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Xixi Tao, Lei Zhang, Xiaohong Zheng, Hua Hao, Xianlong Wang, Lingling Song, Zhi Zeng, Hong Guo
By constructing transport junctions using graphene-based van der Waals (vdW) heterostructures in which a zigzag-edged graphene nanoribbon (ZGNR) is sandwiched between two hexagonal boron-nitride sheets, we computationally demonstrate a new scheme for generating perfect spin-polarized quantum transport in ZGNRs by light irradiation. The mechanism lies in the lift of spin degeneracy of ZGNR induced by the stagger potential it receives from the BN sheets and the subsequent possibility of single spin excitation of electrons from the valence band to the conduction band by properly tuning the photon energy...
December 6, 2017: Nanoscale
Kolyo Marinov, Ahmet Avsar, Kenji Watanabe, Takashi Taniguchi, Andras Kis
Time-reversal symmetry and broken spin degeneracy enable the exploration of spin and valley quantum degrees of freedom in monolayer transition-metal dichalcogenides. While the strength of the large spin splitting in the valance band of these materials is now well-known, probing the 10-100 times smaller splitting in the conduction band poses significant challenges. Since it is easier to achieve n-type conduction in most of them, resolving the energy levels in the conduction band is crucial for the prospect of developing new spintronic and valleytronic devices...
December 5, 2017: Nature Communications
Naihao Chiang, Nan Jiang, Lindsey R Madison, Eric A Pozzi, Michael R Wasielewski, Mark A Ratner, Mark C Hersam, Tamar Seideman, George C Schatz, Richard P Van Duyne
Ultrahigh Vacuum Tip-enhanced Raman spectroscopy (UHV-TERS) combines the atomic-scale imaging capability of scanning probe microscopy (SPM) with the single-molecule chemical sensitivity and structural specificity of surface-enhanced Raman spectroscopy (SERS). Here, we use these techniques in combination with theory (TDDFT) to reveal insights into the influence of intermolecular interactions on the vibrational spectra of a N-N'-bis(2,6-diisopropylphenyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI) self-assembled monolayer adsorbed on single-crystal Ag substrates at room temperature...
December 3, 2017: Journal of the American Chemical Society
Rahul Maitra, Takahito Nakajima
We present an accurate single reference coupled cluster theory in which the conventional Fock operator matrix is suitably dressed to simulate the effect of triple and higher excitations within a singles and doubles framework. The dressing thus invoked originates from a second-order perturbative approximation of a similarity transformed Hamiltonian and induces higher rank excitations through local renormalization of individual occupied and unoccupied orbital lines. Such a dressing is able to recover a significant amount of correlation effects beyond singles and doubles approximation, but only with an economic n5 additional cost...
November 28, 2017: Journal of Chemical Physics
Takuya Okugawa, Kaoru Ohno, Yusuke Noda, Shinichiro Nakamura
We investigate spin-dependent electronic states of antiferromagnetic (AFM) lanthanum chromite (LaCrO<sub>3</sub>), lanthanum manganite (LaMnO<sub>3</sub>), and lanthanum ferrite (LaFeO<sub>3</sub>) using spin-polarized first-principles density functional theory (DFT) with Hubbard <i>U</i> correction. The band structures are calculated for 15 types of their different AFM structures. It is verified for these structures that there is a very simple rule to identify which wave number <b><i>k</i></b> exhibits spin splitting or degeneracy in the band structure...
November 30, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
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
K J Zhang, B Da, Z J Ding
Plasmon coupling in aggregated noble metal systems can provide a path to manipulate the optical response purposefully and possesses a wide range of application. Previously, most studies focused on the coupling behavior of Ag-Ag dimers with the same shape. However, plasmon coupling between nanoparticles at different morphologies can provide a new way to modulate optical properties due to broken of symmetry. In this work, we investigate systematically the coupling modes of asymmetric Ag-Ag heterodimers consisting of different morphologies by the boundary element method (BEM)...
