350 research outputs found
Hydrologic variability and its influence on long‐term peat dynamics
No full textPeatlands are carbon‐rich ecosystems that are extensive in the northern high latitudes where significant 21st century climate changes are expected. In response to climate change, peatlands may become a net source of greenhouse gases, thereby inducing a positive climate feedback effect. In this paper, the impact of precipitation variability and the mean climate state on long‐term peat accumulation is investigated with model simulations. The models couple peat accumulation with the hydrological cycle, which results in peatland bistability, where peatlands may take the physical characteristics from one of two possible alternative stable states. The models consider precipitation as a stochastic forcing variable, temperature‐dependent functions and are parameterized with climatology and peat characteristics to represent the West Siberian Lowlands (WSL) between 55°N and 60°N. Observed WSL peat depths statistically imply bistability. Peatland bistability, however, is eliminated in model simulations with moderate‐to‐large precipitation variability and warmer and wetter climates. This suggests that projected late 21st century climate change would put the thick peatlands in WSL on a transition to thin peatlands. The loss of thick peatlands could significantly increase atmospheric carbon dioxide and provide a positive climate feedback effect. However, the impacts depend on the importance of unaccounted stabilizing factors. The study also shows that precipitation variability induces peatlands to switch between extended periods of accumulation and depletion even if the peatlands are in long‐term equilibrium. Thus, short‐term observations may see only natural fluctuations and new, longer‐term observational strategies are necessary to diagnose if peatlands are undergoing fundamental changes.Rennermalm, Asa K., Nordbotten, Jan M., and Wood, Eric F., "Hydrologic variability and its influence on long‐term peat dynamics." Water Resources Research 46 (Fall 2010), W12546. doi:10.1029/2009WR008242Copyright 2010 by the American Geophysical Union.Peer reviewe
Interannual Variability in Carbon Dioxide Flux from a High Arctic Fen Estimated by Measurements and Modeling
No full textThe response of high arctic ecosystems' carbon dioxide exchange to changing climate is uncertain and may be important from a climate-change perspective. In this study, the net ecosystem carbon dioxide exchange during four growing seasons is examined by combining measurements and modeling from a high arctic fen in northeastern Greenland. The summer-season net ecosystem exchange shows large interannual variations, fluctuating from an uptake of −50 g C m−2 to −123 g C m−2. Through ecosystem modeling, we can observe that leaf area index development and the maximum Rubisco capacity are more important controls on the interannual variability of net ecosystem carbon dioxide exchange than meteorological conditions. Furthermore, we present a hypothesis linking the interannual variability in maximum Rubisco capacity with leaf nitrogen content and leaf area index development. This hypothesis may provide a method to model seasonal net ecosystem carbon dioxide exchange in detail without having to resort to elaborate fitting procedures using measured carbon dioxide flux data.This article was published in Arctic, Antarctic, and Alpine Research (2005), and this Version of Record is archived in RUcore with permission. The published article is available from the Institute of Arctic and Alpine Research (INSTAAR) at: http://instaar.colorado.edu/aaar/journal_issues/abstract.php?id=2353Peer reviewe
Evidence of Meltwater Retention within the Greenland Ice Sheet
No full textGreenland ice sheet mass losses have increased in recent decades with more than half of these attributed to surface meltwater runoff. However, the magnitudes of englacial storage, firn retention, internal refreezing and other hydrologic processes that delay or reduce true water export to the global ocean remain less understood, partly due to a scarcity of in situ measurements. Here, ice sheet surface meltwater runoff and proglacial river discharge between 2008 and 2010 near Kangerlussuaq, southwestern Greenland were used to establish sub- and englacial meltwater storage for a small ice sheet watershed (36–64 km2). This watershed lacks significant potential meltwater storage in firn, surface lakes on the ice sheet and in the proglacial area, and receives limited proglacial precipitation. Thus, ice sheet surface runoff not accounted for by river discharge can reasonably be attributed to retention in sub- and englacial storage. Evidence for meltwater storage within the ice sheet includes (1) characteristic dampened daily river discharge amplitudes relative to ice sheet runoff; (2) three cold-season river discharge anomalies at times with limited ice sheet surface melt, demonstrating that meltwater may be retained up to 1–6 months; (3) annual ice sheet watershed runoff is not balanced by river discharge, and while near water budget closure is possible as much as 54% of melting season ice sheet runoff may not escape to downstream rivers; (4) even the large meltwater retention estimate (54%) is equivalent to less than 1% of the ice sheet volume, which suggests that storage in en- and subglacial cavities and till is plausible. While this study is the first to provide evidence for meltwater retention and delayed release within the Greenland ice sheet, more information is needed to establish how widespread this is along the Greenland ice sheet perimeter.Peer reviewe
