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Jung-Wan Ryu, Nojoon Myoung, Hee Chul Park
We demonstrate mesoscopic transport through quantum states in quasi-1D lattices maintaining the combination of parity and time-reversal symmetries by controlling energy gain and loss. We investigate the phase diagram of the non-Hermitian system where transitions take place between unbroken and broken [Formula: see text]-symmetric phases via exceptional points. Quantum transport in the lattice is measured only in the unbroken phases in the energy band-but not in the broken phases. The broken phase allows for spontaneous symmetry-broken states where the cross-stitch lattice is separated into two identical single lattices corresponding to conditionally degenerate eigenstates...
August 18, 2017: Scientific Reports
Hugo Gattuso, Marco Marazzi, François Dehez, Antonio Monari
Resorting to state-of-the art molecular modeling and simulation techniques we provide full characterization of the photophysical properties of the naturally occurring hypericin chromophore, currently used in photodynamic therapy. In particular, we reveal the different photophysical pathways leading to intersystem-crossing and hence, triplet manifold population that is necessary for the subsequent production of singlet oxygen. In particular we identify an extended region of quasi-degeneracy between the first singlet excited state and three triplet state surfaces...
August 18, 2017: Physical Chemistry Chemical Physics: PCCP
Yingjie Zhang, Weidong Sheng, Yang Li
By using a configuration interaction approach with up to the fifth excitations taken into account, we study the excitonic effect in the optical absorption in graphene nanodots. While the many-electron states are either singlet or doublet in a triangular nanodot system, all the excited singlet states are found to be optically dark in the absorption. These dark excitons are shown to originate mainly from the geometric symmetry of the system and would remain inactive even when the electron-hole or sublattice symmetry is broken...
August 18, 2017: Physical Chemistry Chemical Physics: PCCP
Sune Nørhøj Jespersen, Jonas Lynge Olesen, Brian Hansen, Noam Shemesh
Biophysical modelling of diffusion MRI is necessary to provide specific microstructural tissue properties. However, estimating model parameters from data with limited diffusion gradient strength, such as clinical scanners, has proven unreliable due to a shallow optimization landscape. On the other hand, estimation of diffusion kurtosis (DKI) parameters is more robust, and its parameters may be connected to microstructural parameters, given an appropriate biophysical model. However, it was previously shown that this procedure still does not provide sufficient information to uniquely determine all model parameters...
August 14, 2017: NeuroImage
Liam Sharninghausen, Shashi Bhushan Sinha, Dimitar Y Shopov, Brandon Q Mercado, David Balcells, Gary W Brudvig, Robert H Crabtree
We have prepared and fully characterized two isomers of [IrIV(dpyp)2] (dpyp = meso-2,4-di(2-pyridynyl)-2,4-pentanediolate). These complexes can be cleanly oxidized to [IrV(dpyp)2]+, which to our knowledge represent the first coordination complexes of Ir(V) in an N,O-donor environment. One isomer has been fully characterized in the Ir(V) state, including by x-ray crystallography, XPS, and DFT calculations, all of which support metal-centered oxidation. The unprecedented stability of these Ir(V) complexes is ascribed to the exceptional donor strength of the ligands, their resistance to oxidative degradation, and the presence of four highly donor alkoxide groups in a plane, which breaks the degeneracy of the d-orbitals and favors oxidation...
August 16, 2017: Angewandte Chemie
Haihao Liu, Muhammad Shoufie Ukhtary, Riichiro Saito
The optical properties of a multilayer system of dielectric media with arbitrary N layers is investigated. Each layer is one of two dielectric media, with thickness one-quarter the wavelength of light in that medium, corresponding to a central frequency. Using the transfer matrix method, the transmittance T is calculated for all possible 2^N sequences for small N. Unexpectedly, it is found that instead of 2^N different values of T at the central frequency (T_0), there are either (N/2+1) or (N+1) discrete values of T_0 for even or odd N, respectively...
