scholarly journals Structural chemistry of layered lead halide perovskites containing single octahedral layers

IUCrJ ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 485-513
Author(s):  
Jason A. McNulty ◽  
Philip Lightfoot
Keyword(s):  
Structural Features ◽  
Structural Chemistry ◽  
Mode Analysis ◽  
Organic Species ◽  
Additional Layer ◽  
Structural Distortions ◽  
Structural Architecture ◽  
And Shifts ◽  
Future Work ◽  
Symmetry Mode

We present a comprehensive review of the structural chemistry of hybrid lead halides of stoichiometry APbX 4, A 2PbX4 or A A′PbX 4, where A and A′ are organic ammonium cations and X = Cl, Br or I. These compounds may be considered as layered perovskites, containing isolated, infinite layers of corner-sharing PbX 4 octahedra separated by the organic species. First, over 250 crystal structures were extracted from the CCDC and classified in terms of unit-cell metrics and crystal symmetry. Symmetry mode analysis was then used to identify the nature of key structural distortions of the [PbX 4]∞ layers. Two generic types of distortion are prevalent in this family: tilting of the octahedral units and shifts of the inorganic layers relative to each other. Although the octahedral tilting modes are well known in the crystallography of purely inorganic perovskites, the additional layer-shift modes are shown to enormously enrich the structural options available in layered hybrid perovskites. Some examples and trends are discussed in more detail in order to show how the nature of the interlayer organic species can influence the overall structural architecture; although the main aim of the paper is to encourage workers in the field to make use of the systematic crystallographic methods used here to further understand and rationalize their own compounds, and perhaps to be able to design-in particular structural features in future work.

Crystal structure and symmetry mode analysis of the threefold superstructure of Cs2ZnI4 at 104 K

1999 ◽  
Vol 214 (10) ◽  
Author(s):  
K. Friese ◽  
B. Neubert ◽  
G. Madariaga ◽  
T. Breczewski
Keyword(s):  
Crystal Structure ◽  
High Temperature Phase ◽  
Mode Analysis ◽  
Temperature Phase ◽  
Coordination Polyhedra ◽  
Structural Distortions ◽  
Crystal Structure And Symmetry ◽  
Average Bond ◽  
Symmetry Mode ◽  
Main Change

AbstractIn this work we determined the structure of CsIn comparison to the high temperature phase the main change consists in shifts of the atoms in the direction ofThe volume of the cell of the threefold phase is slightly smaller than three times the volume of theThe average bond distances and the volume of all A-coordination polyhedra in theSymmetry mode analysis of the structural distortions with respect to the

scholarly journals A hybrid CNN-LSTM model for pre-miRNA classification

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abdulkadir Tasdelen ◽  
Baha Sen
Keyword(s):  
Evaluation Criteria ◽  
Mature Mirnas ◽  
Structural Features ◽  
Linear Discriminant ◽  
Sequential Structure ◽  
Precursor Mirnas ◽  
Lstm Network ◽  
Future Work ◽  
Cumulative Evidence

AbstractmiRNAs (or microRNAs) are small, endogenous, and noncoding RNAs construct of about 22 nucleotides. Cumulative evidence from biological experiments shows that miRNAs play a fundamental and important role in various biological processes. Therefore, the classification of miRNA is a critical problem in computational biology. Due to the short length of mature miRNAs, many researchers are working on precursor miRNAs (pre-miRNAs) with longer sequences and more structural features. Pre-miRNAs can be divided into two groups as mirtrons and canonical miRNAs in terms of biogenesis differences. Compared to mirtrons, canonical miRNAs are more conserved and easier to be identified. Many existing pre-miRNA classification methods rely on manual feature extraction. Moreover, these methods focus on either sequential structure or spatial structure of pre-miRNAs. To overcome the limitations of previous models, we propose a nucleotide-level hybrid deep learning method based on a CNN and LSTM network together. The prediction resulted in 0.943 (%95 CI ± 0.014) accuracy, 0.935 (%95 CI ± 0.016) sensitivity, 0.948 (%95 CI ± 0.029) specificity, 0.925 (%95 CI ± 0.016) F1 Score and 0.880 (%95 CI ± 0.028) Matthews Correlation Coefficient. When compared to the closest results, our proposed method revealed the best results for Acc., F1 Score, MCC. These were 2.51%, 1.00%, and 2.43% higher than the closest ones, respectively. The mean of sensitivity ranked first like Linear Discriminant Analysis. The results indicate that the hybrid CNN and LSTM networks can be employed to achieve better performance for pre-miRNA classification. In future work, we study on investigation of new classification models that deliver better performance in terms of all the evaluation criteria.

