Thoughts of Leaving: An Exploration of Why New York City Middle School Teachers Consider Leaving Their Classrooms

This report explores the conditions under which middle-school teachers in New York City leave their schools, and the consequences of this turnover. The focus on middle schools stems from the widely-held view that the middle grades are a critical turning point in the lives of children, and that many New York City school children lose academic momentum in these grades, setting them on trajectories of failure as they move towards high school and life beyond it. This report is based on a survey of more than 4,000 full-time middle school teachers working in 125 of the nearly 200 middle schools in New York City serving children in grades six through eight in the 2009-10 school year. The participating teachers reported whether they had considered leaving their current school or leaving teaching during that school year, and the reasons that they considered leaving. The report links their responses to teachers' reports about their own backgrounds and experiences, to the demographic characteristics of the schools in which they teach, and to the collective perceptions of all of the teachers in a school about that school as a workplace. This report is part of a three-year, mixed-methods study of teacher turnover in New York City middle schools

Ecological Art: Art with a Purpose

Ecological art is purposeful and often prescriptive: the actions and directions intended by the artists for activists to undertake often are clearly represented. Yet, ecological art has been no more successful than, for example, targeted scientific research, deposits on returnable bottles, or land-protection campaigns at slowing global warming, reducing the amount of waste we generate every day, or halting the ongoing sixth mass extinction in the history of the Earth. Here, we consider the idea that prescriptive ecological art provides insufficient mental space for creative reflection about future scenarios of, and responses to, environmental change. We ask whether, by presenting a limited range of possibilities in ecological art, we limit the range of options that viewers consider in deciding on possible actions that they could take to slow or halt environmental decline. We conclude by asking how we artists and scientists can best engage diverse audiences in critically thinking about, and taking action to mitigate, environmental change. These questions and issues are addressed through a discussion of two of our recent ecological art installations: Hemlock Hospice and Warming Warning

UNMAS and Gender Mainstreaming in Mine Action

In order to further the development of proper protection from and response to landmines and explosive remnants of war in conflict and post-conflict countries, the United Nations Mine Action Service and the International Mine Action Standards Review Board are taking the necessary steps to ensure gender perspectives become an integral part of national mine-action plans. This article briefly describes the evolution of gender mainstreaming in mine action and how UNMAS has addressed the issue

SHERPA: A Flexible, Modular Spacecraft for Orbit Transfer and On-Orbit Operations

The Department of Defense Space Test Program is responsible for launching small experimental payloads and demonstration technologies as directed by the Space Experiments Review Board (SERB). The Shuttle Expendable Rocket for Payload Augmentation (SHERPA) program will develop a highly functional space vehicle – with several variants – that incorporates a scaleable, modular architecture to support a wide variety of missions, technologies, and configurations. The initial application of SHERPA will be as an orbit transfer vehicle designed to raise a payload from a low Space Transportation System (STS) flight altitude to an orbit with a nominal one-year lifetime. This capability will allow STP to take advantage of the low-cost Space Shuttle launch services and still achieve the mission lifetimes required for experiments. In this paper, analysis and design of the SHERPA scalable, modular architecture will be discussed. In addition, applicable requirements and constraints levied upon the design by the customer, secondary payload deployment mechanisms, such as the Canister for All Payload Ejections (CAPE), STS safety, the concept of operations, and envisioned applications, will be addressed

Predicting food-web structure with metacommunity models

Synthesis Metacommunity theory aims to elucidate the relative influence of local and regional-scale processes in generating diversity patterns across the landscape. Metacommunity research has focused largely on assemblages of competing organisms within a single trophic level. Here, we test the ability of metacommunity models to predict the network structure of the aquatic food web found in the leaves of the northern pitcher plant Sarracenia purpurea. The species-sorting and patch-dynamics models most accurately reproduced nine food web properties, suggesting that local-scale interactions play an important role in structuring Sarracenia food webs. Our approach can be applied to any well-resolved food web for which data are available from multiple locations. The metacommunity framework explores the relative influence of local and regional-scale processes in generating diversity patterns across the landscape. Metacommunity models and empirical studies have focused mostly on assemblages of competing organisms within a single trophic level. Studies of multi-trophic metacommunities are predominantly restricted to simplified trophic motifs and rarely consider entire food webs. We tested the ability of the patch-dynamics, species-sorting, mass-effects, and neutral metacommunity models, as well as three hybrid models, to reproduce empirical patterns of food web structure and composition in the complex aquatic food web found in the northern pitcher plant Sarracenia purpurea. We used empirical data to determine regional species pools and estimate dispersal probabilities, simulated local food-web dynamics, dispersed species from regional pools into local food webs at rates based on the assumptions of each metacommunity model, and tested their relative fits to empirical data on food-web structure. The species-sorting and patch-dynamics models most accurately reproduced nine food web properties, suggesting that local-scale interactions were important in structuring Sarracenia food webs. However, differences in dispersal abilities were also important in models that accurately reproduced empirical food web properties. Although the models were tested using pitcher-plant food webs, the approach we have developed can be applied to any well-resolved food web for which data are available from multiple locations. © 2012 The Authors. Oikos © 2012 Nordic Society Oikos

Local to Continental-Scale Variation in the Richness and Composition of an Aquatic Food Web

Organismic and Evolutionary Biolog

Sensitivity of codispersion to noise and error in ecological and environmental data

