RAT J1953+1859: a dwarf nova discovered through high amplitude QPOs in quiescence

We report the discovery of an accreting binary, RAT J1953+1859, made during the RApid Temporal Survey (RATS) on the Isaac Newton Telescope. It showed high amplitude (0.3 mag) quasi-periodic oscillations on a time-scale of ∼20 min. Further observations made using the Nordic Optical Telescope showed it to be ∼4 mag brighter than in the discovery images. These photometric observations, together with radial velocity data taken using the William Herschel Telescope, point to an orbital period of ∼90 min. These data suggest that RAT J1953+1859 is a dwarf novae of the SU UMa type. What makes RAT J1953+1859 unusual is that it is the first such system to be discovered as a result of high amplitude QPOs during quiescence. This suggests that high-cadence wide-field surveys could be another means to discover cataclysmic variables as a result of their short period variability.     

Biogeochemical transformation of Fe minerals in a petroleum-contaminated aquifer

The Bemidji aquifer in Minnesota, USA is a well-studied site of subsurface petroleum contamination. The site contains an anoxic groundwater plume where soluble petroleum constituents serve as an energy source for a region of methanogenesis near the source and bacterial Fe(III) reduction further down gradient. Methanogenesis apparently begins when bioavailable Fe(III) is exhausted within the sediment. Past studies indicate that Geobacter species and Geothrix fermentens-like organisms are the primary dissimilatory Fe-reducing bacteria at this site. The Fe mineralogy of the pristine aquifer sediments and samples from the methanogenic (source) and Fe(III) reducing zones were characterized in this study to identify microbiologic changes to Fe valence and mineral distribution, and to identify whether new biogenic mineral phases had formed. Methods applied included X-ray diffraction; X-ray fluorescence (XRF); and chemical extraction; optical, transmission, and scanning electron microscopy; and Mössbauer spectroscopy.All of the sediments were low in total Fe content (≈ 1%) and exhibited complex Fe-mineralogy. The bulk pristine sediment and its sand, silt, and clay-sized fractions were studied in detail. The pristine sediments contained Fe(II) and Fe(III) mineral phases. Ferrous iron represented approximately 50% of Fe_TOT. The relative Fe(II) concentration increased in the sand fraction, and its primary mineralogic residence was clinochlore with minor concentrations found as a ferroan calcite grain cement in carbonate lithic fragments. Fe(III) existed in silicates (epidote, clinochlore, muscovite) and Fe(III) oxides of detrital and authigenic origin. The detrital Fe(III) oxides included hematite and goethite in the form of mm-sized nodular concretions and smaller-sized dispersed crystallites, and euhedral magnetite grains. Authigenic Fe(III) oxides increased in concentration with decreasing particle size through the silt and clay fraction. Chemical extraction and Mössbauer analysis indicated that this was a ferrihydrite like-phase. Quantitative mineralogic and Fe(II/III) ratio comparisons between the pristine and contaminated sediments were not possible because of textural differences. However, comparisons between the texturally-similar source (where bioavailable Fe(III) had been exhausted) and Fe(III) reducing zone sediments (where bioavailable Fe(III) remained) indicated that dispersed detrital, crystalline Fe(III) oxides and a portion of the authigenic, poorly crystalline Fe(III) oxide fraction had been depleted from the source zone sediment by microbiologic activity. Little or no effect of microbiologic activity was observed on silicate Fe(III). The presence of residual “ferrihydrite” in the most bioreduced, anoxic plume sediment (source) implied that a portion of the authigenic Fe(III) oxides were biologically inaccessible in weathered, lithic fragment interiors. Little evidence was found for the modern biogenesis of authigenic ferrous-containing mineral phases, perhaps with the exception of thin siderite or ferroan calcite surface precipitates on carbonate lithic fragments within source zone sediments.     

Evidence of biogeomorphic patterning in a low‐relief karst landscape

Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self‐reinforcing processes at local scales expand patches, while self‐inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short‐hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil‐surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism. Copyright © 2014 John Wiley & Sons, Ltd.     

Organochlorine contaminant exposure and associations with hematological and humoral immune functional assays with dam age as a factor in free-ranging northern fur seal pups (Callorhinus ursinus)

Potential effects of organochlorine contaminant (OC) exposure on humoral immune function and health of free-ranging northern fur seals were investigated. Forty-two "neonates" were captured for blood sample collection and re-sampled as "pups" 29-51 days later. OCs were extracted from whole blood to identify polychlorinated biphenyl congeners and chlorinated pesticides by high performance liquid chromatography. Humoral immune function was assessed by antibody responses to vaccination and immunoglobulin concentrations. Additional health status indicators included leukocyte counts and haptoglobin concentrations. Mean OC concentrations were higher in neonates than at recapture. Neonates of young dams had higher mean OC concentrations than neonates of older dams. A higher proportion of old dam's pups developed a twofold or greater increase in antigen-specific antibodies compared to young dam's pups. Higher OC exposure and poor immune responses in first-born pups may indicate a higher risk of secondary morbidity and mortality than pups of multiparous dams.     

