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M Sundermann, H Yavaş, K Chen, D J Kim, Z Fisk, D Kasinathan, M W Haverkort, P Thalmeier, A Severing, L H Tjeng
We investigated the crystal-electric field ground state of the 4f manifold in the strongly correlated topological insulator SmB_{6} using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the Γ_{8} quartet state of the Sm f^{5}  J=5/2 configuration governs the ground-state symmetry and, hence, the topological properties of SmB_{6}. Our findings contradict the results of density functional calculations reported so far...
January 5, 2018: Physical Review Letters
Daliang Zhang, Yihan Zhu, Lingmei Liu, Xiangrong Ying, Chia-En Hsiung, Rachid Sougrat, Kun Li, Yu Han
High-resolution imaging of electron beam-sensitive materials is one of the most difficult applications of transmission electron microscopy (TEM). The challenges are manifold, including the acquisition of images with extremely low beam doses, the time-constrained search for crystal zone axes, the precise image alignment, and the accurate determination of the defocus value. We develop a suite of methods to fulfill these requirements and acquire atomic-resolution TEM images of several metal organic frameworks that are generally recognized as highly sensitive to electron beams...
January 18, 2018: Science
Nicholas Lubbers, Turab Lookman, Kipton Barros
We apply recent advances in machine learning and computer vision to a central problem in materials informatics: the statistical representation of microstructural images. We use activations in a pretrained convolutional neural network to provide a high-dimensional characterization of a set of synthetic microstructural images. Next, we use manifold learning to obtain a low-dimensional embedding of this statistical characterization. We show that the low-dimensional embedding extracts the parameters used to generate the images...
November 2017: Physical Review. E
Zhuocheng Xiao, Jiwei Zhang, Andrew T Sornborger, Louis Tao
Line attractors in neuronal networks have been suggested to be the basis of many brain functions, such as working memory, oculomotor control, head movement, locomotion, and sensory processing. In this paper, we make the connection between line attractors and pulse gating in feed-forward neuronal networks. In this context, because of their neutral stability along a one-dimensional manifold, line attractors are associated with a time-translational invariance that allows graded information to be propagated from one neuronal population to the next...
November 2017: Physical Review. E
Matteo Bernard Bertagni, Carlo Camporeale
The interaction of a gravity-driven water film with an evolving solid substrate (calcite or ice) results in the formation of fascinating wavy patterns similar both in caves and in ice-falls. Due to their remarkable similarity, we adopt a unified approach in the study of pattern formation of longitudinally oriented organ-pipe-like structures, called flutings. Since the morphogenesis of cave patterns can evolve for millennia, they have an additional value as silent repositories of past climates. Fluting formation is studied with the aid of gradient expansion and center manifold projection...
November 2017: Physical Review. E
Rafael Gallego, Ernest Montbrió, Diego Pazó
Fifty years ago Arthur Winfree proposed a deeply influential mean-field model for the collective synchronization of large populations of phase oscillators. Here we provide a detailed analysis of the model for some special, analytically tractable cases. Adopting the thermodynamic limit, we derive an ordinary differential equation that exactly describes the temporal evolution of the macroscopic variables in the Ott-Antonsen invariant manifold. The low-dimensional model is then thoroughly investigated for a variety of pulse types and sinusoidal phase response curves (PRCs)...
October 2017: Physical Review. E
I Reyes-Ramírez, J Gonzalez-Ayala, A Calvo Hernández, M Santillán
In this paper we address the stability of a low-dissipation (LD) heat engine (HE) under maximum power conditions. The LD system dynamics are analyzed in terms of the contact times between the engine and the external heat reservoirs, which determine the amount of heat exchanged by the system. We study two different scenarios that secure the existence of a single stable steady state. In these scenarios, contact times dynamics are governed by restitutive forces that are linear functions of either the heat amounts exchanged per cycle, or the corresponding heat fluxes...
