270 research outputs found

    Towards a directed homotopy type theory

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    In this paper, we present a directed homotopy type theory for reasoning synthetically about (higher) categories, directed homotopy theory, and its applications to concurrency. We specify a new `homomorphism' type former for Martin-L\"of type theory which is roughly analogous to the identity type former originally introduced by Martin-L\"of. The homomorphism type former is meant to capture the notions of morphism (from the theory of categories) and directed path (from directed homotopy theory) just as the identity type former is known to capture the notions of isomorphism (from the theory of groupoids) and path (from homotopy theory). Our main result is an interpretation of these homomorphism types into Cat, the category of small categories. There, the interpretation of each homomorphism type hom(a,b) is indeed the set of morphisms between the objects a and b of a category C. We end the paper with an analysis of the interpretation in Cat with which we argue that our homomorphism types are indeed the directed version of Martin-L\"of's identity types

    The role of market feasibility in multi-family investment : lessons learned from four case studies

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1993.by Stephanie Paige Warren.M.S

    Temporal Variation in Optical Properties of Chromophoric Dissolved Organic Matter (CDOM) in Southern California Coastal Waters with Nearshore Kelp and Seagrass

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    Optical properties of chromophoric dissolved organic matter (CDOM) were measured in surf zone waters in diurnal field studies at a Southern California beach with nearshore kelp and seagrass beds and intertidal plant wrack. Absorption coefficients (aCDOM(300 nm)) ranged from 0.35 m21 to 3.7 m21 with short-term variability\u3c1 h, increases at ebb and flood tides and higher values (6 m21) during an offshore storm event. Spectral slopes (S) ranged from 0.0028 nm21 to 0.017 nm21, with higher values after the storm; S was generally inversely correlated with aCDOM(300 nm). 3-D excitation–emission matrix spectra (EEMs) for samples with lower S values had humic-type peaks associated with terrestrial material (A, C), marine microbial material (M) and protein peaks, characteristic of freshly produced organic material. Samples with high S values had no or reduced protein peaks, consistent with aged material. Fluorescent indexes (f450/f500 \u3e2.5, BIX\u3e1.1) were consistent with microbial aquatic sources. Leachates of senescent kelp and seagrass had protein and humic-type EEM peaks. After solar simulator irradiation (4 h), protein peaks rapidly photochemically degraded, humic-type peak C increased in intensity and peak M disappeared. Optical characteristics of kelp leachates were most similar to field samples, consistent with minimal contributions from sea grass, a small component of the biomass at this site. Increases in aCDOM(300 nm) with decreases in S are attributed to the input of freshly produced autochthonous organic material at ebbing and flooding tides, from exudation and microbial processing of senescent plant wrack and nearshore macroalgal vegetation. Other allochthonous sources are hypothesized to be ground water seepage and terrestrial runoff

    Wildlife Habitat Management on College and University Campuses

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    With the increasing involvement of higher education institutions in sustainability movements, it remains unclear to what extent college and university campuses address wildlife habitat. Many campuses encompass significant areas of green space with potential to support diverse wildlife taxa. However, sustainability rating systems generally emphasize efforts like recycling and energy conservation over green landscaping and grounds maintenance. We sought to examine the types of wildlife habitat projects occurring at schools across the United States and whether or not factors like school type (public or private), size (number of students), urban vs. rural setting, and funding played roles in the implementation of such initiatives. Using case studies compiled by the National Wildlife Federation’s Campus Ecology program, we documented wildlife habitat-related projects at 60 campuses. Ten management actions derived from nationwide guidelines were used to describe the projects carried out by these institutions, and we recorded data about cost, funding, and outreach and education methods. We explored potential relationships among management actions and with school characteristics. We extracted themes in project types, along with challenges and responses to those challenges. Native plant species selection and sustainable lawn maintenance and landscaping were the most common management actions among the 60 campuses. According to the case studies we examined, we found that factors like school type, size, and location did not affect the engagement of a campus in wildlife habitat initiatives, nor did they influence the project expenditures or funding received by a campus. Our results suggest that many wildlife habitat initiatives are feasible for higher education institutions and may be successfully implemented at relatively low costs through simple, but deliberate management actions

