Physical parameters of near-Earth asteroid 1982 DV

Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km.     

Post-solidification cooling and the age of Io's lava flows

The modeling of thermal emission from active lava flows must account for the cooling of the lava after solidification. Models of lava cooling applied to data collected by the Galileo spacecraft have, until now, not taken this into consideration. This is a flaw as lava flows on Io are thought to be relatively thin with a range in thickness from ∼1 to 13 m. Once a flow is completely solidified (a rapid process on a geological time scale), the surface cools faster than the surface of a partially molten flow. Cooling via the base of the lava flow is also important and accelerates the solidification of the flow compared to the rate for the ‘semi-infinite’ approximation (which is only valid for very deep lava bodies). We introduce a new model which incorporates the solidification and basal cooling features. This model gives a superior reproduction of the cooling of the 1997 Pillan lava flows on Io observed by the Galileo spacecraft. We also use the new model to determine what observations are necessary to constrain lava emplacement style at Loki Patera. Flows exhibit different cooling profiles from that expected from a lava lake. We model cooling with a finite-element code and make quantitative predictions for the behavior of lava flows and other lava bodies that can be tested against observations both on Io and Earth. For example, a 10-m-thick ultramafic flow, like those emplaced at Pillan Patera in 1997, solidifies in ∼450 days (at which point the surface temperature has cooled to ∼280 K) and takes another 390 days to cool to 249 K. Observations over a sufficient period of time reveal divergent cooling trends for different lava bodies [examples: lava flows and lava lakes have different cooling trends after the flow has solidified (flows cool faster)]. Thin flows solidify and cool faster than flows of greater thickness. The model can therefore be used as a diagnostic tool for constraining possible emplacement mechanisms and compositions of bodies of lava in remote-sensing data.     

The arsenic source term for an in-pit uranium mine tailings facility and its long-term impact on the regional groundwater

Detailed field sampling and analyses and laboratory-based diffusion-cell experiments were used in conjunction with 3-D reactive transport modeling (MODFLOW and MT3D99) to quantify the fate and long-term (10 ka) transport of As in the Rabbit Lake In-pit Tailings Management Facility (RLITMF), northern Saskatchewan, Canada. The RLITMF (300 m × 425 m × 90 m thick) was engineered to ensure solute transport within the RLITMF is dominated by diffusion. Concentrations of As in the tailings pore fluids ranged from 0.24 to 140 mg/L (n = 43). Arsenic speciation analyses indicate 90% of this arsenic exists as As⁵⁺. This observation is supported by pH–Eh measurements of pore fluids (n = 135). Geochemical analyses yielded a strong inverse correlation between the Fe/As molar ratio in the tailings solids and the corresponding concentration of dissolved As, which is attributed to the adsorption of As to secondary 2-line ferrihydrite present in the tailings. Diffusion-cell testing yielded values for the effective diffusion coefficient, sorption coefficient, and effective porosity of As in the tailings of 4.5 × 10⁻¹⁰ m²/s, 2–4 cm³/g and 0.36, respectively. Reactive transport simulations using the field and laboratory data show adsorption of As to the tailings and diffusive transport of dissolved As in the tailings should reduce the source term concentration of As to between 40% and 70% of the initial concentrations over the 10 ka simulation period. Based on these simulations, the As concentrations in the regional groundwater, 50 m down gradient of the tailings facility, should be maintained at background concentrations of 0.001 mg/L over the 10 ka period. These findings suggest the engineered in-pit disposal of U mine tailings can provide long-term protection for the local groundwater regime from As contamination.     

Characterizing Observed Environmental Variability With HF Doppler Radar Surface Current Mappers and Acoustic Doppler Current Profilers: Environmental Variability in the Coastal Ocean

A network of high-frequency (HF) radars is deployed along the New Jersey coast providing synoptic current maps across the entire shelf. These data serve a variety of user groups from scientific research to Coast Guard search and rescue. In addition, model forecasts have been shown to improve with surface current assimilation. In all applications, there is a need for better definitions and assessment of the measurement uncertainty. During a summer coastal predictive skill experiment in 2001, an array of in situ current profilers was deployed near two HF radar sites, one long-range and one standard-range system. Comparison statistics were calculated between different vertical bins on the same current profiler, between different current profilers, and between the current profilers and the different HF radars. The velocity difference in the vertical and horizontal directions were then characterized using the observed root-mean-square (rms) differences. We further focused on two cases, one with relatively high vertical variability, and the second with relatively low vertical variability. Observed differences between the top bin of the current profiler and the HF radar were influenced by both system accuracy and the environment. Using the in situ current profilers, the environmental variability over scales based on the HF radar sampling was quantified. HF radar comparisons with the current profilers were on the same order as the observed environmental difference over the same scales, indicating that the environment has a significant influence on the observed differences. Velocity variability in the vertical and horizontal directions both contribute to these differences. When the potential effects of the vertical variability could be minimized, the remaining difference between the current profiler and the HF radar was similar to the measured horizontal velocity difference (~2.5 cm/s) and below the resolution of the raw radial data at the time of the deployment     

Spring and summer phytoplankton communities in the Chukchi and Eastern Beaufort Seas

Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios.     

Dislocations in CaTiO3 perovskite deformed at high-temperature: a transmission electron microscopy study

Dislocation configurations in natural single crystals of CaTiO₃ perovskite deformed in high-temperature creep were examined and characterized by transmission electron microscopy. Screw dislocations with Burgers vector [100]_pc and [011]_pc, dissociated on the $(01\bar 1)_{{\text{pc}}} $ plane, form rectangular networks with extended four-fold nodes in the shape of octagons, a configuration never observed in any of the previously investigated perovskites, except CaGeO₃. Screw dislocations with Burgers vector [101]_pc and $(\bar 101)_{{\text{pc}}} $ , on the (010)_pc plane, react to form a twist wall; the dislocations with Burgers vector [002] produced by the reaction decompose into two perfect dislocations [001]_pc. This results in a new configuration, never observed before, with three-fold nodes at the corners of rectangles. Both the octagonal extended nodes and the junctions decomposed into perfect dislocations are seen in samples deformed indifferently by slip on {100}_pc or {110}_pc planes, but they seem to appear only above 1520 K, in the cubic phase.     

The anthracite smokers of eastern pennsylvania: PS2 (g)P_{S_2 (g)} -T stability diagram by TL analysis

Coal seams and culm banks associated with mine fires in the anthracite region of eastern Pennsylvania have been burning for decades. Many of the fires may have ignited by spontaneous combustion or by the burning of trash. Minerals associated with the combustion of anthracite form by the condensation of gas exhaled through surficial gas vents or anthracite smokers. A Pressure-Temperature (P-T) stability diagram is constructed for the condensation of orthorhombic sulfur from anthracite gas using Thermodynamic Loop Analysis (TL analysis). This method of analyzing chemical systems incorporates Kirchhoff's Law into a four step procedure structured around a closed thermodynamic cycle or thermodynamic loop. The four steps, referred to us The Four S S of Thermodynamic Loop Analysis, include: (1) Set Up—graphical characterization of the problem. (2) Sum—the application of thermodynamic principles. (3) Substitute—the use of materials data available from the literature, and (4) Solve—computation of one or more variables. The example presented demonstrates that thermodynamic loops can incorporate any number of polymorphic phase transformations. In addition, thermodynamic loop analysis is applicable to any geologic process involving the condensation of minerals from a gas. The stability diagram derived by TL analysis may have applicability in monitoring the release of sulfur gas into the atmosphere.