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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
Kendra K Frederick, Vladimir K Michaelis, Marc A Caporini, Loren B Andreas, Galia T Debelouchina, Robert G Griffin, Susan Lindquist
The yeast prion protein Sup35NM is a self-propagating amyloid. Despite intense study, there is no consensus on the organization of monomers within Sup35NM fibrils. Some studies point to a β-helical arrangement, whereas others suggest a parallel in-register organization. Intermolecular contacts are often determined by experiments that probe long-range heteronuclear contacts for fibrils templated from a 1:1 mixture of (13)C- and (15)N-labeled monomers. However, for Sup35NM, like many large proteins, chemical shift degeneracy limits the usefulness of this approach...
March 22, 2017: Proceedings of the National Academy of Sciences of the United States of America
Jennifer Lu, Kelin Ru, Ida Candiloro, Alexander Dobrovic, Darren Korbie, Matt Trau
Multiplex bisulfite-PCR sequencing is a convenient and scalable method for the quantitative determination of the methylation state of target DNA regions. A challenge of this application is the presence of CpGs in the same region where primers are being placed. A common solution to the presence of CpGs within a primer-binding region is to substitute a base degeneracy at the cytosine position. However, the efficacy of different substitutions and the extent to which bias towards methylated or unmethylated templates may occur has never been evaluated in bisulfite multiplex sequencing applications...
March 22, 2017: Scientific Reports
Fengjia Fan, Oleksandr Voznyy, Randy P Sabatini, Kristopher T Bicanic, Michael M Adachi, James R McBride, Kemar R Reid, Young-Shin Park, Xiyan Li, Ankit Jain, Rafael Quintero-Bermudez, Mayuran Saravanapavanantham, Min Liu, Marek Korkusinski, Pawel Hawrylak, Victor I Klimov, Sandra J Rosenthal, Sjoerd Hoogland, Edward H Sargent
Colloidal quantum dots (CQDs) feature a low degeneracy of electronic states at the band edges compared with the corresponding bulk material, as well as a narrow emission linewidth. Unfortunately for potential laser applications, this degeneracy is incompletely lifted in the valence band, spreading the hole population among several states at room temperature. This leads to increased optical gain thresholds, demanding high photoexcitation levels to achieve population inversion (more electrons in excited states than in ground states-the condition for optical gain)...
March 20, 2017: Nature
Alexander I Greenwood, Mary C Clay, Chad M Rienstra
Typically, the process of NMR-based structure determination relies on accurately measuring a large number of internuclear distances to serve as restraints for simulated annealing calculations. In solids, the rotational-echo double-resonance (REDOR) experiment is a widely used approach to determine heteronuclear dipolar couplings corresponding to distances usually in the range of 1.5-8Å. A challenge in the interpretation of REDOR data is the degeneracy of symmetric subunits in an oligomer or equivalent molecules in a crystal lattice, which produce REDOR trajectories that depend explicitly on two or more distances instead of one...
February 28, 2017: Journal of Magnetic Resonance
Benoît Boucher, Rabih Al Rahal Al Orabi, Bruno Fontaine, Yuri Grin, Régis Gautier, Jean-François Halet
The possible existence of group 6 TM3 compounds with T = Cr, Mo, W and M = Ga, In is investigated with the aid of density functional theory calculations. Their most probable crystal structure is expected to be of the FeGa3 type tetragonal space group P42/mnm. All compounds are computed to be semiconductors with a band gap ranging from 0.08 to 0.43 eV, at the modified Becke-Johnson level of theory. The thermoelectric properties are analyzed via calculations based on Boltzmann transport equation under a constant relaxation time approximation...
March 20, 2017: Inorganic Chemistry
Yujie Zhou, Bryan Gin-Ge Chen, Nitin Upadhyaya, Vincenzo Vitelli
We study the dynamical response of a diatomic periodic chain of rotors coupled by springs, whose unit cell breaks spatial inversion symmetry. In the continuum description, we derive a nonlinear field theory which admits topological kinks and antikinks as nonlinear excitations but where a topological boundary term breaks the symmetry between the two and energetically favors the kink configuration. Using a cobweb plot, we develop a fixed-point analysis for the kink motion and demonstrate that kinks propagate without the Peierls-Nabarro potential energy barrier typically associated with lattice models...
