Finite element modelling has been used to simulate the development of segment structures, deformed layer segments separated by veins, such as boudins, mullions, and bone-boudins. A parameter sensitivity analysis is used to compare the influence of the nature of the flow, the relative viscosities of veins in necks and the host rock, and the initial geometry of the layer segments. Parameter fields have been determined for the relative viscosity of veins and layers, and the kinematic vorticity number of flow. Reworked segment structures can have several shapes such as bone-, bulging, shortened bone-boudins and their asymmetric equivalents such as domino- and shearband-boudin geometry. The model for asymmetric reworked segment structures is applied to such features from the Lower Ugab Metaturbidites in NW Namibia. The model suggests that these structures form where the neck veins are stronger than the boudinaged layer, with a significant simple shear component of the bulk flow. The quartz filled necks in the Lower Ugab are therefore stronger than the quartz-rich wall rock in greenschist facies where the progressive deformation occurred. Bone-boudins are usually interpreted to form in transpressional flow, but simulations of the rotation of tension gashes show that they can also form in simple shear or slightly transtensional shear flow. 相似文献
Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal‐scale strike‐slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal‐scale vertical strike‐slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike‐slip fault zone, and the segments were separated by another 30 km of lateral motion. Strike‐slip core complexes like the Qazaz Dome may be common and may have an important local effect on crustal strength. 相似文献
The Permanent International Association of Navigation Congresses was founded in 1885 with the aim of organizing international conferences for the dissemination of knowledge related to navigation in the field of civil engineering. To date, 28 congresses have been held, now with a four-year interval; the 28th Congress was held in 1994 in Seville, Spain. PIANC has become a leading authority, particularly in the field of engineering. Several studies, for instance on the dimensions of ships and waterways and on signalling, have led to international standardization and PIANC congresses have often recommended further international studies of specific subjects. The congresses are each attended by approximately 900 participants from around 50 countries world-wide. They are state, municipal and harbour officials, consultants, scientists and academics at technical universities, contractors and many other participants from the navigation industry. There is a strong governmental influence in the organization, as the governments of about 40 countries support PIANC both financially and by the participation of senior civil servants.
In the two sections of the congresses, inland navigation and ocean navigation, 10 subjects are discussed. PIANC has always followed recent developments such as trends in shipping, reception facilities for ferries, special arrangements for the handling of containers, oil, gas and of dangerous or environmentally noxious goods. Not only the technical aspects of navigation, such as canals, dams, ports and maritime structures, are discussed, but also economics, port management and port capacity and safety. Environmental aspects, for instance of maintenance dredging and the disposal of dredged materials, are important topics. PIANC has long been interested in coastal problems, as these affect ports. As many ports extend into the sea, PIANC has considered ocean engineering including artificial islands, maritime constructions, salvage and the removal of wrecks and navigation under arctic conditions. PIANC is also active in the field of sport and pleasure navigation. Since 1982 PIANC has organized international working groups to report on specific topics. At present there are about 35 active working groups and 23 reports have been published. Their members are from about 30 countries. They may convene several times each year or work by correspondence. The recommendations of the working groups represent recent advances and are widely distributed. For instance, the report Beneficial Uses of Dredging Material was presented for discussion to the London Dumping Convention. Membership of PIANC is open to organizations and individuals. In most countries a national section is the contact point for the members. The General-Secretariat is in Brussels, Belgium. 相似文献
Any early Universe phase transition occurring after inflation has the potential to populate the Universe with relic magnetic monopoles. Observations of galactic magnetic fields, as well as observations matched with models for extragalactic magnetic fields, lead to the conclusion that monopoles of mass 1015 GeV are accelerated in these fields to relativistic velocities. We explore the possible signatures of a cosmic flux of relativistic monopoles impinging on the Earth. The electromagnetically induced signatures of monopoles are reliable. The hadronically induced signatures are highly model-dependent. Among our findings are (i) the electromagnetic energy losses of monopoles continuously initiate a protracted shower of small intensity; (ii) monopoles may traverse the Earth’s diameter, making them a probe of the Earth’s interior structure; (iii) in addition to the direct monopole Cherenkov signal presently employed, a very attractive search strategy for monopoles is detection of their coherent radio-Cherenkov signal produced by the charge-excess in the e+–e− shower––in fact, Cherenkov-detectors have the potential to discover a monopole flux (or limit it) several orders of magnitude below the theoretical Parker limit of 10−15 cm−2 s−1 sr−1; (iv) it is conceivable (but not compelling) that bound states of colored monopoles may be the primary particles initiating the air showers observed above the GZK cutoff. 相似文献
A 38‐km‐long ancient aqueduct channel that served Roman Ephesos, Turkey was dislocated vertically over 3 m by a single seismic event on a normal fault. A new channel was constructed downstream from the fault in Roman times, next to and partly on top of the original channel. Archaeological investigations and study of carbonate deposits suggest a causative seismic event in the second half of the second century CE, probably in 178 CE, after the original channel had functioned for <35 years. The ?çme Tepe fault was identified as responsible for the displacement and may still constitute a seismic and tsunami hazard for the Turkish west coast, specifically for the city of Ku?adas?. Ancient aqueducts, of which more than 1400 are presently known, are a promising and almost untapped archive for archaeoseismic studies, especially in the Mediterranean area. 相似文献
In a pilot study three samples of diamictons from boreholes in the Dutch sector of the North Sea have been thin sectioned. In the thin sections the granulometry, structure and plasmic fabric of the diamictons have been studied. On the basis of this study two of the samples have been interpreted as flow tills, while one sample has been interpreted as a basal (lodgement) till. 相似文献
We propose an object detection algorithm which is efficient and fast enough to be used in (almost) real time with the limited
computer capacities onboard satellites. For stars below the saturation limit of the CCD detectors it is based on a four neighbourhood
local maximum criterion in order to find the centre of a stellar image. For saturated stars it is based on the assumption
that the image is increasing monotonically towards the centre in the unsaturated part of the image. The algorithm also calculates
approximate stellar magnitudes and efficiently rejects most of the cosmics which would otherwise lead to a large number of
false detections. The quality of the algorithm was evaluated with the help of a large set of simulated data for the DIVA satellite
mission; different assumptions were made for the noise level, and the presence of cosmics or for a variable sky background.We
could show that our algorithm fulfills the requirements for DIVA; only in the case of simulated images which included the
bright galaxy M31 some fainter stars could not be detected in the galaxy's vicinity. Since stellar images contain large areas
without any stars, we propose an additional block-skipping algorithm which can be coded on special-purpose hardware.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献