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Roberto L Moreira, Ricardo P S M Lobo, Anderson Dias
A comprehensive set of optical vibrational modes of monoclinic taurine crystals was determined by Raman scattering, and infrared reflectivity and transmission spectroscopies. By using appropriate scattering/reflection geometries, the vibrational modes were resolved by polarization and the most relevant modes of the crystal could be assigned. In particular, we were able to review the symmetry of the gerade modes and to resolve ambiguities in the literature. Owing to the non-orthogonal character of Bu modes in monoclinic crystals (lying on the optic axial plane), we carried out a generalized Lorentz dispersion analysis consisting of simultaneous adjust of infrared-reflectivity spectra at various light polarization angles...
July 14, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Dan Wang, Weizhong Chen, Shanqing Huang, Yafeng He, Xichun Liu, Qingyuan Hu, Tianbiao Wei, Hong Shang, Jianhua Gan, Hao Chen
Pseudomonas aeruginosa (P. aeruginosa) is a major opportunistic human pathogen, causing serious nosocomial infections among immunocompromised patients by multi-determinant virulence and high antibiotic resistance. The CzcR-CzcS signal transduction system in P. aeruginosa is primarily involved in metal detoxification and antibiotic resistance through co-regulating cross-resistance between Zn(II) and carbapenem antibiotics. Although the intracellular regulatory pathway is well-established, the mechanism by which extracellular sensor domain of histidine kinase (HK) CzcS responds to Zn(II) stimulus to trigger downstream signal transduction remains unclear...
July 21, 2017: PLoS Pathogens
Q Hu, G Vidal
The generalization of the multiscale entanglement renormalization ansatz (MERA) to continuous systems, or cMERA [Haegeman et al., Phys. Rev. Lett. 110, 100402 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.100402], is expected to become a powerful variational ansatz for the ground state of strongly interacting quantum field theories. In this Letter, we investigate, in the simpler context of Gaussian cMERA for free theories, the extent to which the cMERA state |Ψ^{Λ}⟩ with finite UV cutoff Λ can capture the spacetime symmetries of the ground state |Ψ⟩...
July 7, 2017: Physical Review Letters
Luca Di Luzio, Enrico Nardi, Lorenzo Ubaldi
A SU(N)_{L}×SU(N)_{R} gauge theory for a scalar multiplet Y transforming in the bifundamental representation (N,N[over ¯]) preserves, for N>4, an accidental U(1) symmetry first broken at operator dimension N. A vacuum expectation value for Y can break the symmetry to H_{s}=SU(N)_{L+R} or to H_{h}=SU(N-1)_{L}×SU(N-1)_{R}×U(1)_{L+R}. In the first case the accidental U(1) gets also broken, yielding a pseudo-Nambu-Goldstone boson with mass suppression controlled by N. In the second case a global U(1) remains unbroken...
July 7, 2017: Physical Review Letters
David T Stephen, Dong-Sheng Wang, Abhishodh Prakash, Tzu-Chieh Wei, Robert Raussendorf
We consider ground states of quantum spin chains with symmetry-protected topological (SPT) order as resources for measurement-based quantum computation (MBQC). We show that, for a wide range of SPT phases, the computational power of ground states is uniform throughout each phase. This computational power, defined as the Lie group of executable gates in MBQC, is determined by the same algebraic information that labels the SPT phase itself. We prove that these Lie groups always contain a full set of single-qubit gates, thereby affirming the long-standing conjecture that general SPT phases can serve as computationally useful phases of matter...
July 7, 2017: Physical Review Letters
Michele Ceotto, Giovanni Di Liberto, Riccardo Conte
A new semiclassical "divide-and-conquer" method is presented with the aim of demonstrating that quantum dynamics simulations of high dimensional molecular systems are doable. The method is first tested by calculating the quantum vibrational power spectra of water, methane, and benzene-three molecules of increasing dimensionality for which benchmark quantum results are available-and then applied to C_{60}, a system characterized by 174 vibrational degrees of freedom. Results show that the approach can accurately account for quantum anharmonicities, purely quantum features like overtones, and the removal of degeneracy when the molecular symmetry is broken...
July 7, 2017: Physical Review Letters
Vincenzo Alba, Maurizio Fagotti
Nonequilibrium time evolution in isolated many-body quantum systems generally results in thermalization. However, the relaxation process can be very slow, and quasistationary nonthermal plateaux are often observed at intermediate times. The paradigmatic example is a quantum quench in an integrable model with weak integrability breaking; for a long time, the state cannot escape the constraints imposed by the approximate integrability. We unveil a new mechanism of prethermalization, based on the presence of a symmetry of the prequench Hamiltonian, which is spontaneously broken at zero temperature and is explicitly broken by the postquench Hamiltonian...
