405 research outputs found
Giant magnetoimpedance in crystalline Mumetal
We studied giant magnetoimpedance (GMI) effect in commercial crystalline
Mumetal, with the emphasis to sample thickness dependence and annealing
effects. By using appropriate heat treatment one can achieve GMI ratios as high
as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best
GMI characteristics obtained for amorphous and nanocrystalline soft magnetic
materials.Comment: 8 pages, 3 figure
Negative Magnetoresistance in the Nearest-neighbor Hopping Conduction
We propose a size effect which leads to the negative magnetoresistance in
granular metal-insulator materials in which the hopping between two nearest
neighbor clusters is the main transport mechanism. We show that the hopping
probability increases with magnetic field. This is originated from the level
crossing in a few-electron cluster. Thus, the overlap of electronic states of
two neighboring clusters increases, and the negative magnetoresistance is
resulted.Comment: Latex file, no figur
Quantum Size Effect transition in percolating nanocomposite films
We report on unique electronic properties in Fe-SiO2 nanocomposite thin films
in the vicinity of the percolation threshold. The electronic transport is
dominated by quantum corrections to the metallic conduction of the Infinite
Cluster (IC). At low temperature, mesoscopic effects revealed on the
conductivity, Hall effect experiments and low frequency electrical noise
(random telegraph noise and 1/f noise) strongly support the existence of a
temperature-induced Quantum Size Effect (QSE) transition in the metallic
conduction path. Below a critical temperature related to the geometrical
constriction sizes of the IC, the electronic conductivity is mainly governed by
active tunnel conductance across barriers in the metallic network. The high 1/f
noise level and the random telegraph noise are consistently explained by random
potential modulation of the barriers transmittance due to local Coulomb
charges. Our results provide evidence that a lowering of the temperature is
somehow equivalent to a decrease of the metal fraction in the vicinity of the
percolation limit.Comment: 21 pages, 8 figure
Trophic links of the chaffinch (Fringilla coelebs) in transformed forest ecosystems of North-Eastern Ukraine
The сhaffinch (Fringilla coelebs Linnaeus, 1758; Passeriformes, Fringillidae) is one of the most colourful forest species of birds living in Europe, West Asia and North Africa. The diet of this species was studied as a contribution to the conservation of the population of this species in transformed forests of the north-eastern part of Ukraine. Four forest ecosystems were studied: three model sites in oak forests, transformed under intensive recreation pressure, and one model site in a pine-oak forest. A total of 39 invertebrate taxa, dominated by Insecta (93.0%) were found. The orders Coleoptera (32.6%) and Lepidoptera (63.5%) prevailed in the diet of finch nestlings, the highest number of taxa (52.3–76.2%) was represented by phytophages. The phytophagous species also constituted the majority of the consumed prey items (44.0–55.6%). Environmental conditions provided an important effect on the diet structure. The most favourable foraging conditions for the species were found in protected natural areas. According to the analysis, the finch foraging efficiency was similar in all the studied sites. The highest biodiversity indices were found in a protected area of Homilshanski Forests National Nature Park. Results of the research have indicated the crucial role of Fringilla coelebs in the population management of potentially dangerous agricultural pests
Dielectric responses of the layered cobalt oxysulfide Sr_2Cu_2CoO_2S_2 with CoO_2 square-planes
We have studied the dielectric responses of the layered cobalt oxysulfide
SrCuCoOS with the CoO square-planes. With decreasing
temperature below the N\'eel temperature, the resistivity increases like a
semiconductor, and the thermopower decreases like a metal. The dielectric
constant is highly dependent on temperature, and the dielectric relaxation is
systematically changed with temperature, which is strongly correlated to the
magnetic states. These behaviors suggest that carriers distributed
homogeneously in the paramagnetic state at high temperatures are expelled from
the antiferromagnetically ordered spin domain below the N\'eel temperature.Comment: 3 pages, 4 eps figures, to be published in J. Appl. Phy
Structure and distribution of the slope fish community in the vicinity of the sub-Antarctic Prince Edward Archipelago
Demersal fish community structure, distribution and trophic relationships on the slope (depth range 200–1500 m) of the sub-Antarctic Prince Edward Islands and surrounding sea rises were investigated during a pilot survey conducted in April 2001 onboard fishing vessel MV Iris. A total of 56 fish taxa were collected during the survey, of which 44 were identified to the species level, seven to the genus level and five to the family level. Among the identified taxa, 36 constituted new records for the area investigated. Total catch per unit effort (cpue) during the survey ranged from 1•1 to 241•2 individuals h 1. Both average fish diversity and total cpue positively correlated with trawling depth. Overall, mean sampling depth and near-bottom temperature explained 56% of total fish cpue. Hierarchal cluster analysis identified three distinct fish assemblages with pronounced dominant species. Major shifts in fish community composition occurred at 500–600 m and 800–900 m depth strata and could probably be a result of physical and biological vertical zonation. Analysis of the diet of selected fish species showed that they were generalist feeders, consuming predominantly pelagic, including epipelagic, meso- and benthopelagic, prey. Diets of six species and nitrogen stable isotope signatures of 22 species revealed that with a few exceptions most fishes occupied the fourth trophic level and were tertiary consumers. Wide variability in carbon isotopic signatures is discussed with respect to alternative, e.g. possible importance of high Antarctic and chemoautotrophic v. photoautotrophic sub-Antarctic primary production, organic matter sources at the base of deep-sea food webs
Trophic links of the song thrush (Turdus philomelos) in transformed forest ecosystems of North-Eastern Ukraine
The diet spectrum of the song thrush (Turdus philomelos Brehm, 1831; Passeriformes, Turdidae) was studied with the aim of supporting the population of the species in transformed forests of North-Eastern Ukraine. Four forest ecosystems were surveyed: three model sites in oak woodlands with different stages of recreational digression, and the fourth model site in a pine-oak forest. A total of 45 invertebrate taxa with the dominance of Insecta (64.6%, n = 1321), Oligochaеta (16.7%), and Gastropoda (12.0%) were revealed in the diet of the song thrush. At the level of orders, Lepidoptera (66.2%) was dominant. In the qualitative structure of the song thrush nestling diet, the highest number of taxa (40.5–59.1%) was represented by phytophages. Phytophagous species also comprised the majority of the consumed prey items (44.7–80.3%). Environmental conditions are an important factor, affecting the diet composition of birds. The most favourable foraging conditions for the thrushes were revealed in natural protected areas. The analysis has shown a fairly even foraging efficiency of the thrushes in all the studied sites. The highest biodiversity indices were found in a protected area of the National Nature Park “Homilshanski Forests”. The results of the research indicate an important role of T. philomelos in the population management of potentially dangerous agricultural pests
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