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201.
Research investigations on three-dimensional (3-D) rectangular hydraulic fracture configurations with varying degrees of fluid lag are reported. This paper demonstrates that a 3-D fracture model coupled with fluid lag (a small region of reduced pressure) at the fracture tip can predict very large excess pressure measurements for hydraulic fracture processes. Predictions of fracture propagation based on critical stress intensity factors are extremely sensitive to the pressure profile at the tip of a propagating fracture. This strong sensitivity to the pressure profile at the tip of a hydraulic fracture is more strongly pronounced in 3-D models versus 2-D models because 3-D fractures are clamped at the top and bottom, and pressures in the 3-D fractures that are far removed from the fracture tip have little effect on the stress intensity factor at the fracture tip. This rationale for the excess pressure mechanism is in marked contrast to the crack tip process damage zone assumptions and attendant high rock fracture toughness value hypotheses advanced in the literature. A comparison with field data is presented to illustrate the proposed fracture fluid pressure sensitivity phenomenon. This paper does not attempt to calculate the length of the fluid lag region in a propagating fracture but instead attempts to show that the pressure profile at the tip of the propagating fracture plays a major role in fracture propagation, and this role is magnified in 3-D models. © 1997 by John Wiley & Sons, Ltd. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 229–240 (1997). 相似文献
202.
The effect of gauge length on axially incident P‐waves measured using fibre optic distributed vibration sensing 下载免费PDF全文
Distributed vibration sensing, also known as distributed acoustic sensing, is a relatively new method for recording vertical seismic profile data using a fibre optic cable as the sensor. The signal obtained from such systems is a distributed measurement over a length of fibre referred to as the gauge length. In this paper, we show that gauge length selection is one of the most important acquisition parameters for a distributed vibration sensing survey. If the gauge length is too small, then the signal‐to‐noise ratio will be poor. If the gauge length is too large, resolution will be reduced and the shape of the wavelet will be distorted. The optimum gauge length, as derived here, is a function of the velocity and frequencies of the seismic waves being measured. If these attributes vary considerably over the depth of a survey, then the use of different gauge lengths is recommended. The significant increases in data quality resulting from the use of multiple gauge length values are demonstrated using field data. 相似文献
203.
The time integration method proposed by Kolay and Ricles, which was claimed to be both explicit and unconditionally stable, is shown to be implicit in the sense of requiring the factorization of an effective stiffness matrix where an explicit method needs no solver. Its original derivation procedure employed discrete control theory concepts, which are in fact, equivalent to conventional recurrence relation concepts aiming to match its spectral properties with those of the three-parameter optimal/generalized-α method, thus giving rise to an implicit method within the class of linear multistep methods. It is shown that the resulting method possesses several added computational drawbacks due to its derivation procedure, such as additional effective stiffness inversions and a degraded order of accuracy in general. 相似文献
204.
国际工程教育认证中全员达标要求以及行业对网络GIS的强技术需求,给网络GIS课程教学体系带来了机遇和挑战。针对现有网络GIS课程教学体系仍以传统灌输模式为主的问题,本文分析了网络GIS课程特点和教学现状,提出了全员全栈式教学体系,设计了面向不同类型教学对象的多层次教学内容和教学方法,可以满足工程教育认证的全员达标要求;提出了以知识点为单元的细粒度技术教学设计,通过技术点的组合可以实现全栈式技术人才培养;最后,本文结合项目案例给出了技术教学设计与实施的示范。本文提出的教学体系为培养面向工程认证和行业需求的网络GIS技术人才提供了教学参考。 相似文献
205.
The densities of self-established non-indigenous prickly pears (Opuntia ficus-indica) in rangelands of the Karoo recorded on 3434 km of road transects, were on average 800 times greater below telegraph and transmission poles than away from poles, and 200 times greater next to wire fences along roads than in open rangelands. We suggest that this uneven establishment pattern is mainly due to the dispersal of Opuntia ficus-indica seeds by crows and other vertebrates (chiefly primates). Cape (Corvus capensis) and pied crows (C. albus) feed on fruits of Opuntia ficus-indica in the Karoo, and regurgitate pellets containing viable seeds of these plants below nest sites, roosts and occasional perch sites. Crows use man-made structures such as wire fences, telegraph and transmission poles and windmills for perching, roosting and nesting. Crow pellets, containing regurgitated bones and viable seeds of Opuntia spp., and other alien and indigenous plants, are most common around such perch sites. Crows are frequently associated with roads in the Karoo because they scavenge on road kills in the Karoo as well as feeding on fruits, insects and reptiles in road verges. We suggest that dispersal of seeds by crows is important for range extension and establishment of new Opuntia populations. 相似文献
206.
The littoral drift rose (LDR) concept is presented herein for improvement in understanding of longshore sediment transport and consequent shoreline processes in areas with smooth (gradually varying) offshore bathymetry extending over a coastal region where the deep water wave climate is reasonably uniform. The concept of the littoral drift rose (LDR) is presented and LDRs are shown to provide insight into coastal evolution and shoreline stability (or instability) for a given region having uniform wave climate. This paper reviews earlier documented applications and work using LDRs and provides an interpretation of earlier findings of shoreline stability using LDRs. Previously known but undocumented findings are also discussed herein which show that the wave climate and hence the LDR can be synthesized into an equivalent LDR developed from one wave component of given magnitude and direction. Practical applications using LDRs are presented, which show that the magnitude and direction of littoral drift throughout a region can be interpreted from limited measured, calculated, or observed data on littoral drift at two locations in the region. 相似文献
207.
