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981.
N. Al-Shayea 《Rock Mechanics and Rock Engineering》2002,35(4):271-297
Summary
A fracture toughness study was conducted on a limestone rock formation from a petroleum reservoir in Saudi Arabia, and results
were compared with those for outcrop specimens from the same geological formation. The objective was to investigate the possibility
of using outcrop specimens to estimate the fracture toughness behavior of reservoir rock at in-situ conditions of temperature and confining pressure. The study was made on reservoir specimens from a depth of about 3.5 km,
at both ambient and reservoir conditions. Mixed mode I–II fracture toughness at reservoir conditions of high temperature and
confining pressure was studied using straight notched Brazilian disk (SNBD) specimens under diametrical compression. Tests
were conducted at ambient conditions, at an effective confining pressure (σ3) of 28 MPa (4000 psi), and at a temperature of 116°C. The results showed a substantial increase in fracture toughness under confining pressure. Under σ3=28 MPa, the pure mode-I fracture toughness (K
IC), increased by a factor of about 3.2, and the pure mode-II fracture toughness (K
IIC) increased by a factor of 4.4, compared to those under ambient conditions. On the other hand, K
IC at 116°C was only 25% more than that at ambient conditions. These results were compared with recent results for outcrop specimens
from the same geological formation. The results reveal that outcrop specimens can be successfully used to predict the fracture
behavior of reservoir specimens at in-situ conditions, in spite of some differences at ambient conditions. Additionally, fracture toughness envelopes were obtained
for reservoir specimens at ambient and high pressure conditions, in both positive and negative regions.
Received September 14, 2000; accepted February 22, 2002 Published online September 2, 2002 相似文献
982.
Papadimitriou P. Voulgaris N. Kassaras I. Kaviris G. Delibasis N. Makropoulos K. 《Natural Hazards》2002,27(1-2):15-33
On 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occurred close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment M0 = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located, 1813 of which present RMS < 0.1 s and ERH, ERZ < 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N–S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain. 相似文献
983.
Identifying and quantifying urban recharge: a review 总被引:12,自引:1,他引:12
David N. Lerner 《Hydrogeology Journal》2002,10(1):143-152
The sources of and pathways for groundwater recharge in urban areas are more numerous and complex than in rural environments.
Buildings, roads, and other surface infrastructure combine with man-made drainage networks to change the pathways for precipitation.
Some direct recharge is lost, but additional recharge can occur from storm drainage systems. Large amounts of water are imported
into most cities for supply, distributed through underground pipes, and collected again in sewers or septic tanks. The leaks
from these pipe networks often provide substantial recharge. Sources of recharge in urban areas are identified through piezometry,
chemical signatures, and water balances. All three approaches have problems. Recharge is quantified either by individual components
(direct recharge, water-mains leakage, septic tanks, etc.) or holistically. Working with individual components requires large
amounts of data, much of which is uncertain and is likely to lead to large uncertainties in the final result. Recommended
holistic approaches include the use of groundwater modelling and solute balances, where various types of data are integrated.
Urban recharge remains an under-researched topic, with few high-quality case studies reported in the literature.
Electronic Publication 相似文献
984.
Yu. N. Efremov 《Astronomy Reports》2002,46(10):791-804
The nature of stellar complexes with peculiar populations and morphologies is investigated. The existence in the LMC of complexes made up of isolated stars, on the one hand, and consisting exclusively of clusters, on the other hand, could be due to different turbulence patterns in the initial gaseous medium. Arc-shaped stellar complexes are unlikely to be the result of star formation in a gaseous shell swept up by a central source of pressure, and instead probably reflect the shape of a bow shock that develops when a sufficiently dense cloud is subject to dynamical pressure. A peculiar arc-shaped complex in NGC 6946, which contains a young, massive cluster, may be the result of an oblique infall of a high-velocity cloud onto a region of the gaseous disk of the Galaxy with a strong, regular magnetic field; the properties of this complex can be explained as the result of a collision of the resulting shocks. The arc-shaped complexes in the LMC were also probably produced by high-velocity clouds moving obliquely through the more tenuous gas of the LMC disk. A similar complex in NGC 300 may owe its origin to the effect produced on a dense cloud by the shock from an extremely powerful external explosion, whose stellar remnant may have survived as an X-ray source now located along the line of symmetry of the arc of the complex. The rareness of such structures can be explained by the narrow range of conditions under which they can develop. 相似文献
985.
