What type was SN 1987A?

A comparison is made of the light and colour curves of the SN 1987A in the first 280 days with the mean properties of type II supernovae. The conclusion is that even though it has H lines, and was not a typical type II supernova, but a peculiar object from a photometric point of view. The implications for inclusion of SN 1987A in the context of the usual Minkowski-Zwicky classification are explicitly discussed.     

An analysis of 3.5 kHz acoustic reflections and sediment physical properties

Near-bottom normal incidence acoustic reflection data and sediment physical property data are used to study the relationships between acoustic reflections and sediment physical properties. A pinger-hydrophone experiment was performed to obtain the necessary acoustic reflection data. In addition, a standard piston core was retrieved in the acoustic survey area for physical property analysis. The piston core was sampled and 13 properties were measured at 55 locations within the top 12 m of the core. Correlation studies amongst the sediment physical properties resulted in the following strong correlations: acoustic impedance ($\text{Z}$) and porosity ($\text{N}$), (0.96); water content ($\text{WC}$) and $\text{Z}$, (0.95); bulk density ($\text{BD}$) and $\text{Z}$, (0.99).The empirical orthonormal function (EOF) method was employed for acoustic signal analysis. This method assumes no a-priori models of the sediment or causality. The EOF method reduced the acoustic data to 8 functions that contained 97.6% of the sample variance. The EOFs were subsequently analysed by using cepstrum analysis which reveals time delay information and enhances detecting zones of reflectivity. The result of the sediment physical property and cepstrum analysis indicates that zones of reflectivity are essentially zones of relatively high acoustic impedance, low porosity, and low phi (high mean grain size).     

Magnetic anomalies in the canary basin and the Mesozoic evolution of the central North Atlantic

The data from a recent magnetic compilation by Verhoefet al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography.Deceased 11 November 1991     

Extension of the solution of Kepler's equation to high eccentricities

The classic Lagrange's expansion of the solutionE(e, M) of Kepler's equation in powers of eccentricity is extended to highly eccentric orbits, 0.6627 ... <e<1. The solutionE(e, M) is developed in powers of (e–e*), wheree* is a fixed value of the eccentricity. The coefficients of the expansion are given in terms of the derivatives of the Bessel functionsJ _n (ne). The expansion is convergent for values of the eccentricity such that |e–e*|<(e*), where the radius of convergence (e*) is a positive real number, which is calculated numerically.     

Development of site-specific design ground motions in Western and Eastern North America

This paper presents results recently obtained for generating site-specific ground motions needed for design of critical facilities. The general approach followed in developing these ground motions using either deterministic or probabilistic criteria is specification of motions for rock outcrop or very firm soil conditions followed by adjustments for site-specific conditions. Central issues in this process include development of appropriate attenuation relations and their uncertainties, differences in expected motions between Western and Eastern North America, and incorporation of site-specific adjustments that maintain the same hazard level as the control motions, while incorporating uncertainties in local dynamic material properties. For tectonically active regions, such as the Western United States (WUS), sufficient strong motion data exist to constrain empirical attenuation relations for M up to about 7 and for distances greater than about 10–15 km. Motions for larger magnitudes and closer distances are largely driven by extrapolations of empirical relations and uncertainties need to be substantially increased for these cases.

For the Eastern United States (CEUS), due to the paucity of strong motion data for cratonic regions worldwide, estimation of strong ground motions for engineering design is based entirely on calibrated models. The models are usually calibrated and validated in the WUS where sufficient strong motion data are available and then recalibrated for applications to the CEUS. Recalibration generally entails revising parameters based on available CEUS ground motion data as well as indirect inferences through intensity observations. Known differences in model parameters such as crustal structure between WUS and CEUS are generally accommodated as well. These procedures are examined and discussed.     

断层参数对承压水体上采煤的影响分析

根据流固耦合理论,采用有限元数值模拟的方法,针对承压水体上采煤过程中断层参数(断距、倾角)对煤层、围岩的应力、变形和水压力变化的影响进行了模拟分析,探讨了存在断层时突水的机理和可能的突水点位置,并定量分析了防水煤柱的预留距离。得出以下结论:(1)当存在正断层时,多发生断层破坏型突水,而底板破坏型突水发生的几率较小;(2)突水性质和突水发生位置受断层断距和倾角的影响不大,煤层和采煤工作面附近的底板围岩都可能成为突水涌出点;(3)随着断层断距和倾角的增加,防水煤柱的合理留设距离应随之增大。以上结果可为实际矿井采煤防突水设计提供参考。 更多还原     

Advances and Practices on the Research,Prevention and Control of Land Subsidence in Coastal Cities

Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea-level rise at regional scale. Although it is a well-known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International G...     