Shocked chromites in fossil L chondrites: A Raman spectroscopy and transmission electron microscopy study 下载免费PDF全文
Surya S. Rout Philipp R. Heck Nestor J. Zaluzec Takayuki Ishii Jianguo Wen Dean J. Miller Birger Schmitz 《Meteoritics & planetary science》2017,52(9):1776-1796
Chromites from Middle Ordovician fossil L chondrites and from matrix and shock‐melt veins in Catherwood, Tenham, and Coorara L chondrites were studied using Raman spectroscopy and TEM. Raman spectra of chromites from fossil L chondrites showed similarities with chromites from matrix and shock‐melt veins in the studied L chondrite falls and finds. Chromites from shock‐melt veins of L chondrites show polycrystallinity, while the chromite grains in fossil L chondrites are single crystals. In addition, chromites from shock‐melt veins in the studied L chondrites have high densities of planar fractures within the subgrains and many subgrains show intergrowths of chromite and xieite. Matrix chromite of Tenham has similar dislocation densities and planar fractures as a chromite from the fossil meteorite Golvsten 001 and higher dislocation densities than in chromite from the fossil meteorite Sextummen 003. Using this observation and knowing that the matrix of Tenham experienced 20–22 GPa and <1000° C, an upper limit for the P,T conditions of chromite from Golvsten 001 and Sextummen 003 can be estimated to be 20–22 GPa and 1000° C (shock stage S3–S6) and 20 GPa and 1000° C (S3–S5), respectively, and we conclude that the studied fossil meteorite chromites are from matrix. 相似文献
208.
Atom‐probe tomography and transmission electron microscopy of the kamacite–taenite interface in the fast‐cooled Bristol IVA iron meteorite 下载免费PDF全文
Surya S. Rout Philipp R. Heck Dieter Isheim Thomas Stephan Nestor J. Zaluzec Dean J. Miller Andrew M. Davis David N. Seidman 《Meteoritics & planetary science》2017,52(12):2707-2729
We report the first combined atom‐probe tomography (APT) and transmission electron microscopy (TEM) study of a kamacite–tetrataenite (K–T) interface region within an iron meteorite, Bristol (IVA). Ten APT nanotips were prepared from the K–T interface with focused ion beam scanning electron microscopy (FIB‐SEM) and then studied using TEM followed by APT. Near the K‐T interface, we found 3.8 ± 0.5 wt% Ni in kamacite and 53.4 ± 0.5 wt% Ni in tetrataenite. High‐Ni precipitate regions of the cloudy zone (CZ) have 50.4 ± 0.8 wt% Ni. A region near the CZ and martensite interface has <10 nm sized Ni‐rich precipitates with 38.4 ± 0.7 wt% Ni present within a low‐Ni matrix having 25.5 ± 0.6 wt% Ni. We found that Cu is predominantly concentrated in tetrataenite, whereas Co, P, and Cr are concentrated in kamacite. Phosphorus is preferentially concentrated along the K‐T interface. This study is the first precise measurement of the phase composition at high spatial resolution and in 3‐D of the K‐T interface region in a IVA iron meteorite and furthers our knowledge of the phase composition changes in a fast‐cooled iron meteorite below 400 °C. We demonstrate that APT in conjunction with TEM is a useful approach to study the major, minor, and trace elemental composition of nanoscale features within fast‐cooled iron meteorites. 相似文献
209.
A. Giunta E. Bozzo F. Bernardini G. Israel L. Stella M. Falanga S. Campana A. Bazzano A. J. Dean M. Mendez 《Monthly notices of the Royal Astronomical Society》2009,399(2):744-749
IGR J18483−0311 was discovered with INTEGRAL in 2003 and later classified as a supergiant fast X-ray transient. It was observed in outburst many times, but its quiescent state is still poorly known. Here, we present the results of XMM–Newton , Swift and Chandra observations of IGR J18483−0311. These data improved the X-ray position of the source, and provided new information on the timing and spectral properties of IGR J18483−0311 in quiescence. We report the detection of pulsations in the quiescent X-ray emission of this source, and give for the first time a measurement of the spin-period derivative of this source. In IGR J18483−0311, the measured spin-period derivative of −(1.3 ± 0.3) × 10−9 s s−1 likely results from light travel time effects in the binary. We compare the most recent observational results of IGR J18483−0311 and SAX J1818.6−1703, the two supergiant fast X-ray transients for which a similar orbital period has been measured. 相似文献
210.
A geochemical study of the Sweet Home Mine,Colorado Mineral Belt,USA: hydrothermal fluid evolution above a hypothesized granite cupola 总被引:1,自引:0,他引:1
Volker Lüders Rolf L. Romer H. Albert Gilg Robert J. Bodnar Thomas Pettke Dean Misantoni 《Mineralium Deposita》2009,44(4):415-434
Deposition of quartz–molybdenite–pyrite–topaz–muscovite–fluorite and subsequent hübnerite and sulfide–fluorite–rhodochrosite
mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby
world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and
is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric
water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage
quartz–molybdenite–pyrite–topaz–muscovite–fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating
pressure regime at temperatures of about 400°C as indicated by CO2-bearing, moderately saline (7.5–12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz
demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents
than those reported from porphyry–Cu–Au–Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated
magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the
periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic
pressure regime from low-salinity ± CO2-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly
negative δ34S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ18O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly
variable 87Sr/86Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more
radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed
from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that
were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion. 相似文献