Ian J. Duncan

Diffusion of 40Ar in biotite: Temperature, pressure and compositional effects

Abstract The measured radiogenic 40Ar loss from sized biotite (56% annite) samples following isothermalhydrothermal treatment have provided model diffusion coefficients in the temperature interval 600°C to 750°C, calculated on the assumption that Ar transport proceeds parallel to cleavage. These data yield an array on an Arrhenius plot with a slope corresponding to an activation energy 47.0 ± 2 kcal-mol−1 and a frequency factor of 0.077+0.21−0.06 cm2-sec−1. Together with previous diffusion data for micas in the annitephlogopite series, our results indicate a strong compositional effect, with increasing Fe Mg ratio corresponding to an increase in diffusivity. An effective diffusion radius of about 150 μm for biotite is inferred from the experimental data which compares favorably with that estimated from geological studies. A pressure effect on activation energy corresponding to an activation volume of about 14 cm3-mol−1 is observed. These data yield closure temperature estimates for this biotite composition cooling at rates of 100°C-Ma−1, 10°C-Ma−1 and 1°C-Ma−1 of 345°C, 310°C and 280°C, respectively. 40 Ar 39 Ar age-spectrum analysis of a hydrothermally treated biotite yields a complex release pattern casting doubt on the general usefulness of such measurements for geochronological purposes.

The Energy-Water Nexus in Texas

Understanding the nexus between energy and water - water used for energy and energy used for water - has become increasing important in a changing world. As growing populations demand more energy supplies and water resources, research aims to analyze the interconnectedness of these two resources. Our study sought to quantify the energy-water relationship in Texas, specifically the relationship between electricity generation and water resources as it pertains to policy and society. We examined the water requirements for various types of electricity generating facilities, for typical systems both nationwide and in Texas. We also addressed the energy requirements of water supply and wastewater treatment systems, comparing national averages with Texas-specific values. Analysis of available data for Texas reveals that approximately 595,000 megaliters of water annually - enough water for over three million people for a year - are consumed by cooling the states thermoelectric power plants while generating approximately 400 terawatt-hours of electricity. At the same time, each year Texas uses an estimated 2.1 to 2.7 terawatt- hours of electricity for water systems and 1.8 to 2.0 terawatt-hours for wastewater systems - enough electricity for about 100,000 people for a year. In preparing our analysis, it became clear that substantially more site-specific data are necessary for a full understanding of the nature of the energy-water nexus and the sustainability of economic growth in Texas. We recommend that Texas increase efforts to collect accurate data on the withdrawal and consumption of cooling and process water at power plants, as well as data on electricity consumption for public water supply and wastewater treatment plants and distribution systems. The overarching conclusion of our work is that increased efficiency advances the sustainable use of both energy and water. Improving water efficiency will reduce power demand, and improving energy efficiency will reduce water demand. Greater efficiency in usage of either energy or water will help stretch our finite supplies of both, as well as reduce costs to water and power consumers.

ABDOMINAL PIGMENTATION VARIATION IN DROSOPHILA POLYMORPHA: GEOGRAPHIC VARIATION IN THE TRAIT, AND UNDERLYING PHYLOGEOGRAPHY

Abstract Drosophila polymorpha is a widespread species that exhibits abdominal pigmentation variation throughout its range. To gain insight into this variation we combined phenotypic and genotypic data to test a series of nested hypotheses. First, we tested the null hypothesis that geographic variation in pigmentation is due to neutral factors. We used nested clade analysis to examine the distribution of haplotypes from a nuclear and a mitochrondrial locus. Restricted gene flow via isolation by distance, the primary inference of this phylogeographic analysis, was then used to generate and test the hypothesis of increasing average abdominal pigmentation difference with increasing geographic distance. We found no correlation between geographic distance and phenotypic distance. We then tested the hypothesis that pigmentation is affected by environmental differences among localities. We found a significant effect of habitat type on the average abdominal pigmentation phenotype of different localities. Finally, we tested the hypothesis that pigmentation in D. polymorpha is associated with desiccation resistance. We found that dark individuals of both sexes survived significantly longer in a desiccating environment than light individuals. These patterns combined lead us to hypothesize that abdominal pigmentation variation in D. polymorpha is important in mediating the organisms interactions with local ecological factors.

