Cannon Ice Free Radiative Convection

Ice-free radiative convection drives spring mixing in a large lake

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In this work we highlight the importance of radiative convection as a mixing mechanism in a large, ice-free lake (Lake Michigan, USA), where solar heating of waters below the temperature of maximum density drives vertical convection during the vernal turnover. Measurements taken over a 2-week period at a 55-m deep site demonstrate the ability of radiative convection to mix the entire water column. Observations show a diurnal cycle in which solar heating drives a steady deepening of the convective mixed layer throughout the day (dHCML/dt = 12.8 m/hr), followed by surface-cooling-induced restratification during the night. Radiative convection is linked to a dramatic enhancement in turbulence characteristics, including both turbulent kinetic energy dissipation (ϵ: 10−9–10−7 W/kg) and turbulent scalar diffusivity (Kz: 10−3–10−1 m2/s), suggesting that radiative convection plays a major role in driving vertical mixing throughout the water column during the isothermal spring.

Observations of turbulence and mean flow in the low‐energy hypolimnetic boundary layer of a large lake

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Near-bed measurements are reported for both mean flow and turbulence structure in the deep hypolimnetic waters of Lake Michigan (55 m depth) during stratified and unstratified periods to determine validity and restrictions of the expected law-of-the-wall (LOW) behavior. Near-bed currents were weak (U50 = 3, 16 cm s−1 for mean, maximum currents respectively at 50 cm elevation), dominated by subinertial energy across all seasons, and showed little seasonal variation in spite of the strong seasonality to wind forcing. Velocity structure for wave-free conditions showed strong log-linear trends within 1 mab, with over 98% of the 2152 velocity profiles producing significant log-linear fits within the bottom meter and a strictly logarithmic velocity profile extending to only 66 cmab on average (Cd 50 = 0.0052; zo = 0.0015 m). Stratification was dynamically unimportant to mean flow and turbulence, but fitted log-linear length scales suggest that deviations from strictly logarithmic velocity structure may be explained by flow unsteadiness. Turbulent quantities measured within 1 m of the bed including dissipation, turbulent kinetic energy, and turbulent length scales followed LOW expectations in the mean, but individual estimates deviated by several orders of magnitude. The observed deviations from LOW turbulent structure were found to be correlated with the log-linear length scales fit to mean velocity profiles and were consistent with the effects of flow unsteadiness.

Assessment and characterization of writing exercises and core engineering textbooks

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Writing has been identified as a critical skill and element of the engineering profession, yet it is rarely included in sophomore-level and junior-level courses. Textbooks often influence how courses are structured, and reading assignments and homework problems are frequently assigned directly from textbooks. In this project, textbooks are systematically searched for writing-based problems in four core engineering courses: fluid mechanics, thermodynamics, statics, and circuits. The authors focused efforts on identifying learning activities that could potentially allow students to practice writing, learn through writing, and use writing to relate course content to broader applications and contexts. Results included the total number of end-of-chapter questions with writing components and the classification of types of writing prompts. Analysis showed a limited availability of questions with writing components in textbooks and a missed opportunity to incorporate important writing education within the context of technical engineering concepts.

Engineering instructors on writing: Perceptions, practices, and needs

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Background- With communication skills deemed increasingly important for engineering graduates, we wanted to understand how writing is currently included in engineering classes, what challenges are caused by including writing in such classes, and what resources would be most useful to help engineering instructors more easily include writing in engineering classes. Literature review- Writing is a necessary skill for engineering graduates and has received increased attention in engineering classes. However, despite many instructors’ beliefs that writing is an important skill for engineers, it is not typically taught in a systematic and comprehensive way across the engineering curriculum. Research questions- 1. What perceptions of writing, and specifically writing in engineering, do engineering instructors hold? 2. To what extent do engineering instructors report incorporation of writing activities and assignments in their classes? 3. What barriers do engineering instructors perceive as inhibiting the inclusion of more writing in engineering courses? 4. What resources do engineering instructors desire to expand and improve the inclusion of writing in engineering courses? Research methods: A survey was completed by engineering instructional staff (n = 190 respondents, 10.7% response rate) from seven institutions as well as by some members of the Big10+ Engineering Deans Mailing List. Instructors were asked about their general perceptions about writing in engineering and were also asked to consider the most recent engineering course that they taught and reflect on how they included (or did not include) writing in their course. Findings and conclusions- As expected, we found that most engineering instructional staff agree that writing skills are very important in engineering. Yet, we found that constraints on time and resources kept instructors from including more writing in their courses. This paper concludes with a discussion of our efforts to develop resources, such as rubrics, graded writing examples, and strategies for developing writing prompts, to help instructors include more writing in their engineering courses.

