1,427 research outputs found
Properties of Resonating-Valence-Bond Spin Liquids and Critical Dimer Models
We use Monte Carlo simulations to study properties of Anderson's
resonating-valence-bond (RVB) spin-liquid state on the square lattice (i.e.,
the equal superposition of all pairing of spins into nearest-neighbor singlet
pairs) and compare with the classical dimer model (CDM). The latter system also
corresponds to the ground state of the Rokhsar-Kivelson quantum dimer model at
its critical point. We find that although spin-spin correlations decay
exponentially in the RVB, four-spin valence-bond-solid (VBS) correlations are
critical, qualitatively like the well-known dimer-dimer correlations of the
CDM, but decaying more slowly (as with , compared with
for the CDM). We also compute the distribution of monomer (defect) pair
separations, which decay by a larger exponent in the RVB than in the CDM. We
further study both models in their different winding number sectors and
evaluate the relative weights of different sectors. Like the CDM, all the
observed RVB behaviors can be understood in the framework of a mapping to a
"height" model characterized by a gradient-squared stiffness constant . Four
independent measurements consistently show a value , with the same kinds of numerical evaluations of give
results in agreement with the rigorously known value . The
background of a nonzero winding number gradient introduces spatial
anisotropies and an increase in the effective K, both of which can be
understood as a consequence of anharmonic terms in the height-model free
energy, which are of relevance to the recently proposed scenario of "Cantor
deconfinement" in extended quantum dimer models. We also study ensembles in
which fourth-neighbor (bipartite) bonds are allowed, at a density controlled by
a tunable fugacity, resulting (as expected) in a smooth reduction of K.Comment: 26 pages, 21 figures. v3: final versio
A comparison of parent reported outcome with experience of services
PublishedJournal ArticlePurpose - Routine outcome monitoring (ROM) is currently seen as a key driver for service improvement at individual, team and service level. The purpose this paper is to explore the relationships between a patient (parent) reported outcome measure (PROM), a practitioner reported outcome measure, and a patient (parent) reported experience measure (PREM). Design/methodology/approach - A cohort of 302 primary school-age children was recruited and followed for one year from consecutively accepted referrals to three teams within two English Child and Adolescent Mental Health Services (CAMHS). Parents completed the Strengths and Difficulties Questionnaire (a PROM) and practitioners completed the Clinician Global Assessment Scale at baseline, six and 12 months; parents completed the Experience of Services Questionnaire (a PREM) at six and 12 months. Findings - PROM and practitioner reported outcome measure data suggested poor clinical outcome in terms of symptoms, impact and levels of functioning but were accompanied by PREM evidence of high levels of satisfaction. There was an unexpectedly low correlation (o0.2) between both measures of outcome and satisfaction. Originality/value - This paper fulfils a need to explore the relationships between different outcome measures to contribute to the understanding of ROM its validity
Bethe Ansatz solution of a decagonal rectangle triangle random tiling
A random tiling of rectangles and triangles displaying a decagonal phase is
solved by Bethe Ansatz. Analogously to the solutions of the dodecagonal square
triangle and the octagonal rectangle triangle tiling an exact expression for
the maximum of the entropy is found.Comment: 17 pages, 4 figures, some remarks added and typos correcte
Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud
This paper examines the ultraviolet and X-ray photons generated by hot gas in
the Galactic thick disk or halo in the Draco region of the northern hemisphere.
Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O
VIII, sampling temperatures of ~100,000 to ~3,000,000 K. We measured the O VI,
O VII and O VIII intensities from FUSE and XMM-Newton data and subtracted off
the local contributions in order to deduce the thick disk/halo contributions.
These were supplemented with published C IV intensity and O VI column density
measurements. Our estimate of the thermal pressure in the O VI-rich thick
disk/halo gas, p_{th}/k = 6500^{+2500}_{-2600} K cm^{-3}, suggests that the
thick disk/halo is more highly pressurized than would be expected from
theoretical analyses. The ratios of C IV to O VI to O VII to O VIII,
intensities were compared with those predicted by theoretical models. Gas which
was heated to 3,000,000 K then allowed to cool radiatively cannot produce
enough C IV or O VI-generated photons per O VII or O VIII-generated photon.
