133 research outputs found

    Influence of chronic Helicobacter pylori infection on systemic and neuroinflammation and its impact on cognition

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    Helicobacter pylori is the major bacterial colonizer of the human stomach. It is estimated that approximately 50% of humans worldwide are chronically infected with this bacterium. Epidemiologically, H. pylori is recognized as the major risk factor and etiological agent of peptic ulcer disease and gastric adenocarcinoma. Most animal models utilized for evaluating H. pylori infection have examined the gastric effects of chronic infection with regard to ulcer and cancer development. However, interest into the potential extra-gastric influences of chronic H. pylori infection has been growing in the field. Utilizing a Sprague-Dawley rat based model for chronic H. pylori infection, the role of chronic infection in the development of systemic and neuro-inflammation was evaluated. High sensitivity ELISA assays were utilized to determine the change in key inflammatory markers locally within the stomach, systemically in the plasma and within the liver and the spleen, and within the central nervous system in the hippocampus and cerebellum. Eradication studies were conducted to determine the causal relationship between H. pylori infection and observed levels of inflammation. Finally, cognitive behavioral studies were conducted to evaluate the potential influence of chronic H. pylori infection on cognitive function and health. Altogether, these studies illustrate a model by which chronic infection established during early life modulates the immune system response to generate a mild, but chronically sustained, systemic and neuro-inflammatory state which is associated with impairment of pre-frontal cortex mediated cognition. Furthermore, it is proposed that the development of these cognitive impairments arise during key developmental windows resulting in persistence of the impairment after successful eradication of H. pylori

    Superradiant Decay of Cyclotron Resonance of Two-Dimensional Electron Gases

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    We report on the observation of collective radiative decay, or superradiance, of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay rate of coherent CR oscillations increases linearly with the electron density in a wide range, which is a hallmark of superradiant damping. Our fully quantum mechanical theory provides a universal formula for the decay rate, which reproduces our experimental data without any adjustable parameter. These results firmly establish the many-body nature of CR decoherence in this system, despite the fact that the CR frequency is immune to electron-electron interactions due to Kohn's theorem.Comment: 5 pages, 4 figure

    Density imbalance effect on the Coulomb drag upturn in an electron-hole bialyer

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    A low-temperature upturn of the Coulomb drag resistivity measured in an undoped electron-hole bilayer (uEHBL) device, possibly manifesting from exciton formation or condensation, was recently observed. The effects of density imbalance on this upturn are examined. Measurements of drag as a function of temperature in a uEHBL with a 20 nm wide Al.90_{.90}Ga.10_{.10}As barrier layer at various density imbalances are presented. The results show drag increasing as the density of either two dimensional system was reduced, both within and above the upturn temperature regime. A comparison of the data with numerical calculations of drag in the presence of electron-hole pairing fluctuations, which qualitatively reproduce the drag upturn behavior, is also presented. The calculations, however, predict a peak in drag at matched densities, which is not reflected by the measurements.Comment: 4 pages, 4 figures, submitted to PRB Rapi

    Major flaws in conflict prevention policies towards Africa : the conceptual deficits of international actors’ approaches and how to overcome them

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    Current thinking on African conflicts suffers from misinterpretations oversimplification, lack of focus, lack of conceptual clarity, state-centrism and lack of vision). The paper analyses a variety of the dominant explanations of major international actors and donors, showing how these frequently do not distinguish with sufficient clarity between the ‘root causes’ of a conflict, its aggravating factors and its triggers. Specifically, a correct assessment of conflict prolonging (or sustaining) factors is of vital importance in Africa’s lingering confrontations. Broader approaches (e.g. “structural stability”) offer a better analytical framework than familiar one-dimensional explanations. Moreover, for explaining and dealing with violent conflicts a shift of attention from the nation-state towards the local and sub-regional level is needed.Aktuelle Analysen afrikanischer Gewaltkonflikte sind hĂ€ufig voller Fehlinterpretationen (Mangel an Differenzierung, Genauigkeit und konzeptioneller Klarheit, Staatszentriertheit, fehlende mittelfristige Zielvorstellungen). Breitere AnsĂ€tze (z. B. das Modell der Strukturellen StabilitĂ€t) könnten die Grundlage fĂŒr bessere Analyseraster und Politiken sein als eindimensionale ErklĂ€rungen. hĂ€ufig differenzieren ErklĂ€rungsansĂ€tze nicht mit ausreichender Klarheit zwischen Ursachen, verschĂ€rfenden und auslösenden Faktoren. Insbesondere die richtige Einordnung konfliktverlĂ€ngernder Faktoren ist in den jahrzehntelangen gewaltsamen Auseinandersetzungen in Afrika von zentraler Bedeutung. Das Diskussionspapier stellt die große Variationsbreite dominanter ErklĂ€rungsmuster der wichtigsten internationalen Geber und Akteure gegenĂŒber und fordert einen Perspektivenwechsel zum Einbezug der lokalen und der subregionalen Ebene fĂŒr die ErklĂ€rung und Bearbeitung gewaltsamer Konflikte
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