5,238 research outputs found
An electric-field representation of the harmonic XY model
The two-dimensional harmonic XY (HXY) model is a spin model in which the
classical spins interact via a piecewise parabolic potential. We argue that the
HXY model should be regarded as the canonical classical lattice spin model of
phase fluctuations in two-dimensional condensates, as it is the simplest model
that guarantees the modular symmetry of the experimental systems. Here we
formulate a lattice electric-field representation of the HXY model and contrast
this with an analogous representation of the Villain model and the
two-dimensional Coulomb gas with a purely rotational auxiliary field. We find
that the HXY model is a spin-model analogue of a lattice electric-field model
of the Coulomb gas with an auxiliary field, but with a temperature-dependent
vacuum (electric) permittivity that encodes the coupling of the spin vortices
to their background spin-wave medium. The spin vortices map to the Coulomb
charges, while the spin-wave fluctuations correspond to auxiliary-field
fluctuations. The coupling explains the striking differences in the
high-temperature asymptotes of the specific heats of the HXY model and the
Coulomb gas with an auxiliary field. Our results elucidate the propagation of
effective long-range interactions throughout the HXY model (whose interactions
are purely local) by the lattice electric fields. They also imply that global
spin-twist excitations (topological-sector fluctuations) generated by local
spin dynamics are ergodically excluded in the low-temperature phase. We discuss
the relevance of these results to condensate physics.Comment: 13 pages, 10 figure
Topological-sector fluctuations and ergodicity breaking at the Berezinskii-Kosterlitz-Thouless transition
The Berezinskii-Kosterlitz-Thouless (BKT) phase transition drives the
unbinding of topological defects in many two-dimensional systems. In the
two-dimensional Coulomb gas, it corresponds to an insulator-conductor
transition driven by charge deconfinement. We investigate the global
topological properties of this transition, both analytically and by numerical
simulation, using a lattice-field description of the two-dimensional Coulomb
gas on a torus. The BKT transition is shown to be an ergodicity breaking
between the topological sectors of the electric field, which implies a
definition of topological order in terms of broken ergodicity. The breakdown of
local topological order at the BKT transition leads to the excitation of global
topological defects in the electric field, corresponding to different
topological sectors. The quantized nature of these classical excitations, and
their strict suppression by ergodicity breaking in the low-temperature phase,
afford striking global signatures of topological-sector fluctuations at the BKT
transition. We discuss how these signatures could be detected in experiments
on, for example, magnetic films and cold-atom systems.Comment: 11 pages, 6 figure
Phase order in superfluid helium films
Classic experimental data on helium films are transformed to estimate a
finite-size phase order parameter that measures the thermal degradation of the
condensate fraction in the two-dimensional superfluid. The order parameter is
found to evolve thermally with the exponent , a
characteristic, in analogous magnetic systems, of the
Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Universal scaling near
the BKT fixed point generates a collapse of experimental data on helium and
ferromagnetic films, and implies new experiments and theoretical protocols to
explore the phase order. These results give a striking example of experimental
finite-size scaling in a critical system that is broadly relevant to
two-dimensional Bose fluids.Comment: 6 pages, 2 figure
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Child Exploitation and the FIFA World Cup: A review of risks and protective interventions
This review was commissioned by the Child Abuse Programme (CAP) of Oak Foundation, a large international philanthropic organisation. It forms part of CAP’s effort to win societal rejection of practices such as the sexual exploitation of children and adolescents around major sporting events (MSEs), and to embed prevention and protection from exploitation as a permanent concern for global sports-related bodies. This review is intended to inform action in countries that host MSEs and to provide some suggestions on how hosting countries can avoid past pitfalls and mistakes in relation to child exploitation, especially economic and sexual exploitation. Importantly, it also acts as a call to action by those responsible for commissioning and staging MSEs, such as FIFA and the IOC, to anticipate, prepare for and adopt risk mitigation strategies and interventions. Positive leadership from these culturally powerful bodies could prove decisive in shifting hearts, minds and actions in the direction of improved safety for children
Interaction of Liposomal Drug Delivery Systems with Cells and Tissues: Microscopic Studies
Liposomes , as drug carriers, can be administered into the body by several routes e.g. intravenously, intraperitoneally, intramuscularly, intratracheally and topically among others. Radiolabelled markers are suitable to monitor the distribution and elimination of liposomes, but the tissue deposition of intact liposomes, the mode and sites of drug release from the liposomes and liposome-cell interactions cannot be investigated morphologically. Microscopic techniques could provide information regarding the intact state of liposomes and possibly the dynamics of liposomes in tissues provided that they can be identified with certainty in vivo. This is a formidable problem and in spite of several attempts, there is still a lot of work and new ideas needed to overcome this problem.
This paper gives a detailed review of liposome markers used in light and electron microscopy. The use of markers or the technique involved in the identification of liposomes in cells or t issues is discussed.
The feasibility of using colloidal iron, a new electron dense marker, as a marker for intravenously injected liposomes was investigated in mice. Intact multilamellar vesicles containing colloidal iron were identified in the liver, spleen and lung of mice injected with liposomes. The liver and the spleen are organs for the storage of iron containing proteins (ferritin, hemosiderin), therefore studying the disposition of colloidal iron from the liposomes was not possible. However, in organs not containing iron, e.g. lung, the presence of colloidal iron can easily be recognized. The colloidal iron marker may be suitable to label liposomes targeted to the brain , heart or certain tumors
Stellar spectroscopy: Fermions and holographic Lifshitz criticality
Electron stars are fluids of charged fermions in Anti-de Sitter spacetime.
