2,059 research outputs found
Effects of permafrost thaw on nitrogen availability and plant soil interaction in a boreal Alaska lowland
Thesis (M.S.) University of Alaska Fairbanks, 2014Permafrost thaw in boreal peatlands causes an ecosystem state change as black spruce forests with permafrost transition into saturated, non-forested collapse scar bogs or fens. Previous studies have suggested that permafrost thaw can increase soil nitrogen (N) bioavailability. However, it is unclear whether these changes in N availability are directly related to changes in N pools or mineralization rates in surface soils (active layer dynamics), or whether increasing N can be attributed to N mobilization from thawing permafrost soil organic matter at depth. I examined plant species composition and aspects of N cycling along triplicate permafrost-thaw gradients in interior Alaskan peatlands. Each gradient comprised plots situated in a 1) forested plateau with intact permafrost (hereafter called permafrost forest) 2) forest experiencing active thaw (drunken forest), 3) moat representing initial stages of complete thaw (moat), and 4) collapse scar bog representing post-thaw succession following complete permafrost thaw (collapse bog). I found that both organic and inorganic N concentrations in soil solution increased with thaw. Drunken forests with active permafrost thaw had the greatest mean concentrations of total dissolved N relative to the other gradient plots. Elevated levels of dissolved N in the drunken forest plots were due primarily to high concentrations of large molecular DON. The moat and collapse scar bog plots had greater inorganic N concentrations on average than the permafrost forest or the drunken forest, suggesting that changes in plantavailable N do not occur immediately upon thaw, but are influenced by vegetation or soil succession occurring decades to centuries after thaw is initiated. However, across all of the community types, I found that deeper soil horizons corresponded to greater concentrations of DIN and DON when thaw was deepest (September), suggesting that permafrost soil horizons are playing a role in changing N availability post-thaw. Vegetation responses to permafrost thaw included changes in plant community composition, deeper rooting profiles, and changes in foliar N and ÎŽÂčâ”N values. Plant foliar and litterfall N concentrations increased with collapse bog succession and showed relationships with concentrations of DIN, suggesting that plants are utilizing additional mineralized N. Together, my results suggest that the conversion of lowland permafrost forests to collapse scar bogs increases N availability both by increasing turnover of the permafrost organic matter pool as well as through longer-term successional processes. At least some plants are able to capitalize on "new" sources of N available post-thaw, but it is unclear from my results whether plants are able to acquire N mobilized by thawing permafrost organic matter deeper in soil profiles
Na(V)1.5 sodium channel window currents contribute to spontaneous firing in olfactory sensory neurons
Olfactory sensory neurons (OSNs) fire spontaneously as well as in response to odor; both forms of firing are physiologically important. We studied voltage-gated Na+ channels in OSNs to assess their role in spontaneous activity. Whole cell patch-clamp recordings from OSNs demonstrated both tetrodotoxin-sensitive and tetrodotoxin-resistant components of Na+ current. RT-PCR showed mRNAs for five of the nine different Na+ channel α-subunits in olfactory tissue; only one was tetrodotoxin resistant, the so-called cardiac subtype NaV1.5. Immunohistochemical analysis indicated that NaV1.5 is present in the apical knob of OSN dendrites but not in the axon. The NaV1.5 channels in OSNs exhibited two important features: 1) a half-inactivation potential near â100 mV, well below the resting potential, and 2) a window current centered near the resting potential. The negative half-inactivation potential renders most NaV1.5 channels in OSNs inactivated at the resting potential, while the window current indicates that the minor fraction of noninactivated NaV1.5 channels have a small probability of opening spontaneously at the resting potential. When the tetrodotoxin-sensitive Na+ channels were blocked by nanomolar tetrodotoxin at the resting potential, spontaneous firing was suppressed as expected. Furthermore, selectively blocking NaV1.5 channels with Zn2+ in the absence of tetrodotoxin also suppressed spontaneous