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Artykuły w czasopismach na temat "Structural Inversion Symmetry"
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D’Iorio, Matthew, i Ken Dewar. "Replication-associated inversions are the dominant form of bacterial chromosome structural variation". Life Science Alliance 6, nr 1 (19.10.2022): e202201434. http://dx.doi.org/10.26508/lsa.202201434.
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The structural arrangements of bacterial chromosomes vary widely between closely related species and can result in significant phenotypic outcomes. The appearance of large-scale chromosomal inversions that are symmetric relative to markers for the origin of replication (OriC) has been previously observed; however, the overall prevalence of replication-associated structural rearrangements (RASRs) in bacteria and their causal mechanisms are currently unknown. Here, we systematically identify the locations of RASRs in species with multiple complete-sequenced genomes and investigate potential mediating biological mechanisms. We found that 247 of 313 species contained sequences with at least one large (>50 Kb) inversion in their sequence comparisons, and the aggregated inversion distances away from symmetry were normally distributed with a mean of zero. Many inversions that were offset from dnaA were found to be centered on a different marker for theOriC. Instances of flanking repeats provide evidence that breaks formed during the replication process could be repaired to opposing positions. We also found a strong relationship between the later stages of replication and the range in distance variation from symmetry.
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Budzianowski, Armand, i Andrzej Katrusiak. "Coupling of the lactone-ring conformation with crystal symmetry in 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin". Acta Crystallographica Section B Structural Science 58, nr 1 (24.01.2001): 125–33. http://dx.doi.org/10.1107/s0108768101017955.
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Conformational disorder and inversions of the lactone ring induce structural transformations in the crystals of 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin, C14H18O3. The onset of ordering of the lactone ring at 300 K proceeds continuously, changes the space group from P21/m to P21/c and doubles the unit cell; the abrupt inversion of the lactone rings at 225 K changes the crystal translational symmetry in the (010) plane. The mechanism combining the molecular conformation and dynamics with the crystal structure, its symmetry, and phase transitions is presented.
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Kobayashi, Aoi, Yoshiki Takano i Satoshi Demura. "Observation of the Specific Heat Jump in the Se-Substituted MoTe2 Single Crystals". Materials 15, nr 11 (25.05.2022): 3782. http://dx.doi.org/10.3390/ma15113782.
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1T’-MoTe2 has gained considerable attention owing to its topological character. This material undergoes spatial inversion symmetry at 300 K. A structural transition to the Td phase, which is represented by a kink in the resistivity, was observed below 250 K without inversion symmetry along the c-axis, while superconductivity was observed at 0.1 K. Substitution of Se into this material suppressed the appearance of the kink structure and increased the superconducting transition temperature to 2 K, which is consistent with previously reported results on polycrystalline samples. However, a specific heat jump was observed in the obtained single crystals, which did not exhibit kink structures in their resistivity. The results suggest that the Td structure was not suppressed entirely after Se substitution and that superconductivity was achieved without inversion symmetry.
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Norell, Jesper, Raphael M. Jay, Markus Hantschmann, Sebastian Eckert, Meiyuan Guo, Kelly J. Gaffney, Philippe Wernet, Marcus Lundberg, Alexander Föhlisch i Michael Odelius. "Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species". Physical Chemistry Chemical Physics 20, nr 10 (2018): 7243–53. http://dx.doi.org/10.1039/c7cp08326b.
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Krüger, Ekkehard. "Structural Distortion Stabilizing the Antiferromagnetic and Insulating Ground State of NiO". Symmetry 12, nr 1 (26.12.2019): 56. http://dx.doi.org/10.3390/sym12010056.
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We report evidence that the experimentally observed small deformation of antiferromagnetic NiO modifies the symmetry of the crystal in such a way that the antiferromagnetic state becomes an eigenstate of the electronic Hamiltonian. This deformation closely resembles a rhombohedral contraction, but does not possess the perfect symmetry of a trigonal (rhombohedral) space group. We determine the monoclinic base centered magnetic space group of the antiferromagnetic structure within the deformed crystal which is strongly influenced by the time-inversion symmetry of the Hamiltonian. The antiferromagnetic state is evidently stabilized by a nonadiabatic atomic-like motion of the electrons near the Fermi level. This atomic-like motion is characterized by the symmetry of the Bloch functions near the Fermi level and provides in NiO a perfect basis for a Mott insulator in the antiferromagnetic phase.
