined fountain, and thereafter generates
a PDC moving parallel to the ground surface. It is possible for the burst phase to comprise an overpressured jet, which requires
injection of momentum from an orifice; however some exploding sources may have different geometry and a jet is not necessarily
formed. A major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be
attributed to shock waves within an overpressured jet, or alternatively to dynamic pressures and shocks within the energetic
collapse and PDC phases. Internal shock structures related to unsteady flow and compressibility effects can occur in each
phase. We withhold judgment about published shock models as a primary explanation for the damage sustained at MSH until modern
3D numerical modeling is accomplished, but argue that much of the damage observed in directed blasts can be reasonably interpreted
to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified PDC.
This view is reinforced by recent modeling cited for SHV. In distal and peripheral regions, solids concentration, maximum
particle size, current speed, and dynamic pressure are diminished, resulting in lesser damage and enhanced influence by local
topography on the PDC. Despite the different scales of the blasts (devastated areas were respectively 500, 600, and >10 km2 for BZ, MSH, and SHV), and some complexity involving retrogressive slide blocks and clusters of explosions, their pyroclastic
deposits demonstrate strong similarity. Juvenile material composes >50% of the deposits, implying for the blasts a dominantly
magmatic mechanism although hydrothermal explosions also occurred. The character of the magma fragmented by explosions (highly
viscous, phenocryst-rich, variable microlite content) determined the bimodal distributions of juvenile clast density and vesicularity.
Thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater, and laterally
from the axial region. The proximal stratigraphy of the blast deposits comprises four layers named A, B, C, D from bottom
to top. Layer A is represented by very poorly sorted debris with admixtures of vegetation and soil, with a strongly erosive
ground contact; its appearance varies at different sites due to different ground conditions at the time of the blasts. The
layer reflects intense turbulent boundary shear between the basal part of the energetic head of the PDC and the substrate.
Layer B exhibits relatively well-sorted fines-depleted debris with some charred plant fragments; its deposition occurred by
rapid suspension sedimentation in rapidly waning, high-concentration conditions. Layer C is mainly a poorly sorted massive
layer enriched by fines with its uppermost part laminated, created by rapid sedimentation under moderate-concentration, weakly
tractive conditions, with the uppermost laminated part reflecting a dilute depositional regime with grain-by-grain traction
deposition. By analogy to laboratory experiments, mixing at the flow head of the PDC created a turbulent dilute wake above
the body of a gravity current, with layer B deposited by the flow body and layer C by the wake. The uppermost layer D of fines
and accretionary lapilli is an ash fallout deposit of the finest particles from the high-rising buoyant thermal plume derived
from the sediment-depleted pyroclastic density current. The strong similarity among these eruptions and their deposits suggests
that these cases represent similar source, transport and depositional phenomena. 相似文献
9.
通过对福州乌鸦咀泉电导率观测资料的分析,针对2006年4月至10月该测值出现的高值异常现象进行深入分析,并对可能出现的影响因素进行逐个分析排除,认为该异常为中国台湾屏东海外7.2级地震的震前异常。 相似文献
10.
Denis Fougerouse Steven M. Reddy Christopher L. Kirkland David W. Saxey William D. Rickard Robert M. Hough 《地学前缘(英文版)》2019,10(1):55-63
The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite(FeS_2), we have combined electron backscatter diffraction(EBSD) and atom probe microscopy(APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth(~3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a highangle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization.Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ~2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation. 相似文献