The gravitational field of a disk     

Fred T. Krogh  Edward W. Ng  William V. Snyder 《Celestial Mechanics and Dynamical Astronomy》1982,26(4):395-405

This note gives the gravitational potential of the disk {(x, y, z):x ² +y ² p ² , z=0} and the gravitational field at the point (x, y, z). Formulas for a ring can be obtained as the difference of our results for two different values ofp. Results are obtained in terms of elliptic integrals and we indicate how these functions can be computed efficiently. Formulas necessary for the computation of partial derivatives are also given.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract NAS7-100, sponsored by the National Aeronautics and Space Administration.  相似文献   

孔隙水压力对岩石裂纹扩展影响的数值模拟   总被引：1，自引：0，他引：1  

唐春安  杨天鸿  李连崇  梁正召  ThamL.G.  LeeK.K.  TsuiY. 《岩土力学》2003,(Z2)

应用岩石破坏过程渗流-应力-损伤(FSD)耦合分析软件F-RFPA2D,通过对孔隙水压作用下岩石试件加载破坏过程的数值模拟,对孔隙水压力大小和梯度对岩石试样中裂纹的萌生和扩展进行了数值模拟研究。模拟结果再现了孔隙水压力作用下裂纹萌生扩展的全过程,表明孔隙水压力大小和梯度对岩石中裂纹的萌生和扩展模式都有很大的影响。  相似文献   

A diatom model for inferring sea level change in the coastal waters of Hong Kong     

Sai L. Ng  Fung S. Sin 《Journal of Paleolimnology》2003,30(4):427-440

Diatoms were identified and enumerated from surface sediments of 25 sites in Double Haven, Hong Kong. The relationship between diatom species distribution and 14 environmental variables was examined using Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA). Water depth was identified as the most important environmental variable influencing the distribution of diatoms in Double Haven. Subsequently a Weighted Average (WA) calibration model was developed to infer water depth. The reliability of the model was evaluated by the error of prediction (RMSE_boot= 3.479) and the correlation (r ²= 0.7342) between observed and diatom-inferred values. This predictive calibration model has the potential to infer past sea level change in Hong Kong and the adjacent coastal areas.  相似文献   

Socio-spatial polarization and the (re-)distribution of deprived groups in world cities: A case study of Hong Kong     

Huiwei Chen  Mee Kam Ng  Murat Es  Joanna Lee  Winnie W. S. Mak  Yuying Tong 《Urban geography》2018,39(7):969-987

This paper draws on theoretical discussions of world cities to analyze socio-spatial polarization and (re-)distribution of deprived groups in Hong Kong in the 2000s. Intensifying global economic restructuring processes have induced socio-economic polarization, thereby producing deprived groups although the spatial outcomes may depend on the city-specific context. When local policies do not counteract the polarization trend, a spatial manifestation of widening socio-economic gaps can be expected. Intensified pro-growth policies adopted since Hong Kong’s return to Chinese rule in 1997 and during its economic recession in the early 2000s have worsened the impact of globalization-induced socio-economic and spatial restructuring. Census data from 2001 and 2011 show increasingly differentiated socio-economic profiles at the district level. The analysis offered in this study also points to a decreased socially mixed society in 2011 when the deprived groups lived in districts with less presence of the advantaged population.  相似文献   

Comparison of a 3‐D DEM simulation with MRI data     

Tang‐Tat Ng  Changming Wang 《国际地质力学数值与分析法杂志》2001,25(5):497-507

This paper presents a comparison of a granular material studied experimentally and numerically. Simple shear tests were performed inside the magnetic core of magnetic resonance imaging (MRI) equipment. Spherical pharmaceutical pills were used as the granular material, with each pill's centre location determined by MRI. These centre locations in the initial assembly were then used as the initial configuration in the numerical simulation using the discrete element method. The contact properties between pharmaceutical pills used in the numerical simulation were obtained experimentally. The numerical predication was compared with experimental data at both macroscopic and microscopic levels. Good agreement was found at both levels. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Initial Time Dependence of Abundances in Solar Energetic Particle Events     

Reames DV  Ng CK  Tylka AJ 《The Astrophysical journal》2000,531(1):L83-L86

We compare the initial behavior of Fe/O and He/H abundance ratios and their relationship to the evolution of the proton energy spectra in "small" and "large" gradual solar energetic particle (SEP) events. The results are qualitatively consistent with the behavior predicted by the theory of Ng et al. published in 1999. He/H ratios that initially rise with time are a signature of scattering by non-Kolmogorov Alfvén wave spectra generated by intense beams of shock-accelerated protons streaming outward in large gradual SEP events.  相似文献   

Simply Obtained Global Radiation, Soil Temperature and SoilMoisture in an Alley Cropping System in Semi-Arid Kenya     

D. N. Mungai  C. J. Stigter  C. L. Coulson  J. K. Ng’ang’a 《Theoretical and Applied Climatology》2000,65(1-2):63-78

Summary  Global radiation, soil temperature and soil moisture data were obtained from a 4–6 year old Cassia siamea/maize (CM) alley cropping (or hedgerow intercropping) system, at a semi-arid site at Machakos, Kenya, in the late eighties. With the growing need to explore and manage variations in agro-ecosystems these results deserve new attention. They quantify, in a simple but detailed manner, the influence of hedgerows on the microclimate of their intercrop and for comparison provide a sole maize (SM) control. Due to inhomogeneity of Cassia and maize, as well as limited budgets, the sampling methodology and the choice of appropriate equipment, including the sensors, demanded special attention. The diurnal patterns of soil temperatures at 7.5 cm depth represented well the shading patterns of the hedgerows. This can be developed into an operational auxiliary methodology of integrated shade quantification. With proper precautions, the developed sampling methodologies showed appropriately the time integrated values of the three microclimatic parameters with enough detail to understand yield differences between treatments and between rows. This approach may therefore be recommended for on-farm quantification of even greater spatial variability of parameters. The limitations of the selected methods are highlighted. Experiences with some alternative methods are also discussed. Received September 2, 1998/Revised June 28, 1999  相似文献   

应力状态对膨胀土SWCC的影响研究   总被引：14，自引：0，他引：14  

龚壁卫  吴宏伟  王斌 《岩土力学》2004,25(12):1915-1918

探讨了应力对膨胀土的土-水特征曲线的影响。试验研究表明：膨胀土的首次干湿循环过程的“滞后”现象明显。应力状态对膨胀土的土-水特征曲线影响显著,与常规试验方法相比,一维固结状态和各向等压应力状态下的土-水特征曲线更具线性关系,干湿循环甚至出现了逆向回滞现象。  相似文献   

An assessment of the water budget for contrasting vegetation covers associated with waste management     

Isa A. M. Yunusa  Melanie J. B. Zeppel  Sigfredo Fuentes    Catriona M. O. Macinnis‐Ng  Anthony R. Palmer  Derek Eamus 《水文研究》2010,24(9):1149-1158

  相似文献   

Froude characteristics of both dense granular and water flows in flume modelling     

C. E. Choi  C. W. W. Ng  S. C. H. Au-Yeung  G. R. Goodwin 《Landslides》2015,12(6):1197-1206

  相似文献