The main purpose of this study was to compare the effectiveness of the cooperative learning based on conceptual change conditions and traditionally designed science instruction on 7th grade students&rsquo / understanding of chemical and physical changes and classification of matter concepts and attitudes toward science as a school subject. In this study 102 seventh grade students from four classes of a Science Course instructed by the two teachers from ODT&Uuml / G.V. &Ouml / zel ilk&ouml / gretim Okulu took part. One of the classes of each teacher was randomly assigned as experimental group, which were instructed with cooperative learning based on conceptual change conditions and the other classes were assigned as control group, which were instructed traditionally. This study was conducted during the 2004-2005 fall semester over a period of four weeks. In this study, to examine the effect of the treatment on dependent variables / science achievement related to chemical and physical changes and classification of matter concepts measured with Classification and Changes of Matter Concepts Test, and science attitude scores measured with Attitude Scale Toward Science as a school subject. Science Process Skills Test was used at the beginning of the study to determine students&rsquo / science process skills. ANCOVA and ANOVA were used testing the hypotheses of the study. The results showed that the cooperative learning based on conceptual change conditions group had a significantly higher scores with respect to achievement related to chemical and physical changes and classification of matter concepts than the traditionally designed science instruction group. However, there is no significant difference between the mean scores of cooperative learning based on conceptual change conditions group and traditionally designed science instruction group with respect to attitudes toward science as a school subject. Science process skills were a strong predictor for the achievement related to chemical and physical changes and classification of matter concepts. It may be useful to use the results of this study and instruments and strategies developed for this study for classroom teachers in order to help students to reduce or eliminate their misconceptions.

Le traitement thermique est basé sur la modification chimique des biopolymères par thermodégradation, en évitant l'ajout de produits chimiques. Ce traitement améliore la stabilité dimensionnelle et la durabilité fongique du bois. Ces améliorations se font au détriment des propriétés mécaniques qui ont tendance à s'affaiblir. Aujourd'hui, plusieurs types de procédés sont utilisés. Ils se distinguent entre autre par la nature du milieu dans lequelle se déroule le traitement. La durabilité de ce nouveau matériau bois est liée au degré de thermodégradation, dépendant des conditions et de l'intensité du traitement. Un pilote de traitement par conduction, travaillant sous vide ou sous azote, mesurant la masse en dynamique est utilisé afin de mieux comprendre l'influence de l'atmosphère. Les résultats obtenus montrent que l'utilisation du vide permet d'éliminer, de l'enceinte de traitement, les produits volatils formées au cours du traitement conduisant à des taux de lignine de Klason plus faibles du fait de la non recondensation des produits de dégradation. Cette limitation de recondensation des produits volatiles engendre des pertes de masse, pour une même intensité de traitement plus faibles, confirmés par des taux de polysaccharides plus élevés pour un traitement sous vide. Des études de cinétiques des réactions de thermodégradation ont confirmé la plus grande sensibilité des feuillus vis-à-vis de la thermodégradation (comparé aux résineux). De plus, ces analyses ont permis d'identifier les principaux produits de thermodégradation du bois qui varient en fonction de l'intensité du traitement et a permis de montrer une thermosensibilité plus importante de la lignine que de l'holocelluloses pour la gamme de températures utilisée. Le fruit de ces travaux est donc une progression significative des connaissances de bases sur les mécanismes de thermodégradation et leurs relations avec les paramètres de traitement / Thermal treatment is based on biopolymer chemical degradation by heat transfer, without additional chemical products impregnation. This process improves the dimensional stability and the decay resistance of wood. These improvements come at the expense of wood mechanical properties of wood which weak. Several types of heating processes exist currently differing mainly by the nature of the inert atmosphere used during treatment. The durability of this new wood material is correlated to the degree of polymers thermal degradation depending on the conditions and the treatment intensity. A conducting heat treatment pilot using nitrogen or vacuum and allowing dynamic record of mass loss is used to understand better the atmosphere influence. The results show that utilization of vacuum permit the elimination of volatile products formed during heat treatment and accumulated in oven, leading to lower extractives and Klason lignin contents due to the non recondensation of thermal degradation products. Limitation of the formation of recondensation products generates a lower mass loss for same treatment intensity and explains the lower polysaccharides degradation during a vacuum process. Fine chemical analyses and the study about thermal degradation reaction kinetics have allowed confirming the higher sensibility of hardwood than softwood to thermal degradation. In addition, these analyses have permitted the volatile thermal degradation products identification related to the treatment intensity. Subsequently, results have shown a higher thermal sensibility of lignin than holocelluloses for temperatures below 230°C. This work is a significant increase in basic knowledge about the mechanisms of wood thermal degradation and their relations with the processing parameters