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Weng, Ze F., W. D. Sam Motherwell i Jacqueline M. Cole. "Tormat: a program for the automated structural alignment of molecular conformations". Journal of Applied Crystallography 41, nr 5 (16.08.2008): 955–57. http://dx.doi.org/10.1107/s002188980802308x.
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A method is described which enables automated superimposition of molecular conformations by the matching of chemical graphs, allowing for topological symmetry in the molecular structure. This algorithm is implemented in the programTormat. The implemented method makes allowance for enantiomer inversion, explicit and implicit treatment of H atoms, and partial structure alignment.
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Nishimura, T., M. Haruta, D. H. Kim, Y. Shiota, H. Iwaki, D. Kan, T. Moriyama, H. Kurata i T. Ono. "Fabrication of Ferrimagnetic Co/Gd/Pt Multilayers with Structural Inversion Symmetry Breaking". Journal of the Magnetics Society of Japan 44, nr 1 (1.01.2020): 9–14. http://dx.doi.org/10.3379/msjmag.2001r002.
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Krüger, Ekkehard, i Horst P. Strunk. "Structural Distortion in Antiferromagnetic BaFe2As2 as a Result of Time-Inversion Symmetry". Journal of Superconductivity and Novel Magnetism 27, nr 2 (27.08.2013): 601–12. http://dx.doi.org/10.1007/s10948-013-2324-z.
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Marković, Igor, Matthew D. Watson, Oliver J. Clark, Federico Mazzola, Edgar Abarca Morales, Chris A. Hooley, Helge Rosner i in. "Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7". Proceedings of the National Academy of Sciences 117, nr 27 (23.06.2020): 15524–29. http://dx.doi.org/10.1073/pnas.2003671117.
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The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure ofCa3Ru2O7, a4doxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spin-reorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.
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Dewangan, Pawan, i Ilya Tsvankin. "Modeling and inversion of PS-wave moveout asymmetry for tilted TI media: Part 2 — Dipping TTI layer". GEOPHYSICS 71, nr 4 (lipiec 2006): D123—D134. http://dx.doi.org/10.1190/1.2210987.
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Dipping transversely isotropic layers with a tilted symmetry axis (TTI media) cause serious imaging problems in fold-and-thrust belts and near salt domes. Here, we apply the modified [Formula: see text] method introduced in Part 1 to the inversion of long-offset PP and PS reflection data for the parameters of a TTI layer with the symmetry axis orthogonal to the bedding. The inversion algorithm combines the time- and offset-asymmetry attributes of the PSV-wave with the hyperbolic PP- and SS-wave moveout in the symmetry-axis plane (i.e., the vertical plane that contains the symmetry axis). The weak-anisotropy approximations for the moveout-asymmetry attributes, verified by numerical analysis, indicate that small-offset (leading) terms do not contain independent information for the inversion. Therefore, the parameter-estimation algorithm relies on PS data recorded at large offsets (the offset-to-depth ratio has to reach at least two), which makes the results generally less stable than those for a horizontal TTI layer in Part1. The least-resolved parameter is Thomsen’s coefficient [Formula: see text]that does not directly influence the moveout of either pure or converted modes. Still, the contribution of the PS-wave asymmetry attributes helps to constrain the TTI model for large tilts [Formula: see text] of the symmetry axis [Formula: see text]. The accuracy of the inversion for large tilts can be improved further by using wide-azimuth PP and PS reflections. With high-quality PS data, the inversion remains feasible for moderate tilts [Formula: see text], but it breaks down for models with smaller values of [Formula: see text] in which the moveout asymmetry is too weak. The tilt itself and several combinations of the medium parameters (e.g., the ratio of the P- and S-wave velocities in the symmetry direction), however, are well constrained for all symmetry-axis orientations. The results of Parts 1 and 2 show that 2D measurements of the PS-wave asymmetry attributes can be used effectively in anisotropic velocity analysis for TTI media. In addition to providing an improved velocity model for imaging beneath TTI beds, our algorithms yield information for lithology discrimination and structural interpretation.
Rozprawy doktorskie na temat "Structural Inversion Symmetry"
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Yoshida, Suguru. "Structure-Property Correlations in Complex Oxides with Broken Inversion Symmetry". Kyoto University, 2020. http://hdl.handle.net/2433/253287.
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Bawden, Lewis. "A spin- and angle-resolved photoemission study of coupled spin-orbital textures driven by global and local inversion symmetry breaking". Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/12049.
