2,398 research outputs found
A method for assessing the success and failure of community-level interventions in the presence of network diffusion, social reinforcement, and related social effects
Prevention and intervention work done within community settings often face
unique analytic challenges for rigorous evaluations. Since community prevention
work (often geographically isolated) cannot be controlled in the same way other
prevention programs and these communities have an increased level of
interpersonal interactions, rigorous evaluations are needed. Even when the
`gold standard' randomized control trials are implemented within community
intervention work, the threats to internal validity can be called into question
given informal social spread of information in closed network settings. A new
prevention evaluation method is presented here to disentangle the social
influences assumed to influence prevention effects within communities. We
formally introduce the method and it's utility for a suicide prevention program
implemented in several Alaska Native villages. The results show promise to
explore eight sociological measures of intervention effects in the face of
social diffusion, social reinforcement, and direct treatment. Policy and
research implication are discussed.Comment: 18 pages, 5 figure
Lorentz shear modulus of fractional quantum Hall states
We show that the Lorentz shear modulus of macroscopically homogeneous
electronic states in the lowest Landau level is proportional to the bulk
modulus of an equivalent system of interacting classical particles in the
thermodynamic limit. Making use of this correspondence we calculate the Lorentz
shear modulus of Laughlin's fractional quantum Hall states at filling factor
( an odd integer) and find that it is equal to ,
where is the density of particles and the sign depends on the direction of
magnetic field. This is in agreement with the recent result obtained by Read in
arXiv:0805.2507 and corrects our previous result published in Phys. Rev. B {\bf
76}, 161305 (R) (2007).Comment: 8 pages, 3 figure
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Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins.
Human gut Bacteroides use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B12 transport in B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut
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