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91.
Kamal A. Ali Robert J. Stern William I. Manton Peter R. Johnson Sumit K. Mukherjee 《International Journal of Earth Sciences》2010,99(4):705-726
The Neoproterozoic Atud diamictite in Wadi Kareim and Wadi Mobarak in the Eastern Desert of Egypt and the Nuwaybah formation
in NW Saudi Arabia consist of poorly sorted, polymictic breccia, with clasts up to 1 m of granitoid, quartz porphyry, quartzite,
basalt, greywacke, marble, arkose, and microconglomerate in fine-grained matrix. Stratigraphic relations indicate that the
diamictite was deposited in a marine environment. Integrated field investigation, petrographic study and U–Pb SHRIMP zircon
ages demonstrate that the Atud and Nuwaybah are correlative. The distribution of zircon ages indicate that ~750 Ma ages are
dominant with a significant component of older materials, characterized by minor Mesoproterozoic and more abundant Paleoproterozoic
and Neoarchean ages. Some matrix and metasedimentary clast zircons yield ages that are a few 10s of Ma younger than the age
of the youngest clast (754 ± 15 Ma), suggesting Atud/Nuwaybah diamictite deposition ~750 Ma or slightly later, broadly consistent
with being deposited during the Sturtian glaciation (740–660 Ma). The Paleoproterozoic and Neoarchean clasts have no source
within the ensimatic Arabian–Nubian Shield. The distribution of the pre-Neoproterozoic ages are similar to the distribution
of the pre-Neoproterozoic ages in Yemen and Saharan Metacraton, suggesting that these clasts have been transported hundreds
of kilometers, maybe by ice-rafting. The Atud diamictite may represent important evidence for Cryogenian “Snowball Earth”
in the Arabian–Nubian Shield. 相似文献
92.
CFD, system-based and EFD study of ship dynamic instability events: Surf-riding, periodic motion, and broaching 总被引:1,自引:0,他引:1
Hamid Sadat-Hosseini Frederick Stern Naoya Umeda Shinya Yamamura 《Ocean Engineering》2011,38(1):88-110
CFD and system-based simulation are used to predict broaching, surf-riding, and periodic motion for the ONR Tumblehome model, including captive and free model test validation studies. CFD shows close agreement with EFD for calm water resistance, static heel (except for sway force and yaw moment), and static drift (except for roll moment). CFD predictions of static heel in following waves also compare well with EFD except for surge force, sway force, and pitch angle. Froude-Krylov calculations of wave-induced surge force in following waves provides good agreement for high Froude number, but significantly overestimates for Froude number less than 0.2. On the other hand, CFD successfully reproduces the reduction of the wave-induced surge force near Froude number 0.2, probably because CFD can capture the 3D wave pattern. CFD free model simulations are performed for several speeds and headings and validated for the first time for surf-riding, broaching, and periodic motions. System-based simulations are carried out based on inputs from EFD, CFD, and Froude-Krylov for a dense grid of speeds and headings to predict the instability map, which were found to produce fairly similar results. 相似文献
93.
Computations of self-propulsion free to sink and trim and of motions in head waves of the KRISO Container Ship (KCS) model 总被引:2,自引:0,他引:2
Two computations of the KCS model with motions are presented. Self-propulsion in model scale free to sink and trim are studied with the rotating discretized propeller from the Hamburg Model Basin (HSVA) at Fr = 0.26. This case is particularly complex to simulate due to the close proximity of the propeller to the rudder. The second case involves pitch and heave in regular head waves. Computations were performed with CFDShip-Iowa version 4.5, a RANS/DES CFD code designed for ship hydrodynamics. The self-propulsion computations were carried out following the procedure described in Carrica et al. [1], in which a speed controller is used to find the propeller rotational speed that results in the specified ship velocity. The rate of revolutions n, sinkage, trim, thrust and torque coefficients KT, KQ and resistance coefficient CT(SP) are thus obtained. Comparisons between CFD and EFD show that the rate of revolutions n, thrust and torque coefficients KT and KQ have higher prediction accuracies than sinkage and trim. For the simulation of pitch and heave in head waves, the geometry includes KCS hull and rudder under three conditions with two Froude numbers and three wave length and amplitude combinations. 0th and 1st harmonic amplitudes and 1st harmonic phase are computed for total resistance coefficient CT, heave motion z and pitch angle θ. Comparisons between CFD and EFD show that pitch and heave are much better predicted than the resistance. In both cases comparisons with simulations by other authors presented at the G2010 CFD Workshop [2] using different CFD methodologies are included. 相似文献
94.
