174 research outputs found
Neutron Diffuse Scattering from Polar Nanoregions in the Relaxor Pb(Mg1/3Nb2/3)O3
We have studied the neutron diffuse scattering in the relaxor PMN. The
diffuse scattering appears around the Burns temperature (~620K), indicating its
origin from the polar nanoregions (PNR). While the relative diffuse intensities
are consistent with previous reports, they are entirely different from those of
the lowest-energy TO phonon. Because of that, it has been considered that this
TO mode could not be the ferroelectric soft mode. Recently, a neutron
scattering study has unambiguously shown that the TO mode does soften on
cooling. If the diffuse scattering in PMN originates from the soft mode
condensation, then the atomic displacements must satisfy the center of mass
condition. But, the atomic displacements determined from diffuse scattering
intensities do not fulfill this condition. To resolve this contradiction, we
propose a simple model in which the total atomic displacement consists of two
components: is created by the soft mode condensation, satisfying
the center of mass condition, and, represents a uniform
displacement of the PNR along their polar direction relative to the surrounding
(unpolarized) cubic matrix. Within this framework, we can successfully describe
the neutron diffuse scattering intensities observed in PMN.Comment: 7 pages, 7 figures (Revised: 11-16-2001
Temperature independent diffuse scattering and elastic lattice deformations in relaxor PbMg1/3Nb2/3O3
The results of diffuse neutron scattering experiment on PbMg1/3Nb2/3O3 single
crystal above the Burns temperature are reported. It is shown that the high
temperature elastic diffuse component is highly anisotropic in low-symmetry
Brillouin zones and this anisotropy can be described using Huang scattering
formalism assuming that the scattering originates from mesoscopic lattice
deformations due to elastic defects. The qualitative agreement between this
model and the experimental data is achieved with simple isotropic defects. It
is demonstrated that weak satellite maxima near the Bragg reflections can be
interpreted as the finite resolution effect.Comment: 7 pages, 7 figure
Clinical symptoms and ECG data in women with acute coronary syndrome
Background. There are many differences in chest pain symptoms between men and women in terms of location, nature, and additional symptoms. The issue of describing the differences in chest pain in men and women with acute coronary syndrome (ACS), as well as their correlation with changes in the electrocardiogram (ECG) and coronary angiography (CAG) remains relevant.Methods. The study included 588 patients of the cardiology department of the Novokuznetsk City Clinical Hospital No. 1 from 2013 to 2017 with a diagnosis of ACS. Depending on the gender, the subjects were divided into two groups: Group I – 330 men; Group II – 258 women.Results. ACS with ST elevation was more common in men (45.8 %) than in women (33.3 %; p = 0.002). There were no pathological ECG changes in women in 58.1 % of cases, in men – in 45.5 % (p < 0.001). ECG type Q/ST elevation was detected more often in men (45.8 %) than in women (33.3 %; p = 0.002). The absence of coronary artery lesions was observed in 27.9 % of men and 44.2 % of women (p < 0.001). Hemodynamically significant coronary artery stenosis was more common in men (57.6 %) than in women (38.7 %; p < 0.001). In a typical angina clinic, hemodynamically significant coronary artery disease in patients with Q/without ST elevation ACS was detected in 40.2 % of men and in 58.5 % of women (p = 0.002). In the atypical angina clinic, hemodynamically significant lesions of coronary artery were more common in men (40.6 %) than in women (34.1 %; p = 0.02).Conclusion. In women atypical chest pains and intact coronary arteries were detected more often than in men, and hemodynamically significant coronary artery stenosis were found less often than in men. In men, a more pronounced pathology of the coronary arteries in ACS was revealed, in women – great difficulties in diagnosing ACS
A Neutron Elastic Diffuse Scattering Study of PMN
We have performed elastic diffuse neutron scattering studies on the relaxor
Pb(MgNb)O (PMN). The measured intensity distribution near a
(100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly
with extended intensity in the (110) and (10) directions. The
temperature dependence of the diffuse scattering shows that both the size of
the polar nanoregions (PNR) and the integrated diffuse intensity increase with
cooling even for temperatures below the Curie temperature K.Comment: Submitted to PR
Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry
The NaNO nanocomposite ferroelectric material in porous glass was
studied by neutron diffraction. For the first time the details of the crystal
