Acceleration and Stabilization Methods for Monte Carlo Reactor Core k-Eigenvalue Problems.

Typical Monte Carlo (MC) reactor core k-eigenvalue simulations are large and complex, requiring many inactive cycles to converge the fission source. In a 2009 publication, a hybrid MC method was proposed in which the fission source convergence is “accelerated” at the end of each inactive MC cycle using the solution of a discrete low-order Coarse Mesh Finite-Difference (CMFD) equation. This method has been implemented in several codes, but is sometimes unstable. In this work, we extend existing research on this CMFD-MC method and its variants. To delve deeper into the numerical stability issue, we perform a Fourier analysis on the “non-random” CMFD-MC iteration scheme (which assumes an infinite number of particles per cycle). Spectral radius results indicate that the CMFD-MC method becomes unstable for certain coarse-grid/ scattering ratio combinations, even in the infinite-particle limit. We also investigate a new MC iteration strategy, in which particles are allowed to undergo a fixed maximum number of collisions per cycle. We call this the Limited-Collision Monte Carlo (LCMC) method. This particular strategy was chosen to significantly shorten the computation time per MC cycle; however, a Fourier analysis predicts (and numerical results support) that this iteration is less stable than CMFD-MC for a given coarse grid size when the number of permitted collisions per cycle is small. This observation led us to design and implement a new simulation procedure, which makes use of both the CMFD-MC and LCMC iterations. Our iteration scheme employs standard CMFD-MC during inactive cycles to efficiently converge the fission source, then transitions to the modified Limited-Collision Monte Carlo (LCMC) algorithm to improve the efficiency of active cycles. By implementing this procedure, we show that it is possible to solve reactor core k-eigenvalue problems using two different MC algorithms. We refer to this simulation strategy as the “mixed” method (indicating a hybrid simulation, employing both the CMFD-MC and LCMC iteration schemes). Results for a large 1-D problem indicate a factor of 3-5 improvement in the solution Figure of Merit (FOM) over the current “state of the art” method.PhDNuclear Engineering and Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120765/1/keadyk_1.pd

Population Demography and Herbivory of Trillium Grandiflorum

Numerous pedicellate and sessile Trillium species are endemic to eastern North America, where white-tailed deer (Odocoileus virginianus) populations have been growing in recent decades. Deer feed on Trillium plants, and because they often consume all leaves and flowers, the photosynthetic capacity of browsed plants is greatly diminished. To determine if deer can influence Trillium population dynamics, we review two recent studies that applied matrix population models to understand how deer browsing affects Trillium grandijlorum. Research conducted in the Great Lakes region indicated Trillium populations in which 6-12% plants were browsed declined 3.6% per year. Simulations show that with additional browsing, the rate of population decline accelerates. Similar research conducted in the Appalachian plateau region by a different researcher yielded nearly identical results. We apply insights from these matrix population models to two additional conservation problems in Trillium: unsustainable collecting of wild plants and forest fragmentation. Because other Trillium in the eastern United States are similar morphologically and ecologically, our results from Trillium grandiflorum might be generalized to apply to other members of the genus

Longitudinal Study of a State 4-H Fashion Revue

The 4-H fashion revue contest gives young people the opportunity to create their own garment and present it in front of judges and an audience. To come to the conclusions reported here, the participant entry forms, participant evaluations, and judges’ comments representing seven years (2006-2013) of state fashion revue participation in Pennsylvania were analyzed. No differences were found in cost or time allocation among those who placed as award winners and those who did not place. Data and participant comments indicated that participants gained some life skills. In addition, more than one-third of the youth involved in these contests were found to mend for their family and friends as part of their 4-H textile and clothing experiences

Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean.

Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and models of global N2 fixation. The Arctic is particularly sensitive to climate change, and N2 fixation may increase in Arctic waters under future climate scenarios

Community-Based Responses to Justice-Involved Young Adults

In this paper, we propose a different kind of criminal justice for young men and women. We propose new institutional methods and processes for young adult justice, for those ages 18 to 24, that can meet the realities of life for today’s disadvantaged youth involved in crime and the criminal justice system. What we envision seeks to extend the reach of the juvenile court while also using it as a basis for a new system that reflects a modern understanding of the transition into adulthood. Our central recommendation is that the age of juvenile court jurisdiction be raised to at least 21 years old1 with additional, gradually diminishing protections for young adults up to age 24 or 25. Such a system recognizes the diminished capacity for responsible decision-making in youth while harnessing the opportunities presented by their ability to grow, adapt and change. Additionally, such a system would recognize the diminished opportunities and greater demands that now face young adults, particularly in the disadvantaged communities that supply the adult correctional system

In Situ Diazotroph Population Dynamics Under Different Resource Ratios in the North Pacific Subtropical Gyre.

