scholarly journals Influence of unit cell parameters of tetrachiral mechanical metamaterial on its effective properties

2021 ◽  
Vol 8 (1) ◽  
pp. 150-157
Author(s):  
Linar R. Akhmetshin ◽  
◽  
Igor Yu. Smolin ◽  
◽  
◽  
...  
Keyword(s):  
Rotation Angle ◽  
Effective Properties ◽  
Three Dimensional ◽  
Unit Cell ◽  
The Finite Element Method ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Chiral Structures ◽  
Unit Cells ◽  
Loading Axis

In the paper, we study the mechanical behavior of a three-dimensional chiral mechanical metamaterial using numerical modeling. A feature of chiral structures is that during their uniaxial loading a twisting is observed along the loading axis. A rod of the mechanical metamaterial composed of 3 × 3 × 9 unit cells along the corresponding three orthogonal axes. The relative strain of uniaxial compression of the sample in the simulation did not exceed 3.3%. The simulation was performed by the finite element method in a threedimensional case. Original results on the dependencies of the rotation angle and the reaction of the rigidly fixed support of the metamaterial sample on the parameters characterizing the structure of the unit cell of the metamaterial are presented in this context. All the dependencies, except one, are nonlinear with portions of large and small changes.

Redefinition of satimolite

2018 ◽  
Vol 82 (5) ◽  
pp. 1033-1047 ◽  
Author(s):  
Igor V. Pekov ◽  
Natalia V. Zubkova ◽  
Dmitry A. Ksenofontov ◽  
Nikita V. Chukanov ◽  
Vasiliy O. Yapaskurt ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Rietveld Method ◽  
Three Dimensional ◽  
Direct Methods ◽  
Salt Dome ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Octahedral Clusters

ABSTRACTThe borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal-structure determination, infrared spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R$\bar{3}$m, unit-cell parameters are: a = 15.1431(8), c = 14.4558(14) Å and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, Rwp = 0.0761 and Rall = 0.0667). The structure of satimolite is unique for minerals. It contains 12-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [M7O6(OH)18] with M = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

Systematic crystallographic refinement of triclinic unit cells

1998 ◽  
Vol 13 (1) ◽  
pp. 22-31
Author(s):  
Ludo K. Frevel
Keyword(s):  
Powder Diffraction ◽  
Unit Cell ◽  
Simultaneous Equations ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Triclinic Phase ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Limits Of Error

Combining the exhaustive indexing of triclinic powder diffraction patterns with a crystallographic determination of unit cell parameters from pinacoid and prism reflections yields unit cell parameters with realistic limits of error. Additionally a referee method has been developed by which the six reciprocal cell parameters of a triclinic phase are determined by solving an exhaustive set of linear simultaneous equations in six unknowns.

scholarly journals Synthesis, Crystal structure, Vibrational, Optical and Dielectric properties Of 2-(2-Aminoethyl)-1-methylpyrrolidinum chloride hexachlorobismuthate (III) monohydrate [C7H18N2]2ClBiCl6.H2O

2013 ◽  
Vol 9 (3) ◽  
pp. 2005-2022 ◽  
Author(s):  
Fayçal Ben Tahar ◽  
Chakib Hrizi ◽  
Slaheddine Chaabouni ◽  
Nassira Chniba-Boudjada ◽  
Nicolas Ratel Ramond ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Dielectric Properties ◽  
Room Temperature ◽  
Three Dimensional ◽  
Free Water ◽  
Unit Cell ◽  
Water Molecules ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Vis Spectroscopy

Synthesis, crystal structure, vibrational and dielectric properties of [C7H18N2]2ClBiCl6.H2O are reported. The compound crystallizes at room temperature in the orthorhombic system, space group P212121, with the following unit cell parameters : a = 7.5500(6) Å, b = 18.3780(2) Å, c = 19.8980(13) Å, V = 2760.9(4) Å3 and four molecules per unit cell. The structure has been solved by three-dimensional Patterson synthesis and refined by least-squares analysis (R1 = 0.0463, wR2 = 0.0764). The crystal structure of the title compound, [C7H18N2]2ClBiCl6.H2O consists of 2-(2-Aminoethyl)-1-methylpyrrolidinium cations, [BiCl6]3- anions, Cl- anions and free water molecules. The Bi(III) cation is coordinated by six Cl- anions in slightly distorsed octahedral geometry. In the crystal, extensive intermolecular N-H…Cl hydrogen bonds occur. The charge-transfer (CT) interactions between 2-(2-Aminoethyl)-1-methylpyrrolidinium cation and the anionic hosts have been revealed by structural analysis and UV-vis spectroscopy. The dielectric properties have been investigated at temperature range from 100 to 300 K at various frequencies (1 KHz – 1 MHz). The evolution of dielectric constant as a function of temperature and frequency of pellet has been investigated in order to determine some related parameters.