August 15, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Vahid Satarifard, Maziar Heidari, Samaneh Mashaghi, Sander J Tans, Mohammad Reza Ejtehadi, Alireza Mashaghi
Spatial confinement limits the conformational space accessible to biomolecules but the implications for bimolecular topology are not yet known. Folded linear biopolymers can be seen as molecular circuits formed by intramolecular contacts. The pairwise arrangement of intra-chain contacts can be categorized as parallel, series or cross, and has been identified as a topological property. Using molecular dynamics simulations, we determine the contact order distributions and topological circuits of short semi-flexible linear and ring polymer chains with a persistence length of lp under a spherical confinement of radius Rc...
August 14, 2017: Nanoscale
Jian Chen, Shenfang Yuan, Lei Qiu, Hui Wang, Weibo Yang
Accurate on-line prognosis of fatigue crack propagation is of great meaning for prognostics and health management (PHM) technologies to ensure structural integrity, which is a challenging task because of uncertainties which arise from sources such as intrinsic material properties, loading, and environmental factors. The particle filter algorithm has been proved to be a powerful tool to deal with prognostic problems those are affected by uncertainties. However, most studies adopted the basic particle filter algorithm, which uses the transition probability density function as the importance density and may suffer from serious particle degeneracy problem...
July 25, 2017: Ultrasonics
Yinan Shu, B Scott Fales, Wei-Tao Peng, Benjamin G Levine
Defects are known to introduce pathways for the nonradiative recombination of electronic excitations in semiconductors, but implicating a specific defect as a nonradiative center remains challenging for both experiment and theory. In this Perspective, we present recent progress toward this goal involving the identification and characterization of defect-induced conical intersections (DICIs), points of degeneracy between the ground and first excited electronic states of semiconductor materials that arise from the deformation of specific defects...
August 16, 2017: Journal of Physical Chemistry Letters
Yuanfei Bi, Anna Porras, Tianshu Li
Despite the significance of gas hydrates in diverse areas, a quantitative knowledge of hydrate formation at a molecular level is missing. The impediment to acquiring this understanding is primarily attributed to the stochastic nature and ultra-fine scales of nucleation events, posing a great challenge for both experiment and simulation to explore hydrate nucleation. Here we employ advanced molecular simulation methods, including forward flux sampling (FFS), pB histogram analysis, and backward flux sampling, to overcome the limit of direct molecular simulation for exploring both the free energy landscape and molecular pathways of hydrate nucleation...
December 7, 2016: Journal of Chemical Physics
Shigenori Tanaka
Correlational and thermodynamic properties of homogeneous electron liquids at finite temperatures are theoretically analyzed in terms of dielectric response formalism with the hypernetted-chain (HNC) approximation and its modified version. The static structure factor and the local-field correction to describe the strong Coulomb-coupling effects beyond the random-phase approximation are self-consistently calculated through solution to integral equations in the paramagnetic (spin unpolarized) and ferromagnetic (spin polarized) states...
December 7, 2016: Journal of Chemical Physics
Weijian Chen, Şahin Kaya Özdemir, Guangming Zhao, Jan Wiersig, Lan Yang
Sensors play an important part in many aspects of daily life such as infrared sensors in home security systems, particle sensors for environmental monitoring and motion sensors in mobile phones. High-quality optical microcavities are prime candidates for sensing applications because of their ability to enhance light-matter interactions in a very confined volume. Examples of such devices include mechanical transducers, magnetometers, single-particle absorption spectrometers, and microcavity sensors for sizing single particles and detecting nanometre-scale objects such as single nanoparticles and atomic ions...
August 9, 2017: Nature
Hossein Hodaei, Absar U Hassan, Steffen Wittek, Hipolito Garcia-Gracia, Ramy El-Ganainy, Demetrios N Christodoulides, Mercedeh Khajavikhan
Non-Hermitian degeneracies, also known as exceptional points, have recently emerged as a new way to engineer the response of open physical systems, that is, those that interact with the environment. They correspond to points in parameter space at which the eigenvalues of the underlying system and the corresponding eigenvectors simultaneously coalesce. In optics, the abrupt nature of the phase transitions that are encountered around exceptional points has been shown to lead to many intriguing phenomena, such as loss-induced transparency, unidirectional invisibility, band merging, topological chirality and laser mode selectivity...
