1,677 research outputs found

    Recursive estimation of 3D features using a moving camera

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    This paper presents a scheme allowing to estimate parameters which describe geometrical structures in a 3 D scene by only using informations issued front a sequence of images provided by a mobile vision sensor with known motion . We fisrt recall the basic used models: points and lines, and then we relate their perspective projection in the image plane to the camera motion . Some techniques of recursive filtering are used into the sequence of images to incrementaly build the 3 D scene all along the diplacement of the camera . Some experimental results in the field of robotics are given .On présente un schéma d'estimation de primitives géométriques 3D à partir d'informations continues dans une séquence d'images fournie par une caméra mobile dont le mouvement est conn

    Rank-(n – 1) convexity and quasiconvexity for divergence free fields

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    The CAST experiment at CERN (European Organization of Nuclear Research) searches for axions from the sun. The axion is a pseudoscalar particle that was motivated by theory thirty years ago, with the intention to solve the strong CP problem. Together with the neutralino, the axion is one of the most promising dark matter candidates. The CAST experiment has been taking data during the last two years, setting an upper limit on the coupling of axions to photons more restrictive than from any other solar axion search in the mass range below 0.1 eV. In 2005 CAST will enter a new experimental phase extending the sensitivity of the experiment to higher axion masses. The CAST experiment strongly profits from technology developed for high energy physics and for X-ray astronomy: A superconducting prototype LHC magnet is used to convert potential axions to detectable X-rays in the 1-10 keV range via the inverse Primakoff effect. The most sensitive detector system of CAST is a spin-off from space technology, a Wolter I type X-ray optics in combination with a prototype pn-CCD developed for ESA's XMM-Newton mission. As in other rare event searches, background suppression and a thorough shielding concept is essential to improve the sensitivity of the experiment to the best possible. In this context CAST offers the opportunity to study the background of pn-CCDs and its long term behavior in a terrestrial environment with possible implications for future space applications. We will present a systematic study of the detector background of the pn-CCD of CAST based on the data acquired since 2002 including preliminary results of our background simulations.Comment: 11 pages, 8 figures, to appear in Proc. SPIE 5898, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XI

    Structural, textural and acidic properties of Cu-, Fe- and Cr-doped Ti-pillared montmorillonites

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    Montmorillonite has been treated with Ti-based solutions, alone or doped with Cu2 +, Fe3 + or Cr3 + cations, yielding new intercalated solids, which have been calcined at various temperatures to test the stability of the so-formed pillars. The solids calcined at 500 °C were fully characterized by chemical analysis, X-ray diffraction, FT-IR spectroscopy, thermal analyses, nitrogen adsorption and acidity evaluation. The evolution of the specific surface area, porosity and acidic properties is discussed, analysing the effect of pillaring and doping procedures on these propertie

    Effect of dopants on the structure of titanium oxide used as a photocatalyst for the removal of emergent contaminants

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    Photocatalysts composed of titanium dioxide modified with B, F, N and P have been synthesized, characterized and applied to the degradation of caffeine, diclofenac, ibuprofen and salicylic acid. The modified TiO2 samples were prepared by the sol–gel technique starting from titanium(IV) isopropoxide and using H3BO3, NH4F, N(C2H5OH)3 and H3PO4 as precursors of the modifiers, with the content varying between 0 and 5 wt%. Structural characterization was based on nitrogen physisorption at −196 °C, powder X-ray diffraction (PXRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA) and X-ray photoelectron spectroscopy (XPS). The structural properties of the modified TiO2 solids were significantly different depending on the nature and amount of modifiers and the calcination temperature. TiO2 in the anatase phase was obtained in all cases and was stable upon calcination at 400 °C. The photocatalytic degradation of caffeine, diclofenac, ibuprofen and salicylic acid by modified TiO2 was investigated under ultraviolet irradiation at 25 °C. The photocatalytic degradation behavior followed the order: caffeine > diclofenac = ibuprofen > salicylic acid. B-doped TiO2 was the most efficient catalyst in the degradation of these selected emerging contaminants

