Parametric dictionary design for sparse coding

Abstract—This paper introduces a new dictionary design method for sparse coding of a class of signals. It has been shown that one can sparsely approximate some natural signals using an overcomplete set of parametric functions, e.g. [1], [2]. A problem in using these parametric dictionaries is how to choose the parameters. In practice these parameters have been chosen by an expert or through a set of experiments. In the sparse approximation context, it has been shown that an incoherent dictionary is appropriate for the sparse approximation methods. In this paper we first characterize the dictionary design problem, subject to a constraint on the dictionary. Then we briefly explain that equiangular tight frames have minimum coherence. The complexity of the problem does not allow it to be solved exactly. We introduce a practical method to approximately solve it. Some experiments show the advantages one gets by using these dictionaries

Lead, zinc and copper mineralisation in basal Carboniferous sediments at Westwater, south Scotland

A zioneo f lead, zinc and copperm ineralisatioins developedo ver a minimum I of 4 km of strikeo f basal Carboniferoucse mentstoneg roup sedimentsa nd immediatelyu nderlyingB irrenswarkL avas atwestwater,n ear Laqholm in south Scotland. Grades so far obtained from sparse rock exposures and from shallow boreholes a fissure sulphides are usuallyO .l-O.j%o f combinedm etals over 1-2 m of thickness,bu t vein of higher grade and a relativelyt hick zone of disseminated were also located. Galena, sphalerite,c halcopyritea ndbaryte occur mainly in thin dolomitev eins but disseminationosf galenaa re also presenti n sandstoneu nits. The mineralisatioins of low temperaturet ype I was emplaceda long northeasterlyt rendingn ormal faultsa nd cross faults regardeda s late Carboniferouisn age. and Mineralisatiohna s been controlledb y faulting,r egionalf aciesv aziation and local lithologicalv ariationa s well as by stratigraphipco sition. These controlsa re applicablei n furthere xplorationo f Lower Carboniferourso cks in both south and central Scotland. The heavy mineral fraction of stream sediment is the optimums amplingt ype in reconnaissanceex plorationo f areas of calcareous . rocks such as the Lower Carboniferouso f south Scotlanda nd basal till sampling is the most effectivem ethod of follow-upe xplorationi n those areas where glaciald epositsa re widespreada nd often thick

The Locality of Chieftainship: Territory, Authority and Local Politics in Northern Malawi, 1870-1974

Discussions about colonial chieftaincy in Africa have tended to focus upon the ways in which indirect rule structured and framed traditional authority; for the majority of contemporary historians of British colonialism the question has been to what extent Lord Lugard’s blueprint for effective native administration, The Dual Mandate, invented, shaped, and restructured political and social identity. Whilst acknowledging the importance of these neo-traditional perspectives which focus much on the ways in which colonial frameworks ethnicised and tribalised African society, this thesis argues that indirect rule was as much a spatialising process as it was a tribalising one. Colonial tools of territoriality mapped politics in geographically bounded ways and as a result associating power with place began to assume new importance in the ways African leadership was defined, and given authority. By further exploring the spatial context of traditional power in colonial Malawi through the example of a Tumbuka chief named Timothy Chawinga, this thesis reveals new conclusions about the nature of chieftainship in Northern Malawi. It also provokes new questions about how we understand the role of African traditional authorities more generally, in both the past and the present.CNWS, University of Leiden; Leids Universeit Fonds; British Institute in Eastern AfricaColonial and Global Histor

A contribution to the taxonomy and ecology of the Ostracoda (Crustacea) from Verlorenvlei (Western Cape, South Africa)

Two preliminary surveys (one during the dry season and one during the wet season) of the ostracod fauna of Verlorenvlei (Western Cape) are presented. Fifteen species were found; two are reported for the first time from Africa. Various species are indicative of slightly saline to even hypersaline conditions. The morphology and ecology of the various species are briefly discussed, in order to allow future palaeo-environmental reconstructions based on ostracod fossils from this locality

