133 research outputs found
Influence of chronic Helicobacter pylori infection on systemic and neuroinflammation and its impact on cognition
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
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
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 AlGaAs 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 actorsâ approaches and how to overcome them
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 âroot causesâ of a conflict, its aggravating factors and its triggers. Specifically, a correct assessment of conflict prolonging (or sustaining) factors is of vital importance in Africaâs lingering confrontations. Broader approaches (e.g. âstructural stabilityâ) 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 groĂe 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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LDRD final report on continuous wave intersubband terahertz sources.
There is a general lack of compact electromagnetic radiation sources between 1 and 10 terahertz (THz). This a challenging spectral region lying between optical devices at high frequencies and electronic devices at low frequencies. While technologically very underdeveloped the THz region has the promise to be of significant technological importance, yet demonstrating its relevance has proven difficult due to the immaturity of the area. While the last decade has seen much experimental work in ultra-short pulsed terahertz sources, many applications will require continuous wave (cw) sources, which are just beginning to demonstrate adequate performance for application use. In this project, we proposed examination of two potential THz sources based on intersubband semiconductor transitions, which were as yet unproven. In particular we wished to explore quantum cascade lasers based sources and electronic based harmonic generators. Shortly after the beginning of the project, we shifted our emphasis to the quantum cascade lasers due to two events; the publication of the first THz quantum cascade laser by another group thereby proving feasibility, and the temporary shut down of the UC Santa Barbara free-electron lasers which were to be used as the pump source for the harmonic generation. The development efforts focused on two separate cascade laser thrusts. The ultimate goal of the first thrust was for a quantum cascade laser to simultaneously emit two mid-infrared frequencies differing by a few THz and to use these to pump a non-linear optical material to generate THz radiation via parametric interactions in a specifically engineered intersubband transition. While the final goal was not realized by the end of the project, many of the completed steps leading to the goal will be described in the report. The second thrust was to develop direct THz QC lasers operating at terahertz frequencies. This is simpler than a mixing approach, and has now been demonstrated by a few groups with wavelengths spanning 65-150 microns. We developed and refined the MBE growth for THz for both internally and externally designed QC lasers. Processing related issues continued to plague many of our demonstration efforts and will also be addressed in this report
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