413 research outputs found
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
On the example of exceptional families of viruses we i) show the existence of
a completely new type of matter organization in nanoparticles, in which the
regions with a chiral pentagonal quasicrystalline order of protein positions
are arranged in a structure commensurate with the spherical topology and
dodecahedral geometry, ii) generalize the classical theory of quasicrystals
(QCs) to explain this organization, and iii) establish the relation between
local chiral QC order and nonzero curvature of the dodecahedral capsid faces.Comment: 8 pages, 3 figure
Charge transfer via a two-strand superexchange bridge in DNA
Charge transfer in a DNA duplex chain is studied by constructing a system
with virtual electrodes connected at the ends of each DNA strand. The systeym
is described by the tight-binding model and its transport is analyzed by the
transfer matrix method. The very weak distance dependence in long
(G:C)(T:A)_M(G:C)_3 DNA chain observed in experiment [B. Giese, et al., Nature
412, 318 (2001)] is explained by a unistep two-strand superexchange bridge
without the need for the multi-step thermally-induced hopping mechanism or the
dephasing effect. The crossover number M_c of (T:A) base pairs, where crossover
between strong and weak distance dependence occurs, reflects the ratio of
intra- and inter-strand neighboring base-base couplings.Comment: accepted for publication in Phys. Rev. Let
Trapping of giant-planet cores - I. Vortex aided trapping at the outer dead zone edge
In this paper the migration of a 10 Earth-mass planetary core is investigated
at the outer boundary of the dead zone of a protoplanetary disc by means of 2D
hydrodynamic simulations done with the graphics processor unit version of the
FARGO code. In the dead zone, the effective viscosity is greatly reduced due to
the disc self-shielding against stellar UV radiation, X-rays from the stellar
magnetosphere and interstellar cosmic rays. As a consequence, mass accumulation
occurs near the outer dead zone edge, which is assumed to trap planetary cores
enhancing the efficiency of the core-accretion scenario to form giant planets.
Contrary to the perfect trapping of planetary cores in 1D models, our 2D
numerical simulations show that the trapping effect is greatly dependent on the
width of the region where viscosity reduction is taking place. Planet trapping
happens exclusively if the viscosity reduction is sharp enough to allow the
development of large-scale vortices due to the Rossby wave instability. The
trapping is only temporarily, and its duration is inversely proportional to the
width of the viscosity transition. However, if the Rossby wave instability is
not excited, a ring-like axisymmetric density jump forms, which cannot trap the
10 Earth-mass planetary cores. We revealed that the stellar torque exerted on
the planet plays an important role in the migration history as the barycentre
of the system significantly shifts away from the star due to highly
non-axisymmetric density distribution of the disc. Our results still support
the idea of planet formation at density/pressure maximum, since the migration
of cores is considerably slowed down enabling them further growth and runaway
gas accretion in the vicinity of an overdense region.Comment: 23 pages, 31 figures, accepted for publication in MNRA
Chiral Observables and Modular Invariants
Various definitions of chiral observables in a given Moebius covariant
two-dimensional theory are shown to be equivalent. Their representation theory
in the vacuum Hilbert space of the 2D theory is studied. It shares the general
characteristics of modular invariant partition functions, although SL(2,Z)
transformation properties are not assumed. First steps towards classification
are made.Comment: 28 pages, 1 figur
Circular Modes for Flat Beams in LHC
Typically x/y optical coupling is considered as unwanted and thus
suppressed--particular exclusions are electron and ionization coolers. Could
some special coupled modes be effectively applied for the LHC complex?
Apparently, the answer is positive: use of the circular modes in the injectors
with their transformation into planar modes in the LHC allows both the space
charge and beam-beam luminosity limitations to be significantly reduced, if not
practically eliminated.Comment: 3 p
Spectral properties of a narrow-band Anderson model
We consider single-particle spectra of a symmetric narrow-band Anderson
impurity model, where the host bandwidth is small compared to the
hybridization strength . Simple 2nd order perturbation theory (2PT)
in is found to produce a rich spectral structure, that leads to rather good
agreement with extant Lanczos results and offers a transparent picture of the
underlying physics. It also leads naturally to two distinct regimes of spectral
behaviour, and (with the quasi-particle
weight), whose existence and essential characteristics are discussed and shown
to be independent of 2PT itself. The self-energy is also
examined beyond the confines of PT. It is argued that on frequency scales of
order , the self-energy in {\em strong} coupling
is given precisely by the 2PT result, and we point out that the resultant poles
in connect continuously to that characteristic of the atomic
limit. This in turn offers a natural rationale for the known inability of the
skeleton expansion to capture such behaviour, and points to the intrinsic
dangers of partial infinite-order summations that are based on PT in .Comment: 10 pages, 2 Postscript figures, uses RevTex 3.1; accepted for
publication in Phys. Rev. B1
How to add a boundary condition
Given a conformal QFT local net of von Neumann algebras B_2 on the
two-dimensional Minkowski spacetime with irreducible subnet A\otimes\A, where A
is a completely rational net on the left/right light-ray, we show how to
consistently add a boundary to B_2: we provide a procedure to construct a
Boundary CFT net B of von Neumann algebras on the half-plane x>0, associated
with A, and locally isomorphic to B_2. All such locally isomorphic Boundary CFT
nets arise in this way. There are only finitely many locally isomorphic
Boundary CFT nets and we get them all together. In essence, we show how to
directly redefine the C* representation of the restriction of B_2 to the
half-plane by means of subfactors and local conformal nets of von Neumann
algebras on S^1.Comment: 20 page
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