19,227 research outputs found

    ROSAT-HRI detection of the Class I protostar YLW16A in the rho Ophiuchi dark cloud

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    I analyze unpublished or partially published archival ROSAT data of the rho Ophiuchi dark cloud. This set of seven overlapping ROSAT HRI pointings, composed of eight ~one-hour exposures, detects mainly the X-ray brightest T Tauri stars of this star-forming region. Only two HRI sources are new X-ray sources, and their optical counterparts are proposed as new Weak T Tauri star candidates. Meanwhile the ROSAT HRI caught during just one exposure a weak X-ray source (maximum likelihood=10; SNR=4.1\sigma for Gaussian statistics) among a group of three embedded young stellar objects including two Class I protostars. Previous ROSAT PSPC, ASCA GIS observations, and as I argue here one Einstein IPC observation, have already detected an X-ray source in this area, but this higher angular resolution data show clearly that X-rays are emitted by the Class I protostar YLW16A. This is the second Class I protostar detected by the ROSAT HRI in this dark cloud. The determination of the intrinsic X-ray luminosity of this event, L_X[0.1-2.4 keV]=(9.4-450)*1E30 erg/s, critically depends on the source absorption estimate. Improvements will be obtained only by the direct determination of this parameter from fitting of Chandra and XMM-Newton spectra.Comment: 4 pages, 2 figures, 2 tables. Accepted for publication in A&

    Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

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    Recently, in a study the X-ray flaring activity of Sgr A* with Chandra and XMM-Newton public observations from 1999 to 2014 and 2014 Swift data, it has been argued that the "bright and very bright" flaring rate raised from 2014 Aug. 31. Thanks to 482ks of observations performed in 2015 with Chandra, XMM-Newton and Swift, we test the significance of this rise of flaring rate and determine the threshold of unabsorbed flare flux or fluence leading to any flaring-rate change. The mean unabsorbed fluxes of the 107 flares detected in the 1999-2015 observations are consistently computed from the extracted spectra and calibration files, assuming the same spectral parameters. We construct the observed flare fluxes and durations distribution for the XMM-Newton and Chandra flares and correct it from the detection biases to estimate the intrinsic distribution from which we determine the average flare detection efficiency for each observation. We apply the BB algorithm on the flare arrival times corrected from the corresponding efficiency. We confirm a constant overall flaring rate in 1999-2015 and a rise in the flaring rate for the most luminous/energetic flares from 2014 Aug. 31 (4 months after the passage of the DSO/G2 close to Sgr A*). We also identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 Aug. and Nov., respectively (10 and 7 months before the pericenter of the DSO/G2). The decay of the faint flaring rate is difficult to explain by the tidal disruption of the DSO/G2, whose stellar nature is now well established, since it occurred well before its pericenter. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long time period may be later released by several bright flares during a shorter time period. (abridged)Comment: Accepted in A&A in 2017 April 2

    The Urban High School's Challenge: Ensuring Literacy for Every Child

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    Looks at comprehensive adolescent literacy reform initiatives in school districts across the nation that are beginning to address the need for effecting systemic change by teaching reading to all students

    Variables influencing transport mode choice: a generalized cots approach

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    The decision variables that influence transport mode choice are numerous. From a careful appraisal of the literature review it appears that two main typologies of variables can be identified: costs related to the transport of the goods and other service’s attributes that play a crucial role in the selection. Each of these two categories has been already revised in previous researches and some fundamental findings are reported in this paper as a preliminary base for the development of the present study. The analysis of the literature review will revise the internal costs variables, or out of pocket money, and the influence of qualitative attributes as decision variables. The paper will conclude with a review of the external costs and their hypothetical internalization in the calculation of transport cost. The paper will be organized as follows: a literature review on elements affecting mode choice, the third paragraph will deal with the methodological approach of generalized cost function that will be applied in paragraph four on the selected corridors. Some conclusions and further recommendations for research will terminate the paper.Intermodal transport, Generalized costs, External cost

    Modeling a Fluidized-Bed Reactor for the Catalytic Polymerization ff Ethylene: Particle Size Distribution Effects

