295 research outputs found

    Accidental parabolics and relatively hyperbolic groups

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    By constructing, in the relative case, objects analoguous to Rips and Sela's canonical representatives, we prove that the set of images by morphisms without accidental parabolic, of a finitely presented group in a relatively hyperbolic group, is finite, up to conjugacy.Comment: Revision, 24 pages, 4 figure

    Radioactivity Investigation of Sand from the Northern Region of Tlemcen-Algeria, Using Well-Shape NaI(Tl) Detector

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    The presence of natural radioactivity in sand and other building materials results in internal and external exposure to the general public. Therefore, it is desirable to determine the concentration of naturally occurring radionuclides. Sand is one of the main components in building construction beside cements, granites and bricks. Thus, this research has been carried out in order to investigate the levels of natural radioactivity and associated radiation hazard in some Algerian sand. The natural radioactivity due to the presence of 226Ra, 232Th and 40K in sand samples used as building materials in Tlemcen province - Algeria was measured by gamma spectrometry using NaI(Tl) scintillation well-shaped detector. In this context, sand samples were collected from four different locations of northern areas of Tlemcen city, Behira seabeach sand, Targa sand, Boukdasen sand, Sidi Bourzin sand. The measured activity in the sand samples ranged from 4.70 to 7.85 Bq.kg-1, 0.80 to 3.00Bq.kg-1 and 22 to 53 Bq.kg-1 for 226Ra, 232Th and 40K, respectively. The concentrations of these natural radionuclides were compared with the reported data for other countries and were found significantly lower than the worldwide average as reported by United Nations Scientific Committee on the Effects of Atomic Radiation (1,2). Radium equivalent activities were calculated (9.25 to 16.39) Bq·kg–1for the analyzed samples to assess radiation hazards arising due to the presence of these radionuclides in the samples. Most of the calculated radium equivalent activities are lower than the limit set in the OECD report at 370Bq.kg–1(3). The measured representative level index values for the investigated samples varied in the range (0.068 to 0.118) Bq.kg-1. External and internal hazard index (Hex,Hin), the specific dose rates indoor (D) and the annual effective dose (DE) due to gamma radiation from building materials was calculated. Keywords. Sand, natural radioactivity, gamma radiation, absorbed dose, radiation exposure, Potassium, Thorium, Uranium, NaI(Tl) Detector, Tlemcen

    Natural Radioactivity in Red Clay Brick Manufactured in Tlemcen-Algeria, Using Well-Shape NaI(Tl) Detector

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    The presence of natural radioactivity in brick and other building materials results in internal and external exposure to the general public. Therefore, it is desirable to determine the concentration of naturally occurring radionuclides. Bricks are one of the main components in building construction beside cements, granites and sand. Thus, this research has been carried out in order to investigate the levels of natural radioactivity and associated radiation hazard in Algerian red brick. The natural radioactivity due to the presence of 226Ra, 232Th and 40K in brick samples used as building materials in Tlemcen province - Algeria was measured by gamma spectrometry using NaI(Tl) scintillation well-shaped detector. In this context, brick samples were collected from two manufactories Tafna and Tounan. The mean values of activity concentrations for 226Ra, 232Th and 40K were found to be in the main value of 15.5Bq.kg-1, 11Bq.kg-1, and 196.5Bq.kg-1, respectively. The concentrations of these natural radionuclides were compared with the reported data for other countries and were found significantly lower than the world wide average (1,2). Radium equivalent activities were calculated (41.3 to 51.4) Bq.kg–1 for the analyzed samples to assess the radiation hazards arising due to the presence of these radionuclides in the samples. The calculated radium equivalent activities are lower than the limit set by the OECD report 370 Bq.kg–1 (3). The measured representative level index values for the investigated samples varied in the range (0.31 to 0.38) Bq.kg1.  External and internal hazard index (Hex,Hin), the specific dose rates in door (D) and the annual effective dose (DE) due to gamma radiation from building materials was calculated. Keywords: Brick, natural radioactivity, gamma radiation, absorbed dose, radiation exposure, Potassium, Thorium, Uranium; NaI(Tl) detector, Tlemcen

