6,227 research outputs found
Conceptualising the geographic world: the dimensions of negotiation in crowdsourced cartography
In crowdsourced cartographic projects, mappers coordinate their efforts
through online tools to produce digital geospatial artefacts, such as maps and
gazetteers, which were once the exclusive territory of professional surveyors and
cartographers. In order to produce meaningful and coherent data, contributors
need to negotiate a shared conceptualisation that defines the domain concepts,
such as road, building, train station, forest, and lake, enabling the communi-
cation of geographic knowledge. Considering the OpenStreetMap Wiki website
as a case study, this article investigates the nature of this negotiation, driven
by a small group of mappers in a context of high contribution inequality. De-
spite the apparent consensus on the conceptualisation, the negotiation keeps
unfolding in a tension between alternative representations, which are often in-
commensurable, i.e., hard to integrate and reconcile. In this study, we identify
six complementary dimensions of incommensurability that recur in the nego-
tiation: (i) ontology, (ii) cartography, (iii) culture and language, (iv) lexical
definitions, (v) granularity, and (vi) semantic overload and duplication
Movements Around Transit Tunnels in Mixed Ground
This paper describes the ground movements measured at a Test Section during construction of twin rapid transit tunnels in Cambridge, Massachusetts. The Test Section was located in an area of rock, soft ground and mixed face tunneling, with the alignment of the twin tunnels approximately 100 feet below ground surface. Overburden soils consist primarily of a very dense, saturated glacial till containing cobbles and boulders, with a weakly metamorphosed, fractured shale bedrock below. Instrumentation at the Test Section was installed in three cross-sections: one with the tunnel headings entirely in rock, a second with the tunnel headings in soft ground, and a third in a mixed face area. The field measurements are analyzed to show the effects of ground losses at the tunnel headings vs. distance away from headings, the effects of single vs. twin tunnel construction, and the effects of mixed face vs. rock and soft ground tunneling on ground movements
Statistical Mechanics of Semi-Supervised Clustering in Sparse Graphs
We theoretically study semi-supervised clustering in sparse graphs in the
presence of pairwise constraints on the cluster assignments of nodes. We focus
on bi-cluster graphs, and study the impact of semi-supervision for varying
constraint density and overlap between the clusters. Recent results for
unsupervised clustering in sparse graphs indicate that there is a critical
ratio of within-cluster and between-cluster connectivities below which clusters
cannot be recovered with better than random accuracy. The goal of this paper is
to examine the impact of pairwise constraints on the clustering accuracy. Our
results suggests that the addition of constraints does not provide automatic
improvement over the unsupervised case. When the density of the constraints is
sufficiently small, their only impact is to shift the detection threshold while
preserving the criticality. Conversely, if the density of (hard) constraints is
above the percolation threshold, the criticality is suppressed and the
detection threshold disappears.Comment: 8 pages, 4 figure
A portable diagnostic device for cardiac magnetic field mapping
In this paper we present a portable magnetocardiography device. The focus of this development was delivering a rapid assessment of chest pain in an emergency department. The aim was therefore to produce an inexpensive device that could be rapidly deployed in a noisy unshielded ward environment. We found that induction coil magnetometers with a coil design optimized for magnetic field mapping possess sufficient sensitivity (104fT /â Hz noise floor at 10Hz) and response (813fT /”V at 10Hz) for cycle averaged magnetocardiography and are able to measure depolarisation signals in an unshielded environment. We were unable to observe repolarisation signals to a reasonable fidelity. We present the design of the induction coil sensor array and signal processing routine along with data demonstrating performance in a hospital environment
Single and Composite Hot Subdwarf Stars in the Light of 2MASS Photometry
Utilizing the Two Micron All Sky Survey (2MASS) Second Incremental Data
Release Catalog, we have retrieved near-IR magnitudes for several hundred hot
subdwarfs (sdO and sdB stars) drawn from the "Catalogue of Spectroscopically
Identified Hot Subdwarfs" (Kilkenny, Heber, & Drilling 1988, 1992). This sample
size greatly exceeds that of previous studies of hot subdwarfs. Examining 2MASS
photometry alone or in combination with visual photometry (Johnson BV or
Stromgren uvby) available in the literature, we show that it is possible to
identify hot subdwarf stars that exhibit atypically red IR colors that can be
attributed to the presence of an unresolved late type companion. Utilizing this
large sample, we attempt for the first time to define an approximately volume
limited sample of hot subdwarfs. We discuss the considerations, biases, and
difficulties in defining such a sample.