November 21, 2017: Ultramicroscopy
Malin Nilsson, I-Ju Chen, Sebastian Lehmann, Vendula Maulerova, Kimberly A Dick, Claes Thelander
We use crystal-phase tuning during epitaxial growth of InAs nanowires to create quantum dots with very strong confinement. A set of gate electrodes are used to reproducibly split the quantum dots into even smaller pairs, for which we can control the populations down to the last electron. The double quantum dots, which are parallel-coupled to source and drain, show clear and stable odd-even level pairing due to spin degeneracy and the strong confinement. The combination of hard-wall barriers to source and drain, shallow inter-dot tunnel barriers, and very high single-particle excitation energies allow an order of magnitude tuning of the strength for the first intramolecular bond...
November 27, 2017: Nano Letters
Suresh Rayavarapu, Sanjeev Kheria, Dinesh R Shinde, Rajesh G Gonnade, Gangadhar J Sanjayan
Self-complementary quadruple hydrogen bonded systems have shown potential as key building blocks for developing various supramolecular polymers. Opportunities for the introduction of multiple functionalities would further augment, in principle, their application potential. Herein, we report a novel modular approach to simultaneously introduce two closely aligned side chains into AADD-type self-complementary quadruple hydrogen-bonding systems. Dithiane-tethered ureidopyrimidinone has been used as a reactive intermediate to efficiently attach closely aligned side chains by simply reacting with amines to form highly stable molecular duplexes...
November 24, 2017: Organic & Biomolecular Chemistry
Jiazhong Hu, Alban Urvoy, Zachary Vendeiro, Valentin Crépel, Wenlan Chen, Vladan Vuletić
Protocols for attaining quantum degeneracy in atomic gases almost exclusively rely on evaporative cooling, a time-consuming final step associated with substantial atom loss. We demonstrate direct laser cooling of a gas of rubidium-87 (87Rb) atoms to quantum degeneracy. The method is fast and induces little atom loss. The atoms are trapped in a two-dimensional optical lattice that enables cycles of compression to increase the density, followed by Raman sideband cooling to decrease the temperature. From a starting number of 2000 atoms, 1400 atoms reach quantum degeneracy in 300 milliseconds, as confirmed by a bimodal velocity distribution...
November 24, 2017: Science
Rosita E Yocgo, Ephifania Geza, Emile R Chimusa, Gaston K Mazandu
BACKGROUND: Advances in forward and reverse genetic techniques have enabled the discovery and identification of several plant defence genes based on quantifiable disease phenotypes in mutant populations. Existing models for testing the effect of gene inactivation or genes causing these phenotypes do not take into account eventual uncertainty of these datasets and potential noise inherent in the biological experiment used, which may mask downstream analysis and limit the use of these datasets...
November 23, 2017: BMC Plant Biology
Xuedong Wang, Tiancheng Li, Shudong Sun, Juan M Corchado
We review some advances of the particle filtering (PF) algorithm that have been achieved in the last decade in the context of target tracking, with regard to either a single target or multiple targets in the presence of false or missing data. The first part of our review is on remarkable achievements that have been made for the single-target PF from several aspects including importance proposal, computing efficiency, particle degeneracy/impoverishment and constrained/multi-modal systems. The second part of our review is on analyzing the intractable challenges raised within the general multitarget (multi-sensor) tracking due to random target birth and termination, false alarm, misdetection, measurement-to-track (M2T) uncertainty and track uncertainty...
November 23, 2017: Sensors
Siham M Hussein, Iain F Crowe, Nick Clark, Milan Milosevic, Aravind Vijayaraghavan, Frederic Y Gardes, Goran Z Mashanovich, Matthew P Halsall
We present a Raman mapping study of monolayer graphene G and 2D bands, after integration on silicon strip-waveguide-based micro-ring resonators (MRRs) to characterize the effects of the graphene transfer processes on its structural and optoelectronic properties. Analysis of the Raman G and 2D peak positions and relative intensities reveal that the graphene is electrically intrinsic where it is suspended over the MRR but is moderately hole-doped where it sits on top of the waveguide structure. This is suggestive of Fermi level 'pinning' at the graphene-silicon heterogeneous interface, and we estimate that the Fermi level shifts down by approximately 0...