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The effect of spin-orbit coupling had once been thought to be a minor perturbation to the low energy band structure that could be ignored. Instead, a surge in recent theoretical and experimental efforts have shown spin-orbit interactions to have significant consequences. The main objective of this thesis is to investigate the role of the orbital sector and crystal symmetries in governing the spin texture in materials that have strong spin- orbit interactions. This can be accessed through a combination of spin- and angle-resolved photoemission spectroscopy (ARPES and spin-ARPES), both of which are powerful techniques for probing the one-electron band structure plus interactions, and supported by density functional theory calculations (DFT). We focus first on a globally inversion asymmetric material, the layered semiconductor BiTeI, which hosts a giant spin-splitting of its bulk bands. We show that these spin-split bands develop a previously undiscovered, momentum-space ordering of the atomic orbitals. We demonstrate this orbital texture to be atomic element specific by exploiting resonant enhancements in ARPES. These orbital textures drive a hierarchy of spin textures that are then tied to the constituent atomic layers. This opens routes to controlling the spin-splitting through manipulation of the atomic orbitals. This is contrasted against a material where inversion symmetry is globally upheld but locally broken within each monolayer of a two layer unit cell. Through our ARPES and spin-ARPES measurements of 2H-NbSe2, we discover the first experimental evidence for a strong out-of-plane spin polarisation that persists up to the Fermi surface in this globally inversion sym- metric material. This is found to be intrinsically linked to the orbital character and dimensionality of the underlying bands. So far, previous theories underpinning this (and related) materials' collective phases assume a spin- degenerate Fermi sea. We therefore expect this spin-polarisation to play a role in determining the underlying mechanism for the charge density wave phase and superconductivity. Through these studies, this thesis then develops the importance of global versus local inversion symmetry breaking and uncovers how this is intricately tied to the underlying atomic orbital configuration.
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Evick, Jason W. "Chamber Symphony No.1(Evick)/ Symmetrical and Structural Features in Sonata No.2, Mvt.1, violin and piano.(Béla Bartók)". Youngstown State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1229115279.
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Lin, Yi-Shiuan, i 林儀玹. "Effect of breaking bulk-inversion symmetry on the quantum spin Hall physics of CdTe/HgTe/CdTe structures". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/20762633581801131542.
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碩士國立交通大學
電子物理系所
101
In this thesis, we consider the effects of the Dresselhaus spin orbital interaction (DSOI), a form of breaking inversion symmetry, on the topological physics of a well known topological structure, namely, the CdTe/HgTe/CdTe quantum well. Related system such as a quantum channel formed out of the above quantum well is also considered. Instead of using model 2D Hamiltonian, and quasi-1D Hamiltonian, for the quantum well and quantum channel, respectively, we have calculated these Hamiltonians from the 3D Kane model. This includes our introduction of the DSOI at the 3D Kane model. Our finding is that the DSOI does not destroy the topological physics (the edge states) but has caused intricate effect on the edge states. This is most evident in the case of a quantum channel, when the edge state, under the effect of the DSOI, is caused to exhibit an edge-switching behavior. Furthermore, in the presence of a potential barrier, the transmission exhibits Fano-type characteristics that can be fine-tuned by the barrier height. There is also a feature of forcing the edge-switching to occur in the immediate vicinity of the transmission region. A detail Fano-type process analysis has been performed to confirm the above finding.
Książki na temat "Structural Inversion Symmetry"
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van der Wal, Jenneke. A Featural Typology of Bantu Agreement. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780198844280.001.0001.
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The Bantu languages are in some sense remarkably uniform (subject, verb, order (SVO) basic word order, noun classes, verbal morphology), but this extensive language family also show a wealth of morphosyntactic variation. Two core areas in which such variation is attested are subject and object agreement. The book explores the variation in Bantu subject and object marking on the basis of data from 75 Bantu languages, discovering striking patterns (the Relation between Asymmetry and Non-Doubling Object Marking (RANDOM), and the Asymmetry Wants Single Object Marking (AWSOM) correlation), and providing a novel syntactic analysis. This analysis takes into account not just phi agreement, but also nominal licensing and information structure. A Person feature, associated with animacy, definiteness, or givenness, is shown to be responsible for differential object agreement, while at the same time accounting for doubling vs. non-doubling object marking—a hybrid solution to an age-old debate in Bantu comparative morphosyntax. It is furthermore proposed that low functional heads can Case-license flexibly downwards or upwards, depending on the relative topicality of the two arguments involved. This accounts for the properties of symmetric object marking in ditransitives (for Appl), and subject inversion constructions (for v). By keeping Agree constant and systematically determining which featural parameters are responsible for the attested variation, the proposed analysis argues for an emergentist view of features and parameters (following Biberauer 2018, 2019), and against both Strong Uniformity and Strong Modularity.
