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T Petersen, J D Zuegel, J Bromage
A high-energy, extended-cavity femtosecond BiBO optical parametric oscillator synchronously pumped by a 1.0-ps, 1030-nm Yb:YAG, thin-disk pump laser is presented. The oscillator operated near degeneracy in a noncollinear interaction geometry, producing signal wavelength tunability from 1.99 to 2.20 μm. The signal pulses have an average power exceeding 2 W, producing 455-fs pulses at 7.08 MHz with energies up to 350 nJ, showing increased potential for tunable sources of scalable ultrafast pulses in the infrared...
April 17, 2017: Optics Express
Ioannis Rousochatzakis, Natalia B Perkins
We show that the off-diagonal exchange anisotropy drives Mott insulators with strong spin-orbit coupling to a classical spin liquid regime, characterized by an infinite number of ground states and Ising variables living on closed or open strings. Depending on the sign of the anisotropy, quantum fluctuations either fail to lift the degeneracy down to very low temperatures, or select noncoplanar magnetic states with unconventional spin correlations. The results apply to all 2D and 3D tricoordinated materials with bond-directional anisotropy and provide a consistent interpretation of the suppression of the x-ray magnetic circular dichroism signal reported recently for β-Li_{2}IrO_{3} under pressure...
April 7, 2017: Physical Review Letters
L Pinto da Silva, C M Magalhães, D M A Crista, J C G Esteves da Silva
Coelenterazine, a member of the imidazopyrazinone class of chemiluminescent substrates, presents significant potential as a dynamic probe of reactive oxygen species in a biological environment, such as a superoxide anion, in which these species are important in cellular biology and pathology. The objective of the current study was to understand in what way the efficiency of singlet and triplet chemiexcitation could be modulated, towards a more efficient use of imidazopyrazinone-based compounds as dynamic chemiluminescent probes...
April 21, 2017: Photochemical & Photobiological Sciences
Carlos G Avendaño, Arturo Reyes
We theoretically study the dispersion relation for axially propagating electromagnetic waves throughout a one-dimensional helical structure whose pitch and dielectric and magnetic properties are spatial random functions with specific statistical characteristics. In the system of coordinates rotating with the helix, by using a matrix formalism, we write the set of differential equations that governs the expected value of the electromagnetic field amplitudes and we obtain the corresponding dispersion relation...
March 2017: Physical Review. E
Luiz H Santos, Taylor L Hughes
We explore a scenario where local interactions form one-dimensional gapped interfaces between a pair of distinct chiral two-dimensional topological states-referred to as phases 1 and 2-such that each gapped region terminates at a domain wall separating the chiral gapless edge states of these phases. We show that this type of T junction supports pointlike fractionalized excitations obeying parafermion statistics, thus implying that the one-dimensional gapped interface forms an effective topological parafermionic wire possessing a nontrivial ground state degeneracy...
March 31, 2017: Physical Review Letters
J Ren, H Hodaei, G Harari, A U Hassan, W Chow, M Soltani, D Christodoulides, M Khajavikhan
We propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non-Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed (Ω), thus enhancing the sensitivity to low angular rotations by orders of magnitudes. In addition, at its maximum sensitivity limit, the measurable spectral splitting is independent of the radius of the rings involved. This Letter paves the way toward a new class of ultrasensitive miniature ring laser gyroscopes on chip...
April 15, 2017: Optics Letters
José Manuel Méndez Martínez, Jesús Urías
Derive the quantitative predictions of constraint-based models require of conversion algorithms to enumerate and construct the skeleton graph conformed by the extreme points of the feasible region, where all constraints in the model are fulfilled. The conversion is problematic when the system of linear constraints is degenerate. This paper describes a conversion algorithm that combines the best of two methods: the incremental slicing of cones that defeats degeneracy and pivoting for a swift traversal of the set of extreme points...
2017: PloS One
Katrin Zimmermann, Anna Jordan, Frédéric Gay, Kenji Watanabe, Takashi Taniguchi, Zheng Han, Vincent Bouchiat, Hermann Sellier, Benjamin Sacépé
Charge carriers in the quantum Hall regime propagate via one-dimensional conducting channels that form along the edges of a two-dimensional electron gas. Controlling their transmission through a gate-tunable constriction, also called quantum point contact, is fundamental for many coherent transport experiments. However, in graphene, tailoring a constriction with electrostatic gates remains challenging due to the formation of p-n junctions below gate electrodes along which electron and hole edge channels co-propagate and mix, short circuiting the constriction...
April 13, 2017: Nature Communications
Colin Campbell, Steven Aucott, Justin Ruths, Derek Ruths, Katriona Shea, Réka Albert
Many dynamic systems display complex emergent phenomena. By directly controlling a subset of system components (nodes) via external intervention it is possible to indirectly control every other component in the system. When the system is linear or can be approximated sufficiently well by a linear model, methods exist to identify the number and connectivity of a minimum set of external inputs (constituting a so-called minimal control topology, or MCT). In general, many MCTs exist for a given network; here we characterize a broad ensemble of empirical networks in terms of the fraction of nodes and edges that are always, sometimes, or never a part of an MCT...
April 12, 2017: Scientific Reports
Yi-Ting Hsu, Abolhassan Vaezi, Mark H Fischer, Eun-Ah Kim
Theoretically, it has been known that breaking spin degeneracy and effectively realizing spinless fermions is a promising path to topological superconductors. Yet, topological superconductors are rare to date. Here we propose to realize spinless fermions by splitting the spin degeneracy in momentum space. Specifically, we identify monolayer hole-doped transition metal dichalcogenide (TMD)s as candidates for topological superconductors out of such momentum-space-split spinless fermions. Although electron-doped TMDs have recently been found superconducting, the observed superconductivity is unlikely topological because of the near spin degeneracy...
