18,106 research outputs found

    Nodal-line semimetals from Weyl superlattices

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    The existence and topological classification of lower-dimensional Fermi surfaces is often tied to the crystal symmetries of the underlying lattice systems. Artificially engineered lattices, such as heterostructures and other superlattices, provide promising avenues to realize desired crystal symmetries that protect lower-dimensional Fermi surface, such as nodal lines. In this work, we investigate a Weyl semimetal subjected to spatially periodic onsite potential, giving rise to several phases, including a nodal-line semimetal phase. In contrast to proposals that purely focus on lattice symmetries, the emergence of the nodal line in this setup does not require small spin-orbit coupling, but rather relies on its presence. We show that the stability of the nodal line is understood from reflection symmetry and a combination of a fractional lattice translation and charge-conjugation symmetry. Depending on the choice of parameters, this model exhibits drumhead surface states that are exponentially localized at the surface, or weakly localized surface states that decay into the bulk at all energies.Comment: 11 pages, 8 figures, Editors' Suggestio

    The Casimir force of Quantum Spring in the (D+1)-dimensional spacetime

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    The Casimir effect for a massless scalar field on the helix boundary condition which is named as quantum spring is studied in our recent paper\cite{Feng}. In this paper, the Casimir effect of the quantum spring is investigated in (D+1)(D+1)-dimensional spacetime for the massless and massive scalar fields by using the zeta function techniques. We obtain the exact results of the Casimir energy and Casimir force for any DD, which indicate a Z2Z_2 symmetry of the two space dimensions. The Casimir energy and Casimir force have different expressions for odd and even dimensional space in the massless case but in both cases the force is attractive. In the case of odd-dimensional space, the Casimir energy density can be expressed by the Bernoulli numbers, while in the even case it can be expressed by the ζ\zeta-function. And we also show that the Casimir force has a maximum value which depends on the spacetime dimensions. In particular, for a massive scalar field, we found that the Casimir force varies as the mass of the field changes.Comment: 9 pages, 5 figures, v2, massive case added, refs. adde

    Energy shift of the three-particle system in a finite volume

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    Using the three-particle quantization condition recently obtained in the particle-dimer framework, the finite-volume energy shift of the two lowest three-particle scattering states is derived up to and including order L6L^{-6}. Furthermore, assuming that a stable dimer exists in the infinite volume, the shift for the lowest particle-dimer scattering state is obtained up to and including order L3L^{-3}. The result for the lowest three-particle state agrees with the results from the literature, and the result for the lowest particle-dimer state reproduces the one obtained by using the Luescher equation.Comment: Final version published in Phys. Rev. D. Corrected typos: factor of 2 in Eq. (115) [previously Eq. (114)] and factor 6 in Eq. (120) [previously Eq. (119)

    Diffusion-limited loop formation of semiflexible polymers: Kramers theory and the intertwined time scales of chain relaxation and closing

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    We show that Kramers rate theory gives a straightforward, accurate estimate of the closing time τc\tau_c of a semiflexible polymer that is valid in cases of physical interest. The calculation also reveals how the time scales of chain relaxation and closing are intertwined, illuminating an apparent conflict between two ways of calculating τc\tau_c in the flexible limit.Comment: Europhys. Lett., 2003 (in press). 8 pages, 3 figures. See also, physics/0101087 for physicist's approach to and the importance of semiflexible polymer looping, in DNA replicatio

    Comparative study of CXC chemokines modulation in brown trout (Salmo trutta) following infection with a bacterial or viral pathogen

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    Acknowledgements We would like to acknowledge Richard Paley, Tom Hill and Georgina Rimmer for their collaboration during brown trout infection challenges in CEFAS-Weymouth biosecurity facilities. Bartolomeo Gorgoglione, Stephen W. Feist and Nick G. H. Taylor were supported by a DEFRA grant (F1198).Peer reviewedPostprin

    Spectroscopy of q3qˉ3\rm{q}^3\bar{\rm{q}}^3-States in Quark Model and Baryon-Antibaryon Enhancements