Części książek na temat "Structural Inversion Symmetry"
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"Symmetry in Crystals". W Pharmaceutical Crystallography: A Guide to Structure and Analysis, 28–47. The Royal Society of Chemistry, 2019. http://dx.doi.org/10.1039/bk9781782629665-00028.
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In addition to their inherent translational symmetry, most crystals display other kinds of symmetry. Since a crystal is periodic by translation, a symmetry element such as a rotation axis, mirror plane or inversion centre within a crystal must be repeated at all positions that are equivalent by translation. Hence, these symmetry elements are present as sets distributed regularly through the crystal. Describing the positions of the symmetry elements within the unit cell is an efficient description of the symmetry elements through the entire crystal. It is shown in this chapter how the symmetry operations produce relationships between atomic coordinates, and how this leads to further efficiency in the description of a crystal structure. In addition to point symmetry operations (rotations, mirrors and inversions), space symmetry operations (screws and glides) are introduced.
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"Symmetry in Diffraction Patterns". W Pharmaceutical Crystallography: A Guide to Structure and Analysis, 107–24. The Royal Society of Chemistry, 2019. http://dx.doi.org/10.1039/bk9781782629665-00107.
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Symmetry in the atomic positions within the unit cell leads to symmetry in the intensities of the diffracted beams. The intensity-weighted reciprocal lattice is introduced as a tool to visualise a single-crystal X-ray diffraction pattern. The symmetry of the diffraction pattern is the point symmetry of this object. It comprises the point symmetry parts of all symmetry operations in the space group. Space symmetry operations (screws, glides and centring translations) are distinguished from point symmetry operations by additional systematic intensity absences amongst specific groups of diffracted beams. The combination of the point group of a diffraction pattern and any systematic absences reveals the crystal's space group. Under normal scattering conditions, the diffraction pattern always contains an inversion centre, so I(hkl)=I(h̄k̄l̄). This inversion centre combines with the true point group of the diffraction pattern to give its Laue group, which is usually what is measured. Under conditions where significant anomalous scattering occurs, the true point group can be measured and it is possible to determine the absolute structure (handedness) of a non-centrosymmetric crystal structure. This allows absolute configuration to be determined for chiral API molecules that crystallise in non-centrosymmetric space groups.
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Newnham, Robert E. "Symmetry". W Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0005.
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All single crystals possess translational symmetry, and most possess other symmetry elements as well. In this chapter we describe the 32 crystallographic point groups used for single crystals. The seven Curie groups used for textured polycrystalline materials are enumerated in the next chapter. We live in a three-dimensional world which means that there are basically four kinds of geometric symmetry operations relating one part of this world to another. The four primary types of symmetry are translation, rotation, reflection, and inversion. As pictured in Fig. 3.1, these symmetry operators operate on a point with coordinates Z1, Z2, Z3 and carry it to a new position. By definition, all crystals have a unit cell that is repeated many times in space, a point Z1, Z2, Z3 is repeated over and over again as one unit cell is translated to the next. A mirror plane perpendicular to one of the principal axes is a two-dimensional symmetry element that reverses the sign of one coordinate. Rotation axes are one-dimensional symmetry elements that change two coordinates, while an inversion center is a zero-dimensional point that changes all three coordinates. In developing an understanding of the macroscopic properties of crystals, we recognize that the scale of physical property measurements is much larger than the unit cell dimensions. It is for this reason that we are not concerned about translational symmetry and work with the 32 point group symmetries rather than the 230 space groups. This greatly simplifies the structure–property relationships in crystal physics. Aside from the identity operator 1, there are only four types of rotational symmetry consistent with the translation symmetry common to all crystals. Fig. 3.2 shows why. Parallelograms, equilateral triangles, squares, and hexagons will pack together to fill space but, pentagons symmetry axes are found in crystals. This is the starting point for generating the 32 crystal classes. When taken in combination with mirror planes and inversion centers, these four types of rotation axes are capable of forming 32 self-consistent three-dimensional symmetry patterns around a point. These are the so-called 32 crystal classes or crystallographic point groups.
