COMMERCIALIZATION OF SMALL-SCALE AGRICULTURE IN ZIMBABWE: SOME EMERGING PATTERNS OF SPATIAL DIFFERENTIATION     

Lovemore M. Zinyama  B.A.  M.Phil.  Dip. Econ. 《Singapore journal of tropical geography》1989,9(2):151-162

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VEGETATION MAPPING IN AFRICA: A CRITIQUE     

Richard Whitlow  B.A.  M.Phil. 《Singapore journal of tropical geography》1985,6(1):64-77

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THE DROUGHT OF 1970–77 IN UPPER VOLTA     

E. Ofori-Sarpong  M.A.  M.Phil. 《Singapore journal of tropical geography》1983,4(1):53-61

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Testing variograms for positive-definiteness     

Margaret Armstrong  Phil Diamond 《Mathematical Geology》1984,16(4):407-421

A method based on Bochner's theorem is described for demonstrating the positive-definiteness of variogram models and for generating classes of valid variogram functions.Work performed while on leave at the Centre de Géostatistique et de Morphologie Mathématique.  相似文献   

Measuring Urban Sustainability: the potential and pitfalls of city rankings     

Phil McManus 《The Australian geographer》2012,43(4):411-424

Measuring the sustainability of a city, and ranking the city against other cities, is increasingly seen as a way to achieve urban sustainability. A number of studies have highlighted how Sydney is unsustainable, with two recent ranking exercises appearing to confirm these findings by placing Sydney below many other Australian cities for urban sustainability. These two exercises are situated within international moves towards ranking cities. The article explores the assumptions and criteria used by Mercer in its Eco-City Index and the Australian Conservation Foundation in its Sustainable Cities Index. The conclusion discusses how Sydney could become more sustainable, and identifies why normative urban sustainability rankings should be recognised for their potential while simultaneously being treated with caution.  相似文献   

The role of closed ecological systems in carbon cycle modelling     

Alexandru Milcu  Martin Lukac  Phil Ineson 《Climatic change》2012,112(3-4):709-716

Acquiring a mechanistic understanding of the role of biotic feedbacks for the links between atmospheric CO₂ concentrations and temperature is essential for trustworthy climate predictions. Currently, computer-based simulations are the only available tool to estimate the global impact of biotic feedbacks on future atmospheric CO₂ and temperatures. Here we propose an alternative and complementary approach by using materially closed, energetically open analogue/physical models of the carbon cycle. We argue that there is unexplored potential in using a materially closed approach to improve our understanding of the magnitude and direction of many biotic carbon feedbacks and that recent technological advances make this feasible. We also suggest how such systems could be designed and discuss the advantages and limitations of establishing physical models of the global carbon cycle.  相似文献   

Assessment of surface air warming in northeast China, with emphasis on the impacts of urbanization   总被引：3，自引：1，他引：2  

Qingxiang Li  Wei Li  Peng Si  Gao Xiaorong  Wenjie Dong  Phil Jones  Jiayou Huang  Lijuan Cao 《Theoretical and Applied Climatology》2010,99(3-4):469-478

Based on homogenized land surface air temperature (SAT) data (derived from China Homogenized Historical Temperature (CHHT) 1.0), the warming trends over Northeast China are detected in this paper, and the impacts of urban heat islands (UHIs) evaluated. Results show that this region is undergoing rapid warming: the trends of annual mean minimum temperature (MMIT), mean temperature (MT), and mean maximum temperature (MMAT) are 0.40 C decade^?1, 0.32 C decade^?1, and 0.23 C decade^?1, respectively. Regional average temperature series built with these networks including and excluding “typical urban stations” are compared for the periods of 1954–2005. Although impacts of UHIs on the absolute annual and seasonal temperature are identified, UHI contributions to the long-term trends are less than 10% of the regional total warming during the period. The large warming trend during the period is due to a regime shift in around 1988, which accounted for about 51% of the regional warming.  相似文献   

XUV Photometer System (XPS): Improved Solar Irradiance Algorithm Using CHIANTI Spectral Models     

Thomas N. Woods  Phillip C. Chamberlin  W. K. Peterson  R. R. Meier  Phil G. Richards  Douglas J. Strickland  Gang Lu  Liying Qian  Stanley C. Solomon  B. A. Iijima  A. J. Mannucci  B. T. Tsurutani 《Solar physics》2008,250(2):235-267

Solar soft X-ray (XUV) radiation is highly variable on all time scales and strongly affects Earth’s ionosphere and upper atmosphere; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. Although there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the broad bands measured in the XUV range. In particular, the simple conversion of the XUV photometer signal into irradiance, in which a static solar spectrum is assumed, overestimates the flare variations by more than a factor of two as compared to the atmospheric response to the flares. To address this deficiency in the simple conversion, an improved algorithm using CHIANTI spectral models has been developed to process the XUV Photometer System (XPS) measurements with its broadband photometers. Model spectra representative of quiet Sun, active region, and flares are combined to match the signals from the XPS and produce spectra from 0.1 to 40 nm in 0.1-nm intervals for the XPS Level 4 data product. The two XPS instruments are aboard NASA’s Solar Radiation and Climate Experiment (SORCE) and Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) satellites. In addition, the XPS responsivities have been updated for the latest XPS data processing version. The new XPS results are consistent with daily variations from the previous simple conversion technique used for XPS and are also consistent with spectral measurements made at wavelengths longer than 27 nm. Most importantly, the XPS flare variations are reduced by factors of 2 – 4 at wavelengths shorter than 14 nm and are more consistent, for the first time, with atmospheric response to solar flares. Along with the details of the new XPS algorithm, several comparisons to dayglow and photoelectron measurements and model results are also presented to help verify the accuracy of the new XUV irradiance spectra.  相似文献   

Short communication: public interest in rip currents relative to other natural hazards: evidence from Google search data     

Houser  Chris  Vlodarchyk  Brent  Wernette  Phil 《Natural Hazards》2019,97(3):1395-1405

Natural Hazards - Informing and warning beach users about the danger posed by the rip current hazard remain a difficult challenge. Recent evidence suggests that warning signs and flags alone have...  相似文献   

A comparison of unsupervised segmentation parameter optimization approaches using moderate- and high-resolution imagery     

Heather Grybas  Lindsay Melendy  Russell G. Congalton 《地理信息系统科学与遥感》2017,54(4):515-533

Unsupervised segmentation optimization methods have been proposed to aid in selecting an “optimal” set of scale parameters quickly and objectively for object-based image analysis. The goal of this study was to qualitatively assess three unsupervised approaches using both moderate-resolution Landsat and high-resolution Ikonos imagery from two study sites with different landscape characteristics to demonstrate the continued need for analyst intervention during the segmentation process. The results demonstrate that these methods selected parameters that were optimal for the scene which varied with method, image type, and site complexity. Several takeaways from this exercise are as follows: (1) some methods do not work as intended, (2) single-scale unsupervised optimization procedures cannot be expected to properly segment all the features of interest in the image every time, and (3) many multi-scale approaches require subjectively chosen weights or thresholds or additional testing to determine those values that meet the objective. Visual inspection of segmentation results is still required in order to assess over and under-segmentation as no method can be expected to select the best parameters for land cover classifications every time. These approaches should instead be used to narrow down parameter values in order to save time.  相似文献