Une épistémologie pour la didactique : spéculations autour d’un aménagement conceptuel

La théorie didactique souffre des difficultés qu'elle éprouve à s'intégrer le constructivisme. On essaie ici une explication: le constructivisme est asymétrique. Alors qu'il a réussi à éliminer le recours à l'objet extérieur, il continue à attribuer la connaissance au « sujet en soi ». On esquisse ici une conversion épistémologique qui préparerait l'acceptation de paradigmes constructivistes par la didactique. Enfin, quelques exemples illustrent la voie par laquelle l'épistémologie didactique peut structurer la recherche pratique et théorique.It has been difficult to integrate constructivism within the paradigms of didactic theory. In this paper, the author attempts to explain this situation: constructivism is asymetrical. Although constructivism eliminated recourse to an external object, it has continued to recognize "the subject in itself". This article suggests an epistemologic change that would allow constructivist paradigms within didactic theory. In conclusion, the author presents some examples which illustrate how "didactic epistemology" can structure practical and theoretical research.La teoria didactica sufre de las dificultades encontradas para integrarse al constructivismo. Se prueba aca una explicacion: el constructivismo es asimétrico: cuando ha logrado eliminar el recurso del objeto exterior, continua a atribuir el conocimiento al "sujeto en si". Este articulo esboza una conversion epistemologica que prepararia la aceptacion de paradigmas constructivistas a través de la didactica. Enfin, algunos ejemplos ilustran la via por la cual la "epistemologia didactica" puede estructurar la investigacion practica y teorica.Die didaktische Théorie leidet an den Schwierigkeiten, die sie bei der Integration des Konstruktivismus hat. Hier wird eine Erklârung versucht: der Konstruktivismus ist asymmetrisch; wâhrend er die Zuhilfenahme des àusseren Bezugsobjektes uberwunden hat, schreibt er weiterhin die Erkenntnis dem "Subjekt an sich" zu. Dieser Artikel skizziert eine epistemologische Konversion, die zur Annahme konstruktivistischer Paradigmen durch die Didaktik fiihren kônnte. Endlich illustrieren einige Beispiele die Art und Weise, wie die "didaktische Epistëmologie" die praktische und theoretische Forschung strukturieren kann

Improving the acquisition of spatial knowledge when navigating with an augmented reality navigation system

Navigation is a process humans use whenever they move. There are more complex tasks like finding our way in a new city and easier tasks like getting a cup of coffee. Daniel Montello (2005, p. 2) defines navigation as “the coordinated and goal-directed movement through the environment by organisms or intelligent machines”. When navigating in an unknown environment, humans often rely on assisted wayfinding by some sort of navigation aid. During the last years, the preferred navigation system shifted from printed maps to electronic and thus dynamic navigation systems on our smartphones. Recently, mixed reality and virtual reality approaches such as augmented reality (AR) have become an interesting alternative to the classical smartphone navigation. This although, the first attempts to AR were already made in the middle of the last century. The major advantages of AR navigation systems are that localisation and above all also tracking tasks are made by the system and that the navigation instructions are directly laid into the environment. The main drawback, on the other hand, is that the more tasks are made by the system, the less spatial learning is achieved by a human. The goal of this thesis is to examine ways to improve the process of spatial learning on assisted wayfinding. An experiment where participants are guided through a test environment by an AR system is set up to test these ways. After completing the route, the participants had to fill out a questionnaire about landmarks and intersections, which they had encountered on the route. The concrete goals of the thesis are to find out (1) whether giving more spatial information will improve spatial learning, (2) whether the placement of navigation instructions has an influence (positive or negative) on spatial learning, (3) whether the type of landmark has an influence on how well it is recalled and (4) how well landmark and route knowledge is built after having completed the route once. The results of the experiment suggest that giving background information to certain landmarks do not lead to a significantly different performance in spatial learning (p = .691). The result could also show that there is no difference whether a landmark is highlighted by a navigation instruction or not (p = .330). The analyses of landmark and route knowledge has shown that the participants have built less landmark knowledge than route knowledge after the run, as they have approx. 50 % of the landmarks correct but 67 % of the intersections. Interesting and in this case significant is the difference between the types of landmarks (p = .018). 3D objects are recalled much better than other landmarks. Also significant (p = 6.14e-3) but unfortunately not very robust is the influence of the age on the acquisition of route knowledge. As the age distribution is very unbalanced, these results have to be interpreted with caution. Following the findings of this thesis, it is suggested to conduct a series of experiments with an eye tracker to learn more about how the visual focus of people using AR as a wayfinding assistance behaves

