Testing of the late-ordovician Pre-GICE warm water carbonate hypothesis in Alabama

The Guttenberg Carbon Isotope Excursion (GICE) (uppermost Sandbian-lower Katian, Late Ordovician) has been suggested to represent the transition from a Cambrian-Ordovician greenhouse world to Late Ordovician icehouse world. This transition is thought to coincide with a proposed shift from deposition of warm water carbonate rocks to cool water carbonate rocks in the North American midcontinent. We used oxygen isotopes (d18O) of conodonts to test the idea that the rocks below the GICE interval represent a consistently warm environment. Conodonts were isolated from samples of the Chickamauga Group collected at the Tidwell Hollow section in Blount County, AL, from the Red Mountain Expressway section in Birmingham, AL, and from Dickeyville, WI. These successions underlie strata that biostratigraphically correlate with the GICE interval. Conodonts at Tidwell Hollow include Appalachignathus sp. and Phragmodus flexuosus near the base of the Chickamauga Group and Oulodus oregonia and Aphelognathus kimmswickensis near its top. These taxa indicate that the interval studied ranges from the Plectodina aculeata Zone to at least the Plectodina tenuis Zone, spanning from below and through the GICE. Conodonts from the Red Mountain Expressway section were collected only to 22m below the Millbrig K-bentonite, where Belodina compressa and Curtognathus spp. dominate the fauna. At 10m below the Millbrig, Polyplacognathus ramosus occurs and the top of the section contains a fauna that includes Phragmodus undatus and Icriodella superba. Results indicate that the sampled interval ranges from the Belodina compressa Zone to the Phragmodus undatus Zone, an interval which is below and up to the GICE. The conodont d18O values indicate that the rocks below the GICE in Alabama represent a consistently warm environment throughout the Chickamauga Group below the Millbrig K-bentonite Bed, supporting the idea that the pre-GICE environment was relatively stable, and that the GICE, along with the changes in d18O in the GICE interval, could reflect a perturbation in the Ordovician climate

Linear characters of Sylow subgroups of symmetric groups

Let $p$ be any prime. Let $P_n$ be a Sylow $p$-subgroup of the symmetric group $S_n$. Let $\phi$ and $\psi$ be linear characters of $P_n$ and let $N$ be the normaliser of $P_n$ in $S_n$. In this article we show that the inductions of $\phi$ and $\psi$ to $S_n$ are equal if, and only if, $\phi$ and $\psi$ are $N$--conjugate. This is an analogue for symmetric groups of a result of Navarro for $p$-solvable groups.Comment: 27 pages, reviewer comments and corrections incorporate

On Problems in the Representation Theory of Symmetric Groups

In this thesis, we study the representation theory of the symmetric groups $\mathfrak{S}_n$, their Sylow $p$-subgroups $P_n$ and related algebras. For all primes $p$ and natural numbers $n$, we determine the maximum number of distinct irreducible constituents of degree coprime to $p$ of restrictions of irreducible characters of $\mathfrak{S}_n$ to $\mathfrak{S}_{n-1}$, and show that every value between 1 and this maximum is attained. These results can be stated graph-theoretically in terms of the Young lattice, which describes branching for symmetric groups. We present new graph isomorphisms between certain subgraphs of the Young lattice and find self-similar structures. This generalises from $p=2$ to all $p$ work of Ayyer, Prasad and Spallone which was central in the construction of character correspondences for symmetric groups in the context of the McKay Conjecture, a fundamental open problem in the representation theory of finite groups. Linear characters of Sylow subgroups have also played a central role in character correspondences verifying the McKay Conjecture, becoming the focus of much current interest. For instance, a consequence of recent work of Giannelli and Navarro shows the existence of linear constituents in the restriction of every irreducible character of a symmetric group to its Sylow $p$-subgroups. We now identify these linear constituents, using a mixture of algebraic and combinatorial techniques including Mackey theory and an analysis of Littlewood--Richardson coefficients. We determine precisely when the trivial character of $P_n$ appears as a constituent of the restriction of an irreducible character of $\mathfrak{S}_n$, for all $n$ and odd $p$. As a consequence, we determine the irreducible characters of the Hecke algebra corresponding to the induced permutation character. Analogous results are obtained for the alternating groups $\mathfrak{A}_n$. We then extend our scope to arbitrary linear characters of $P_n$, proving in particular that for all $p$, given linear characters $\phi$ and $\phi'$ of $P_n$, their inductions to $\mathfrak{S}_n$ are equal if and only if $\phi$ and $\phi'$ are $N_{\mathfrak{S}_n}(P_n)$--conjugate. Finally, we consider the representation theory of Schur algebras in all characteristics. We classify the classical Schur algebras $S(n,r)$ which are Ringel self-dual, using decomposition numbers for symmetric groups, tilting module multiplicities and combinatorial methods