How to Undertake a Clinically Relevant Systematic Review in a Rapidly Evolving Field: Magnetic Resonance Angiography

Objectives: The aim was to determine which generations of the evolving technology of magnetic resonance angiography (MRA) are currently of clinical relevance in two clinical applications. Our purpose was to plan a systematic review that would be valuable both to purchasers driven by cost-effectiveness and to practicing clinicians. Methods: Information was gathered from a search of major bibliographic databases, from a short questionnaire sent to 500 U.K. vascular radiologists and vascular surgeons, and from local clinical The authors thank A. Jackson and all those who completed a questionnaire. This work was carried out with the financial support of the Secretary of State for Health under the NHS Health Technology Assessment Programme, project 97/13/04. The views and opinions expressed do not necessarily reflect those of the Secretary of State for Health. In part, this work was undertaken by the Leeds Teaching Hospitals NHS Trust, which received funding from the NHS Executive. The views expressed in this publication are those of the authors and not necessarily those of the NHS Executive.experts. We asked which of the MRA techniques were currently used and, assuming availability, what would be their technique of choice. Results: There were 206 published articles that satisfied preliminary inclusion criteria: 69 discussed 2D time of flight (TOF); 47, 3D TOF; and 38, contrast-enhanced techniques. There were 162 questionnaires returned (60 radiologists, 102 surgeons). Of the total respondents, 77/162 (48%) used MRA in the assessment of carotid artery stenosis; 47/77 (61%) used 2D TOF; 32/77 (42%), 3D TOF; and 26/77 (34%), contrast-enhanced techniques. Thirty-five of 162 (22%) respondents used MRA in the assessment of peripheral vascular disease (PVD); 15/35 (43%) used 2D TOF, 4/35 (11%) used 3D TOF, and 22/35 (63%) used contrast-enhanced techniques. For those wishing to use MRA, contrast-enhanced techniques were the method of choice. Conclusions: The TOF methods that represent earlier generations of the technology remain clinically relevant, and will therefore be included in our systematic review. To ensure complete and relevant coverage in reviews of other evolving technologies, it would be advisable to obtain data for guidance in a similar way

Nonlinear Transient Field Problems with Phase Change using the Boundary Element Method

Peer reviewe

Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review

Objective To determine if sufficient evidence exists to support the use of magnetic resonance angiography as a means of selecting patients with recently symptomatic high grade carotid stenosis for surgery. Design Systematic review of published research on the diagnostic performance of magnetic resonance angiography, 1990-9. Main outcome measures Performance characteristics of diagnostic test. Results 126 potentially relevant articles were identified, but many articles failed to examine die performance of magnetic resonance angiography as a diagnostic test at the surgical decision thresholds used in major clinical trials on endarterectomy. 26 articles were included in a meta-analysis that showed a maximal joint sensitivity and specificity of 99% (95% confidence interval 98% to 100%) for identifying 70-99% stenosis and 90% (81% to 99%) for identifying 50-99% stenosis. Only four articles evaluated contrast enhanced magnetic resonance angiography. Conclusions Magnetic resonance angiography is accurate for selecting patients for carotid endarterectomy at the surgical decision thresholds established in the major endarterectomy trials, but the evidence is not very robust because of the heterogeneity of the studies included. Research is to determine the diagnostic performance of the most recent developments in magnetic resonance angiography, including contrast enhanced techniques, as well as to assess the impact of magnetic resonance angiography on surgical decision making and outcomes

Monitoring changes in genetic diversity

DNA is the most elemental level of biodiversity, drives the process of speciation, and underpins other levels of biodiversity, including functional traits, species and ecosystems. Until recently biodiversity indicators have largely overlooked data from the molecular tools that are available for measuring variation at the DNA level. More direct analysis of trends in genetic diversity are now feasible and are ready to be incorporated into biodiversity monitoring. This chapter explores the current state-of-the-art in genetic monitoring, with an emphasis on new molecular tools and the richness of data they provide to supplement existing approaches. We also briefly consider proxy approaches that may be useful for many-species, global scale monitoring cases