Optical conductivity of colossal magnetorestistance compounds: Role of orbital degeneracy in the ferromagnetic phase

Recent optical conductivity $\sigma(\omega)$ experiments have revealed an anomalous spectral distribution in the ferromagnetic phase of the perovskite system $La_{1-x}Sr_xMnO_3$. Using finite temperature diagonalization techniques we investigate $\sigma(\omega)$ for a model that contains only the $e_g$-orbital degrees of freedom. Due to strong correlations the orbital model appears as a generalized t-J model with anisotopic interactions and 3-site hopping. In the orbital t-J model $\sigma(\omega)$ is characterized by a broad incoherent spectrum with increasing intensity as temperature is lowered, and a Drude peak with small weight, consistent with experiment. Our calculations for two-dimensional systems, which may have some particular relevance for the double-layer manganites, show that the scattering from orbital fluctuations can explain the order of magnitude of the incoherent part of $\sigma(\omega)$ in the low temperature ferromagnetic phase. Moreover orbital correlation functions are studied and it is shown that $x^2$-$y^2$ orbital order is prefered in the doped planar model at low temperature.Comment: Revtex, 14 pages, 14 figure

Spectroscopic observations of comet Austin (1989c)

Longslit CCD spectra (lambda = 5100-6400 A, delta(lambda) approximately 3 A) were obtained with the Michigan-Dartmouth-MIT 1.3 meter telescope in May 1990 (r = 0.74 AU, delta = 0.50 AU). The spectra were reduced with the Interactive data Reduction and Analysis Facility (IRAF). Spectral extractions offset sunward and tailward from the nucleus were analyzed. Species identified in the spectra include the following: C2, NH2(10-0), NH2(9-0), H2O(+), and CO(+). Spatial extractions of rotational line intensities in the NH2(10-0) band extend approximately 10(exp 4.5) km from the nucleus. A fit of the vectorial model to the NH2(10-0) spatial profile is consistent with an NH3 parent molecule. The NH2 production rate and an ammonia to water abundance ratio, NH3/H2O approximately 3 percent, were derived. The ammonia abundance obtained for comet Austin is consistent with that found for several other comets and is indicative of comet formation under very homogeneous conditions

Montaigne on reading

Montaigne’s wide and critical reading contributed enormously to his writing. that we know more about Montaigne’s reading than any other Renaissance author. This chapter begins by discussing the books Montaigne read and the comments he made on his reading. It argues that we should take seriously his advice to read in order to become wise, by discovering one’s own views, rather than to become learned, by summarizing the views of others. It describes Montaigne’s method of writing in reaction to his reading (especially the re-reading of his own text) by building fragments, such as axioms, proverbs, narratives and comparisons into logical sequences, using seven basic types of logical connection and the ways in which Montaigne uses quotations taken from history and poetry in the Essays, concluding with a discussion of the use of quotations in “Of vanity” (III, 9)

Reading and Rhetoric in Montaigne and Shakespeare

This book is available as open access through the Bloomsbury Open Access programme and is available on www.bloomsburycollections.com. Shakespare and Montaigne are the English and French writers of the sixteenth century who have the most to say to modern readers. Shakespeare certainly drew on Montaigne's essay 'On Cannibals' in writing The Tempest and debates have raged amongst scholars about the playwright's obligations to Montaigne in passages from earlier plays including Hamlet, King Lear and Measure for Measure. Peter Mack argues that rather than continuing the undeterminable quarrel about how early in his career Shakespeare came to Montaigne, we should focus on the similar techniques they apply to shared sources. Grammar school education in the sixteenth century placed a special emphasis on reading classical texts in order to reuse both the ideas and the rhetoric. This book examines the ways in which Montaigne and Shakespeare used their reading and argued with it to create something new. It is the most sustained account available of the similarities and differences between these two great writers, casting light on their ethical and philosophical views and on how these were conveyed to their audience

Peter Mack Letters

Letters addressed to O.M. Tenny, Chester N.H. on Aug. 3 and Dec. 26, 1906. Written on purchase order with header Peter Mack, Prepared Palm Plants

Reading and Rhetoric in Montaigne and Shakespeare

This book is available as open access through the Bloomsbury Open Access programme and is available on www.bloomsburycollections.com. Shakespare and Montaigne are the English and French writers of the sixteenth century who have the most to say to modern readers. Shakespeare certainly drew on Montaigne's essay 'On Cannibals' in writing The Tempest and debates have raged amongst scholars about the playwright's obligations to Montaigne in passages from earlier plays including Hamlet, King Lear and Measure for Measure. Peter Mack argues that rather than continuing the undeterminable quarrel about how early in his career Shakespeare came to Montaigne, we should focus on the similar techniques they apply to shared sources. Grammar school education in the sixteenth century placed a special emphasis on reading classical texts in order to reuse both the ideas and the rhetoric. This book examines the ways in which Montaigne and Shakespeare used their reading and argued with it to create something new. It is the most sustained account available of the similarities and differences between these two great writers, casting light on their ethical and philosophical views and on how these were conveyed to their audience

Global stability of swept flow around a parabolic body: Features of the global spectrum

International audienceThe global temporal stability of three-dimensional compressible flow about a yawed parabolic body of infinite span is investigated using an iterative eigenvalue technique in combination with direct numerical simulations. The computed global spectrum provides a comprehensive picture of the temporal perturbation dynamics of the flow, and a wide and rich variety of modes has been uncovered for the investigated parameter choices: stable and unstable boundary-layer modes, different types of stable and unstable acoustic modes, and stable wavepacket modes have been found. A parameter study varying the spanwise perturbation wavenumber and the sweep Reynolds number reproduced a preferred spanwise length scale and a critical Reynolds number for a boundary-layer or acoustic instability. Convex leading-edge curvature has been found to have a strongly stabilizing effect on boundary-layer modes but only a weakly stabilizing effect on acoustic modes. Furthermore, for certain parameter choices, the acoustic modes have been found to dominate the boundary-layer modes. © 2011 Cambridge University Press

Global stability of swept flow around a parabolic body: The neutral curve

International audienceThe onset of transition in the leading-edge region of a swept blunt body depends crucially on the stability characteristics of the flow. Modelling this flow configuration by swept compressible flow around a parabolic body, a global approach is taken to extract pertinent stability information via a DNS-based iterative eigenvalue solver. Global modes combining features from boundary-layer and acoustic instabilities are presented. A parameter study, varying the spanwise disturbance wavenumber and the sweep Reynolds number, showed the existence of unstable boundary-layer and acoustic modes. The corresponding neutral curve displays two overlapping regions of exponential growth and two critical Reynolds numbers, one for boundary-layer instabilities and one for acoustic instabilities. The employed global approach establishes a first neutral curve, delineating stable from unstable parameter configurations, for the complex flow about a swept parabolic body with corresponding implications for swept leading-edge flow. © 2011 Cambridge University Press