Charge order in Magnetite. An LDA+UU study

The electronic structure of the monoclinic structure of Fe$_3$O$_4$ is studied using both the local density approximation (LDA) and the LDA+$U$. The LDA gives only a small charge disproportionation, thus excluding that the structural distortion should be sufficient to give a charge order. The LDA+$U$ results in a charge disproportion along the c-axis in good agreement with the experiment. We also show how the effective $U$ can be calculated within the augmented plane wave methods

A micromechanics-enhanced finite element formulation for modelling heterogeneous materials

In the analysis of composite materials with heterogeneous microstructures, full resolution of the heterogeneities using classical numerical approaches can be computationally prohibitive. This paper presents a micromechanics-enhanced finite element formulation that accurately captures the mechanical behaviour of heterogeneous materials in a computationally efficient manner. The strategy exploits analytical solutions derived by Eshelby for ellipsoidal inclusions in order to determine the mechanical perturbation fields as a result of the underlying heterogeneities. Approximation functions for these perturbation fields are then incorporated into a finite element formulation to augment those of the macroscopic fields. A significant feature of this approach is that the finite element mesh does not explicitly resolve the heterogeneities and that no additional degrees of freedom are introduced. In this paper, hybrid-Trefftz stress finite elements are utilised and performance of the proposed formulation is demonstrated with numerical examples. The method is restricted here to elastic particulate composites with ellipsoidal inclusions but it has been designed to be extensible to a wider class of materials comprising arbitrary shaped inclusions.Comment: 28 pages, 12 figures, 2 table

Influence of soil tillage on oats yield in Central Bohemia Region

ArticleThe paper describes results of the field experiment with two technologies of oats crop stand establishment. First technology is conventional technology and second is no - tillage technology. The arti cle describes an experiment which was conducted in years 2013 – 2017. The experiments were located in Nesperská Lhota at Central Bohemia region. Altitude of selected field is 460 m. The experimental field is covered by a light cambi - soil. The differences bet ween the two technologies stand establishment are discussed. Statistical evaluation was performed on both methods in the parameter number of tillers per m 2 and yield. Crop yield is the basic indicator of agricultural production and usually affected by qual ity of soil tillage. One of the parameters affecting the yield is tillage (technology, working tools, depth, turning of soil etc.). Tillage depends mainly on the depth of processing and other quality parameters. An examination of the crop yield is necessar y in terms of sensitivity, depending on agro - technical conditions. Among those can be included processing plant soil nutrition and plant protection. It's always necessary commemorate, in these experiments can't be excluded some parameters like locality or meteorological parameter influences. Field trial was conceived as multi - year experiment with minimal changes of agro - technical conditions. During the experiment, the positive effect of conventional technology on crop yields was found. This difference was r eflected in the number of tillers and in total yield. The measurement shows the beneficial effect of the loosening of soil on the state of the oat crops. The results of experiment show that, the average yield in 5 years observation was 2.11 t ha - 1 for no - t ill technology and 4.22 t ha - 1 for conv entional technology of tillage

Changes in soil properties and possibilities of reducing environmental risks due to the application of biological activators in conditions of very heavy soils

This study aims at verifying the effect of farmyard manure (FYM) and of selected activators (Z'fix and NeoSol) on changes of soil properties. Their application should lead to improvement of soil physical properties and of organic matter fixation, to reduction of environmental risks, e.g. of tillage energy requirements. Experimental variants (0.7 ha each) were as follows: I (FYM with Z'fix); II (FYM with Z'fix + NeoSol); III (FYM); IV (Control NPK only). FYM was applied at rates: 50 t ha-1 (2014); 30 t ha-1 (2016). Additional NPK fertilizer (I–IV) was applied according to annual crop nutrient normative. The agent Z'fix was used as an activator of FYM biological transformation (5.5 kg t -1 ). The agent NeoSol was used as soil activator (200 kg ha-1 ; annually). In order to verify the effect, cone index, bulk density, tillage implement draft and chemical soil components (Humus, C/N ration and Ntot) were measured annually. Compared to the control, the application of FYM combined with the mentioned agents (I–III) increased Ntot more than two times. Moreover, it decreased (I–III) bulk density by 8.7%. Tillage implement draft decreased by 3% after the application of FYM with Z’fix (I, II). The study confirmed that FYM application combined with utilization of activators positively influenced soil fertility and helped to reduce environmental risks

