14,299 research outputs found
Independent Component Analysis for Improved Defect Detection in Guided Wave Monitoring
Guided wave sensors are widely used in a number of industries and have found particular application in the oil and gas industry for the inspection of pipework. Traditionally this type of sensor was used for one-off inspections, but in recent years there has been a move towards permanent installation of the sensor. This has enabled highly repeatable readings of the same section of pipe, potentially allowing improvements in defect detection and classification. This paper proposes a novel approach using independent component analysis to decompose repeat guided wave signals into constituent independent components. This separates the defect from coherent noise caused by changing environmental conditions, improving detectability. This paper demonstrates independent component analysis applied to guided wave signals from a range of industrial inspection scenarios. The analysis is performed on test data from pipe loops that have been subject to multiple temperature cycles both in undamaged and damaged states. In addition to processing data from experimental damaged conditions, simulated damage signals have been added to “undamaged” experimental data, so enabling multiple different damage scenarios to be investigated. The algorithm has also been used to process guided wave signals from finite element simulations of a pipe with distributed shallow general corrosion, within which there is a patch of severe corrosion. In all these scenarios, the independent component analysis algorithm was able to extract the defect signal, rejecting coherent noise
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Primate malarias: Diversity, distribution and insights for zoonotic Plasmodium
Protozoans within the genus Plasmodium are well-known as the causative agents of malaria in humans. Numerous Plasmodium species parasites also infect a wide range of non-human primate hosts in tropical and sub-tropical regions worldwide. Studying this diversity can provide critical insight into our understanding of human malarias, as several human malaria species are a result of host switches from non-human primates. Current spillover of a monkey malaria, Plasmodium knowlesi, in Southeast Asia highlights the permeability of species barriers in Plasmodium. Also recently, surveys of apes in Africa uncovered a previously undescribed diversity of Plasmodium in chimpanzees and gorillas. Therefore, we carried out a meta-analysis to quantify the global distribution, host range, and diversity of known non-human primate malaria species. We used published records of Plasmodium parasites found in non-human primates to estimate the total diversity of non-human primate malarias globally. We estimate that at least three undescribed primate malaria species exist in sampled primates, and many more likely exist in unstudied species. The diversity of malaria parasites is especially uncertain in regions of low sampling such as Madagascar, and taxonomic groups such as African Old World Monkeys and gibbons. Presence–absence data of malaria across primates enables us to highlight the close association of forested regions and non-human primate malarias. This distribution potentially reflects a long coevolution of primates, forest-adapted mosquitoes, and malaria parasites. The diversity and distribution of primate malaria are an essential prerequisite to understanding the mechanisms and circumstances that allow Plasmodium to jump species barriers, both in the evolution of malaria parasites and current cases of spillover into humans
Uniform in time estimates for the weak error of the Euler method for SDEs and a Pathwise Approach to Derivative Estimates for Diffusion Semigroups
We present a criterion for uniform in time convergence of the weak error of
the Euler scheme for Stochastic Differential equations (SDEs). The criterion
requires i) exponential decay in time of the space-derivatives of the semigroup
associated with the SDE and ii) bounds on (some) moments of the Euler
approximation. We show by means of examples (and counterexamples) how both i)
and ii) are needed to obtain the desired result. If the weak error converges to
zero uniformly in time, then convergence of ergodic averages follows as well.
We also show that Lyapunov-type conditions are neither sufficient nor necessary
in order for the weak error of the Euler approximation to converge uniformly in
time and clarify relations between the validity of Lyapunov conditions, i) and
ii).
Conditions for ii) to hold are studied in the literature. Here we produce
sufficient conditions for i) to hold. The study of derivative estimates has
attracted a lot of attention, however not many results are known in order to
guarantee exponentially fast decay of the derivatives. Exponential decay of
derivatives typically follows from coercive-type conditions involving the
vector fields appearing in the equation and their commutators; here we focus on
the case in which such coercive-type conditions are non-uniform in space. To
the best of our knowledge, this situation is unexplored in the literature, at
least on a systematic level. To obtain results under such space-inhomogeneous
conditions we initiate a pathwise approach to the study of derivative estimates
for diffusion semigroups and combine this pathwise method with the use of Large
Deviation Principles.Comment: 47 pages and 9 figure
A theoretical and semiemprical correction to the long-range dispersion power law of stretched graphite
In recent years intercalated and pillared graphitic systems have come under
increasing scrutiny because of their potential for modern energy technologies.