Producing enough C IV and O VI emission requires heating additional gas to
100,000 < T < 1,000,000 K. However, shock heating, which provides heating
across this temperature range, overproduces O VI relative to the others.
Obtaining the observed mix may require a combination of several processes,
including some amount of shock heating, heat conduction, and mixing, as well as
radiative cooling of very hot gas.Comment: 10 pages, 2 figures. Accepted for publication in the Astrophysical
Journa
Gapless Bosonic Excitation without symmetry breaking: Novel Algebraic Spin liquid with soft Gravitons
A novel quantum ground state of matter is realized in a bosonic model on
three dimensional fcc lattice with emergent low energy excitations. The novel
phase obtained is a stable gapless boson liquid phase, with algebraic boson
density correlations. The stability of this phase is protected against the
instanton effect and superfluidity by self-duality and large gauge symmetries
on both sides of the duality. The gapless collective excitations of this phase
closely resemble the graviton, although they have a soft
dispersion relation. There are three branches of gapless excitations in this
phase, one of which is gapless scalar trace mode, the other two have the same
polarization and gauge symmetries as the gravitons. The dynamics of this novel
phase is described by a new set of Maxwell's equations. The defects carrying
gauge charges can drive the system into the superfluid order when the defects
are condensed; also the topological defects are coupled to the dual gauge field
in the same manner as the charge defects couple to the original gauge field,
after the condensation of the topological defects, the system is driven into
the Mott Insulator phase. In the 2 dimensional case, the gapless soft graviton
as well as the algebraic liquid phase are destroyed by the vertex operators in
the dual theory, and the stripe order is most likely to take place close to the
2 dimensional quantum critical point at which the vertex operators are tuned to
zero.Comment: 11 pages, 9 figure
Coulomb and Liquid Dimer Models in Three Dimensions
We study classical hard-core dimer models on three-dimensional lattices using
analytical approaches and Monte Carlo simulations. On the bipartite cubic
lattice, a local gauge field generalization of the height representation used
on the square lattice predicts that the dimers are in a critical Coulomb phase
with algebraic, dipolar, correlations, in excellent agreement with our
large-scale Monte Carlo simulations. The non-bipartite FCC and Fisher lattices
lack such a representation, and we find that these models have both confined
and exponentially deconfined but no critical phases. We conjecture that
extended critical phases are realized only on bipartite lattices, even in
higher dimensions.Comment: 4 pages with corrections and update
Heisenberg antiferromagnet on Cayley trees: low-energy spectrum and even/odd site imbalance
To understand the role of local sublattice imbalance in low-energy spectra of
s=1/2 quantum antiferromagnets, we study the s=1/2 quantum nearest neighbor
Heisenberg antiferromagnet on the coordination 3 Cayley tree. We perform
many-body calculations using an implementation of the density matrix
renormalization group (DMRG) technique for generic tree graphs. We discover
that the bond-centered Cayley tree has a quasidegenerate set of a low-lying
tower of states and an "anomalous" singlet-triplet finite-size gap scaling. For
understanding the construction of the first excited state from the many-body
ground state, we consider a wave function ansatz given by the single-mode
approximation, which yields a high overlap with the DMRG wave function.
Observing the ground-state entanglement spectrum leads us to a picture of the
low-energy degrees of freedom being "giant spins" arising out of sublattice
imbalance, which helps us analytically understand the scaling of the
finite-size spin gap. The Schwinger-boson mean-field theory has been
generalized to nonuniform lattices, and ground states have been found which are
spatially inhomogeneous in the mean-field parameters.Comment: 19 pages, 12 figures, 6 tables. Changes made to manuscript after
referee suggestions: parts reorganized, clarified discussion on Fibonacci
tree, typos correcte
Mechanisms of action in mindfulness-based cognitive therapy (MBCT) and mindfulness-based stress reduction (MBSR) in people with physical and/or psychological conditions: A systematic review
ReviewThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Background
Recently, there has been an increased interest in studying the effects of mindfulness-based interventions for people with psychological and physical problems. However, the mechanisms of action in these interventions that lead to beneficial physical and psychological outcomes have yet to be clearly identified.
