Anisotropic Effects in Geometrically Isotropic Lattices

For spacings and element dimensions small with respect to wavelength the directric constant of a completely general lattice of identical elements may be represented by a tensor (k_e). In many applications of artificial dielectrics it is important that the dielectric act as an isotropic medium for microwaves. This requires that (k_e) reduce to a scalar. The dielectric constant tensor will reduce to a scalar only if the lattice is cubical and the geometry and the material of the elements is restricted so that the induced fields may be represented by a set of three mutually perpendicular static dipoles at the lattice points. Isotropy further requires that the moment of the resultant dipoles be proportional to the inducing field and that the proportionality factor be a scalar independent of direction. However, at shorter wavelengths, the representation of the lattice elements by static dipoles will not be valid and the medium becomes anisotropic. This paper evaluates the anisotropy produced by an arbitrary ratio of element spacing to wavelength, and demonstrates that there is a basic anisotropy associated with the granularity of an array composed of isotropic elements arranged in structurally isotropic patterns

Elephant Butte Irrigation District

Presented during the Third international conference on irrigation and drainage held March 30 - April 2, 2005 in San Diego, California. The theme of the conference was "Water district management and governance."Includes bibliographical references.Relationships between farm size, irrigation practices, and on-farm irrigation efficiency in the Elephant Butte Irrigation District, New Mexico, U.S.A. are explored using water delivery data supplied by the District. The study area is experiencing rapid population growth, development, and competition for existing water supplies. Analysis of pecan and alfalfa water delivery data, fieldwork, and interviews with irrigators found extremely long irrigation durations, inefficient irrigation practices, inadequate on-farm infrastructure, and little interest in making improvements to the current irrigation system or methods on the smallest farms. These findings are attributed to the nature of residential, lifestyle, or retirement agriculture. Irrigation practices on large farms are notably different from small farms: irrigation durations are shorter, less water is applied, producers are commercially oriented, and have high levels of on-farm efficiency. Many small producers appear to view irrigation as a consumptive, recreational, social, or lifestyle activity, rather than an income generating pursuit. Small farm operators are likely to show limited interest in improving on-farm irrigation infrastructure, adopting management intensive irrigation technologies or practices, or making significant irrigation investments. Easement and common property disputes over ditch maintenance between owners of small parcels also create disincentives for infrastructure improvements.Sponsored by USCID; co-sponsored by Association of California Water Agencies and International Network for Participatory Irrigation Management

Changing face of western irrigated agriculture: structure, water management, and policy implications, The

Presented during the Third international conference on irrigation and drainage held March 30 - April 2, 2005 in San Diego, California. The theme of the conference was "Water district management and governance."Includes bibliographical references.The structure of U.S. agriculture is dualistic and likely to become more so in the future. A small percentage of farms produce the majority of output, and almost three-fourths of U.S. farms sell less than $50,000 worth of goods annually. Farms in the lower sales categories tend to have chronic negative net farm incomes, and many have no intention of earning a living from agriculture. Much of this residential, lifestyle, or retirement agriculture occurs on the urban fringe and in rural areas just beyond the urban fringe. In the arid western U.S., much of it is located in irrigated river valleys, which are also centers of population and economic activity. New Mexico's Elephant Butte Irrigation District (EBID) is located in one of the fastest growing counties in the United States. The region is experiencing water rights adjudication, rapid population growth, economic diversification, and increased competition for water resources. Recent research in the District found large differences in irrigation practices, efficiencies, and on-farm infrastructure relative to farm size. The small, residential, lifestyle, or retirement farms are notably different from the larger, commercially oriented farms. Many small producers view irrigation as a recreational, social, or lifestyle activity, rather than an income generating pursuit. The small farms have limited on-farm infrastructure, low irrigation efficiencies, and little interest in making irrigation improvements. Large, commercially oriented farms have high levels of on-farm irrigation efficiency due to deficit irrigation practices and investments in infrastructure. The Elephant Butte research led to questions about changes in agricultural structure, water management, and water resource policy implications in other western U.S. irrigated districts. We hypothesized that the trends in agricultural structure found in the EBID would appear in other irrigated areas in the West. Analysis of limited U.S. Census of Agriculture data for a sample of western counties supports this hypothesis for some regions. The water policy implications of the findings are discussed.Sponsored by USCID; co-sponsored by Association of California Water Agencies and International Network for Participatory Irrigation Management