Plantograf V18 – new construction and properties

ArticleThe article describes Plantograf V18, a planar tactile transducer, which converts the applied pressure into electric signal and enables a graphical presentation of the measured data; the new version V18 comes with some significant improvements and modifications. The device may be used ev erywhere where the pressure distribution between an object and surface is to be determined, e.g. in medicine or automotive industry. The article contains the detailed description of the transducer design and its electronic control circuits, as well as the yet unpublished measurements of pressure sensitivity with 3.5 mm electrodes

Finite element analysis of bond behavior in a steel reinforced concrete structure strengthened carbon fibre reinforced polymer (CFRP) strips

The article deals with the analysis of influence of carbon-fibre reinforced polymer (CFRP) on stress distribution in a steel reinforced concrete beam loaded by four-point bending flexural test. Simulation of the delamination is modelled by FEM with a cohesion zone material model. Distribution of cracks with CFRP strengthening is analysed, too. Finally, the fatigue life tests analysis was executed for the steel specimen (W.Nr. 1.0429 – concrete steel), which was used in the reinforced concrete beam. The fatigue test results are used to plot the fatigue life curve

Comparison of tillage systems in terms of water infiltration into the soil during the autumn season

ArticleThe soil belongs to the most valuable parts of the planet Earth. It is, endangered by water erosion, which causes huge destruction every year, or damage to farmland. More than half of the agricultural land in the Czech Republic is threatened by water erosion. The measurement was performed in the location Nesperská Lhota. The trial has been established on loamy sand Cambisol. In the field experiment, there were created 6 different variants which wad differed by soil tillage and crop. In the individual variants maize and oats were located. The field trial has been existing for a long time, as it was founded in 2009. Two measuring methods of water infiltration were used for the measurements: a mini disk infiltrometer and a single ring. The measurement was performed in the period of September 2016 before the harvest of maize. The soil aggregates were already stabilized at that time after all tillage operations. The measurement result showed the difference between the methods of soil tillage. The greatest ability of infiltration had a variant of maize with inter-row oats. Surprisingly, it was followed by maize, which was processed by ploughing technology. The lowest infiltration capacity was showed by oats reduced by soil tillage. A variant without vegetation had the second lowest infiltration. Our results obtained at rate of water infiltration into the soil affirm the need to control measures in the late vegetative stages. It is important for most of the rainfall to be quickly infiltrated so that it prevents the formation of massive surface runoff

Effect of PTO-driven tillage machines on soil particles transfer

ArticleDisplacement of soil particles by erosion can be seen as a major threat to the quali ty of agricultural land in the conditions of Czech Republic. While the effects of water and wind erosion have long been investigated and reported, the effect of soil tillage technology on soil particles translocation are relatively new area of agriculture research. Soil tillage may contribute to the undesirable translocation of soil particles towards lower - lying parts of fields especially on slopes. The effect of soil tillage implements on soil particle translocation has not been sufficiently explained yet. The object of this research was to assess the influence of PTO (power takeoff) - driven tillage machines on soil particle translocation during secondary tillage (soil preparation). Measurements to determine the displacement of soil particles were performed in location Nesperská Lhota in the Central Bohemia Region. Measurements were performed on a sandy loam cambisol after harvest winter cereals (winter wheat). To indicate displacement of soil particles was used grit of white limestone (size 10 – 16 mm). Limest one was put down into the trench with known position orthogonal to the direction of working operations. Subsequently were performed working operations in the specified sequence. Limestone particles were counted and weighed in each section. It was detected by measuring the different nature of displacement for each machine. Statistical significance of differences in the weight of translocated particles was evaluated for different type of machines

Photoluminescence rings in Corbino disk at quantizing magnetic fields

Spatially resolved photoluminescence of modulation doped AlGaAs/GaAs heterojunction was investigated in a sample of Corbino disk geometry subject to strong perpendicular magnetic fields. Significant spatial modulation of the photoluminescence was observed in form of one or more concentric rings which travelled across the sample when the magnetic field strength was varied. A topology of the observed structure excludes the possibility of being a trace of an external current. The effect is attributed to formation of compressible and incompressible stripes in a 2DEG density gradient across the sample.Comment: 5 two-column pages, 4 figures (one of them in color