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"Space Groups". W Pharmaceutical Crystallography: A Guide to Structure and Analysis, 48–67. The Royal Society of Chemistry, 2019. http://dx.doi.org/10.1039/bk9781782629665-00048.
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This chapter describes how the symmetry operations in a crystal combine to form a space group and how the space group provides a general framework to describe a crystal structure. The simplest space group comprises just the three translational symmetry operations of the crystal. Other space groups also include non-translational symmetry operations such as rotations, mirrors, inversions, screws and glides. The requirement for all of the symmetry operations to be consistent with each other, and in particular with the translational periodicity of the crystal, means that the number of possible space group types is limited to exactly 230. The relationships between the symmetry operations and the atomic coordinates are expressed by the general equivalent positions, which provide the information to generate the complete contents of the unit cell from a minimal set of coordinates called the asymmetric unit. Various ways are discussed in which crystals are classified by their symmetry, with an especially important distinction made between centrosymmetric, non-centrosymmetric and chiral space groups.
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Hook, Julian. "Groups II". W Exploring Musical Spaces, 209–51. Oxford University PressNew York, 2023. http://dx.doi.org/10.1093/oso/9780190246013.003.0006.
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Abstract This chapter opens Part Two, devoted to the study of transformation theory, with some additional topics in group theory that arise in musical applications. Transformation groups on finite spaces may be regarded as permutation groups; permutation groups on pitch-class space include not only the groups of transpositions and inversions but also the multiplication group, the affine group, and the symmetric group. Another musical illustration of permutations involves the rearrangement of lines in invertible counterpoint. The structure of a finite group may be represented in the form of a group table or a Cayley diagram (a kind of graph). Other concepts discussed include homomorphisms and isomorphisms of groups, direct-product groups, normal subgroups, and quotient groups. Groups underlie many examples of symmetry in music, as formalized through the study of equivalence relations, orbits, and stabilizers.
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Schwerdtfeger, Peter, i Patricia Hunt. "Symmetry-broken inversion structures for group 15 EX3 halides". W Advances in Molecular Structure Research Volume 5, 223–62. Elsevier, 1999. http://dx.doi.org/10.1016/s1087-3295(99)80008-5.
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"Disorder and Twinning". W Pharmaceutical Crystallography: A Guide to Structure and Analysis, 236–59. The Royal Society of Chemistry, 2019. http://dx.doi.org/10.1039/bk9781782629665-00236.
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Often, crystals deviate to some extent from the idealised description. Disorder breaks the symmetry of the space group at a local level so the structure must be described as an average of local alternatives. In severe cases of disorder, such as solvent molecules occupying several positions and orientations, it may be difficult to produce any sensible atomic model. An alternative approach in that case is solvent-masking, which optimises electron density values on a grid within a defined solvent-accessible volume. Twinning refers to the circumstance where a measured crystal comprises misaligned domains of the same structure. The measured diffraction pattern is an overlay of the diffraction patterns for each domain. Two cases can be identified which impose different practical problems on measurement and processing of X-ray data. Merohedral twinning refers to the circumstance where the diffraction patterns overlap exactly, while non-merohedral twinning refers to non-overlapping diffraction patterns. Inversion twinning is a special case of merohedral twinning which impacts on determination of absolute structure.
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Newnham, Robert E. "Optical activity and enantiomorphism". W Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0032.
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When plane-polarized light enters a crystal it divides into right- and lefthanded circularly polarized waves. If the crystal possesses handedness, the two waves travel with different speeds, and are soon out of phase. On leaving the crystal, the circularly polarized waves recombine to form a plane polarized wave, but with the plane of polarization rotated through an angle αt. The crystal thickness t is in mm, and α is the optical activity coefficient expressed in degrees/mm. The polarization vector of the combined wave can be visualized as a helix, turning α ◦/mm path length in the optically-active medium. Because of the low symmetry of a helix, optical activity is not observed in many high symmetry crystals. Point groups possessing a center of symmetry are inactive. In relating α to crystal chemistry it is convenient to divide optically-active materials into two categories: Those which retain optical activity in liquid form, and those which do not. It has long been known that optically-active solutions crystallize to give optically-active solids. This follows from the fact that molecules lacking mirror or inversion symmetry can never crystallize in a pattern containing such symmetry elements. Thus one way of obtaining optically-active materials is to begin with optically-active molecules, as in Rochelle salt, tartaric acid and cane sugar. Few of these crystals are very stable, however, and the optical activity coefficients are usually small, typically 2◦/mm. The same is true of many inorganic solids, though they are seldom optically active in the liquid state. For NaClO3 and MgSO4·7H2O, α is about 3◦/mm. Quartz and selenium, however, have coefficients an order of magnitude larger, showing the importance of helical structures to optical activity. Both compounds crystallize as right- and left-handed forms in space groups P312 and P322, with helices spiraling around the trigonal screw axes. Quartz contains nearly regular SiO4 tetrahedra with Si–O distances of 1.61 Å. Levorotatory quartz belongs to space group P312 and contains right-handed helices; enantiomorphic dextrorotatory quartz crystallizes in P322. Trigonal selenium also contains helical chains.
