1,720,979 research outputs found
Characterization of sorption behavior and mass transfer properties of four central africa tropical woods: Ayous, Sapele, Frake, Lotofa
Get PDFThis study provides the sorption isotherm, its hysteresis and their mass transfer properties of four Central Africa Tropical woods widely used for building construction: frake (Terminalia Superba), lotofa (Sterculia Rhinopetala), sapele (Entandrophragma Cylindricum) and ayous (Triplochiton Scleroxylon). Characterization of these four species in particular and Central Africa tropical woods in general were necessary to develop conservation and treatment of wood after first transformation using the drying. Also, moisture transport on wooden material used such as wall buildings can be facilitating to found the thermal comfort. Measurements of isotherms were performed using a dynamic vapor sorption apparatus (Surface Measurement Systems) at 20 and 40°C with air relative humidity ranged from 0% to 90%. Mass diffusivity was determined in steady state using a specific vaporimeter. Air permeability was determined using a specialized device developed to measure over a wide range of permeability values. Permeability and mass transfer properties were determined in the tangential direction with a ‘’false’’ quartersawn board (sapele and lotofa) and in the radial direction with a flatsawn board (ayous and frake). Samples of sapele, ayous and frake are heartwood when lotofa contains as well as heartwood than sapwood. Results obtained showed that the temperature effect on sorption behavior was quite low. We observed also a low difference between the sorption behavior of these different species and hysteresis of sorption decreases when temperature increases. Hailwood-Horrobin model’s explains plausibly the experimental sorption isotherms data. Results on characterization of mass transfer properties showed that, in the steady state, mass diffusivity decreases exponentially when basal density increases. Mass diffusivity was higher in desorption than in adsorption phase. The gaseous permeability of these species was between than those of Australian hardwoods and temperate woods. It was difficult to define a relationship between permeability and mass diffusivity
Sorption behavior of four tropical woods using a dynamic vapor sorption standard analysis system
Get PDFSorption behavior of four tropical woods coming from Cameroon is studied using a Dynamic Vapor Sorption-Intrinsic apparatus. Sorption isotherms at 20°C and 40°C of Triplochiton scleroxylon (obeche), Entandrophragma cylindricum (sapele), Sterculia rhinopetala (lotofa) and Terminalia superba (frake also called limba) are compared to those in the literature with methods using saturated salts for lotofa and frake with satisfactory results. Experimental values are fitted using two sorption isotherm models. Sorption hysteresis is greatest in sapele and least in frake. When temperature increases, differences in the hysteresis of sorption among the woods decreases. Hystereses of all studied woods ranged from 0,5 to 3%. Our studied woods have lower equilibrium moisture content probably caused by the higher values of extractives content. The water sorbed molecules on multilayer during both adsorption and desorption at 20°C and 40°C is greater in the case of frake and lower in the case of lotofa. The water sorbed molecules on multilayer of sapele is greater than those of obeche. The predominance of multilayer over monolayer of our woods is from 0,2 to 0,4 relative humidity in adsorption phase, and from 0,3 to 0,4 relative humidity in desorption phase
Modeling and simulation of an industrial indirect solar dryer for Iroko wood ("Chlorophora excelsa") in a tropical environment
Get PDFThis paper presents a modeling of an instrumental indirect solar wood dryer less expensive functioning in a Cameroonian climate applied to the climate of Yaoundé. The dryer is easy to build and electric energy is only used for the fan. Applications are done on Iroko wood (Chlorophora excelsa), a tropical wood 50mm thick most utilized in Africa. A satisfactory agreement between experimental and numerical results was found. Influences of thickness, wood initial water content and airflow rate were studied
Study on the effect of conical and parabolic solar concentrator designs on hybrid solar dryers for apricots under variable conditions: A numerical simulation approach
No full textInternational audienc
Modeling and simulation of the drying of beech timber (Fagus Sylvatica) using oscillating regimes
No full textInternational audienceThis paper represents a numerical study of the massive (60mm) and thin (38mm) wood drying using oscillating drying regimes applied on beech timber (Fagus sylvatica). All thermo-physical properties relative of studied wood are taken from the literature on appropriate experiments. We showed that Luikov's model can be used to predict temperature and moisture content evolutions using oscillating regimes. First numerically tests on 60mm timber wood consists in increasing and decreasing alternation of the drying parameters (temperature), at the rising 12-15°C and at the descent 10-12°C, every alternation being higher than the precedent with 2-4°C. Second numerical test consists to oscillate the values of equilibrium moisture content with the oscillation amplitudes of ±10% and ±20% at the frequencies of 6hours. These practical experiments are detailed in the literature. Luikov's model gives satisfactory results, according to the experiments obtained in the literature. But, convective transfer coefficients are function of each experiment and we observed a short difference between oscillation amplitudes of ±10% and ±20% on moisture content evolution. Thus, Luikov's model can be a tool to study oscillation drying timber in order to reduce consumption of energy during the drying process
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
- …
