1,720,959 research outputs found
A new active method for continuous radon measurements based on a multiple cell proportional counter
No full textA new active method for continuous airborne radon activity concentration measurements is developed. It is based upon the use of a specially designed radon Multiple Cell Proportional Counter (MCPC). The constructed MCPC prototype is described and its operation principle presented. This gas-flow counter is a pile-up of 20 adjacent multiwire proportional counters. It uses argon–propane (1%) as the main counting gas mixture to which an appropriate fraction of ambient air is admixed. The airborne radon activity concentration is to be continuously measured through a periodic integral counting of the a particles emitted by 222Rn and its short-lived decay products within the sensitive volume. A Monte Carlo simulation program, taking into account the major physical processes that determine directly the detector performances, has been written and used for design optimization purposes. The simulation results show that the admixture of 10% of ambient air seems to be sufficient to continuously assess radon activity concentration levels ranging from about 15 Bqm3 up to 2.6105kBqm3 for an integral counting time period of 10 min. The expected radon sensitivity is about 1.16 cpm/10 Bqm3 with a radon counting efficiency of about 180%. The detector a-pulse height spectra obtained by simulation show a very good agreement with those delivered by the constructed MCPC prototype in its minimal configuration
Experimental analysis of steam condensation patterns within a pressure suppression system operating at sub-atmospheric pressure conditions
Get PDFFor some specific applications, the pressure suppression systems should be maintained at sub-atmospheric pressure, such as in fusion plants systems. This operation conditions differ considerably from those experienced in the suppression pools of BWR operating at atmospheric pressure. The steam condensation in water at sub-atmospheric conditions is not sufficiently known, if not at all; therefore its effectiveness has to be investigated experimentally. In fact the steam condensation at sub-atmospheric pressure requires a subcooling capacity 2.5 times higher than that at atmospheric pressure. In consideration of that, a low scale experimental facility was designed and built at the University of Pisa. More than 350 steam condensation tests were performed in broad influencing parameters range (e. g. pressure within the condensation tank, water temperature and steam mass flux) to study of effectiveness of the steam condensation. In doing that, different sparger configurations (with single or multiple holes) were considered to check possible interference of condensing steam jets and bubble coalescence. Results indicate a high efficiency of condensation for all the examined conditions. The 3D map of the condensation regimes demonstrate they are dependent only on the downstream exit pressure, the water temperature and the steam mass flux per hole
Effect of air on gas multiplication characteristics in argon-propane (1%) based proportional counters for airborne radon monitoring
No full textAiming for the development of a new technique of on-line airborne radon activity concentration measurement, the effect of air on some detection properties of argon–propane (1%)-based proportional counters is investigated when a fraction of 2%, 6% and 10% of it is successively and intentionally admixed to the counting gas in a single-wire proportional counter. The influence of the electron attachment, principally due to oxygen component, on the ionization saturation plateau and the gas amplification process is particularly examined. The previously developed semimicroscopic gas gain formula is found to describe well the gas gain data obtained in each of the gas mixtures analyzed, thus allowing a consistent examination of the air effect on the relevant gas constants. Finally, the possibility to use such air-mixed counting gases in specially designed gas-flow proportional counters intended for new on-line measurement methods of airborne radon (222Rn) activity concentration appeared quite viable
Experimental investigation of steam condensation in water tank at sub-atmospheric pressure
Get PDFThe International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System (VVPSS) limits the Vacuum Vessel (VV) internal pressure, in case of loss of coolant (LOCA) or other pressurizing accidents from the in-vessel components, to 150 kPa (abs). This is key safety function because a large internal pressure could lead to a breach of the primary confinement barrier. Safety is ensured by discharging the steam evolved during the accident event to the VVPSS suppression tanks where it is condensed. Steam condensation occurs at sub-atmospheric pressure condition. Moreover, being this latter not standard for traditional nuclear systems, this investigation is quite new (not studied in detail before) and deals with an experimental investigation of the direct contact condensation at VVPSS prototypical thermal-hydraulic conditions. To the purpose, a small-scale experimental rig was properly designed and built at Lab. B. Guerrini of DICI-University of Pisa as well as different temperature, pressure and steam mass (flow rate per hole) conditions and sparger patterns have been investigated. The experimental test matrix is also presented in this study. The obtained results show high efficiency of condensation for all examined conditions. The main condensation regimes at sub-atmospheric pressure conditions were identified. In addition, a comparison was done between the condensation regimes experimentally determined and those available in the literature, which were obtained at atmospheric pressure. Finally, results demonstrated to be representative of the real configuration at ITER reactor
Investigation of vibrations caused by the steam condensation at sub-atmospheric condition in VVPSS
No full textFusion technology deployment passes through the design of safety systems aimed to protect the Vacuum Vessel (VV) from pressurizing accidents event such as LOVA (Loss Of Vacuum Accident) or the failure of the Tokamak Water Cooling System (TWCS) causing the LOCA (Loss Of Coolant Accident). One of important safety systems of the ITER plant is the Vacuum Vessel Pressure Suppression System (VVPSS), which is designed to protect the VV by the steam condensation at sub-atmospheric pressure conditions in Suppression Tanks. The aim of this study is to investigate vibrations phenomenon, originated during the steam-water direct contact condensation (DCC) at sub-atmospheric conditions, and determine any correlations between the steam jet dynamic and water temperature (TW), steam mass flux (GS) and downstream pressure (PW). According to the thermal hydraulic conditions characterising the DCC, vibrations may evolve because of the latent heat of the phase change (large amount of heat transmitted quickly to the water). In the paper also presents the numerical investigations performed by means of proper FEM code, the set-up procedure and the experimental activity carried out at Lab. B. Guerrini of DICI- University of Pisa. This latter allowed correlating the different steam condensation regimes (chugging, condensation oscillation, etc.) to the acceleration and force, to be in turn used to determine the strength capacity of the VVPSS
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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