Drought and the water-energy nexus in Texas

Texas experienced the most extreme drought on record in 2011 with up to 100 days of triple digit temperatures resulting in record electricity demand and historically low reservoir levels. We quantified water and electricity demand and supply for each power plant during the drought relative to 2010 (baseline). Drought raised electricity demands/generation by 6%, increasing water demands/consumption for electricity by 9%. Reductions in monitored reservoir storage <50% of capacity in 2011 would suggest drought vulnerability, but data show that the power plants were flexible enough at the plant level to adapt by switching to less water-intensive technologies. Natural gas, now 50% of power generation in Texas, enhances drought resilience by increasing the flexibility of power plant generators, including gas combustion turbines to complement increasing wind generation and combined cycle generators with 30% of cooling water requirements of traditional steam turbine plants. These reductions in water use are projected to continue to 2030 with increased use of natural gas and renewables. Although water use for gas production is controversial, these data show that water saved by using natural gas combined cycle plants relative to coal steam turbine plants is 25‐50 times greater than the amount of water used in hydraulic fracturing to extract the gas.

Structural evolution of the Thor-Odin gneiss dome

Abstract The Thor-Odin dome is a large structural culmination along the eastern margin of the Shuswap terrain. Previous workers have presented divergent models for the origin of the dome. Some have proposed that it is a product of diapiric uprise of material from the lower crust; alternatively, the dome is interpreted to have formed from the interference of later folding. This study presents the results of a detailed analysis of new data on the structure, pattern of strain variation and metamorphic fabric of the dome. These data together with new geochronological and metamorphic phase assemblage information provide the basis for a revised interpretation of the evolution of the Thor-Odin gneiss dome. The pre-doming evolution of the Thor-Odin gneiss dome was characterized by the formation of large-scale nappe structures and the imbrication of Archean basement rocks with the Cambrian and younger cover rock sequence. The first period of deformation (Phase One) consisted of large-scale infolding of the cover rock sequence into the basement rocks. The Pingston fold in the core of the dome is a product of this event. The second period of deformation (Phase Two) was marked by the forcing of wedges of basement into the cores of northerly-directed nappes. These structures had no observable effect on the central core zone, which is here termed the Autochthonous Core Gneiss Domain. The third period of deformation (Phase Three) was co-axial with Phase Two and consisted of imbrication and refolding of the upper levels of the stack of Phase Two nappes. The actual domal shape was formed by fold interference of Phases Four, Five and Six, which were upright, chevron-style, flexural-slip folds with northwest, southwest and northerly-trending axial planes. The “doming” events occurred at upper crustal levels, probably during the Tertiary. Analysis of the strain pattern suggests that little of the total deformational strain is related to these dome-forming deformations. This outline of the events that formed the dome is consistent with the new geochronological results and interpretation of metamorphic phase assemblages. Cordierite-gedrite-sillimanite assemblages, previously interpreted as indicating 1000 MPa pressure, probably formed under reduced water fugacities and 500–700 MPa total pressure. The Thor-Odin gneiss dome thus provides no evidence for lower crustal upwelling related either to dome formation or to the formation of the Rocky Mountain thrust belt.

Control of bithorax complex functions by the segmentation gene fushi tarazu of D. melanogaster

The properties of three dominant alleles of ftz are described. These alleles cause transformations of the first abdominal segment to the third and cause alternate segment pattern deletions that are out of phase with respect to those caused by ftz null alleles. To explain the effects of these mutations, a model is proposed in which ftz+ has two roles: to subdivide the body into parasegments and to activate appropriate bithorax complex functions in alternate parasegments. According to this model, the effects of the novel ftz alleles can be understood as arising from a slight widening of the blastoderm stripes of ftz expression.

