89 research outputs found
BOUNDARY CONDITIONS FOR THE SCALAR FIELD IN THE PRESENCE OF SIGNATURE CHANGE
We show that, contrary to recent criticism, our previous work yields a
reasonable class of solutions for the massless scalar field in the presence of
signature change.Comment: 11 pages, Plain Tex, no figure
Initial Value Problems and Signature Change
We make a rigorous study of classical field equations on a 2-dimensional
signature changing spacetime using the techniques of operator theory. Boundary
conditions at the surface of signature change are determined by forming
self-adjoint extensions of the Schr\"odinger Hamiltonian. We show that the
initial value problem for the Klein--Gordon equation on this spacetime is
ill-posed in the sense that its solutions are unstable. Furthermore, if the
initial data is smooth and compactly supported away from the surface of
signature change, the solution has divergent -norm after finite time.Comment: 33 pages, LaTeX The introduction has been altered, and new work
(relating our previous results to continuous signature change) has been
include
On metric-connection compatibility and the signature change of space-time
We discuss and investigate the problem of existence of metric-compatible
linear connections for a given space-time metric which is, generally, assumed
to be semi-pseudo-Riemannian. We prove that under sufficiently general
conditions such connections exist iff the rank and signature of the metric are
constant. On this base we analyze possible changes of the space-time signature.Comment: 18 standard LaTeX 2e pages. The packages AMS-LaTeX and amsfonts are
require
Diffeomorphism algebra of two dimensional free massless scalar field with signature change
We study a model of free massless scalar fields on a two dimensional cylinder
with metric that admits a change of signature between Lorentzian and Euclidean
type (ET), across the two timelike hypersurfaces (with respect to Lorentzian
region). Considering a long strip-shaped region of the cylinder, denoted by an
angle \theta, as the signature changed region it is shown that the energy
spectrum depends on the angle \theta and in a sense differs from ordinary one
for low energies. Morever diffeomorphism algebra of corresponding infinite
conserved charges is different from '' Virasoro'' algebra and approaches to it
at higher energies. The central term is also modified but does not approach to
the ordinary one at higher energies.Comment: 18 pages, Latex, 2 ps figure
ISML: an interface specification meta-language
In this paper we present an abstract metaphor model situated within a model-based user interface framework. The inclusion of metaphors in graphical user interfaces is a well established, but mostly craft-based strategy to design. A substantial body of notations and tools can be found within the model-based user interface design literature, however an explicit treatment of metaphor and its mappings to other design views has yet to be addressed. We introduce the Interface Specification Meta-Language (ISML) framework and demonstrate its use in comparing the semantic and syntactic features of an interactive system. Challenges facing this research are outlined and further work proposed
Compactification, topology change and surgery theory
We study the process of compactification as a topology change. It is shown
how the mediating spacetime topology, or cobordism, may be simplified through
surgery. Within the causal Lorentzian approach to quantum gravity, it is shown
that any topology change in dimensions may be achieved via a causally
continuous cobordism. This extends the known result for 4 dimensions.
Therefore, there is no selection rule for compactification at the level of
causal continuity. Theorems from surgery theory and handle theory are seen to
be very relevant for understanding topology change in higher dimensions.
Compactification via parallelisable cobordisms is particularly amenable to
study with these tools.Comment: 1+19 pages. LaTeX. 9 associated eps files. Discussion of disconnected
case adde
Signature change events: A challenge for quantum gravity?
Within the framework of either Euclidian (functional-integral) quantum
gravity or canonical general relativity the signature of the manifold is a
priori unconstrained. Furthermore, recent developments in the emergent
spacetime programme have led to a physically feasible implementation of
signature change events. This suggests that it is time to revisit the sometimes
controversial topic of signature change in general relativity. Specifically, we
shall focus on the behaviour of a quantum field subjected to a manifold
containing regions of different signature. We emphasise that, regardless of the
underlying classical theory, there are severe problems associated with any
quantum field theory residing on a signature-changing background. (Such as the
production of what is naively an infinite number of particles, with an infinite
energy density.) From the viewpoint of quantum gravity phenomenology, we
discuss possible consequences of an effective Lorentz symmetry breaking scale.
