18,106 research outputs found
Nodal-line semimetals from Weyl superlattices
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
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 -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 , which indicate a
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
-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
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 .
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 . 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
We show that Kramers rate theory gives a straightforward, accurate estimate
of the closing time 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 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
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 -States in Quark Model and Baryon-Antibaryon Enhancements
We study the mass spectrum of the 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 and
are considered. In the spectrum
we find rather stable states which have the same quantum number with particle
resonances which are corresponding to the enhancement,
enhancement and enhancement with
spin- or . This imply these enhancements are NOT
experimental artifacts. The color-spin-flavor structures of ,
, and enhancements are revealed. The
existence of spin-
enhancements is predicted.Comment: 45 pages, 5 figure
The WISE AGN Catalog
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 chain family NaCaVO determined by muon-spin rotation
We present muon-spin rotation measurements on polycrystalline samples of the
complete family of the antiferromagnetic (AF) chain compounds,
NaCaVO. In this family, we explore the magnetic properties
from the metallic NaVO to the insulating CaVO. We find a
critical which separates the low and high Na-concentration
dependent transition temperature and its magnetic ground state. In the
compounds, the magnetic ordered phase is characterized by a single homogenous
phase and the formation of incommensurate spin-density-wave order. Whereas in
the compounds, multiple sub-phases appear with temperature and .
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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