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Gérald Faussurier, Christophe Blancard
We present the relativistic expressions of standard nonrelativistic microreversibility relations that can be used in collisional-radiative equilibrium models to calculate the transition rates including the free electron degeneracy for collisional excitation and deexcitation, collisional ionization and three-body recombination, dielectronic capture and autoionization, photoexcitation and photodeexcitation, and radiative recombination and photoionization. Semiempirical expressions or more refined calculations can be used for the cross sections of interest as long as they are calculated by taking into account either nonrelativistic, relativistic, or ultrarelativistic effects for both the bound and free electrons...
June 2017: Physical Review. E
Wenjian Hu, Rajiv R P Singh, Richard T Scalettar
We apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models-the square- and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-1 Ising (BSI) model, and the two-dimensional XY model-and we examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow the exploration of different phases and symmetry-breaking, but they can distinguish phase-transition types and locate critical points...
June 2017: Physical Review. E
B S Kim, W S Kyung, J J Seo, J Y Kwon, J D Denlinger, C Kim, S R Park
Direct band-gap semiconductors play the central role in optoelectronics. In this regard, monolayer (ML) MX2 (M = Mo, W; X = S, Se) has drawn increasing attention due to its novel optoelectronic properties stemming from the direct band-gap and valley degeneracy. Unfortunately, the more practically usable bulk and multilayer MX2 have indirect-gaps. It is thus highly desired to turn bulk and multilayer MX2 into direct band-gap semiconductors by controlling external parameters. Here, we report angle-resolved photoemission spectroscopy (ARPES) results from Rb dosed MoSe2 that suggest possibility for electric field induced indirect to direct band-gap transition in bulk MoSe2...
July 12, 2017: Scientific Reports
Riccardo Pisoni, Yongjin Lee, Hiske Overweg, Marius Eich, Pauline Simonet, Kenji Watanabe, Takashi Taniguchi, Roman Gorbachev, Thomas Ihn, Klaus Ensslin
We have realized encapsulated trilayer MoS2 devices with gated graphene contacts. In the bulk, we observe an electron mobility as high as 7000 cm(2)/(V s) at a density of 3 × 10(12) cm(-2) at a temperature of 1.9 K. Shubnikov-de Haas oscillations start at magnetic fields as low as 0.9 T. The observed 3-fold Landau level degeneracy can be understood based on the valley Zeeman effect. Negatively biased split gate electrodes allow us to form a channel that can be completely pinched off for sufficiently large gate voltages...
July 7, 2017: Nano Letters
Yanguang Zhou, Xiaojing Gong, Ben Xu, Ming Hu
Thermoelectric (TE) materials manifest themselves to enable direct conversion of temperature differences to electric power and vice versa. Though remarkable advances have been achieved in the past decades for various TE systems, the energy conversion efficiency of TE devices, which is characterized by a dimensionless figure-of-merit (ZT = S(2)σT/(κel + κph)), generally remains a poor factor that severely limits TE devices' competitiveness and range of employment. The bottleneck for substantially boosting the ZT coefficient lies in the strong interdependence of the physical parameters involved in electronic (S and σ, and κel) and phononic (κph) transport...
July 20, 2017: Nanoscale
J S Burdess, B J Gallacher, H T Grigg, Z X Hu, C Dale, N Keegan, J Hedley, C Fu, J Spoors
Resonance based biosensors are used in the detection of biological molecules for medical diagnostics. Sensing in a liquid environment is very desirable for this application, but presents a significant challenge for resonators based upon conventional technologies. In this paper, the major originality lies in the development and exposition of a fundamental theory enabling design of an original elastic resonant sensor whose modes are engineered to simultaneously possess three separate but complementary dynamical properties: namely, (1) in-plane displacement of the free interface whereby the SH waves are uncoupled from the SV and P waves; (2) intrinsic modal trapping; and finally, (3) cyclic symmetry and modal degeneracy...