firing, indicating that NaV1.5 channels are required for spontaneous activity despite resting inactivation. We propose that window currents produced by noninactivated NaV1.5 channels are one source of the generator potentials that trigger spontaneous firing, while the upstroke and propagation of action potentials in OSNs are borne by the tetrodotoxin-sensitive Na+ channel subtypes.This work was aided by support from Boston University, the Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD) P30 DC-04657; D. Restrepo, principal investigator], and NIDCD Grants DC-04863 to V. Dionne and DC-006070 to D. Restrepo and T. E. Finger. (Boston University; P30 DC-04657 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)]; DC-04863 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)]; DC-006070 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)])https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4122723/Accepted manuscrip
Das iranische Atomprogramm und der Westen: Bilanz und Ausblick der nuklearen Nichtverbreitung in europÀischen FachaufsÀtzen
Die Frage, ob und wie der Iran zu einem Verzicht auf ein militĂ€risches Atomprogramm bewegt werden kann, ist fĂŒr die Zukunft sowohl der internationalen Sicherheit als auch speziell des globalen Nichtverbreitungsregimes von groĂer Bedeutung. Am 31. August 2006 lieĂ Teheran das vom UN-Sicherheitsrat gestellte Ultimatum verstreichen und widersetzte sich damit der Forderung, die Entwicklung eines eigenen Brennstoffkreislaufs zumindest vorĂŒbergehend auszusetzen. Die internationale Staatengemeinschaft ist nun herausgefordert, auf die VerstöĂe des Iran wirksam und geschlossen zu reagieren. In den BeitrĂ€gen einschlĂ€giger Fachzeitschriften wird unter anderem der Frage nachgegangen, welche Motive der Iran haben könnte, Nuklearwaffen zu entwickeln. Einige Autoren unterziehen die diplomatischen BemĂŒhungen der EU-3 einer kritischen Analyse. Angesichts der Gefahr einer Erosion des Nichtverbreitungsregimes werden auĂerdem mögliche Handlungsoptionen der internationalen Gemeinschaft diskutiert. (Autorenreferat
Simulation and observations of stratospheric aerosols from the 2009 Sarychev volcanic eruption
We used a general circulation model of Earthâs climate to conduct simulations of the 12-16 June 2009 eruption of Sarychev volcano (48.1°N, 153.2°E). The model simulates the formation and transport of the stratospheric sulfate aerosol cloud from the eruption and the resulting climate response. We compared optical depth results from these simulations with limb scatter measurements from the Optical Spectrograph and InfraRed Imaging System (OSIRIS), in situ measurements from balloon-borne instruments lofted from Laramie, Wyoming (41.3°N, 105.7°W), and five lidar stations located throughout the Northern Hemisphere. The aerosol cloud covered most of the Northern Hemisphere, extending slightly into the tropics, with peak backscatter measured between 12 and 16 km in altitude. Aerosol concentrations returned to near background levels by Spring, 2010. After accounting for expected sources of discrepancy between each of the data sources, the magnitudes and spatial distributions of aerosol optical depth due to the eruption largely agree. In conducting the simulations, we likely overestimated both particle size and the amount of SO2 injected into the stratosphere, resulting in modeled optical depth values that were a factor of 2-4 too high. Model results of optical depth due to the eruption show a peak too late in high latitudes and too early in low latitudes, suggesting a problem with stratospheric circulation in the model. The model also shows a higher annual decay rate in optical depth than is observed, showing an inaccuracy in seasonal deposition rates. The modeled deposition rate of sulfate aerosols from the Sarychev eruption is higher than the rate calculated for aerosols from the 1991 eruption of Mt. Pinatubo
Over-optimism in unsupervised microbiome analysis: Insights from network learning and clustering