    Parabolic groups acting on one-dimensional compact spaces

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    Given a class of compact spaces, we ask which groups can be maximal parabolic subgroups of a relatively hyperbolic group whose boundary is in the class. We investigate the class of 1-dimensional connected boundaries. We get that any non-torsion infinite f.g. group is a maximal parabolic subgroup of some relatively hyperbolic group with connected one-dimensional boundary without global cut point. For boundaries homeomorphic to a Sierpinski carpet or a 2-sphere, the only maximal parabolic subgroups allowed are virtual surface groups (hyperbolic, or virtually Z+Z\mathbb{Z} + \mathbb{Z}).Comment: 10 pages. Added a precision on local connectedness for Lemma 2.3, thanks to B. Bowditc

    Assessment of dysarthric speech through rhythm metrics

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    AbstractThis paper reports the results of acoustic investigation based on rhythmic classifications of speech from duration measurements carried out to distinguish dysarthric speech from healthy speech. The Nemours database of American dysarthric speakers is used throughout experiments conducted for this study. The speakers are eleven young adult males with dysarthria caused by cerebral palsy (CP) or head trauma (HT) and one non-dysarthric adult male. Eight different sentences for each speaker were segmented manually to vocalic and intervocalic segmentation (176 sentences). Seventy-four different sentences for each speaker were automatically segmented to voiced and non-voiced intervals (1628 sentences). A two-parameters classification related to rhythm metrics was used to determine the most relevant measures investigated through bi-dimensional representations. Results show the relevance of rhythm metrics to distinguish healthy speech from dysarthrias and to discriminate the levels of dysarthria severity. The majority of parameters was more than 54% successful in classifying speech into its appropriate group (90% for the dysarthric patient classification in the feature space (%V, ΔV)). The results were not significant for voiced and unvoiced intervals relatively to the vocalic and intervocalic intervals (the highest recognition rates were: 62.98 and 90.30% for dysarthric patient and healthy control classification respectively in the feature space (ΔDNV, %DV))

    Transition to Product Service Systems: methodology based on scenarios identification, modelling and evaluation

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    Part 4: Transition Towards Product-Service SystemsInternational audienceThe paper proposes a methodology to support the organisational shift towards product Services Systems. Its backbone is the evaluation of economic impact of such a shift. However, in order to efficiently accommodate organisational changes and include company specificities, other steps are required prior to evaluation. These are context analysis, scenarios identification and modelling. The novelty of the paper lies in (i) including organisational changes in the evaluation and (ii) managing the contextualization to company specificities

    An Intelligent and Low-cost Eye-tracking System for Motorized Wheelchair Control

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    In the 34 developed and 156 developing countries, there are about 132 million disabled people who need a wheelchair constituting 1.86% of the world population. Moreover, there are millions of people suffering from diseases related to motor disabilities, which cause inability to produce controlled movement in any of the limbs or even head.The paper proposes a system to aid people with motor disabilities by restoring their ability to move effectively and effortlessly without having to rely on others utilizing an eye-controlled electric wheelchair. The system input was images of the users eye that were processed to estimate the gaze direction and the wheelchair was moved accordingly. To accomplish such a feat, four user-specific methods were developed, implemented and tested; all of which were based on a benchmark database created by the authors.The first three techniques were automatic, employ correlation and were variants of template matching, while the last one uses convolutional neural networks (CNNs). Different metrics to quantitatively evaluate the performance of each algorithm in terms of accuracy and latency were computed and overall comparison is presented. CNN exhibited the best performance (i.e. 99.3% classification accuracy), and thus it was the model of choice for the gaze estimator, which commands the wheelchair motion. The system was evaluated carefully on 8 subjects achieving 99% accuracy in changing illumination conditions outdoor and indoor. This required modifying a motorized wheelchair to adapt it to the predictions output by the gaze estimation algorithm. The wheelchair control can bypass any decision made by the gaze estimator and immediately halt its motion with the help of an array of proximity sensors, if the measured distance goes below a well-defined safety margin.Comment: Accepted for publication in Sensor, 19 Figure, 3 Table
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