Major advances in understanding the diversity, distribution, and activity of marine N2-fixing microorganisms (diazotrophs) have been made in the past decades, however, large gaps in knowledge remain about the environmental controls on growth and mortality rates. In order to measure diazotroph net growth rates and microzooplankton grazing rates on diazotrophs, nutrient perturbation experiments and dilution grazing experiments were conducted using free-floating in situ incubation arrays in the vicinity of Station ALOHA in March 2016. Net growth rates for targeted diazotroph taxa as well as Prochlorococcus, Synechococcus and photosynthetic picoeukaryotes were determined under high (H) and low (L) nitrate:phosphate (NP) ratio conditions at four depths in the photic zone (25, 45, 75, and 100 m) using quantitative PCR and flow cytometry. Changes in the prokaryote community composition in response to HNP and LNP treatments were characterized using 16S rRNA variable region tag sequencing. Microzooplankton grazing rates on diazotrophs were measured using a modified dilution technique at two depths in the photic zone (15 and 125 m). Net growth rates for most of the targeted diazotrophs after 48 h were not stimulated as expected by LNP conditions, rather enhanced growth rates were often measured in HNP treatments. Interestingly, net growth rates of the uncultivated prymnesiophyte symbiont UCYN-A1 were stimulated in HNP treatments at 75 and 100 m, suggesting that N used for growth was acquired through continuing to fix N2 in the presence of nitrate. Net growth rates for UCYN-A1, UCYN-C, Crocosphaera sp. (UCYN-B) and the diatom symbiont Richelia (associated with Rhizosolenia) were uniformly high at 45 m (up to 1.6 ± 0.5 d-1), implying that all were growing optimally at the onset of the experiment at that depth. Differences in microzooplankton grazing rates on UCYN-A1 and UCYN-C in 15 m waters indicate that the grazer assemblage preyed preferentially on UCYN-A1. Deeper in the water column (125 m), both diazotrophs were grazed at substantial rates, suggesting grazing pressure may increase with depth in the photic zone. Constraining in situ diazotroph growth and mortality rates are important steps for improving parameterization for diazotrophs in global ecosystem models

Economic Geography and the Financial Crisis: Full Steam Ahead?

This article considers whether the growing theoretical and methodological diversity or pluralistic nature of economic geographycontributes to its lack of engagement outside the discipline and academy. Although we are enthusiastic about the vibrancy thispluralism brings, we also speculate that it contributes to the discipline’s tendency to fall short of significantly impacting keydebates in the social sciences. In particular, we consider the disciplinary challenges to influencing mainstream debates overfinancialization and the recent financial crisis and the recurring lament that economic geography “misses the boat” by failingto significantly impact key scholarly and policy issues. Specifically, we suggest that methodological and theoretical diversity,local contextualization, and relational analysis, all of which we support as vital to the discipline, make it difficult to isolate adisciplinary core. We conclude that pluralism produces a vibrant discipline with unique explanatory power but that it also hasimportant impacts on the design, execution, and influence of geographers’ research outside the discipline

Diverse diazotrophs are present on sinking particles in the North Pacific Subtropical Gyre.

Sinking particles transport carbon and nutrients from the surface ocean into the deep sea and are considered hot spots for bacterial diversity and activity. In the oligotrophic oceans, nitrogen (N2)-fixing organisms (diazotrophs) are an important source of new N but the extent to which these organisms are present and exported on sinking particles is not well known. Sinking particles were collected every 6 h over a 2-day period using net traps deployed at 150 m in the North Pacific Subtropical Gyre. The bacterial community and composition of diazotrophs associated with individual and bulk sinking particles was assessed using 16S rRNA and nifH gene amplicon sequencing. The bacterial community composition in bulk particles remained remarkably consistent throughout time and space while large variations of individually picked particles were observed. This difference suggests that unique biogeochemical conditions within individual particles may offer distinct ecological niches for specialized bacterial taxa. Compared to surrounding seawater, particle samples were enriched in different size classes of globally significant N2-fixing cyanobacteria including Trichodesmium, symbionts of diatoms, and the unicellular cyanobacteria Crocosphaera and UCYN-A. The particles also contained nifH gene sequences of diverse non-cyanobacterial diazotrophs suggesting that particles could be loci for N2 fixation by heterotrophic bacteria. The results demonstrate that diverse diazotrophs were present on particles and that new N may thereby be directly exported from surface waters on sinking particles

Combating Alarm Fatigue: The Quest for More Accurate and Safer Clinical Monitoring Equipment

As the demand for health-care services continues to increase, clinically efficient and cost-effective patient monitoring takes on a critically important role. Key considerations inherent to this area of concern include patient safety, reliability, ease of use, and cost containment. Unfortunately, even the most modern patient monitoring systems carry significant drawbacks that limit their effectiveness and/or applicability. Major opportunities for improvement in both equipment design and monitor utilization have been identified, including the presence of excessive false and nuisance alarms. When poorly optimized, clinical alarm activity can affect patient safety and may have a negative impact on care providers, leading to inappropriate alarm response time due to the so-called alarm fatigue (AF). Ultimately, consequences of AF include missed alerts of clinical significance, with substantial risk for patient harm and potentially fatal outcomes. Targeted quality improvement initiatives and staff training, as well as the proactive incorporation of technological improvements, are the best approaches to address key barriers to the optimal utilization of clinical alarms, AF reduction, better patient care, and improved provider job satisfaction