July 7, 2017: Physical Review Letters
Han-Jin Noh, Jinwon Jeong, En-Jin Cho, Kyoo Kim, B I Min, Byeong-Gyu Park
A Dirac fermion in a topological Dirac semimetal is a quadruple-degenerate quasiparticle state with a relativistic linear dispersion. Breaking either time-reversal or inversion symmetry turns this system into a Weyl semimetal that hosts double-degenerate Weyl fermion states with opposite chiralities. These two kinds of quasiparticles, although described by a relativistic Dirac equation, do not necessarily obey Lorentz invariance, allowing the existence of so-called type-II fermions. The recent theoretical discovery of type-II Weyl fermions evokes the prediction of type-II Dirac fermions in PtSe_{2}-type transition metal dichalcogenides, expecting experimental confirmation...
July 7, 2017: Physical Review Letters
Yanfeng Ge, Wenhui Wan, Yong Liu, Ying Zhang
Recently, type-II Dirac fermion, a new topological state, is proposed in the Al3V family. It breaks the Lorentz symmetry and has unique physical properties. We use the first-principles calculations to investigate the elec- tronic transport limited by the phonon scattering. The electronic resistivity in the xy plane is estimated to be 24.1 μΩ·cm for Al3V and is much lower than that along z direction. The heavy electronic effective mass a- long z direction and the main electron-phonon coupling, originating from the phonon modes vibrating along z direction, lead to the anisotropic electronic transport, which is also found in other members of Al3V family...
July 21, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Shiqing Deng, Shaobo Cheng, Changsong Xu, Binghui Ge, Xuefeng Sun, Rong Yu, Wenhui Duan, Jing Zhu
The broken symmetry along with anomalous defect structures and charging conditions at multiferroics surface can alter both crystal structures and electronic configurations, bringing in emergent physical properties. Extraordinary surface states are induced into original mutually-coupled order parameters in such strongly correlated oxides, which flourish in diverse properties, however remain less explored. Here, we report the peculiar surface ferroelectric states and reconfigurable functionalities driven by the relaxation of surface and consequent changes in O-2p and Y-4d orbital (p-d) hybridization within a representative hexagonal multiferroics YMnO3...
July 21, 2017: ACS Applied Materials & Interfaces
Minoru Akutsu, Kiichirou Koyasu, Junko Atobe, Ken Miyajima, Masaaki Mitsui, Hironori Tsunoyama, Atsushi Nakajima
The geometric and electronic properties of silicon-atom-doped aluminum clusters, AlnSim (n = 7-30, m = 0-2), were investigated experimentally. The size dependences of the ionization energy and electron affinity of AlnSim show that the stability of AlnSim is governed by the total number of valence electrons in the clusters, where Al and Si atoms behave as trivalent and tetravalent atoms, respectively. Together with theoretical calculations, it has been revealed that neutral Al10Si and Al12Si have a cage-like geometry with central Si atom encapsulation and closed electronic structures of superatomic orbitals (SAOs), and also that they both exhibit geometric robustness against reductive and oxidative changes as cage-like binary superatoms of Si@Al10 and Si@Al12...
July 21, 2017: Physical Chemistry Chemical Physics: PCCP
Kyung Jin Park, Ji-Hyeok Huh, Dae-Woong Jung, Jin-Sung Park, Gwan H Choi, Gaehang Lee, Pil J Yoo, Hong-Gyu Park, Gi-Ra Yi, Seungwoo Lee
Atomic force microscopy (AFM) nanomanipulation has been viewed as a deterministic method for the assembly of plasmonic metamolecules because it enables unprecedented engineering of clusters with exquisite control over particle number and geometry. Nevertheless, the dimensionality of plasmonic metamolecules via AFM nanomanipulation is limited to 2D, so as to restrict the design space of available artificial electromagnetisms. Here, we show that "2D" nanomanipulation of the AFM tip can be used to assemble "3D" plasmonic metamolecules in a versatile and deterministic way by dribbling highly spherical and smooth gold nanospheres (NSs) on a nanohole template rather than on a flat surface...
July 20, 2017: Scientific Reports
Koichi Tamura, Shigehiko Hayashi
The mitochondrial ADP/ATP carrier (AAC) is a membrane transporter that exchanges a cytosolic ADP for a matrix ATP. Atomic structures in an outward-facing (OF) form which binds an ADP from the intermembrane space have been solved by X-ray crystallography, and revealed their unique pseudo three-fold symmetry fold which is qualitatively different from pseudo two-fold symmetry of most transporters of which atomic structures have been solved. However, any atomic-level information on an inward-facing (IF) form, which binds an ATP from the matrix side and is fixed by binding of an inhibitor, bongkrekic acid (BA), is not available, and thus its alternating access mechanism for the transport process is unknown...
