7,069 research outputs found
A microbial symbiosis factor prevents intestinal inflammatory disease
Humans are colonized by multitudes of commensal organisms representing members of five of the six kingdoms of life; however, our gastrointestinal tract provides residence to both beneficial and potentially pathogenic microorganisms. Imbalances in the composition of the bacterial microbiota, known as dysbiosis, are postulated to be a major factor in human disorders such as inflammatory bowel disease. We report here that the prominent human symbiont Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus, a commensal bacterium with pathogenic potential. This beneficial activity requires a single microbial molecule (polysaccharide A, PSA). In animals harbouring B. fragilis not expressing PSA, H. hepaticus colonization leads to disease and pro-inflammatory cytokine production in colonic tissues. Purified PSA administered to animals is required to suppress pro-inflammatory interleukin-17 production by intestinal immune cells and also inhibits in vitro reactions in cell cultures. Furthermore, PSA protects from inflammatory disease through a functional requirement for interleukin-10-producing CD4+ T cells. These results show that molecules of the bacterial microbiota can mediate the critical balance between health and disease. Harnessing the immunomodulatory capacity of symbiosis factors such as PSA might potentially provide therapeutics for human inflammatory disorders on the basis of entirely novel biological principles
A study of air-to-ground sound propagation using an instrumented meteorological tower
The results of an exploratory NASA study, leading to a better understanding of the effects of meteorological conditions on the propagation of aircraft noise, are reported. The experimental program utilized a known sound source fixed atop an instrumented meteorological tower. The basic experimental scheme consisted of measuring the amplitude of sound radiated toward the ground along a line of microphones fixed to a tower guy wire. Experimental results show the feasibility of this approach in the acquisition of data indicating the variations encountered in the time-averaged and instantaneous amplitudes of propagated sound. The investigation included a consideration of ground reflections, a comparison of measured attenuations with predicted atmospheric absorption losses, and an evaluation of the amplitude fluctuations of recorded sound pressures
Heterotic T-Duality and the Renormalization Group
We consider target space duality transformations for heterotic sigma models
and strings away from renormalization group fixed points. By imposing certain
consistency requirements between the T-duality symmetry and renormalization
group flows, the one loop gauge beta function is uniquely determined, without
any diagram calculations. Classical T-duality symmetry is a valid quantum
symmetry of the heterotic sigma model, severely constraining its
renormalization flows at this one loop order. The issue of heterotic anomalies
and their cancelation is addressed from this duality constraining viewpoint.Comment: 17 pages, Late
The Starting Lineup: Key Microbial Players in Intestinal Immunity and Homeostasis
The complexity of microbiota inhabiting the intestine is increasingly apparent. Delicate balance of numerous bacterial species can affect development of the immune system, how susceptible a host is to pathogenic organisms, and the auto-inflammatory state of the host. In the last decade, with the increased use of germ-free mice, gnotobiotic mice, and animal models in which a germ-free animal has been colonized with a foreign microbiota such as humanized mice, it has been possible to delineate relationships that specific bacteria have with the host immune system and to show what role they may play in overall host health. These models have not only allowed us to tease out the roles of individual species, but have also allowed the discovery and characterization of functionally unknown organisms. For example, segmented filamentous bacteria (SFB) have been shown to play a vital role in expansion of IL-17 producing cells. Prior to linking their key role in immune system development, little was known about these organisms. Bacteroides fragilis can rescue some of the immune defects of gnotobiotic mice after mono-colonization and have anti-inflammatory properties that can alleviate colitis and experimental allergic encephalitis in murine models. Additionally, Clostridium species have most recently been shown to expand regulatory T-cell populations leading to anti-inflammatory conditions. This review will highlight and summarize some of the major findings within the last decade concerning the role of select groups of bacteria including SFB, Clostridium, Bacteroides, Bifidobacterium, and Lactobacillus, and their impact on host mucosal immune systems
Shock waves in a one-dimensional Bose gas: from a Bose-Einstein condensate to a Tonks gas
We derive and analyze shock-wave solutions of hydrodynamic equations
describing repulsively interacting one dimensional Bose gas. We also use the
number-conserving Bogolubov approach to verify accuracy of the Gross-Pitaevskii
equation in shock wave problems. We show that quantum corrections to dynamics
of shocks (dark-shock-originated solitons) in a Bose-Einstein condensate are
negligible (important) for a realistic set of system parameters. We point out
possible signatures of a Bose-Einstein condensate -- Tonks crossover in shock
dynamics. Our findings can be directly verified in different experimental
setups.Comment: 10 pages, small corrections with respect to the last submission,
version accepted in Phys. Rev.
Local weather, food resources and breeding stage influence Thrush Nightingale movement
Insectivorous migrants breeding at northern latitudes often time the breeding period with the seasonal peak of food resources. Whether this general pattern transfers to movement behaviour during the breeding season requires detailed study from a local perspective. We investigated fine-scale environmental correlates of movements by six actively-breeding adult Thrush Nightingales (Luscinia luscinia) at a breeding site in Denmark, using radio tracking and multiple regression models. Overall, the chick-rearing period coincided with the peak of vegetation greenness at the site. Adults flew further from nesting areas during stable weather and as vegetation greenness decreased. Adults were more active at higher environmental temperatures and when fledglings were older but still dependent on adults. These changes in local movements likely reflect adjustments to chick developmental needs and to specific local environmental conditions, including resource availability
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