    Exploring Stakeholders’ Perceptions of Urban Growth Scenarios for Metropolitan Boston (USA): The Relationship Between Urban Trees and Perceived Density

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    Achieving multiple goals rather than trading one goal off for another is the essence of sustainability. Visualizing alternative futures in a participatory planning process helps disentangle complex planning issues particularly when stakeholders may perceive key goals as imposing potential tradeoffs, such as increased housing for a growing population and availability of green space. This study explored the effects of using visualization and scenarios as planning tools in a workshop with stakeholders in the Boston Metro Area, Massachusetts (USA), in achieving multiple benefits of sustainable future growth of the region. We applied mixed methods sequential explanatory design and a survey instrument with a landscape preference survey designed to garner stakeholders\u27 preference and acceptability of perceived urban density versus urban greening in four future growth scenarios reflecting multiple goals in sustainability. The results of the landscape preference survey demonstrated that increasing tree canopy appears to ameliorate the low ratings of high-rise buildings for the region\u27s urban development. In addition, the scenario planning process, especially the use of small group discussions, represented an effective tool in facilitating stakeholders\u27 discussion about achieving the multiple benefits of the three goals of sustainability: Environment, Economy, Equity. This study provided theoretical and applied insights for planners in the use of visualization and scenario planning methodologies to engage stakeholders in the participatory planning process. It revealed the potential for a policy decision shift among stakeholders in the Boston region, namely that higher density urban development would likely be more acceptable to them when combined with a simultaneous increase in tree canopy cover. Through practices like these, stakeholders are more likely to consider policies and designs that embrace a variety of goals for their community’s future instead of simplistically placing one goal in opposition to another or trading them off against each other

    Exploring the Ecology of Establishing Oak Trees in Urban Settings of the Northeast

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    Urban forests notoriously lack diversity in the biological communities that inhabit them, from the age and species composition of street trees to wildlife populations. In reaction to invasions of nonnative insects and diseases as well as predicted response to climate change, an emerging number of community foresters and tree wardens are expanding their urban tree planting practices to include a broader assemblage of tree species. These include oaks, among other species able to tolerate and adapt to urban conditions. Oaks are potentially favorable in regions like the northeastern U.S., where they grow extensively in rural forests and demonstrate potential resistance to specific urban pests that have caused challenges for other historically popular and extensively planted street trees. Additionally, they are known to feature a number of wildlife benefits, and their ranges in the Northeast are predicted to expand under many future climate change forecast models. We examine the role of oaks in the urban environment through the lens of the urban forest diversity deficit, reviewing topics that include diversity recommendations, threats by nonnative insects and diseases, and the human-wildlife interface. The goal of this work is to encourage careful consideration of where and when to plant oak trees to help professionals address issues of uniformity, while achieving benefits for urban forest ecosystems and residents

    Balancing Urban Biodiversity Needs and Resident Preferences for Vacant Lot Management

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    Urban vacant lots are often a contentious feature in cities, seen as overgrown, messy eyesores that plague neighborhoods. We propose a shift in this perception to locations of urban potential, because vacant lots may serve as informal greenspaces that maximize urban biodiversity while satisfying residents’ preferences for their design and use. Our goal was to assess what kind of vacant lots are ecologically valuable by assessing their biotic contents and residents’ preferences within a variety of settings. We surveyed 150 vacant lots throughout Baltimore, Maryland for their plant and bird communities, classified the lot’s setting within the urban matrix, and surveyed residents. Remnant vacant lots had greater vegetative structure and bird species richness as compared to other lot origins, while vacant lot settings had limited effects on their contents. Residents preferred well-maintained lots with more trees and less artificial cover, support of which may increase local biodiversity in vacant lots. Collectively, we propose that vacant lots with a mixture of remnant and planted vegetation can act as sustainable urban greenspaces with the potential for some locations to enhance urban tree cover and bird habitat, while balancing the needs and preferences of city residents
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