Simulated Annealing and Bayesian Posterior Distribution Analysis Applied to Spectral Emission Line Fitting

Spectral-line fitting problems are extremely common in all remote-sensing disciplines, solar physics included. Spectra in solar physics are frequently parameterized by using a model for the background and the emission lines, and various computational techniques are used to find values to the parameters given the data. However, the most commonly-used techniques, such as least-squares fitting, are highly dependent on the initial parameter values used and are therefore biased. In addition, these routines occasionally fail because of ill-conditioning. Simulated annealing and Bayesian posterior distribution analysis offer different approaches to finding parameter values through a directed, but random, search of the parameter space. The algorithms proposed here easily incorporate any other available information about the emission spectrum, which is shown to improve the fit. Example algorithms are given and their performance is compared to a least-squares algorithm for test data – a single emission line, a blended line, and very low signal-to-noise-ratio data. It is found that the algorithms proposed here perform at least as well or better than standard fitting practices, particularly in the case of very low signal-to-noise ratio data. A hybrid simulated annealing and Bayesian posterior algorithm is used to analyze a Mg x line contaminated by an O IV triplet, as observed by the Coronal Diagnostic Spectrometer onboard SOHO. The benefits of these algorithms are also discussed.     

The probable extragalactic nature of some low surface brightness clouds at high galactic latitude

Low surface brightness clouds observed at optical, infrared, and radio wavelengths are discussed. We present evidence that some clouds at high galactic latitudes are associated with the Local Group, M81, and possibly even with higher redshift extragalactic objects.Low temperature clouds at high latitude must affect at some level the short wave length side of the cosmic background radiation. If some of these clouds are extragalactic there should be a further effect on the interpretation of CBR measures.     

Phase-mixing in Dissipative Alfvén Waves

The phase-mixing mechanism first proposed as a coronal heating mechanism by Heyvaerts and Priest (1983) is examined using a length-scale analysis adapted from Cally (1991). This allows parameter ranges other than those studied by Heyvaerts and Priest (1983) to be described, together with a detailed examination of the transfer of energy to both longer and shorter length-scales as the Alfvén wave front evolves in the solar corona. The results of Heyvaerts and Priest (1983) are largely confirmed, but with some notable differences. Energy initially at smaller length-scales decays faster than their rate, because the plasma is more strongly dissipative at smaller length-scales. The full inclusion of diffusion across field lines also leads to smoother Alfvén wavefronts.     

COCORP deep seismic reflection traverses of the U.S. Cordillera

Summary. COCORP seismic reflection traverses of the U.S. Cordillera at 40°N and 48.5°N latitude reveal some fundamental similarities as well as significant differences in reflection patterns. On both traverses, autochthonous crust beneath thin-skinned thrust belts of the eastern part of the Cordillera is unreflective; immediately to the west the Cordilleran interior is very reflective above a flat, prominent reflection Moho. Mesozoic accreted terranes in the western part of the orogen are underlain on both traverses by very complex reflection patterns, in constrast to more easily deciphered patterns beneath areas of Cenozoic accretion. The prominent reflection Moho beneath the orogenic interior on both transects probably evolved through a combination of magmatic and deformational processes during Cenozoic extension. The main differences between the two traverses lie in the reflection patterns of the middle and lower crust in the Cordilleran interior; these differences are probably related to the way Cenozoic extension was accommodated at depth. Laminated middle and lower crust above the reflection Moho in the western Basin and Range (40°N) may be related to magmatism, ductile pure shear and large-scale transposition during Cenozoic extension. By contrast, beneath the eastern Basin and Range (40°N), and the orogenic interior in the NW United States (48.5°N), Cenozoic extension was probably accommodated along dipping deformation zones throughout the crust.     

Numerical simulations of rotating cooling flows in galaxy cluster environments

We have used 2D numerical simulations to study the evolution of galaxy cluster cooling flows undergoing a rotational perturbation. We show that such rotations in the intracluster medium may arise from cluster/subcluster mergers. Our galaxy cluster initial conditions involve spherically symmetric, steady-state cooling flows with varying mass-dropout strengths. The rotational perturbation serves to break the symmetry for each of the initial cooling flows, resulting in the formation of thin, gaseous disc-like structure extending radially out to ∼10 kpc. Disc-like structure formed for low mass-dropout strength simulations appears to contain cooling condensations whereas disc-like structure in higher mass-dropout strength simulations appears smooth. This is due to the influence of mass-dropout on the degree of cooling, which serves to reduce the strength of thermal instabilities by the removal of 'cold' gas from the flow. Morphological comparisons of the disc-like structure formed in our simulations are made to structure observed in the X-ray emitting gas of A4059. Comparisons of the gas dynamics within the disc-like structure are also made to the solid-body rotation profile observed from emission-line gas within the central galaxy of Hydra A. The influence of grid effects on the simulations is also discussed.     

