From the physiographic and morphological characterization of the lands located in areas of high mountain slopes, the pedogeomorphological homogeneity in two sectors located at the Alto Motatan Subbasin of the Miranda municipality at Merida state, Venezuela, was determined. 18 soil profiles were described, considering the physiographic characteristics of the sectors under study and the morphological characteristics of the epipedon and endopedon. With this information an original data matrix was built, from which the grouping were made for homogeneity analysis, by applying the Automated Information System of Land Homogeneity (AISLH) to calculate the Index of Multiple Homogeneity (IMH). In the sector I, located at the area of the Alisal-El Pedregal and Cruz Chiquita irrigation committees, the roots and tubers crops (carrot and potato) predominate. Sector II included the area of the Rincon de La Venta irrigation committee and was intended for agricultural use under green leafy vegetable crops. The results showed that the soils grouped in the sector I (transitional life zone to subalpine paramo) were more homogeneous than the soils in sector II (montane wet forest). It's concluded that the analysis allows to generated basic information for planning purposes of use, management and soil conservation in mountainous areas.

The main objective was to determine the index value of the carrying capacity of specific land use (W) in four (04) irrigation committees, located at the subbasin "Alto Motatan", Merida state, Venezuela. The productive agricultural system prevailing is the horticulture of height under irrigation, characterized for the utilization of management land practices that cause an environmental impact of high relevance. The methodology is a non experimental design, descriptive and quantitative, based on the application of a questionnaire to each of the owners of 56 "sample-plots" selected from 154 plots distributed in the four irrigation committees. The sampling was not probabilistic, stratified and voluntary. The W values were determined by a parametric model modified for this study. The results allowed verifying that there was an inverse relationship between the values of W and the average time of culture use (Tc) of the vegetables irrigated in the irrigation committees selected for this study. It concluded that the hierarchical order of decreasing values of W determined in these irrigation committees was as follows: Rincon del Picacho > Cruz Chiquita > Alisal-El Pedregal > Rincon de la Venta.

Memorias VII Congreso Nacional y 1er Congreso Internacional de Investigacion de la Universidad de Carabobo. La Investigacion en el Siglo XXI: Oportunidades y Retos”

A procedure expressed as a model based on the system theory, that will facilitate the carrying out of studies for the measurement of underground water wells has been proposed. The application of this procedure will allow, on one hand, to perform the recognition, description and measurement of qualitative and quantitative variables of underground water and well infrastructure, and on the other hand, to order the implicit sequence of activities in the study of subterranean water wells located in areas of oil exploration and production. The model consists of the three kinds of Data Flow Diagrams (DFD): DFD of context, analysis and expanded DFD. The building of the Data Flow Diagrams made it possible to determine the logical sequence of the necessary steps to be carried out, in appropriate and precise form, studies of water wells in geoseismic surveys. The utilization of the proposed procedure is recommended for the evaluation of the impact of vibrations produced during the acquisition of seismic data on well characteristics.

Physical suitability of three soil classes previously identified in groups and characterized through a methodology, that enables agricultural technicians and experienced farmers to define group of soils in a more understandable way, was determined. The study area covered 30,365 hectares of an alluvial sector in the Motatan River lowlands, Trujillo state, Venezuela. Land Evaluation was made using the maximum limitation method. Different grass requirements were determined: guinea (Panicum maximum), brachiaria (Urochloa decumbes) and German Grass (Echinochloa plectostachium). The characteristics of the three soil classes were compared as to grass requirements. The three soil classes qualified with the same degree of physical aptitude for each grass, differing as to the restrictive quality. In this manner: Soil classes A and C were considered marginally suitable (A3) for Guinea and Brachiaria grasses, and the restrictive quality was pH. They were moderately suitable (A2) for German grass, where drainage and texture were the restrictive qualities. Soil class B was marginally suitable (A3) for Guinea and Brachiaria grasses, where drainage was the restrictive quality, and moderately suitable (A2) for German grass, where pH was the restrictive quality. Guinea and Brachiaria grasses can improve their final classification if pH is modified for soil classes A and B or if the drainage of soil class B is modified, while German grass would only improve its suitability if the pH of soil class B is modified. To each class of physical aptitude (qualitative) a quantitative class was estimated according to the expected grass yield.

The Venezuelan Land and Agricultural Development Law, dated 1111312001, aims to establish the foundations of integral and sustainable rural development in order to increase the productivity of the land and, moreover to establish equity and fair distribution of the land. Nevertheless, for the Venezuelan private sector the aforementioned law constitutes an expropriation threat that would limit the productive use of the land. However, the main purpose of the law is to develop agricultural production in line with the dietary demands of the Venezuelan population, having as a fundamental premise the elimination of the large estates through the suitable redistribution of the great expanses of land that have remained idle and uncultivated for many years. The purpose of this study is to analyze the scope of some significant aspects of this law, principally those related to the ownership of the land, the type of use made of the land and the security of food production.

