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China Ocean Engineering - Conventional design of pier structures is based on the assumption of fully rigid joints. In practice, the real connections are semi-rigid that cause changes in dynamic... 相似文献
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Fathi Namouni 《Astrophysics and Space Science》2011,331(2):575-595
Dynamical friction arises from the interaction of a perturber and the gravitational wake it excites in the ambient medium.
We study the effects of the presence of a boundary on dynamical friction by studying analytically the interaction of perturber
with uniform rectilinear motion in a uniform homogeneous medium with a reflecting planar boundary. Wake reflection at a medium’s
boundary may occur at the edges of truncated disks perturbed by planetary or stellar companions as well as in numerical simulations
of planet-disk interaction with no-outflow boundary conditions. In this paper, we show that the presence of the boundary modifies
the behaviour of dynamical friction significantly. We find that perturbers are invariably pushed away from the boundary and
reach a terminal subsonic velocity near Mach 0.37 regardless of initial velocity. Dynamical friction may even be reversed
for Mach numbers less than 0.37 thereby accelerating instead of decelerating the perturber. Perturbers moving parallel to
the boundary feel additional friction orthogonal to the direction of motion that is much stronger than the standard friction
along the direction of motion. These results indicate that the common use of the standard Chandrasekhar formula as a short
hand estimate of dynamical friction may be inadequate as observed in various numerical simulations. 相似文献
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Jesús Falcón-Barroso Roland Bacon Martin Bureau Michele Cappellari Roger L. Davies P. T. de Zeeuw Eric Emsellem Kambiz Fathi Davor Krajnovi&#; Harald Kuntschner Richard M. McDermid Reynier F. Peletier Marc Sarzi 《Monthly notices of the Royal Astronomical Society》2006,369(2):529-566
We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O iii ]/Hβ ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954. 相似文献
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GeoJournal - City development strategy (CDS) is an urban strategic planning approach that has already been implemented in over 200 cities worldwide. Nevertheless, its preparation process is... 相似文献
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Jesús Falcn-Barroso Marc Sarzi Roland Bacon Martin Bureau Michele Cappellari Roger L. Davies Eric Emsellem Kambiz Fathi Davor Krajnovi&#x; Harald Kuntschner Richard M. McDermid Reynier F. Peletier Tim de Zeeuw 《New Astronomy Reviews》2006,49(10-12):515
We present results of our ongoing study of the morphology and kinematics of the ionised gas in 48 representative nearby elliptical and lenticular galaxies using the SAURON integral-field spectrograph on the 4.2m William Herschel Telescope. Making use of a recently developed technique, emission is detected in 75% of the galaxies. The ionised-gas distributions display varied morphologies, ranging from regular gas disks to filamentary structures. Additionally, the emission-line kinematic maps show, in general, regular motions with smooth variations in kinematic position angle. In most of the galaxies, the ionised-gas kinematics is decoupled from the stellar counterpart, but only some of them present signatures of recent accretion of gaseous material. The presence of dust is very common in our sample and is usually accompanied by gas emission. Our analysis of the [Oiii]/Hβ emission-line ratios, both across the whole sample as well as within the individual galaxies, suggests that there is no unique mechanism triggering the ionisation of the gas. 相似文献
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Marie-Pierre Aubry William A. Berggren Christian Dupuis Holeil Ghaly David Ward Chris King Robert W. O'B. Knox Khaled Ouda Moustafa Youssef Wael Fathi Galal 《地学学报》2009,21(4):237-256
We present a review of archaeological and geological studies on the West Bank as a basis for discussing the geological setting of the tombs and geologically related problems with a view to providing archaeologists with a framework in which to conduct their investigations on the restoration, preservation and management of the antique monuments. Whereas the geology of the Upper Nile Valley appears to be deceptively simple, the lithological succession is vertically variable, and we have recognized and defined several new lithological units within the upper Esna Shale Formation. We have been able to delineate lithological (shale/limestone) contacts in several tombs and observed that the main chambers in some were excavated below the Esna Shale in the Tarawan Chalk Formation. We have been able to document changing dip in the strata (warping) in several tombs, and to delineate two major orientations of fractures in the field. Investigations behind the Temple of Hatshepsut, in the Valley of the Kings and around Deir El Medina have revealed four broad regional structures. We confirm that the hills located near the Nile Valley, such as Sheik Abdel Qurna, do not belong to the tabular structure of the Theban Mountain, but are discrete displaced blocks including the Thebes Limestone, as supported by Google Earth photographs. 相似文献
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