Structure Preserving Non-Photorealistic Rendering Framework for Image Abstraction and Stylization of Low-Illuminated and Underexposed Images

2021 ◽  
Vol 11 (2) ◽  
pp. 22-45
Author(s):  
Pavan Kumar ◽  
Poornima B. ◽  
Nagendraswamy H. S. ◽  
Manjunath C.
Keyword(s):  
Structural Features ◽  
Image Features ◽  
Visual Features ◽  
Structure Preserving ◽  
Photorealistic Rendering ◽  
Assessment Techniques ◽  
Contemporary Work ◽  
Image Abstraction ◽  
Future Work ◽  
Background Content

The proposed abstraction framework manipulates the visual-features from low-illuminated and underexposed images while retaining the prominent structural, medium scale details, tonal information, and suppresses the superfluous details like noise, complexity, and irregular gradient. The significant image features are refined at every stage of the work by comprehensively integrating a series of AnshuTMO and NPR filters through rigorous experiments. The work effectively preserves the structural features in the foreground of an image and diminishes the background content of an image. Effectiveness of the work has been validated by conducting experiments on the standard datasets such as Mould, Wang, and many other interesting datasets and the obtained results are compared with similar contemporary work cited in the literature. In addition, user visual feedback and the quality assessment techniques were used to evaluate the work. Image abstraction and stylization applications, constraints, challenges, and future work in the fields of NPR domain are also envisaged in this paper.

scholarly journals A survey of PbZrxTi1−xO3structural models using symmetry mode analysis

2013 ◽  
Vol 69 (a1) ◽  
pp. s485-s485
Author(s):  
Balazs Kocsis ◽  
J. M. Perez-Mato ◽  
E. Tasci ◽  
M. I. Aroyo ◽  
G. de la Flor
Keyword(s):  
Mode Analysis ◽  
Symmetry Mode

scholarly journals Switchable Rashba anisotropy in layered hybrid organic–inorganic perovskite by hybrid improper ferroelectricity

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Fei Wang ◽  
Heng Gao ◽  
Coen de Graaf ◽  
Josep M. Poblet ◽  
Branton J. Campbell ◽  
...  
Keyword(s):  
Optoelectronic Devices ◽  
Mode Analysis ◽  
Inversion Symmetry ◽  
Photovoltaic Materials ◽  
Model Hamiltonian ◽  
Experimental Values ◽  
Spin Orbit Interactions ◽  
Spin Texture ◽  
Symmetry Mode ◽  
Striking Effect

AbstractHybrid organic–inorganic perovskites (HOIPs) are introducing exotic directions in the photovoltaic materials landscape. The coexistence of inversion symmetry breaking and spin–orbit interactions play a key role in their optoelectronic properties. We perform a detailed study on a recently synthesized ferroelectric layered HOIP, (AMP)PbI4 (AMP = 4-aminomethyl-piperidinium). The calculated polarization and Rashba parameters are in excellent agreement with experimental values. Moreover, we report a striking effect, i.e., an extraordinarily large Rashba anisotropy that is tunable by ferroelectric polarization: as polarization is reversed, not only the spin texture chirality is inverted, but also the major and minor axes of the Rashba anisotropy ellipse in k-space are interchanged—a pseudo rotation. A k·p model Hamiltonian and symmetry-mode analysis reveal a quadrilinear coupling between the cation-rotation modes responsible for the Rashba ellipse pseudo-rotation, the framework rotation, and the polarization. These findings may provide different avenues for spin-optoelectronic devices such as spin valves or spin FETs.

A crystallographic approach to symmetry-mode analysis of phase transitions

1997 ◽  
Vol 63 (1-4) ◽  
pp. 235-255 ◽  
Author(s):  
M. I. Aroyo ◽  
J. M. Perez-mato
Keyword(s):  
Phase Transitions ◽  
Mode Analysis ◽  
Symmetry Mode

SYNOPSIS OF THE NEOTROPICAL GENUS OZAENA OLIVIER: CLASSIFICATION AND RECONSTRUCTED EVOLUTIONARY HISTORY (COLEOPTERA: CARABIDAE: OZAENINI)

1990 ◽  
Vol 122 (5) ◽  
pp. 779-815 ◽  
Author(s):  
George E. Ball ◽  
Danny Shpeley
Keyword(s):  
South America ◽  
Sister Group ◽  
Structural Features ◽  
Character Evolution ◽  
Type Locality ◽  
Sister Taxon ◽  
Fore Tibia ◽  
Sensilla Basiconica ◽  
Extant Species ◽  
And Shifts