October 2017: Physical Review. E
A G Magner, K Arita
The Fedoriuk-Maslov catastrophe theory of caustics and turning points is extended to solve the bifurcation problems by the improved stationary phase method (ISPM). The trace formulas for the radial power-law (RPL) potentials are presented by the ISPM based on the second- and third-order expansion of the classical action near the stationary point. A considerable enhancement of contributions of the two orbits (pair consisting of the parent and newborn orbits) at their bifurcation is shown. The ISPM trace formula is proposed for a simple bifurcation scenario of Hamiltonian systems with continuous symmetries, where the contributions of the bifurcating parent orbits vanish upon approaching the bifurcation point due to the reduction of the end-point manifold...
October 2017: Physical Review. E
Lachlan D Smith, Paul B Umbanhowar, Julio M Ottino, Richard M Lueptow
While structures and bifurcations controlling tracer particle transport and mixing have been studied extensively for systems with only stretching-and-folding, and to a lesser extent for systems with only cutting-and-shuffling, few studies have considered systems with a combination of both. We demonstrate two bifurcations for nonmixing islands associated with elliptic periodic points that only occur in systems with combined cutting-and-shuffling and stretching-and-folding, using as an example a map approximating biaxial rotation of a less-than-half-full spherical granular tumbler...
October 2017: Physical Review. E
Oleg Alekseev, Mark Mineev-Weinstein
We develop statistical mechanics for stochastic growth processes and apply it to Laplacian growth by using its remarkable connection with a random matrix theory. The Laplacian growth equation is obtained from the variation principle and describes adiabatic (quasistatic) thermodynamic processes in the two-dimensional Dyson gas. By using Einstein's theory of thermodynamic fluctuations we consider transitional probabilities between thermodynamic states, which are in a one-to-one correspondence with simply connected domains occupied by gas...
July 2017: Physical Review. E
Chol-Ung Choe, Ryong-Son Kim, Ji-Song Ri
We consider a ring of phase oscillators with nonlocal coupling strength and heterogeneous phase lags. We analyze the effects of heterogeneity in the phase lags on the existence and stability of a variety of steady states. A nonlocal coupling with heterogeneous phase lags that allows the system to be solved analytically is suggested and the stability of solutions along the Ott-Antonsen invariant manifold is explored. We present a complete bifurcation diagram for stationary patterns including the uniform drift and modulated drift states as well as chimera state, which reveals that the stable modulated drift state and a continuum of metastable drift states could occur due to the heterogeneity of the phase lags...
September 2017: Physical Review. E
Po-Chang Su, Ju Shen, Wanxin Xu, Sen-Ching S Cheung, Ying Luo
From object tracking to 3D reconstruction, RGB-Depth (RGB-D) camera networks play an increasingly important role in many vision and graphics applications. Practical applications often use sparsely-placed cameras to maximize visibility, while using as few cameras as possible to minimize cost. In general, it is challenging to calibrate sparse camera networks due to the lack of shared scene features across different camera views. In this paper, we propose a novel algorithm that can accurately and rapidly calibrate the geometric relationships across an arbitrary number of RGB-D cameras on a network...
January 15, 2018: Sensors
Wenjie Dou, Gaohan Miao, Joseph E Subotnik
We present a universal expression for the electronic friction as felt by a set of classical nuclear degrees of freedom (DOFs) coupled to a manifold of quantum electronic DOFs; no assumptions are made regarding the nature of the electronic Hamiltonian and electron-electron repulsions are allowed. Our derivation is based on a quantum-classical Liouville equation for the coupled electronic-nuclear motion, followed by an adiabatic approximation whereby electronic transitions are assumed to equilibrate faster than nuclear movement...
July 28, 2017: Physical Review Letters
Neal P Mankad
The rational development of catalytic reactions involving cooperative behavior between two catalytic reactive sites represents a frontier area of research from which novel reactivity and selectivity patterns emerge. Within this context, this Feature highlights the development of a cooperative system involving transition metal Lewis acid/base pairs. Bimetallic systems consisting of copper carbene Lewis acids and metal carbonyl anion Lewis bases, (NHC)Cu-[MCO], are easily synthesized from readily available organometallic building blocks (NHC = N-heterocyclic carbene; [MCO]- = metal carbonyl anion, e...