February 2017: Physical Review. E
Eri Nakatani-Webster, Abhinav Nath
Amyloid formation is implicated in a number of human diseases, and is thought to proceed via a nucleation-dependent polymerization mechanism. Experimenters often wish to relate changes in amyloid formation kinetics, for example, in response to small molecules to specific mechanistic steps along this pathway. However, fitting kinetic fibril formation data to a complex model including explicit rate constants results in an ill-posed problem with a vast number of potential solutions. The levels of uncertainty remaining in parameters calculated from these models, arising both from experimental noise and high levels of degeneracy or codependency in parameters, is often unclear...
March 14, 2017: Biophysical Journal
Luis A Diambra
Degeneracy in the genetic code implies that different codons can encode the same amino acid. Usage preference of synonymous codons has been observed in all domains of life. There is much evidence suggesting that this bias has a major role on protein elongation rate, contributing to differential expression and to co-translational folding. In addition to codon usage bias, other preference variations have been observed such as codon pairs. In this paper, I report that codon pairs have significant different frequency usage for coding either lowly or highly abundant proteins...
2017: PeerJ
T P Bennett, M B Proctor, M Kaczmarek, G D'Alessandro
The viscosity of complex, anisotropic fluids, such as liquid crystals or their colloidal suspensions, is characterized by a number of coefficients. Methods to measure them are, typically, sensitive only to their particular combinations, hence unable to determine them individually. Using an Ericksen-Leslie model and propagation of light through aligned layers of such materials, we show theoretically and verify experimentally how this degeneracy can be lifted by exploiting both the amplitude and frequency of the voltage applied to the cell as control parameters...
March 6, 2017: Journal of Colloid and Interface Science
M A Sentef, A Tokuno, A Georges, C Kollath
We investigate the nonequilibrium dynamics of competing coexisting superconducting (SC) and charge-density wave (CDW) orders in an attractive Hubbard model. A time-periodic laser field A[over →](t) lifts the SC-CDW degeneracy, since the CDW couples linearly to the field (A[over →]), whereas SC couples in second order (A[over →]^{2}) due to gauge invariance. This leads to a striking resonance: When the photon energy is red detuned compared to the equilibrium single-particle energy gap, CDW is enhanced and SC is suppressed, while this behavior is reversed for blue detuning...
February 24, 2017: Physical Review Letters
Dashiell L P Vitullo, Cody C Leary, Patrick Gregg, Roger A Smith, Dileep V Reddy, Siddharth Ramachandran, Michael G Raymer
The interaction of spin and intrinsic orbital angular momentum of light is observed, as evidenced by length-dependent rotations of both spatial patterns and optical polarization in a cylindrically symmetric isotropic optical fiber. Such rotations occur in a straight few-mode fiber when superpositions of two modes with parallel and antiparallel orientation of spin and intrinsic orbital angular momentum (IOAM=2ℏ) are excited, resulting from a degeneracy splitting of the propagation constants of the modes.
February 24, 2017: Physical Review Letters
Petter Brodin
Different human immune system components coordinate to ensure effective control of pathogens. Israel et al. (2017) examine the immune system of a patient with an inborn genetic error, presenting as impaired TLR signaling and staphylococcal disease, and uncover a beautiful example of degeneracy between innate and adaptive branches of immunity.
March 8, 2017: Cell Host & Microbe
Adham Naji, Mina H Soliman
Shape symmetry in dual-mode planar electromagnetic resonators results in their ability to host two degenerate resonant modes. As the designer enforces a controllable break in the symmetry, the degeneracy is removed and the two modes couple, exchanging energy and elevating the resonator into its desirable second-order resonance operation. The amount of coupling is controlled by the degree of asymmetry introduced. However, this mode coupling (or splitting) usually comes at a price. The centre frequency of the perturbed resonator is inadvertently drifted from its original value prior to coupling...
