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1.
A. P. Dudka 《Crystallography Reports》2008,53(2):351-355
The methods of automation of the procedure for crystal structure model refinement from experimental diffraction data, implemented in the ASTRA program package, are described. Such tools as statistical tests, parameter scanning, and data scanning reduce the time necessary for structural investigation. At strong correlations between parameters, especially when the data set is limited, parameter scanning has an advantage over the full-matrix refinement. 相似文献
2.
Rastsvetaeva R. K. Chukanov N. V. Möckel S. Dudka A. P. Aksenov S. M. 《Crystallography Reports》2020,65(1):27-32
Crystallography Reports - The crystal structure of a high-symmetry representative of the eudialyte group from the Norra Kärr massif (Sweden) has been investigated by X-ray diffraction analysis... 相似文献
3.
Sizova N. L. Golovina T. G. Konstantinova A. F. Dudka A. P. 《Crystallography Reports》2021,66(6):1045-1050
Crystallography Reports - The anisotropy of microhardness and fracture of the (0001) basal plane of langasite crystal has been studied using Berkovich indentation under a load of 100 g at different... 相似文献
4.
A. P. Dudka 《Crystallography Reports》2018,63(2):172-177
An accurate structure analysis of a Ba3TaGa3Si2O14 single crystal from langasite family was performed using four X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector (sp. gr. P321, Z = 1, sinθ/λ ≤ 1.35 Å–1; at 295 K a = 8.516(1) Å, c = 5.1910(6) Å, R/wR = 0.58/0.56%, Δρmin/Δρmax =–0.73/0.42 e/Å3, 4414 independent reflections; at 106 K a = 8.5109(9) Å, c = 5.1861(9) Å, R/wR = 0.75/0.86%, Δρmin/Δρmax =–0.81/1.06 e/Å3, 4382 reflections). The distinguishing feature of the Ba3TaGa3Si2O14 structure is a strong disorder of the Ga atom at the 3f site. Structural transformations in the series of Сa3TaGa3Si2O14–Sr3TaGa3Si2O14–Ba3TaGa3Si2O14–Ba3TaFe3Si2O14 crystals were analyzed. 相似文献
5.
A. P. Dudka 《Crystallography Reports》2007,52(4):749-754
A program for the refinement of the model of aspherical atoms within the Stewart-Hansen-Coppens formalism has been developed. Deformation scattering up to the 8th expansion order in multipoles has been taken into account for the first time. The program was tested for 11 crystals. The effect of the result of interpolation of radial scattering curves on the model parameters is considered. The importance of introduction of multipoles of high (5th–8th) orders into the model for a number of crystals is shown. The use of the extended multipole model for a silicon crystal revealed some new specific features of the electronic structure: consideration of multipoles up to the 7th order makes it possible to explain the intensity of the forbidden 222 reflection. 相似文献
6.
A. P. Dudka I. A. Verin V. N. Molchanov M. K. Blomberg O. A. Alekseeva N. I. Sorokina N. E. Novikova V. I. Simonov 《Crystallography Reports》2005,50(1):36-41
The structure of a K0.93Ti0.93Nb0.07OPO4 single crystal is studied at the temperature 30 K. The measurements are performed on a four-circle HUBER-5042 diffractometer with a DISPLEX DE-202 cryostat. Processing of the diffraction data and the preliminary refinement of the model are performed using the ASTRA program package. The final refinement of the structure model is made using the JANA2000 program complex. The refinement shows that the structure of a K0.93Ti0.93Nb0.07OPO4 crystal at T = 30 K is similar to its structure at room temperature. No phase transitions are revealed. Slight temperature-induced displacements of the potassium positions in the large cavities of the mixed framework are established. 相似文献
7.
E. S. Smirnova O. A. Alekseeva A. P. Dudka I. A. Verin V. V. Artemov L. N. Bezmaternykh I. A. Gudim K. V. Frolov I. S. Lyubutin 《Crystallography Reports》2016,61(4):558-565
The structure of GdFe3(BO3)4 single crystals has been studied by X-ray diffraction at 293 and 90 K. The crystals are grown from a flux in the Bi2Mo3O12–B2O3–Li2MoO4–Gd2O3–Fe2O3 system. The results of chemical analysis and structural study show that these crystals contain bismuth as an impurity. It is found that bismuth atoms are located at gadolinium sites in the structure. A decrease in the temperature is accompanied by a lowering of the symmetry from sp. gr. R32 (at 293 K) to sp. gr. P3121 (at 90 K). The presence of two types of iron chains with different geometries at 90 K promotes a change in the magnetic properties of these crystals with a decrease in the temperature. 相似文献
8.
The accumulation of amyloid plaques, or misfolded fragments of proteins, leads to the development of a condition known as amyloidosis, which is clinically recognized as a systemic disease. Amyloidosis plays a special role in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease, and rheumatoid arthritis (RA). The occurrence of amyloidosis correlates with the aging process of the organism, and since nowadays, old age is determined by the comfort of functioning and the elimination of unpleasant disease symptoms in the elderly, exposure to this subject is justified. In Alzheimer’s disease, amyloid plaques negatively affect glutaminergic and cholinergic transmission and loss of sympathetic protein, while in RA, amyloids stimulated by the activity of the immune system affect the degradation of the osteoarticular bond. The following monograph draws attention to the over-reactivity of the immune system in AD and RA, describes the functionality of the blood–brain barrier as an intermediary medium between RA and AD, and indicates the direction of research to date, focusing on determining the relationship and the cause–effect link between these disorders. The paper presents possible directions for the treatment of amyloidosis, with particular emphasis on innovative therapies. 相似文献
9.
An accurate X-ray diffraction study of a Nd3Ga5SiO14 crystal (sp. gr. P321, Z = 1) has been performed using repeated X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector at 295 and 90 K. The asymmetry of the disorder in the atomic positions in Nd3Ga5SiO14 is described in two alternative ways: in terms of anharmonic atomic displacements (at 295 K R/wR = 0.80/0.92%; at 90 K R/wR = 0.82/0.76%) and using a split model (at 295 K R/wR = 0.85/0.97%; at 90 K R/wR = 0.80/0.74%). An analysis of the probability density function of finding an atom at a particular point in space shows that most of the atoms in the unit cell are asymmetrically or highly anisotropically disordered in the vicinity of their sites. Electron density regions for cations and anions that form pseudohelices were found. Such regions mimic a screw axis of symmetry and are responsible for the chirality of the structure. 相似文献
10.
An accurate X-ray diffraction study of Sr3TaGa3Si2O14 (STGS) crystal (a = 8.3023(10) Å, c = 5.0853(2) Å, sp. gr. P321, Z = 1, R/wR = 0.59/0.52%, 4004 independent reflections) is performed. The use of two independent data sets obtained on diffractometers with point and 2D detectors made it possible to determine the model structure characterized by the best reproducibility of parameters. The ordered distribution of atoms over crystallographic positions and the anharmonic character of displacements of all cations and one oxygen atom are established. 相似文献