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lattice degeneration

San-Dong Guo, Peng Chen
Topological semimetals are currently attracting increasing interest due to their potential applications in topological qubits and low-power electronics, which are closely related to their thermal transport properties. Recently, the triply degenerate nodal points near the Fermi level of WC are observed by using angle-resolved photoemission spectroscopy. In this work, by solving the Boltzmann transport equation based on first-principles calculations, we systematically investigate the phonon transport properties of topological semimetals WC and WN...
April 14, 2018: Journal of Chemical Physics
Franck Pichaud
The fly photoreceptor has long been used as a model to study sensory neuron morphogenesis and retinal degeneration. In particular, elucidating how these cells are built continues to help further our understanding of the mechanisms of polarized cell morphogenesis, intracellular trafficking and the causes of human retinal pathologies. The conserved PAR complex, which in flies consists of Cdc42-PAR6-aPKC-Bazooka, and the transmembrane protein Crumbs (Crb) are key players during photoreceptor morphogenesis. While the PAR complex regulates polarity in many cell types, Crb function in polarity is relatively specific to epithelial cells...
2018: Frontiers in Cellular Neuroscience
Guangqian Ding, Cong Wang, Guoying Gao, Kailun Yao, Chaochao Dun, Chunbao Feng, Dengfeng Li, Gang Zhang
High band degeneracy and glassy phonon transport are two remarkable features of highly efficient thermoelectric (TE) materials. The former promotes the power factor, while the latter aims to break the lower limit of lattice thermal conductivity through phonon scattering. Herein, we use the unique possibility offered by a two-dimensional superlattice-monolayer structure (SLM) to engineer the band degeneracy, charge density and phonon spectrum to maximize the thermoelectric figure of merit (ZT). First-principles calculations with Boltzmann transport equations reveal that the conduction bands of ZrSe2/HfSe2 SLM possess a highly degenerate level which gives a high n-type power factor; at the same time, the stair-like density of states yields a high Seebeck coefficient...
April 4, 2018: Nanoscale
David Z Chen, Victor Koh, Marcus Tan, Colin S Tan, Gerard Nah, Liang Shen, Mayuri Bhargava, Ching-Yu Cheng, Paul Zhao, Tien Yin Wong, Seang-Mei Saw
PURPOSE: To determine the type and prevalence of peripheral retinal changes and its relationship with axial length (AL) in a population of young Asian adult males. METHODS: This was a cross-sectional study of male subjects aged between 19 and 25 years old. High myopes [spherical equivalent refraction, (SER) < -6.00 D] were recruited and underwent further ocular investigations including dilated retinal photography and binocular indirect ophthalmoscopy by two trained ophthalmologists...
March 25, 2018: Acta Ophthalmologica
G Edward Marti, Ross B Hutson, Akihisa Goban, Sara L Campbell, Nicola Poli, Jun Ye
We implement imaging spectroscopy of the optical clock transition of lattice-trapped degenerate fermionic Sr in the Mott-insulating regime, combining micron spatial resolution with submillihertz spectral precision. We use these tools to demonstrate atomic coherence for up to 15 s on the clock transition and reach a record frequency precision of 2.5×10^{-19}. We perform the most rapid evaluation of trapping light shifts and record a 150 mHz linewidth, the narrowest Rabi line shape observed on a coherent optical transition...
March 9, 2018: Physical Review Letters
Thérèse M Sassalos, Taylor S Fields, Robert Levine, Hua Gao
PURPOSE: To report a rare case of peripheral retinal neovascularization in a patient diagnosed with cutis marmorata telangiectatica congenita (CMTC). METHODS: Observational case report. RESULTS: A 16-year-old girl was referred to clinic for retinal evaluation. The patient had a clinical diagnosis of CMTC later confirmed by skin biopsy. Examination revealed temporal peripheral retinal sheathing, as well as lattice degeneration in both eyes...
March 14, 2018: Retinal Cases & Brief Reports
Lorenz Hruby, Nishant Dogra, Manuele Landini, Tobias Donner, Tilman Esslinger
We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity...
