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https://www.readbyqxmd.com/read/28342572/exploring-the-atomic-structure-of-1-8nm-monolayer-protected-gold-clusters-with-aberration-corrected-stem
#1
Jian Liu, Nan Jian, Isabel Ornelas, Alexander J Pattison, Tanja Lahtinen, Kirsi Salorinne, Hannu Häkkinen, Richard E Palmer
Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au144(SCH2CH2Ph)60 provided by two different research groups...
November 22, 2016: Ultramicroscopy
https://www.readbyqxmd.com/read/28334152/repeated-and-diverse-losses-of-corolla-bilateral-symmetry-in-the-lamiaceae
#2
Jinshun Zhong, Jill C Preston, Lena C Hileman, Elizabeth A Kellogg
Background and Aims: Independent evolution of derived complex characters provides a unique opportunity to assess whether and how similar genetic changes correlate with morphological convergence. Bilaterally symmetrical corollas have evolved multiple times independently from radially symmetrical ancestors and likely represent adaptations to attract specific pollinators. On the other hand, losses of bilateral corolla symmetry have occurred sporadically in various groups, due to either modification of bilaterally symmetrical corollas in late development or early establishment of radial symmetry...
March 1, 2017: Annals of Botany
https://www.readbyqxmd.com/read/28318225/in-plane-anisotropies-of-polarized-raman-response-and-electrical-conductivity-in-layered-tin-selenide
#3
Xiaolong Xu, Qingjun Song, Haifeng Wang, Pan Li, Kun Zhang, Yilun Wang, Kai Yuan, Zichen Yang, Yu Ye, Lun Dai
The group IV-VI compound tin selenide (SnSe) has recently attracted particular interest due to its unexpectedly low thermal conductivity and high power factor, showing great promise for thermoelectric applications. With an orthorhombic lattice structure, SnSe displays intriguing anisotropic properties due to the low symmetry of the puckered in-plane lattice structure. When thermoelectric materials, like SnSe, have decreased dimensionality, their thermoelectric conversion efficiency may be improved due to increased power factor and decreased thermal conductivity...
March 20, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28306294/nonlinear-zel-dovich-effect-parametric-amplification-from-medium-rotation
#4
Daniele Faccio, Ewan M Wright
The interaction of light with rotating media has attracted recent interest for both fundamental and applied studies including rotational Doppler shift measurements. It is also possible to obtain amplification through the scattering of light with orbital angular momentum from a rotating and absorbing cylinder, as proposed by Zel'dovich more than forty years ago. This amplification mechanism has never been observed experimentally yet has connections to other fields such as Penrose superradiance in rotating black holes...
March 3, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28248487/practical-stereochemistry
#5
Richard M Kellogg
The relationship between fundamental and applied is often uneasy, particularly in modern political climates. A familiar political view, aimed negatively at the scientific community, is that the former is a waste of money whereas the latter gives value for investment. The answer that fundamental is required as the basis for practical suffers from the fact that the timelines between fundamental and practical are often long and the routes contorted and unexpected. This has been my experience. In this Account, examples are given from the research in which I have been involved wherein quite fundamental considerations have led to various applications...
March 1, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28240902/organic-cation-rotation-and-immobilization-in-pure-and-mixed-methylammonium-lead-halide-perovskites
#6
Oleg Selig, Aditya Sadhanala, Christian Müller, Robert Lovrincic, Zhuoying Chen, Yves L A Rezus, Jarvist M Frost, Thomas L C Jansen, Artem A Bakulin
Three-dimensional lead-halide perovskites have attracted a lot of attention due to their ability to combine solution processing with outstanding optoelectronic properties. Despite their soft ionic nature these materials demonstrate a surprisingly low level of electronic disorder resulting in sharp band edges and narrow distributions of the electronic energies. Understanding how structural and dynamic disorder impacts the optoelectronic properties of these perovskites is important for many applications. Here we combine ultrafast two-dimensional vibrational spectroscopy and molecular dynamics simulations to study the dynamics of the organic methylammonium (MA) cation orientation in a range of pure and mixed trihalide perovskite materials...
March 9, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28211709/pt-symmetric-real-dirac-fermions-and-semimetals
#7
Y X Zhao, Y Lu
Recently, Weyl fermions have attracted increasing interest in condensed matter physics due to their rich phenomenology originated from their nontrivial monopole charges. Here, we present a theory of real Dirac points that can be understood as real monopoles in momentum space, serving as a real generalization of Weyl fermions with the reality being endowed by the PT symmetry. The real counterparts of topological features of Weyl semimetals, such as Nielsen-Ninomiya no-go theorem, 2D subtopological insulators, and Fermi arcs, are studied in the PT symmetric Dirac semimetals and the underlying reality-dependent topological structures are discussed...
