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1.
The upper 30 cm of the soil profile, which hosts the majority of the root biomass, can be considered as the shallow agricultural root zone of most temperate crops. The electromagnetic wave velocity in the soil obtained from reflection hyperbolas in ground-penetrating radar (GPR) data can be used to estimate soil moisture (SM). Finding shallow hyperbolas in a radargram and minimizing the subjective error associated with the hyperbola fitting are the main challenges in this approach. Nevertheless, we were motivated by the recent improvements of hyperbola fitting algorithms, which can reduce the subjective error and processing time. To overcome the difficulty of finding very shallow hyperbolas, we applied the hyperbola fitting method to reflections ranging from 27- to 50-cm depth using a 500-MHz centre-frequency GPR and compared the estimated moisture with vertically installed, 30-cm-long time-domain reflectometry (TDR) sensors. We also compared TDR and GPR sample areas in a 2-D plane using different GPR survey types and different hyperbola depths. SM measured with TDR and GPR were not significantly different according to Mann–Whitney's test. Our analyses showed that a root mean square error of 0.03 m3 m−3 was found between the two methods. In conclusion, the proposed method might be suitable to estimate SM with an acceptable accuracy within the root zone if the soil profile is fairly uniform within the application depth range. 相似文献
2.
Abhishek Kumar Singh Anirban Lakshman Amares Chattopadhyay 《Geomechanics and Geoengineering》2016,11(3):201-218
Heterogeneity, being a trivial feature inside the earth or in a geostructure, makes a strong basis for its consideration in the study of geomechanics. Inclusion of the concept of heterogeneity along with irregularity in the medium brings a novelty to the existing literature related to the study of the moving load. The present study investigates the effects of linear and exponential heterogeneity on the dynamic response due to a normal load moving with constant velocity on a rough irregular heterogeneous isotropic half-space in a comparative approach. Expressions for both normal and shear stresses for either case of heterogeneity have been established in closed form. Substantial effects of the affecting parameters such as depth, irregularity factor, maximum depth of irregularity, frictional coefficient, linear heterogeneity parameter and exponential heterogeneity parameter on normal and shear stresses for both the cases of heterogeneity have been observed. Numerical computation has been carried out and the effects of said parameters have been meticulously examined by means of graphs. Moreover, different cases of heterogeneity and homogeneity along with various types of irregularity namely rectangular, parabolic and no irregularity are compared which serve as a focal theme of the study. 相似文献
3.
Abhishek Kumar Singh Amrita Das Anirban Lakshman Amares Chattopadhyay 《Acta Geophysica》2016,64(5):1340-1369
The presence of porosity and reinforcement in a medium is an important factor affecting seismic wave propagation and plays vital role in many geophysical prospects. Also, the presence of salt and ore deposits, mountains, basins, mountain roots, etc. is responsible for the existence of corrugated boundary surfaces of constituent layers. Such facts brought motivation for the present paper which deals with the propagation of SH-wave in a heterogeneous fluid-saturated poroelastic layer with corrugated boundaries lying over an initially stressed fibre-reinforced elastic halfspace. Closed form of dispersion relation has been obtained and is found in well agreement to classical Love wave equation for isotropic case. The effect of corrugation, wave number, undulation, position parameter, horizontal compressive/tensile initial stress and heterogeneity on phase velocity has been analysed through numerical computation and graphical illustration. Moreover, comparative study exploring the effect of presence and absence of reinforcement in half-space on dispersion curve is the major highlight of the current study. 相似文献
4.
Sri Lanka has one of the lowest fertility rates among poor countries of the world. The fertility decline which began in the
1950s has held steady during the last four decades, despite low levels of economic development. Widespread use of contraception
is the primary cause of the fertility decline. However, there is no one single homogenous body of people that can be characterized
as a ‘modern’ contracepting population through which new methods of family planning have spatially diffused. There is evidence
that the overall fertility decline began even before the establishment of the modern family planning program in Sri Lanka.
