N2 fixation by subsurface populations of Trichodesmium : an important source of new nitrogen to the North Atlantic Ocean

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 2011Trichodesmium, a genus of diazotrophic cyanobacteria, is an important contributor to the marine nitrogen (N) and carbon (C) cycles. The extent to which Trichodesmium dinitrogen (N2) fixation contributes to the marine N cycle has been modeled based on abundance data and rate estimates from surface populations. However, recent data show that Trichodesmium populations have a broad vertical distribution. The presence of previously unaccounted for subsurface populations suggests that past estimates of the contribution of new N by Trichodesmium to the North Atlantic may be artificially low. Herein, culture and field studies were combined to examine trends in N2 fixation in discrete surface and subsurface Trichodesmium populations in the western North Atlantic. Surface populations were dominated by the raft colony morphology of Trichodesmium and surface N2 fixation rates ranged from (33 to 156 μmol h-1 mol C-1). Subsurface populations were dominated by the puff colony morphology. Subsurface N2 fixation was typically detectable, but consistently lower than surface population rates (9 to 88 μmol h-1 mol C-1). In an analysis of the entire field dataset, N2 fixation rates varied non-linearly as a function of in situ irradiance. This trend in N2 fixation versus in situ irradiance is consistent with field and culture observations in the literature (Bell et al., 2005; Capone et al., 2005), however other models that predict N2 fixation based on light predict higher subsurface N2 fixation than what was detected in this study. In culture, N2 fixation in Trichodesmium was proportional to light level over the range of irradiances tested (10 to 70 μmol quanta m-2 s-1) and over long and short time scales, suggesting subtle changes in the light field could depress subsurface N2 fixation. Since the subsurface samples were dominated by the puff colony morphology, it is unclear if the subsurface N2 fixation rates are the result of the intrinsic responses of different species of Trichodesmium, or light driven population segregation within a single species, among other possibilities including the effects of temperature and nutrient availability. Regardless, the subsurface rates presented herein indicate that N2 fixation by subsurface populations represents an undersampled source of new N to the western north Atlantic. This result is consistent with the findings of Davis and McGillicuddy (2006), who suggest that subsurface populations of Trichodesmium increase the average N2 fixation rate in the North Atlantic by 2.9 to 3.3 times over estimates based solely on surface estimates (Davis and McGillicuddy, 2006).My graduate work has been supported by the Woods Hole Oceanographic Institution Academic Programs Office, the Center for Microbial Oceanography: Research and Education (#CCF-424599), and NSF Biological Oceanography (#OCE-0925284)

Stabilization of Iron Oxide Nanoparticles for Homogenous Integration Into Cellulose Nano Fibrils

Cellulose nanofibrils is one of the future potential giants in the medical implant industry. Its unique properties make it the ideal material for use in both permanent prosthetic devices and non- permanent implants such as screws and plates. To increase the usability of this material, the addition of super paramagnetic iron oxide nanoparticles is needed to gain MRI and X-Ray visibility. The methodology for how to homogeneously integrate these particles into the system using the addition of coating agents is explored. This research demonstrates that the addition of coating agents to the iron oxide nanoparticles can affect both the pH flocculation behavior and the adhesion of the particles to fibrils. In addition, the research finds that the addition of coating agents affects the physical characteristics of the fibrils themselves

CPAR Research Brief: Comparing Results of the 2014 Nebraska Metro and Rural Polls on Resident Views of Community Change and Outlook

Nebraskans’ views of their community’s future in the next 10 years: How viewpoints differ by personal and community factors

Nebraska Metro and Rural Residents’ Views of the Problems that Metro and Rural Areas should be Trying to Address: An Analysis of Open‐Ended Survey Questions in the 2014 Nebraska Metro and Rural Polls

Researchers and policymakers across the state of Nebraska have often discussed the need for a statewide poll to understand residents’ perceptions of their communities, personal well‐being and community issues. Separate initiatives have periodically surveyed metropolitan and rural Nebraskans on these issues. However, to date, no single effort has obtained statewide coverage at the level necessary to report attitudinal differences across metropolitan and rural Nebraska. The Nebraska Metro and Nebraska Rural Polls represent a unique effort in the state of Nebraska to obtain directly comparable data on statewide residents. This report provides a detailed analysis of a subset of responses to the 2014 Nebraska Metro and Rural Polls. In 2014, the University of Nebraska at Omaha and University of Nebraska‐Lincoln partnered to conduct similar but distinct polls of metropolitan and nonmetropolitan residents that provided statewide coverage of all 93 Nebraska counties. The polls used a common methodology and nearly identical shared question set, so results from the Metro and Rural Polls are directly comparable. Included on these questionnaires were a set of open‐ended question items. The wording for these questions read as follows in the Metro Poll: “Q8: In your opinion, what are the three most important problems in the Lincoln and Omaha metro areas that should be addressed?” “Q9: In your opinion, what are the three most important problems in rural parts of Nebraska that should be addressed?” The Rural Poll had the same wording but used the opposite order to ask about rural problems first and metro problems second. These questions were designed to gauge the extent to which rural and metro Nebraskans understand and share problems faced in other parts of the state. The questions provided no response options, but instructed respondents to list what they viewed as the top three problems in each area, with numbered blank lines provided for each. Open‐ended survey questions of this type can be useful for encouraging respondents to give substantive answers that are grounded in their own knowledge base or feelings. Because respondents are answering “off the top of their heads,” these types of questions are useful for tapping into issues commonly faced by community residents. Respondents from the same areas may provide similar answers grounded in shared concerns. However, these types of questions can also elicit surprising responses that provide insight into unexpected issues affecting respondents. This document will summarize the findings from the 2014 Nebraska Metro and Rural Polls related to these open‐ended questions and respondents’ perceptions of problems for metropolitan and rural areas to address

