6,136 research outputs found
Quantum causal histories
Quantum causal histories are defined to be causal sets with Hilbert spaces
attached to each event and local unitary evolution operators. The reflexivity,
antisymmetry, and transitivity properties of a causal set are preserved in the
quantum history as conditions on the evolution operators. A quantum causal
history in which transitivity holds can be treated as ``directed'' topological
quantum field theory. Two examples of such histories are described.Comment: 16 pages, epsfig latex. Some clarifications, minor corrections and
references added. Version to appear in Classical and Quantum Gravit
Factors related to discontinued clinic attendance by patients with podoconiosis in southern Ethiopia: a qualitative study
Background
Podoconiosis is a lymphoedema of non-infectious cause which results in long-term ill health in affected individuals. Simple, effective treatment is available in certain parts of Ethiopia, but evidence indicates that not all patients continue collecting treatment supplies from clinic sites once started. We used qualitative techniques to explore factors related to discontinued attendance at outreach clinics of a non-government organization in southern Ethiopia.
Methods
A cross-sectional qualitative study was conducted in four clinic sites through unstructured in-depth interviews, key informant interviews and focus group discussions with the involvement of 88 study subjects.
Results
Discontinuation of clinic visits is common among podoconiosis patients. The reasons were: remoteness from the clinic sites, unrealistic expectation of ‘special’ aid, worry about increasing stigma, illness and misconceptions about treatment.
Conclusions
Several of these factors are remediable through community and individual information and education. Appropriate routes to deliver this information must be identified. Certain factors (such as distance to clinic sites and stigma) require substantial expansion of services or liaison with village-level government health services
Rossby adjustment over a step
The adjustment of a rotating fluid to a geostrophic equilibrium is now a classical problem in the theory of rotating fluids and is associated with the name of Rossby because of his pioneering work in this subject. The case of particular interest here is the one where the fluid is initially at rest but has a discontinuity in surface elevation along a certain line. If the bottom is flat, the adjustment gives rise to a jet flowing along the line of the initial discontinuity, the width of the jet being the Rossby radius of deformation. This paper examines how the flow is modified when the bottom is not flat, but has a step-like discontinuity running perpendicular to the line of the initial jump in surface elevation, giving rise to double Kelvin waves which propagate along the step. Flow is thus diverted parallel to the step, and behind the wave front there is no mass flux across the step.The effect of adding a vertical coast perpendicular to the step is also considered. When the double Kelvin wave propagates offshore, it leaves behind a state with no transport across the step. With propagation toward the coast, however, there is pinching of the longshore current into a narrow boundary layer.The problem is examined using (a) linear analysis, (b) laboratory experiments, and (c) numerical experiments
The matrix Kadomtsev--Petviashvili equation as a source of integrable nonlinear equations
A new integrable class of Davey--Stewartson type systems of nonlinear partial
differential equations (NPDEs) in 2+1 dimensions is derived from the matrix
Kadomtsev--Petviashvili equation by means of an asymptotically exact nonlinear
reduction method based on Fourier expansion and spatio-temporal rescaling. The
integrability by the inverse scattering method is explicitly demonstrated, by
applying the reduction technique also to the Lax pair of the starting matrix
equation and thereby obtaining the Lax pair for the new class of systems of
equations. The characteristics of the reduction method suggest that the new
systems are likely to be of applicative relevance. A reduction to a system of
two interacting complex fields is briefly described.Comment: arxiv version is already officia
On a discrete Davey-Stewartson system
We propose a differential difference equation in and study it by
Hirota's bilinear method. This equation has a singular continuum limit into a
system which admits the reduction to the Davey-Stewartson equation. The
solutions of this discrete DS system are characterized by Casorati and Grammian
determinants. Based on the bilinear form of this discrete DS system, we
construct the bilinear B\"{a}cklund transformation which enables us to obtain
its Lax pair.Comment: 12 pages, 2 figure
Synchronous oceanic spreading and continental rifting in West Antarctica
Magnetic anomalies associated with new ocean crust formation in the Adare Basin off north-western Ross Sea (43 – 26 Ma) can be traced directly into the Northern Basin that underlies the adjacent morphological continental shelf, implying a continuity in the emplacement of oceanic crust. Steep gravity gradients along the margins of the Northern Basin, particularly in the east, suggest that little extension and thinning of continental crust occurred before it ruptured and the new oceanic crust formed, unlike most other continental rifts and the Victoria Land Basin further south. A pre-existing weak crust and localisation of strain by strike slip faulting are proposed as the factors allowing the rapid rupture of continental crust
The provision of nutritional advice and care for cancer patients: a UK national survey of healthcare professionals.