Our analysis showed four broad regional regimes of fertility transition with considerable social and place-to-place differences
in method-specific rates of contraception among them. Non-modern ‘traditional techniques’ of contraception which are widely
used are an important part of fertility regulation. Sterilization is the most common method of modern contraception in all
regions. Less than a tenth of the protected couples use methods such as the pill and the IUD; moreover, these methods are
often discontinued after initial use. Traditional methods are an important part of the contraceptive mix in Sri Lanka, and
it would be inadvisable to discourage the use of such practices.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
OpenStreetMap (OSM) is an online public access database that allows for the collaborative collection of local geographic information. We employ this mapping technology to discuss a new social theory of poverty that moves away from income poverty to an economy that directly produces individuals' basic needs. Focusing on urban farming in Philadelphia as an example, we use OSM to support the argument that money, land, labor, and capital do not limit food production in the city. OSM is a type of “commons” that allows community members to depict features of interest to them that might otherwise be underrepresented in official or commercially produced maps such as Google Maps. Using the concept of facilitated volunteered geographic information (VGI) we developed an open framework for combining residents' local knowledge of food resources with expert guidance in data input. We believe this helps overcome problems with ad hoc data submission efforts to which collaborative online projects are susceptible. The program for “tagging” food resources in OSM was deployed in a public “map-a-thon” event we organized in Philadelphia, bringing together technical experts and food enthusiasts. To share the results, we present the Philly Fresh Food Map as an interactive online Web map that can be used and updated by the public. 相似文献
6.
A formula to compute evaporation from open water surfaces is derived using wind profile characteristics. The mass transfer coefficient is given as a function of the shape and size of the water body in addition to the turbulent boundary layer parameters. The formula has been applied successfully to lakes and reservoirs of areas ranging from a fraction of an acre to thousands of acres. It is also given in a simplified form for application to cases where the wind profile measurements are not made. 相似文献
7.
Kanthi K. A. S. Yapa 《Journal of Earth System Science》2000,109(4):427-432
Remotely sensed data on ocean colour of waters surrounding Sri Lanka received from the Coastal Zone Colour Scanner (CZCS)
are processed and analyzed. Raw data of 1 km resolution on relatively cloud free days during 1978–1986 are processed to produce
sea surface chlorophyll maps within latitudes 4.5N-11N and longitudes 78E-85E, a region in the Indian Ocean surrounding Sri
Lanka. The processed data include about 110 single day maps and composite averages for each month and season. The months of
July, August and September are omitted in the calculation of averages due to insufficient data. The waters in the Gulf of
Mannar and Palk Bay areas show high chlorophyll-a concentrations throughout the year. However, these high values may represent
other suspended particles and dissolved organic matter besides chlorophyll-a as this region is shallow (< 100 m). Regions
with high chlorophyll concentrations (> 0.5 mg m-3) along the coast and western ocean region can be seen in the months of October and November, after the southwest monsoon
period. As high surface chlorophyll concentrations may indicate high productivity, these regions need extensive measurements
of primary production and also continuous monitoring of fish catches, during and after the southwest monsoon. Studies of particle
composition in shallow water areas, in particular waters in Palk Bay and Gulf of Mannar, should be carried out in order to
elucidate the effect of non-phytogenic. 相似文献
8.
Yapa LS 《The Journal of geography》1985,84(6):242-247
The author rejects neo-Malthusian concepts of population problems in developing countries and develops the hypothesis that overpopulation exists where people lack the basic means of subsistence or suffer massive unemployment, both symptoms of dependent capitalism according to the author. Population problems are analyzed in the context of divisions among social classes and resource utilization based on these divisions. The need for developing societies to gain independence from imported technology is stressed. 相似文献
9.
The ability to calculate the oil droplet size distribution (DSD) and its dynamic behavior in the water column is important in oil spill modeling. Breaking waves disperse oil from a surface slick into the water column as droplets of varying sizes. Oil droplets undergo further breakup and coalescence in the water column due to the turbulence. Available models simulate oil DSD based on empirical/equilibrium equations. However, the oil DSD evolution due to subsequent droplet breakup and coalescence in the water column can be best represented by a dynamic population model. This paper develops a phenomenological model to calculate the oil DSD in wave breaking conditions and ocean turbulence and is based on droplet breakup and coalescence. Its results are compared with data from laboratory experiments that include different oil types, different weathering times, and different breaking wave heights. The model comparisons showed a good agreement with experimental data. 相似文献
10.
Lakshman S. Yapa 《The Professional geographer》1979,31(4):371-376
Theories of economic development have focused exclusively on the improvement of production forces and have disregarded questions of social and ecological relations of production. Among geographers, the exclusive focus on production forces can be seen in their work on the spatial diffusion of technological innovation. The costly errors of Green Revolution agriculture in the Third World illustrate the hazards of that approach. A full assessment of the role of technology in development requires a perspective of ecopolitical economy. This viewpoint is explained using the Green Revolution as an example. 相似文献