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991.
Mohammad Saadatseresht Clive S. Fraser Farhad Samadzadegan Ali Azizi 《The Photogrammetric Record》2004,19(107):219-236
The aim of this paper is to present a method whereby accuracy enhancement of an existing photogrammetric network is achieved through the automatic selection of additional camera stations. The determination of the positions of these 'accuracy fulfilment' camera stations is based upon what has been termed 'visibility uncertainty prediction modelling' of visibility constraints derived from the existing network geometry. Following a review of vision constraints in network design, the concepts of visibility uncertainty prediction and visibility uncertainty spheres are introduced. These provide a mechanism to predict the visibility of current object target points for the new accuracy fulfilment images. This in turn aids in network design improvement. The visibility uncertainty modelling is then illustrated for two close range photogrammetric network configurations, for which the test results demonstrate that the proposed model can reliably predict target visibility with an overall certainty of 75%. 相似文献
992.
993.
Optimum design of structures for earthquake is achieved by simulated annealing. To reduce the computational work, a fast wavelet transform is used by means of which the number of points in the earthquake record is decreased. The record is decomposed into two parts. One part contains the low frequency of the record, and the other contains the high frequency of the record. The low‐frequency content is the effective part, since most of the energy of the record is contained in this part of the record. Thus, the low‐frequency part of the record is used for dynamic analysis. Then, using a wavelet neural network, the dynamic responses of the structures are approximated. By such approximation, the dynamic analysis of the structure becomes unnecessary in the process of optimization. The wavelet neural networks have been employed as a general approximation tool for the time history dynamic analysis. A number of structures are designed for optimal weight and the results are compared to those corresponding to the exact dynamic analysis. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
994.
Edmond Halley's work on two London churches makes them the first buildings planned using modern scientific techniques, argue Jason R Ali and Peter Cunich. 相似文献
995.
The use of statistical techniques in studying the causes of geochemical variations in aquifers can provide important results
which cannot be derived in other ways. In this study, data from the Wadi Shueib catchment area in Jordan is evaluated, using
principle component factor and multivariate factor analysis in order to better understand the variablility in groundwater
chemistry and evaluate the sources of pollution and the susceptibility of these aquifers to the different sources of pollution.
This study clearly demonstrates that these statistical techniques can help determine the various mechanisms causing chemical
variation in the aquifers and the relative susceptibility of each aquifer to different types of pollution.
Received: 13 March 1996 · Accepted: 18 June 1996 相似文献
996.
Ali M. Bouhifd Alan Whittington Pascal Richet 《Contributions to Mineralogy and Petrology》2001,142(2):235-243
The volumes and expansivities of four hydrous phonolite glasses and liquids have been measured by dilatometry from 300 K up to the glass transition and over a 50 K interval just above the glass transition. The partial molar volume of water is independent of the water content for the glass and liquid phases, with values of about 11.0ǂ.5 and 17.1ǂ.9 cm3/mol at 300 and 800 K, respectively. The partial molar thermal expansivity of water in phonolite glasses is about 8᎒-5 K-1, a result similar to recently published values for different silicate compositions, and about 36.5᎒-5 K-1 in phonolite liquids. The implications for melt density and water dissolution are discussed. 相似文献
997.
998.
999.
Alain Demant Patrick Lestrade Ruananza T Lubala Ali B Kampunzu Jacques Durieux 《Bulletin of Volcanology》1994,56(1):47-61
Three major phases are distinguished during the growth of Nyiragongo, an active volcano at the western limit of the Virunga
Range, Zaire. Lavas erupted during phase 1 are strongly undersaturated melilitites characterized by the presence of kalsilite
phenocrysts, perovskite, and the abundance of calcite in the matrix. Such lavas crop out mainly on the inner crater wall and
progressively evolve toward more aphyric melilite nephelinites well represented on the flanks of the volcano. Adventive vents
lying at the base of the cone developed along radial fracture systems and erupted olivine and/or clinopyroxene – rich melilitites
or nephelinites. Stage 2 lavas are melilite-free nephelinites. Clinopyroxene is the main phenocryst and feldspathoids are
abundant in the lavas exposed on the crater wall. These flows result from periodic overflowing of a magma column from an open
crater. Extensive fissure flows which erupted from the base of the cone at the end of this stage are related to widespread
draining out of magma which in turn induces the formation of the summit pit crater. Magmas erupted during stage 3 are relatively
aphyric melilite nephelinites and the main volcanological characteristic is the permanent lava lake observed into the pit
crater until the 1977 eruption. Fluctuations of the level of the lava lake was responsible for the development of the inner
terraces. Periodic overflowing of the lava lake from the central pit formed the nepheline aggregate lava flows. Petrography
and major element geochemistry allow the determination of the principal petrogenetic processes. Melilitites and nephelinites
erupted from the summit crater are lavas derived, via clinopyroxene fractionation, from a more primitive melt. The abundance
of feldspathoids in these lavas is in keeping with nepheline flotation. Aphyric melilite nephelinites covering the flanks
and the extensive fissure flows have a homogeneous chemical composition; rocks from the historical lava lake are slightly
more evolved. All these lavas differentiated in a shallow reservoir. Lavas erupted from the parasitic vents are mainly olivine
and/or clinopyroxene-phyric rocks. Rushayite and picrites from Muja cone are peculiar high-magnesium lavas resulting from
the addition of olivine xenocrysts to melilitic or nephelinitic melts. Fluid and melt inclusions in olivine and clinopyroxene
phenocrysts indicate a crystallization depth of 10–14 km. A model involving two reservoirs located at different depths and
periodically connected is proposed to explain the petrography of the lavas; this hypothesis is in accordance with geophysical
data.
Received: July 8, 1993/Accepted: September 10, 1993 相似文献
1000.