June 2017: Journal of the Acoustical Society of America
Vladimir M Fomin, Roman Olegovich Rezaev, Evgenii Levchenko, Daniel Grimm, Oliver G Schmidt
Superconducting micro- and nanohelices are proposed for the first time. A theoretical investigation of the superconducting state in the helical coils at the micro- and nanoscale is performed within the time-dependent Ginzburg-Landau approach. The pattern and number of vortices in a stationary distribution are determined by their confinement to the ultrathin helical spiral and can therefore be efficiently controlled by the spiral stripe width and the spiral pitch distance for both dense and sparse spirals. Quasi-degeneracy of vortex patterns is manifested in the helical spiral when the number of vortices is incommensurable with the total number of half-turns...
July 5, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Kellyn M Patros, Jennifer E Mann, Caroline Chick Jarrold
Anion photoelectron imaging was used to measure the photodetachment spectra of molecular complexes formed between O2(-) and a range of atmospherically relevant polar molecules, including species with a carbonyl group (acetone, formaldehyde) and alcohols (ethanol, propenol, butenol). Experimental spectra are analyzed using a combination of Franck-Condon simulations and electronic structure calculations. Strong charge-dipole interactions and H-bonding stabilize the complex anions relative to the neutrals, resulting in a ca...
July 3, 2017: Journal of Physical Chemistry. A
Fabián A García Daza, Josep Bonet Avalos, Allan D Mackie
Experimental measurements of the relaxation kinetics of copolymeric surfactant exchange for micellar systems unexpectedly show a peculiar logarithmic decay. Several authors use polydispersity as an explanation for this behavior. However, in coarse-grained simulations that preserve microscopic details of the surfactants, we find evidence of the same logarithmic behavior. Since we use a strictly monodisperse distribution of chain lengths such a relaxation process cannot be attributed to polydispersity, but has to be caused by an inherent physical process characteristic of this type of system...
June 16, 2017: Physical Review Letters
Xiao Liang, Longjiang Deng, Fei Huang, Tingting Tang, Chuangtang Wang, Yupeng Zhu, Jun Qin, Yan Zhang, Bo Peng, Lei Bi
We report the magnetic proximity effect (MPE) and valley non-degeneracy in monolayer MoS2 and magnetic semiconductor EuS thin film heterojunctions studied by density functional theory (DFT) with the vdW-DF2 correlations. Magnetic moments are observed in MoS2 due to the MPE when forming chemical or van der Waals (vdW) adsorption states with EuS. Spin-orbit coupling (SOC) leads to observable valley non-degeneracy of MoS2 at the K (K') points in the Brillouin zone. The valley Zeeman splitting energy Ez can reach 5...
July 13, 2017: Nanoscale
Charles-Antoine Collins-Fekete, Sébastien Brousmiche, David C Hansen, Luc Beaulieu, Joao Seco
The relative stopping power (RSP) uncertainty is the largest contributor to the range uncertainty in proton therapy. The purpose of this work was to develop a systematic method that yields accurate and patient-specific RSPs by combining 1) pre-treatment X-ray CT and 2) daily proton radiography of the patient. The method was formulated as a penalized least squares optimization problem (<i>argmin</i>(|<b>A</b><b>x</b>-<b>b</b>|<sub>2</sub><sup>2</sup>))...
June 28, 2017: Physics in Medicine and Biology
Morgan P Kelley, Jing Su, Matthew Urban, Morgan Luckey, Enrique R Batista, Ping Yang, Jenifer C Shafer
Recent reports have suggested the late actinides participate in more covalent interactions than the earlier actinides, however, the origin of this shift in chemistry is not understood. This report considers the chemistry of actinide dipicolinate complexes to identify why covalent interactions become more prominent for heavy actinides. A modest increase actinide:dipicolinate stability constants, that is coincident with significantly increased 5f degeneracy with the dipicolinate molecular orbitals, is observed for Bk and Cf relative to Am and Cm...
June 28, 2017: Journal of the American Chemical Society
Karim Essafi, L D C Jaubert, M Udagawa
In breathing pyrochlores and kagomes, couplings between neighbouring tetrahedra and triangles are free to differ. Breathing lattices thus offer the possibility to explore a different facet of the rich physics of these systems. Here we consider nearest-neighbour classical Heisenberg interactions, both ferromagnetic and antiferromagnetic, and study how the anisotropy of breathing lattices modifies the mode spectrum of pyrochlore and kagome systems. The nature and degeneracy of the flat bands are shown to be preserved for any value of the anisotropy...