Spin States Protected from Intrinsic Electron-Phonon-Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe2_2

We present time-resolved Kerr rotation measurements, showing spin lifetimes of over 100 ns at room temperature in monolayer MoSe$_2$. These long lifetimes are accompanied by an intriguing temperature dependence of the Kerr amplitude, which increases with temperature up to 50 K and then abruptly switches sign. Using ab initio simulations we explain the latter behavior in terms of the intrinsic electron-phonon coupling and the activation of transitions to secondary valleys. The phonon-assisted scattering of the photo-excited electron-hole pairs prepares a valley spin polarization within the first few ps after laser excitation. The sign of the total valley magnetization, and thus the Kerr amplitude, switches as a function of temperature, as conduction and valence band states exhibit different phonon-mediated inter-valley scattering rates. However, the electron-phonon scattering on the ps time scale does not provide an explanation for the long spin lifetimes. Hence, we deduce that the initial spin polarization must be transferred into spin states which are protected from the intrinsic electron-phonon coupling, and are most likely resident charge carriers which are not part of the itinerant valence or conduction band states.Comment: 18 pages, 17 figure

Aquaponics Ideas for PK-12 classrooms Building upon Ioponics Lessons

Undergraduate science teaching majors will be providing a series of short presentations including the “Effects of Biophilia on Secondary Science Classrooms”, “Blatticomposting in the Classroom with NE Iowa area school districts”, and “Aquaponics Ideas for PK-12 classrooms Building upon Ioponics Lessons”

Smartphone-based pathogen diagnosis in urinary sepsis patients.

BackgroundThere is an urgent need for rapid, sensitive, and affordable diagnostics for microbial infections at the point-of-care. Although a number of innovative systems have been reported that transform mobile phones into potential diagnostic tools, the translational challenge to clinical diagnostics remains a significant hurdle to overcome.MethodsA smartphone-based real-time loop-mediated isothermal amplification (smaRT-LAMP) system was developed for pathogen ID in urinary sepsis patients. The free, custom-built mobile phone app allows the phone to serve as a stand-alone device for quantitative diagnostics, allowing the determination of genome copy-number of bacterial pathogens in real time.FindingsA head-to-head comparative bacterial analysis of urine from sepsis patients revealed that the performance of smaRT-LAMP matched that of clinical diagnostics at the admitting hospital in a fraction of the time (~1 h vs. 18-28 h). Among patients with bacteremic complications of their urinary sepsis, pathogen ID from the urine matched that from the blood - potentially allowing pathogen diagnosis shortly after hospital admission. Additionally, smaRT-LAMP did not exhibit false positives in sepsis patients with clinically negative urine cultures.InterpretationThe smaRT-LAMP system is effective against diverse Gram-negative and -positive pathogens and biological specimens, costs less than $100 US to fabricate (in addition to the smartphone), and is configurable for the simultaneous detection of multiple pathogens. SmaRT-LAMP thus offers the potential to deliver rapid diagnosis and treatment of urinary tract infections and urinary sepsis with a simple test that can be performed at low cost at the point-of-care. FUND: National Institutes of Health, Chan-Zuckerberg Biohub, Bill and Melinda Gates Foundation

Nebraska Metro Poll, A Research Report: Perceptions of Crime and Personal Safety in Metropolitan Nebraska

The 2014 Nebraska Metro Poll represents a critical effort to understand the perceptions and concerns of metropolitan Nebraskans. This survey expanded the work of the Omaha Conditions Survey, conducted by the Center for Public Affairs Research (CPAR) periodically since 1990. The Metro Poll builds on this foundation by including survey responses from the seven Nebraska counties that comprise the Omaha and Lincoln metro areas. Insights into the concerns faced by local residents are valuable for leaders and decision-makers seeking to understand the priorities and the views of the public

Nebraska Metro Poll, A Research Report: Perceptions of Community, Personal Well-Being, and Outlook on the Future

The 2014 Nebraska Metro Poll continues an on‐going effort to understand the perceptions and concerns of urban residents. The Metro Poll expands upon the efforts of the Omaha Conditions Survey conducted by the Center for Public Affairs Research (CPAR) periodically since 1990 to now include survey responses from the seven counties that comprise both the Omaha and Lincoln metro areas. With the knowledge and insights gained from surveying local residents, leaders and decision‐makers can be better informed on the views and priorities that the public shares