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    Particle size distributions in the output stream of commercial, fluidized-bed reactors for ethylene polymerization are analyzed using a mathematical model. The impact on the overall reactor performance of the universe of sizes for the particles in the bed, with only a fraction of them being extracted in the product flow, is studied. For the output stream, product size distribution is modeled using both triangular and generalized gamma functions. Extraction system parameters are employed to model the particle quantity and sizes. The importance of the proper modeling of the extraction system is shown through the analysis of the effects several output schemes have on the particle size distribution inside the fluidized-bed. Some of the main reactor variables, such as yield and temperature, are studied for several distributions. Operating variables, such as catalyst feed rate, are varied according to the reactor capacity in a typical, 12 meter bed, 130,000 ton/year reactor. Predictions indicate higher output rates for higher catalyst loads, as expected. A shift towards smaller particle sizes in the product and in the bed is observed when increasing catalyst load. Bed fluidization and heat exchange conditions are shown as affected by size distributions. Results show that it is appropriate to include both product and bed particle diameter distribution when studying the reactor performance.Fil: Grosso, Walter. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - Santa Fe. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂ­mica. Universidad Nacional del Litoral. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂ­mica; ArgentinaFil: Chiovetta, Mario Gabriel. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - Santa Fe. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂ­mica. Universidad Nacional del Litoral. Instituto de Desarrollo TecnolĂłgico para la Industria QuĂ­mica; Argentin

    First-principles perturbative computation of dielectric and Born charge tensors in finite electric fields

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    We present a perturbative treatment of the response properties of insulating crystals under a dc bias field, and use this to study the effects of such bias fields on the Born effective charge tensor and dielectric tensor of insulators. We start out by expanding a variational field-dependent total-energy functional with respect to the electric field within the framework of density-functional perturbation theory. The second-order term in the expansion of the total energy is then minimized with respect to the first-order wave functions, from which the Born effective charge tensor and dielectric tensor are easily computed. We demonstrate an implementation of the method and perform illustrative calculations for the III-V semiconductors AlAs and GaAs under finite bias field

    Recognizing and forecasting the sign of financial local trends using hidden Markov models

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    The problem of forecasting financial time series has received great attention in the past, from both Econometrics and Pattern Recognition researchers. In this context, most of the efforts were spent to represent and model the volatility of the financial indicators in long time series. In this paper a different problem is faced, the prediction of increases and decreases in short (local) financial trends. This problem, poorly considered by the researchers, needs specific models, able to capture the movement in the short time and the asymmetries between increase and decrease periods. The methodology presented in this paper explicitly considers both aspects, encoding the financial returns in binary values (representing the signs of the returns), which are subsequently modelled using two separate Hidden Markov models, one for increases and one for decreases, respectively. The approach has been tested with different experiments with the Dow Jones index and other shares of the same market of different risk, with encouraging results

    Towards a flexible open-source software library for multi-layered scholarly textual studies: An Arabic case study dealing with semi-automatic language processing

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    This paper presents both the general model and a case study of the Computational and Collaborative Philology Library (CoPhiLib), an ongoing initiative underway at the Institute for Computational Linguistics (ILC) of the National Research Council (CNR), Pisa, Italy. The library, designed and organized as a reusable, abstract and open-source software component, aims at solving the needs of multi-lingual and cross-lingual analysis by exposing common Application Programming Interfaces (APIs). The core modules, coded by the Java programming language, constitute the groundwork of a Web platform designed to deal with textual scholarly needs. The Web application, implemented according to the Java Enterprise specifications, focuses on multi-layered analysis for the study of literary documents and related multimedia sources. This ambitious challenge seeks to obtain the management of textual resources, on the one hand by abstracting from current language, on the other hand by decoupling from the specific requirements of single projects. This goal is achieved thanks to methodologies declared by the 'agile process', and by putting into effect suitable use case modeling, design patterns, and component-based architectures. The reusability and flexibility of the system have been tested on an Arabic case study: the system allows users to choose the morphological engine (such as AraMorph or Al-Khalil), along with linguistic granularity (i.e. with or without declension). Finally, the application enables the construction of annotated resources for further statistical engines (training set). © 2014 IEEE

    Evaluating frequency and quality of pathogen-specific T cells.

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    It is generally accepted that enumeration and characterization of antigen-specific T cells provide essential information about potency of the immune response. Here, we report a new technique to determine the frequency and potency of antigen-specific CD8 T cells. The assay measures changes of intracellular Ca(2+) in real time by fluorescent microscopy in individual CD8 T cells responding to cognate peptides. The T cells form continuous monolayer, enabling the cells to present the peptides to each other. This approach allows us to evaluate the kinetics of intracellular Ca(2+) signalling that characterizes the quality of T cell response. We demonstrate the usefulness of the assay examining the frequency and quality of cytomegalovirus-specific CD8 T cells from healthy donor and patient after haploidentical stem cell transplantation. The new assay has a potential to provide essential information determining the status of the immune system, disease morbidity, potency of therapeutic intervention and vaccine efficacy
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