In recent years, unsupervised analysis of microbiome data, such as microbial network analysis and clustering, has increased in popularity. Many new statistical and computational methods have been proposed for these tasks. This multiplicity of analysis strategies poses a challenge for researchers, who are often unsure which method(s) to use and might be tempted to try different methods on their dataset to look for the âbestâ ones. However, if only the best results are selectively reported, this may cause over-optimism: the âbestâ method is overly fitted to the specific dataset, and the results might be non-replicable on validation data. Such effects will ultimately hinder research progress. Yet so far, these topics have been given little attention in the context of unsupervised microbiome analysis. In our illustrative study, we aim to quantify over-optimism effects in this context. We model the approach of a hypothetical microbiome researcher who undertakes four unsupervised research tasks: clustering of bacterial genera, hub detection in microbial networks, differential microbial network analysis, and clustering of samples. While these tasks are unsupervised, the researcher might still have certain expectations as to what constitutes interesting results. We translate these expectations into concrete evaluation criteria that the hypothetical researcher might want to optimize. We then randomly split an exemplary dataset from the American Gut Project into discovery and validation sets multiple times. For each research task, multiple method combinations (e.g., methods for data normalization, network generation, and/or clustering) are tried on the discovery data, and the combination that yields the best result according to the evaluation criterion is chosen. While the hypothetical researcher might only report this result, we also apply the âbestâ method combination to the validation dataset. The results are then compared between discovery and validation data. In all four research tasks, there are notable over-optimism effects; the results on the validation data set are worse compared to the discovery data, averaged over multiple random splits into discovery/validation data. Our study thus highlights the importance of validation and replication in microbiome analysis to obtain reliable results and demonstrates that the issue of over-optimism goes beyond the context of statistical testing and fishing for significance
Die virtuelle Exkursion als Lehr- und Lernumgebung in Schule und Hochschule
Die Deutsche Gesellschaft fĂŒr Geographie (DGfG) bezeichnet die Geographie als Wissenschaft vom Raum, in deren Mittelpunkt die Erde als System mit ihren TeilrĂ€umen unterschiedlicher Abgrenzung und unterschiedlichen MaĂstĂ€ben steht. Das Schulfach Geographie beschĂ€ftigt sich ebenfalls mit Raumkategorien, wobei der Beitrag des Faches in der Auseinandersetzung mit Wechselbeziehungen zwischen Natur und Gesellschaft in RĂ€umen unterschiedlicher Art und GröĂe zu sehen ist (DGfG 2012). Die entsprechende Methode wird als Raumanalyse bezeichnet und setzt sich aus mehreren Teilmethoden zusammen (Kultusministerium Sachsen-Anhalt 2009). Ein Raum kann sowohl mithilfe von Methoden der realen Begegnung, z. B. in Form einer Exkursion, als auch mit Methoden der medialen Anschauung (z. B. durch Bilder und Filme) analysiert werden. Die virtuelle Exkursion als multimediale Lehr- und Lernumgebung bietet eine neue Möglichkeit, geographische RĂ€ume virtuell, multimedial sowie interaktiv zu erkunden. Im vorliegenden Beitrag werden der Begriff der virtuellen Exkursion und deren Merkmale an dem konkreten Beispiel des Elbeeinzugsgebietes erlĂ€utert sowie deren Einsatzmöglichkeiten in Schule und Hochschule diskutiert. AbschlieĂend wird ein Vorschlag fĂŒr die Bewertung von virtuellen Exkursionen im Rahmen von PrĂŒfungsleistungen vorgestellt
Reiche Lebenswelten in NS-Deutschland
Research on Nazi Germany until the 1980s mainly described social inequality from the workersâ perspective. The top of the social hierarchy was at the most considered as co-responsible for the rise of National Socialism. More recent research on the âVolksgemeinschaftâ (ethnic community of the German nation) also perceived material inequality at best only marginally, as a background for research on gender, race and ethnicity, on visualization strategies, everyday practices and violence: gender and race dominate the image of the âVolksgemeinschaftâ, class remained a stepchild of the debate. The article therefore examines the power of an entrepreneurial family to fashion their social, economic and political environment even under National Socialism (Gestaltungsmacht, -chancen) and considers the opportunities and spaces opened or closed by the Nazi regime. Three perspectives of investigation are distinguished, always with the focus on this very capacity to âfashionâ the world: inequality, legitimate wealth and entrepreneurship in Nazi ideology; entrepreneurial action as the shaping of oneâs own environment; the shaping of private life as an expression of wealth.
