Nowa wersja platformy, zawierająca wyłącznie zasoby pełnotekstowe, jest już dostępna.
Przejdź na https://bibliotekanauki.pl
Ograniczanie wyników
Czasopisma help
Lata help
Autorzy help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 53

Liczba wyników na stronie
first rewind previous Strona / 3 next fast forward last
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  pola
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 3 next fast forward last
EN
A wedge cell of the wedge angle of the order of few milliradians was used to measure threshold magnetic fields for the magnetic Freedericksz transition [1-3]. A nematic liquid crystal filling the cell was of planar orientation enforced by the treatment of the flat boundary plates. A system of interference fringes appeared in the cell placed in normally incident light between analyser and polariser crossed. In the vicinity of each fringe, the cell could be considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness, the same relates to any cell of slowly-varying thickness and flat cover plates. The threshold magnetic field magnitudes were interpreted as eigenvalues of the boundary eigenvalue problem for the operator of the second derivative; the interaction between the nematics and the substrate was described by the Rapini-Papoular formula [3] (i.e., weak coupling was considered). The resulting formulae were used to determine the polar anchoring energy coefficient and the anisotropy of diamagnetic susceptibility after the threshold fields measured. The method was applied to characterise the nematic liquid crystal 5CB and the coupling between it and the substrates made of poly(amic acid) MP2 [4, 5]. The estimates of material parameters agreed pretty well with those determined by the composite method [6].
6
75%
EN
In 2001-2004 148 phytosciological releves using the Braun-Blanquet method were recorded in abandoned meadows and the abandoned arable fields adjacent to them, presently overgrown by grassland with weil developed turf. The study area was located in the San valley on alluvial soils. On the basis of the collected material, 6 associations and 10 temporarily distinguished plant communities were distinguished. Out of them 7 were classified in the class Molinio-Arrhenatheretea, 4 in Phragmitetea, 2 in Artemisietea, and 3 were difficult to assign to a clear syntaxonomic position. Phytoindicative analysis of habitat showed that all of the communities were semi-heliophilous (L = 5.9 - 7.4). They occurred on soil with varying soil moisture (F = 3.8 - 8.8), soil pH (R = 4.9 - 7.4) and nitrogen content (N = 3.8 - 8.1). In all the communities, the accumulation of unmown, aboveground biomass was observed. In abandoned meadows in wet or periodically excessively moist soils Deschampsia caespitosa, Juncus effusus and perennial dicots (Filipendula ulmaria, Lythrum salicaria, Cirsium rivulare, Lysimachia vulgaris) spread. In the remaining communities the species characteristic of the class Molinio-Arrhenatheretea was frequent and ahundant, among others: Poa pratensis, Festuca rubra, Festuca pratensis, Rumex acetosa and Vicia cracca. In all the distinguished communities the specics from the classes Artemisietea, Agropyretea and the alliance Agropyro-Rumicion crispi from the class Molinio-Arrhenatheretea were present. Regardless of habitat conditions the most frequent species were: Cirsium arvense, Urtica dioica, Galium rivale, Anthriscus sylvestris, Agropyron repens, Equisetum arvense, Mentha longifolia, Carex hirta, and Ranunculus repens, whereas Calystegia sepium, Eupatorium cannabinum, Epilobium hirsutum and Myosoton aquaticum grew nearly exclusively on wet sites and Saponaria officinalis and Reseda lutea on the dry ones. As far as grasslands originating from the spontaneous creation of turf in recently abandoned arable land are concerned, meadow species from the class Molinio-Arrhenatheretea, with some species from the class Stellarietea mediaei, dominated. In all the phytocoenoses, except for the Urtica dioica community, the presence of trees and shrubs initiating the succession towards secondary woodland was observed. In wetter sites Salix cinerea, Salix alba, Salix triandra, Salix purpurea and Salix viminalis occurred, and in the moderately moist and dry sites Crataegus monogyna, Crataegus rhipidophylla, Rosa canina, Prunus spinosa, Pyrus pyraster, Cerasus avium and Salix capreai were most frequent. The low number of constant species (constancy III-V) and the dominance of sporadic species indicate that the communities are far from stable. The most consistent composition was displayed by Festuca rubra-Poa pratensis, Carex brizaicles, Bromus erectus communities and the Caricetum acutiformis association. Floristically, the richest was the Bromus erectus community (mean no. of species per releve - 33.2.), and the poorest was the Phalaris arundinacea community (17.7 species).
PL
Teren zalewowy jest to pas ziemi leżący wzdłuż cieków wodnych, porośnięty często łęgowymi zespołami roślinnymi związanymi funkcjonalnie z wylewami rzeki i stanowiący strefę przejściową do ekosystemów roślin grądowych. Bardzo często roślinność występująca w tym pasie złożona jest z roślin jednorocznych, krzewów oraz drzew, o różnej wysokości i charakteryzujących się różnym zagęszczeniem. Część z tych obszarów wykorzystywana jest rolniczo jako pastwiska i łąki, z których można uzyskać paszę dla zwierząt. Na podstawie dokumentacji fotograficznej terenów zalewowych i badań terenowych przeprowadzanych w powyżej zbiornika Jeziorsko wykazano istotne różnice w sposobie zagospodarowania w analizowanych przekrojach dolinowych. Znacznie mniejszy rozwój roślinności krzewiastej, a właściwie jej brak obserwuje się na obszarach wykorzystanych do wypasu bydła.
EN
Flood plains are a specific sedimentary environment. They constitute a natural clarifier tank and filter for rivers carrying various impurities including: heavy metals and biogenic elements, which are transported during floods and floods. Much of these pollutants are accumulated on the river bank called a bufferstrip. It comprises a strip of land lying along the watercourses, often overgrown with riparian plant associations related functionally to the flooding of the river and forming a transition zone ecosystem of oak-hornbeam forest plants. The vegetation found in this strip is very often made up of annual plants, shrubs and trees of different heights and characterized by diversified density. Some of these areas are used for agriculture as pastures and meadows, providing animal feed. On the basis of aerial photographs, maps and studies, significant differences in the way development in the analyzed part of valley is shown. Much smaller growth of shrubs of a complete lack thereof is observed in the areas used for grazing cattle. Despite the favorable conditions (access to water and light), the continuous grazing on vegetation by animals did not develop in a manner threatening the reduction of floodplains bandwidth.
first rewind previous Strona / 3 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.