E.A. Sagredo P.I. Moreno R. Villa-Martínez M.R. Kaplan P.W. Kubik C.R. Stern 《Geomorphology》2011,125(1):92-108
We present a new record from the Última Esperanza region (51°25’-52°25'S), southwestern Patagonia, to unravel the timing and structure of glacial fluctuations during the Last Glacial Termination (T1). This sector of southern South America represents the only windward-facing continental landmass in the Southern Hemisphere that intersects the core of the Southern Westerly Wind belt.Geomorphic, stratigraphic and geochronological evidence indicate the following stages during and since the Last Glacial Maximum (LGM): (i) deposition of prominent moraine complexes during at least two advances dated between ~ 39 and > 17.5 ka; (ii) development of an ice-dammed proglacial lake (glacial lake Puerto Consuelo) accompanying ice recession; (iii) active deposition of moraine complexes at intermediate positions followed by recession at ≥ 15.2 ka; (iv) lake level drop and subsequent stabilization between 15.2-12.8 ka; (v) a glacial readvance in glacial lake Puerto Consuelo between 14.8-12.8 ka; (vi) ice recession, stabilization, and lake level lowering between 12.8-10.3 ka; and (vii) glacial withdrawal and disappearance of glacial lake Puerto Consuelo prior to 10.3 ka. By comparing our results with the chronologies from neighboring regions we explore whether there was a consistent temporal/geographic pattern of glacial fluctuations during the LGM and T1, and examine their implications at regional, hemispheric, and global scales. The correspondence of these variations with key paleoclimate events recorded in the Southern and the Northern Hemispheres suggest a common forcing that, most likely, propagated through the atmosphere. Regional heterogeneities at millennial timescales probably reflect the influence of processes related to deep ocean circulation, and changes in the position/intensity of the Antarctic Polar Front and Southern Westerly Winds. 相似文献
95.
Paul D. Feldman S. Alan Stern Joel Wm. Parker Michael F. A'Hearn Michel C. Festou 《Icarus》2007,187(1):104-108
We report on spectroscopic observations of periodic Comet 9P/Tempel 1 by the Alice ultraviolet spectrograph on the Rosetta spacecraft in conjunction with NASA's Deep Impact mission. Our objectives were to measure an increase in atomic and molecular emissions produced by the excavation of volatile sub-surface material. We unambiguously detected atomic oxygen emission from the quiescent coma but no enhancement at the 10% (1-σ) level following the impact. We derive a quiescent H2O production rate of 9×1027 molecules s−1 with an estimated uncertainty of ∼30%. Our upper limits to the volatiles produced by the impact are consistent with other estimates. 相似文献
96.
Womack M. Homich A. Festou M. C. Mangum J. Uhl W. T. Stern S. A. 《Earth, Moon, and Planets》1997,77(3):259-264
On-the-Fly maps of emission from the HCO+ J = 3-2 transition at 267.6 GHz were obtained of C/1995 O1 (Hale-Bopp) on 1997 Mar 15.6 UT using the NRAO 12-m telescope
with high spatial resolution. Unlike the relatively symmetric and centralized maps of the neutral species CO, HCN and H2CO, the spatial extent of HCO+ emission is very diffuse with a complex structure characterized by at least two physically different regions. The bulk of
the HCO+ emission peaks in intensity ∼175,000 km anti-sunward from the nuclear position. This peak emission does not fall directly
along the anti-sunward direction, but is rotated by ∼10 degrees toward the east from the anti-sunward direction. A substantial
void, or decrease, of HCO+ emission is observed within ∼ 55,000 km of the nucleus. The HCO+ emission in this void is roughly half the intensity of the emission observed 100,000 km away. This decrease of HCO+ emission near the nucleus may indicate that production or excitation of HCO+ is inhibited, or perhaps that HCO+ is easily destroyed in the inner coma, especially within ∼50,000 km of the nucleus. This void roughly coincides with the
approximate location and size of the so-called “diamagnetic cavity” in the coma and may mark a significant transition region
in the inner coma of Hale-Bopp
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
97.
Michael A. Dopita Michiel Reuland Wil van Breugel Wim de Vries S. A. Stanford Huub Röttgering George Miley Bram Venemans Hy Spinrad Steve Dawson Arjun Dey Mark Lacy Daniel Stern Andrew Bunker 《Astrophysics and Space Science》2007,311(1-3):305-309
We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics
with typical velocity dispersions of a few hundred km s−1 and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated
with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km s−1. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of ∼60 kpc along the
radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most
of their interstellar medium before evolving to become “red and dead” Elliptical galaxies. 相似文献
98.
