239 research outputs found
Finite amplitudes helical waves on the surface of the conducting fluid earth core as an example of the self-exciting homopolar heterogeneous dynamo
International audienceHelical waves of the finite amplitude on a surface of the fluid conducting Earth core are examined for generation of the magnetic field. Estimates are made for the differentially rotating cylindrical conducting fluid body, with the helical surface wave structure on its top. This structure is similar to the self-exciting Faraday-disk homopolar heterogeneous dynamo. Estimations of angular velocity and magnetic field magnitude for a polar vortex on the surface of the Earth's liquid outer core gives reasonable numbers and proves this hypothesis to be of value for further detailed analysis. As magnetic field generation by the helical structure is a surface effect, it is possible to find connection between Earth magnetic field fluctuations and fast relief changes on the iron fluid core ? the silicate mantle boundary of the Earth
Modes of magnetic resonance of S=1 dimer chain compound NTENP
The spin dynamics of a quasi one dimensional bond alternating spin-gap
antiferromagnet Ni(CHN)NO(ClO) (abbreviated as NTENP) is
studied by means of electron spin resonance (ESR) technique. Five modes of ESR
transitions are observed and identified: transitions between singlet ground
state and excited triplet states, three modes of transitions between spin
sublevels of collective triplet states and antiferromagnetic resonance
absorption in the field-induced antiferromagnetically ordered phase.
Singlet-triplet and intra-triplet modes demonstrate a doublet structure which
is due to two maxima in the density of magnon states in the low-frequency
range. A joint analysis of the observed spectra and other experimental results
allows to test the applicability of the fermionic and bosonic models. We
conclude that the fermionic approach is more appropriate for the particular
case of NTENP.Comment: 11 pages, 11 figures, published in Phys.Rev.
Magnetic resonance study of the spin-reorientation transitions in the quasi-one-dimensional antiferromagnet BaCu2Si2O7
A quasi-one dimensional antiferromagnet with a strong reduction of the
ordered spin component, BaCu2Si2O7, is studied by the magnetic resonance
technique in a wide field and frequency range. Besides of conventional
spin-flop transition at the magnetic field parallel to the easy axis of spin
ordering, magnetic resonance spectra indicate additional spin-reorientation
transitions in all three principal orientations of magnetic field. At these
additional transitions the spins rotate in the plane perpendicular to the
magnetic field keeping the mutual arrangement of ordered spin components. The
observed magnetic resonance spectra and spin-reorientation phase transitions
are quantitatively described by a model including the anisotropy of transverse
susceptibility with respect to the order parameter orientation. The anisotropy
of the transverse susceptibility and the strong reduction of the anisotropy
energy due to the quantum spin fluctuations are proposed to be the reason of
the spin reorientations which are observed.Comment: RevTeX, 9 pages, 7 figure
DEVELOPING THE METHODS OF FOOD PRESERVATIVES EXTRACTION FROM COMPLEX MATRICES FOR BIOASSAY PURPOSE
The presence of food additives in food products may be associated with the risk of their toxic effects on human body. Therefore, the study of approaches to testing their safety seems to be a particularly urgent task. The aim of this study was to determine the conditions for extracting food preservatives from the samples of preserved pureed vegetables for further bioassay of the extract obtained in the Allium test. Onion roots were used as a test object in this method. Two extraction methods of benzoic and sorbic acids added to pureed vegetables have been developed. Distilled water and acetone were used as extracting solutions. The extraction efficiency was evaluated on Shimadzu Prominence LC-20 liquid chromatograph (Japan) in the ultraviolet range, wavelength 235 nm (benzoic acid), 285 nm (sorbic acid). According to the results of studies using both water and acetone as extractants, the degree of preservatives extraction was approximately the same and quite high. In the quantitative calculation of the preservatives content in pureed vegetables, the value of the correction factor was 0.8. However, due to certain production characteristics of this product, i. e. the stage of cauliflower homogenization, obtaining an extract with acetone seems to be more acceptable for the Allium test conditions.The presence of food additives in food products may be associated with the risk of their toxic effects on human body. Therefore, the study of approaches to testing their safety seems to be a particularly urgent task. The aim of this study was to determine the conditions for extracting food preservatives from the samples of preserved pureed vegetables for further bioassay of the extract obtained in the Allium test. Onion roots were used as a test object in this method. Two extraction methods of benzoic and sorbic acids added to pureed vegetables have been developed. Distilled water and acetone were used as extracting solutions. The extraction efficiency was evaluated on Shimadzu Prominence LC-20 liquid chromatograph (Japan) in the ultraviolet range, wavelength 235 nm (benzoic acid), 285 nm (sorbic acid). According to the results of studies using both water and acetone as extractants, the degree of preservatives extraction was approximately the same and quite high. In the quantitative calculation of the preservatives content in pureed vegetables, the value of the correction factor was 0.8. However, due to certain production characteristics of this product, i. e. the stage of cauliflower homogenization, obtaining an extract with acetone seems to be more acceptable for the Allium test conditions
Electron spin resonance study of anisotropic interactions in a two-dimensional spin gap magnet PHCC
Fine details of the excitation spectrum of the two-dimensional spin-gap
magnet PHCC are revealed by electron spin resonance investigations. The values
of anisotropy parameters and the orientations of the anisotropy axes are
determined by accurate measurements of the angular, frequency-field and
temperature dependences of the resonance absorption. The properties of a
spin-gap magnet in the vicinity of critical field are discussed in terms of
sublevel splittings and g-factor anisotropy.Comment: submitted to PR
Novel magnetic phases in a Gd2Ti2O7 pyrochlore for a field applied along the [100] axis
We report on longitudinal and transverse magnetisation measurements performed
on single crystal samples of Gd2Ti2O7 for a magnetic field applied along the
[100] direction. The measurements reveal the presence of previously unreported
phases in fields below 10 kOe in an addition to the higher-field-induced phases
that are also seen for H//[111], [110], and [112]. The proposed H-T phase
diagram for the [100] direction looks distinctly different from all the other
directions studied previously.Comment: 4 pages, 5 figure
ESR study of the spin ladder with uniform Dzyaloshinskii-Moria interaction
Evolution of the ESR absorption in a strong-leg spin ladder magnet
(CHN)CuBr (abbreviated as DIMPY) is studied from 300K to
400mK. Temperature dependence of the ESR relaxation follows a staircase of
crossovers between different relaxation regimes. We ague that the main
mechanism of ESR line broadening in DIMPY is uniform Dzyaloshinskii-Moria
interaction (K) with an effective longitudinal component along
an exchange bond of Cu ions within the legs resulting from the low crystal
symmetry of DIMPY and nontrivial orbital ordering. The same
Dzyaloshinskii-Moriya interaction results in the lifting of the triplet
excitation degeneracy, revealed through the weak splitting of the ESR
absorption at low temperatures.Comment: 13 pages, submitted to PRB, Fig.3 update
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