Richard Gagnon

Use of the inverse synthesis method for the determination of the optical constants of paper in the far infrared

Optical thin film methods were used to determine the refractive index and absorption coefficient of paper at 70.5,96.5, and 118.8 μm. Transmittances and reflectances were measured of paper, two quartz and two TPX plates, as well as of the paper pressed between the quartz and TPX plates. Measurements were performed at angles of incidence between 0 and 50°. The optical constants found provided a reasonable fit between the experimental points and the calculated performance. The small residual departures between the two sets of data are probably due to inhomogeneities within the paper.

Reperer des conceptions en classe: Mythe ou realite

RésuméDans cet article, l’utilisation de réseaux conceptuels pour repérer les conceptions d’élèves se rapportantà des phénomènes thermiques est explorée. Des informations sur ces conceptions, obtenues par le biais de 16 entrevues semi-structurées individuelles, sont rapprochées d’une approximation de la structure cognitive des élèves, obtenue par le biais d’une épreuve de rendementà correction critériée traditionnelle, analysée et pondéréeà la lumière d’une structure conceptuelle de référence des phénomènes thermiques. Cette seconde méthode est appelée ≪méthode des réseaux conceptuels pondérés≫ (RCP). Un degré de concordance significatif entre la méthode des entrevues semi-structurées et la méthode RCP résulte de ce rapprochement, laissant entrevoir pour les enseignantes et les enseignants la possibilité de repérer plus facilement qu’au moyen d’entrevues les conceptions de leurs élèves, dans la pratique ordinaire de leur enseignement.Executive summaryThe research reported in this article was aimed, ultimately, at (1) verifying whether students’ conceptions of particular scientific or technical subjects could be uncovered and interpreted by means that are less burdensome and more practical than interview techniques; and (2) determining to what extent such means can be successfully used by teachers in an ordinary classroom situation. It was from this perspective that the method of ‘réseaux conceptuels pondérés (RCP)‘—or weighted conceptual networks (WCNs)—was developed.In a previous article (Gagnon & Ettayebi, 1998), the authors showed how a traditional performance test and accompanying criterion-referenced marking scheme could be analysed using a reference conceptual structure from the field under study so as to inform teachers of their students’ conceptions on that subject. In the same article, the authors described how this analysis is conducted and how these test results can be used to obtain what they have termed the effective cognitive structure of each student with respect to this field of knowledge—that is, a practical approximation of a student’s cognitive structure, which is made up of concepts and principles that are interrelated to varying degrees.In the present article, the authors compare the effective cognitive structures of eight students in relation to thermal phenomena with a series of conceptual elements evidenced during 16 semi-structured interviews. A high degree of agreement (84.9%) between the two categories of information was achieved by comparing students’ interview statements with the degree of interrelatedness of the respective effective conceptual structures and by assessing the compatibility of these statements. The authors conclude that in the cases studied, the WCN method generates information concerning individuals’ conceptions on the subject of thermal phenomena that significantly agrees with information gathered using the interview methods, despite occasional disagreement and undecidability.The WCN method proved to be practical within the framework of this experiment, and it is very unlikely that this aspect of the approach poses any problems, generally speaking. Firstly, students remained totally unaware of the process, as, in their view, they were taking a traditional performance test Secondly, teachers administered what, in their view, represented a traditional test and made corrections according to their usual practice.The results of the research described here seem to suggest that a traditional criterion-referenced performance test can, effectively, provide rich and relevant indications concerning students’ conceptions of scientific and technical subjects if, from the outset, the questions making up this test are carefully analysed with respect to an appropriate reference conceptual structure, and provided that the test questions have been developed with discernment. Simple numerical conversion of the grades received by students on this test, combined with the prudent interpretation of results, will enable interested teachers to viably identify their students* conceptions, partially profile students’ strengths and weaknesses, and foster a classroom experience that is better suited to specific learning needs. However, in order to demonstrate the generality of these results, this experiment must be extended to other fields of study, other students, and other teachers.

Comparison between two genetic algorithms minimizing carbon footprint of energy and materials in a residential building

The emergence of building performance optimization is recognized as a way to achieve sustainable building designs. In this paper, the problem consists in minimizing simultaneously the emissions of greenhouse gases (GHG) related to building energy consumption and those related to building materials. This multi-objective optimization problem involves variables with different hierarchical levels, i.e. variables that can become obsolete depending on the value of the other variables. To solve it, NSGA-II is compared with an algorithm designed specifically to deal with hierarchical variables, namely sNSGA. Evaluation metrics such as convergence, diversity and hypervolume show that both algorithms handle hierarchical variables, but the analysis of the Pareto front confirms that in the present case, NSGA-II is better to identify optimal solutions than sNSGA. All the optimal solutions are made of buildings with wooden envelopes and relied either on heat pumps or on electrical heaters for proving heating.

Optical Polarizing Effect Of Paper At Submillimetre Wavelengths

The use of submillimetre (SMM) waves for non destructive testing of paper has already been demonstrated. This report presents the basic results wich led to the use of SMM waves to monitor the fibre orientation anisotropy in paper. The measurement of moisture content and basis weight is also covered. An experiment to test the effect of moisture content on the polarizing properties of paper is presented. Measures were made for three wavelengths (70, 96 and 118 microns) and for moisture content covering the region 0 to 40 %. The effect of bound water to cellulose surface will be introduced to explain the results.

Far-Infrared Dielectric Properties Of Adsorbed Water In A Cellulose-Air Matrix

A standard three components mixture model for the dielectric constant is compared to the measured transmittance and reflectance of FIR radiation through a wet cellulose matrix. This model reproduces, at least qualitatively, the peculiar behaviour of the reflectance versus water content curve. However, the absorption coefficient for water content above 5% can only be reproduced if we postulate that the water adsorbed between 5% and 10% in volume possesses an anomalously high absorption coefficient. This is interpreted in terms of the flickering clusters model for water and the structure breaking role of the cellulose surface.