2017: PloS One
Lei Wang, Shengcai Zhu, Meikun Shen, Haiwen Tian, Songhai Xie, Hongbin Zhang, Yahong Zhang, Yi Tang
Screw dislocation structure in crystal are origin of symmetry breaking in a wide range of dense phase crystals. Preparation of such analogous structure in framework phase crystals is of great importance in zeolites but still a challenge. On the basis of crystal structure-solving and model building, we found that the two specific intergrowths in MTW zeolite produce this complex fractal and spiral structure. With the structure determined parameters (spiral pitch h, screw angle θ and spatial angle ψ) of Burgers circuit, the screw dislocation structure can be constructed by two different dimensional intergrowth sections...
July 20, 2017: Angewandte Chemie
Lei Xu, Ziba Zangeneh, Ravi Yadav, Stanislav Avdoshenko, Jeroen van den Brink, Anton Jesche, Liviu Hozoi
A remarkably large magnetic anisotropy energy of 305 K is computed by quantum chemistry methods for divalent Fe(2+) d(6) substitutes at Li-ion sites with D6h point-group symmetry within the solid-state matrix of Li3N. This is similar to values calculated by the same approach and confirmed experimentally for linearly coordinated monovalent Fe(1+) d(7) species, among the largest so far in the research area of single-molecule magnets. Our ab initio results therefore mark a new exciting exploration path in the search for superior single-molecule magnets, rooted in the configuration of d(6) transition-metal ions with linear or quasilinear nearest-neighbor coordination...
July 20, 2017: Nanoscale
Kevin E Riley, Khanh-An Tran
Halogen bonds involving cationic halogen bond donors and anionic halogen bond acceptors have recently been recognized as being important in stabilizing the crystal structures of many salts. Theoretical characterization of these types of interactions, most importantly in terms of their directionality, has been limited. Here we generate high-quality symmetry adapted perturbation theory potential energy curves of a H3N-C[triple bond, length as m-dash]C-Br(+)Cl(-) model system in order to characterize halogen bonds involving charged species, in terms of contributions from electrostatics, exchange, induction, and dispersion, with special emphasis on analyzing contributions that are most responsible for the directionality of these interactions...
July 20, 2017: Faraday Discussions
G L Jiang, W J Chen, Biao Wang, Jian Shao, Yue Zheng
Both electrodes and substrates are factors of great significance for the performance of ferroelectric tunnel junctions (FTJs) in designing functional nanodevices. To provide a comprehensive view on the polarization stability in FTJs due to the effects of an electrode and a substrate misfit strain, in this work we calculated more than 1000 FTJ structures by utilizing an ab initio density functional theory (DFT) method, via changing the symmetry of the FTJ structure (i.e., both asymmetric and symmetric FTJs), electrodes (including Au, Ag, Cu, Pt, Co, Fe, and SrRuO3), barrier thickness (ranging from 2 to 10 unit cells), polarization direction (both positive and negative polarizations) and epitaxial strain (i...
July 20, 2017: Physical Chemistry Chemical Physics: PCCP
A Vispa, D Monserrat, G J Cuello, F Fernandez-Alonso, S Mukhopadhyay, F Demmel, J Ll Tamarit, L C Pardo
Globular molecules of 1-chloroadamantane form a plastic phase in which the molecules rotate in a restrained way, but with their centers of mass forming a crystalline ordered lattice. Plastic phases can be regarded as test cases for the study of disordered phases since, contrary to what happens in the liquid phase, there is a lack of stochastic translational degrees of freedom. When the temperature is increased, a hump in the specific heat curve is observed indicating a change in the energetic footprint of the dynamics of the molecules...
July 20, 2017: Physical Chemistry Chemical Physics: PCCP
Barry Bradlyn, L Elcoro, Jennifer Cano, M G Vergniory, Zhijun Wang, C Felser, M I Aroyo, B Andrei Bernevig
Since the discovery of topological insulators and semimetals, there has been much research into predicting and experimentally discovering distinct classes of these materials, in which the topology of electronic states leads to robust surface states and electromagnetic responses. This apparent success, however, masks a fundamental shortcoming: topological insulators represent only a few hundred of the 200,000 stoichiometric compounds in material databases. However, it is unclear whether this low number is indicative of the esoteric nature of topological insulators or of a fundamental problem with the current approaches to finding them...
July 19, 2017: Nature
Shuyan Lin, Li Zhang, Gadi V P Reddy, Cang Hui, Johan Gielis, Yulong Ding, Peijian Shi
The size and shape of plant leaves change with growth, and an accurate description of leaf shape is crucial for describing plant morphogenesis and development. Bilateral symmetry, which has been widely observed but poorly examined, occurs in both dicot and monocot leaves, including all nominated bamboo species (approximately 1,300 species), of which at least 500 are found in China. Although there are apparent differences in leaf size among bamboo species due to genetic and environmental profiles, bamboo leaves have bilateral symmetry with parallel venation and appear similar across species...
October 2016: Ecology and Evolution
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