Regulation of plankton and nutrient dynamics by profundal quagga mussels in Lake Michigan: a one-dimensional model

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Invasive dreissenid mussels have altered plankton abundance and nutrient cycling in the Great Lakes. In this study, a 1-D hydrodynamic-biogeochemical coupled model is developed to investigate their effects at a mid-depth offshore site in Lake Michigan. Model simulation shows that water surface temperature and vertical thermal structure can be well reproduced. Driven by the simulated vertical mixing, the biological model solves the transport and transformation of nutrients, plankton and detritus in the water column. Mussel grazing and excretion are added at the bottom boundary. The biological model predicts a notable decline of phytoplankton biomass and considerable increase of dissolved phosphorus (DP) in the entire water column at the end of spring. However, the reduction of phytoplankton and the increase of DP are limited to the bottom 20 m in summer as a result of the strong stratification. Model results also show that mussels can maximize particle delivery to the benthos, as the modeled benthic diffusive flux of particulate phosphorus exceeds the passive settling rate by 4.2× on average. Model simulation over a 10-month period indicates that profundal mussels have the potential to significantly change the distribution of energy and nutrients in the water column, even in a deep and stratified environment.

Physicochemical characteristics of a southern Lake Michigan river plume

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Riverine inputs are a major source of nutrients to the Laurentian Great Lakes and have important effects on nearshore biological processes, where mixing between river and lake water leads to formation of heterogeneous river plumes. We examined the physical and chemical characteristics of the St. Joseph River plume in southern Lake Michigan between May and October 2011, and in October 2012, June 2013 and April 2014. Specific electric conductivity and stable isotopes of water were used to quantify the fraction of river water (FRW) at sampling sites in Lake Michigan. Both tracers predicted similar patterns of FRW among sites; however, there was a systematic offset between the two methods, and specific electric conductivity method under-predicted the FRW by ~5%. We observed a distinct, seasonally varying river plume, with plume size correlated with flow rate of St. Joseph River. Within the plume, sediments and nutrients were non-conservative and exhibited significant and seasonally varying losses that we attribute to settling of particle-bound nutrients and/or nutrients in particulate phase below the plume. The characteristics and the spatiotemporal heterogeneity of the river plume documented here may have important implications for the nearshore biogeochemistry of the Great Lakes and for understanding the roles of these features in ecological processes in nearshore areas.

Asynchrony in the inter-annual recruitment of lake whitefish Coregonus clupeaformis in the Great Lakes region

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Spatially separated fish populations may display synchrony in annual recruitment if the factors that drive recruitment success, particularly abiotic factors such as temperature, are synchronised across broad spatial scales. We examined inter-annual variation in recruitment among lake whitefish (Coregonus clupeaformis) populations in lakes Huron, Michigan and Superior using fishery-dependent and -independent data from 1971 to 2014. Relative year-class strength (RYCS) was calculated from catch-curve residuals for each year class across multiple sampling years. Pairwise comparison of RYCS among datasets revealed no significant associations either within or between lakes, suggesting that recruitment of lake whitefish is spatially asynchronous. There was no consistent correlation between pairwise agreement and the distance between datasets, and models to estimate the spatial scale of recruitment synchrony did not fit well to these data. This suggests that inter-annual recruitment variation of lake whitefish is asynchronous across broad spatial scales in the Great Lakes. While our method primarily evaluated year-to-year recruitment variation, it is plausible that recruitment of lake whitefish varies at coarser temporal scales (e.g. decadal). Nonetheless, our findings differ from research on some other Coregonus species and suggest that local biotic or density-dependent factors may contribute strongly to lake whitefish recruitment rather than inter-annual variability in broad-scale abiotic factors.