Significance of cytochrome P450 system responses and levels of bile fluorescent aromatic compounds in marine wildlife following oil spills

The relationships among cytochrome P450 induction in marine wildlife species, levels of fluorescent aromatic compounds (FAC) in their bile, the chemical composition of the inducing compounds, the significance of the exposure pathway, and any resulting injury, as a consequence of exposure to crude oil following a spill, are reviewed. Fish collected after oil spills often show increases in cytochrome P450 system activity, cytochrome P4501A (CYP1A) and bile fluorescent aromatic compounds (FAC), that are correlated with exposure to polycyclic aromatic hydrocarbons (PAH) in the oil. There is also some evidence for increases in bile FAC and induction of cytochrome P450 in marine birds and mammals after oil spills. However, when observed, increases in these exposure indicators are transitory and generally decrease to background levels within one year after the exposure. Laboratory studies have shown induction of cytochrome P450 systems occurs after exposure of fish to crude oil in water, sediment or food. Most of the PAH found in crude oil (dominantly 2- and 3-ring PAH) are not strong inducers of cytochrome P450. Exposure to the 4-ring chrysenes or the photooxidized products of the PAH may account for the cytochrome P450 responses in fish collected from oil-spill sites. The contribution of non-spill background PAH, particularly combustion-derived (pyrogenic) PAH, to bile FAC and cytochrome P450 system responses can be confounding and needs to be considered when evaluating oil spill effects. The ubiquity of pyrogenic PAH makes it important to fully characterize all sources of PAH, including PAH from natural resources, e.g. retene, in oil spill studies. In addition, such parameters as species, sex, age, ambient temperature and season need to be taken into account. While increases in fish bile FAC and cytochrome P450 system responses, can together, be sensitive general indicators of PAH exposure after an oil spill, there is little unequivocal evidence to suggest a linkage to higher order biological effects, e.g. toxicity, lesions, reproductive failure.     

Early Diagenesis of Plant Pigments in Hudson River Sediments

Plant pigment concentrations were measured using high performance liquid chromatography in Hudson River sediments. Sedimentation rates and mixing characteristics were determined from depth profiles of the naturally occurring radionuclides ⁷Be, ²¹⁰Pb. Previous estimates of the mean-lives (1/λ) of plant pigments (chlorophylls a and b, fucoxanthin) from laboratory experiments, indicate a range of c. 20-40 days. However, in the field, we observed that these pigments decreased less rapidly with depth and penetrated deeper than ⁷Be (mean-life 77 days) in Hudson sediments 95% of the time. Assuming similar mixing processes for particles carrying ⁷Be and pigments, this indicates that pigment decay rates in the field are slower than the 0·013 day^-1 decay rate of ⁷Be, hence, more than 2-fold slower than the derived laboratory rates. We believe that high inputs of vascular plant detritus in the Hudson may increase the complexation of humic substances with pigments resulting in slower decay rates.While most pigments showed an exponential decrease with sediment depth, lutein concentrations generally increased with depth. This pattern of decay resistance is in agreement with laboratory experiments which show that lutein is the most decay resistant among dominant pigments. These data along with other studies demonstrate that the carotenoids lacking the 5,6-epoxide group (i.e., lutein) are more decay resistant than pigments that contain it (i.e., fucoxanthin).     

Burial dolomitization driven by modified seawater and basal aquifer‐sourced brines: Insights from the Middle and Upper Devonian of the Western Canadian Sedimentary Basin

Dolomitization in the Western Canadian Sedimentary Basin has been extensively researched, producing vast geochemical datasets. This provides a unique opportunity to assess the regional sources and flux of dolomitizing fluids on a larger scale than previous studies. A meta‐analysis was conducted on stable isotope, strontium isotope (⁸⁷Sr/⁸⁶Sr), fluid inclusion and lithium‐rich formation water data published over 30 years, with new petrographic, X‐ray diffraction, stable isotope and rare‐earth element (REE+Y) data. The Middle to Upper Devonian Swan Hills Formation, Leduc Formation and Wabamun Group contain replacement dolomite (RD) cross‐cut by stylolites, suggesting replacement dolomitization occurred during shallow burial. Stable isotope, REE+Y and ⁸⁷Sr/⁸⁶Sr data indicate RD formed from Devonian seawater, then recrystallized during burial. Apart from the Wabamun Group of the Peace River Arch (PRA), saddle dolomite cement (SDC) is more δ¹⁸O_(PDB) depleted than RD, and cross‐cuts stylolites, suggesting precipitation during deep burial. SDC ⁸⁷Sr/⁸⁶Sr data indicate contributions from ⁸⁷Sr‐rich basinal brines in the West Shale Basin (WSB) and PRA, and authigenic quartz/albite suggests basinal brines interacted with underlying clastic aquifers before ascending faults into carbonate strata. The absence of quartz/albite within dolomites of the East Shale Basin (ESB) suggests dolomitizing fluids only interacted with carbonate strata. We conclude that replacement dolomitization resulted from connate Devonian seawater circulating through aquifers and faults during shallow burial. SDC precipitated during deep burial from basinal brines sourced from basal carbonates (ESB) and clastic aquifers (WSB, PRA). Lithium‐rich formation waters suggest basinal brines originated as residual evapo‐concentrated Middle Devonian seawater that interacted with basal aquifers and ascended faults during the Antler and Laramide Orogenies. These results corroborate those of previous studies but are verified by new integrated analysis of multiple datasets. New insights emphasize the importance of basal aquifers and residual evapo‐concentrated seawater in dolomitization, which is potentially applicable to other regionally dolomitized basins.     

Size Matters to Lesbians,Too: Queer Feminist Interventions into the Scale of Big Data

How can we recognize those whose lives and data become attached to the far-from-groundbreaking framework of “small data”? Specifically, how can marginalized people who do not have the resources to produce, self-categorize, analyze, or store “big data” claim their place in the big data debates? I examine the place of lesbians and queer women in the big data debates through the Lesbian Herstory Archive's not “big” enough lesbian, gay, bisexual, trans, and queer (LGBTQ) organizing history data set—perhaps the largest data set known to exist on LGBTQ activist history—as one such alternative. In a contribution to critical data studies, I take a queer feminist approach to the scale of big data by reading for the imbricated scales and situated knowledge of data.