Modeling benzene plume elongation mechanisms exerted by ethanol using RT3D with a general substrate interaction module

Copyright © 2008 American Geophysical Union (AGU)A mathematical model was developed to evaluate the effect of the common fuel additive ethanol on benzene fate and transport in fuel-contaminated groundwater and to discern the most influential benzene plume elongation mechanisms. The model, developed as a module for the Reactive Transport in 3 Dimensions (RT3D) model, includes commonly considered fate and transport processes (advection, dispersion, adsorption, biodegradation, and depletion of molecular oxygen during biodegradation) and substrate interactions previously not considered (e.g., a decrease in the specific benzene utilization rate due to metabolic flux dilution and/or catabolite repression) as well as microbial population shifts. Benzene plume elongation predictions, based on literature model parameters, were on the order of 40% for a constant source of E10 gasoline (10% vol/vol ethanol), which compares favorably to field observations. For low benzene concentrations (<1 mg/L), oxygen depletion during ethanol degradation was the principal mechanism hindering benzene natural attenuation. For higher benzene concentrations (exerting an oxygen demand higher than the available dissolved oxygen), metabolic flux dilution was the dominant plume elongation process. If oxygen were not limiting, as might be the case in zones undergoing aerobic biostimulation, model simulations showed that microbial growth on ethanol could offset negative substrate interactions and enhance benzene degradation, resulting in shorter plumes than baseline conditions without ethanol

Equilibrium Climate Sensitivity and the Relative Weightings of Various Climate Forcings on Local Temperature Records

Thesis advisor: Jeremy ShakunAs recently measured amounts of global atmospheric carbon dioxide concentrations have risen 40% from pre-Industrial levels and will likely reach double by mid-century, climate scientists have expressed concern over the future state of the climate system, and have attempted to gauge the consequences of such a large forcing. The principal parameter for climate scientists is equilibrium climate sensitivity, which is the change in temperature following a doubling of atmospheric CO2 concentrations. Current estimates of climate sensitivity span too expansive of a range to provide a clear understanding of the magnitude of temperature changes one can expect. Therefore, I conduct many individual multivariate analyses as a means of narrowing these ranges of sensitivity and to investigate geographical distributions of sensitivity, at the very least. To do so, I analyze four major climate forcings: greenhouse gas, atmospheric dust, ice volume, and insolation. Using several multiple linear regressions, I calculate the relative weighting of each forcing in driving the temperature signal in 47 local temperature proxy records. The paleoclimate proxy records chosen span glacial cycles over the past 800 kyr. These results provide insight into the geographical distributions of the relative influences of each of the forcings, while working to constrain the range of sensitivity estimates through the weighting of the greenhouse gas forcing. Separating out the individual climate inputs allows me to conclude what percentage of climate change was caused by CO2 in the past, and by implication how much warming might be expected due to GHG forcing in the future.Thesis (BS) — Boston College, 2015.Submitted to: Boston College. College of Arts and Sciences.Discipline: Earth and Environmental Sciences

A multi-faceted engineering study of aerodynamic errors of the Service Aircraft Instrumentation Package (SAIP)

The general objectives of this research are to investigate, identify, and quantify the aerodynamic sources of altitude determination errors of the U. S. Navy's Service Aircraft Instrumentation Package (SAIP) and to make recommendations to remedy these errors. This multi-faceted study includes aero- panel methods, computational fluid dynamics (CFD), wind tunnel testing, and flight test evaluations. The Airflow Sensor Assembly (ASA), a device similar to a calibrated pitot static tube, was intended to meet the SAIP's required specifications for altitude determination. However, the ASA is housed in the five inch diameter body of the SAIP and mounted on a variety of host aircraft. The over-pressure generated by the SAIP body as well as the wing/pylon system engulf the static pressure ports creating altitude errors well out of performance limits. This over-pressure associated with these bodies was apparently not accounted for during design and acquisition and extensive modifications will be needed to offset or eliminate their effectsLieutenant, United States NavyApproved for public release; distribution is unlimited

Professional Learning Communities As A Framework For School Counselor Collaboration And Data Use: An Action Research Study