Purpose
The aim of this paper is to review, systematically, the evidence to date on the mechanisms of action in mindfulness interventions in populations with physical and/or psychological conditions.
Method
Searches of seven databases (PsycINFO, Medline (Ovid), Cochrane Central Register of Controlled Trials, EMBASE, CINAHL, AMED, ClinicalTrials.gov) were undertaken in June 2014 and July 2015. We evaluated to what extent the studies we identified met the criteria suggested by Kazdin for establishing mechanisms of action within a psychological treatment (2007, 2009).
Results
We identified four trials examining mechanisms of mindfulness interventions in those with comorbid psychological and physical health problems and 14 in those with psychological conditions. These studies examined a diverse range of potential mechanisms, including mindfulness and rumination. Of these candidate mechanisms, the most consistent finding was that greater self-reported change in mindfulness mediated superior clinical outcomes. However, very few studies fully met the Kazdin criteria for examining treatment mechanisms.
Conclusion
There was evidence that global changes in mindfulness are linked to better outcomes. This evidence pertained more to interventions targeting psychological rather than physical health conditions. While there is promising evidence that MBCT/MBSR intervention effects are mediated by hypothesised mechanisms, there is a lack of methodological rigour in the field of testing mechanisms of action for both MBCT and MBSR, which precludes definitive conclusions
The relationship between exclusion from school and mental health: a secondary analysis of the British Child and Adolescent Mental Health Surveys 2004 and 2007
This is the author accepted manuscript. The final version is available from CUP via the DOI in this record.Background
Children with poor mental health often struggle at school. The relationship between childhood psychiatric disorder and exclusion from school has not been frequently studied, but both are associated with poor adult outcomes. We undertook a secondary analysis of the British Child and Adolescent Mental Health Surveys from 2004 and its follow up in 2007 to explore the relationship between exclusion from school and psychopathology. We predicted poorer mental health among
those excluded.
Method
Psychopathology was measured using the Strengths and Difficulties Questionnaire, while psychiatric disorder was assessed using the Development and Well-Being Assessment and applying DSM IV criteria. Exclusion from school and socio-demographic characteristics were reported by parents. Multivariable regression models were used to examine the impact of individual factors on exclusion from school or psychological distress.
Results
Exclusion from school was commoner among boys, secondary school pupils, and those living
in socio-economically deprived circumstances. Poor general health and learning disability among
children and poor parental mental health were also associated with exclusion. There were consistently high levels of psychological distress among those who had experienced exclusion at baseline and follow up.
Conclusions
We detected a bi-directional association between psychological distress and exclusion. Efforts to identify and support children who struggle with school may therefore prevent both future exclusion and future psychiatric disorder.Claire Parker's PhD studentship was supported by the National Institute for Health Research (NIHR)
Collaboration for Leadership in Applied Health Research and Care South West Peninsula. Javid Salim
worked on this paper while an Academic Clinical Fellow, also funded by NIHR. The initial surveys were
funded by the English Departments of Health with contributions from their Scottish and Welsh
counterparts, and data collection was led by the Office for National Statistics
Phason elasticity of a three-dimensional quasicrystal: transfer-matrix method
We introduce a new transfer matrix method for calculating the thermodynamic
properties of random-tiling models of quasicrystals in any number of
dimensions, and describe how it may be used to calculate the phason elastic
properties of these models, which are related to experimental measurables such
as phason Debye-Waller factors, and diffuse scattering wings near Bragg peaks.
We apply our method to the canonical-cell model of the icosahedral phase,
making use of results from a previously-presented calculation in which the
possible structures for this model under specific periodic boundary conditions
were cataloged using a computational technique. We give results for the
configurational entropy density and the two fundamental elastic constants for a
range of system sizes. The method is general enough allow a similar calculation
to be performed for any other random tiling model.Comment: 38 pages, 3 PostScript figures, self-expanding uuencoded compressed
tar file, LaTeX using RevTeX macros and epsfig.st
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