931 research outputs found
Anomalously high potentials observed on ISEE
Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge
A new class of trapped light filaments
New class light filament identified in Raman radiation of intense ruby laser bea
On the entanglement entropy for a XY spin chain
The entanglement entropy for the ground state of a XY spin chain is related
to the corner transfer matrices of the triangular Ising model and expressed in
closed form.Comment: 4 pages, 2 figure
Sustaining municipal parks in an era of neoliberal austerity: The contested commercialisation of Gunnersbury Park
This paper analyses a potentially path shaping moment for the UK’s public parks by analysing a pivotal case study of park neoliberalisation. Like many municipal parks, Gunnersbury Park in West London is experiencing the effects of local government budget cuts. Governance, policy and physical changes have been introduced to reduce dependence on public funding and the result is a more commercially oriented park. This case is used to better understand how the period of neoliberal austerity 2010-2020 reshaped municipal parks. The paper highlights concerns over the transparency and accountability of the social enterprise that now manages Gunnersbury Park. It also shows how neoliberalisation and commercialisation are manifested in the park landscape: free events are replaced with ticketed ones, spaces for sport are transformed into bookable facilities, cafes are taken over by corporate chains and playgrounds are supplemented with paid entry alternatives. One of the main consequences is the financial and symbolic exclusion of those unable or unwilling to pay. The paper explores who has contested the recent changes, and why. Opponents are dismissed as idealistic NIMBYs but, by refusing to accept the post-political inevitability of park neoliberalisation, they are helping to ensure Gunnersbury Park’s remains a public and open space. The case is contextualised by situating it within a review of new park governance arrangements across London, and by comparing neoliberalisation processes here with those affecting New York parks. Ultimately, the research highlights the pitfalls of shifting away from the public funding and public management of municipal parks.
Dynamics of lattice spins as a model of arrhythmia
We consider evolution of initial disturbances in spatially extended systems
with autonomous rhythmic activity, such as the heart. We consider the case when
the activity is stable with respect to very smooth (changing little across the
medium) disturbances and construct lattice models for description of
not-so-smooth disturbances, in particular, topological defects; these models
are modifications of the diffusive XY model. We find that when the activity on
each lattice site is very rigid in maintaining its form, the topological
defects - vortices or spirals - nucleate a transition to a disordered,
turbulent state.Comment: 17 pages, revtex, 3 figure
A Spin - 3/2 Ising Model on a Square Lattice
The spin - 3/2 Ising model on a square lattice is investigated. It is shown
that this model is reducible to an eight - vertex model on a surface in the
parameter space spanned by coupling constants J, K, L and M. It is shown that
this model is equivalent to an exactly solvable free fermion model along two
lines in the parameter space.Comment: LaTeX, 7 pages, 1 figure upon request; JETP Letters, in pres
Analysis of a three-component model phase diagram by Catastrophe Theory
We analyze the thermodynamical potential of a lattice gas model with three
components and five parameters using the methods of Catastrophe Theory. We find
the highest singularity, which has codimension five, and establish its
transversality. Hence the corresponding seven-degree Landau potential, the
canonical form Wigwam or , constitutes the adequate starting point to
study the overall phase diagram of this model.Comment: 16 pages, Latex file, submitted to Phys. Rev.
Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler
Most studies of Coherent Synchrotron Radiation (CSR) have only considered the
radiation from independent dipole magnets. However, in the damping rings of
future linear colliders, a large fraction of the radiation power will be
emitted in damping wigglers. In this paper, the longitudinal wakefield and
impedance due to CSR in a wiggler are derived in the limit of a large wiggler
parameter . After an appropriate scaling, the results can be expressed in
terms of universal functions, which are independent of . Analytical
asymptotic results are obtained for the wakefield in the limit of large and
small distances, and for the impedance in the limit of small and high
frequencies.Comment: 10 pages, 8 figure
Analysis of a three-component model phase diagram by Catastrophe Theory: Potentials with two Order Parameters
In this work we classify the singularities obtained from the Gibbs potential
of a lattice gas model with three components, two order parameters and five
control parameters applying the general theorems provided by Catastrophe
Theory. In particular, we clearly establish the existence of Landau potentials
in two variables or, in other words, corank 2 canonical forms that are
associated to the hyperbolic umbilic, D_{+4}, its dual the elliptic umbilic,
D_{-4}, and the parabolic umbilic, D_5, catastrophes. The transversality of the
potential with two order parameters is explicitely shown for each case. Thus we
complete the Catastrophe Theory analysis of the three-component lattice model,
initiated in a previous paper.Comment: 17 pages, 3 EPS figures, Latex file, continuation of Phys. Rev. B57,
13527 (1998) (cond-mat/9707015), submitted to Phys. Rev.
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