Broken rotation symmetry in the fractional quantum Hall system

We demonstrate that the two-dimensonal electron system in a strong perpendicular magnetic field has stable states which break rotational but not translational symmetry. The Laughlin fluid becomes unstable to these states in quantum wells whose thickness exceeds a critical value which depends on the electron density. The order parameter at 1/3 reduced density resembles that of a nematic liquid crystal, in that a residual two-fold rotation axis is present in the low symmetry phase. At filling factors 1/5 and 1/7, there are states with four- and six-fold axes, as well. We discuss the experimental detection of these phases.Comment: 8 pages, LaTex 3.1, figures attache

Self-assembled monolayers beyond thiols : dithiocarbamates - from pure layers to ternary assembly systems

Since microelectronics started to play its dominant role in the innovation of technologic and electronic instruments the reduction of the size of transistors and other functional devices was in the main focus of research and development. Therefore molecular nanotechnology and molecular electronics attracted a great deal of attention in the last years. The understanding of the fundamentals of electron transport through molecules is essential for the development and exploration of possible electronic components. Many different approaches have been introduced so far to characterise metal-molecule-metal junctions. The most reliable measurements on single molecular junctions were done on break junctions, metal gaps, which have been produced by the combination of metal microfabrication and metal electromigration as well as on the Scanning Tunneling Microscope. The molecules under investigation were almost exclusively thiol functionalised. A detailed understanding of a molecule and how it affects the transport properties of a metallic nano-gap must include the exact gap structure, the molecular backbone and the interfacial structure of the chemical/physical linker of the molecule to the metal contacts. The aim of this work was to investigate the electron transport abilities of molecules – containing dithiocarbamate (DTC) as the linker group – on the single molecular level. Therefore the chemisorption process was investigated for different aromatic and non aromatic thiol and DTC compounds by Scanning Tunneling Microscopy, X-Ray Photoelectron Spectroscopy (XPS) and Cyclic Voltammetry (CV). The obtained results were published under the title: Dithiocarbamates: Functional and Versatile Linkers for the Formation of Self-Assembled Monolayers. The most important findings presented in that publication were that the dithiocarbamates as sodium salts and also the oxidized form of dithiocarbamates the thiurams are chemisorbing in a bidentate structure on Au(111). The thiurams are decomposing at the disulfide bridge as the sodium dithiocarbamate releases the cation. Reductive desorption experiments were accomplished in a home built electrochemical set-up, which allowed for the investigation of the same samples, investigated by XPS and STM before. Comparing all these data quantitatively it was shown that the reductive desorption is a one electron transfer process. A second publication was written on the novel and very interesting surface structure of diethyldithiocarbamate: Supramolecular surface assembly of dithiocarbamates on Au(111): Chiral trimeric domains and amorphous structures. Here we report on a first time observation that chemisorbing molecules are forming trimeric complexes, which are hexagonally packed. This is the first experimental evidence of a chemisorbing supramolecular surface assembly. The next experiments were designed in order to produce STM accessible molecular surface structures i.e. islands of one molecular species placed within a matrix of another thiol compound. Therefore we investigated the formation of mixed monolayers at the solid liquid interface of a non-polar and a polar thiol species. These results will be published as: Co-assembly – concentration and mixing dependent structures: Mechanisms of molecular 2D ordering investigated by NEXAFS and STM. The most important result from this work is a detailed model, which can explain all the observed effects as there are ostwald ripening of vacancy islands, the existence of a minimal stable island size of the low dosed species and the diffusion limits of thiol adsorption. The formation of ternary assemblies comprising dithiocarbamate and thiol linked molecules within an alkanethiols self-assembled monolayer matrix made the first comparative dithiocarbamate/thiol STM study possible. A gel-assisted assembly technique enabled us to produce molecular gradient-assemblies. The combination of NEXAFS and STM lead to the identification of the molecules bound to the surface. Finally the STM data analysis lead to the first experimental evidence on the single molecular level, that dithiocarbamate is a more conductive linker than a thiolate linker. The results of these investigations were submitted under the title: Gelassisted host/guest assembly of dithiocarbamates and thiols: Analysis of local orientation and conductivity within ternary assemblies