332 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
The Fermi surface reconstruction in stripe phases of cuprates
Mean-field study of the stripe structures is conducted for a hole-doped
Hubbard model. For bond-directed stripes, the Fermi surface consists of
segments of an open surface and the boundaries of the hole pockets which appear
in the diagonal region of momenta under certain conditions. Segments of the
first type are due to one-dimensional bands of states localized on the domain
walls. The relation of bands to the doping and temperature dependences of the
Hall constant is discussed. In connection with the observation of quantum
magnetic oscillations, a systematic search for the electron pockets has been
carried out. It is shown that the formation of such pockets in bilayer models
is quite possible.Comment: 4 pages, 3 figure
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 influence of mechanochemical modification on prevention of toxic ability of humic acids towards phenanthrene in aquatic environment
Целью работы является количественная оценка взаимодействия фенантрена с модифицированными гуминовыми кислотами в водной среде. Изменение структуры и свойств ГК после модификации было изучено методами ИК-, {1}Н ЯМР - спектроскопии и потенциометрического титрования. Доказано что применение тиомочевины в качестве модифицирующего агента значительно увеличивает связывающую способность гуминовых кислот по отношению к фенантрену
The influence of mechanochemical modification on prevention of toxic ability of humic acids towards phenanthrene in aquatic environment
The aim of the research work is to quantify interaction between phenanthrene with modified humic acids in aquatic environment. The changes in the structure and properties of humic acids after modifications were studied with 1Н NMR spectroscopy and potentiometric titration methods. Our research demonstrates that the application of thiourea as a modified agent increases the binding capacity of humic acids towards phenanthrene
Express method for assessing proteolysis in cheese and aromatic addi- tives with cheese flavor
The method based on the determination of the amount of active amino groups using o-Phthaldialdehyde (OPA method) can be applied in practice to assess accurately the degree of proteolysis in cheeses. The work establishes that the OPA method gives results that strictly correlate (R2 > 0.80, p < 0.01) with the results of assessing the degree of proteolysis by the Kjeldahl method. The results of the OPA method, expressed in the absorption intensity of the colored sample at a wavelength of 340 nm (OD340), can be converted to the content of soluble nitrogenous substances in cheese (WSN), using the calibration relationship between these indicators.The accuracy of the calibration relationship between WSN and OD340 can be increased (R2 > 0.91, p< 0.01) when using the OPA method in relation to a homogeneous group of cheeses produced by the same technology using the same type of milk clotting enzyme and lactic acid starter culture and having a similar shape of the molecular mass distribution of proteolysis products.The OPA method can be used to assess the content of proteolysis products, which form cheese flavor, in EMС. The results of assessing the degree of proteolysis by the OPA method (OD340) are proportional to both the total content of soluble nitrogen and the proportion of nitrogenous substances in it with a mass of less than 0.5 kDa, which make the greatest contribution to the formation of cheese flavor.The advantage of using the OPA method for assessing proteolysis in cheeses and EMC instead of the Kjeldahl method is a simpler measurement procedure and the possibility of studying more samples in less time
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