39,769 research outputs found

### Massive Fields and the 2D String

The first massive level of closed bosonic string theory is studied.
Free-field equations are derived by imposing Weyl invariance on the world
sheet. A two-parameter solution to the equation of motion and constraints is
found in two dimensions with a flat linear-dilaton background. One-to-one
tachyon scattering is studied in this background. The results support Dhar,
Mandal and Wadia's proposal that 2D critical string theory corresponds to the
c=1 matrix model in which both sides of the Fermi sea are excited.Comment: 17 pages, Latex. V2: One ref added, minor rephrasing of the first
paragraph in Sec.3.1, typos in (56) and (57) correcte

### Condensation Transitions in a One-Dimensional Zero-Range Process with a Single Defect Site

Condensation occurs in nonequilibrium steady states when a finite fraction of
particles in the system occupies a single lattice site. We study condensation
transitions in a one-dimensional zero-range process with a single defect site.
The system is analysed in the grand canonical and canonical ensembles and the
two are contrasted. Two distinct condensation mechanisms are found in the grand
canonical ensemble. Discrepancies between the infinite and large but finite
systems' particle current versus particle density diagrams are investigated and
an explanation for how the finite current goes above a maximum value predicted
for infinite systems is found in the canonical ensemble.Comment: 18 pages, 4 figures, revtex

### Correlation function algebra for inhomogeneous fluids

We consider variational (density functional) models of fluids confined in
parallel-plate geometries (with walls situated in the planes z=0 and z=L
respectively) and focus on the structure of the pair correlation function
G(r_1,r_2). We show that for local variational models there exist two
non-trivial identities relating both the transverse Fourier transform G(z_\mu,
z_\nu;q) and the zeroth moment G_0(z_\mu,z_\nu) at different positions z_1, z_2
and z_3. These relations form an algebra which severely restricts the possible
form of the function G_0(z_\mu,z_\nu). For the common situations in which the
equilibrium one-body (magnetization/number density) profile m_0(z) exhibits an
odd or even reflection symmetry in the z=L/2 plane the algebra simplifies
considerably and is used to relate the correlation function to the finite-size
excess free-energy \gamma(L). We rederive non-trivial scaling expressions for
the finite-size contribution to the free-energy at bulk criticality and for
systems where large scale interfacial fluctuations are present. Extensions to
non-planar geometries are also considered.Comment: 15 pages, RevTex, 4 eps figures. To appear in J.Phys.Condens.Matte

### Spontaneous Jamming in One-Dimensional Systems

We study the phenomenon of jamming in driven diffusive systems. We introduce
a simple microscopic model in which jamming of a conserved driven species is
mediated by the presence of a non-conserved quantity, causing an effective long
range interaction of the driven species. We study the model analytically and
numerically, providing strong evidence that jamming occurs; however, this
proceeds via a strict phase transition (with spontaneous symmetry breaking)
only in a prescribed limit. Outside this limit, the nearby transition
(characterised by an essential singularity) induces sharp crossovers and
transient coarsening phenomena. We discuss the relevance of the model to two
physical situations: the clustering of buses, and the clogging of a suspension
forced along a pipe.Comment: 8 pages, 4 figures, uses epsfig. Submitted to Europhysics Letter

### Alternating steady state in one-dimensional flocking

We study flocking in one dimension, introducing a lattice model in which
particles can move either left or right. We find that the model exhibits a
continuous nonequilibrium phase transition from a condensed phase, in which a
single `flock' contains a finite fraction of the particles, to a homogeneous
phase; we study the transition using numerical finite-size scaling.
Surprisingly, in the condensed phase the steady state is alternating, with the
mean direction of motion of particles reversing stochastically on a timescale
proportional to the logarithm of the system size. We present a simple argument
to explain this logarithmic dependence. We argue that the reversals are
essential to the survival of the condensate. Thus, the discrete directional
symmetry is not spontaneously broken.Comment: 8 pages LaTeX2e, 5 figures. Uses epsfig and IOP style. Submitted to
J. Phys. A (Math. Gen.

### Gender differences in public perceptions on National Health Insurance

Background. Implementation of National Health Insurance (NHI) commenced recently. With the promise of addressing drastic inequalities in the health sector, NHI has the potential to positively transform the health system. In particular, NHI could have a significant positive impact on females, who are disadvantaged under the current system, with higher rates of poor health and lower rates of medical scheme membership compared with males. Despite NHIâ€™s transformative potential, however, the public discourse on NHI as portrayed in the mediasuggests that it is an unpopular policy. The evidence presented in this paper is to the contrary.Objectives. To assess the general publicâ€™s opinion on NHI and to explore gender differences in perceptions.Methods. This paper reports on findings from a 2010 cross-sectional nationally representative survey of the South African population that assessed social attitudes, including perceptions on NHI. Sex-disaggregated data were analysed in SPSS version 20.Results and conclusions. There is broad public acceptance of NHI, indicating that an overwhelming majority of South Africans would prefer an NHI system to the current two-tiered system. Support for NHI has increased since similar studies in 2005 and 2008, with the simultaneous growth of public discourse on the policy. More females than males support NHI, reflecting the potential of the NHI system to have a positive impact on gender equality and the health of women and girls

### Periodically driven stochastic un- and refolding transitions of biopolymers

Mechanical single molecule experiments probe the energy profile of
biomolecules. We show that in the case of a profile with two minima (like
folded/unfolded) periodic driving leads to a stochastic resonance-like
phenomenon. We demonstrate that the analysis of such data can be used to
extract four basic parameters of such a transition and discuss the statistical
requirements of the data acquisition. As advantages of the proposed scheme, a
polymeric linker is explicitly included and thermal fluctuations within each
well need not to be resolved.Comment: 7 pages, 5 figures, submitted to EP

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