Surficial Geology and Geomorphology of the Western Olympus Range, Antarctica: Implications for Ice-sheet History

A widespread erosion surface passes across bedrock and sedimentary deposits in the western Dry Valleys sector of the Transantarctic Mountains (TAM), southern Victoria Land, Antarctica. The surface includes stoss-and-lee slopes, channels, potholes, scoured basins, and corrugated bedrock. These features have been taken to represent subglacial meltwater erosion beneath a greatly expanded East Antarctic Ice Sheet (EAIS) in the mid-Miocene (Denton et al. 1984, Marchant et al. 1993a). Sedimentary deposits that are typically associated with ice-sheet wastage, such as outwash, are not present on the erosion surface. The lack of these deposits indicates that the expanded ice-sheet postulated to be responsible for the erosion surface probably sublimated from the mountains under a polar desert climate. By this hypothesis, the nearly perfect preservation of geomorphic features on the erosion surface suggests that the Dry Valleys region has been locked in polar desert conditions since the erosion surface was carved in mid-Miocene time. The adjacent ENS probably remained stable under such climate conditions. An alternate hypothesis suggests that the erosional features are the product of wind-deflation and chemical weathering of the land surface (Selby 1985, Isaac et al. 1996, Healy 1976). The wind-deflation hypothesis implies that the surface may be forming under present-day polar desert processes and has nothing to do with ice-sheet history. Chronology is one means of discriminating between these hypotheses. When was the erosion surface carved? Is it ancient (consistent with the subglacial erosion hypothesis), or is it still forming (consistent with the wind-deflation hypothesis)? From a study of the glacial geology and geomorphology of the western Olympus Range in the Dry Valleys region, I present here the stratigraphic context and chronology of the erosion surface and three sedimentary units, Circe till, Electra colluvium, and Alpine till. Circe till is a fine-grained diamicton with striated clasts that was deposited beneath wet-based glacial ice. Circe till everywhere rests on bedrock. Electra colluvium is a highly oxydized, clast-rich diamicton that overlies Circe till in stratigraphic section. The areal distribution of both of these units is patchy and non-uniform. Circe till and Electra Colluvium are cut by the erosion surface. Alpine moraines drape over the erosional features in the western Olympus Range. The moraines are undssected and arcuate in plan view. This undisturbed morphology indicates that the erosion surface has not been active since at least the time of moraine deposition. Thus, the age of the moraines provides a minimum age on the carving of the erosion surface. This study presents 3 ~ e cosmogenic surface exposure ages of twelve boulders from three moraines that rest on the erosion surface. The preliminary ages range from 0.90 Ma to 1.12 Ma, possibly 5.50 Ma. These are minimum values because surface weathering of the boulders was not considered in the exposure-age calibrations. The oldest moraine has remained unaltered for at least 1.12 Ma. Therefore, the erosion surface has not been active in at least 1.12 Ma. These surface exposure age dates constitute an argument against the wind-deflation hypothesis

Activities development for 2 word combinations on pre-sentence level TAGS

This paper presents activities to assist teachers of hearing impaired students to develop 2-word combinations for use in instruction in conjunction with the Teacher Assessment of Grammatical Structures Pre-Sentence Level (TAGS-P). The paper presents activity procedures and materials to guide teachers in teaching 2-word combinations

Pushing coarse-grained models beyond the continuum limit using equation learning

Mathematical modelling of biological population dynamics often involves proposing high fidelity discrete agent-based models that capture stochasticity and individual-level processes. These models are often considered in conjunction with an approximate coarse-grained differential equation that captures population-level features only. These coarse-grained models are only accurate in certain asymptotic parameter regimes, such as enforcing that the time scale of individual motility far exceeds the time scale of birth/death processes. When these coarse-grained models are accurate, the discrete model still abides by conservation laws at the microscopic level, which implies that there is some macroscopic conservation law that can describe the macroscopic dynamics. In this work, we introduce an equation learning framework to find accurate coarse-grained models when standard continuum limit approaches are inaccurate. We demonstrate our approach using a discrete mechanical model of epithelial tissues, considering a series of four case studies that illustrate how we can learn macroscopic equations describing mechanical relaxation, cell proliferation, and the equation governing the dynamics of the free boundary of the tissue. While our presentation focuses on this biological application, our approach is more broadly applicable across a range of scenarios where discrete models are approximated by approximate continuum-limit descriptions. All code and data to reproduce this work are available at https://github.com/DanielVandH/StepwiseEQL.jl.Comment: 42 pages, 18 figure

Screening for autistic spectrum disorder at the 18-month developmental assessment: a population-based study

VanDenHeuvel A, Fitzgerald M, Greiner B, Perry IJ. Screening for autistic spectrum disorder at the 18-month developmental assessment: a population-based study. Ir Med J. 2007;100(8):565-7.The objectives of this study were to assess the feasibility of administering the CHecklist for Autism in Toddlers (CHAT) at the 18-month developmental check, estimate the prevalence of screening positive for autism at the first and second administrations of the CHAT and estimate the prevalence of diagnosed cases of autism. A cross-sectional study design was utilised and data was collected at child developmental screening clinics in counties Cork and Kerry. The sample group consisted of infants attending the routine 18-month developmental assessment, who were broadly representative of infants in the catchment area. The main outcome measure was a medium or high-risk score following two administrations of the CHAT screening instrument and a positive diagnosis of autism after clinical assessment. The CHAT was administered to 2117 infants (79% of those approached) of whom 29 were scored at medium or high risk at first screening, resulting in a prevalence rate of 137 per 10,000 (95% CI: 87-187). A total of 7 of the 29 first screen positive infants were positive (medium or high risk) at second screening, 12 were low risk and 10 parents refused to participate. On subsequent clinical assessment of the 7 infants screening positive on first and second assessment and assessment of 5 of the 10 infants whose parents declined second screening, 7 children received a diagnosis of autism. Thus the overall prevalence of clinically diagnosed autism following this screening exercise was 33.1 per 10,000 (95% CI: 13.3 to 68.0). The CHAT instrument is a useful tool to help identify childhood autism among infants. Routine use of this instrument at 18-month developmental assessment merits consideration