March 8, 2017: Scientific Reports
William P Carbery, Archana Verma, Daniel B Turner
Transient absorption measurements conducted using broadband, 6 fs laser pulses reveal unexpected femtosecond dynamics in the [IrBr6](2-) model system. Vibrational spectra and the X-ray crystal structure indicate that these dynamics are not induced by a Jahn-Teller distortion, a type of conical intersection typically associated with the spectral features of transition metal compounds. Two-dimensional electronic spectra of [IrBr6](2-) contain 23 cross peaks, which necessarily arise from spin-orbit coupling. Real-valued 2D spectra support a spectroscopic basis where strong nonadiabatic coupling, ascribed to multiple conical intersections, mediates rapid energy relaxation to the lowest-energy excited state...
March 8, 2017: Journal of Physical Chemistry Letters
Tiejun Zhu, Yintu Liu, Chenguang Fu, Joseph P Heremans, Jeffrey G Snyder, Xinbing Zhao
The past two decades have witnessed the rapid growth of thermoelectric (TE) research. Novel concepts and paradigms are described here that have emerged, targeting superior TE materials and higher TE performance. These superior aspects include band convergence, "phonon-glass electron-crystal", multiscale phonon scattering, resonant states, anharmonicity, etc. Based on these concepts, some new TE materials with distinct features have been identified, including solids with high band degeneracy, with cages in which atoms rattle, with nanostructures at various length scales, etc...
March 6, 2017: Advanced Materials
Cyril Martins, Markus Aichhorn, Silke Biermann
The interplay of spin-orbit coupling and Coulomb correlations has become a hot topic in condensed matter theory and is especially at stake in 4d and 5d transition metal oxides, like iridates or rhodates. Here, we review recent advances in dynamical mean-field theory(DMFT)-based electronic structure calculations for treating such compounds, introducing all necessary implementation details. We also discuss the evaluation of Hubbard interactions in spin-orbit materials. As an example, we perform DMFT calculations on insulating strontium iridate (Sr<sub>2</sub>IrO<sub>4</sub>) and its 4d metallic counterpart strontium rhodate (Sr<sub>2</sub>RhO<sub>4</sub>)...
March 6, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
T Berlijn, P C Snijders, O Delaire, H-D Zhou, T A Maier, H-B Cao, S-X Chi, M Matsuda, Y Wang, M R Koehler, P R C Kent, H H Weitering
Bulk rutile RuO_{2} has long been considered a Pauli paramagnet. Here we report that RuO_{2} exhibits a hitherto undetected lattice distortion below approximately 900 K. The distortion is accompanied by antiferromagnetic order up to at least 300 K with a small room temperature magnetic moment of approximately 0.05μ_{B} as evidenced by polarized neutron diffraction. Density functional theory plus U (DFT+U) calculations indicate that antiferromagnetism is favored even for small values of the Hubbard U of the order of 1 eV...
February 17, 2017: Physical Review Letters
Salvatore Mandrà, Zheng Zhu, Helmut G Katzgraber
We study the performance of the D-Wave 2X quantum annealing machine on systems with well-controlled ground-state degeneracy. While obtaining the ground state of a spin-glass benchmark instance represents a difficult task, the gold standard for any optimization algorithm or machine is to sample all solutions that minimize the Hamiltonian with more or less equal probability. Our results show that while naive transverse-field quantum annealing on the D-Wave 2X device can find the ground-state energy of the problems, it is not well suited in identifying all degenerate ground-state configurations associated with a particular instance...
February 17, 2017: Physical Review Letters
Jun Luo, Li You, Jiye Zhang, Kai Guo, Hangtian Zhu, Lin Gu, Zhenzhong Yang, Xin Li, Jiong Yang, Wenqing Zhang
Thermoelectric properties of Na-doped PbTe-SrTe system have been improved by the addition of Mn. The substitution of Mn for Pb modifies the band structure of the PbTe-SrTe alloy, which enlarges the band gap and increases the valence band degeneracy. This leads to increased thermopowers and power factors near room temperature, and the electronic contribution to the total thermal conductivity is also substantially reduced due to increased resistivity. Moreover, alloying of MnTe within the PbTe matrix introduces low angle grain boundaries, and significantly reduces the lattice thermal conductivity due to the dislocation scattering...
March 3, 2017: ACS Applied Materials & Interfaces
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