ISM Abundances in Sculptor Group Dwarf Irregular Galaxies

Using the CTIO 4-m telescope, we have obtained optical spectra of HII regions in five Sculptor Group dwarf irregular galaxies. We derive oxygen, nitrogen, and sulfur abundances from the HII region spectra. Oxygen abundances are derived via three different methods (the ``direct'' method, the empirical method guided by photoionization modeling of McGaugh (1991), and the purely empirical method of Pilyugin (2000)) and are compared. Significant systematic differences are found between the three methods, and we suggest that a recalibration of the empirical abundance scale is required. The N/O ratio for the metal-poor dI ESO 473-G24 of log (N/O) = -1.43 +/- 0.03 lies well above the plateau of log (N/O) = -1.60 +/- 0.02 found by Izotov & Thuan (1999) for a collection of metal-poor blue compact galaxies. This shows that not all galaxies with 12 + log (O/H) < 7.6 have identical elemental abundance ratios, and this implies that the Izotov & Thuan scenario for low metallicity galaxies is not universal. Measurements of the HII regions in NGC 625 yield log (N/O) = -1.25. Assuming N production by intermediate mass stars, this relatively high N/O ratio may be indicative of a long quiescent period prior to the recent active burst of star formation. The oxygen abundances in the Sculptor Group dIs are in good agreement with the relationship between metallicity and luminosity observed in the Local Group dIs. The Sculptor Group dIs, in general, lie closer to the simple closed box model evolutionary path than the Local Group dIs. The higher gas contents, lower average star formation rates, and closer resemblance to closed box evolution could all be indicative of evolution in a relatively low density environment.Comment: 40 pages, 9 figures, accepted for Feb 2003 A

Gene expression differs in susceptible and resistant amphibians exposed to Batrachochytrium dendrobatidis.

Chytridiomycosis, the disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has devastated global amphibian biodiversity. Nevertheless, some hosts avoid disease after Bd exposure even as others experience near-complete extirpation. It remains unclear whether the amphibian adaptive immune system plays a role in Bd defence. Here, we describe gene expression in two host species-one susceptible to chytridiomycosis and one resistant-following exposure to two Bd isolates that differ in virulence. Susceptible wood frogs (Rana sylvatica) had high infection loads and mortality when exposed to the more virulent Bd isolate but lower infection loads and no fatal disease when exposed to the less virulent isolate. Resistant American bullfrogs (R. catesbeiana) had high survival across treatments and rapidly cleared Bd infection or avoided infection entirely. We found widespread upregulation of adaptive immune genes and downregulation of important metabolic and cellular maintenance components in wood frogs after Bd exposure, whereas American bullfrogs showed little gene expression change and no evidence of an adaptive immune response. Wood frog responses suggest that adaptive immune defences may be ineffective against virulent Bd isolates that can cause rapid physiological dysfunction. By contrast, American bullfrogs exhibited robust resistance to Bd that is likely attributable, at least in part, to their continued upkeep of metabolic and skin integrity pathways as well as greater antimicrobial peptide expression compared to wood frogs, regardless of exposure. Greater understanding of these defences will ultimately help conservationists manage chytridiomycosis

Application of Artificial Neural Networks to Identify Equilibration in Computer Simulations

Determining which microstates generated by a thermodynamic simulation are representative of the ensemble for which sampling is desired is a ubiquitous, underspecified problem. Artificial neural networks are one type of machine learning algorithm that can provide a reproducible way to apply pattern recognition heuristics to underspecified problems. Here we use the open-source TensorFlow machine learning library and apply it to the problem of identifying which hypothetical observation sequences from a computer simulation are equilibrated and which are not. We generate training populations and test populations of observation sequences with embedded linear and exponential correlations. We train a two-neuron artificial network to distinguish the correlated and uncorrelated sequences. We find that this simple network is good enough for \u3e 98% accuracy in identifying exponentially-decaying energy trajectories from molecular simulations

Improving Resolution and Understanding Controls on GPR Response in Carbonate Strata: Implications for Attribute Analysis

This is the publisher's version, also available electronically from "http://mr.crossref.org".For more than a decade, environmental, engineering, groundwater, and shallow stratigraphic studies have demonstrated and advanced the usefulness of ground-penetrating radar (GPR) in lithified and unconsolidated sedimentary deposits (e.g., see Neal, 2004 and references therein). Despite the advances, important questions still remain on factors that control the actual appearance and characteristics of GPR reflections and diffractions in any given setting. ?? 2007 Society of Exploration Geophysicists

Star Formation in Sculptor Group Dwarf Irregular Galaxies and the Nature of "Transition" Galaxies

We present new H-alpha narrow band imaging of the HII regions in eight Sculptor Group dwarf irregular (dI) galaxies. Comparing the Sculptor Group dIs to the Local Group dIs, we find that the Sculptor Group dIs have, on average, lower values of SFR when normalized to either galaxy luminosity or gas mass (although there is considerable overlap between the two samples). The properties of ``transition'' (dSph/dIrr) galaxies in Sculptor and the Local Group are also compared and found to be similar. The transition galaxies are typically among the lowest luminosities of the gas rich dwarf galaxies. Relative to the dwarf irregular galaxies, the transition galaxies are found preferentially nearer to spiral galaxies, and are found nearer to the center of the mass distribution in the local cloud. While most of these systems are consistent with normal dI galaxies which currently exhibit temporarily interrupted star formation, the observed density-morphology relationship (which is weaker than that observed for the dwarf spheroidal galaxies) indicates that environmental processes such as ``tidal stirring'' may play a role in causing their lower SFRs.Comment: 35 pages, 10 figures, accepted for Feb 2003 AJ, companion to astro-ph/021117