We find that, of the hot subdwarfs in Kilkenny et al., about 40% in a
magnitude limited sample have colors that are consistent with the presence of
an unresolved late type companion. Binary stars are over-represented in a
magnitude limited sample. In an approximately volume limited sample the
fraction of composite-color binaries is about 30%.Comment: to appear in Sept 2003 AJ, 41 pages total, 12 figures, 2 tables are
truncated (full tables to appear in electronic journal or available by
request
Recommended from our members
High-energy resolution, high-angular acceptance crystal monochromator
The design principles, construction and characterization of a 4- bounce dispersive crystal monochromator is discussed. This monochromator is designed to reduce the bandpass of synchrotron radiation to 10--50 meV level, without sacrificing angular acceptance. This is achieved by combining an asymmetrically-cut, low order reflection with a symmetrically-cut, high order reflection in a nested configuration. This monochromator is being used as a beam conditioner for nuclear resonant scattering of synchrotron radiation to produce x-rays with {mu}eV{minus}neV resolution in the hard x-ray regime
Amphetamine-type stimulant use and HIV/STI risk behaviour among young female sex workers in Phnom Penh, Cambodia
Background: Use of amphetamine-type substances (ATS) has been linked to increased risk of HIV and other sexually transmitted infections (STI) worldwide. In Cambodia, recent ATS use is independently associated with incident STI infection among young female sex workers (FSW). Methods: We conducted 33 in-depth interviews with women (15-29 years old) engaged in sex work to explore ATS use and vulnerability to HIV/STI. Results: Participants reported that ATS, primarily methamphetamine in pill and crystalline forms (yama), were cheap, widely available and commonly used. Yama was described as a âpower drugâ (thnam kamlang) which enabled women to work long hours and serve more customers. Use of ATS by clients was also common, with some providing drugs for women and/or encouraging their use, often resulting in prolonged sexual activity. Requests for unprotected sex were also more common among intoxicated clients and strategies typically employed to negotiate condom use were less effective. Conclusion: ATS use was highly functional for young women engaged in sex work, facilitating a sense of power and agency and highlighting the occupational significance and normalization of ATS in this setting. This highly gendered dynamic supports the limited but emerging literature on women's use of ATS, which to date has been heavily focused on men. Results indicate an urgent need to increase awareness of the risks associated with ATS use, to provide women with alternative and sustainable options for income generation, to better regulate the conditions of sex work, and to work with FSWs and their clients to develop and promote culturally appropriate harm reduction interventions. Keywords: sex work; amphetamine-type substances; HIV; sexually transmitted infections; risk behaviour; vulnerabilityNI
What Can Proton Beam Therapy Achieve for Patients with Pectus Excavatum Requiring Left Breast, Axilla and Internal Mammary Nodal Radiotherapy?
AIMS: Exposure of the heart to radiation increases the risk of ischaemic heart disease, proportionate to the mean heart dose (MHD). Radiotherapy techniques including proton beam therapy (PBT) can reduce MHD. The aims of this study were to quantify the MHD reduction achievable by PBT compared with volumetric modulated arc therapy in breath hold (VMAT-BH) in patients with pectus excavatum (PEx), to identify an anatomical metric from a computed tomography scan that might indicate which patients will achieve the greatest MHD reductions from PBT. MATERIALS AND METHODS: Sixteen patients with PEx (Haller Index â„2.7) were identified from radiotherapy planning computed tomography images. Left breast/chest wall, axilla (I-IV) and internal mammary node (IMN) volumes were delineated. VMAT and PBT plans were prepared, all satisfying target coverage constraints. Signed-rank comparisons of techniques were undertaken for the mean dose to the heart, ipsilateral lung and contralateral breast. Spearman's rho correlations were calculated for anatomical metrics against MHD reduction achieved by PBT. RESULTS: The mean MHD for VMAT-BH plans was 4.1 Gy compared with 0.7 Gy for PBT plans. PBT reduced MHD by an average of 3.4 Gy (range 2.8-4.4 Gy) compared with VMAT-BH (P < 0.001). PBT significantly reduced the mean dose to the ipsilateral lung (4.7 Gy, P < 0.001) and contralateral breast (2.7 Gy, P < 0.001). The distance (mm) at the most inferomedial extent of IMN volume (IMN to heart distance) negatively correlated with MHD reduction achieved by PBT (Spearman's rho -0.88 (95% confidence interval -0.96 to -0.67, P < 0.001)). CONCLUSION: For patients with PEx requiring left-sided breast and IMN radiotherapy, a clinically significant MHD reduction is achievable using PBT, compared with the optimal photon technique (VMAT-BH). This is a patient group in whom PBT could have the greatest benefit
Treatment Failure in Coeliac Disease: A Practical Guide to Investigation and Treatment of Non-responsive and Refractory Coeliac Disease
Abstract Coeliac disease is a common condition affecting up to 1% of the European adult population. Whilst the majority of patients will respond to a gluten free diet with resolution of symptoms and an improvement in histology, a significant minority have persistent problems. Refractory coeliac disease is a relatively uncommon cause of non-response to gluten free diet with potentially serious consequences of severe malabsorption and a high rate of progression to lymphoma. This review provides a practical guide to the investigation of patients who do not respond to a gluten free diet. We will highlight the differences between the more common non-responsive coeliac disease and the rare entity of refractory coeliac disease and discuss current management and treatment options for both non-responsive coeliac disease and refractory coeliac disease
- âŠ