March 8, 2018: Proceedings of the National Academy of Sciences of the United States of America
Petr Karpov, Serguei Brazovskii
Experiments on optical and STM injection of carriers in layered MX2 materials revealed the formation of nanoscale patterns with networks and globules of domain walls. This is thought to be responsible for the metallization transition of the Mott insulator and for stabilization of a "hidden" state. In response, here we present studies of the classical charged lattice gas model emulating the superlattice of polarons ubiquitous to the material of choice 1T - TaS2 . The injection pulse was simulated by introducing a small random concentration of voids which subsequent evolution was followed by means of Monte Carlo cooling...
March 6, 2018: Scientific Reports
Juan Li, Shuqi Zheng, Teng Fang, Luo Yue, Shuai Zhang, Guiwu Lu
N-type Mg3 Sb2 -based Zintl compounds are proved to be high-performance thermoelectric materials with multiple degenerate valleys and low lattice thermal conductivity. Here, we investigate the electronic band structure and the thermoelectric properties of n-type Mg3 Sb2 using first-principles density functional theory. A high ZT of 3.1 at 725 K is obtained when the minimum lattice thermal conductivity and the optimal carrier concentration are reached. The calculated thermoelectric performance demonstrates that Mg3 Sb2 possesses an isotropic character in thermoelectric transport...
March 2, 2018: Physical Chemistry Chemical Physics: PCCP
Kimberly H Hartstein, Carl K Brozek, Stijn O M Hinterding, Daniel R Gamelin
Copper-sulfide nanocrystals can accommodate considerable densities of delocalized valence-band holes, introducing localized surface plasmon resonances (LSPRs) attractive for infrared plasmonic applications. Chemical control over nanocrystal shape, composition, and charge-carrier densities further broadens their scope of potential properties and applications. Although a great deal of control over LSPRs in these materials has been demonstrated, structural complexities have inhibited detailed descriptions of the microscopic chemical processes that transform them from nearly intrinsic to degenerately doped semiconductors...
February 20, 2018: Journal of the American Chemical Society
Hatem Brahmi, Ram Neupane, Lixin Xie, Shivkant Singh, Milad Yarali, Giwan Katwal, Shuo Chen, Maggie Paulose, Oomman K Varghese, Anastassios Mavrokefalos
Manipulating the transport properties of titania nanotubes (NTs) is paramount in guaranteeing the material's successful implementation in various solid state applications. Here we present the unique semiconducting properties of individual titania NTs as revealed from thermoelectric and structural studies performed on the same individual NTs. The NTs were in the anatase phase fabricated by anodic oxidation and doped with intrinsic defects created by reducing the lattice thermally. Despite their polycrystalline nature and nanoscale walls, the doped NTs were found to be 4-5 orders of magnitude more electrically conducting than TiO2 nanowires and thin films, with values approaching the bulk single crystal conductivity...
February 8, 2018: Nanoscale
M Bakarezos, E Tzianaki, S Petrakis, G Tsibidis, P A Loukakos, V Dimitriou, C Kosmidis, M Tatarakis, N A Papadogiannis
Nanoacoustic strains are generated in Silicon by chirped femtosecond laser pulses using thin Titanium films as transducers. We investigate the effect that the generating laser pulse chirp has on the amplitude of the induced strains, manifested as Brillouin oscillations observed in degenerate femtosecond pump-probe transient reflectivity measurements. The strain amplitude is larger when negatively chirped pulses are used, which is attributed to the more efficient conversion of laser pulse light into acoustic strain in the Titanium transducer...
January 25, 2018: Ultrasonics
Daniella A Ferluccio, Ronald I Smith, Jim Buckman, Jan-Willem G Bos
The half-Heuslers NbCoSn and NbCoSb have promising thermoelectric properties. Here, an investigation of the NbCo1+y Sn1-z Sbz (y = 0, 0.05; 0 ≤ z ≤ 1) solid-solution is presented. In addition, the p-type doping of NbCoSn using Ti and Zr substitution is investigated. Rietveld analysis reveals the gradual creation of Nb vacancies to compensate for the n-type doping caused by the substitution of Sb in NbCoSn. This leads to a similar valence electron count (∼18.25) for the NbCo1+y Sn1-z Sbz samples (z > 0)...