Recruitment dynchrony of Yellow Perch (Perca flavescens, Percidae) in the Great Lakes Region, 1966-2008

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Population-level reproductive success (recruitment) of many fish populations is characterized by high inter-annual variation and related to annual variation in key environmental factors (e.g., climate). When such environmental factors are annually correlated across broad spatial scales, spatially separated populations may display recruitment synchrony (i.e., the Moran effect). We investigated inter-annual (1966–2008) variation in yellow perch (Perca flavescens, Percidae) recruitment using 16 datasets describing populations located in four of the five Laurentian Great Lakes (Erie, Huron, Michigan, and Ontario) and Lake St. Clair. We indexed relative year class strength using catch-curve residuals for each year-class across 2–4 years and compared relative year-class strength among sampling locations. Results indicate that perch recruitment is positively synchronized across the region. In addition, the spatial scale of this synchrony appears to be broader than previous estimates for both yellow perch and freshwater fish in general. To investigate potential factors influencing relative year-class strength, we related year-class strength to regional indices of annual climatic conditions (spring-summer air temperature, winter air temperature, and spring precipitation) using data from 14 weather stations across the Great Lakes region. We found that mean spring-summer temperature is significantly positively related to recruitment success among Great Lakes yellow perch populations.

Why this flip wasn’t a flop: What the numbers don’t tell you about flipped classes

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This paper details the conversion of a large, required Civil Engineering fluid mechanics course into a more student-centered, active learning-oriented course through the flipping of one lecture per week. In the flipped class, students collaboratively solve homework problems in groups while receiving “expert” feedback from instructors and TAs. To offset the lost lectures, some course material that has been delivered in traditional lectures has been placed online in the form of short videos and textbook readings, with low-stakes quizzes for assessment.

Student learning gains were quantitatively assessed by comparing quiz and final exam scores for three semesters (1 pre-flip and 2 post-flip). To maintain some element of consistency across the course transformation, a comprehensive, multiple-choice final exam has served to provide quantitative metrics on which the course improvement can be gaged. In addition, quiz questions remained relatively similar across semesters. One-way ANOVAs revealed a statically significant difference on quiz performance, with post-flip students performing better than those in pre-flip semesters. In addition, students in the final iteration of the course transformation significantly outperformed previous students on final exams by about 7%.

Taken together, the numbers suggest that the process of flipping a large fluid mechanics course is associated with small but positive improvements to quiz and final exam performance. However, it is best to rely on other indicators beyond course performance in order to more accurately depict the impact of a course transformation. To supplement the results of the quantitative analyses, student comments about the course and instructor observations of the transformation implementation were assessed. Students found the work sessions to be very effective, enjoyed collaborating with peers and the instructor, and thought the online videos were helpful. The instructor indicated that the benefits of the flipped class include the following: heightened student engagement during class periods; greatly increased instructor awareness of student perceptions, challenges, personal issues, and conceptual bottlenecks; eventual reduction in instructor preparation time; improved instructor-student relationships; and a better focus on more important course objectives.

Challenges and opportunities for recruiting students to undergraduate civil engineering programs

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Society needs more civil engineers, with the projected near-term need for civil engineers greater than any other engineering discipline. Ailing national infrastructure and projected retirement rates have led to job projections suggesting that the near-term need for civil engineering graduates is almost double that of any other engineering discipline. This need, combined with other attractive attributes of civil engineering, should make civil engineering a top engineering major at many undergraduate universities. In spite of the career opportunities readily available to graduating civil engineers, and in spite of the general increasing trend in the number of total undergraduate engineering students, undergraduate civil engineering programs, taken as a whole, have struggled to maintain and grow their numbers. Individually, many undergraduate programs struggle to recruit students to civil engineering, and this poses a major problem not only to individual programs but to the profession itself.

We analyzed a set of civil engineering student surveys to determine the factors, attitudes, and experiences that typically lead students to select careers in civil engineering and found several common responses, many of which can be leveraged to promote the discipline. The data suggest that about one half of our students pre-select civil engineering prior to beginning as first-year engineering students, and that the top reasons for their selection of civil engineering include: a passion for building things; a desire to make a difference; flexible career options; and a love for math and science (which presumably is shared by young engineers of all disciplines).

We present data from another survey carried out with undergraduate students in other engineering majors, as to why students select other disciplines and how civil engineering is perceived. This survey highlights several perceptions about civil engineering among first year engineers. These include the misperception of civil engineering as a narrow field focused only around bridges, buildings, and roads, as well as the perception of civil engineers earning low salaries.

These student perceptions pose challenges to civil engineering recruiters, but also afford opportunities for clarification and improved recruitment, especially for programs that allow students to select their engineering discipline during their first year of college. We conclude this paper with a set of talking points we have deployed at our own university that directly address the above challenges and opportunities.