Using the example of the Bielefeld entrepreneur family Oetker-Kaselowsky, the lifestyle and fashioning power of rich Germans under National Socialism are examined. They represent the large number of bourgeois families in Germany, where âtheâ company was the core of economic interests, where the nexus of family and company developed enormous binding power. The sphere of action of this family remained largely national. Given the defeats in both world wars and the expansive policies of the Nazi regime, ânationalâ was, of course, not a constant but a fluid variable between 1918 and 1949. However, the family not only reacted to the political course of time, it also adapted it for its own purposes, for example in the companyâs social policies, in the development of new business fields and in the formation of organizational structures. The display of wealth was unproblematic as long as it was socially and regime-compatible: it was socially compatible because it had a function for public welfare and patronage; it was the object of propagandistic reinterpretation, thus demonstrating the connection of wealth to the purposes of the âVolksgemeinschaftâ. The representation of wealth and social difference was compatible with the regime, since it integrated the new political elite of Nazi Germany.Soziale Ungleichheit wurde in der NS-Forschung bis in die 1980er Jahre vor allem aus der Arbeiterperspektive beschrieben. Die Spitzen der Sozialhierarchie kamen höchstens als Mitverantwortliche fĂŒr den Aufstieg des Nationalsozialismus in Betracht. Auch die jĂŒngere Forschung zur âVolksgemeinschaftâ nahm materielle Ungleichheit allenfalls am Rande wahr, als Hintergrundfolie einer auf Geschlecht, Rasse und ethnische Zugehörigkeit, auf Visualisierungsstrategien, Alltagspraktiken und Gewalt gerichteten Forschung: Gender und race dominieren das Bild von der âVolksgemeinschaftâ, class blieb ein Stiefkind der Debatte. Der Artikel fragt deshalb nach der Gestaltungsmacht einer Unternehmerfamilie im Nationalsozialismus sowie nach den Chancen und RĂ€umen, die der NS eröffnete oder verschloss. Drei Untersuchungsperspektiven werden unterschieden, wobei im Zentrum die Frage nach den Gestaltungschancen liegt, die Reichtum auch wĂ€hrend des NS eröffnete: Ungleichheit, legitimer Reichtum und Unternehmertum in der NS-Ideologie; unternehmerisches Handeln als Gestaltung der eigenen Umwelt; die Gestaltung der privaten LebensfĂŒhrung als Ausdruck von Reichtum.
Am Beispiel der Bielefelder Unternehmerfamilie Oetker-Kaselowsky werden Lebensstil und Gestaltungsmacht reicher Deutscher im Nationalsozialismus untersucht. Sie stehen stellvertretend fĂŒr die Vielzahl wirtschaftsbĂŒrgerlicher Familien in Deutschland, in denen âdasâ Unternehmen der Kern der ökonomischen Interessen war, bei denen der Nexus von Familie und Unternehmen enorme Bindungskraft entwickelte. Der Handlungsraum dieser Familie blieb weitgehend national bestimmt. Angesichts der Niederlagen in beiden Weltkriegen und der expansiven Politik des NS-Regimes war ânationalâ freilich zwischen 1918 und 1949 keine feste, sondern eine fluide GröĂe. Die Familie reagierte aber nicht nur auf die politischen ZeitlĂ€ufte, sie adaptierte sie auch fĂŒr ihre eigenen Zwecke, etwa in der betrieblichen Sozialpolitik, bei der Entwicklung neuer GeschĂ€ftsfelder und bei der Anpassung von Organisationsstrukturen. Dabei war die Zurschaustellung von Reichtum unproblematisch, solange