Understanding Greenland ice sheet hydrology using an integrated multi-scale approach
No full textImproved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes within an integrated system. This letter describes a systems approach to the study of Greenland ice sheet hydrology, emphasizing component interconnections and feedbacks, and highlighting research and observational needs.Peer reviewe
Data visualization and optimization techniques for urban planning
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 69-71).In this thesis we describe a number of data visualization and optimization techniques for urban planning. Many of these techniques originate from contributions to the Social Computing Group's "You Are Here" project, which publishes maps intended to be viewed as a blend between art and urban planning tools. In particular these maps and this thesis focus on the topics of education and transportation. Eventually we hope to evolve these maps into social technologies that make it easier for communities to create the change they seek.by Asa Oines.M. Eng
De relatie tussen verwerking en morfologie van PC/ASA mengsels: De detectie van mengbaarheid in deze mengsels
No full textIn dit verslag wordt het onderzoek beschreven dat verricht is aan een PC/ASA mengsel. Als PolyCarbonaat is Lexan 141 gekozen en als het Acrylonitri1-Styreen-Acrylester Luran S778T. Dit mengsel is interessant om te onderzoeken vanwege de fysische crosslinks, die in het ASA voorkomen en welke een bicontinue structuur bevorderen. Het ASA bezit een zwichtspanning, die zorgt voor stabiliteit van de gevormde structuur. Eerder onderzoek aan het incompatibele systeem PP/ASA leverde niet de gewenste bicontinue structuur over een groot samenstellingsgebied op, zodat een compatibeler systeem (zoals PC/ASA zou moeten zijn) onderzocht is. Het mengsel is gemaakt met een extruder, waarbij zowel een meng- als transportschroef is gebruikt. Dit is gedaan om het effect van de soort verwerking op de reologische en mechanische eigenschappen en morfologie te bekijken. De mengsels zijn gekarakteriseerd en bekeken op mengbaarheid met DSC, DMTA, DETA en m. b. v een torsiemeting. De reologische metingen zijn uitgevoerd met een capillair reometer en met een plaat/plaat apparaat. Dezelfde capillair reometer is ook gebruikt om de mengsels te extruderen met een opgelegde afschuifsnelheid. Met een trekbank zijn de E-moduli van de mengsels bepaald. Verder is de morfologie van de mengsels onderzocht. Hiertoe zijn de mengsels, voor en na extractie onder een Scanning Electronen Microscoop bekeken. Tevens is de Transmissie Electronen Microscoop gebruikt om een beter onderscheid tussen de fasen te krijgen. De diverse methoden om de mengbaarheid te onderzoeken leveren een verschuiving op van de glas-rubberovergang van het PC. Gecombineerd met de TEM-beelden wordt aangenomen dat dit het gevolg is van een verplaatsing van laag moleculaire additieven naar de grenslaag tussen PC en het Styreen-Acrylonitri 1 (SAN). De verschuiving zegt in feite dus niets over de mengbaarheid tussen PC en ASA. Het mengsel vertoont bij hoge afschuifsnelheden (>10 s ) een NDB-gedrag en bij lagere afschuifsnelheden een PNDB-gedrag. Er kan niet echt een verband tussen reologie en morfologie gelegd worden. Bij de mechanische metingen wordt over een zeer groot samenstellingsgebied een synergistisch gedrag van de E-modulus gevonden. In het bicontinue gebied kan dit verklaard worden door de in elkaar grijpende fasen, die moeilijk uit elkaar getrokken kunnen worden en de goede hechting tussen de fasen. Een plateau van G' (bepaald onder torsie) tussen de glas-rubberovergangen van PC en SAN duidt op een continue PC-fase. Het morfologisch onderzoek levert een bicontinu gebied op van ±30-60% ASA. Nergens is de bicontinuïteit volledig, daar er altijd nog een fijne dispersie ASA aanwezig is in de continue PC-fase. De extractieresultaten bevestigen dit ook. Tussen de meng- en transportschroefmengsels wordt geen noemenswaardig verschil gevonden in eigenschappen of morfologie. Vanwege de "dode" ruimte in de gebruikte extruder kan dit veroorzaakt zijn door het verdwijnen van de door de schroeven gevormde structuur in deze ruimte. De uiteindelijke structuur wordt dan bepaald in de spuitmond van de extruder, waardoor de voorgeschiedenis niet meer van invloed is.Applied SciencesTechnologie van Macromoleculaire Stoffe
Revolutionary memorials : embracing poems /
No full text"General Burgoyne's proclamation" is from the Providence gazette of Aug. 16th, 1777. The account of the death of Jane M'Crea consists of a letter from Asa Fitch (Published in the Proceedings of the Historical society of New Jersey, v.5, p. 164) and some extracts from Charles Neilson's account of Burgoyne campaign.Includes reprint of original t.-p. (with author name inseted): Poems, occasioned by several circumstances and occurrences in the present grand contest of America for liberty. By the Rev. Wheeler Case, of Duchess-County, N.Y. Printed by Theo. and Samuel Green. 1778.Mode of access: Internet
How to be a woman. Models of masochism and sacrifice in young adult fiction
