Computer prediction of large reflector antenna radiation properties

A FORTRAN program for calculating reflector antenna radiation patterns was rewritten and extended to include reflectors composed of a number of panels. These individual panels must be analytic surfaces. The theoretical foundation for the program is as follows: Geometrical optics techniques are used to trace rays from a feed antenna to the reflector surface and back to a mathematical plane just in front of the reflector. The resulting tangential electric field distribution, assumed to be the only source of forward radiation, is integrated numerically to calculate the radiation pattern for a desired set of angles. When the reflector is composed of more than one panel, each panel is treated as a separated antenna, the ray-tracing procedure and integration being repeated for each panel. The results of the individual aperture plane integrations are stored and summed to yield the relative electric field strength over the angles of interest. An example and several test cases are included to demonstrate the use of the program and verify the new method of computation

Reuse of waste material "waste sludge water" from a concrete plant in cement composites: A case study

This paper presents the results of research dealing with the use of recycled waste sludge water from a concrete plant (CP) as partial or complete replacement of mixing water in cement mixtures. The need to recycle waste sludge water generated as a by-product (waste sludge water) during the production of fresh concrete in the concrete plant results from the environmental and economic problems associated with the operation of the concrete plant. Mixing water was replaced with recycled waste sludge water in the amount of 25%, 50%, 75%, and 100%. In order to determine the effect of partial or complete replacement of mixing water with waste sludge water from the concrete plant in the production of cement composites, laboratory tests of waste sludge water were carried out to determine whether the waste sludge water complies with the requirements for mixing water defined in CSN EN 1008. The tests also determined the properties of fresh cement mortar and hardened cement composites. These were tests of the beginning and end of cement mortar setting, and the strength characteristics (flexural strength, compressive strength). The results of these tests show that it is possible to replace the mixing water by waste sludge water from the concrete plant in the amount of up to 25% without significantly affecting the tested properties, in comparison with the formula containing pure mixing water.Web of Science921art. no. 451

Prediction of water retention of soils from the humid tropics by the nonparametric k-nearest neighbor approach

Nonparametric approaches such as the k-nearest neighbor (k-NN) approach are considered attractive for pedotransfer modeling in hydrology; however, they have not been applied to predict water retention of highly weathered soils in the humid tropics. Therefore, the objectives of this study were: to apply the k-NN approach to predict soil water retention in a humid tropical region; to test its ability to predict soil water content at eight different matric potentials; to test the benefit of using more input attributes than most previous studies and their combinations; to discuss the importance of particular input attributes in the prediction of soil water retention at low, intermediate, and high matric potentials; and to compare this approach with two published tropical pedotransfer functions (PTFs) based on multiple linear regression (MLR). The overall estimation error ranges generated by the k-NN approach were statistically different but comparable to the two examined MLR PTFs. When the best combination of input variables (sand + silt + clay + bulk density + cation exchange capacity) was used, the overall error was remarkably low: 0.0360 to 0.0390 m(3) m(-3) in the dry and very wet ranges and 0.0490 to 0.0510 m(3) m(-3) in the intermediate range (i.e., -3 to -50 kPa) of the soil water retention curve. This k-NN variant can be considered as a competitive alternative to more classical, equation-based PTFs due to the accuracy of the water retention estimation and, as an added benefit, its flexibility to incorporate new data without the need to redevelop new equations. This is highly beneficial in developing countries where soil databases for agricultural planning are at present sparse, though slowly developing

New generation of hydraulic pedotransfer functions for Europe

A range of continental-scale soil datasets exists in Europe with different spatial representation and based on different principles. We developed comprehensive pedotransfer functions (PTFs) for applications principally on spatial datasets with continental coverage. The PTF development included the prediction of soil water retention at various matric potentials and prediction of parameters to characterize soil moisture retention and the hydraulic conductivity curve (MRC and HCC) of European soils. We developed PTFs with a hierarchical approach, determined by the input requirements. The PTFs were derived by using three statistical methods: (i) linear regression where there were quantitative input variables, (ii) a regression tree for qualitative, quantitative and mixed types of information and (iii) mean statistics of developer-defined soil groups (class PTF) when only qualitative input parameters were available. Data of the recently established European Hydropedological Data Inventory (EU-HYDI), which holds the most comprehensive geographical and thematic coverage of hydro-pedological data in Europe, were used to train and test the PTFs. The applied modelling techniques and the EU-HYDI allowed the development of hydraulic PTFs that are more reliable and applicable for a greater variety of input parameters than those previously available for Europe. Therefore the new set of PTFs offers tailored advanced tools for a wide range of applications in the continent

Získávání cinvalditu z odpadů po těžbě a úpravě

Lithium je nejlehčím kovem periodické soustavy prvků, jehož světové zásoby v dostupných ložiscích se odhadují na 20Mt, přičemž v České republice tvoří Li jako doprovodný prvek Sn-W zrudnění přibližně 1% sbětových zásob. Nezanedbatelné zásoby Li představují take odpady z předchozí těžby a úpravy Sn-W rud v oblasti Krušnohoří, obsahující zhruba 0,2% Li. Světová spotřeba lithia se odhaduje na 6kt ročně a očekává se, stejně jako u ceny, její postupná vzrůst. Vzhledem k tomu, že spotřeba Li v České republice se kryje dovozem, bylo by vhodné alespoň částečně omezit tuto závislost a využít české zdroje Li pro jeho výrobu. jako nejschůdnější se v počátcích jeví využití stávajících odvalů odpadů z gravitační úpravy Sn-W rud v odhadovaném množství 3,5 Mt na bývalém ložisku Cínovec.Lithium is the lightest metal in the periodic table of elements, whose world reserves in the available deposits are estimated to be 20Mt, and in the Czech Republic Li makes up about 1% of the world reserves as the residual element in Sn-W ore mineralization. Significant reserves of Li are also represented in waste from the former mining and processing of Sn-W ores in the Krušné hory region, containing about 0.2% Li. The world consumption of lithium is estimated 6 kt/year and a gradual increase is expected, as well as an increase of the price. With regard to the fact that the consumption of Li in the Czech Republic is covered by the import, it would be suitable to eliminate this dependence to some extent and utilize the Czech resources of Li for production. At the beginning, the easiest method seems to be utilization of the present waste piles from the gravity processing of Sn-W ores in the estimated amount of 3.5 Mt in the former deposit of Cínovec. This paper is devoted to the possibilities of extracting Li-concentrates from raw materials