The American School Counselor Association (ASCA) calls on school counselors to take part in collaborative work experiences using data to address problems of practice. School counselors experience professional isolation leading to underperformance (Elliot et al., 2004; Stone-Johnson, 2015). School structures that lack collaborative experiences for school counselors leads to isolation (Bardhoshi et al., 2014). The purpose of this action research study was to assess the influence of a professional learning community (PLC) on the perceptions of school counselors to perform the elements of a PLC, their use of data to solve problems of practice, and their perceptions of benefits and challenges to collaboration within a PLC (DuFour & Eaker, 1998). This qualitative study sought to understand the experiences of 6 high school counselors in one suburban school district as they took part in one cycle of a multicycle action research PLC to address school engagement. Qualitative data sources included semi-structured interviews, PLC transcripts, and one focus group. Data were analyzed using a constant comparative approach. Findings indicate: (a) school counselors perceived themselves as capable of positively contributing to the elements of PLCs, (b) PLCs positively influenced school counselors’ data use to make decisions, and (c) school counselors perceived both benefits and challenges to PLC implementation. Results of this study can be used to understand the influence of PLCs on school counselor practices as they move from isolated practice toward comprehensive school counseling practice

Lighting Pathways to Success in STEM: A Virtual Laboratory Meeting Programme (LaMP) Mutually Benefits Mentees and Host Laboratories

Developing robust professional networks can help shape the trajectories of early career scientists. Yet, historical inequities in science, technology, engineering, and mathematics (STEM) fields make access to these networks highly variable across academic programmes, and senior academics often have little time for mentoring. Here, we illustrate the success of a virtual Laboratory Meeting Programme (LaMP). In this programme, we matched students (mentees) with a more experienced scientist (mentors) from a research group. The mentees then attended the mentors’ laboratory meetings during the academic year with two laboratory meetings specifically dedicated to the mentee’s professional development. Survey results indicate that mentees expanded their knowledge of the hidden curriculum as well as their professional network, while only requiring a few extra hours of their mentor’s time over eight months. In addition, host laboratories benefitted from mentees sharing new perspectives and knowledge in laboratory meetings. Diversity of the mentees was significantly higher than the mentors, suggesting that the programme increased the participation of traditionally under-represented groups. Finally, we found that providing a stipend was very important to many mentees. We conclude that virtual LaMPs can be an inclusive and costeffective way to foster trainee development and increase diversity within STEM fields with little additional time commitment

What explains rare and conspicuous colours in a snail? A test of time-series data against models of drift, migration or selection

It is intriguing that conspicuous colour morphs of a prey species may be maintained at low frequencies alongside cryptic morphs. Negative frequency-dependent selection by predators using search images ('apostatic selection') is often suggested without rejecting alternative explanations. Using a maximum likelihood approach we fitted predictions from models of genetic drift, migration, constant selection, heterozygote advantage or negative frequency-dependent selection to time-series data of colour frequencies in isolated populations of a marine snail (Littorina saxatilis), re-established with perturbed colour morph frequencies and followed for >20 generations. Snails of conspicuous colours (white, red, banded) are naturally rare in the study area (usually <10%) but frequencies were manipulated to levels of ~50% (one colour per population) in 8 populations at the start of the experiment in 1992. In 2013, frequencies had declined to ~15-45%. Drift alone could not explain these changes. Migration could not be rejected in any population, but required rates much higher than those recorded. Directional selection was rejected in three populations in favour of balancing selection. Heterozygote advantage and negative frequency-dependent selection could not be distinguished statistically, although overall the results favoured the latter. Populations varied idiosyncratically as mild or variable colour selection (3-11%) interacted with demographic stochasticity, and the overall conclusion was that multiple mechanisms may contribute to maintaining the polymorphisms.Heredity advance online publication, 21 September 2016; doi:10.1038/hdy.2016.77

Determinants of the efficacy of natural selection on coding and noncoding variability in two passerine species

Population genetic theory predicts that selection should be more effective when the effective population size (Ne) is larger, and that the efficacy of selection should correlate positively with recombination rate. Here, we analyzed the genomes of ten great tits and ten zebra finches. Nucleotide diversity at 4-fold degenerate sites indicates that zebra finches have a 2.83-fold larger Ne. We obtained clear evidence that purifying selection is more effective in zebra finches. The proportion of substitutions at 0-fold degenerate sites fixed by positive selection (α) is high in both species (great tit 48%; zebra finch 64%) and is significantly higher in zebra finches. When α was estimated on GC-conservative changes (i.e., between A and T and between G and C), the estimates reduced in both species (great tit 22%; zebra finch 53%). A theoretical model presented herein suggests that failing to control for the effects of GC-biased gene conversion (gBGC) is potentially a contributor to the overestimation of α, and that this effect cannot be alleviated by first fitting a demographic model to neutral variants. We present the first estimates in birds for α in the untranslated regions, and found evidence for substantial adaptive changes. Finally, although purifying selection is stronger in high-recombination regions, we obtained mixed evidence for α increasing with recombination rate, especially after accounting for gBGC. These results highlight that it is important to consider the potential confounding effects of gBGC when quantifying selection and that our understanding of what determines the efficacy of selection is incomplete