scholarly journals Synthesis, Crystal structure of hepta (pyridinium) bis (hexachlorobismuthate (III)) nitrate [C5H6N]7(BiCl6)2(NO3)

2013 ◽  
Vol 9 (2) ◽  
pp. 1975-1987
Author(s):  
Ben Tahar Fayçal ◽  
Perez Olivier ◽  
Slaheddine Chaabouni
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Title Compound ◽  
Room Temperature ◽  
Three Dimensional ◽  
Unit Cell ◽  
Unit Cell Parameters ◽  
Monoclinic System ◽  
Cell Parameters ◽  
Dimensional Network

An hepta (pyridinium) bis (hexachlorobismuthate (III)) nitrate, (C5H6N)7(BiCl6)2(NO3) crystallizes at room temperature in the monoclinic system, space group P21/n, with the following unit-cell parameters: a = 9.555(1) Å, b = 16.847(1) Å, c = 32.522(1) Å, β = 94.37° , V = 5219.8 Å3 and four molecules per unit cell. Its crystal structure was determined and refined down to R1 = 0.0504, wR2 = 0.0667. The structure of the title compound, (C5H6N)7(BiCl6)2(NO3) consists of seven monoprotonated pyridinium (C5H6N)+ cations, two independent octahedron [BiCl6]3- and an isolated NO3- anion. These entities are linked together through N-H.....Cl and N-H.....O hydrogen bonds, originating from the (C5H6N)+ groups and the isolated anion of nitrate to forming a three dimensional network.

scholarly journals Macromolecular phasing using diffraction from multiple crystal forms

2021 ◽  
Vol 77 (1) ◽  
pp. 19-35
Author(s):  
Markus Metz ◽  
Romain D. Arnal ◽  
Wolfgang Brehm ◽  
Henry N. Chapman ◽  
Andrew J. Morgan ◽  
...  
Keyword(s):  
Unit Cell ◽  
Macromolecular Crystallography ◽  
Unit Cell Parameters ◽  
Crystal Forms ◽  
Cell Parameters ◽  
Unit Cells ◽  
Group Symmetries ◽  
Iterated Projections ◽  
Molecular Envelope

A phasing algorithm for macromolecular crystallography is proposed that utilizes diffraction data from multiple crystal forms – crystals of the same molecule with different unit-cell packings (different unit-cell parameters or space-group symmetries). The approach is based on the method of iterated projections, starting with no initial phase information. The practicality of the method is demonstrated by simulation using known structures that exist in multiple crystal forms, assuming some information on the molecular envelope and positional relationships between the molecules in the different unit cells. With incorporation of new or existing methods for determination of these parameters, the approach has potential as a method for ab initio phasing.

Interesting Solvent Area in Crystal Structures of Two Natural Ergot Alkaloids

2005 ◽  
Vol 70 (1) ◽  
pp. 41-50 ◽  
Author(s):  
Blanka Klepetářová ◽  
Jan Čejka ◽  
Bohumil Kratochvíl ◽  
Svetlana Pakhomova ◽  
Ivana Císařová ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Three Dimensional ◽  
Ergot Alkaloids ◽  
Unit Cell ◽  
Dimensional Structure ◽  
Chemical Similarity ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Benzene Solvate ◽  
Similarity Structures

The structures of ergotamine bis(benzene) solvate (1) and ergocristine bis(benzene) solvate (2) are reported. Both structures crystallise in theP212121space group with cell parameters:1,a= 14.2968(3) Å,b= 15.4700(2) Å,c= 17.8123(4) Å, andV= 3939.57(13) Å3;2,a= 11.8358(2) Å,b= 17.6469(3) Å,c= 19.7125(3) Å, andV= 4117.25(12) Å3. Unexpectedly, despite the chemical similarity, structures of1and2significantly differ not only in the unit cell parameters, but also in the packing. Whereas in1solvent cavities are separated, there is only one unusual continuous solvent area in2filled with benzene, forming independent three-dimensional structure.