Varnish, sediment, and rock controls on spectral reflectance of outcrops in arid regions

Field observations in the Meatiq Dome, Eastern Desert, Egypt, show that amphibolite weathers to form massive outcrops and dense desert pavements that are extensively varnished. Laboratory-based reflectance spectra of representative samples (covering 5 cm 2 ) and spectra extracted from Landsat thematic mapper data (covering 2.25 x ∼10 4 m 2 ) confirm that varnish dominates the reflectance properties of amphibolite outcrops. Field, laboratory, and Landsat data indicate that granite gneiss weathers to expose mainly bare rock, whereas granitic out-crops evolve to a mix of rock and locally generated sediment. Penetrative foliation in quartz phyllonite leads to production of slab-shaped clasts that cover the surface. The data show that mass wasting of the slabs results in a mix of rock, varnish, and sediment exposures. Outcrop reflectance properties for arid regions are thus dependent on both rock mineralogy and texture, because both parameters modulate bedrock weathering and erosion.

Energy-Water Nexus in Texas

In “Energy-Water Nexus in Texas”, author Amy Hardberger discusses the water requirements of producing energy in Texas. In the first half of the article she addresses the use of water for energy, the need for energy to access water, and the current energy-water nexus in Texas. The second half of the report focuses on future energy-water use in Texas along with the policy decisions that could affect use. Hardberger stresses the importance of the energy-water nexus in planning and management. Next, she makes several policy recommendations including a requirement water and energy analyses in new power plant applications. In closing, Hardberger reminds the reader that improving water efficiency will help reduce costs to consumers and help further the supply of water and energy.

Controls on Water Use for Thermoelectric Generation: Case Study Texas, U.S.

Large-scale U.S. dependence on thermoelectric (steam electric) generation requiring water for cooling underscores the need to understand controls on this water use. The study objective was to quantify water consumption and withdrawal for thermoelectric generation, identifying controls, using Texas as a case study. Water consumption for thermoelectricity in Texas in 2010 totaled ∼0.43 million acre feet (maf; 0.53 km3), accounting for ∼4% of total state water consumption. High water withdrawals (26.2 maf, 32.3 km3) mostly reflect circulation between ponds and power plants, with only two-thirds of this water required for cooling. Controls on water consumption include (1) generator technology/thermal efficiency and (2) cooling system, resulting in statewide consumption intensity for natural gas combined cycle generators with mostly cooling towers (0.19 gal/kWh) being 63% lower than that of traditional coal, nuclear, or natural gas steam turbine generators with mostly cooling ponds (0.52 gal/kWh). The primary control on water withdrawals is cooling system, with ∼2 orders of magnitude lower withdrawals for cooling towers relative to once-through ponds statewide. Increases in natural gas combined cycle plants with cooling towers in response to high production of low-cost natural gas has greatly reduced water demand for thermoelectric cooling since 2000.

Direct control of antennal identity by the spineless-aristapedia gene of Drosophila

SummaryLoss-of-function mutations in the spineless-aristapedia gene of Drosophila (ssa mutants) cause transformations of the distal antenna to distal second leg, deletions or fusions of the tarsi from all three legs, a general reduction in bristle size, and sterility. Because ssa mutants are pleiotropic, it has been suggested that ss+ has some rather general function and that the ssa antennal transformation is an indirect consequence of perturbations in the expression of other genes that more directly control antennal or second leg identity. Here we test whether the ssa transformation results from aberrant expression of Antennapedia (Antp), a homeotic gene thought to specify directly the identity of the second thoracic segment. We find that Antp−ssa mitotic recombination clones in the distal antenna behave identically to Antp+ssa clones, and are transformed to second leg. This demonstrates that the ssa antennal transformation is independent of Antp+, and suggests that ss+ may itself directly define distal antennal identity. The results also reveal that Antp+ is not required for the development of distal second leg structures, as these develop apparently normally in Antp−ssa antennal clones. Because Antp− mutations cause deletions or transformations that are restricted to proximal structures, whereas ssa alleles cause similar defects that are distally restricted, we suggest that ss+ and Antp+ may play similar, but complementary, roles in the distal and proximal portions of appendages, respectively.