Desertification processes and impact in rainfed agricultural regions   总被引：1，自引：0，他引：1  

D. W. Sanders 《Climatic change》1986,9(1-2):33-42

About one third of the Earth's land surface lies in the arid and semi-arid regions. This area is important as in addition to supporting 600 million people, it produces much of the world's grain and a substantial amount of animal produce.However, much of this area is now either suffering, or is threatened by the processes of desertification.In this paper, seven different desertification processes—degradation of vegetative cover, wind erosion, water erosion, salinization, soil crusting and compaction, reduction in organic matter, and accumulation of toxic substances— are identified and their effects described.It is pointed out that these processes are usually closely interrelated, the occurrence of one frequently leading to the occurrence of one or more of the others. But whatever the process, the end result is the same—degraded land with a reduced productive capacity.The paper concludes by pointing out that desertification occurs due to man's influence on the environment and we must therefore look beyond the purely physical processes if we are to solve the problems of desertification.  相似文献   

Water erosion control     

D. W. Sanders 《Climatic change》1986,9(1-2):187-194

Under natural conditions, balanced ecological systems develop in which the soil is protected by a cover of different plants. When man modifies the environment, in his attempts to produce more food, fiber and fuel, the ecological system is changed.This often results in the soil being exposed to the processes of accelerated water erosion. In this way, millions of hectares of land, particularly in the semi arid areas are now eroding.This paper stresses that the most important principle in controlling water erosion is to develop a new balanced system which is not only productive but which is also stable.Water erosion control schemes should therefore be based on the selection and introduction of correct land use.Examples are given of the types of measures that may be needed for cultivated, grazing and forestry lands.In some cases, a change in land use may also have to be supported by the construction of physical conservation measures. Some common examples of such measures are briefly described.  相似文献   

The constrained normal form algorithm     

Richard Cushman  Jan A. Sanders 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):181-187

This paper describes an algorithm which brings a regularizable polynomial perturbation of a three degree of freedom Kepler problem into a normal form which Poisson commutes with the Kepler Hamiltonian. We illustrate the alogrithm with an example: the quadratic Zeeman effect. For other applications of this algorithm see [1],[4], and [5]. The authors have written a program in MAPLE which implements the constrained normal form.  相似文献   

A growth-stage scaling model for the wind-driven sea     

J. W. Sanders 《Ocean Dynamics》1976,29(4):136-161

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MICROWAVE RADIOMETRY AND THE GEOGRAPHER     

Norman K. Sanders 《The Professional geographer》1969,21(2):119-121

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A deeper X-ray study of the core of the Perseus galaxy cluster: the power of sound waves and the distribution of metals and cosmic rays     

J. S. Sanders  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2007,381(4):1381-1399

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Solar system constraints on multifield theories of modified dynamics     

R. H. Sanders 《Monthly notices of the Royal Astronomical Society》2006,370(3):1519-1528

Any viable theory of modified Newtonian dynamics (MOND) as modified gravity is likely to require fields in addition to the usual tensor field of General Relativity. For these theories, the MOND phenomenology emerges as an effective fifth force probably associated with a scalar field. Here, I consider the constraints imposed on such theories by Solar system phenomenology, primarily by the absence of significant deviations from inverse-square attraction in the inner Solar system as well as detectable local preferred frame effects. The current examples of multifield theories can be constructed to satisfy these constraints and such theories lead inevitably to an anomalous non-inverse-square force in the outer Solar system.  相似文献   

Fe K emission in the ultraluminous infrared galaxy Arp 220     

K. Iwasawa  D. B. Sanders  A. S. Evans  N. Trentham  G. Miniutti  H. W. W. Spoon 《Monthly notices of the Royal Astronomical Society》2005,357(2):565-571

Prominent Fe Kα line emission is detected in the XMM–Newton spectrum of the ultraluminous infrared galaxy Arp 220. The centroid of the line is found at an energy of 6.7 keV and the equivalent width of the line is  EW ∼ 1.9 keV  (at 3.5σ significance). A few other spectral features are found at various degrees of significance in the lower energy range on a hard 2.5–10 keV continuum  (Γ∼ 1)  . The large EW of the Fe K line poses a problem with interpreting the hard X-ray emission as integrated X-ray binary emission. A thermal emission spectrum with a temperature of   kT ∼ 7 keV  modified by absorption of   N _H≃ 3 × 10²² cm⁻²  , can describe the 2.5–10 keV continuum shape and the Fe K emission. A hot bubble that is shocked internally in a starburst region would have a similar temperature and gives a good explanation for the observed X-ray properties with a high star formation rate. An ensemble of radio supernovae in a dense environment, as suggested from VLBI imaging, could be another possibility, if such powerful supernovae are produced continuously at a high rate. However, the apparent lack of emission from X-ray binaries is incompatible with the high supernova rate (∼2 SNe yr⁻¹) required by both interpretations. Highly photoionized, low-density gas illuminated by a hidden Compton-thick active galactic nucleus is a possible alternative for the hard X-ray emission, which can be tested by examining whether radiative recombination continua from highly ionized Ca and Fe are present in better quality data from a forthcoming observation.  相似文献   

Contour binning: a new technique for spatially resolved X-ray spectroscopy applied to Cassiopeia A     

J. S. Sanders 《Monthly notices of the Royal Astronomical Society》2006,371(2):829-842

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Regional frequency analysis of extreme rainfall events in Jakarta     

Liu  Jiandong  Doan  Chi Dung  Liong  Shie-Yui  Sanders  Richard  Dao  Anh Tuan  Fewtrell  Timothy 《Natural Hazards》2015,75(2):1075-1104

Natural Hazards - Jakarta is vulnerable to flooding and extreme rainfall events are always the main cause of the occurrence of heavy flood events with loss of life and property. The flood in...  相似文献