August 9, 2017: Nature
S M Corrêa, D F S Ferreira, M R S Siqueira, J C Reis-Silva, J F P Leal, C A B da Silva, J Del Nero
In the present work we propose a novel treatment to investigate ballistic electron transport under mechanical strain in a 1-D molecular bridge composed of alternating simple and triple bonds (polyyne) connected between two Single-Wall Carbon Nanotube (SWCNT) electrodes. Calculations with the DFT-NEGF methodology were performed in order to analyze this system at low values of mechanical strain (compression and distension) and at equilibrium length in the presence of bias voltages applied along the longitudinal direction...
August 10, 2017: Physical Chemistry Chemical Physics: PCCP
Robin Guttmann, Alexander F Sax
Weak, intermolecular interactions in amine dimers were studied by using the combination of a dispersionless density functional and a function that describes the dispersion contribution to the interaction energy. The validity of this method was shown by comparison of structural and energetic properties with data obtained with a conventional density functional and the coupled cluster method. The stability of amine dimers was shown to depend on the size, the shape, and the relative orientation of the alkyl substituents, and it was shown that the stabilization energy for large substituents is dominated by dispersion interactions...
August 2017: ChemistryOpen
Dan Zhang, Junyou Yang, Qinghui Jiang, Zhiwei Zhou, Xin Li, Jiwu Xin, Abdul Basit, Yangyang Ren, Xu He, Weijing Chu, Jingdi Hou
The effect of Al-, Ga-, and In-doping on the thermoelectric (TE) properties of Cu3SbSe4 has been comparatively studied on the basis of theoretical prediction and experimental validation. It is found that tiny Al/Ga/In substitution leads to a great enhancement of electrical conductivity with high carrier concentration and also large Seebeck coefficient due to the preserved high band degeneracy and thereby a remarkably high power factor. Ultimately, coupled with the depressed lattice thermal conductivity, all three elements (Al/Ga/In) substituted samples have obtained a highly improved thermoelectric performance with respect to undoped Cu3SbSe4...
August 17, 2017: ACS Applied Materials & Interfaces
Sang-Hoon Lee, Jiwoo Kang, Sanghoon Lee
BACKGROUND AND OBJECTIVES: A robust vessel segmentation and tracking method based on a particle-filtering framework is proposed to cope with increasing demand for a method that can detect and track vessel anomalies. METHODS: We apply the level set method to segment the vessel boundary and a particle filter to track the position and shape variations in the vessel boundary between two adjacent slices. To enhance the segmentation and tracking performances, the importance density of the particle filter is localized by estimating the translation of an object's boundary...
September 2017: Computer Methods and Programs in Biomedicine
Haixia Da, Lei Gao, Weiqiang Ding, Xiaohong Yan
Magnetic exchange field has been demonstrated to be effective in enhancing the valley splitting of monolayer transition-metal dichalcogenides experimentally. However, how magnetic exchange coupling affects the magnetooptical behaviors in massive Dirac systems remains elusive. Using k⃗·p⃗ model and Kubo formula, we theoretically report that optical Hall conductivity and giant magnetooptical effects can be induced in monolayer transition-metal dichalcogenides even if there is no any magnetic field involved when considering magnetic exchange interaction...
August 3, 2017: Journal of Physical Chemistry Letters
Qiaosheng Pan, Enming Miao, Bingxuan Wu, Weikang Chen, Xiujun Lei, Liangguo He
A novel, bio-inspired, single-phase driven piezoelectric linear motor (PLM) using an asymmetric stator was designed, fabricated, and tested to avoid mode degeneracy and to simplify the drive mechanism of a piezoelectric motor. A piezoelectric transducer composed of two piezoelectric stacks and a displacement amplifier was used as the driving element of the PLM. Two simple and specially designed claws performed elliptical motion. A numerical simulation was performed to design the stator and determine the feasibility of the design mechanism of the PLM...
July 2017: Review of Scientific Instruments
Jiajun Zhao, Likun Zhang, Ying Wu
Sound emission is inefficient at low frequencies as limited by source size. This letter presents enhancing emission of monochromatic monopole and multipole sources by enclosing the source with a subwavelength circular enclosure filled of an anisotropic material of a low radial sound speed. The anisotropy is associated with an infinite tangential density along the azimuth. Numerical simulations show that emission gain is produced at frequencies surrounding degenerate Mie resonant frequencies of the enclosure, and meanwhile the radiation directivity pattern is well preserved...
July 2017: Journal of the Acoustical Society of America
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