February 3, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28191927/foldectures-3d-molecular-architectures-from-self-assembly-of-peptide-foldamers
#8
Sung Hyun Yoo, Hee-Seung Lee
The wide range of fascinating supramolecular architectures found in nature, from DNA double helices to giant protein shells, inspires researchers to mimic the diverse shapes and functions of natural systems. Thus, a variety of artificial molecular platforms have been developed by assembling DNA-, peptide-, and protein-based building blocks for medicinal and biological applications. There has also been a significant interest in the research of non-natural oligomers (i.e., foldamers) that fold into well-defined secondary structures analogous to those found in proteins, because the assemblies of foldamers are expected not only to form biomimetic supramolecular architectures that resemble those of nature but also to display unique functions and unprecedented topologies at the same time due to their different folding propensities from those of natural building blocks...
February 13, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28185393/kibble-zurek-scaling-during-defect-formation-in-a-nematic-liquid-crystal
#9
Ingo Dierking, Nicholas Fowler
Symmetry breaking phase transitions are often accompanied by the formation of topological defects, like in cosmological theories of the early universe, superfluids, liquid crystals or solid state systems. This scenario is described by the Kibble-Zurek mechanism, which predicts respective scaling laws for the defect density ρ. One such scaling law suggests a relation ρ~tQ-1/2 with tQ the change of rate of a control parameter. In contrast to the scaling of the defect density during annihilation with ρ~t-1, which is governed by the attraction of defects of the same strength but opposite sign, the defect formation process, which depends on the rate of change of a physical quantity initiating the transition, is only very scarcely investigated...
February 10, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/28185330/smectic-layer-origami-via-preprogrammed-photoalignment
#10
Ling-Ling Ma, Ming-Jie Tang, Wei Hu, Ze-Qun Cui, Shi-Jun Ge, Peng Chen, Lu-Jian Chen, Hao Qian, Li-Feng Chi, Yan-Qing Lu
Hierarchical architecture is of vital importance in soft materials. Focal conic domains (FCDs) of smectic liquid crystals, characterized by an ordered lamellar structure, attract intensive attention. Simultaneously tailoring the geometry and clustering characteristics of FCDs remains a challenge. Here, the 3D smectic layer origami via a 2D preprogrammed photoalignment film is accomplished. Full control of hierarchical superstructures is demonstrated, including the domain size, shape, and orientation, and the lattice symmetry of fragmented toric FCDs...
February 10, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28182489/do-capuchin-monkeys-sapajus-apella-prefer-symmetrical-face-shapes
#11
Annika Paukner, Lauren J Wooddell, Carmen E Lefevre, Eric Lonsdorf, Elizabeth Lonsdorf
In humans, facial symmetry has been linked to an individual's genetic quality, and facial symmetry has a small yet significant effect on ratings of facial attractiveness. The same evolutionary processes underlying these phenomena may also convey a selective advantage to symmetrical individuals of other primate species, yet to date, few studies have examined sensitivity to facial symmetry in nonhuman primates. Here we presented images of symmetrical and asymmetrical human and monkey faces to tufted capuchin monkeys (Sapajus apella) and hypothesized that capuchins would visually prefer symmetrical faces of opposite-sex conspecifics...
February 2017: Journal of Comparative Psychology
https://www.readbyqxmd.com/read/28157123/a-three-dimensional-zn-ii-coordination-polymer-constructed-from-1-1-biphenyl-2-2-4-4-tetracarboxylate-and-1-4-bis-1h-imidazol-1-yl-benzene-ligands-exhibiting-photoluminescence
#12
Feng Su, Liping Lu, Chengyong Zhou, Xiaoxia Wang, Long Sun, Chun Han
Ligands based on polycarboxylic acids are excellent building blocks for the construction of coordination polymers; they may bind to a variety of metal ions and form clusters, as well as extended chain or network structures. Among these building blocks, biphenyltetracarboxylic acids (H4bpta) with C2 symmetry have recently attracted attention because of their variable bridging and multidentate chelating modes. The new luminescent three-dimensional coordination polymer poly[(μ5-1,1'-biphenyl-2,2',4,4'-tetracarboxylato)bis[μ2-1,4-bis(1H-imidazol-1-yl)benzene]dizinc(II)], [Zn2(C16H6O8)(C12H10N4)]n, was synthesized solvothermally and characterized by single-crystal X-ray diffraction, elemental analysis and IR spectroscopy...
February 1, 2017: Acta Crystallographica. Section C, Structural Chemistry
https://www.readbyqxmd.com/read/28155897/predictors-of-facial-attractiveness-and-health-in-humans
#13
Yong Zhi Foo, Leigh W Simmons, Gillian Rhodes
Facial attractiveness has been suggested to provide signals of biological quality, particularly health, in humans. The attractive traits that have been implicated as signals of biological quality include sexual dimorphism, symmetry, averageness, adiposity, and carotenoid-based skin colour. In this study, we first provide a comprehensive examination of the traits that predict attractiveness. In men, attractiveness was predicted positively by masculinity, symmetry, averageness, and negatively by adiposity. In women, attractiveness was predicted positively by femininity and negatively by adiposity...