Atom chips on direct bonded copper substrates

We present the use of direct bonded copper (DBC) for the straightforward fabrication of high power atom chips. Atom chips using DBC have several benefits: excellent copper/substrate adhesion, high purity, thick (> 100 microns) copper layers, high substrate thermal conductivity, high aspect ratio wires, the potential for rapid (< 8 hr) fabrication, and three dimensional atom chip structures. Two mask options for DBC atom chip fabrication are presented, as well as two methods for etching wire patterns into the copper layer. The wire aspect ratio that optimizes the magnetic field gradient as a function of power dissipation is determined to be 0.84:1 (height:width). The optimal wire thickness as a function of magnetic trapping height is also determined. A test chip, able to support 100 A of current for 2 s without failing, is used to determine the thermal impedance of the DBC. An assembly using two DBC atom chips to provide magnetic confinement is also shown.Comment: 8 pages, 5 figure

The Mahogany Peaks fault, a late Cretaceous-Paleocene(?) normal fault in the hinterland of the Sevier orogen

The contact separating Ordovician rocks from the underlying lower part of the Raft River Mountains sequence, northwestern Utah, is reinterpreted as a large-displacement low-angle normal fault, the Mahogany Peaks fault, that excised 4-5 km of structural section. High delta(13)C values identified in marble in the lower part of the Raft River Mountains sequence suggest a Proterozoic, rather than Cambrian age. Metamorphic conditions of hanging wall Ordovician and footwall Proterozoic strata are upper greenschist and middle amphibolite facies, respectively, and quantitative geothermometry indicates a temperature discontinuity of about 100 degrees C. A discordance in muscovite Ar-40/Ar-39 cooling ages between hanging wall and footwall strata in eastern exposures, and the lack of a corresponding cooling age discordance in western exposures, suggest a component of west dip for the fault. The juxtaposition of younger over older and colder over hotter rocks, the muscovite cooling age discordance with older over younger, and top-to-the-west shearing down-structure are consistent with an extensional origin. The age of faulting is bracketed between 90 and 47 Ma, and may be synchronous with footwall cooling at about 60-70 Ma. Recognition of the Mahogany Peaks fault, its extensional origin, and its probable latest Cretaceous to Paleocene age provides further evidence that episodes of extension at mid-crustal levels in the hinterland of the Sevier orogenic belt were synchronous with protracted shortening in the foreland fold and thrust belt, and that the Sevier orogen acted as a dynamic orogenic wedge

Substantial carbon loss respired from a corn-soybean agroecosystem highlights the importance of careful management as we adapt to changing climate

Understanding agroecosystem carbon (C) cycle response to climate change and management is vital for maintaining their long-term C storage. We demonstrate this importance through an in-depth examination of a ten-year eddy covariance dataset from a corn-corn-soybean crop rotation grown in the Midwest United States. Ten-year average annual net ecosystem exchange (NEE) showed a net C sink of -0.39 Mg C ha-1 yr-1. However, NEE in 2014 and 2015 from the corn ecosystem was 3.58 and 2.56 Mg C ha-1 yr-1, respectively. Most C loss occurred during the growing season, when photosynthesis should dominate and C fluxes should reflect a net ecosystem gain. Partitioning NEE into gross primary productivity (GPP) and ecosystem respiration (ER) showed this C \u27burp\u27 was driven by higher ER, with a 51% (2014) and 57% (2015) increase from the ten-year average (15.84 Mg C ha-1 yr-1). GPP was also higher than average (16.24 Mg C ha-1 yr-1) by 25% (2014) and 37% (2015), but this was not enough to offset the C emitted from ER. This increased ER was likely driven by enhanced soil microbial respiration associated with ideal growing season climate, substrate availability, nutrient additions, and a potential legacy effect from drought

4D Seismic to Image a Thin Carbonate Reservoir During a Miscible CO2 Flood: Hall-Gurney Field, Kansas, USA

This is the publisher's version, also available electronically from "http://mr.crossref.org".The movement of miscible CO2 injected into a shallow (900 m) thin (3.6-6m) carbonate reservoir was monitored using the high-resolution parallel progressive blanking (PPB) approach. The approach concentrated on repeatability during acquisition and processing, and use of amplitude envelope 4D horizon attributes. Comparison of production data and reservoir simulations to seismic images provided a measure of the effectiveness of time-lapse (TL) to detect weak anomalies associated with changes in fluid concentration. Specifically, the method aided in the analysis of high-resolution data to distinguish subtle seismic characteristics and associated trends related to depositional lithofacies and geometries and structural elements of this carbonate reservoir that impact fluid character and EOR efforts. Additional Publication Detail

Perspective on Coarse-Graining, Cognitive Load, and Materials Simulation

The predictive capabilities of computational materials science today derive from overlapping advances in simulation tools, modeling techniques, and best practices. We outline this ecosystem of molecular simulations by explaining how important contributions in each of these areas have fed into each other. The combined output of these tools, techniques, and practices is the ability for researchers to advance understanding by efficiently combining simple models with powerful software. As specific examples, we show how the prediction of organic photovoltaic morphologies have improved by orders of magnitude over the last decade, and how the processing of reacting epoxy thermosets can now be investigated with million-particle models. We discuss these two materials systems and the training of materials simulators through the lens of cognitive load theory. For students, the broad view of ecosystem components should facilitate understanding how the key parts relate to each other first, followed by targeted exploration. In this way, the paper is organized in loose analogy to a coarse-grained model: The main components provide basic framing and accelerated sampling from which deeper research is better contextualized. For mentors, this paper is organized to provide a snapshot in time of the current simulation ecosystem and an on-ramp for simulation experts into the literature on pedagogical practice