The gravitational field of a disk

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.     

孔隙水压力对岩石裂纹扩展影响的数值模拟

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。     

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

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.     

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

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.     

Investigating plant root effects on soil electrical conductivity: An integrated field monitoring and statistical modelling approach

Plants have been shown to affect soil water content and temperature. Previous studies were conducted mainly in forestry and agricultural soils, where conditions of soil and vegetation are different from those in an urban landscape. In an urban landscape, the influence of plant roots on electrical conductivity, soil water content and temperature is still not clear. This study aims to investigate the effects of soil water content and temperature on electrical conductivity in vegetated soils through an integrated field monitoring and computational modelling approach. A new relationship between soil electrical conductivity and water content as well as temperature is proposed. Field monitoring was conducted in both vegetated (tree species) and bare soils. The monitoring included measurements of soil water content, soil temperature and soil electrical conductivity. This was followed by response surface regression modelling. Measured results show that soil temperature at shallow depths was lower in vegetated soil than that in the bare soil. This observation was also consistent with the higher soil water content and hence, higher electrical conductivity under tree canopy. The model developed could predict nonlinear relationships between electrical conductivity and soil temperature and water content. Uncertainty analysis indicated normal distribution for electrical conductivity under variation of soil temperature and water content. © 2018 John Wiley & Sons, Ltd.     

Aquifer Treatment of Sea Water to Remove Natural Organic Matter Before Desalination

An investigation of a sea water reverse osmosis desalination facility located in western Saudi Arabia has shown that aquifer treatment of the raw sea water provides a high degree of removal of natural organic matter (NOM) that causes membrane biofouling. The aquifer is a carbonate system that has a good hydraulic connection to the sea and 14 wells are used to induce sea water movement 400 to 450 m from the sea to the wells. During aquifer transport virtually all of the algae, over 90% of the bacteria, over 90% of the biopolymer fraction of NOM, and high percentages of the humic substance, building blocks, and some of the low molecular weight fractions of NOM are removed. Between 44 and over 90% of the transparent exopolymer particles (TEP) are removed with a corresponding significant reduction in concentration of the colloidal fraction of TEP. The removal rate for TEP appears to be greater in carbonate aquifers compared to siliciclastic systems. Although the production wells range in age from 4 months to 14 years, no significant difference in the degree of water treatment provided by the aquifer was found.     

Marine spatial planning: Lessons learned from the Portuguese debate

This paper presents and discusses legal, methodological and political frameworks for the development of the proposed Portuguese Marine Spatial Plan initiated in 2008. It considers lessons learned and is informed by discussions that have taken place since publication of the ‘Roadmap for Maritime Spatial Planning: Achieving Common Principles in the EU’. New goals are based on horizontal planning tools that cut across sea-related sectoral policies and support joined up policy making. It is in this context that Marine Spatial Planning (MSP) emerged as an essential process for sustainable decision making. The OSPAR Commission undertook an overview of national planning systems within its administrative boundaries, which confirmed spatial plans reduced conflicts. However, problems exist accessing good quality data and dealing with entrenched sectoral views. Furthermore, the transboundary nature of marine resources requires cooperation between neighbouring states. In 2006, Portugal developed a ‘National Sea Strategy’ that recognized the importance of developing its maritime space while valuing marine habitats and biodiversity. MSP development of the Portuguese sea commenced in 2008 and findings are now evaluated. They showed adaptation of existing tools to be possible and desirable, provided undertaken cautiously and found conceptual ambiguities were barriers to conflict resolution. Furthermore they showed management strategies should be designed and analysed on a case by case basis, recognising temporal and spatial variations.     

Comparison of a 3‐D DEM simulation with MRI data

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.     

Initial Time Dependence of Abundances in Solar Energetic Particle Events

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.     

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

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