They are candidate holographic duals for gauge theories at finite charge
density and exhibit emergent Lifshitz scaling at low energies. This paper
computes in detail the field theory Green's function G^R(w,k) of the
gauge-invariant fermionic operators making up the star. The Green's function
contains a large number of closely spaced Fermi surfaces, the volumes of which
add up to the total charge density in accordance with the Luttinger count.
Excitations of the Fermi surfaces are long lived for w <~ k^z. Beyond w ~ k^z
the fermionic quasiparticles dissipate strongly into the critical Lifshitz
sector. Fermions near this critical dispersion relation give interesting
contributions to the optical conductivity.Comment: 38 pages + appendices. 9 figure
The holographic quantum effective potential at finite temperature and density
We develop a formalism that allows the computation of the quantum effective
potential of a scalar order parameter in a class of holographic theories at
finite temperature and charge density. The effective potential is a valuable
tool for studying the ground state of the theory, symmetry breaking patterns
and phase transitions. We derive general formulae for the effective potential
and apply them to determine the phase transition temperature and density in the
scaling region.Comment: 27 page
RG flow of transport quantities
The RG flow equation of various transport quantities are studied in arbitrary
spacetime dimensions, in the fixed as well as fluctuating background geometry
both for the Maxwellian and DBI type of actions. The regularity condition on
the flow equation of the conductivity at the horizon for the DBI action
reproduces naturally the leading order result of {\it Hartnoll et al.}, [{\it
JHEP}, {\bf 04}, 120 (2010)]. Motivated by the result of {\it van der Marel et
al.}, [{\it science}, {\bf 425}, 271 (2003], we studied, analytically, the
conductivity versus frequency plane by dividing it into three distinct parts:
and . In order to compare, we choose 3+1
dimensional bulk spacetime for the computation of the conductivity. In the
range, the conductivity does not show up the Drude like form in any
spacetime dimensions. In the range and staying away from the
horizon, for the DBI action with unit dynamical exponent, non-zero magnetic
field and charge density, the conductivity goes as , whereas the
phase of the conductivity, goes as,
and . There exists a universal
quantity at the horizon that is the phase angle of conductivity, which either
vanishes or an integral multiple of . Furthermore, we calculate the
temperature dependence to the thermoelectric and the thermal conductivity at
the horizon. The charge diffusion constant for the DBI action is studied.Comment: 1+68 pages, 12 figures and 4 appendices; V2: The charge diffusion
constant is calculated for arbitrary spacetime dimensions and related
references added; v3: Connection with the RG flow of 1010.4036 is made; v4:
Several corrections, typos fixed and a ref. adde
Mental health service user experiences of targeted violence and hostility and help-seeking in the UK: a scoping review
The aim of this research scoping review was to assemble an evidence base for the UK on mental health service user experiences and perspectives on mental health-related targeted violence and hostility ('disability hate crime'). It also aims to address some of the gaps in the knowledge on risk management, help-seeking and prevention from the perspectives of those who experienced targeted violence and hostility because of their mental health problems or psychiatric status. Seven key mental health and social care bibliographic databases were searched for relevant UK research studies from 1990 until 2016. Grey literature was identified through online searches. A scoping review charting approach and thematic analysis methodology were used to analyse the studies. In total 13 studies were finally included, over half of which used survey methods. All studies included people with experiences of mental health problems. The studies provide information on: the types of potential hate crime; indicate where incidents take place; give some insight into the victims' relationship with the perpetrators; the location of incidents as well as the psychological, social, financial and physical impacts on the victim; the types of help-seeking behaviours adopted by the victims; a range coping strategies that people with mental health problems adopted in response to experiences of targeted violence or abuse. This scoping review provides a UK-based overview of mental health service user concepts and experiences of mental health-related targeted violence and hostility ('disability hate crime'). It reveals some specific issues relating to mental health and disability hate crime. Further investigation into disability hate crime with a specific focus on mental health is required. This is a UK-based overview, which offers a useful comparator for researchers, practitioners and policy-makers internationally
Holographic non-relativistic fermionic fixed point by the charged dilatonic black hole
Driven by the landscape of garden-variety condensed matter systems, we have
investigated how the dual spectral function behaves at the non-relativistic as
well as relativistic fermionic fixed point by considering the probe Dirac
fermion in an extremal charged dilatonic black hole with zero entropy. Although
the pattern for both of the appearance of flat band and emergence of Fermi
surface is qualitatively similar to that given by the probe fermion in the
extremal Reissner-Nordstrom AdS black hole, we find a distinctly different low
energy behavior around the Fermi surface, which can be traced back to the
different near horizon geometry. In particular, with the peculiar near horizon
geometry of our extremal charged dilatonic black hole, the low energy behavior
exhibits the universal linear dispersion relation and scaling property, where
the former indicates that the dual liquid is a Fermi one while the latter
implies that the dual liquid is not exactly of Landau Fermi type
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