Andrew Bunker Joanna Smith Hyron Spinrad Daniel Stern Stephen Warren 《Astrophysics and Space Science》2003,284(2):357-360
We have discovered extended Lyman-α emission around a z=4.5 QSO in a deep long-slit spectrum with Keck/LRIS at moderate spectral resolution (R≈ 1000). The line emission extends 5 arcsec beyond the continuum of the QSO and is spatially asymmetric. This extended line
emission has a spectral extent of 1000km/s, much narrower in velocity spread than the broad Lyman-α from the QSO itself and
slightly offset in redshift. No evidence of continuum is seen for the extended emission line region, suggesting that this
recombination line is powered by reprocessed QSO Lyman continuum flux rather than by local star formation. This phenomenon
is rare in QSOs which are not radio loud, and this is the first time it has been observed at z>4. It seems likely that the QSO is illuminating the surrounding cold gas of the host galaxy, with the ionizing photons producing
Lyman-α fluorescence. As suggested by Haiman and Rees (2001), this `fuzz' around a distant quasar may place strong constraints
on galaxy formation and the extended distribution of cold, neutral gas.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
99.
The ‘subduction initiation rule’: a key for linking ophiolites,intra-oceanic forearcs,and subduction initiation 总被引:9,自引:1,他引:8
We establish the ‘subduction initiation rule’ (SIR) which predicts that most ophiolites form during subduction initiation
(SI) and that the diagnostic magmatic chemostratigraphic progression for SIR ophiolites is from less to more HFSE-depleted and LILE-enriched compositions.
This chemostratigraphic evolution reflects formation of what ultimately becomes forearc lithosphere as a result of mantle
melting that is progressively influenced by subduction zone enrichment during SI. The magmatic chemostratigraphic progression
for the Izu–Bonin–Mariana (IBM) forearc and most Tethyan ophiolites is specifically from MORB-like to arc-like (volcanic arc
basalts or VAB ± boninites or BON) because SI progressed until establishment of a mature subduction zone. MORB-like lavas
result from decompression melting of upwelling asthenosphere and are the first magmatic expression of SI. The contribution
of fluids from dehydrating oceanic crust and sediments on the sinking slab is negligible in early SI, but continued melting
results in a depleted, harzburgitic residue that is progressively metasomatized by fluids from the sinking slab; subsequent
partial melting of this residue yields ‘typical’ SSZ-like lavas in the latter stages of SI. If SI is arrested early, e.g.,
as a result of collision, ‘MORB-only’ ophiolites might be expected. Consequently, MORB- and SSZ-only ophiolites may represent
end-members of the SI ophiolite spectrum. The chemostratigraphic similarity of the Mariana forearc with that of ophiolites
that follow the SIR intimates that a model linking such ophiolites, oceanic forearcs, and SI is globally applicable. 相似文献
100.
Matrix Corrections and Error Analysis in High‐Precision SIMS 18O/16O Measurements of Ca–Mg–Fe Garnet
We report technical and data treatment methods for making accurate, high‐precision measurements of 18O/16O in Ca–Mg–Fe garnet utilising the Cameca IMS 1280 multi‐collector ion microprobe. Matrix effects were similar to those shown by previous work, whereby Ca abundance is correlated with instrumental mass fractionation (IMF). After correction for this effect, there appeared to be no significant secondary effect associated with Mg/Fe2+ for routine operational conditions. In contrast, investigation of the IMF associated with Mn‐ or Cr‐rich garnet showed that these substitutions are significant and require a more complex calibration scheme. The Ca‐related calibration applied to low‐Cr, low‐Mn garnet was reproducible across different sample mounts and under a range of instrument settings and therefore should be applicable to similar instruments of this type. The repeatability of the measurements was often better than ± 0.2‰ (2s), a precision that is similar to the repeatability of bulk techniques. At this precision, the uncertainties due to spot‐to‐spot repeatability were at the same magnitude as those associated with matrix corrections (± 0.1–0.3‰) and the uncertainties in reference materials (± 0.1–0.2‰). Therefore, it is necessary to accurately estimate and propagate uncertainties associated with these parameters – in some cases, uncertainties in reference materials or matrix corrections dominate the uncertainty budget. 相似文献