In a previous work (ICAME'97) we presented the Mössbauer results for a non-stoichiometric sample of the quasi-two-dimensional (2D) dichalcogenide CuFeTe2, where a Spin Density Wave (SDW) ground state with T SDW=256±15 K was proposed. Here we report the study of the magnetic and electric properties determined by magnetic susceptibility, Mössbauer spectroscopy and resistance measurements, of an almost stoichiometric sample prepared by the vertical Bridgman growth technique. The SDW behavior is supported by the results obtained by the following different techniques: Magnetic susceptibility: A magnetic transition is observed at T SDW=308 K with a Pauli paramagnetic behavior above this temperature. Mössbauer effect: The shape of the spectra and the thermal evolution of the hyperfine field are characteristic of the SDW's in quasi-2D systems. Electrical resistance: There is a metal–semiconductor transition along the layers as the temperature decreases indicating the opening of a gap at the Fermi level.

(57)Fe Mossbauer absorption measurements are reported indicating that CuFeSe(2) and CuFeTe(2) have both a ground state of spin-density waves (SDW) nature. For the selenide it is a transverse commensurate SDW with T(N) = 71 K and for the telluride it is an incommensurate SDW with T(N) = 308 K. (C) 1999 Elsevier Science B.V. All rights reserved.

57 Fe Mossbauer absorption measurements are reported indicating that CuFeSe 2 and CuFeTe 2 have both a ground state of spin-density waves (SDW) nature. For the selenide it is a transverse commensurate SDW with T N =71 K and for the telluride it is an incommensurate SDW with T N =308 K.

The Mössbauer measurements at variable temperature (from liquid helium to room temperature) on the layered compound CuFeTe 2 have been able to determine the existence of a magnetically ordered state below T N = 254 ± 15 K. The general shape of the spectra and the magnitudes of the hyperfine fields let us to propose a Spin Density Wave (SDW) behavior for this compound.

The syngas reaction has been studied using a laterite iron mineral, promoted with K and Mn. In situ activation under syngas, as well as pre-treatment with H2 followed by CO under mild and more severe conditions were tested. These activation procedures led to different iron phase compositions and to different catalytic selectivities. The C2-C4/CH4 ratio was significantly lower for those catalysts which after reaction showed the presence of hexagonal carbide and magnetite compared to the solid, which showed the highest proportion of Hägg carbide.

Results of Mössbauer spectroscopy for the chalcopyrite-type of alloys CuFe(S1−zSe z )2 in the range of composition 0≤z≤0.45 are presented. Room temperature spectra show two contributions: one is a magnetic spectrum (six lines) with a value of the hyperfine field near to that of chalcopyrite (z=0, in which an antiferromagnetic order occurs belowT=823 K), the other having only one line. The relative area of the single-line contribution increases asz increases. Forz=0.2, we also made Mössbauer measurements as a function of temperature. The ratio of the two contributions evolves according to a Boltzmann law, in which the single line corresponds to the excited state at 81 K above the antiferromagnetic ground state.

Two series of iron-pentasil molecular sieve catalysts were synthesized. One series consisted of H-ZSM-5 type zeolites with different silicon/aluminium ratios impregnated with ferric nitrate, and the other included ferrisilicates with different silicon/iron ratios. The catalytic tests on syngas conversion were effected at 0.7–2.1 MPa at between 240–300° C in a flow system with a fixed bed reactor. The characterization of the solids shows that in the impregnated series, the iron was transformed into α-iron and carbide phases by means of treatment with hydrogen, carbon monoxide and by the effect of the syngas under the reaction conditions. On the other hand, in the ferrisilicate series, the iron retains the ionic form [iron (III)-iron (II) ], regardless of the treatment, thereby indicating its incorporation into the structure of the solid. The catalytic behaviour of both series also differs. The solids produced by impregnation were seen to produce mostly hydrocarbons in the petrol range with the expected selectivity properties, whereas the ferrisilicates were selective towards the formation of i-C4.

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In the family of the semimagnetic semiconductors of chalcopyrite type (CuFeS2), eskebornite CuFeSe2 presents an unexpected behavior in which the metallic character, a different crystallographic structure and a magnetically ordered phase below T(N) = 70 K are its principal features.

The determination, by Mössbauer57Fe spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a “parallel-magnetic-field-to-the-gamma-rays” configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensitics. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example. Mössbauer experimental results obtained at room temperature for natural pyrite (FeS2) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.

The study of the magnetic, transport and Mössbauer properties of eskebornite, CuFeSe2, shows significant differences from that of its homologous sulfide, chalcopyrite (CuFeS2). From room temperature down to 77 K, CuFeSe2 is paramagnetic and metallic with a non-magnetic Mössbauer spectrum showing two equally populated sites for iron with very small quadrupole splitting. It seems clear that the electronic state of iron has evolved in going from chalcopyrite to eskebornite, in which it has a very weak magnetism.