February 7, 2018: Physical Chemistry Chemical Physics: PCCP
E Jurčišinová, M Jurčišin
We investigate in detail the process of adiabatic cooling in the framework of the exactly solvable antiferromagnetic spin-1/2 Ising model in the presence of the external magnetic field on an approximate lattice with pyrochlore structure. The behavior of the entropy of the model is studied and exact values of the residual entropies of all ground states are found. The temperature variation of the system under adiabatic (de)magnetization is investigated and the central role of the macroscopically degenerated ground states in cooling processes is explicitly demonstrated...
November 2017: Physical Review. E
Konrad Jerzy Kapcia, Jan Barański, Andrzej Ptok
The phenomenon associated with inhomogeneous distribution of electron density is known as a charge ordering. In this work, we study the zero-bandwidth limit of the extended Hubbard model, which can be considered as a simple effective model of charge ordered insulators. It consists of the on-site interaction U and the intersite density-density interactions W_{1} and W_{2} between nearest neighbors and next-nearest neighbors, respectively. We derived the exact ground state diagrams for different lattice dimensionalities and discuss effects of small finite temperatures in the limit of high dimensions...
October 2017: Physical Review. E
R M Liu, W Z Zhuo, J Chen, M H Qin, M Zeng, X B Lu, X S Gao, J-M Liu
We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses...
July 2017: Physical Review. E
Bogdan Galilo, Derek K K Lee, Ryan Barnett
In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states...
November 17, 2017: Physical Review Letters
Dorothee Braun, Martin Schmidbauer, Michael Hanke, Jutta Schwarzkopf
The formation process of a ferroelectric multi-rank domain pattern in the thickness range of 7-52 nm is investigated for monoclinic K0.9 Na0.1 NbO3 strained epitaxial films on (110) NdScO3 substrates. Although the elastic strain energy density is degenerated for two pseudocubic orientations, a distinctive hierarchy of domain evolution is observed with exclusive in-plane a1 a2 domains for very thin films and the retarded onset of a ferroelectric MC phase at larger film thickness. This is accompanied by a thickness dependent transformation from stripe domains to a herringbone pattern and, eventually, for the thickest film, to a checkerboard-like structure...
November 29, 2017: Nanotechnology
Shan-Shan Wang, Ying Liu, Zhi-Ming Yu, Xian-Lei Sheng, Shengyuan A Yang
Nonsymmorphic symmetries, which involve fractional lattice translations, can generate exotic types of fermionic excitations in crystalline materials. Here we propose a topological phase arising from nonsymmorphic symmetries-the hourglass Dirac chain metal, and predict its realization in the rhenium dioxide. We show that ReO2 features hourglass-type dispersion in the bulk electronic structure dictated by its nonsymmorphic space group. Due to time reversal and inversion symmetries, each band has an additional two-fold degeneracy, making the neck crossing-point of the hourglass four-fold degenerate...
November 29, 2017: Nature Communications
Sarra Gattoussi, Quraish Ghadiali, Rosa Dolz-Marco, K Bailey Freund
PURPOSE: We describe with multimodal imaging the presentation and follow-up for a patient with idiopathic multifocal choroiditis and a transient peripapillary white ring. METHODS: Case report. RESULTS: A 39-year-old Asian woman was initially seen for an evaluation of lattice degeneration in 2015. Her medical history included Graves disease and psoriasis. Best-corrected visual acuity was 20/25 in her right eye and 20/25 in her left eye. Ultra-widefield fundus autofluorescence imaging showed a curvilinear hyperautofluorescent line in her right eye...
November 22, 2017: Retinal Cases & Brief Reports
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