3,229 research outputs found
Dynamics of cosmic strings and springs; a covariant formulation
A general family of charge-current carrying cosmic string models is
investigated. In the special case of circular configurations in arbitrary
axially symmetric gravitational and electromagnetic backgrounds the dynamics is
determined by simple point particle Hamiltonians. A certain "duality"
transformation relates our results to previous ones, obtained by Carter et.
al., for an infinitely long open stationary string in an arbitrary stationary
background.Comment: 11 pages, Latex, Nordita preprint 93/28
Position-dependent mass models and their nonlinear characterization
We consider the specific models of Zhu-Kroemer and BenDaniel-Duke in a
sech-mass background and point out interesting correspondences with the
stationary 1-soliton and 2-soliton solutions of the KdV equation in a
supersymmetric framework.Comment: 8 Pages, Latex version, Two new references are added, To appear in
J.Phys.A (Fast Track Communication
h analogue of Newton's binomial formula
In this letter, the --analogue of Newton's binomial formula is obtained in
the --deformed quantum plane which does not have any --analogue. For
, this is just the usual one as it should be. Furthermore, the binomial
coefficients reduce to for . \\ Some properties of the
--binomial coefficients are also given. \\ Finally, I hope that such results
will contribute to an introduction of the --analogue of the well--known
functions, --special functions and --deformed analysis.Comment: 6 pages, latex Jounal-ref: J. Phys. A: Math. Gen. 31 (1998) L75
Polymer translocation through a nanopore under an applied external field
We investigate the dynamics of polymer translocation through a nanopore under
an externally applied field using the 2D fluctuating bond model with
single-segment Monte Carlo moves. We concentrate on the influence of the field
strength , length of the chain , and length of the pore on forced
translocation. As our main result, we find a crossover scaling for the
translocation time with the chain length from for
relatively short polymers to for longer chains, where
is the Flory exponent. We demonstrate that this crossover is due to the
change in the dependence of the translocation velocity v on the chain length.
For relatively short chains , which crosses over to for long polymers. The reason for this is that with increasing
there is a high density of segments near the exit of the pore, which slows down
the translocation process due to slow relaxation of the chain. For the case of
a long nanopore for which , the radius of gyration along
the pore, is smaller than the pore length, we find no clear scaling of the
translocation time with the chain length. For large , however, the
asymptotic scaling is recovered. In this regime, is almost independent of . We have previously found that for a polymer,
which is initially placed in the middle of the pore, there is a minimum in the
escape time for . We show here that this minimum
persists for a weak fields such that is less than some critical value,
but vanishes for large values of .Comment: 25 Pages, 10 figures. Submitted to J. Chem. Phys. J. Chem. Phys. 124,
in press (2006
Meanfield treatment of Bragg scattering from a Bose-Einstein condensate
A unified semiclassical treatment of Bragg scattering from Bose-Einstein
condensates is presented. The formalism is based on the Gross-Pitaevskii
equation driven by classical light fields far detuned from atomic resonance. An
approximate analytic solution is obtained and provides quantitative
understanding of the atomic momentum state oscillations, as well as a simple
expression for the momentum linewidth of the scattering process. The validity
regime of the analytic solution is derived, and tested by three dimensional
cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen
The Chagos Islands cases: the empire strikes back
Good governance requires the accommodation of multiple interests in the cause of decision making. However, undue regard for particular sectional interests can take their toll upon public faith in government administration. Historically, broad conceptions of the good of the commonwealth were employed to outweigh the interests of groups that resisted colonisation. In the decision making of the British Empire, the standard approach for justifying the marginalisation of the interests of colonised groups was that they were uncivilised and that particular hardships were the price to be paid for bringing to them the imperial dividend of industrial society. It is widely assumed that with the dismantling of the British Empire, such impulses and their accompanying jurisprudence became a thing of the past. Even as decolonisation proceeded apace after the Second World War, however, the United Kingdom maintained control of strategically important islands with a view towards sustaining its global role. In an infamous example from this twilight period of empire, in the 1960s imperial interests were used to justify the expulsion of the Chagos islanders from the British Indian Ocean Territory (BIOT). Into the twenty-first century, this forced elision of the UK’s interests with the imperial “common good” continues to take centre stage in courtroom battles over the islanders’ rights, being cited before domestic and international tribunals in order to maintain the Chagossians’ exclusion from their homeland. This article considers the new jurisprudence of imperialism which has emerged in a string of decisions which have continued to marginalise the Chagossians’ interests
A Bisognano-Wichmann-like Theorem in a Certain Case of a Non Bifurcate Event Horizon related to an Extreme Reissner-Nordstr\"om Black Hole
Thermal Wightman functions of a massless scalar field are studied within the
framework of a ``near horizon'' static background model of an extremal R-N
black hole. This model is built up by using global Carter-like coordinates over
an infinite set of Bertotti-Robinson submanifolds glued together. The
analytical extendibility beyond the horizon is imposed as constraints on
(thermal) Wightman's functions defined on a Bertotti-Robinson sub manifold. It
turns out that only the Bertotti-Robinson vacuum state, i.e. , satisfies
the above requirement. Furthermore the extension of this state onto the whole
manifold is proved to coincide exactly with the vacuum state in the global
Carter-like coordinates. Hence a theorem similar to Bisognano-Wichmann theorem
for the Minkowski space-time in terms of Wightman functions holds with
vanishing ``Unruh-Rindler temperature''. Furtermore, the Carter-like vacuum
restricted to a Bertotti-Robinson region, resulting a pure state there, has
vanishing entropy despite of the presence of event horizons. Some comments on
the real extreme R-N black hole are given
On-site correlation in valence and core states of ferromagnetic nickel
We present a method which allows to include narrow-band correlation effects
into the description of both valence and core states and we apply it to the
prototypical case of nickel. The results of an ab-initio band calculation are
used as input mean-field eigenstates for the calculation of self-energy
corrections and spectral functions according to a three-body scattering
solution of a multi-orbital Hubbard hamiltonian. The calculated quasi-particle
spectra show a remarkable agreement with photoemission data in terms of band
width, exchange splitting, satellite energy position of valence states, spin
polarization of both the main line and the satellite of the 3p core level.Comment: 14 pages, 10 PostScript figures, RevTeX, submitted to PR
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