Streszczenia konferencji na temat "Structural Inversion Symmetry"
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Ognev, A., A. S. Samardak, A. Samardak, L. Chebotkevich, A. V. Sadovnikov, S. Nikitov, A. Gerasimenko i in. "Interface roughness driven magnetic anisotropy and Dzyaloshinskii- Moriya interaction in thin films with broken structural inversion symmetry." W 2018 IEEE International Magnetic Conference (INTERMAG). IEEE, 2018. http://dx.doi.org/10.1109/intmag.2018.8508625.
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Toemtrisna, Nop, Peter Moroshkin i Jimmy Xu. "Circular Dichroism Induced by Spin Momentum Locking Detected in Optical Rectification". W CLEO: Applications and Technology. Washington, D.C.: Optica Publishing Group, 2023. http://dx.doi.org/10.1364/cleo_at.2023.jw2a.116.
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With an inversion-symmetric structure, circular dichroism is detected in optical rectification. The effect is attributed to symmetry breaking and extrinsic chirality arising from the spin-momentum locking between surface plasmon polariton and the circularly polarized light.
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Czuprynski, Kenneth D., John B. Fahnline i Suzanne M. Shontz. "Parallel Boundary Element Solutions of Block Circulant Linear Systems for Acoustic Radiation Problems With Rotationally Symmetric Boundary Surfaces". W ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ncad2012-0445.
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We propose a distributed parallel algorithm for the solution of block circulant linear systems arising from acoustic radiation problems with rotationally symmetric boundary surfaces. When large structural acoustics problems are solved using a coupling finite element/boundary element formulation, the most time consuming part of the analysis is the solution of the linear system of equations for the boundary element computation. In general, the problem is solved frequency by frequency, and the coefficient matrix for the boundary element analysis is fully populated and exhibits no exploitable structure. This typically limits the number of acoustic degrees of freedom to 10–20 thousand. Because acoustic boundary element calculations require approximately six elements per wavelength to produce accurate solutions, the formation is limited to relatively low frequencies. However, when the outer surface of the structure is rotationally symmetric, the system of linear equations becomes block circulant. Building upon a known inversion formula for block circulant matrices, a parallel algorithm for the efficient solution of linear systems arising from acoustic radiation problems with rotationally symmetric boundary surfaces is developed. We show through a runtime, speedup, and efficiency analysis that the reductions in computation time are significant for an increasing number of processors.
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Li, Shiyao, Guangbo Hao, Yingyue Chen, Jiaxiang Zhu i Giovanni Berselli. "Nonlinear Analysis of a Class of Inversion-Based Compliant Cross-Spring Pivots". W ASME 2021 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/detc2021-69028.
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Abstract This paper presents a nonlinear model of an inversion-based generalized cross-spring pivot (IG-CSP) using the beam constraint model (BCM), which can be employed for the geometric error analysis and the characteristic analysis of an inversion-based symmetric cross-spring pivot (IS-CSP). The load-dependent effects are classified in two ways, including structure load-dependent effects and beam load-dependent effects, where the loading positions, geometric parameters of elastic flexures, and axial forces are the main contributing factors. The closed-form load-rotation relations of an IS-CSP and a non-inversion-based symmetric cross-spring pivot (NIS-CSP) are derived with consideration of the three contributing factors for analyzing the load-dependent effects. The load-dependent effects of IS-CSP and NIS-CSP are compared when the loading position is fixed. The rotational stiffness of the IS-CSP or NIS-CSP can be designed to increase, decrease, or remain constant with axial forces, by regulating the balance between the loading positions and the geometric parameters. The closed-form solution of the center shift of an IS-CSP is derived. The effects of axial forces on the IS-CSP center shift are analyzed and compared with those of a NIS-CSP. Finally, based on the nonlinear analysis results of IS-CSP and NIS-CSP, two new compound symmetric cross-spring pivots are presented and analyzed via analytical and FEA models.