No full textBuffy, Bella, Veronica, Katniss, Clary, Tris and Saba : For two decades post-feminist heroines have faced life-threatening trials as part of their progress to womanhood. In this chapter I consider how young adult popular fictions operate as forms of pedagogy for young women by offering them particular models of maturity and womanhood. I explore the recurrence and reformulation of a persistent pattern of behaviour in which heroines engage in risky and/or masochistic behaviours for which they are emotionally rewarded.. These recurrences function as a form of vicarious experiential learning in which readers and viewers learn that emotional gratification and adult status are conferred through self-harm and self-sacrifice. Popular culture is not a monolithic form and young adult fictions are no exception. An analysis of fictional examples of this behaviour pattern challenges the idea that heroines today are empowered agents as a result of the legacy of feminism. At the same time, the analysis belies any notion that fictions are universally hegemonic and oppressive – fictions can and do disrupt and interrogate this pattern of emotional masochism. Scholars of public pedagogy have explored the complexities, contradictions and subtleties of the pedagogical process. Sandlin O’Malley and Burdick (2011) in their review of public pedagogy literature acknowledge that some scholarship has demonstrated how “the teaching and learning inherent within daily life can be both oppressive and resistant” (p. 144). Jubas and Knutson (2012) also see public pedagogy as an arena where contradictions and tensions are in play. They argue that we can see “New examples of dialectic or tensions … between the authority of the producer and the consumer; between traditional structures which ground identities and help people make sense of cultural texts, and personal agency which frees people to choose and invent identities and meanings” (p. 86). This analysis aims to contribute to understandings of the complexities of public pedagogy by showing how fictions aimed primarily at young women both resist and accommodate patriarchy
Differences and similarities in perceptions of interactions with Artificial Social Agents between German and English speakers
No full textHumans interact with various Artificial Social Agents (ASAs) on a daily basis. ASAs range from the Honda robot ASIMO to Apple’s Siri. To measure the perception of human-ASA interactions, a standardized questionnaire was created. Yet, this questionnaire was so far only available in English and Chinese. It has been found that culture can affect how these interactions are perceived. The aim of this study is to answer the question: What are the differences and similarities of the English and German human-ASA interaction interpretations? In this paper, we translate the questionnaire into German, validate it. Once proven valid, we give the English and German questionnaire on bilingual participants who watch a human-ASA interaction video and rate it in both languages. We measure the differences and similarities between the English and German responses. At the end, we combine the finding from the questionnaire results with examples from literature to form recommendations for future ASA developments. We conclude that an average good level of correlation between the two languages for the 90 questionnaire items (ICC M = 0.65, SD = 0.14, range [0.27, 0.90]), on the construct level (ICC M = 0.8, SD = 0.1, range [0.51, 0.92]), and for the 24 representative items (M = 0.67, SD = 0.14, range[0.31, 0.90]). Additionally, we found systematic differences between the English questionnaire scores of the bilingual sample seen in this study and a previously established mixed-English sample.CSE3000 Research ProjectComputer Science and Engineerin
Mandarin Chinese translation of the Artificial-Social-Agent questionnaire instrument for evaluating human-agent interaction
No full textThe Artificial-Social-Agent (ASA) questionnaire is an instrument for evaluating human-ASA interaction. It consists of 19 constructs and related dimensions measured by either 24 questionnaire items (short version) or 90 questionnaire items (long version). The questionnaire was built and validated by a research community effort to make evaluation results more comparable between agents and findings more generalizable. The current questionnaire is in English, which limits its use to only a population with an adequate command of the English language. Translating the questionnaire into more languages allows for the inclusion of other populations and the possibility of comparing them. Therefore, this paper presents a Mandarin Chinese translation of the questionnaire. After three construction cycles that included forward and backward translation, we gave both the final version of the translated and original English questionnaire to 242 bilingual crowd-workers to evaluate 14 ASAs. Results show on average a good level of correlation on the construct/dimension level (ICC M = 0.79, SD = 0.09, range [0.61, 0.95]) and on the item level (ICC M = 0.62, SD = 0.14, range [0.19, 0.92]) between the two languages for the long version, and for the short version (ICC M = 0.66, SD = 0.12, range [0.41, 0.92]). The analysis also established correction values for converting questionnaire item scores between Chinese and English questionnaires. Moreover, we also found systematic differences in English questionnaire scores between the bilingual sample and a previously collected mixed-international English-speaking sample. We hope this and the Chinese questionnaire translation will motivate researchers to study human-ASA interaction among a Chinese literate population and to study cultural similarities and differences in this area.Interactive Intelligenc
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