245 research outputs found
Proton configurations in the hydrogen bonds of KH2PO4 as seen by resonant x-ray diffraction
KH2PO4 (KDP) belongs to the class of hydrogen-bonded ferroelectrics, whose
paraelectric to ferroelectric phase transition is driven by the ordering of the
protons in the hydrogen bonds. We demonstrate that forbidden reflections of
KDP, when measured at an x-ray absorption edge, are highly sensitive to the
asymmetry of proton configurations. The change of average symmetry caused by
the "freezing" of the protons during the phase transition is clearly evidenced.
In the paraelectric phase, we identify in the resonant spectra of the forbidden
reflections a contribution related to the transient proton configurations in
the hydrogen bonds, which violates the high average symmetry of the sites of
the resonant atoms. The analysis of the temperature dependence reveals a change
of relative probabilities of the different proton configurations. They follow
the Arrhenius law, and the activation energies of polar and Slater
configurations are 18.6 and 7.3 meV, respectively
An X-ray study of the Dzyaloshinskii-Moriya interaction in the weak ferromagnet FeBO3
International audienceWe report on the axis, magnitude and direction of the Dzyaloshinskii-Moriya (DM) interaction in the weak ferromagnet FeBO3. The latter relies on the determination of the phase of the magnetic x-ray scattering amplitude. We outline a new technique based on interference with forbidden quadrupole resonant scattering to obtain this phase information
Phase transition of KDP observed by Resonant X-ray Diffraction at forbidden reflections
International audienceWe report observations of space-group-forbidden Bragg reflections in Potassium (KH2PO4), at the potassium K edge. We find clear evidence for a transition from one class of space-group-forbidden reflections, where scattering is ruled out by the electric dipole approximation, to a second class, in the ferroelectric phase, where scattering can proceed due to resonant anisotropy within the dipole approximation. The change of symmetry is clearly evidenced by the sudden change of intensity and energy spectrum of the forbidden reflections
The formation of strategies for effective management of business environment of the region
This study is aimed to explore the opportunities of creating conditions which is necessary for successful development of small and medium enterprises of Russia and the Belgorod region in particular in the chemical industry of leather and footwear sector. The system of criteria for the assessment of the entrepreneurial activity of small and medium enterprises is proposed. The directions of development of small and medium enterprises in the chemical industry of leather and footwear sector are designedyesБелгородский государственный университе
Influence of spin structures and nesting on Fermi surface and a pseudogap anisotropy in t-t'-U Hubbard model
Influence of two type of spin structures on the form of the Fermi surface
(FS) and a photoemission intensity map is studied for t-t'-U Hubbard model.
Mean field calculations are done for the stripe phase and for the spiral spin
structure. It is shown, that unlike a case of electron doping, the hole-doped
models are unstable with respect to formation of such structures. The pseudogap
anisotropies are different for h- and e- doping. In accordance with ARPES data
for La2SrxCuO4 the stripe phase is characterized by quasi-one-dimensional
segments of FS at k=(\pi,0) and by suppression of spectral weight in diagonal
direction. It is shown that spiral structures display the polarisation
anisotropy: different segments of FS correspond to electros with different spin
polarisations.Comment: 12 pages, 4 figure
Inhibition of mutagenic activation of orthoaminoazotoluene increases its carcinogenicity for mouse liver
Various mutationally impaired genes are often found in malignant tumors of animals and humans. At the same time, a large number of carcinogens demonstrate positive activity in different in vitro tests for mutagenicity. These findings are indicative of a geno- toxic mechanism of carcinogen action. It is considered that chemically active carcinogens induce mutations (and tumors) directly interacting with DNA, while inactive substances are mutagenically activated in the processes of cellular metabolism in target tissues. The aminoazo dyes was found to be activated by N-hydroxilation and subsequent conjugation with sulfuric acid catalyzed by the enzyme sulfotransferase. Previously we found that it is activated metabolites of ortho-aminoazotoluene that are responsible for its inhibitory effect on hormonal induction of tyrosinaminotransferase activity in the liver of sensitive mice. Inhibition of sulfoconjugation of 4-aminoazobenzene, another hepatocarcinogen for mice, by pentaclorophenol was reported to reduce its both mutagenic and carcinogenic activity. In this paper, we confirmed this observation. But we found that, when used ortho-aminoazotoluene, pentaclorophenol inhibited its mutagenic activity, but significantly stimulated the hepatocarcinogenic potency. It seems that carcinogenic action is provoked by unmetabolysed ortho-aminoazotoluene per se or some of its nonsulfated derivatives. The results of our comparative study with ortho-aminoazotoluene and 3.4-benzopyrene are in contradiction with the genotoxic theory of carcinogenesis: both are similarly activated by mouse liver enzymes, but induce tumors in different tissues: the former, hepatocellular carcinomas and the latter, splenic lymphoma. The conclusion was made that the accepted notion about the mechanism of carcinogenesis has to be revised
Formation of ultracold RbCs molecules by photoassociation
The formation of ultracold metastable RbCs molecules is observed in a double
species magneto-optical trap through photoassociation below the
^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous
emission. The molecules are detected by resonance enhanced two-photon
ionization. Using accurate quantum chemistry calculations of the potential
energy curves and transition dipole moment, we interpret the observed
photoassociation process as occurring at short internuclear distance, in
contrast with most previous cold atom photoassociation studies. The vibrational
levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^-
electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation
limit. The computed vibrational distribution of the produced molecules shows
that they are stabilized in deeply bound vibrational states of the lowest
triplet state. We also predict that a noticeable fraction of molecules is
produced in the lowest level of the electronic ground state
Satellite holmium M-edge spectra from the magnetic phase via resonant x-ray scattering
Developing an expression of resonant x-ray scattering (RXS) amplitude which
is convenient for investigating the contributions from the higher rank tensor
on the basis of a localized electron picture, we analyze the RXS spectra from
the magnetic phases of Ho near the absorption edges. At the
edge in the uniform helical phase, the calculated spectra of the absorption
coefficient, the RXS intensities at the first and second satellite spots
capture the properties the experimental data possess, such as the spectral
shapes and the peak positions. This demonstrates the plausibility of the
adoption of the localized picture in this material and the effectiveness of the
spectral shape analysis. The latter point is markedly valuable since the
azimuthal angle dependence, which is one of the most useful informations RXS
can provides, is lacking in the experimental conditions. Then, by focusing on
the temperature dependence of the spectral shape at the second satellite spot,
we expect that the spectrum is the contribution of the pure rank two profile in
the uniform helical and the conical phases while that is dominated by the rank
one profile in the intermediate temperature phase, so-called spin slip phase.
The change of the spectral shape as a function of temperature indicates a
direct evidence of the change of magnetic structures undergoing. Furthermore,
we predict that the intensity, which is the same order observed at the second
satellite spot, is expected at the fourth satellite spot from the conical phase
in the electric dipolar transition.Comment: 24 pages, 5 figure
Dzyaloshinskii--Moriya interaction: How to measure its sign in weak ferromagnetics?
Three experimental techniques sensitive to the sign of the
Dzyaloshinskii--Moriya interaction are discussed: neutron diffraction,
Moessbauer gamma-ray diffraction, and resonant x-ray scattering. Classical
examples of hematite (alpha-Fe2O3) and MnCO3 crystals are considered in detailComment: 5 pages, 1 figure; to be published in JETP Letter
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