Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph Polarimetric Calibration

We present a polarimetric characterization and correction for the Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph (SOHO/LASCO) C2 and C3 white light coronagraphs. By measuring the uncorrected polarization angles in solar minimum C2 coronal images, we have determined that the coronagraph acts as an optical phase retarder which converts a small fraction of the incoming radiation polarization from linear to circular. In addition, from the measurements of polarization angle in C3 coronal images we have determined that a component of the instrumentally scattered light in that instrument is polarized. We infer the retardation angle for C2 and compute the corresponding Mueller matrix, and determine the polarized stray light spatial profile in C3. The C2 Mueller matrix and C3 polarized stray light profiles are used to correct for instrumental effects in solar minimum coronal observations to obtain polarized brightness between two and thirty-two solar radii, which show deep polar coronal holes extending to the limit of the field of view.     

Rapid inactivation of seven Bacillus spp. under simulated Mars UV irradiation

Seven Bacillus spp. were exposed to simulations of Mars-normal UV fluence rates in order to study the effects of UV irradiation on microbial survival. A UV illumination system was calibrated to deliver 9.78 W m⁻² (35.2 kJ m⁻² h⁻¹) of UVC + UVB irradiation (200-320 nm) to microbial samples, thus creating a clear-sky simulation (0.5 optical depth) of equatorial Mars. The Bacillus spp. studied were: B. licheniformis KL-196, B. megaterium KL-197, B. nealsonii FO-092, B. pumilus FO-36B, B. pumilus SAFR-032, B. subtilis 42HS1, and B. subtilis HA101. The bacteria were prepared as thin monolayers of endospores on aluminum coupons in order to simulate contaminated spacecraft surfaces. Bacterial monolayers were exposed to Mars UV irradiation for time-steps of 0, 0.25, 0.5, 1, 5, 15, 30, 60, 120, or 180 min. The surviving endospores were then assayed with a Most Probable Numbers (MPN) procedure and with a culture-based assay that utilized a bacillus spore germination medium. Results indicated that B. pumilus SAFR-032 was the most resistant, and B. subtilis 42HS-1 and B. megaterium were the most sensitive of the seven strains exposed to martian UV fluence rates. Bacillus subtilis 42HS1 and B. megaterium were inactivated after 30 min exposure to Mars UV, while B. pumilus SAFR-032 required 180 min for full inactivation in both assays. Spores of B. pumilus SAFR-032 exhibited significantly different inactivation kinetics suggesting that this wild type isolate also was more resistant than the standard dosimetric strain, B. subtilis HA101. Although the various Bacillus spp. exhibited diverse levels of UV resistance, none were immune to UV irradiation, and, thus, all species would be expected to be inactivated on Sun-exposed spacecraft surfaces within a few tens-of-minutes to a few hours on sol 1 under clear-sky conditions on equatorial Mars. The inactivation kinetics of all seven Bacillus spp. support the conclusion that significant levels of bioload reductions are possible on Sun-exposed spacecraft surfaces in very short time periods under clear-sky conditions on Mars. However, the presence of UV resistant microbes on spacecraft surfaces rapidly covered in dust during landing operations, and non-Sun-exposed surfaces of spacecraft remain concerns that must continue to be addressed through adequate spacecraft sanitizing procedures prior to launch.     

The influence of groundwater abstraction on interpreting climate controls and extreme recharge events from well hydrographs in semi-arid South Africa

There is a scarcity of long-term groundwater hydrographs from sub-Saharan Africa to investigate groundwater sustainability, processes and controls. This paper presents an analysis of 21 hydrographs from semi-arid South Africa. Hydrographs from 1980 to 2000 were converted to standardised groundwater level indices and rationalised into four types (C1–C4) using hierarchical cluster analysis. Mean hydrographs for each type were cross-correlated with standardised precipitation and streamflow indices. Relationships with the El Niño–Southern Oscillation (ENSO) were also investigated. The four hydrograph types show a transition of autocorrelation over increasing timescales and increasingly subdued responses to rainfall. Type C1 strongly relates to rainfall, responding in most years, whereas C4 notably responds to only a single extreme event in 2000 and has limited relationship with rainfall. Types C2, C3 and C4 have stronger statistical relationships with standardised streamflow than standardised rainfall. C3 and C4 changes are significantly (p <?0.05) correlated to the mean wet season ENSO anomaly, indicating a tendency for substantial or minimal recharge to occur during extreme negative and positive ENSO years, respectively. The range of different hydrograph types, sometimes within only a few kilometres of each other, appears to be a result of abstraction interference and cannot be confidently attributed to variations in climate or hydrogeological setting. It is possible that high groundwater abstraction near C3/C4 sites masks frequent small-scale recharge events observed at C1/C2 sites, resulting in extreme events associated with negative ENSO years being more visible in the time series.

     

Variations in population vulnerability to tectonic and landslide-related tsunami hazards in Alaska

Natural Hazards - Effective tsunami risk reduction requires an understanding of how at-risk populations are specifically vulnerable to tsunami threats. Vulnerability assessments primarily have been...     

Geochemical indicators of interbasin groundwater flow within the southern Rio Grande Valley, southwestern USA

Increased groundwater withdrawals for the growing population in the Rio Grande Valley and likely alteration of recharge to local aquifers with climate change necessitates an understanding of the groundwater connection between the Jornada del Muerto Basin and the adjoining and more heavily used aquifer in the Mesilla Basin. Separating the Jornada and Mesilla aquifers is a buried bedrock high from Tertiary intrusions. This bedrock high or divide restricts and/or retards interbasin flow from the Jornada aquifer into the Mesilla aquifer. The potentiometric surface of the southern Jornada aquifer near part of the bedrock high indicates a flow direction away from the divide because of a previously identified damming effect, but a groundwater outlet from the southern Jornada aquifer is necessary to balance inputs from the overall Jornada aquifer. Differences in geochemical constituents (major ions, δD, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr) indicate a deeper connection between the two aquifers through the Tertiary intrusions where Jornada water is geochemically altered because of a geothermal influence. Jornada groundwater likely is migrating through the bedrock high in deeper pathways formed by faults of the Jornada Fault Zone, in addition to Jornada water that overtops the bedrock high as previously identified as the only connection between the two aquifers. Increased groundwater withdrawals and lowering of the potentiometric surface of the Jornada aquifer may alter this contribution ratio with less overtopping of the bedrock high and a continued deeper flowpath contribution that could potentially increase salinity values in the Mesilla Basin near the divide.     

Geometallurgical Modeling at Olympic Dam Mine, South Australia

Modeling of geometallurgical variables is becoming increasingly important for improved management of mineral resources. Mineral processing circuits are complex and depend on the interaction of a large number of properties of the ore feed. At the Olympic Dam mine in South Australia, plant performance variables of interest include the recovery of Cu and U₃O₈, acid consumption, net recovery, drop weight index, and bond mill work index. There are an insufficient number of pilot plant trials (841) to consider direct three-dimensional spatial modeling for the entire deposit. The more extensively sampled head grades, mineral associations, grain sizes, and mineralogy variables are modeled and used to predict plant performance. A two-stage linear regression model of the available data is developed and provides a predictive model with correlations to the plant performance variables ranging from 0.65–0.90. There are a total of 204 variables that have sufficient sampling to be considered in this regression model. After developing the relationships between the 204 input variables and the six performance variables, the input variables are simulated with sequential Gaussian simulation and used to generate models of recovery of Cu and U₃O₈, acid consumption, net recovery, drop weight index, and bond mill work index. These final models are suitable for mine and plant optimization.