Scattering from a thin perfectly-conducting square plate

Extensive numerical experiments on the scattering from a thin perfectly conducting square plate have been carried out to assess the performance of the exact analytical expressions for the electromagnetic field of a rectangular patch with uniform and linear distributions of current, in connection with the method of moments. Two solution schemes, employing pulses and roof-top functions for approximating the surface current on the plate, have been used. Convergence rates and results for the two solution schemes are compared with each other, as well as with an efficient solution by A.W. Glisson and D.R. Wilton (1980). The overall performance indicated by the numerical experiments suggests that it would be useful to use the exact numerical expressions in the solution of problems where accurate computation of the field radiated by such current sources is required     

On the electromagnetic field of a rectangular patch of uniform andlinear distributions of current in the source region

Exact analytical expressions for the magnetic vector potential and the electric and magnetic fields of a rectangular patch of uniform and linear distributions of electric current in an unbounded homogeneous medium have been given by the authors in a previous paper (see ibid., vol.37, p.1503-9, December 1989). In this paper, these expressions are utilized to investigate the nature of the electromagnetic field of such current distributions in the source region. Specifically, the singular parts and points of singularity of the various functions involved in the analytical expressions, as well as those of the field components of both current distributions, are obtained and tabulated     

A memory-economic frontwidth reduction algorithm

A simple element numbering algorithm is described which yields near-minimal frontwidths for two- and three-dimensional finite element assemblies. Renumbering of E elements requires an immediate-access computer memory size which is proportional to the square root of E in two-dimensional problems, and to the two-thirds power of E in three dimensions. This very small memory requirement allows processing of large problems in minicomputers. When used in large computers, page-swapping operations are minimized.     

Assessment from space of mangroves evolution in the Mekong Delta,in relation to extensive shrimp farming

This study is an attempt to produce an assessment of the impact of shrimp aquaculture in the Mekong Delta (Viet Nam) on mangrove ecosystems. For this exercise we selected two sub-areas (Ca Mau and Tra Vinh provinces) encompassing a variety of land uses and ecological conditions. Twenty stations in Tra Vinh and 15 stations in Ca Mau have been surveyed several times from September 2000 to March 2002. Field investigations included mangrove soils studies, measurements of pH and salinity of the water, analysis of mangrove flora, and density and structure of the vegetation. Four Syst@me Probatoire de l'Observation de la Terre (SPOT) scenes were used for the discrimination of mangrove types and for the delineation of landscape units. For the first time, five ecologically distinct landscape classes were identified and delineated. Their possible links with the farming and yields of high valued species of shrimps, especially the giant tiger shrimp (Penaeus monodon) destined for export markets, need further studies. Since 1965, about 30% of mangrove ecosystems have been lost in Ca Mau Province and more than 30% of present mangroves are replanted monospecific stands. To the best of our knowledge, this is the first study which demonstrates that, in spite of deep and ancient man interactions in the Mekong Delta, five ecologically distinct classes of land use can be defined. Satellite surveys confirm a clear distribution of landscape units with possible links with shrimp aquaculture potentialities.     

Antimicrobial evaluation of novel buccoadhesive films containing Myrrh extract

This study describes the formulation of new buccoadhesive films containing Myrrh extract as a natural and safe antimicrobial agent to give a long local medication. Buccoadhesive films of Myrrh extract were developed using solvent evaporation technique. The fabricated Myrrh extract films were evaluated for their palatability, weight, surface pH, and their content uniformity. In addition, tensile strength and the percentage of elongation of the films as well as in vitro mucoadhesive time were determined. Also, the films were tested for their antimicrobial activities. Obtained results showed that the tested films are elegant in appearance and have neutral pH, palatable by volunteers and have good tensile strength and elasticity. They also exhibited antibacterial activities against different types of bacterial strains as well as antifungal activity against Candida albicans.     

The resonance method for evaluating the impedances of theequivalent network for dielectric posts in a rectangular waveguide

The resonance method is applied to evaluate the impedances of the equivalent network for dielectric posts symmetrically located about a reference plane in a rectangular waveguide. Explicit relationships for the impedances of the equivalent lattice network of the posts in a rectangular waveguide are given in terms of the resonant frequencies of the rectangular cavity constructed by short-circuiting the waveguide at equal distances from the reference plane. A perturbational analysis is carried out to determine the resonant frequencies for a rectangular cavity loaded with slightly lossy circular posts whose largest cross-sectional dimensions are small compared with the wavelength. Sample numerical results for a single loss-free dielectric post illustrating the application of the derived expressions are given     

Analysis of Eastern Mediterranean Oak Forests Over the Period 1965–2003 Using Landscape Indices on a Patch Basis

Although Eastern Mediterranean forests have been exploited for many years, the changing trends in the past 40 years require detailed investigations. Forests in the coastal zone of Lebanon are witnessing major changes mainly because of chaotic urbanisation. The study area at the coastal zone of Lebanon has 96% of its forest cover under oak coppice. The aim of this study is to investigate the applicability of landscape indices on oak forests especially their ability to detect changes between 1965 and 2003. It uses forest canopy closure as another indicator of forest destruction. The 1965 forest map was first checked for its accuracy before being used to extract patch delineations and canopy closures. Landcover types for 2003 were obtained by classifying a SPOT 5 satellite image. FRAGSTATS software was utilised on the 1965 map on a patch basis to calculate patch shapes and sizes. These indices and canopy closures data were investigated for correlation purposes with patterns of forest loss. The edge distances between forest patches in 1965 and new forest patches in 2003 were computed to analyze regeneration processes. Results show that although older forest patches have shown a 48% loss in area, total forest area reached 83%. Abandoned agricultural lands have become new forest. Smaller forest patches (< 40 ha) showed greater losses than large ones. Small and open forest patches recorded greater loss than large and dense patches. Shape indices show no correlation with forest loss. Clearance for agriculture covered 30% of the pre-existing forests, while urban developments accounted for just 4% of forest loss. This research highlights the great need for comprehensive studies of forests using landscape analyses. Such analyses help managers develop practical and relevant conservation measures.     

Modular Neural Network Classifiers: A Comparative Study

There is a wide variety of Modular Neural Network (MNN) classifiers in the literature. They differ according to the design of their architecture, task-decomposition scheme, learning procedure, and multi-module decision-making strategy. Meanwhile, there is a lack of comparative studies in the MNN literature. This paper compares ten MNN classifiers which give a good representation of design varieties, viz., Decoupled; Other-output; ART-BP; Hierarchical; Multiple-experts; Ensemble (majority vote); Ensemble (average vote); Merge-glue; Hierarchical Competitive Neural Net; and Cooperative Modular Neural Net. Two benchmark applications of different degree and nature of complexity are used for performance comparison, and the strength-points and drawbacks of the different networks are outlined. The aim is to help a potential user to choose an appropriate model according to the application in hand and the available computational resources.     

On the realizability of the impedance matrix for lossy dielectricposts in a rectangular waveguide

The equivalent T-network for some lossy dielectric posts in a rectangular waveguide is found to have a negative resistance in the parallel arm although the realizability conditions for the impedance matrix are strictly satisfied. Furthermore, the reactive part of the same impedance is found to be a monotonically decreasing function of frequency. These difficulties are overcome in the case of symmetrical post structures by using lattice networks. A simplified lattice network of lumped elements is developed to approximately realize the impedance matrix for resonant lossy post structures in the bandwidth