Electronic properties of the pseudogap system (TaSe4)2I

The room temperature ``metallic'' properties of the quasi-one-dimensional charge density wave system (TaSe4)2I differ markedly from those expected of either a Fermi or a Luttinger Liquid. We discuss evidence for the simplest possible explanation of the observed behavior of (TaSe4)2I in its conducting phase - namely the existence of large quasi-static fluctuations of structural order, which however remain of finite extent above the charge density wave transition temperature. These fluctuations produce a pseudogap in the density of states. We compute the temperature dependence of the optical and DC conductivities of (TaSe4)2I in its conducting phase, the nature of its core hole spectra, and the NMR relaxation rate. Predictions for these quantities are made on the basis of a Lee, Rice and Anderson model. This model represents the simplest theory of a pseudogap, and gives satisfactory agreement with experiment in the cases where comparisons can be made. In contrast, the predictions of a strongly correlated (Luttinger Liquid) model appear to to contradict the data. The chief remaining discrepancy is that the gap appearing in transport quantities is less than that observed in photoemission. We discuss some possibilities for resolving this issue.Comment: 41 pages latex, 11 ps figures, uses IOP macro

Can Learning about History of Science and Nature of Science in a Student-Centred Classroom Change Science Students’ Conception of Science?

Nature of Science (NOS) covers the aim, development, criticism and explanation of science. This study examines the impact that studying philosophy and history of science has on undergraduate students’ views about the NOS. Studying the NOS helps students to understand what science is, how to characterize the nature of its practitioners’ activities, and what is the significance of the whole enterprise. It is shown that having students study scientific concepts through the eyes of philosophers and historical scientists, actively engages them in the process of inquiry and challenges them to increase their understanding of the NOS. This study showed that studying philosophy and history of science in a student-centered classroom had a strong influence on students’ views about the NOS in that many students changed their views about the NOS. Students who did not change their over-all perception gave much clearer expositions of their views

The Community of Philosophical Inquiry as a place of agon: Exploring children’s experiences of competitiveness in philosophical dialogue

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Navigating disagreement in democratic education: The potential of the Community of Philosophical Inquiry

Democracy is premised on disagreement, yet polarisation, passion and populism are everywhere on the rise. In this troubled political context, democratic educators face the daunting challenge of educating young people to navigate disagreement. The theory that provides the framework for this thesis—agonism—understands political disagreement as ineradicable, inherently passionate and enmeshed in relations of power, and it offers an innovative approach to democratic education with the potential to reduce polarisation and promote political renewal. However, the agonistic approach lacks clear pedagogical methods and empirical research investigating how young people engage with, and experience, agonistic democratic education. This thesis seeks to address these gaps by developing a novel educational framework and by offering the Community of Philosophical Inquiry (CPI)—the dialogical method at the heart of the Philosophy for Children (P4C) programme—as a promising pedagogy to advance the objectives of agonistic democratic education. Yet the CPI faces two sets of challenges: the dangers of mentalisation, harmony and apoliticism jeopardise its agonistic potential, while the dangers of distress and antagonism cast doubt on the suitability of the CPI and existing agonistic pedagogies for young people living in a volatile political context. To explore the CPI’s agonistic potential, a qualitative case-study was conducted with 76 young people (aged 8-17) involved in CPI dialogues in formal and informal educational settings, in Canada and New Zealand. This exploratory study combined interviews, video observation and body mapping to investigate how participants navigated disagreements and addressed political issues in CPI dialogues, and how they emotionally experienced these exchanges. In most cases, participants managed to sustain disagreement, in part by toggling between amicable and heated disagreement dynamics through moves that defused or stoked the emotional atmosphere of the dialogue. However, the amicable and heated dynamics each had an associated drift—the avoidant and the antagonistic drifts—which threatened to derail disagreement. In CPI dialogues, young people examined the abstract and concrete aspects of multiple political issues, envisioned society as it ought to be and reported feeling powerful political emotions. Yet the primarily philosophical way in which they approached political issues did not emphasise relations of power or political action. Lastly, while most participants enjoyed CPI dialogues, a few had strong negative experiences. Overall, these findings suggest that the CPI can only partially advance the objectives of agonistic democratic education, revealing the need to historicise, politicise and supplement the CPI with other pedagogies to empower young people to navigate disagreement and take political action. This study also underscores the importance of careful facilitation to support inclusive and productive dialogues, particularly when discussing complex political issues. Finally, it highlights the pedagogical and theoretical importance of recognising the entanglement of the emotional, epistemic and social aspects of dialogue.</p

Dégradation des monocristaux de polyéthylène en microscopie électronique entre 1 et 2,5 MV. I. Etude à température ambiante

The critical dose of electrons that destroys the crystallinity of polyethylene single crystals was measured for accelerating voltages between 1 and 2.5 MV. In this range, the critical dose remains nearly constant and is 3 times higher than at 100 kV. These results are fitted by a Bethe law corrected to take channelling into account. As a consequence, a critical energy of about 490 eV/nm3 is found. The channelling is more pronounced at lower voltages, at thicknesses of 20 nm and for particular orientations.On a pu mesurer la dose critique d'électrons qui détruit la cristallinité des monocristaux de polyéthylène, pour des tensions d'accélération entre 1 et 2,5 MV. Dans cette gamme d'énergie, la dose critique reste sensiblement constante et 3 fois plus grande qu'à 100 kV. On peut rendre compte de cette loi en calculant le pouvoir d'arrêt des électrons par la formule de Bethe corrigée pour tenir compte de la canalisation. On obtient alors une énergie critique de 490 eV/nm3 environ. La canalisation est plus importante pour les basses tensions, pour des épaisseurs moyennes (20 nm), et pour certaines orientations

Electron microscopy observations of the incommensurate phase in berlinite and quartz : interference contrast in the c-zone axis conditions

The triply modulated incommensurate phase of berlinite and quartz is imaged by electron microscopy in c-zone axis orientation conditions. The systematic study of the images and of the incommensurate diffraction satellites shows that the apparently triangular dark/light contrast pattern obtained with the transmitted beam or a general hk0-reflection and the surrounding satellites can be explained by an interference contrast model similar to that for usual high resolution lattice imaging. This interference image is consistent with the phase relation of the triple incommensurate modulation conjectured by the minimisation of the free energy, according to the existing theoretical work.La phase incommensurable triplement modulée de la berlinite et du quartz est imagée par microscopie électronique dans l'orientation correspondant à l'axe de zone c. Une étude systématique des images et des taches de diffraction satellites révèle que les contrastes en forme de triangles sombres et clairs obtenus avec le faisceau transmis ou une réflexion hk0 et les satellites qui l'entourent, peuvent être expliqués par un modèle de contraste d'interférences analogue à celui des images des plans réticulaires à haute résolution. Cette image d'interférence est en accord avec la relation de phase de la triple modulation incommensurable obtenue par minimisation de l'énergie libre selon les travaux théoriques existants