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Sprague, Robert W., i John N. Lee. "Temperature dependence of the linear optical properties of organic thin films of dye-doped PMMA via surface plasmon spectroscopy". W Optical Interference Coatings. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oic.1992.othd15.
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Interest in organic materials for electro-optic device fabrication is due to the large molecular nonlinearities[1], the relative ease of fabrication[2], the ability to tailor the molecular structure through organic synthesis[3] and the potential for very high-speed low power devices[4]. The observation of an electric-field-induced quasi-permanent ordering[5], which eliminates the inversion symmetry and allows second order processes, has led to much work on the parameters which determine the degree[6] and the stability of alignment. This alignment induces a birefringence in the film[7] which is observed as the index perpendicular to the surface of the film via the surface plasmon[8].
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Dai, Junwen, i Ahmed E. Fouda. "APPLICATION OF ELECTROMAGNETIC TECHNOLOGY FOR CORROSION MONITORING IN WELLS WITH DUAL COMPLETIONS". W 2021 SPWLA 62nd Annual Logging Symposium Online. Society of Petrophysicists and Well Log Analysts, 2021. http://dx.doi.org/10.30632/spwla-2021-0017.
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Monitoring the integrity of well casings is vital for oil and gas well management, which can help maintain production levels, reduce maintenance cost, and protect surrounding environment. An electromagnetic pipe inspection tool with multiple transmitter and receiver arrays operating at multiples frequencies was designed to accurately estimate the individual wall thicknesses of up to five nested pipes. Data acquired from this tool was originally processed based on an axis-symmetric forward model to invert for wall thicknesses of individual pipes. Such processing workflow is only applicable to a typical well completion with a single production tubing inside multiple nested casings. However, in a scenario with dual completions, two production tubings are generally installed to produce from more than one production zone. The presence of more than one tubing breaks the axial-symmetry of the completion structure. In this paper, we propose a new workflow to process data from electromagnetic tools for the application of integrity inspection of non-nested tubulars. A yard test with full-scale mockup demonstrates the performance of the tool. The proposed workflow, including data calibration and model-based inversion, can estimate the magnetic permeability and electrical conductivity of the pipes, along with wall thicknesses, and eccentricity of the tubings with respect to the innermost casing. An in-situ calibration method is applied to mitigate interference from one tubing when the tool is logged inside the other tubing. Model-based inversion enables an accurate estimation of the thickness of outer casings along with the eccentricity of the tubings. In addition, a two-dimensional inversion algorithm is shown to provide more accurate assessment of small corrosion spots. In the yard test, a 150 ft-long mockup includes two strings of 2⅞-in. tubings and two outer casings with four machined defects with different sizes. Logging inside each of the tubing strings was performed, and the two logs are processed to obtain the thicknesses of the tubings, outer casings as well as the eccentricity of the tubings. The inversion results reveal that the tool can accurately detect various kinds of defects on outer casings from one single log, even in the presence of a second tubing. The measurements show that the interference from the adjacent tubing is minimal and its impact on the inversion result can be well mitigated by employing the in-situ calibration. The consistent results from two logs run in each tubing string suggests that it is sufficient to run the tool in only one of the tubing strings, if the goal is solely to inspect corrosion in the outer casings. The techniques presented enable pipe integrity monitoring with a single run inside any one of the tubings and without pulling out any pipes. The data processing workflow based on two-dimensional inversion yields more accurate estimation, which provides critical information to significantly improve the efficiency of well intervention operations, therefore minimizing non-productive time and cost.
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Politi, A., G. L. Oppo i R. Badii. "Conservative-Dissipative Behavior of CO2 Laser with Injected Signal". W Instabilities and Dynamics of Lasers and Nonlinear Optical Systems. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/idlnos.1985.fa7.
