Design and Assessment of an Interactive Digital Tutorial for Undergraduate-Level Sandstone Petrology

This study describes the goals, features and effectiveness of a digital interactive tutorial which was created to provide undergraduates a 'virtual microscope' resource for learning sandstone petrology. The goal of the tutorial is to provide students exposure to the highly visual subject matter of petrography outside the confines of organized laboratory exercises. The hope is that widespread use of such digital interactive formats will allow students to gain high levels of expertise with description and interpretation of earth materials despite the reduced amounts of hands-on laboratory practice that are allowed by modern curricula. Educational levels: Graduate or professional

Petrology and burial diagenesis of Plio-Pleistocene sediments, northern Gulf of Mexico

Plio-Pleistocene sediments and rocks beneath the Louisiana and adjacent Texas shelves are the youngest of several thick packages of terrigenous sediment which prograded into the Gulf of Mexico during the Cenozoic. Comparison of diagenesis in these young sediments (more than 300 samples from 45 wells on the Louisiana-Texas shelf) to diagenesis of older Cenozoic rocks at similar burial depths elsewhere along the Gulf margin confirms that diagenesis is not strictly analogous among the various Cenozoic units. There has been an evolution of diagenesis during filling of the Gulf of Mexico. Differences in diagenesis cannot be attributed to differences in bulk mineralogy of the sands because PIio-Pleistocene sands are lithic arkoses and feldspathic litharenites with essentially the same QFR proportions as observed in subsurface Eocene and Oligocene sandstones along the Texas coast. Unaltered plagioclase is slightly more calcic (average An 24) than unaltered plagioclase in the older rocks. Burial diagenesis in Plio-Pleistocene sediments has involved essentially the same processes as observed in the older rocks, but overall, diagenesis has advanced to a lesser degree at any given depth. Cementation by quartz and carbonate, dissolution of potassium-feldspar and heavy minerals, albitization of plagioclase, and the transformation of smectite to illite have occurred in Plio-Pleistocene sediments, but cements and altered grains are not volumetrically significant shallower than 4 to 4.5 km. The temperature at which reaction of detrital constituents begins (approximately 90° C) is similar to that observed elsewhere in the Gulf, but the zone of reaction is spread over a greater depth range. The similar temperatures observed for the advent of detrital reactions across the Gulf basin suggest that these processes are more highly dependent upon temperature than upon time and that differences observed among the various units may be attributed, at least in part, to variations in the geothermal gradient. The degree of detrital grain alteration observed in these young sediments shows that significant loss of provenance information occurs quite early in the burial history. Alteration in the deep subsurface is very effective in modifying the primary detrital assemblage.Geological Science

Flux Jumping and a Bulk-to-Granular Transition in the Magnetization of a Compacted and Sintered MgB2 Superconductor

The recent discovery of intermediate-temperature superconductivity (ITC) in MgB2 by Akimitsu et al. and its almost simultaneous explanation in terms of a hole-carrier-based pairing mechanism by Hirsch, has triggered an avalanche of studies of its structural, magnetic and transport properties. As a further contribution to the field we report the results of field (H) and temperature (T) dependent magnetization (M) measurements of a pellet of uniform, large-grain sintered MgB2. We show that at low temperatures the size of the pellet and its critical current density, Jc(H) - i.e. its M(H) - ensure low field flux jumping, which of course ceases when M(H) drops below a critical value. With further increase of H and T the individual grains decouple and the M(H) loops drop to lower lying branches, unresolved in the usual full M(H) representation. After taking into account the sample size and grain size, respectively, the bulk sample and the grains were deduced to exhibit the same magnetically determined Jc s (e.g. 105 A/cm2, 20 K, 0T) and hence that for each temperature of measurement Jc(H) decreased monotonically with H over the entire field range, except for a gap within the grain-decoupling zone.Comment: 7 pages, 6 figures, Changes: Fig 6 Vertical scale an order of magnitude out (changed figure and associated text). Also corrected typo in last sectio

Design Considerations for Efficient and Effective Microarray Studies

This paper describes the theoretical and practical issues in experimental design for gene expression microarrays. Specifically, this paper (1) discusses the basic principles of design (randomization, replication, and blocking) as they pertain to microarrays, and (2) provides some general guidelines for statisticians designing microarray studies

