Search Results

You are looking at 1 - 10 of 114 items for

  • Author or Editor: A. Kovács x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

We investigate various number system constructions. After summarizing earlier results we prove that for a given lattice Λ and expansive matrix M: Λ → Λ if ρ(M −1) < 1/2 then there always exists a suitable digit set D for which (Λ, M, D) is a number system. Here ρ means the spectral radius of M −1. We shall prove further that if the polynomial f(x) = c 0 + c 1 x + ··· + c k x kZ[x], c k = 1 satisfies the condition |c 0| > 2 Σ i=1 k |c i| then there is a suitable digit set D for which (Z k, M, D) is a number system, where M is the companion matrix of f(x).

Restricted access

An incubation experiment was set up to investigate the effects of NPK fertilizers, wheat straw and food waste compost in combination with Phylazonit MC biofertilizer on the changes in 0.01 M CaCl 2 extractable nitrogen forms (NO 3 + -N, NH 4 + -N, organic-N fraction) of three types of soils. The quantities and changes in CaCl 2 -NH 4 + -N mainly depended on the adsorption capacity of soils. Higher CaCl 2 extractable NH 4 + -N values were measured in the calcareous chernozem and sandy soil with the application of NPK treatment, while in case of the chernozem soil with loamy texture no significant differences were found between the NPK and control treatments. NH 4 + immobilization appeared in pots given straw treatment. The quantity of CaCl 2 -NH 4 + -N changed within the incubation period, the direction and extent of the change were dependent of the production rates and consumption processes. In all soils the 0.01 M CaCl 2 extractable NO 3 - -N was the largest pool for plant nutrition. The highest CaCl 2 -NO 3 - -N values were found in pots given NPK and combined NPK+straw treatments, while the lowest values were measured in straw-treated pots. Wheat straw, with higher C/N ratio caused a temporary immobilization, followed by remineralization. Food waste compost, with lower C/N ratio, proved to have a good N supplying capacity. The contrasted effect of straw and compost was more conspicuous in sandy soil, in which the original NO 3 - -N content was the lowest. Higher CaCl 2 -organic N values were measured for pots treated with straw and with compost, as compared to the control. During the incubation period the amount of soluble organic-N changed, the direction and extent of the change depended on the soil type and treatments. The effect of Phylazonit MC was on the quantity of CaCl 2 extractable N fractions was not really expressed, and the significancy of the effect varied and was dependent of the soil type. Biofertilizer amendment increased the extractable NO 3 - -N in sandy soil, decreased the negative effect of wheat straw, and it also might help in decomposing wheat straw and food waste compost. The application of Phylazonit MC in the calcareous chernozem caused a significantly higher amount of organic-N, especially in straw-treated pots.

Restricted access

Abstract  

Volatilization and thermochromatographic separation of ultramicro amounts of Mo and Tc from AgCl melt irradiated with 6 60 MeV protons have been studied in vacuum at 600 °C. It has been found that in quartz apparatus Tc, and while using graphite, Mo can be separated from the other leaving elements. On the basis of the experimental results an ion source can be contructed for the on-line nuclear spectroscopic studies of Mo and Tc isotopes.

Restricted access

Cryopreservation appears to be a suitable solution for the maintenance of potato germplasms. The protocol described in this paper can be applied for the vitrification and preservation of meristems. During histo-cytological studies it is possible to observe modifications at the cellular level and to understand the adaptive mechanism to low temperatures. Control potato meristem tissue contained a number of meristematic cells with a gradient of differentiation. After freezing there were a large number of vacuolated cells, some of which exhibited broken cell walls and plasmolysis. The thickening of the cell wall, giving them a sinuous appearance, was observed after freezing and thawing the meristems, with ruptures of the cuticle and epidermal layer.

Restricted access

Liver cells of the twenty-one day old rat embryo are isolated by a modified method and autophagy is studied in them by electron microscopic morphology and morphometry. Immediately after isolation or 2.5 h incubation in nutrient-free medium, embryonic hepatocytes contain high amount of glycogen and only very few autophagic vacuoles. In contrast, all glycogen is lost and 15% of the cytoplasmic volume is occupied by late autophagic vacuoles in hepatocytes after 18 h in the same medium. Presence of 3- methyladenine in the latter case inhibits both the loss of glycogen and the appearance of autophagic vac- uoles while enlarging the multivesicular body compartment. Our findings reveal major differences between isolated embryonic and adult hepatocytes concerning autophagy. Several types of autophagic vacuoles are described in the cell types of the erythropoietic cell lineage. This means that autophagy is an integral part of erythropoiesis not only in bone marrow, but also in embryonic liver that is investigat- ed here for the first time from this point of view. The presence of unclosed isolation membranes and the predominance of early autophagic vacuoles in reticulocytes indicates that the molecular machinery of segregation is still active in this functionally and structurally highly reduced cell type.

