1,057 research outputs found
The development of radiative neutron capture techniques for in-situ elemental analysis of the sea-bed
Imperial Users onl
Potts Models with (17) Invisible States on Thin Graphs
The order of a phase transition is usually determined by the nature of the
symmetry breaking at the phase transition point and the dimension of the model
under consideration. For instance, q-state Potts models in two dimensions
display a second order, continuous transition for q = 2,3,4 and first order for
higher q.
Tamura et al recently introduced Potts models with "invisible" states which
contribute to the entropy but not the internal energy and noted that adding
such invisible states could transmute continuous transitions into first order
transitions. This was observed both in a Bragg-Williams type mean-field
calculation and 2D Monte-Carlo simulations. It was suggested that the invisible
state mechanism for transmuting the order of a transition might play a role
where transition orders inconsistent with the usual scheme had been observed.
In this paper we note that an alternative mean-field approach employing
3-regular random ("thin") graphs also displays this change in the order of the
transition as the number of invisible states is varied, although the number of
states required to effect the transmutation, 17 invisible states when there are
2 visible states, is much higher than in the Bragg-Williams case. The
calculation proceeds by using the equivalence of the Potts model with 2 visible
and r invisible states to the Blume-Emery-Griffiths (BEG) model, so a
by-product is the solution of the BEG model on thin random graphs.Comment: (2) Minor typos corrected, references update
The Gonihedric Ising Model and Glassiness
The Gonihedric 3D Ising model is a lattice spin model in which planar Peierls
boundaries between + and - spins can be created at zero energy cost. Instead of
weighting the area of Peierls boundaries as the case for the usual 3D Ising
model with nearest neighbour interactions, the edges, or "bends" in an
interface are weighted, a concept which is related to the intrinsic curvature
of the boundaries in the continuum.
In these notes we follow a roughly chronological order by first reviewing the
background to the formulation of the model, before moving on to the elucidation
of the equilibrium phase diagram by various means and then to investigation of
the non-equilibrium, glassy behaviour of the model.Comment: To appear as Chapter 7 in Rugged Free-Energy Landscapes - An
Introduction, Springer Lecture Notes in Physics, 736, ed. W. Janke, (2008
(Four) Dual Plaquette 3D Ising Models
A characteristic feature of the 3d plaquette Ising model is its planar
subsystem symmetry. The quantum version of this model has been shown to be
related via a duality to the X-Cube model, which has been paradigmatic in the
new and rapidly developing field of fractons. The relation between the 3d
plaquette Ising and the X-Cube model is similar to that between the 2d quantum
transverse spin Ising model and the Toric Code. Gauging the global symmetry in
the case of the 2d Ising model and considering the gauge invariant sector of
the high temperature phase leads to the Toric Code, whereas gauging the
subsystem symmetry of the 3d quantum transverse spin plaquette Ising model
leads to the X-Cube model. A non-standard dual formulation of the 3d plaquette
Ising model which utilises three flavours of spins has recently been discussed
in the context of dualising the fracton-free sector of the X-Cube model. In
this paper we investigate the classical spin version of this non-standard dual
Hamiltonian and discuss its properties in relation to the more familiar
Ashkin-Teller-like dual and further related dual formulations involving both
link and vertex spins and non-Ising spins.Comment: Reviews results in arXiv:1106.0325 and arXiv:1106.4664 in light of
more recent simulations and fracton literature. Published in special issue of
Entropy dedicated to the memory of Professor Ian Campbel
SecuCode: Intrinsic PUF Entangled Secure Wireless Code Dissemination for Computational RFID Devices
The simplicity of deployment and perpetual operation of energy harvesting
devices provides a compelling proposition for a new class of edge devices for
the Internet of Things. In particular, Computational Radio Frequency
Identification (CRFID) devices are an emerging class of battery-free,
computational, sensing enhanced devices that harvest all of their energy for
operation. Despite wireless connectivity and powering, secure wireless firmware
updates remains an open challenge for CRFID devices due to: intermittent
powering, limited computational capabilities, and the absence of a supervisory
operating system. We present, for the first time, a secure wireless code
dissemination (SecuCode) mechanism for CRFIDs by entangling a device intrinsic
hardware security primitive Static Random Access Memory Physical Unclonable
Function (SRAM PUF) to a firmware update protocol. The design of SecuCode: i)
overcomes the resource-constrained and intermittently powered nature of the
CRFID devices; ii) is fully compatible with existing communication protocols
employed by CRFID devices in particular, ISO-18000-6C protocol; and ii) is
built upon a standard and industry compliant firmware compilation and update
method realized by extending a recent framework for firmware updates provided
by Texas Instruments. We build an end-to-end SecuCode implementation and
conduct extensive experiments to demonstrate standards compliance, evaluate
performance and security.Comment: Accepted to the IEEE Transactions on Dependable and Secure Computin
- …