THE POWER OF STRUCTURED DESIGNS AND MIXED MODELS IN A REAL WORLD EXPERIMENT

Justifications usually given for adopting an automated system pertain to a reduction in labor and an improvement in quality control. A manufacturer of a prototype instrument that automated some of the steps for culturing bacteria wanted to compare the automated system to the manual system. The manufacturer wanted to compare the two systems in 1) Total time needed to isolate the target bacteria, 2) Ability to isolate the target bacteria, 3) Amount of interference from background (non-target) bacterial growth, and 1) Extent of cross (sample to sample) contamination. This paper presents the experimental design used to make these comparisons and how the design helped discover some surprising results about laboratory quality control. The experiment presented illustrates the importance of a good experimental design, the power of current statistical tools, and that a thorough and appropriate analysis of a data set requires side-by-side good detective work by both statistician and client

Anisotropic Transport of Quantum Hall Meron-Pair Excitations

Double-layer quantum Hall systems at total filling factor $\nu_T=1$ can exhibit a commensurate-incommensurate phase transition driven by a magnetic field $B_{\parallel}$ oriented parallel to the layers. Within the commensurate phase, the lowest charge excitations are believed to be linearly-confined Meron pairs, which are energetically favored to align with $B_{\parallel}$. In order to investigate this interesting object, we propose a gated double-layer Hall bar experiment in which $B_{\parallel}$ can be rotated with respect to the direction of a constriction. We demonstrate the strong angle-dependent transport due to the anisotropic nature of linearly-confined Meron pairs and discuss how it would be manifested in experiment.Comment: 4 pages, RevTex, 3 postscript figure

Electron-phonon interactions on a single-branch quantum Hall edge

We consider the effect of electron-phonon interactions on edge states in quantum Hall systems with a single edge branch. The presence of electron-phonon interactions modifies the single-particle propagator for general quantum Hall edges, and, in particular, destroys the Fermi liquid even at integer filling. The effect of the electron-phonon interactions may be detected experimentally in the AC conductance or in the tunneling conductance between integer quantum Hall edges.Comment: 9 pages (revtex) + one postscript file with 2 figures. A complete postscript file with all figures + text (5 pages) is available from http://FY.CHALMERS.SE/~eggert/fqh.ps or by request from [email protected]

Low-temperature behavior of a Magnetic Impurity in a Heisenberg Chain

Using the bosonization technique, we have studied a spin-1/2 magnetic impurity in Heisenberg chain, and shown that the impurity specific heat and spin susceptibility have an anomalous temperature dependence.Comment: 12 pages, Revtex, no figure, to be published in Phys. Rev. Let

Anomalous Exponent of the Spin Correlation Function of a Quantum Hall Edge

The charge and spin correlation functions of partially spin-polarized edge electrons of a quantum Hall bar are studied using effective Hamiltonian and bosonization techniques. In the presence of the Coulomb interaction between the edges with opposite chirality we find a different crossover behavior in spin and charge correlation functions. The crossover of the spin correlation function in the Coulomb dominated regime is characterized by an anomalous exponent, which originates from the finite value of the effective interaction for the spin degree of freedom in the long wavelength limit. The anomalous exponent may be determined by measuring nuclear spin relaxation rates in a narrow quantum Hall bar or in a quantum wire in strong magnetic fields.Comment: 4 pages, Revtex file, no figures. To appear in Physical Revews B, Rapid communication

Anomalous tunneling conductances of a spin singlet \nu=2/3 edge states: Interplay of Zeeman splitting and Long Range Coulomb Interaction

The point contact tunneling conductance between edges of the spin singlet $\nu=2/3,\hat{K}=(3/3/0)$ quantum Hall states is studied both in the quasiparticle tunneling picture and in the electron tunneling picture. Due to the interplay of Zeeman splitting and the long range Coulomb interaction between edges of opposite chirality novel spin excitations emerge, and their effect is characterized by anomalous exponents of the charge and spin tunneling conductances in various temperature ranges. Depending on the kinds of scatterings at the point contact and the tunneling mechanism the anomalous interaction in spin sector may enhance or suppress the tunneling conductances. The effects of novel spin excitation are also relevant to the recent NMR experiments on quantum Hall edges.Comment: Revtex File, 7 pages: To be published in Physical Reviews