3,827 research outputs found
Molecular evolution of the sheep prion protein gene
Transmissible spongiform encephalopathies (TSEs) are infectious, fatal neurodegenerative diseases characterized by aggregates of modified forms of the prion protein (PrP) in the central nervous system. Well known examples include variant Creutzfeldt-Jakob Disease (vCJD) in humans, BSE in cattle, chronic wasting disease in deer and scrapie in sheep and goats. In humans, sheep and deer, disease susceptibility is determined by host genotype at the prion protein gene (PRNP). Here I examine the molecular evolution of PRNP in ruminants and show that variation in sheep appears to have been maintained by balancing selection, a profoundly different process from that seen in other ruminants. Scrapie eradication programs such as those recently implemented in the UK, USA and elsewhere are based on the assumption that PRNP is under positive selection in response to scrapie. If, as these data suggest, that assumption is wrong, eradication programs will disrupt this balancing selection, and may have a negative impact on the fitness or scrapie resistance of national flocks
Non-diagonal solutions of the reflection equation for the trigonometric vertex model
We obtain a class of non-diagonal solutions of the reflection equation for
the trigonometric vertex model. The solutions can be expressed
in terms of intertwinner matrix and its inverse, which intertwine two
trigonometric R-matrices. In addition to a {\it discrete} (positive integer)
parameter , , the solution contains {\it continuous}
boundary parameters.Comment: Latex file, 14 pages; V2, minor typos corrected and a reference adde
On the second reference state and complete eigenstates of the open XXZ chain
The second reference state of the open XXZ spin chain with non-diagonal
boundary terms is studied. The associated Bethe states exactly yield the second
set of eigenvalues proposed recently by functional Bethe Ansatz. In the
quasi-classical limit, two sets of Bethe states give the complete eigenstates
of the associated Gaudin model.Comment: Latex file, 12 pages; New version appears in JHE
High performance Beowulf computer for lattice QCD
We describe the construction of a high performance parallel computer composed
of PC components, as well as the performance test in lattice QCD.Comment: Lattice 2001 (Algorithms and Machines) 3 page
Finite-temperature perturbation theory for quasi-one-dimensional spin-1/2 Heisenberg antiferromagnets
We develop a finite-temperature perturbation theory for quasi-one-dimensional
quantum spin systems, in the manner suggested by H.J. Schulz (1996) and use
this formalism to study their dynamical response. The corrections to the
random-phase approximation formula for the dynamical magnetic susceptibility
obtained with this method involve multi-point correlation functions of the
one-dimensional theory on which the random-phase approximation expansion is
built. This ``anisotropic'' perturbation theory takes the form of a systematic
high-temperature expansion. This formalism is first applied to the estimation
of the N\'eel temperature of S=1/2 cubic lattice Heisenberg antiferromagnets.
It is then applied to the compound CsCuCl, a frustrated S=1/2
antiferromagnet with a Dzyaloshinskii-Moriya anisotropy. Using the next leading
order to the random-phase approximation, we determine the improved values for
the critical temperature and incommensurability. Despite the non-universal
character of these quantities, the calculated values are different by less than
a few percent from the experimental values for both compounds.Comment: 11 pages, 6 figure
elliptic Gaudin model with open boundaries
The elliptic Gaudin model with integrable boundaries specified by
generic non-diagonal K-matrices with free boundary parameters is studied.
The commuting families of Gaudin operators are diagonalized by the algebraic
Bethe ansatz method. The eigenvalues and the corresponding Bethe ansatz
equations are obtained.Comment: 21 pages, Latex fil
Game prototype for understanding safety issues of life boat launching process.
Novel advanced game techniques provide us with new possibilities to mimic a complicated training process, with the benefit of safety enhancement. In this paper, we design and implement a 3D game which imitates the lifeboat launching process. Lifeboat launching is such a complex but vital process which can on one side saving people's life on sea and on the other side associating many potential hazards. It involves both the tractor manoeuvres and boat operations. The primary objective of the game is to allow novices to better understand the sequence of the operations in launching process and manager the potential hazards happening during the launching. There is also great educational significance with the promotion of the game to the general public for enhanced awareness of safety issues. The key modules of the game are designed based on physical simulation which gives the players enhanced plausible cognition and enjoyable interaction
Drinfeld Twists and Algebraic Bethe Ansatz of the Supersymmetric t-J Model
We construct the Drinfeld twists (factorizing -matrices) for the
supersymmetric t-J model. Working in the basis provided by the -matrix (i.e.
the so-called -basis), we obtain completely symmetric representations of the
monodromy matrix and the pseudo-particle creation operators of the model. These
enable us to resolve the hierarchy of the nested Bethe vectors for the
invariant t-J model.Comment: 23 pages, no figure, Latex file, minor misprints are correcte
Coulomb Gaps in One-Dimensional Spin-Polarized Electron Systems
We investigate the density of states (DOS) near the Fermi energy of
one-dimensional spin-polarized electron systems in the quantum regime where the
localization length is comparable to or larger than the inter-particle
distance. The Wigner lattice gap of such a system, in the presence of weak
disorder, can occur precisely at the Fermi energy, coinciding with the Coulomb
gap in position. The interplay between the two is investigated by treating the
long-range Coulomb interaction and the random disorder potential in a
self-consistent Hartree-Fock approximation. The DOS near the Fermi energy is
found to be well described by a power law whose exponent decreases with
increasing disorder strength.Comment: 4 pages, revtex, 4 figures, to be published in Phys. Rev. B as a
Rapid Communicatio
QFT on homothetic Killing twist deformed curved spacetimes
We study the quantum field theory (QFT) of a free, real, massless and
curvature coupled scalar field on self-similar symmetric spacetimes, which are
deformed by an abelian Drinfel'd twist constructed from a Killing and a
homothetic Killing vector field. In contrast to deformations solely by Killing
vector fields, such as the Moyal-Weyl Minkowski spacetime, the equation of
motion and Green's operators are deformed. We show that there is a *-algebra
isomorphism between the QFT on the deformed and the formal power series
extension of the QFT on the undeformed spacetime. We study the convergent
implementation of our deformations for toy-models. For these models it is found
that there is a *-isomorphism between the deformed Weyl algebra and a reduced
undeformed Weyl algebra, where certain strongly localized observables are
excluded. Thus, our models realize the intuitive physical picture that
noncommutative geometry prevents arbitrary localization in spacetime.Comment: 23 pages, no figures; v2: extended discussion of physical
consequences, compatible with version to be published in General Relativity
and Gravitatio
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