August 9, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Y Adiguzel
Based on the Shannon's information communication theory, information amount of the entire length of a polymeric macromolecule can be calculated in bits through adding the entropies of each building block. Proteins, DNA and RNA are such macromolecules. When only the building blocks' variation is considered as the source of entropy, there is seemingly lower information in case of the protein if this approach is applied directly on a protein of specific size and the coding sequence size of the mRNA corresponding to the particular length of the protein...
June 15, 2017: Bio Systems
Shahar Amitai, Raphael Blumenfeld
We identify two orthogonal sources of structural entropy in rattler-free granular systems: affine, involving structural changes that only deform the contact network, and topological, corresponding to different topologies of the contact network. We show that a recently developed connectivity-based granular statistical mechanics separates the two naturally by identifying the structural degrees of freedom with spanning trees on the graph of the contact network. We extend the connectivity-based formalism to include constraints on, and correlations between, degrees of freedom as interactions between branches of the spanning tree...
May 2017: Physical Review. E
I I Klimovskikh, A M Shikin, M M Otrokov, A Ernst, I P Rusinov, O E Tereshchenko, V A Golyashov, J Sánchez-Barriga, A Yu Varykhalov, O Rader, K A Kokh, E V Chulkov
One of the most promising platforms for spintronics and topological quantum computation is the two-dimensional electron gas (2DEG) with strong spin-orbit interaction and out-of-plane ferromagnetism. In proximity to an s-wave superconductor, such 2DEG may be driven into a topologically non-trivial superconducting phase, predicted to support zero-energy Majorana fermion modes. Using angle-resolved photoemission spectroscopy and ab initio calculations, we study the 2DEG at the surface of the vanadium-doped polar semiconductor with a giant Rashba-type splitting, BiTeI...
June 13, 2017: Scientific Reports
Paul F Agris, Amithi Narendran, Kathryn Sarachan, Ville Y P Väre, Emily Eruysal
The posttranscriptional modifications of tRNA's anticodon stem and loop (ASL) domain represent a third level, a third code, to the accuracy and efficiency of translating mRNA codons into the correct amino acid sequence of proteins. Modifications of tRNA's ASL domain are enzymatically synthesized and site specifically located at the anticodon wobble position-34 and 3'-adjacent to the anticodon at position-37. Degeneracy of the 64 Universal Genetic Codes and the limitation in the number of tRNA species require some tRNAs to decode more than one codon...
2017: Enzymes
Chen Li, Jianfeng Lu, Weitao Yang
We analyze four ways of formulating the Kohn-Sham (KS) density functionals with a fractional number of electrons, through extending the constrained search space from the Kohn-Sham and the generalized Kohn-Sham (GKS) non-interacting v-representable density domain for integer systems to four different sets of densities for fractional systems. In particular, these density sets are (I) ensemble interacting N-representable densities, (II) ensemble non-interacting N-representable densities, (III) non-interacting densities by the Janak construction, and (IV) non-interacting densities whose composing orbitals satisfy the Aufbau occupation principle...
June 7, 2017: Journal of Chemical Physics
T Micklitz, M R Norman
We classify line nodes in superconductors with strong spin-orbit interactions and time-reversal symmetry, where the latter may include nonprimitive translations in the magnetic Brillouin zone to account for coexistence with antiferromagnetic order. We find four possible combinations of irreducible representations of the order parameter on high-symmetry planes, two of which allow for line nodes in pseudospin-triplet pairs and two that exclude conventional fully gapped pseudospin-singlet pairs. We show that the former can only be realized in the presence of band-sticking degeneracies, and we verify their topological stability using arguments based on Clifford algebra extensions...
May 19, 2017: Physical Review Letters
L D C Jaubert, T Lin, T S Opel, P C W Holdsworth, M J P Gingras
Motivated by recent realizations of Dy_{2}Ti_{2}O_{7} and Ho_{2}Ti_{2}O_{7} spin ice thin films, and more generally by the physics of confined gauge fields, we study a model spin ice thin film with surfaces perpendicular to the [001] cubic axis. The resulting open boundaries make half of the bonds on the interfaces inequivalent. By tuning the strength of these inequivalent "orphan" bonds, dipolar interactions induce a surface ordering equivalent to a two-dimensional crystallization of magnetic surface charges...
May 19, 2017: Physical Review Letters
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