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Class B lasers1 are described by the so called rate equations for field intensity and population inversion. A suitable nonlinear transformation shows that such equations are fully equivalent to a Toda oscillator with intensity dependent losses2. More precisely, the dissipative terms are proportional to the square root ε = γ η / k of the ratio between the decay rate γ η of population inversion and k of field intensity. In many physical cases (CO2, Nd-Yag etc.) ϵ is ≪1, and the motion, within a first order approximation, is a conservative one. By extending such approximation to the case of an externally injected laser, we obtain a reversible model, that is, a flow invariant the composition of time reversal and a suitable reflection R of coordinates3. Reversibility implies conservativity only with the further assumption that any trajectory is invariant under R-reflection. In particular we have observed that, for critical values of the external amplitude, global symmetry-breaking (SB) transitions occur. More precisely, finite regions in the phase space change their structure from a conservative to a dissipative one. Consequences of these critical phenomena can also be revealed in the original physical system. In fact, the SB yields a stability of the orbit much stronger than that owed to the dissipative terms here neglected.
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Dschung, F., G. Forster, J. Zierhut, J. L. Marqués, J. Schein, R. Haberbosch i B. Guide. "Detailed Analysis of the Plasma Jet of F4 and Delta Torches by Means of Tomography". W ITSC2008, redaktorzy B. R. Marple, M. M. Hyland, Y. C. Lau, C. J. Li, R. S. Lima i G. Montavon. Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH, 2008. http://dx.doi.org/10.31399/asm.cp.itsc2008p0477.
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Abstract One important aspect concerning the coating of surfaces using thermal spray is the improvement of the injection of material particles into the gas jet and thus the deposition efficiency. Therefore a better knowledge of the temperature distribution within the jet is relevant in order to optimize spraying conditions. Particularly interesting is the existence of a well-defined threefold finger structure in the plasma jet produced by triple electrode torches, which allows an efficient injection of coating material due to the existence of zones with higher and lower viscosity. The jet structure, however, lacks rotational symmetry and can therefore not be analyzed by systems relying on the validity of the Abel inversion, thus new systems have to be developed. In this work an innovative tomography device is described that has been designed for this purpose. By circling half around the plasma jet and taking simultaneously intensity images under different view orientations, a three-dimensional intensity distribution of the jet is generated, which can be used to determine the temperature distribution.
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Yoo, S. J. B., M. M. Fejer, R. L. Byer i J. S. Harris. "Second-order optical susceptibilities in asymmetric quantum wells". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/oam.1990.wj6.
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Recently, there have been extensive studies of intersubband transitions. The large oscillator strengths of transitions between subbands of quantum wells1 have led to investigations of their application to lasers, detectors and nonlinear optical devices. In this paper, we discuss the extremely large second order optical susceptibility [χ(2)] predicted and observed2 in structures with inversion symmetry broken through external electric fields or compositional asymmetry. Second order susceptibility of the quantum well system is obtained by solving effective mass Hamiltonian in the conduction band. The large oscillator strengths and relatively narrow linewidths lead one to expect large . Experimental measurements of χ(2) have been obtained for second harmonic generation over the tuning range of CO2 laser in both electric field biased and compositionally asymmetric modulation doped structures, resulting in 28 nm/V and 100 nm/V near resonance, respectively. These are extremely large compared to χ(2)of bulk GaAs, for example, which is 0.38 nm/V at similar wavelengths. In actual frequency conversion devices, the strong absorption at resonance adversely affects efficiency, which ultimately depends on the ratio of χ(2) to absorption. We discuss the design of quantum well devices for large conversion efficiency.
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Herman, W. N., L. M. Hayden, S. Brower, G. A. Lindsay, J. D. Stenger-Smith i R. A. Henry. "A Folded Mainchain NLO Polymer: Optical Properties and Poling Stability". W Organic Thin Films for Photonic Applications. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/otfa.1993.wa.5.
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Nonlinear optical (NLO) organic molecules (chromophores) incorporated into polymers have attracted considerable interest1 for photonics applications due to their fast NLO response time, low cost, ease of fabrication, and large nonlinear second-order electric susceptibility, χ(2). One focus of current research is the enhancement of the thermal and temporal stability of χ(2), which in NLO polymers is dependent on the stability of the Chromophore orientation. This orientation, necessary for the removal of inversion symmetry in order to obtain a nonzero χ(2), can be achieved by electric field poling.2,3 The field is applied at temperatures near or above the glass transition temperature to orient the chromophores and removed only after cooling down to near room temperature. The stability of the resulting order in the thermodynamic nonequilibrium glassy state varies from polymer to polymer. Chemical attachment of the Chromophore to the polymer — as a sidechain,4-6 as part of the main chain,7,8 or in a crosslinked structure8-10 — has been found to retard the relaxation of orientational order.