AbstractDescriptions and illustrations of structural features of adults, a key, and chorological data provide the basis for characterizing the genus Ozaena Olivier and classifying the 10 included species, two of which are new: O. maxi (type locality: Iracubo, CAYENNE), and O. manu (type locality: Manu National Park, Madre de Dios Province, PERU). With a geographical range that extends from ca. 30°S to 30°N in the New World, all species of Ozaena occur in cis-Andean South America, only two ranging farther north: O. dentipes Olivier, to Panama; and O. lemoulti Bänninger to southern Arizona, USA. A reconstructed phylogeny postulates the following: the genus Platycerozaena Bänninger as the sister-group of Ozaena, together these genera comprising the Ozaena genus-group; within Ozaena, the O. dentipes group as sister-taxon of the O. lemoulti + convexa groups; within the O. dentipes group, O. maxi as sister-taxon of O. linearis Bänninger + dentipes; within the O. lemoulti group, the sequence O. ecuadorica Bänn. (O. elavata Bänn. [O. lemoulti + martinezi Ogueta]); and within the O. convexa group, O. grossa Bänn. as sister-taxon of O. convexa Bänn. + manu. Character evolution involves losses, gains, and shifts, in about equal numbers. Convergence is relatively rare, involving only three of 35 characters. The predominant mode of character evolution is simple, with few examples of sequential changes sustained through several speciation events. Basic modifications in evolution of the ground-plan of the Ozaena genus-group include reduction or loss (for example, tactile sense organs, antennal cleaner of the fore tibia, and adhesive vestiture of the male fore tarsi), and enhancement or gain (for example, scale-like sensilla basiconica on pronotum and elytra, concentration of sensilla basiconica in groups on the antennomeres, particularly antennomere 11). Within Ozaena, many modifications to the antennae and mouthparts indicate the importance of these organs to evolution of the group.Based on phylogenetic relationships and the distribution pattern of the extant species, a reconstructed geographical history of Ozaena postulates the following: first, a vicariance event in South America separating the ancestral stock of Ozaena into a northern vicar that gave rise to the O. dentipes group, and a southern vicar that gave rise to the O. lemoulti and convexa groups; followed by cycles of range expansion and contraction that allowed for differentiation of successive stocks of species. The temporal range for these speciation events is estimated to extend over a period of about 12 million years, or from the latter part of the Miocene epoch to the Recent. The most recent speciation events are estimated to be of Pliocene age.Based on lack of differentiation of South American and Middle American representatives of O. dentipes and O. lemoulti respectively, and extent of range in Middle America, these two species are postulated to be relatively recent invaders of the latter area, with O. dentipes being the more recent to arrive.

scholarly journals On-line symmetry-mode analysis of any ferroic structure

2008 ◽  
Vol 64 (a1) ◽  
pp. C527-C528
Author(s):  
J.M. Perez-Mato ◽  
D. Orobengoa ◽  
M.I. Aroyo
Keyword(s):  
Mode Analysis ◽  
On Line ◽  
Symmetry Mode

scholarly journals Discovery Sulfoglycomics and Identification of the Characteristic Fragment Ions for High-Sensitivity Precise Mapping of Adult Zebrafish Brain–Specific Glycotopes

2021 ◽  
Vol 8 ◽  
Author(s):  
Huan-Chuan Tseng ◽  
Cheng-Te Hsiao ◽  
Nao Yamakawa ◽  
Yann Guérardel ◽  
Kay-Hooi Khoo
Keyword(s):  
Full Range ◽  
High Sensitivity ◽  
Structural Features ◽  
Mode Analysis ◽  
Adult Zebrafish ◽  
Organ Specific ◽  
Vertebrate Model ◽  
Functional Relevance ◽  
Diagnostic Ions ◽  
The Brain

Mass spectrometry–based high-sensitivity mapping of terminal glycotopes relies on diagnostic MS2 and/or MS3 ions that can differentiate linkage and define the location of substituents including sulfates. Unambiguous identification of adult zebrafish glycotopes is particularly challenging due to the presence of extra β4-galactosylation on the basic building block of Galβ1-4GlcNAc that can be fucosylated and variably sialylated by N-acetyl, N-glycolyl, or deaminated neuraminic acids. Building on previous groundwork that have identified various organ-specific N- and O-glycans of adult zebrafish, we show here that all the major glycotopes of interest can be readily mapped by direct nano-LC-MS/MS analysis of permethylated glycans. Homing in on the brain-, intestine-, and ovary-derived samples, organ-specific glycomic reference maps based on overlaid extracted ion chromatograms of resolved glycan species, and composite charts of summed intensities of diagnostic MS2 ions representing the distribution and relative abundance of each of the glycotopes and sialic acid variants were established. Moreover, switching to negative mode analysis of sample fractions enriched in negatively charged glycans, we show, for the first time, that a full range of sulfated glycotopes is expressed in adult zebrafish. In particular, 3-O-sulfation of terminal Gal was commonly found, whereas terminal sulfated HexNAc as in GalNAcβ1-4GlcNAc (LacdiNAc), and 3-O-sulfated hexuronic acid as in HNK-1 epitope (SO3-3GlcAβ1-3Galβ1-4GlcNAc) were identified only in the brain and not in the intestine or ovaries analyzed in parallel. Other characteristic structural features of sulfated O- and N-glycans along with their diagnostic ions detected in this discovery mode sulfoglycomic work collectively expand our adult zebrafish glycome atlas, which can now allow for a more complete navigation and probing of the underlying sulfotransferases and glycosyltransferases, in search of the functional relevance of zebrafish-specific glycotopes. Of particular importance is the knowledge of glycomic features distinct from those of humans when using adult zebrafish as an alternative vertebrate model, rather than mouse, for brain-related glyco-neurobiology studies.

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