Kinematical and Dynamical CBED Pattern Models: Increasing the Accuracy of the Unit-Cell Parameter Measurements Based on CBED Patterns

1990 ◽  
Vol 48 (2) ◽  
pp. 540-541
Author(s):  
I.N. Yadhikov ◽  
S.K. Maksimov
Keyword(s):  
Reciprocal Lattice ◽  
Unit Cell ◽  
Reciprocal Lattice Vector ◽  
Unit Cell Parameters ◽  
Lattice Vector ◽  
Cell Parameters ◽  
Accuracy Of Measurements ◽  
The Difference ◽  
Image Position ◽  
Convergent Beam

Convergent beam electron diffraction (CBED) is widely used as a microanalysis tool. By the relative position of HOLZ-lines (Higher Order Laue Zone) in CBED-patterns one can determine the unit cell parameters with a high accuracy up to 0.1%. For this purpose, maps of HOLZ-lines are simulated with the help of a computer so that the best matching of maps with experimental CBED-pattern should be reached. In maps, HOLZ-lines are approximated, as a rule, by straight lines. The actual HOLZ-lines, however, are different from the straights. If we decrease accelerating voltage, the difference is increased and, thus, the accuracy of the unit cell parameters determination by the method becomes lower.To improve the accuracy of measurements it is necessary to give up the HOLZ-lines substitution by the straights. According to the kinematical theory a HOLZ-line is merely a fragment of ellipse arc described by the parametric equationwith arc corresponding to change of β parameter from -90° to +90°, wherevector, h - the distance between Laue zones, g - the value of the reciprocal lattice vector, g‖ - the value of the reciprocal lattice vector projection on zero Laue zone.

Sectioned rubisco crystals in TEM

1990 ◽  
Vol 48 (3) ◽  
pp. 664-665
Author(s):  
Gunnel Karlsson ◽  
Jan-Olov Bovin ◽  
Michael Bosma
Keyword(s):  
Plant Cell ◽  
Carbon Fixation ◽  
Unit Cell ◽  
Protein Crystals ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon

RuBisCO (D-ribulose-l,5-biphosphate carboxylase/oxygenase) is the most aboundant enzyme in the plant cell and it catalyses the key carboxylation reaction of photosynthetic carbon fixation, but also the competing oxygenase reaction of photorespiation. In vitro crystallized RuBisCO has been studied earlier but this investigation concerns in vivo existance of RuBisCO crystals in anthers and leaves ofsugarbeets. For the identification of in vivo protein crystals it is important to be able to determinethe unit cell of cytochemically identified crystals in the same image. In order to obtain the best combination of optimal contrast and resolution we have studied different staining and electron accelerating voltages. It is known that embedding and sectioning can cause deformation and obscure the unit cell parameters.

Three Dimensional Structure of UMo8O26: Ordering of U-Vacancies

2002 ◽  
Vol 718 ◽  
Author(s):  
N.D. Zakharov ◽  
P. Werner
Keyword(s):  
Low Temperatures ◽  
Driving Force ◽  
Three Dimensional ◽  
Solid State Reaction Method ◽  
Dimensional Structure ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Edx Microanalysis

AbstractThe structure and composition of UMo8O26 synthesized by solid state reaction method have been investigated by High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction, and EDX microanalysis. The ordering of U vacancies results in considerable enlargement of unit cell parameters: an=6.44 nm, bn=1.45 nm, cn=1.6 nm. It is build up of four layers piled up in c direction. Each following layer is shifted relative to previous one by vector bn/4. Eight hexagonal tunnels in each layer are filled by U atoms, while the eight others are vacant (V). Interaction between U cations and vacancies is driving force for ordering. The variation of stoichiometry can be a reason for appearance of incommensurate modulations in these crystals. It seems plausible that this structure might also exhibit superconductivity at low temperatures.

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