D. V. Bisikalo A. A. Boyarchuk E. Yu. Kilpio O. A. Kuznetsov 《Astronomy Reports》2002,46(12):1022-1029
A new mechanism is proposed to account for transitions between the quiescent and active states of symbiotic stars. A numerical study of the gas dynamics of the flows in the symbiotic star Z And shows that even small variations in the velocity of the wind from the cool giant can abruptly change the flow structure near the hot component. Such changes alter the accretion regime as the wind velocity increases: disk accretion makes a transition to accretion from the flow. Our calculations indicate that the accretion rate increases by a factor of several tens over a short time interval (~0.1 of the orbital period) during the rearrangement of the flow, when the accretion disk is destroyed. 相似文献
986.
O. V. Verkhodanov A. I. Kopylov Yu. N. Pariiskii N. S. Soboleva A. V. Temirova O. P. Zhelenkova 《Astronomy Reports》2002,46(7):531-542
BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m R <23.5m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (~20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8. 相似文献
987.
V. N. Kholodov 《Lithology and Mineral Resources》2002,37(3):197-209
The article discusses regularities in the distribution of mud volcanoes and characterizes most important mud volcanic provinces of the world. A new morphogenetic classification of mud volcanoes substantiated by results of their study in the Crimean–Caucasian and West Turkmenian regions is proposed. 相似文献
988.
The results of a laser ablation microprobeinductivelycoupled plasma mass spectrometry LuHf isotope study ofzircons in 0·931·67 Ga rocks from southNorway indicate that early Proterozoic protoliths of the BalticShield have present-day 176Hf/177Hf 相似文献
989.
S. Bodorkos M. Sandiford N. H. S. Oliver P. A. Cawood 《Journal of Metamorphic Geology》2002,20(2):217-237
High‐T, low‐P metamorphic rocks of the Palaeoproterozoic central Halls Creek Orogen in northern Australia are characterised by low radiogenic heat production, high upper crustal thermal gradients (locally exceeding 40 °C km?1) sustained for over 30 Myr, and a large number of layered mafic‐ultramafic intrusions with mantle‐related geochemical signatures. In order to account for this combination of geological and thermal characteristics, we model the middle crustal response to a transient mantle‐related heat pulse resulting from a temporary reduction in the thickness of the mantle lithosphere. This mechanism has the potential to raise mid‐crustal temperatures by 150–400 °C within 10–20 Myr following initiation of the mantle temperature anomaly, via conductive dissipation through the crust. The magnitude and timing of maximum temperatures attained depend strongly on the proximity, duration and lateral extent of the thermal anomaly in the mantle lithosphere, and decrease sharply in response to anomalies that are seated deeper than 50–60 km, maintained for <5 Myr in duration and/or have half‐widths <100 km. Maximum temperatures are also intimately linked to the thermal properties of the model crust, primarily due to their influence on the steady‐state (background) thermal gradient. The amplitudes of temperature increases in the crust are principally a function of depth, and are broadly independent of crustal thermal parameters. Mid‐crustal felsic and mafic plutonism is a predictable consequence of perturbed thermal regimes in the mantle and the lowermost crust, and the advection of voluminous magmas has the potential to raise temperatures in the middle crust very quickly. Although pluton‐related thermal signatures significantly dissipate within <10 Myr (even for very large, high‐temperature intrusive bodies), the interaction of pluton‐ and mantle‐related thermal effects has the potential to maintain host rock temperatures in excess of 400–450 °C for up to 30 Myr in some parts of the mid‐crust. The numerical models presented here support the notion that transient mantle‐related heat sources have the capacity to contribute significantly to the thermal budget of metamorphism in high‐T, low‐P metamorphic belts, especially in those characterised by low surface heat flow, very high peak metamorphic geothermal gradients and abundant mafic intrusions. 相似文献
990.
Archaeological investigations in Camels Back Cave, western Utah, recovered a series of small-mammal bone assemblages from stratified deposits dating between ca. 12,000 and 500 14C yr B.P. The cave's early Holocene fauna includes a number of species adapted to montane or mesic habitats containing grasses and/or sagebrush (e.g., Lepus townsendii, Marmota flaviventris, Reithrodontomys megalotis, and Brachylagus idahoensis) which suggest that the region was relatively cool and moist until after 8800 14C yr B.P. Between ca. 8600 and 8100 14C yr B.P. these mammals became locally extinct, taxonomic diversity declined, and there was an increase in species well-adapted to xeric, low-elevation habitats, including ground squirrels, Lepus californicus and Neotoma lepida. The early small-mammal record from Camels Back Cave is similar to the 11,300–6000 14C yr B.P. mammalian sequence from Homestead Cave, northwestern Utah, and provides corroborative data on Bonneville Basin paleoenvironments and mammalian responses to middle Holocene desertification. 相似文献