1,720,978 research outputs found
Experimental analysis and transient numerical simulation of a large diameter pulsating heat pipe in microgravity conditions
Full text linkA multi-parametric transient numerical simulation of the start-up of a large diameter Pulsating Heat Pipe (PHP) specially designed for future experiments on the International Space Station (ISS) are compared to the results obtained during a parabolic flight campaign supported by the European Space Agency. Since the channel diameter is larger than the capillary limit in normal gravity, such a device behaves as a loop thermosyphon on ground and as a PHP in weightless conditions; therefore, the microgravity environment is mandatory for pulsating mode. Because of a short duration of microgravity during a parabolic flight, the data concerns only the transient start-up behavior of the device. One of the most comprehensive models in the literature, namely the in-house 1-D transient code CASCO (French acronym for Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in English), has been configured in terms of geometry, topology, material properties and thermal boundary conditions to model the experimental device. The comparison between numerical and experimental results is performed simultaneously on the temporal evolution of multiple parameters: tube wall temperature, pressure and, wherever possible, velocity of liquid plugs, their length and temperature distribution within them. The simulation results agree with the experiment for different input powers. Temperatures are predicted with a maximum deviation of 7%. Pressure variation trend is qualitatively captured as well as the liquid plug velocity, length and temperature distribution. The model also shows the ability of capturing the instant when the fluid pressure begins to oscillate after the heat load is supplied, which is a fundamental information for the correct design of the engineering model that will be tested on the ISS. We also reveal the existence of strong liquid temperature gradients near the ends of liquid plugs both experimentally and by simulation. Finally, a theoretical prediction of the stable functioning of a large diameter PHP in microgravity is given. Results show that the system provided with an input power of 185W should be able to reach the steady state after 1min and maintain a stable operation from then on
Experimental validation of Large Diameter PHP numerical simulation in Microgravity environment
No full textA large diameter PHP is a particular device operating as Thermosyphon on ground and as a PHP in microgravity conditions. In microgravity environment the ratio between buoyancy forces and surface tension forces decrease, allowing to exploit larger diameter tubes with respect to the capillary limit on ground. A slug/plug flow pattern, typical of a PHP device, is therefore observed in microgravity conditions Different kind hybrid Loop Thermosyphon/Pulsating Heat Pipe devices has been already tested in previous experimental campaign (parabolic flights and sounding rocket). It has been noted that as the microgravity occurs a flow pattern transition from a stratified to a slug-plug regime is clearly observed and simultaneously the flow pressure signal exhibits an oscillating trend. It is kept throughout the entire 0-g period. A new hybrid LT/PHP has been tested during the 67th ESA parabolic flight campaign. The device has been tested in vertical position, bottom heated mode, at eight different power levels (18, 36, 52, 68, 96, 134, 146, 180 W) investigating both the thermal performances and the start-up during the microgravity period. A greyscale and SW IR visualizations have been performed during the entire test period joined with pressure and temperature high frequency signals acquisition. This paper shows the thermal and dynamic analysis of the liquid slugs over time along the microgravity period. In particular it has been measured: the meniscus velocities, the liquid slug lengths and the temperature gradient along the liquid slug over time. They have been correlated with the pressure and temperature signals at the evaporator and the condenser. All the data has been compared with the numerical simulations coming from CASCO model
Experimental validation of a Pulsating Heat Pipe transient model during the start-up in micro-gravity environment
Full text linkA large diameter Pulsating Heat Pipe (PHP) is a device operating as a
thermosyphon on ground and as a PHP under microgravity conditions. Such a prototype
with a transparent (sapphire) tube section in the adiabatic region has been tested during
the 67th ESA parabolic fligH campaign. Infrared visualizations of the fluid in the sapphire
section along with measurements of all the relevant quantities, which characterize the
device state (pressures, temperatures), are acquired during the tests and exploited for
the validation of CASCO code. After accurate implementation of the PHP geometry
and material properties, transient simulations have been carried out. A comparison with
the experiment is possible for one case where the initial PHP state. The transients for
tube wall temperatures, slug velocities, slug length and liquid temperatures show a good
agreement with the experiments during the start-up phase in microgravity conditions
reducing the gap towards the development of a fully validated PHP design tool
Reconstructing the anthropogenic aridization of landscapes in antiquity and in the Middle Ages from isotopic data
No full textThe methods from geochemistry of stable isotopes, and spore-pollen and paleopedological data on climate humidification variation have been used to reveal three time intervals: the beginning of the 4th millennium BC, and the 3rd-4th and 8th-14th centuries AD when the indices of local climate changes showed oppositely directed tendencies, which suggests a contribution of the anthropogenic factor (pasture digression) to the modification of vegetation of the landscapes under investigation. © 2009
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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