2,920 research outputs found
Interfacial Structural Changes and Singularities in Non-Planar Geometries
We consider phase coexistence and criticality in a thin-film Ising magnet
with opposing surface fields and non-planar (corrugated) walls. We show that
the loss of translational invariance has a strong and unexpected non-linear
influence on the interface structure and phase diagram. We identify 4
non-thermodynamic singularities where there is a qualitative change in the
interface shape. In addition, we establish that at the finite-size critical
point, the singularity in the interface shape is characterized by two distint
critical exponents in contrast to the planar case (which is characterised by
one). Similar effects should be observed for prewetting at a corrugated
substrate. Analogy is made with the behaviour of a non-linear forced oscillator
showing chaotic dynamics.Comment: 13 pages, 3 figure
Quantum counter automata
The question of whether quantum real-time one-counter automata (rtQ1CAs) can
outperform their probabilistic counterparts has been open for more than a
decade. We provide an affirmative answer to this question, by demonstrating a
non-context-free language that can be recognized with perfect soundness by a
rtQ1CA. This is the first demonstration of the superiority of a quantum model
to the corresponding classical one in the real-time case with an error bound
less than 1. We also introduce a generalization of the rtQ1CA, the quantum
one-way one-counter automaton (1Q1CA), and show that they too are superior to
the corresponding family of probabilistic machines. For this purpose, we
provide general definitions of these models that reflect the modern approach to
the definition of quantum finite automata, and point out some problems with
previous results. We identify several remaining open problems.Comment: A revised version. 16 pages. A preliminary version of this paper
appeared as A. C. Cem Say, Abuzer Yakary{\i}lmaz, and \c{S}efika
Y\"{u}zsever. Quantum one-way one-counter automata. In R\={u}si\c{n}\v{s}
Freivalds, editor, Randomized and quantum computation, pages 25--34, 2010
(Satellite workshop of MFCS and CSL 2010
Fluid dynamics of dilatant fluid
Dense mixture of granules and liquid often shows a sever shear thickening and
is called a dilatant fluid. We construct a fluid dynamics model for the
dilatant fluid by introducing a phenomenological state variable for a local
state of dispersed particles. With simple assumptions for an equation of the
state variable, we demonstrate that the model can describe basic features of
the dilatant fluid such as the stress-shear rate curve that represents
discontinuous severe shear thickening, hysteresis upon changing shear rate,
instantaneous hardening upon external impact. Analysis of the model reveals
that the shear thickening fluid shows an instability in a shear flow for some
regime and exhibits {\it the shear thickening oscillation}, i.e. the
oscillatory shear flow alternating between the thickened and the relaxed
states. Results of numerical simulations are presented for one and
two-dimensional systems.Comment: 12 pages, 17 figure
Perturbative QCD of hard and soft processes
We discuss some problems concerning the application of perturbative QCD to
high energy processes. In particular for hard processes, we analyze higher
order and higher twist corrections. It is argued that these effects are of
great importance for understanding the behaviour of pion electromagnetic form
factor at moderately large momentum transfers. For soft processes, we show that
summing the contributions of the lowest twist operators leads to a Regge-like
amplitude.Comment: Reproduction of unpublished JINR Report E2-80-521, Dubna 1980. 22
pages 9 figures. To be published in Modern Physics Letters A. Style file is
include
Probing Unquenching Effects in the Gluon Polarisation in Light Mesons
We introduce an extension to the ladder truncated Bethe-Salpeter equation for
mesons and the rainbow truncated quark Dyson-Schwinger equations which includes
quark-loop corrections to the gluon propagator. This truncation scheme obeys
the axialvector Ward-Takahashi identity relating the quark self-energy and the
Bethe-Salpeter kernel. Two different approximations to the Yang-Mills sector
are used as input: the first is a sophisticated truncation of the full
Yang-Mills Dyson-Schwinger equations, the second is a phenomenologically
motivated form. We find that the spectra and decay constants of pseudoscalar
and vector mesons are overall described well for either approach. Meson mass
results for charge eigenstate vector and pseudoscalar meson masses are compared
to lattice data. The effects of unquenching the system are small but not
negligible.Comment: 26 pages, 13 figure
Phenomenological theory of a scalar electronic order: application to skutterudite PrFe4P12
By phenomenological Landau analysis, it is shown that a scalar order
parameter with the point-group symmetry explains most properties
associated with the phase transition in PrFeP at 6.5 K. The
scalar-order model reproduces magnetic and elastic properties in
PrFeP consistently such as (i) the anomaly of the magnetic
susceptibility and elastic constant at the transition temperature, (ii)
anisotropy of the magnetic susceptibility in the presence of uniaxial pressure,
and (iii) the anomaly in the elastic constant in magnetic field. An Ehrenfest
relation is derived which relates the anomaly of the magnetic susceptibility to
that of the elastic constant at the transition.Comment: 16 pages, 9 figure
A Phenomenological Description of the Non-Fermi-Liquid Phase of MnSi
In order to understand the non-Fermi-liquid behavior of MnSi under pressure
we propose a scenario on the basis of the multispiral state of the magnetic
moment.
This state can describe the recent critical experiment of the Bragg sphere in
the neutron scattering which is the key ingredient of the non-Fermi-liquid
behavior.Comment: 3 page
New path description for the M(k+1,2k+3) models and the dual Z_k graded parafermions
We present a new path description for the states of the non-unitary
M(k+1,2k+3) models. This description differs from the one induced by the
Forrester-Baxter solution, in terms of configuration sums, of their
restricted-solid-on-solid model. The proposed path representation is actually
very similar to the one underlying the unitary minimal models M(k+1,k+2), with
an analogous Fermi-gas interpretation. This interpretation leads to fermionic
expressions for the finitized M(k+1,2k+3) characters, whose infinite-length
limit represent new fermionic characters for the irreducible modules. The
M(k+1,2k+3) models are also shown to be related to the Z_k graded parafermions
via a (q to 1/q) duality transformation.Comment: 43 pages (minor typo corrected and minor rewording in the
introduction
Toward Identification of Order Parameters in Skutterudites - a Wonderland of Strong Correlation Physics -
Current status is described toward identifying unconventional order
parameters in filled skutterudites with unique ordering phenomena. The order
parameters in PrFeP and PrRuP are discussed in relation
to associated crystalline electric field (CEF) states and angular form factors.
By phenomenological Landau analysis, it is shown that a scalar order model
explains most properties in both PrFeP and PrRuP with
very different magnetic properties. In particular, the highly anisotropic
susceptibility induced by uniaxial pressure in PrFeP is explained in
terms of two types of couplings. In the case of SmRuP, the main
order parameter at low field is identified as magnetic octupoles. A microscopic
mechanism is proposed how the dipole and octupole degrees of freedom mix under
the point group of skutterudites.Comment: To be published in Proc. International Conference on New Quantum
Phenomena in Skutterudite and Related Systems (Suppl. J. Phys. Soc. Jpn 78,
2008
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