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    We study the mass spectrum of the q3qˉ3\rm{q}^3\bar{\rm{q}}^3 mesons both from the quark model with triquark correlations and from common quark model with colormagnetic interactions and with relative S-waves between quarks. Two cluster configurations (q3)(qˉ3)(\rm{q}^3)-(\bar{\rm{q}}^3) and (q2qˉ)(qqˉ2)(\rm{q}^2\bar{\rm{q}})-(\rm{q}\bar{\rm{q}}^2) are considered. In the spectrum we find rather stable states which have the same quantum number with particle resonances which are corresponding to the ppˉp\bar{p} enhancement, pΛˉp\bar{\Lambda} enhancement and ΛΛˉ\Lambda\bar{\Lambda} enhancement with spin-0\mathbf{0} or 1\mathbf{1}. This imply these enhancements are NOT experimental artifacts. The color-spin-flavor structures of ppˉp\bar{p}, pΛˉp\bar{\Lambda}, and ΛΛˉ\Lambda\bar{\Lambda} enhancements are revealed. The existence of spin-1\mathbf{1} ΛΛˉ,pΛˉ,ppˉ\Lambda\bar{\Lambda}, p\bar{\Lambda}, p\bar{p} enhancements is predicted.Comment: 45 pages, 5 figure

    The WISE AGN Catalog

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    We present two large catalogs of AGN candidates identified across ~75% of the sky from the Wide-field Infrared Survey Explorer's AllWISE Data Release. Both catalogs, some of the largest such catalogs published to date, are selected purely on the basis of mid-IR photometry in the WISE W1 and W2 bands. The catalogs are designed to be appropriate for a broad range of scientific investigations, with one catalog emphasizing reliability while the other emphasizes completeness. Specifically, the R90 catalog consists of 4,543,530 AGN candidates with 90% reliability, while the C75 catalog consists of 20,907,127 AGN candidates with 75% completeness. We provide a detailed discussion of potential artifacts, and excise portions of the sky close to the Galactic Center, Galactic Plane, nearby galaxies, and other expected contaminating sources. Our final catalogs cover 30,093 deg^2 of extragalactic sky. These catalogs are expected to enable a broad range of science, and we present a few simple illustrative cases. From the R90 sample we identify 45 highly variable AGN lacking radio counterparts in the FIRST survey, implying they are unlikely to be blazars. One of these sources, WISEA J142846.71+172353.1, is a mid-IR-identified changing-look quasar at z=0.104. We characterize our catalogs by comparing them to large, wide-area AGN catalogs in the literature, specifically UV-to-near-IR quasar selections from SDSS and XDQSOz, mid-IR selection from Secrest et al. (2015) and X-ray selection from ROSAT. From the latter work, we identify four ROSAT X-ray sources that each are matched to three WISE-selected AGN in the R90 sample within 30". Palomar spectroscopy reveals one of these systems, 2RXS J150158.6+691029, to consist of a triplet of quasars at z=1.133 +/- 0.004, suggestive of a rich group or forming galaxy cluster.(Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplements. Updated with comments from the referee. 20 pages, 15 figures, 8 tables. The WISE AGN Catalogs can be made available upon request by writing to [email protected]

    The magnetic structure of the zigzagzigzag chain family Nax_{x}Ca1x_{1-x}V2_2O4_4 determined by muon-spin rotation

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    We present muon-spin rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzagzigzag chain compounds, Nax_xCa1x_{1-x}V2_2O4_4. In this family, we explore the magnetic properties from the metallic NaV2_2O4_4 to the insulating CaV2_2O4_4. We find a critical xc(0.833)x_c(\sim0.833) which separates the low and high Na-concentration dependent transition temperature and its magnetic ground state. In the x<xcx<x_c compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the x>xcx>x_c compounds, multiple sub-phases appear with temperature and xx. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.Comment: 7 pages, 7 figures, accepted for publication in PR
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