While traditional \emph{ab initio} methods such as the LDA give accurate
geometries for graphite they are poorer at predicting physicial properties such
as cohesive energies and elastic constants perpendicular to the layers because
of the strong dependence on long-range dispersion forces. `Stretching' the
layers via pillars or intercalation further highlights these weaknesses. We use
the ideas developed by [J. F. Dobson et al, Phys. Rev. Lett. {\bf 96}, 073201
(2006)] as a starting point to show that the asymptotic dependence
of the cohesive energy on layer spacing in bigraphene is universal to all
graphitic systems with evenly spaced layers. At spacings appropriate to
intercalates, this differs from and begins to dominate the power
law for dispersion that has been widely used previously. The corrected power
law (and a calculated coefficient) is then unsuccesfully employed in the
semiempirical approach of [M. Hasegawa and K. Nishidate, Phys. Rev. B {\bf 70},
205431 (2004)] (HN). A modified, physicially motivated semiempirical method
including some effects allows the HN method to be used
successfully and gives an absolute increase of about to the predicted
cohesive energy, while still maintaining the correct asymptotics
Architectural implications for context adaptive smart spaces
Buildings and spaces are complex entities containing complex social structures and interactions. A smart space is a composite of the users that inhabit it, the IT infrastructure that supports it, and the sensors and appliances that service it. Rather than separating the IT from the buildings and from the appliances that inhabit them and treating them as separate systems, pervasive computing combines them and allows them to interact. We outline a reactive context architecture that supports this vision of integrated smart spaces and explore some implications for building large-scale pervasive systems
Long-time behaviour of degenerate diffusions: UFG-type SDEs and time-inhomogeneous hypoelliptic processes
We study the long time behaviour of a large class of diffusion processes on
, generated by second order differential operators of (possibly)
degenerate type. The operators that we consider {\em need not} satisfy the
H\"ormander condition. Instead, they satisfy the so-called UFG condition,
introduced by Herman, Lobry and Sussman in the context of geometric control
theory and later by Kusuoka and Stroock, this time with probabilistic
motivations. In this paper we study UFG diffusions and demonstrate the
importance of such a class of processes in several respects: roughly speaking
i) we show that UFG processes constitute a family of SDEs which exhibit
multiple invariant measures and for which one is able to describe a systematic
procedure to determine the basin of attraction of each invariant measure
(equilibrium state). ii) We use an explicit change of coordinates to prove that
every UFG diffusion can be, at least locally, represented as a system
consisting of an SDE coupled with an ODE, where the ODE evolves independently
of the SDE part of the dynamics. iii) As a result, UFG diffusions are
inherently "less smooth" than hypoelliptic SDEs; more precisely, we prove that
UFG processes do not admit a density with respect to Lebesgue measure on the
entire space, but only on suitable time-evolving submanifolds, which we
describe. iv) We show that our results and techniques, which we devised for UFG
processes, can be applied to the study of the long-time behaviour of
non-autonomous hypoelliptic SDEs and therefore produce several results on this
latter class of processes as well. v) Because processes that satisfy the
(uniform) parabolic H\"ormander condition are UFG processes, our paper contains
a wealth of results about the long time behaviour of (uniformly) hypoelliptic
processes which are non-ergodic, in the sense that they exhibit multiple
invariant measures.Comment: 66 page
Changes of partitioning and increased root lengths of spruce and beech exposed to ambient pollution concentrations in southern England
International audienc
Understanding the deformation history of Murchison (CM2): clues from calcite twin stress analysis and high resolution X-ray Computed tomography
Addressing the Global Burden of Trauma in Major Surgery
Despite a technically perfect procedure, surgical stress can determine the success or failure of an operation. Surgical trauma is often referred to as the neglected step-child of global health in terms of patient numbers, mortality, morbidity and costs. A staggering 234 million major surgeries are performed every year, and depending upon country and institution, up to 4% of patients will die before leaving hospital, up to 15% will have serious post-operative morbidity, and 5 to 15% will be readmitted within 30 days. These percentages equate to around 1000 deaths and 4000 major complications every hour, and it has been estimated that 50% may be preventable. New frontline drugs are urgently required to make major surgery safer for the patient and more predictable for the surgeon. We review the basic physiology of the stress response from neuroendocrine to genomic systems, and discuss the paucity of clinical data supporting the use of statins, beta-adrenergic blockers and calcium channel blockers. Since cardiac-related complications are the most common, particularly in the elderly, a key strategy would be to improve ventricular-arterial coupling to safeguard the endothelium and maintain tissue oxygenation. Reduced O2 supply is associated with glycocalyx shedding, decreased endothelial barrier function, fluid leakage, inflammation and coagulopathy. A healthy endothelium may prevent these secondary hit complications, including possibly immunosuppression. Thus the four pillars of whole body resynchronization during surgical trauma, and targets for new therapies, are: 1) the CNS, 2) the heart, 3) arterial supply and venous return functions, and 4) the endothelium. This is termed the Central-Cardio-Vascular-Endothelium (CCVE) coupling hypothesis. Since similar sterile injury cascades exist in critical illness, accidental trauma, hemorrhage, cardiac arrest, infection and burns, new drugs that improve CCVE coupling may find wide utility in civilian and military medicine
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