sie sozial- und regimevertrĂ€glich war: SozialvertrĂ€glich war sie, da sie eine Funktion fĂŒr soziale FĂŒrsorge und MĂ€zenatentum hatte; sie war das Objekt propagandistischer Umdeutung, die die RĂŒckbindung des Reichtums an die Zwecke der âVolksgemeinschaftâ demonstrierte. RegimevertrĂ€glich war die ReprĂ€sentation von Reichtum und sozialer Differenz, da sie die TrĂ€ger des Regimes, die neuen politischen Eliten des NS beteiligte.Jusquâaux annĂ©es 1980, la recherche sur lâAllemagne nazie a dĂ©crit lâinĂ©galitĂ© sociale principalement du point de vue des travailleurs. Le sommet de la hiĂ©rarchie sociale Ă©tait au mieux considĂ©rĂ© comme coresponsable de la montĂ©e du national-socialisme. Des recherches plus rĂ©centes sur la « Volksgemeinschaft » (communautĂ© ethnique) ont Ă©galement perçu lâinĂ©galitĂ© matĂ©rielle au mieux marginalement, comme un fond pour la recherche sur le genre, la race et l'ethnicitĂ©, sur les stratĂ©gies de visualisation, les pratiques quotidiennes et la violence : le genre et la race dominent lâimage de la « Volksgemeinschaft », la classe est curieusement absente du dĂ©bat. Lâarticle examine donc le pouvoir dâune famille entrepreneuriale sous le national-socialisme de façonner leur propre environnement social, Ă©conomique et politique, tout en considĂ©rant les opportunitĂ©s et les espaces ouverts ou fermĂ©s par le rĂ©gime nazi. Trois perspectives dâinvestigation sont distinguĂ©es, lâaccent Ă©tant toujours mis sur les opportunitĂ©s Ă façonner son environnement que la richesse a ouvertes Ă l'Ă©poque nazie : lâinĂ©galitĂ©, la richesse lĂ©gitime et lâesprit dâentrepreneur dans lâidĂ©ologie nazie ; lâaction entrepreneuriale comme façonnage de son propre environnement ; le façonnage de la vie privĂ©e comme une expression de la richesse.
Le mode de vie et le pouvoir de façonnage des riches Allemands sous le national-socialisme sont examinĂ©s Ă lâexemple de la famille dâentrepreneurs Oetker-Kaselowsky de Bielefeld. Ils sont reprĂ©sentatifs du grand nombre de familles bourgeoises, oĂč « lâentreprise » Ă©tait au cĆur des intĂ©rĂȘts Ă©conomiques, oĂč le lien de la famille et de lâentreprise a dĂ©veloppĂ© un Ă©norme pouvoir contraignant. Le champ dâaction de cette famille est restĂ© largement national. Compte tenu des dĂ©faites des deux guerres mondiales et de la politique expansionniste du rĂ©gime nazi, le « national » nâĂ©tait bien sĂ»r pas une constante mais une variable fluide entre 1918 et 1949. Mais la famille nâa pas seulement rĂ©agi Ă lâĂ©volution politique du temps, elle lâa aussi adaptĂ© Ă ses propres besoins, par exemple dans la politique sociale de l'entreprise, dans le dĂ©veloppement de nouveaux secteurs dâactivitĂ© et dans lâadaptation de ses structures organisationnelles. Afficher publiquement la richesse ne posait pas de problĂšme tant que cette richesse Ă©tait reprĂ©sentĂ©e comme compatible avec la « Volksgemeinschaft » et en accord avec le rĂ©gime : La richesse Ă©tait socialement compatible parce quâelle avait une fonction pour lâassistance sociale, le mĂ©cĂ©nat et la dynamique Ă©conomique ; elle Ă©tait lâobjet dâune rĂ©interprĂ©tation propagandiste qui lâa liĂ© aux objectifs de la « Volksgemeinschaft ». DeuxiĂšment, la richesse et les diffĂ©rences sociales associĂ©es Ă©taient reprĂ©sentĂ©es en accord avec le rĂ©gime en intĂ©grant ses porteurs, les nouvelles Ă©lites politiques nazies
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