Optimal Operation and Sustainability of the Multiple Reservoir System in the Yaqui Valley in Sonora, Mexico [abstract]

2 pages

Optimal Operation and Sustainability of the Multiple Reservoir System in the Yaqui Valley in Sonora, Mexico [abstract]

2 pages

Anisotropic Effects in Geometrically Isotropic Lattices

For spacings and element dimensions small with respect to wavelength the directric constant of a completely general lattice of identical elements may be represented by a tensor (k_e). In many applications of artificial dielectrics it is important that the dielectric act as an isotropic medium for microwaves. This requires that (k_e) reduce to a scalar. The dielectric constant tensor will reduce to a scalar only if the lattice is cubical and the geometry and the material of the elements is restricted so that the induced fields may be represented by a set of three mutually perpendicular static dipoles at the lattice points. Isotropy further requires that the moment of the resultant dipoles be proportional to the inducing field and that the proportionality factor be a scalar independent of direction. However, at shorter wavelengths, the representation of the lattice elements by static dipoles will not be valid and the medium becomes anisotropic. This paper evaluates the anisotropy produced by an arbitrary ratio of element spacing to wavelength, and demonstrates that there is a basic anisotropy associated with the granularity of an array composed of isotropic elements arranged in structurally isotropic patterns

Dielectric Properties of a Lattice of Anisotropic Particles

The dielectric properties of lattices composed of identical metallic or dielectric elements of various geometries, such as spheres, discs and strips have been investigated from a molecular point of view by Kock, Corkura and others. These investigations have treated two cases, in both of which, the element size and spacings are small compared to the wave length. The first applies to the case where the spacings are large compared to element size and which therefore neglects interaction effects. The second treats interaction for the special case in which the lattice has the structural isotropy of a cubical array and for which the application of the Clausius-Mosotti relation is valid, when the elements are not too closely packed. The main objective of this note will be to extend the treatment to general uniform lattice structures made of identically shaped and oriented particles of general constitutive characteristics. Thus, it will include the most general case of a uniform lattice with structural anisotropy and both element isotropy and anisotropy at the lattice points

La raison d'être of in situ electro-mobilization, phyto-extraction and phyto- stabilization of lithium tailing in heterogeneous rhizosphere by Brassica juncea and the monocotyledonous plants

The research tested the Brassica juncea ability, to phytoextract and phytostabilize lithium from mine tailings in lieu with vanadium and chromium, sown in a heterogeneous acidic rhizosphere. Five different heterogeneous growth media formulations were prepared from lithium mine tailings, homogenized peat and dewatered municipal biosolids. The Brassica juncea was grown for eighty six days, under homogeneous growing conditions, irrigated bi-daily with organic fertilizer, amended with LiCl, harvested and chemically analyzed. The phytoextraction and phytostabilization data revealed that the Brassica juncea was capable of absorbing more vanadium in its physiological parts rather than lithium and chromium. Likewise the monocotyledonous plant was grown homogeneously on the most favorable growth media, amended with lithium chloride and was able to phytoharness and phytostabilize more lithium rather than chromium per dry weight basis. In botanical efficiency parameters the monocotyledonous plant was ten times more efficient than the Brassica juncea in the bioaccumulation and efficiency removal rates for lithium and twice as much as for chromium. The relative growth rate of the monocotyledonous plant was twice as much as the Brassica juncea. Moreover, it surpassed the monocotyledonous plant in translocation indexes for chromium more than six times and twenty times for lithium. The findings revealed the possibility of a three way symbiosis formed between the hyperaccumulant plant grown in a heterogeneous rhizosphere and coupled with EK system at certain growth periods that will result in an increased electromigration and electrophoresis of heavy metals in the growth media solution

Three-Dimensional Lattices with Isotropic Dielectric Properties

Expressions are derived for the constitutive dielectric parameters of a cubical lattice whose elements consist of a triad of mutually perpendicular polarizable elements. The analysis gives the fundamental relations for the simulation by suitably disposed dipoles, of three-dimensionally isotropic dielectrics with dielectric constants greater than, equal to, and less than unity. Three different approaches have been used. One of these is a complete and rigorous solution which gives the dielectric tensor for the general case of unrestricted spacing to wavelength ratio. This rigorous analysis shows that the Clausius-Mosotti relation often used in predicting the properties of such lattices is a satisfactory approximation only if the spacing is very small with respect to wavelength. Using the general principles developed in the paper, conditions are derived for the realizability of reflectionless media