PURPOSE: People living with and beyond cancer often experience nutrition-related issues and should receive appropriate advice on nutrition that is consistent and evidence based. The aim of this study was to investigate current practice for the provision of nutritional care by healthcare professionals (HCPs) from a UK national survey produced by the National Institute for Health Research (NIHR) Cancer and Nutrition Collaboration. METHODS: An online survey sent to professional groups and networks included questions on discussing nutrition, providing information, awareness of guidelines, confidence in providing nutritional advice, training and strategies for improving nutritional management. RESULTS: There were 610 HCPs who responded including nurses (31%), dietitians (25%), doctors (31%) and speech and language therapists (9%). The majority of HCPs discusses nutrition (94%) and provides information on nutrition (77%). However, only 39% of HCPs reported being aware of nutritional guidelines, and just 20% were completely confident in providing nutritional advice. Awareness of guidelines varied between the different professional groups with most but not all dietitians reporting the greatest awareness of guidelines and GPs the least (p = 0.001). Those HCPs with a greater awareness of guidelines had received training (p = 0.001) and were more likely to report complete confidence in providing nutritional advice (p = 0.001). CONCLUSION: Whilst HCPs discuss nutrition with cancer patients and may provide information, many lack an awareness of guidelines and confidence in providing nutritional advice. To ensure consistency of practice and improvements in patient care, there is scope for enhancing the provision of appropriate nutrition education and training
Statistical Physics of Irregular Low-Density Parity-Check Codes
Low-density parity-check codes with irregular constructions have been
recently shown to outperform the most advanced error-correcting codes to date.
In this paper we apply methods of statistical physics to study the typical
properties of simple irregular codes.
We use the replica method to find a phase transition which coincides with
Shannon's coding bound when appropriate parameters are chosen.
The decoding by belief propagation is also studied using statistical physics
arguments; the theoretical solutions obtained are in good agreement with
simulations. We compare the performance of irregular with that of regular codes
and discuss the factors that contribute to the improvement in performance.Comment: 20 pages, 9 figures, revised version submitted to JP
Finite-dimensional integrable systems associated with Davey-Stewartson I equation
For the Davey-Stewartson I equation, which is an integrable equation in 1+2
dimensions, we have already found its Lax pair in 1+1 dimensional form by
nonlinear constraints. This paper deals with the second nonlinearization of
this 1+1 dimensional system to get three 1+0 dimensional Hamiltonian systems
with a constraint of Neumann type. The full set of involutive conserved
integrals is obtained and their functional independence is proved. Therefore,
the Hamiltonian systems are completely integrable in Liouville sense. A
periodic solution of the Davey-Stewartson I equation is obtained by solving
these classical Hamiltonian systems as an example.Comment: 18 pages, LaTe
Three-dimensional lithospheric deformation and gravity anomalies associated with oblique continental collision in South Island, New Zealand
Isostatic considerations exhibit differences between the northern, central and southern parts of the Pacific–Australian plate collision in South Island, New Zealand. In the northern part mean elevations are moderate and the gravity low is small; the central part contains the highest elevations, and gravity and elevations correspond to each other relatively well; and in the southern part the gravity low is strongest whereas the mean elevations are moderate again. These differences indicate changes in the character of the isostatic compensation and are explained by increased thickening and widening of the crustal root from north to south, and also by the long wavelength gravity response to a mantle density anomaly that increases towards the south. A simple 3‐D gravity model is derived that includes the detailed crustal structures from the South Island GeopHysical Transect (SIGHT) experiment as well as a high‐density anomaly in the mantle inferred from teleseismic data. The model indicates that cold and, therefore, dense upper mantle material penetrates the asthenosphere to a greater extent in the south, similar to the behaviour of an apparently highly ductile lower crust. As plate reconstruction suggests more lithospheric shortening in the north, our model corresponds to lithospheric material escaping laterally to the south, almost perpendicular to the compression caused by lithospheric shortening of the mantle. Therefore, in addition to the prevailing mantle shear in New Zealand, there may also be a component of extrusional mantle creep beneath the Southern Alps orogen, which could have caused some of the observed large seismic anisotropy in this region. We may have also found evidence for submerged Eocene–Miocene oceanic lithosphere beneath the southeastern part of South Island that has been unaccounted for after plate reconstruction
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