April 11, 2017: Nature Communications
Ida L M Candiloro, Thomas Mikeska, Alexander Dobrovic
BACKGROUND: Determining the role of DNA methylation in various biological processes is dependent on the accurate representation of often highly complex patterns. Accurate representation is dependent on unbiased PCR amplification post bisulfite modification, regardless of methylation status of any given epiallele. This is highly dependent on primer design. Particular difficulties are raised by the analysis of CpG-rich regions, which are the usual regions of interest. Here, it is often difficult or impossible to avoid placing primers in CpG-free regions, particularly if one wants to target a specific part of a CpG-rich region...
2017: Clinical Epigenetics
Shota Kita, Yang Li, Philip Camayd-Muñoz, Orad Reshef, Daryl I Vulis, Robert W Day, Eric Mazur, Marko Lončar
Zero-index metamaterials (ZIMs) offer unprecedented ways to manipulate the flow of light, and are of interest for wide range of applications including optical cloaking, super-coupling, and unconventional phase-matching properties in nonlinear optics. Impedance-matched ZIMs can be obtained through a photonic Dirac-cone (PDC) dispersion induced by an accidental degeneracy of an electric monopole and a transverse magnetic dipole mode at the center of the Brillouin zone. Therefore, PDC is very sensitive to fabrication imperfections...
April 3, 2017: Optics Express
Jessica Morrison, Matthias Imboden, David J Bishop
The ability to actively shift the primary resonance of a 2D scanning micromirror allows the user to set the scanning direction, set the scanning frequency, and lift otherwise degenerate modes in a symmetrically designed system. In most cases, resonant scanning micromirrors require frequency stability in order to perform imaging and projection functions properly. This paper suggests a method to tune the tip and tilt resonant frequencies in real time while actively suppressing or allowing degeneracy of the two modes in a symmetric electrothermal micromirror...
April 3, 2017: Optics Express
Haonan Xiong, Wentao Jiang, Yipu Song, Luming Duan
The few-layer graphene quantum dot provides a promising platform for quantum computing with both spin and valley degrees of freedom. Gate-defined quantum dots in particular can avoid noise from edge disorders. In connection with the recent experimental efforts (Song et al 2016 Nano Lett. 16 6245), we investigate the bound state properties of trilayer graphene (TLG) quantum dots (QDs) through numerical simulations. We show that the valley degeneracy can be lifted by breaking the time reversal symmetry through the application of a perpendicular magnetic field...
April 3, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Dawei Di, Alexander S Romanov, Le Yang, Johannes M Richter, Jasmine P H Rivett, Saul Jones, Tudor H Thomas, Mojtaba Abdi Jalebi, Richard H Friend, Mikko Linnolahti, Manfred Bochmann, Dan Credgington
Organic LEDs promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed LEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 ns at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, such that rapid interconversion is possible...
March 30, 2017: Science
Hiromu Kubo, Takashi Hirose, Kenji Matsuda
The effect of different substituents on the fluorescence properties of [5]helicene derivatives was investigated in terms of molecular orbital symmetry. Unsubstituted [5]helicene is nonemissive due to the symmetry-forbidden S1 → S0 transition. However, the fluorescence emission rate constant (kf) of [5]helicenes is efficiently increased by removing the orbital degeneracy involved in the S1 → S0 transition. As a result, we achieved a [5]helicene derivative exhibiting a high fluorescence quantum yield (Φf = 0...
April 7, 2017: Organic Letters
Anindita Das, Rahul K Rathour, Rishikesh Narayanan
Strings on a violin are tuned to generate distinct sound frequencies in a manner that is firmly dependent on finger location along the fingerboard. Sound frequencies emerging from different violins could be very different based on their architecture, the nature of strings and their tuning. Analogously, active neuronal dendrites, dendrites endowed with active channel conductances, are tuned to distinct input frequencies in a manner that is dependent on the dendritic location of the synaptic inputs. Further, disparate channel expression profiles and differences in morphological characteristics could result in dendrites on different neurons of the same subtype tuned to distinct frequency ranges...
2017: Frontiers in Cellular Neuroscience
N Xu, G Autès, C E Matt, B Q Lv, M Y Yao, F Bisti, V N Strocov, D Gawryluk, E Pomjakushina, K Conder, N C Plumb, M Radovic, T Qian, O V Yazyev, J Mesot, H Ding, M Shi
The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides...
March 10, 2017: Physical Review Letters
D V Dmitriev, V Ya Krivnov
We consider a spin-[Formula: see text] kagome-like chain with competing ferro- and antiferromagnetic anisotropic exchange interactions. The ground state phase diagram of this model consists of the ferromagnetic and ferrimagnetic phases. We study the ground state and the low-temperature properties on the phase boundary between these phases. The ground state on this phase boundary is macroscopically degenerate and consists of localized magnon states. We calculate the ground state degeneracy and corresponding residual entropy...
March 24, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
H Balout, P Boulet, M-C Record
The present theoretical study, performed using density-functional theory and Boltzmann transport theory formalisms, shows that under 2.246 % isotropic tensile strain, the two energy-lowest conduction bands of Mg2Si overlap. The two, threefold-degenerated orbitals become a unique, sixfold-degenerated orbital. It is demonstrated that such degeneracy implies an increase of the Seebeck coefficient, of the electrical conductivity, of the power factor, and in fine of the figure of merit.
April 2017: Journal of Molecular Modeling
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