On plethysms and Sylow branching coefficients

We prove a recursive formula for plethysm coefficients of the form $a^\mu_{\lambda,(m)}$, generalising results on plethysms due to Bruns--Conca--Varbaro and de Boeck--Paget--Wildon. From this we deduce a stability result and resolve two conjectures of de Boeck concerning plethysms, as well as obtain new results on Sylow branching coefficients for symmetric groups for the prime 2. Further, letting $P_n$ denote a Sylow 2-subgroup of $S_n$, we show that almost all Sylow branching coefficients of $S_n$ corresponding to the trivial character of $P_n$ are positive.Comment: 35 pages, 6 figures; further explanation and detail added throughout, in particular in Section 5.1, results unchanged; typos corrected; acknowledgements update

Testing the early Late Ordovician cool-water hypothesis with oxygen isotopes from conodont apatite

© 2017 Cambridge University Press. Latest Sandbian to early Katian sequences across Laurentia\u27s epicontinental sea exhibit a transition from lithologies characterized as \u27warm-water\u27 carbonates to those characterized as \u27cool-water\u27carbonates. This shift occurs across the regionally recognized M4/M5 sequence stratigraphic boundary and has been attributed to climatic cooling and glaciation, basin reorganization and upwelling of open ocean water, and/or increased water turbidity and terrigenous input associated with the Taconic tectophase. Documentation of oxygen isotopic trends across the M4/M5 and through bracketing strata provides a potential means of distinguishing among these alternative scenarios; however, oxygen isotopic records generated to date have failed to settle the debate. This lack of resolution is because δ18O records are open to multiple interpretations and potentially confounding factors related to local environmental conditions have not been tested by examining the critical interval in multiple areas and different depositional settings. To begin to address this shortcoming, we present new species-specific and mixed assemblage conodont δ18O values in samples spanning the M4/M5 boundary from the Upper Mississippi Valley, Alabama, and Virginia. The new results are combined with previous studies, providing a record of δ18O variability across SE Laurentia. The combined dataset allows us to test for regional trends at a resolution not previously available. Our results document a ~1.5‰ decrease in values across Laurentia instead of increasing δ18O values across the M4/M5 as predicted in various \u27cool-water\u27 scenarios. In short, these results do not support a shift to \u27cool-water\u27 conditions as an explanation for changes in early Katian carbonates across the M4/M5

Intravital FRAP imaging using an E-cadherin-GFP mouse reveals disease- and drug-dependent dynamic regulation of cell-cell junctions in live tissue

E-cadherin-mediated cell-cell junctions play a prominent role in maintaining the epithelial architecture. The disruption or deregulation of these adhesions in cancer can lead to the collapse of tumor epithelia that precedes invasion and subsequent metastasis. Here we generated an E-cadherin-GFP mouse that enables intravital photobleaching and quantification of E-cadherin mobility in live tissue without affecting normal biology. We demonstrate the broad applications of this mouse by examining E-cadherin regulation in multiple tissues, including mammary, brain, liver, and kidney tissue, while specifically monitoring E-cadherin mobility during disease progression in the pancreas. We assess E-cadherin stability in native pancreatic tissue upon genetic manipulation involving Kras and p53 or in response to anti-invasive drug treatment and gain insights into the dynamic remodeling of E-cadherin during in situ cancer progression. FRAP in the E-cadherin-GFP mouse, therefore, promises to be a valuable tool to fundamentally expand our understanding of E-cadherin-mediated events in native microenvironments

Entanglements of creative agency and digital technology : a sociomaterial study of computer game development

Digital technology, with its distinctive characteristics that result from the fundamental process of digitalization that underpins it, is seen as fundamentally altering processes of creativity. However, we currently have limited understanding of creativity in relation to the development of digital technology. Computer game development, with its combination of esthetic, affective and cultural use features and highly sophisticated digital technologies, is a valuable setting for investigating these issues. In this paper, we explore how computer games are shaped through the interplay between the creative intentions of developers and the digital technologies involved in their production and playing. Drawing on in-depth studies conducted at three leading computer game development studios and a leading producer of the software system used in game development, this paper shows how the game developers' creative ideas for imagined novel game-playing experiences relate to a) the development of relevant digital technologies, and b) the emergence of new game development practices. The article goes on to propose a view of creativity as an on-going flow that, following an initial ‘creative impulse’, ripples through the sociomaterial entanglements of a particular setting, reconfiguring them in the process and spreading out in time and space in often unexpected ways

Making to measure? Reconsidering assessment in professional continuing education

Drawing on studies of teachers, accountants and pharmacists conducted in Canada, this essay examines models for assessing professional learning that currently enjoy widespread use in continuing education. These models include professional growth plans, self-administered tests, and learning logs, and they are often used for regulatory as well as developmental purposes by professional associations. The essay argues what others have critiqued about such self-assessment models: that their assumptions about learning are problematic and limiting in a number of respects, privileging human consciousness and intention, and literally ‘making’ a particular professional subject that is atomised and conservative. The essay goes on to suggest alternative perspectives that are receiving increasing attention in theorising work-related learning and that may offer fruitful questions for re-considering the nature of professional learning and its assessment. Three perspectives in particular are outlined, all of which shift the focus from the learning subject to practice as material, emergent and systemic: complexity theory, actor-network theory and cultural-historical activity theory. The discussion concludes with possible approaches to assessment of professional practice suggested by these perspectives