    Fertility preservation in boys : recent developments and new insights

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    BACKGROUND: Infertility is an important side effect of treatments used for cancer and other non-malignant conditions in males. This may be due to the loss of spermatogonial stem cells (SSCs) and/or altered functionality of testicular somatic cells (e.g. Sertoli cells, Leydig cells). Whereas sperm cryopreservation is the first-line procedure to preserve fertility in post-pubertal males, this option does not exist for prepubertal boys. For patients unable to produce sperm and at high risk of losing their fertility, testicular tissue freezing is now proposed as an alternative experimental option to safeguard their fertility. OBJECTIVE AND RATIONALE: With this review, we aim to provide an update on clinical practices and experimental methods, as well as to describe patient management inclusion strategies used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss. SEARCH METHODS: Based on the expertise of the participating centres and a literature search of the progress in clinical practices, patient management strategies and experimental methods used to preserve and restore the fertility of prepubertal boys at high risk of fertility loss were identified. In addition, a survey was conducted amongst European and North American centres/networks that have published papers on their testicular tissue banking activity. OUTCOMES: Since the first publication on murine SSC transplantation in 1994, remarkable progress has been made towards clinical application: cryopreservation protocols for testicular tissue have been developed in animal models and are now offered to patients in clinics as a still experimental procedure. Transplantation methods have been adapted for human testis, and the efficiency and safety of the technique are being evaluated in mouse and primate models. However, important practical, medical and ethical issues must be resolved before fertility restoration can be applied in the clinic. Since the previous survey conducted in 2012, the implementation of testicular tissue cryopreservation as a means to preserve the fertility of prepubertal boys has increased. Data have been collected from 24 co-ordinating centres worldwide, which are actively offering testis tissue cryobanking to safeguard the future fertility of boys. More than 1033 young patients (age range 3 months to 18 years) have already undergone testicular tissue retrieval and storage for fertility preservation. LIMITATIONS, REASONS FOR CAUTION: The review does not include the data of all reproductive centres worldwide. Other centres might be offering testicular tissue cryopreservation. Therefore, the numbers might be not representative for the entire field in reproductive medicine and biology worldwide. The key ethical issue regarding fertility preservation in prepubertal boys remains the experimental nature of the intervention. WIDER IMPLICATIONS: The revised procedures can be implemented by the multi-disciplinary teams offering and/or developing treatment strategies to preserve the fertility of prepubertal boys who have a high risk of fertility loss.Peer reviewe

    The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system

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    Short-period high-amplitude pulsating stars of Population I (ÎŽ\delta Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. aims heading (mandatory) We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. methods heading (mandatory) An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. results heading (mandatory) In addition to a positive (161 ±\pm 3) x 10−9^{-9} yr−1^{-1} secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short- (144.2 d) and long-term (∌\sim 3400 d) variations, both incompatible with a scenario of stellar evolution. conclusions heading (mandatory) Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M_{\sun}) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star (≄\geq 0.03 \ M_{\sun}), orbiting in ∌\sim 3400 d at a distance of 4.5 AU from the primary.Comment: 7 pages, 5 figures, accepted for publication in A&

    Mesoscopic organization reveals the constraints governing C. elegans nervous system

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    One of the biggest challenges in biology is to understand how activity at the cellular level of neurons, as a result of their mutual interactions, leads to the observed behavior of an organism responding to a variety of environmental stimuli. Investigating the intermediate or mesoscopic level of organization in the nervous system is a vital step towards understanding how the integration of micro-level dynamics results in macro-level functioning. In this paper, we have considered the somatic nervous system of the nematode Caenorhabditis elegans, for which the entire neuronal connectivity diagram is known. We focus on the organization of the system into modules, i.e., neuronal groups having relatively higher connection density compared to that of the overall network. We show that this mesoscopic feature cannot be explained exclusively in terms of considerations, such as optimizing for resource constraints (viz., total wiring cost) and communication efficiency (i.e., network path length). Comparison with other complex networks designed for efficient transport (of signals or resources) implies that neuronal networks form a distinct class. This suggests that the principal function of the network, viz., processing of sensory information resulting in appropriate motor response, may be playing a vital role in determining the connection topology. Using modular spectral analysis, we make explicit the intimate relation between function and structure in the nervous system. This is further brought out by identifying functionally critical neurons purely on the basis of patterns of intra- and inter-modular connections. Our study reveals how the design of the nervous system reflects several constraints, including its key functional role as a processor of information.Comment: Published version, Minor modifications, 16 pages, 9 figure

    Revisiting Date and Party Hubs: Novel Approaches to Role Assignment in Protein Interaction Networks

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    The idea of 'date' and 'party' hubs has been influential in the study of protein-protein interaction networks. Date hubs display low co-expression with their partners, whilst party hubs have high co-expression. It was proposed that party hubs are local coordinators whereas date hubs are global connectors. Here we show that the reported importance of date hubs to network connectivity can in fact be attributed to a tiny subset of them. Crucially, these few, extremely central, hubs do not display particularly low expression correlation, undermining the idea of a link between this quantity and hub function. The date/party distinction was originally motivated by an approximately bimodal distribution of hub co-expression; we show that this feature is not always robust to methodological changes. Additionally, topological properties of hubs do not in general correlate with co-expression. Thus, we suggest that a date/party dichotomy is not meaningful and it might be more useful to conceive of roles for protein-protein interactions rather than individual proteins. We find significant correlations between interaction centrality and the functional similarity of the interacting proteins.Comment: 27 pages, 5 main figures, 4 supplementary figure

    Quantum numbers of the X(3872)X(3872) state and orbital angular momentum in its ρ0Jψ\rho^0 J\psi decay

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    Angular correlations in B+→X(3872)K+B^+\to X(3872) K^+ decays, with X(3872)→ρ0J/ψX(3872)\to \rho^0 J/\psi, ρ0→π+π−\rho^0\to\pi^+\pi^- and J/ψ→Ό+Ό−J/\psi \to\mu^+\mu^-, are used to measure orbital angular momentum contributions and to determine the JPCJ^{PC} value of the X(3872)X(3872) meson. The data correspond to an integrated luminosity of 3.0 fb−1^{-1} of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be JPC=1++J^{PC}=1^{++}. The X(3872)X(3872) is found to decay predominantly through S wave and an upper limit of 4%4\% at 95%95\% C.L. is set on the fraction of D wave.Comment: 16 pages, 4 figure
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