Restricted access

Modern agriculture is one of the main anthropogenic threats to biodiversity. To explore the effects of agricultural intensification we investigated carabids and spiders in two studies; in 2003 in grasslands and two years later in cereal fields in the same region. Both aimed to study the effect of management on arthropod diversity and composition at local and landscape scales. In 2003, we used a paired design for grasslands (extensively vs. intensively grazed). In 2005, a gradient design was applied with a total of seven land-use intensity categories. In both studies, sampling was carried out using funnel traps with the same sampling effort. Linear mixed models showed that high grazing intensity in grasslands had a positive effect on carabid species richness and abundance, but no effect on spiders. Landscape diversity had a positive effect only on carabid abundance. In the case of cereal fields, the management intensity (nitrogen fertiliser kg/ha) had a negative effect on spider richness and no effect on carabids. After variance partitioning, both local and landscape characteristics seem to be important for both cereal and grassland arthropod communities. Based on our results, we think that current and future agri-environmental schemes should be concentrated on cropland extensification. Low intensity croplands could act as a buffer zone around the semi-natural grasslands, at least in this biogeographic region.

Restricted access

Authors give a report on four eriophyoid species which were new for the Hungarian fauna (Aculops berochensis Keifer and Delley; Aculops parakarensis Bagdasarian; Aculus ligustri Keifer; Aculus? crataegumplicans Cotte). Three of them were found on new host-plants.

Restricted access

The aim of the study was to determine the characteristics of Szabolcs-Szatmár-Bereg county in North-Eastern Hungary and to elaborate an environmentally sound agricultural strategy. 50% of Szabolcs-Szatmár-Bereg county is arable land (303,950 ha). After the change of regime there was no significant decrease in the size of the arable land. Cultivation is still practised on soils of poorer quality. Under the changed production conditions, crop cultivation in its present form does not come up to the economic expectations. The sowing structure is not suited to the regional climate and soil conditions; 75% of the arable land is occupied by only 5 species of plant. A change in the cultivation profile (afforestation) can be expected on connected marginal areas where economic calculations indicate that economical cultivation is not possible. A typical feature of the region's cereal production is that it takes up significantly more arable land than is justified: in recent years the average ratio of cereals was 60–65%. In certain microregions the production of protein fodders is recommended for the economical production of better quality meat. There has been an increase in the area sown to triticale, peas, beans and cucumber for seed production. The production of flowers, vegetables, spices and herbs should be promoted; these plants require manual work, so they could play a significant role in solving employment problems. On more unfavourable areas, suitable for the cultivation of agricultural products, the production of low-input plants (e.g. rye, triticale, sorghum) suitable for extensive cultivation should be considered. In small regions with favourable ecological and infrastructural situations the area sown to crops with greater production value and greater labour requirements can be expected to increase.

Restricted access

On areas used for agriculture copper toxicity is one of the most important forms of heavy metal pollution, especially where field crops are to be grown in fields previously used as orchards or vineyards, treated for a long period with pesticides containing copper. Only varieties with good tolerance of soil with a high copper content should be grown on such areas. The selection of copper-tolerant varieties is complicated, however, by the fact that it is difficult to study copper tolerance under field conditions. Heavy metal tolerance is generally tested in hydroponic cultures, in which interfering factors can be minimised, but it is impossible to test a large number of genotypes or segregating generations using this method. Another problem in such experiments is that the conditions existing in hydroponic cultures bear little resemblance to those found in the field, so little information is obtained on the real adaptation of the varieties. The aim of the present experiments was thus to elaborate a soil-based technique suitable for determining the copper tolerance of various genotypes and allowing the simultaneous testing of a large number of genotypes under conditions approaching those found in the field. The results indicate that the copper tolerance of seedlings can be determined by growing them to an age of 2 weeks in soil containing 1000-1500 mg/kg CuSO4 × 5 H2O, since genetic differences in copper tolerance could be clearly distinguished under these conditions. The copper tolerance of plants grown in copper-containing soil exhibited a close correlation with the results obtained in physiological tests in hydroponic culture.

Restricted access