January 15, 2018: Chemical Communications: Chem Comm
Naota Sekiguchi, Takumi Sato, Kiyoshi Ishikawa, Atsushi Hatakeyama
Characteristics of a diffusion-bonded sapphire cell for optical experiments with hot metal vapors were investigated. The sapphire cell consisted of sapphire-crystal plates and a borosilicate-glass tube, which were bonded to each other by diffusion bonding without any binders or glues. The glass tube was attached to a vacuum manifold using the standard method applied in glass processing, filled with a small amount of Rb metal by chasing with a torch, and then sealed. The cell was baked at high temperatures, and optical experiments were then performed using rubidium atoms at room temperature...
January 1, 2018: Applied Optics
Deepak Chand, Priyabrata Panigrahi, Nishant Kumar Varshney, Sureshkumar Ramasamy, C G Suresh
Bile Salt Hydrolase (BSH), a member of Cholylglycine hydrolase family, catalyses the de-conjugation of bile acids and is evolutionarily related to penicillin V acylase (PVA) that hydrolyses a different substrate such as penicillin V. We report the three-dimensional structure of a BSH enzyme from the Gram-positive bacteria Enterococcus faecalis (EfBSH) which has manifold higher hydrolase activity compared to other known BSHs and displays unique allosteric catalytic property. The structural analysis revealed reduced secondary structure content compared to other known BSH structures, particularly devoid of an anti-parallel β-sheet in the assembly loop and part of a β-strand is converted to increase the length of a substrate binding loop 2...
January 8, 2018: Biochimica et Biophysica Acta
Junwei Han, Rong Quan, Dingwen Zhang, Feiping Nie
Given a set of images that contain objects from a common category, object co-segmentation aims at automatically discovering and segmenting such common objects from each image. During the past few years, object co-segmentation has received great attention in the computer vision community. However, the existing approaches are usually designed with misleading assumptions, unscalable priors, or subjective computational models, which do not have sufficient robustness for dealing with complex and unconstrained real-world image contents...
April 2018: IEEE Transactions on Image Processing: a Publication of the IEEE Signal Processing Society
Antonia Dawes
This paper is based on ethnographic research conducted with migrant and Italian street vendors in Naples, southern Italy, in 2012. It tells the story of Via Bologna market which was nearly closed down by the City Hall at the time. Naples is a city where issues of poverty and unemployment pre-date and have been exacerbated by manifold narratives of crisis now unfolding across Europe regarding the economy, political legitimacy, security and migration. Street markets have always been an important and visible economic survival strategy for both Neapolitans and migrants there...
January 10, 2018: British Journal of Sociology
Andrej Michalsen, Andreas Hillert, Andreas Schießl, Dominik Hinzmann
Both acute crises and chronically incriminating circumstances in people's lives may lead to their being afflicted by psychological and somatic ailments. "Burnout" has been coined and established as the term for chronic occupational strain. Many professions claim to be extraordinarily affected by burnout, amongst others physicians and nurses, especially those working in anaesthesiology and critical care. Usually assessed with the Maslach Burnout Inventary, the prevalence of moderate or severe burnout in these areas is estimated at about 30 % amongst nurses and about 40 % to 50 % amongst physicians...
January 2018: Deutsche Medizinische Wochenschrift
Cong Tian, Leonardo Massignan, Tjark H Meyer, Lutz Ackermann
Electrochemistry enabled C-H/N-H functionalizations at room temperature by external oxidant-free cobalt catalysis. Thus, the sustainable cobalt electrocatalysis manifold occurred with excellent levels of chemo and positional selectivity with ample scope, allowing for electrochemical C-H activation under exceedingly mild reaction conditions at room temperature in water.
January 5, 2018: Angewandte Chemie
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