The General Primordial Cosmic Perturbation

We consider the most general primordial cosmological perturbation in a universe filled with photons, baryons, neutrinos, and a hypothetical cold dark matter (CDM) component within the framework of linearized perturbation theory. We give a careful discussion of the different allowed modes, distinguishing modes which are regular at early times, singular at early times, or pure gauge. As well as the familiar growing and decaying adiabatic modes and the baryonic and CDM isocurvature modes we identify two {\it neutrino isocurvature} modes which do not seem to have been discussed before. In the first, the ratio of neutrinos to photons varies spatially but the net density perturbation vanishes. In the second the photon-baryon plasma and the neutrino fluid have a spatially varying relative bulk velocity, balanced so that the net momentum density vanishes. Possible mechanisms which could generate the two neutrino isocurvature modes are discussed. If one allows the most general regular primordial perturbation, all quadratic correlators of observables such as the microwave background anisotropy and matter perturbations are completely determined by a $5\times 5,$ real, symmetric matrix-valued function of co-moving wavenumber. In a companion paper we examine prospects for detecting or constraining the amplitudes of the most general allowed regular perturbations using present and future CMB data.Comment: 18 pages, 2 Postscript figures, uses revtex. Revised 2-2000 Minor errors corrected and some references adde

Constraining Isocurvature Perturbations with CMB Polarization

The role of cosmic microwave background (CMB) polarisation data in constraining the presence of primordial isocurvature modes is examined. While the MAP satellite mission will be unable to simultaneously constrain isocurvature modes and cosmological parameters, the PLANCK mission will be able to set strong limits on the presence of isocurvature modes if it makes a precise measurement of the CMB polarisation sky. We find that if we allow for the possible presence of isocurvature modes, the recently obtained BOOMERANG measurement of the curvature of the universe fails. However, a comparably sensitive polarisation measurement on the same angular scales will permit a determination of the curvature of the universe without the prior assumption of adiabaticity.Comment: 4pages, Latex with four eps figures. (Revised 18 Dec 2000. Minor typos corrected

Mechanism of Mineral Reactions Inferred from Textures of Impure Dolomitic Marbles from East Greenland

Mineral assemblages and chemical compositions of minerals found in impure dolomitic marbles embedded in gneisses and migmatites of the E. Greenland Caledonian fold belt (Scoresby Sund) suggest that the marbles were metamorphosed near 630 °C at 5 kb pressure. The analysis of complex textural and mineralogical relations among minerals such as dolomite, calcite, forsterite, pargasite, chlorite, spinel, diopside and phlogopite led to the conclusion that the major mineralogical features of the rocks were probably caused by sodium metasomatism at constant temperature and pressure. The effect of the inferred sodium metasomatism may be summarized by three schematic reactions all involving modal changes of excess dolomite, calcite, forsterite, chlorite and spinel: (a) nucleation and growth of pargasite, (b) resorption of phlogopite, and (c) growth of pargasite from phlogopit

Reaction Textures and Metamorphic Evolution of Sapphirine-bearing Granulites from the Gruf Complex, Italian Central Alps

Mineral chemistries and textures are described from a suite of sapphirine-bearing granulites from the Gruf Complex of the Italian Central Alps. The granulites contain combinations of garnet, orthopyroxene, sapphirine, sillimanite, cordierite, biotite, quartz, spinel, corundum, staurolite, plagioclase, K-feldspar, ilmenite and rutile, in assemblages with low (usually negative) variance. They are outstanding in that they preserve a textural and chemical record of a protracted metamorphic evolution. Reaction textures are common and include: (i) pseudomorphs (e.g. of sillimanite after kyanite); (ii) relatively coarse-grained monomineralic reaction rims (e.g. of cordierite between sapphirine and quartz); (iii) fine-grained symplectitic coronas (e.g. of orthopyroxene + sapphirine round garnet); (iv) inclusions, in garnet cores, of minerals (e.g. staurolite) not found elsewhere in the rocks. Detailed microprobe study has revealed large chemical variations within each phase. Different textural types of each phase have different compositions, and strong zoning is preserved in garnet (Mg/(Mg + Fe) from 0.30 to 0.61) and coarse sapphirine. Inclusion populations in garnet correlate with host composition. The textural and chemical features are interpreted in terms of successive equilibrium assemblages and reactions. Metamorphic conditions operative at each stage in the evolution are calculated using published geothermometers and geobarometers as well as thermodynamically calibrated MAS and FASH equilibria. The results are used to construct a P—T-time path for the sapphirine-granulites, which can be summarized as follows: (i) Increasing T at high P (>7 kb). Partial melting. (ii) A maximum T of ∼830 °C attained at ∼10 kb. (iii) Almost isothermal decompression, reaching 750 °C at ∼5 kb, under conditions of low μH2O. (iv) Further cooling, and decompression. Localized hydration. Rocks exposed. The P—T-time path is interpreted as the product of a single metamorphic cycle (the tertiary ‘Lepontine' event) and is extrapolated to the Gruf Complex as a whole. When combined with published geochronological data, the results indicate an average uplift rate in excess of 2 mm/yr for the Gruf Complex between 38 and 30 Ma ago. An in situ partial melting origin for the sapphirine-granulites is favoured. Extraction of an iron-rich granitic liquid from a normal pelitic palaeosome could generate a refractory residue with the required Mg, Al-rich composition. The change in bulk solid composition during partial melting is thought to account for the extraordinarity strong zoning in the garnet

Hybrid dialog: Dialogic learning in large lecture classes

Attendance at classical lectures usually leads to rather poor learning success. A wide variety of studies show that while lectures are as effective as any other method for transmitting information, they are inferior in many other dimensions. Lectures are not as effective as discussion methods in promoting thought and they are ineffective at teaching behavioral skills and subject-related values as well as at awakening interest in a subject. Still ex-cathedra teaching is a favored way to cope with a high student-to-teacher ratio. To solve this conflict between organizational and pedagogical requirements, a group of researchers at the Institute of Teacher Education at the University of Zurich has developed a hybrid course setting using an online learning platform. Their setting incorporates a dialog among students within a large lecture class. Furthermore a feedback loop enables the lecturer to continuously adjust the content of the lecture to the learning process of the students. In this article, the authors first present the structure of this setting and then illustrate how to implement it by the web-based open source learning management system OLAT (Online Learning and Training). Based on their research, they focus on key components for the success of their hybrid dialog. They show how individual and group learning can be fostered with corresponding assignments, assessments, and assigned roles such as moderators. Thus, the authors will define their position that the challenge of a large lecture class can be met while successfully implementing social learning and process-oriented assessments of academic achievement