November 22, 2017: Nanoscale Research Letters
Marcel Beining, Lucas Alberto Mongiat, Stephan Wolfgang Schwarzacher, Hermann Cuntz, Peter Jedlicka
Compartmental models are the theoretical tool of choice for understanding single neuron computations. However, many models are incomplete, built ad hoc and require tuning for each novel condition rendering them of limited usability. Here, we present T2N, a powerful interface to control NEURON with Matlab and TREES toolbox, which supports generating models stable over a broad range of reconstructed and synthetic morphologies. We illustrate this for a novel, highly-detailed active model of dentate granule cells (GCs) replicating a wide palette of experiments from various labs...
November 22, 2017: ELife
Bin Liang, Yongbao Li, Wei Ran, Bin Guo, Xuang Xu, Bo Liu, Jiafeng Li, Qiuwen Wu, Fugen Zhou
With robot-controlled linac positioning, the robotic radiotherapy system such as CyberKnife significantly increases the freedom in radiation beam placement, but also imposes more challenges on treatment plan optimization. The resampling mechanism in vendor supplied treatment planning system (MultiPlan) could not fully explore the increased beam direction search space. Besides, a sparse treatment plan (using fewer beams) is desired to improve the treatment efficiency. This study proposes a singular value decomposition linear programming (SVDLP) optimization technique for circular collimator based robotic radiotherapy...
November 17, 2017: Physics in Medicine and Biology
A S Kadyrov, I Bray, M Charlton, I I Fabrikant
The interaction of antiprotons with low-energy positronium atoms is a fundamental three-body problem whose significance is its utility for formation of antihydrogen. Particular importance resides in understanding processes involving excited positronium states. Until recently such studies were performed using classical techniques. However, they become inapplicable in the low-energy domain. Here we report the results of comprehensive quantum calculations, which include initial excited positronium states with principal quantum numbers up to n i = 5...
November 16, 2017: Nature Communications
Yanqing Feng, Hong Xi Sun, Junhui Sun, Zhibin Lu, Yong You
We study the conventional electron--phonon mediated superconducting properties of hole-doped Black Phosphorus by density functional calculations and get a quite large electron--phonon coupling (EPC) constant λ ~ 1.0 with transition temperature TC ~ 10 K, which is comparable to MgB2 when holes are doped into degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency B3g1 optical mode and its phonon displacement which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC...
November 14, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Kelly T Hughes, Fabienne F V Chevance
A complex process translates messenger RNA (mRNA) base sequence into protein amino acid sequence. Transfer RNAs must recognize 3-base codons in the mRNA to insert the correct amino acids into the growing protein. Codon degeneracy makes decoding complicated in that multiple (synonymous) triplets can encode a single amino acid and multiple tRNAs can have the same anticodon. Over the last twenty years, new developments in structural biology, genome sequencing and bioinformatics has elucidated the intricacies of the ribosome structure and the details of the translation process...
November 13, 2017: RNA Biology
Jian Zhou, Puru Jena
Two-dimensional group VI transition-metal dichalcogenides (TMDs) provide a promising platform to encode and manipulate quantum information in the valleytronics. However, the two valleys are energetically degenerate, protected by time-reversal symmetry (TRS). To lift this degeneracy, one needs to break the TRS by either applying an external magnetic field or using a magnetic rare-earth oxide substrate. Here, we predict a different strategy to achieve this goal. We propose that the ferromagnetic group V TMD monolayer, in which the TRS is intrinsically broken, can produce a larger valley and spin splitting...
November 14, 2017: Journal of Physical Chemistry Letters
Dengke Zhang, Xiao-Qing Luo, Yi-Pu Wang, Tie-Fu Li, J Q You
Magnon-polaritons are hybrid light-matter quasiparticles originating from the strong coupling between magnons and photons. They have emerged as a potential candidate for implementing quantum transducers and memories. Owing to the dampings of both photons and magnons, the polaritons have limited lifetimes. However, stationary magnon-polariton states can be reached by a dynamical balance between pumping and losses, so the intrinsically nonequilibrium system may be described by a non-Hermitian Hamiltonian. Here we design a tunable cavity quantum electrodynamics system with a small ferromagnetic sphere in a microwave cavity and engineer the dissipations of photons and magnons to create cavity magnon-polaritons which have non-Hermitian spectral degeneracies...
November 8, 2017: Nature Communications
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