To more fully understand the physics of quantum fields exposed to finite
regions of Euclidean-signature (Riemannian) geometry, we show its similarities
with the quantum barrier penetration problem, and the super-Hubble horizon
modes encountered in cosmology. Finally we raise the question as to whether
signature change transitions could be fully understood and dynamically
generated within (modified) classical general relativity, or whether they
require the knowledge of a full theory of quantum gravity.Comment: 33 pages. 4 figures; V2: 3 references added, no physics changes; V3:
now 24 pages - significantly shortened - argument simplified and more focused
- no physics changes - this version accepted for publication in Classical and
Quantum Gravit
To the emergency room and back again: Circular healthcare pathways for acute functional neurological disorders
Background and objectives
Studies of Functional Neurological Disorders (FND) are usually outpatient-based. To inform service development, we aimed to describe patient pathways through healthcare events, and factors affecting risk of emergency department (ED) reattendance, for people presenting acutely with FND.
Methods
Acute neurology/stroke teams at a UK city hospital were contacted regularly over 8 months to log FND referrals. Electronic documentation was then reviewed for hospital healthcare events over the preceding 8 years. Patient pathways through healthcare events over time were mapped, and mixed effects logistic regression was performed for risk of ED reattendance within 1 year.
Results
In 8 months, 212 patients presented acutely with an initial referral suggesting FND. 20% had subsequent alternative diagnoses, but 162 patients were classified from documentation review as possible (17%), probable (28%) or definite (55%) FND. In the preceding 8 years, these 162 patients had 563 ED attendances and 1693 inpatient nights with functional symptoms, but only 26% were referred for psychological therapy, only 66% had a documented diagnosis, and care pathways looped around ED. Three better practice pathway steps were each associated with lower risk of subsequent ED reattendance: documented FND diagnosis (OR = 0.32, p = 0.004), referral to clinical psychology (OR = 0.35, p = 0.04) and outpatient neurology follow-up (OR = 0.25, p < 0.001).
Conclusion
People that present acutely to a UK city hospital with FND tend to follow looping pathways through hospital healthcare events, centred around ED, with low rates of documented diagnosis and referral for psychological therapy. When better practice occurs, it is associated with lower risk of ED reattendance
Is there a problem with quantum wormhole states in N=1 Supergravity?
The issue concerning the existence of wormhole states in locally
supersymmetric minisuperspace models with matter is addressed. Wormhole states
are apparently absent in models obtained from the more general theory of N=1
supergravity with supermatter. A Hartle-Hawking type solution can be found,
even though some terms (which are scalar field dependent) cannot be determined
in a satisfactory way. A possible cause is investigated here. As far as the
wormhole situation is concerned, we argue here that the type of Lagrange
multipliers and fermionic derivative ordering used can make a difference. A
proposal is made for supersymmetric quantum wormholes to also be invested with
a Hilbert space structure, associated with a maximal analytical extension of
the corresponding minisuperspace.is concerned, we argue here that the type of
Lagrange multipliers and fermionic derivative ordering used can make a
difference. A proposal is made for supersymmetric quantum wormholes to also be
invested with a Hilbert space structure, associated with a maximal analytical
extension of the corresponding minisuperspace.Comment: 22 pages, TeX (some font problems may occur, just press Return),
Based on a essay submitted to the 1995 ravity Research Foundation Awards,
accepted in G.R.
The use of coercive measures in forensic psychiatric care: legal, ethical and practical challenges
The use of coercive measures, namely restraint, seclusion and involuntary medication, remain controversial methods of practice within forensic psychiatry. Ethical and moral debates surrounding the use of coercive measures are compounded by the need to balance care, safety, and security. Despite such tensions, limited research has been conducted in this area. This paper examines the prevalence of coercive measures and factors associated with their use specifically within forensic psychiatry. A systematic review was conducted and fifteen empirical studies were identified, each examining the use of coercive measures in forensic inpatient psychiatry, reported in papers published between January 1980 and January 2012. Findings suggest that patients who are younger or newly admitted tend to be secluded most often. Findings relating to gender, ethnicity and patient diagnoses, however, are equivocal. Patients tend to perceive experiences of coercive measures negatively. Staff perceptions however, appear to be determined by their role in governing or practicing coercive interventions. Findings are discussed in light of variations in hospital settings, policies and sociocultural traditions. While the uses of coercive measures appear to be influenced by a combination of all patient, staff, and environmental factors, further research is required to explore each of these aspects in greater detail
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