U–Pb SHRIMP data constraints on calc-alkaline granitoids with 1.3–1.6 Ga Nd TDM model ages from the central domain of the Borborema province,NE Brazil

The Tabira, Itapetim and Timbaúba granitoids are intruded into metasedimentary sequences and Cariris Velhos (Tonian) orthogneisses from the Central Domain of the Borborema Province, NE Brazil. They have U–Pb SHRIMP ages of 593 ± 7 Ma; 615 ± 9 Ma and 616 ± 5 Ma respectively. The studied granitoids have zircon cores inherited from the protholith, with a large number of analyses showing ²⁰⁶Pb/²³⁸U ages ranging from 950 to 1200 Ma. Oscillatory zoning typical of magmatic zircon is common, although it is faint in some inherited cores.The studied granitoids are calc-alkaline and show Nd T_DM model ages ranging from 1.30 to 1.56 Ga and ?Nd (600 Ma) ranging from ?2.40 to ?5.34. These values are similar to those recorded in the country rocks. The lowest values of ?Nd (600 Ma) were recorded in enclaves of dioritic composition. Nd and U–Pb SHRIMP data suggest a significant participation of the metasedimentary rocks in the protholith of these granitoids. The Mesoproterozoic Nd T_DM model ages recorded in the studied granitoids are interpreted as the result of a hybrid source involving melting of metagraywackes, metamafic rocks of Tonian ages and/or biotite – bearing orthogneisses (Cariris Velhos Orthogneisses). The resulted melting was modified by mingling with juvenile Brasiliano melts, diorite in composition.The Timbaúba granitoids intrusions are coeval with high-T metamorphism and flat-lying foliation forming event in an intracontinental setting, during the Brasiliano convergence and contractional deformation. The Itapetim Pluton was emplaced in the convergence - lateral escape setting and the Tabira granitoids were intruded after the flat-lying foliation event, representing sin transcurrent intrusions.Our data show that within the Central Domain of the Borborema Province, granitoids with similar petrographic and geochemical compositions can have distinct ages and be intruded in distinct tectonic regimes.     

Importance of mixotrophic nanoplankton in Aysén Fjord (Southern Chile) during austral winter

Mixotrophy, the combination of autotrophic and heterotrophic nutrition in the same organism, is widespread in planktonic algae. Several reports from temperate and high-latitude fjords in Scandinavia suggest the occurrence of a niche in late summer and autumn during post-bloom conditions in which mixotrophic algae can become important grazers in pelagic ecosystems, accessing the nutrients bound in their prey to overcome nutrient limitation. Here, we experimentally determined the trophic modes and bacterivory rates for the nanoplankton community (2–20 μm) in Aysén Fjord located in the Chilean Northern Patagonia during two contrasting seasons: winter and spring. While mixotrophic nanoplankton was virtually absent from the system in spring, in winter at occasions it even constituted the dominant trophic group of the nanoplankton with abundances of >900 cells mL^?1. This indicates a second niche for mixotrophs in winter, when mixotrophy allows overcoming light limitation.     

断层EDF技术在复杂断块构造研究中的应用

复杂断块构造具有断层复杂,小断层广泛发育,断层识别难度大,储层分布及连通性复杂,地震成像不清、资料品质较差等特征。对于此类问题,常规地震资料无法满足断层解释精度要求。提出了一种新的断层EDF解释性处理技术,将地震资料处理与解释融为一体,以提高资料的信噪比和断层的识别能力。断层EDF解释性处理技术是利用扩散滤波和中值倾角滤波相结合的断层增强滤波方法来提高资料的信噪比,突出断层和地层的接触关系,再在滤波后的地震资料数据体上进行分频处理,选择最佳成像频带,突出识别不同规模的断层。通过在涠洲A油田的应用,取得了良好的效果。