Codispersion analysis is a new statistical method developed to assess spatial covariation between two spatial processes that may not be isotropic or stationary. Its application to anisotropic ecological datasets have provided new insights into mechanisms underlying observed patterns of species distributions and the relationship between individual species and underlying environmental gradients. However, the performance of the codispersion coefficient when there is noise or measurement error ("contamination") in the data has been addressed only theoretically. Here, we use Monte Carlo simulations and real datasets to investigate the sensitivity of codispersion to four types of contamination commonly seen in many real-world environmental and ecological studies. Three of these involved examining codispersion of a spatial dataset with a contaminated version of itself. The fourth examined differences in codisperson between plants and soil conditions, where the estimates of soil characteristics were based on complete or thinned datasets. In all cases, we found that estimates of codispersion were robust when contamination, such as data thinning, was relatively low (<15\%), but were sensitive to larger percentages of contamination. We also present a useful method for imputing missing spatial data and discuss several aspects of the codispersion coefficient when applied to noisy data to gain more insight about the performance of codispersion in practice.Comment: 20 pages, 14 figure

Geographic Variation in Network Structure of a Nearctic Aquatic Food Web

Aim: The network structure of food webs plays an important role in the maintenance of diversity and ecosystem functioning in ecological communities. Previous research has found that ecosystem size, resource availability, assembly history and biotic interactions can potentially drive food web structure. However, the relative influence of climatic variables that drive broad-scale biogeographic patterns of species richness and composition has not been explored for food web structure. In this study, we assess the influence of broad-scale climatic variables in addition to known drivers of food web structure on replicate observations of a single aquatic food web, sampled from the leaves of the pitcher plant (Sarracenia purpurea), at different geographic sites across a broad latitudinal and climatic range. Location: Using standardized sampling methods, we conducted an extensive ‘snapshot’ survey of 780 replicated aquatic food webs collected from the leaves of the pitcher plant S. purpurea at 39 sites from northern Florida to Newfoundland and westward to eastern British Columbia. Methods: We examined correlations of 15 measures of food web structure at the pitcher and site scales with geographic variation in temperature and precipitation, concentrations of nutrients from atmospheric nitrogen deposition, resource availability, ecosystem size and the abundance of the pitcher plant mosquito (Wyeomyia smithii), a potential keystone species. Results: At the scale of a single pitcher plant leaf, linkage density, species richness, measures of chain length and the proportion of omnivores in a web all increased with pitcher volume. Linkage density and species richness were greater at high-latitude sites, which experience low mean temperatures and precipitation and high annual variation in both of these variables. At the site scale, variation in 8 of the 15 food web metrics decreased at higher latitudes, and variation in measures of chain length increased with the abundance of mosquitoes. Main conclusions: Ecosystem size and climatic variables related to latitude were most strongly correlated with network structure of the Sarracenia food web. However, in spite of large sample sizes, thorough standardized sampling and the large geographic extent of the survey, even the best-fitting models explained less than 40% of the variation in food web structure. In contrast to biogeographic patterns of species richness, food web structure was largely independent of broad-scale climatic variables. The large proportion of unexplained variance in our analyses suggests that stochastic assembly may be an important determinant of local food web structure.Organismic and Evolutionary Biolog

Using codispersion analysis to characterize spatial patterns in species co-occurrences

Visualizing and quantifying spatial patterns of co-occurrence (i.e., of two or more species, or of species and underlying environmental variables) can suggest hypotheses about processes that structure species assemblages and their relevant spatial scales. Statistical models of spatial co-occurrence generally assume that underlying spatial processes are isotropic and stationary but many ecologically realistic spatial processes are anisotropic and non-stationary. Here, we introduce codispersion analysis to ecologists and use it to detect and quantify anisotropic and nonstationary patterns and their relevant spatial scales in bivariate co-occurrence data. Simulated data illustrated that codispersion analysis can accurately characterize complex spatial patterns. Analysis of co-occurrence of common tree species growing in a 35-ha plot revealed both positive and negative codispersion between different species; positive codispersion values reflected positive correlation in species abundance (aggregation), whereas negative codispersion values reflected negative correlation in species abundance (segregation). Comparisons of observed patterns with those simulated using two different null models showed that the codispersion of most species pairs differed significantly from random expectation. We conclude that codispersion analysis can be a useful exploratory tool to guide ecologists interested in modeling spatial processes.Organismic and Evolutionary Biolog

De novo identification of differentially methylated regions in the human genome

Background: The identification and characterisation of differentially methylated regions (DMRs) between phenotypes in the human genome is of prime interest in epigenetics. We present a novel method, DMRcate, that fits replicated methylation measurements from the Illumina HM450K BeadChip (or 450K array) spatially across the genome using a Gaussian kernel. DMRcate identifies and ranks the most differentially methylated regions across the genome based on tunable kernel smoothing of the differential methylation (DM) signal. The method is agnostic to both genomic annotation and local change in the direction of the DM signal, removes the bias incurred from irregularly spaced methylation sites, and assigns significance to each DMR called via comparison to a null model. Results: We show that, for both simulated and real data, the predictive performance of DMRcate is superior to those of Bumphunter and Probe Lasso, and commensurate with that of comb-p. For the real data, we validate all array-derived DMRs from the candidate methods on a suite of DMRs derived from whole-genome bisulfite sequencing called from the same DNA samples, using two separate phenotype comparisons. Conclusions: The agglomeration of genomically localised individual methylation sites into discrete DMRs is currently best served by a combination of DM-signal smoothing and subsequent threshold specification. The findings also suggest the design of the 450K array shows preference for CpG sites that are more likely to be differentially methylated, but its overall coverage does not adequately reflect the depth and complexity of methylation signatures afforded by sequencing. For the convenience of the research community we have created a user-friendly R software package called DMRcate, downloadable from Bioconductor and compatible with existing preprocessing packages, which allows others to apply the same DMR-finding method on 450K array data