Surf zone characterization from Unmanned Aerial Vehicle imagery

We investigate the issues and methods for estimating nearshore bathymetry based on wave celerity measurements obtained using time series imagery from small unmanned aircraft systems (SUAS). In contrast to time series imagery from fixed cameras or from larger aircraft, SUAS data are usually short, gappy in time, and unsteady in aim in high frequency ways that are not reflected by the filtered navigation metadata. These issues were first investigated using fixed camera proxy data that have been intentionally degraded to mimic these problems. It has been found that records as short as 50 s or less can yield good bathymetry results. Gaps in records associated with inadvertent look-away during unsteady flight would normally prevent use of the required standard Fast Fourier Transform methods. However, we found that a full Fourier Transform could be implemented on the remaining valid record segments and was effective if at least 50% of total record length remained intact. Errors in image geo-navigation were stabilized based on fixed ground fiducials within a required land portion of the image. The elements of a future method that could remove this requirement were then outlined. Two test SUAS data runs were analyzed and compared to survey ground truth data. A 54-s data run at Eglin Air Force Base on the Gulf of Mexico yielded a good bathymetry product that compared well with survey data (standard deviation of 0.51 m in depths ranging from 0 to 4 m). A shorter (30.5 s) record from Silver Strand Beach (near Coronado) on the US west coast provided a good approximation of the surveyed bathymetry but was excessively deep offshore and had larger errors (1.19 m for true depths ranging from 0 to 6 m), consistent with the short record length. Seventy-three percent of the bathymetry estimates lay within 1 m of the truth for most of the nearshore.     

DME/TACAN interference mitigation for GNSS: algorithms and flight test results

The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm.     

Identifying Aquifer Type in Fractured Rock Aquifers using Harmonic Analysis

Determining aquifer type, unconfined, semi‐confined, or confined, by drilling or performing pumping tests has inherent problems (i.e., cost and complex field issues) while sometimes yielding inconclusive results. An improved method to cost‐effectively determine aquifer type would be beneficial for hydraulic mapping of complex aquifer systems like fractured rock aquifers. Earth tides are known to influence water levels in wells penetrating confined aquifers or unconfined thick, low‐porosity aquifers. Water‐level fluctuations in wells tapping confined and unconfined aquifers are also influenced by changes in barometric pressure. Harmonic analyses of water‐level fluctuations of a thick (～1000 m) carbonate aquifer located in south‐central Oklahoma (Arbuckle‐Simpson aquifer) were utilized in nine wells to identify aquifer type by evaluating the influence of earth tides and barometric‐pressure variations using signal identification. On the basis of the results, portions of the aquifer responded hydraulically as each type of aquifer even though there was no significant variation in lithostratigraphy. The aquifer type was depth dependent with confined conditions becoming more prevalent with depth. The results demonstrate that harmonic analysis is an accurate and low‐cost method to determine aquifer type.     

Upper limits for H2SO4 in the mesosphere of Venus

Rapid temporal variability of SO₂ and SO in the Venus 85–100 km mesosphere (Sandor, B.J., Clancy, R.T., Moriarty-Schieven G.H. [2007]. Bull. Am. Astron. Soc. 39, 503; Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60) requires in situ sources and sinks for these molecules. While many loss mechanisms are recognized, no process for in situ production is known. Observational investigations to find, or constrain other potential sulfur reservoirs offer one method toward understanding the applicable photochemistry. Here, we report upper limits for gas-phase H₂SO₄ (sulfuric acid) abundances in Venus’ 85–100 km upper mesosphere, derived from 16 ground-based sub-mm spectroscopic observations in the period 2004–2008. Unlike the ubiquitous sulfuric acid solid/liquid aerosol, the gas phase would be photochemically active, potentially both source and sink for SO and SO₂. H₂SO₄ is retrieved from sub-mm lines located in the same bandpass as the SO₂ and SO lines described by Sandor et al. (Sandor, B.J., Clancy, R.T., Moriarty-Schieven, G.H., Mills, F.P. [2010]. Icarus 208, 49–60). H₂SO₄ upper limits reported here are thus simultaneous and spatially coincident with measurements of SO₂ and SO, providing for analysis of the three sulfur species collectively. The average H₂SO₄ abundance over 16 observations is 1 ± 2 ppb (i.e. <3 ppb). Upper limits for individual observations range from 3 to 44 ppb, where quality of the observing weather is the dominant constraint on measurement precision. The sum of H₂SO₄, SO₂ and SO varies widely. In one comparison, the sum [H₂SO₄ + SO₂ + SO] measured on one date differs by 10-σ from the sum measured 2 months later. We conclude that upper mesospheric sulfur atoms are not conserved among the three molecules, that H₂SO₄ is not a significant sulfur reservoir for balancing the observed variations of [SO₂ + SO], and is not relevant to the (still unknown) photochemistry responsible for observed behavior of SO₂ and SO. Having ruled out H₂SO₄, we infer that elemental sulfur is the most probable candidate for the needed third reservoir.     

A case of offshore convective initiation by interacting land breezes near Darwin, Australia

A case of offshore convective initiation by interacting land breezes near Darwin, Australia is investigated using convection-permitting model simulations, radar-derived precipitation observations, thermodynamic profiles from radiosonde soundings and surface measurements. These analyses elucidate the convergence of two land breezes in the Van Diemen Gulf, one originating from the Tiwi Islands and the other from mainland Australia; the convergence is sufficient to initiate a line of convection that forms parallel to the mainland coast in the early morning. While differing in small-scale features, the modeled system shows reasonably good agreement with the observed precipitation accumulations. However, using simulations with different initialization times and examining a second case, it is shown that the representation of the land-breeze system and subsequent convective initiation is very sensitive to the upstream wind and thermodynamic conditions, making correct simulation of these processes challenging.