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

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

Transition from quantum Hall to compressible states in the second Landau level: new light on the ν\nu=5/2 enigma

Quantum Hall states at filling fraction $\nu$=5/2 are examined by numerical diagonalization. Spin-polarized and -unpolarized states of systems with $N\le 18$ electrons are studied, neglecting effects of Landau level mixing. We find that the ground state is spin polarized. It is incompressible and has a large overlap with paired states like the Pfaffian. For a given sample, the energy gap is about 11 times smaller than at $\nu$=1/3. Evidence is presented of phase transitions to compressible states, driven by the interaction strength at short distance. A reinterpretation of experiments is suggested.Comment: This paper has already appeared in PRL, but has not been on the we