February 3, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28097726/role-of-the-edge-properties-in-hydrogen-evolution-reaction-on-mos2
#14
Petr Lazar, Michal Otyepka
Molybdenum disulfide, in particular its edges, has attracted considerable attention as possible substitute of platinum catalysts for hydrogen evolution reaction. Complex nature of the reaction complicates its detailed experimental investigations, which are mostly indirect and sample dependent. Therefore, we employed density functional theory calculations to study how the properties of MoS2 Mo-edge influence the thermodynamics of hydrogen adsorption onto the edge. We discuss the effect of the computational model (one-dimensional nanostripe), border symmetry imposed by its length, sulfur saturation of the edge, and dimensionality of the material...
January 18, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28081013/magneto-photoluminescence-measurements-of-tungsten-disulphide-monolayers
#15
Jan Kuhnert, Arash Rahimi-Iman, Wolfram Heimbrodt
Layered transition-metal dichalcogenides have attracted great interest in the last few years. Thinned down to the monolayer limit they change from an indirect band structure to a direct band gap in the visible region. Due to the monolayer thickness the inversion symmetry of the crystal is broken and spin and valley are coupled to each other. The degeneracy between the two equivalent valleys, K and K', respectively, can be lifted by applying an external magnetic field. Here, we present photoluminescence measurements of CVD-grown tungsten disulphide (WS2) monolayers at temperatures of 2 K...
March 1, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/28077290/hidden-symmetries-of-dna-molecule
#16
Alexander A Tulub, Vassily E Stefanov
Despite the fact that DNA molecule is studied up and down, we know very little about the role of DNA triplets in coding amino acids and stop-codons. The paper aims to fill this gap through attracting spintronic ideas and carrying out QM/MM computations on a full-turn DNA fragment. The computations reveal two hidden symmetries: the spin splitting (the Rashba effect), confined within each triplet, and the quantum "phase" link between the triplet nature (in total, 64 triplets) and the corresponding amino acid and three stop-codons...
January 8, 2017: Journal of Theoretical Biology
https://www.readbyqxmd.com/read/28005333/spin-orbit-coupling-induced-gap-in-graphene-on-pt-111-with-intercalated-pb-monolayer
#17
Ilya I Klimovskikh, Mikhail M Otrokov, Vladimir Yu Voroshnin, Daria Sostina, Luca Petaccia, Giovanni Di Santo, Sangeeta Thakur, Evgueni V Chulkov, Alexander M Shikin
Graphene is one of the most promising materials for nanoelectronics owing to its unique Dirac cone-like dispersion of the electronic state and high mobility of the charge carriers. However, to facilitate the implementation of the graphene-based devices, an essential change of its electronic structure, a creation of the band gap should controllably be done. Brought about by two fundamentally different mechanisms, a sublattice symmetry breaking or an induced strong spin-orbit interaction, the band gap appearance can drive graphene into a narrow-gap semiconductor or a 2D topological insulator phase, respectively, with both cases being technologically relevant...
January 6, 2017: ACS Nano
https://www.readbyqxmd.com/read/27993004/toward-the-rational-design-of-novel-noncentrosymmetric-materials-factors-influencing-the-framework-structures
#18
Kang Min Ok
Solid-state materials with extended structures have revealed many interesting structure-related characteristics. Among many, materials crystallizing in noncentrosymmetric (NCS) space groups have attracted massive attention attributable to a variety of superb functional properties such as ferroelectricity, pyroelectricity, piezoelectricity, and nonlinear optical (NLO) properties. In fact, the characteristics are pivotal to many industrial applications such as laser systems, optical communications, photolithography, energy harvesting, detectors, and memories...
December 20, 2016: Accounts of Chemical Research
https://www.readbyqxmd.com/read/27966798/chiral-superstructure-mesophases-of-achiral-bent-shaped-molecules-hierarchical-chirality-amplification-and-physical-properties
#19
Khoa V Le, Hideo Takezoe, Fumito Araoka
Chiral mesophases in achiral bent-shaped molecules have attracted particular attention since their discovery in the middle 1990s, not only because of their homochirality and polarity, but also due to their unique physical/physicochemical properties. Here, the most intriguing results in the studies of such symmetry-broken states, mainly helical-nanofilament (HNF) and dark-conglomerate (DC) phases, are reviewed. Firstly, basic information on the typical appearance and optical activity in these phases is introduced...
December 14, 2016: Advanced Materials
https://www.readbyqxmd.com/read/27966756/karyotype-asymmetry-in-cynodon-rich-poaceae-accessions
#20
R B Chiavegatto, C M P Paula, F Souza Sobrinho, F R G Benites, V H Techio
Cynodon is a genus of plants with forage potential that has attracted the interest of breeders. These species have high morphological variability in a large number of varieties and cytotypes, hampering identification. This study aimed to determine the karyotype asymmetry index among accessions of Cynodon to discriminate between them. Karyotype symmetry was based on three estimates, which were compared. The basic number for the genus is x = 9. The results of the chromosome count and DNA quantification, respectively, were as follows: two diploid accessions (2n = 2x = 18 and 1...
December 2, 2016: Genetics and Molecular Research: GMR
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