structure including positions and anisotropic thermal parameters were
determined for the solid material, embedded in a porous matrix, in ferro- and
paraelectric phases. It is demonstrated that in the ferroelectric phase the
structure is consistent with bulk data but above transition temperature the
giant growth of amplitudes of thermal vibrations is observed, resulting in the
formation of a "premelted state". Such a conclusion is in a good agreement with
the results of dielectric measurements published earlier.Comment: 4 pages, 4 figure
Strong Influence of the diffuse component on the lattice dynamics in Pb(MgNb)O
The temperature and zone dependence of the lattice dynamics in
Pb(MgNb)O is characterized using neutron inelastic
scattering. A strong correlation between the diffuse and phonon scattering is
measured. The lattice dynamics in Brillouin zones where the diffuse scattering
is strong is observed to display qualitatively different behavior than those
zones where the diffuse scattering is weak. In the (220) and (200) zones, where
there is a weak diffuse component, the dynamics are well described by coupled
harmonic oscillators. Compared with SrTiO, the coupling is weak and
isotropic, resulting in only a small transfer of spectral weight from one mode
to another. A comparison of the scattering in these zones to the (110) zone,
where a strong diffuse component is present, reveals a strong coupling of the
diffuse (or central) component to the acoustic mode. We speculate that the
coupling to the central peak is the reason for several recent conflicting
interpretations of the lattice dynamics based on data from zones with a strong
diffuse component.Comment: 7 pages, 7 figure
Coexistence of the Critical Slowing Down and Glassy Freezing in Relaxor Ferroelectrics
We have developed a dynamical model for the dielectric response in relaxor
ferroelectrics which explicitly takes into account the coexistence of the
critical slowing down and glassy freezing. The application of the model to the
experiment in PMN allowed for the reconstruction of the nonequilibrium spin
glass state order parameter and its comparison with the results of recent NMR
experiment (Blinc et al., Phys. Rev. Lett. 83, No. 2 (1999)). It is shown that
the degree of the local freezing is rather small even at temperatures where the
field-cooled permittivity exceeds the frequency dependent permittivity by an
order of magnitude. This observation indicates the significant role of the
critical slowing down (accompanying the glass freezing) in the system dynamics.
Also the theory predicts an important interrelationship between the frequency
dependent permittivity and the zero-field-cooled permittivity, which proved to
be consistent with the experiment in PMN (A. Levstik et. al., Phys. Rev. B 57,
11204 (1998))
Competing orders in PZN-xPT and PMN-xPT relaxor ferroelectrics
Neutron and x-ray scattering studies on relaxor ferroelectric systems
Pb(ZnNb)O (PZN), Pb(MgNb)O (PMN), and
their solid solutions with PbTiO (PT) have shown that inhomogeneities and
disorder play important roles in the materials properties. Although a
long-range polar order can be established at low temperature - sometimes with
the help of an external electric field; short-range local structures called the
``polar nano-regions'' (PNR) still persist. Both the bulk structure and the PNR
have been studied in details. The coexistence and competition of long- and
short-range polar orders and how they affect the structural and dynamical
properties of relaxor materials are discussed.Comment: Article submitted for JPSJ Special Topics (Novel States of Matter
Induced by Frustration
Temperature Sensitive Nanocapsule of Complex Structural Form for Methane Storage
The processes of methane adsorption, storage and desorption by the nanocapsule are investigated with molecular-dynamic modeling method. The specific nanocapsule shape defines its functioning uniqueness: methane is adsorbed under 40 MPa and at normal temperature with further blocking of methane molecules the K@C601+ endohedral complex in the nanocapsule by external electric field, the storage is performed under normal external conditions, and methane desorption is performed at 350 K. The methane content in the nanocapsule during storage reaches 11.09 mass%. The nanocapsule consists of tree parts: storage chamber, junction and blocking chamber. The storage chamber comprises the nanotube (20,20). The blocking chamber is a short nanotube (20,20) with three holes. The junction consists of the nanotube (10,10) and nanotube (8,8); moreover, the nanotube (8,8) is connected with the storage chamber and nanotube (10,10) with the blocking chamber. The blocking chamber is opened and closed by the transfer of the K@C601+ endohedral complex under electrostatic field action
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