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排序方式: 共有74条查询结果,搜索用时 15 毫秒
51.
A method is developed to construct conditionally periodic solutions of Hamiltonian systems in the case of deep resonance and in the presence of more than one resonant vector (multiple resonance). The method depends on modification of a standard perturbation method. It is applicable to systems with more than one degree of freedom. 相似文献
52.
Attenuations of the vertical and horizontal response spectra of the 17 October 1989 Loma Prieta, California, earthquake are developed through analyses of the ground motion at 53 sites within a 100 km radius of the source. The analyses are performed on the spectral ordinates for 16 incremental periods ranging from 0.05 to 2.0 sec. The response spectra are modelled empirically for two different site conditions characterized by rock and stiff-soil geologies. Data analysis is performed by the application of a non-linear multivariate regression procedure allowing for distance and site factor as independent variables. Variation of the vertical-to-horizontal (V/H) spectral ratios with wave frequency and distance shows the same behaviour as observed previously in the widely separated geographic regions of northeastern Taiwan and east-central Iran. The predicted ratios at sites underlain by stiff soil are generally higher than the commonly used value of 2/3 at high frequencies ( > 5 Hz) in the near-source region (R < 30 km), but reduce to 1/2 or less at longer periods and farther distances. This behaviour is also observed at rock sites; however, it is somewhat less pronounced. With a faster attenuation of spectral ordinates at higher frequencies, the shape of the response spectrum is found to change with distance. As expected, the spectral attenuation with distance is generally higher for the vertical spectrum than for the horizontal spectrum. The difference is particularly significant at the higher-frequency end of spectrum. Site amplification factors for stiff soil with respect to rock geology varies between 1.17 and 1.72 for horizontal spectrum and 1.01 and 1.81 for vertical spectrum. Spectral amplifications at four sites underlain by soft soil and artificial fill, are also evaluated. This is done by a comparison of the observed spectra with those predicted for rock geology at corresponding distances. As expected, the resulting amplification factors at soft-soil sites show significant increase relative to those at sites underlain by rock. 相似文献
53.
In the present problem, acceleration covariance in MHD turbulent flow of dusty fluid with Coriolis force have been obtained.The obtained result shows that the defining scalars (r,t), (r, t), (r, t) of the acceleration covariance in the presence of Coriolis force depends on the defining scalars of tensorsQ
ij, Hij,
i,j,S
ik,jandT
ij,kalready defined in the text. 相似文献
54.
Amin?AbdiEmail author Yousef?Hassanzadeh Siamak?Talatahari Ahmad?Fakheri-Fard Rasoul?Mirabbasi 《Theoretical and Applied Climatology》2017,129(1-2):21-32
Application of the copulas can be useful for the accurate multivariate frequency analysis of hydrological phenomena. There are many copula functions and some methods were proposed for estimating the copula parameters. Since the copula functions are mathematically complicated, estimating of the copula parameter is an effortful work. In the present study, an optimization-based method (OBM) is proposed to obtain the parameters of copulas. The usefulness of the proposed method is illustrated on drought events. For this purpose, three commonly used copulas of Archimedean family, namely, Clayton, Frank, and Gumbel copulas are used to construct the joint probability distribution of drought characteristics of 60 gauging sites located in East-Azarbaijan province, Iran. The performance of OBM was compared with two conventional methods, namely, method of moments and inference function for margins. The results illustrate the supremacy of the OBM to estimate the copula parameters compared to the other considered methods. 相似文献
55.
We present Culgoora spectrograph and radioheliograph observations as well as a model of type IIIb bursts; the latter are defined as chains of striae of slow or no frequency drift, the chain as a whole drifting like a normal type III burst.The 80 MHz source positions are studied for a group of IIIb bursts, a IIIb precursor and harmonic pairs of 1:2 frequency ratio. It is found that the IIIb position may vary in a IIIb group. No significant difference was found between the source positions of a IIIb precursor and the following III burst. For one event we found that the fundamental IIIb burst showed a high degree of circular polarization (46%), while its second harmonic, a normal type III burst, was unpolarized.We suggest that the main cause for the striae in type IIIb bursts is the existence of filamentary, density irregularities along the path of the electron stream. The denser filaments initially reduce the value of the density gradient along the electrons' path and thereby enhance their emissions over a small range of plasma frequencies. If the radio emission from the filaments dominates the emission from the ambient rarified plasma, striae appear in the spectrum and a type IIIb burst results. This condition is more easily satisfied at the fundamental frequency and for electron streams of relatively high density.Radiophysics Publication RPP 1758, October, 1974, (2nd version).On leave from the Dept. of Astronomy, University of Tokyo, Tokyo, Japan.On leave from the Dept. of Astronomy, Cairo University, Cairo, Egypt. 相似文献
56.
57.
Guntoro Pratama Istiadi Ghorbani Yousef Butcher Alan R. Kuva Jukka Rosenkranz Jan 《Natural Resources Research》2020,29(6):3567-3567
Natural Resources Research - The original version of the article unfortunately contained an error in Table 9. In article PDF, Table 7 was inadvertently repeated in place of... 相似文献
58.
Natural Hazards - The aim of this study is to analyze the synoptic and analyzing the mechanisms of flood occurrence on April 1, 2019, in the western half of Iran. In order to statistically analyze... 相似文献
59.
Assessing NDVI Spatial Pattern as Related to Irrigation and Soil Salinity Management in Al-Hassa Oasis,Saudi Arabia 总被引:5,自引:0,他引:5
Yousef Y. Aldakheel 《Journal of the Indian Society of Remote Sensing》2011,39(2):171-180
Sustainability of irrigated agriculture in arid and semi arid lands depends, mainly on the level of soil salinity and the
quality of irrigation water. Remotely sensed data can provide information about the extent of vegetated irrigated areas. Al-Hassa
oasis, Saudi Arabia is probably the largest oasis in the world depends mostly on tapped ground water to irrigate mainly date
palm groves for its economic survival. This study tried to investigate the extent of soil salinity and the quality of irrigation
water and the relationship with vegetation growth, employing NDVI derived from Landsat satellite imagery. 相似文献
60.
This paper presents a finite element model for analysing the behaviour of granular material wrapped with polyethylene bags under vertical compression and cyclic shearing. The simple Mohr–Coulomb model is used to represent the soil behaviour. The polyethylene bag is represented by a linear-elastic–perfect-plastic model. The soil-bag interface is modelled with contact constraints. The main purpose of the numerical analysis is to validate the anticipated performance of soilbags under various loading conditions and hence the effectiveness of soilbags as a method of ground improvement. 相似文献