Two-way coupling of FENE dumbbells with a turbulent shear flow

We present numerical studies for finitely extensible nonlinear elastic (FENE) dumbbells which are dispersed in a turbulent plane shear flow at moderate Reynolds number. The polymer ensemble is described on the mesoscopic level by a set of stochastic ordinary differential equations with Brownian noise. The dynamics of the Newtonian solvent is determined by the Navier-Stokes equations. Momentum transfer of the dumbbells with the solvent is implemented by an additional volume forcing term in the Navier-Stokes equations, such that both components of the resulting viscoelastic fluid are connected by a two-way coupling. The dynamics of the dumbbells is given then by Newton's second law of motion including small inertia effects. We investigate the dynamics of the flow for different degrees of dumbbell elasticity and inertia, as given by Weissenberg and Stokes numbers, respectively. For the parameters accessible in our study, the magnitude of the feedback of the polymers on the macroscopic properties of turbulence remains small as quantified by the global energy budget and the Reynolds stresses. A reduction of the turbulent drag by up to 20% is observed for the larger particle inertia. The angular statistics of the dumbbells shows an increasing alignment with the mean flow direction for both, increasing elasticity and inertia. This goes in line with a growing asymmetry of the probability density function of the transverse derivative of the streamwise turbulent velocity component. We find that dumbbells get stretched referentially in regions where vortex stretching or bi-axial strain dominate the local dynamics and topology of the velocity gradient tensor.Comment: 20 pages, 10 Postscript figures (Figures 5 and 10 in reduced quality

How Does Light Rail Transit Affect Urban Land Use?

This paper estimates the effect of the Hiawatha Light Rail Transit (LRT) line on land use change in Minneapolis, MN, between 2000 and 2010. I use a binomial logit model and find that within the 1-mile submarket near LRT, the effect of distance to LRT stations on land use change had a different radius and magnitude depending on existing land use. The effect of LRT on conversions of low-density housing to denser uses only extended out to 90 feet from stations after LRT went into operation. Vacant and industrial land were the most likely to experience land use change, especially in working class, mixed land use neighborhoods with higher population densities. In general, the effect of LRT on land use change was limited in high income neighborhoods. Zoning policy changes around stations had a small but significant positive effect on land use change

BNFinder: exact and efficient method for learning Bayesian networks

Motivation: Bayesian methods are widely used in many different areas of research. Recently, it has become a very popular tool for biological network reconstruction, due to its ability to handle noisy data. Even though there are many software packages allowing for Bayesian network reconstruction, only few of them are freely available to researchers. Moreover, they usually require at least basic programming abilities, which restricts their potential user base. Our goal was to provide software which would be freely available, efficient and usable to non-programmers

Sacred communities: contestations and connections

This article discusses a project whose purpose was to review existing qualitative and quantitative data from two separate studies to provide new insights about everyday religion and belonging. Researchers engaged in knowledge exchange and dialogue with new and former research participants, with other researchers involved in similar research, and with wider academic networks beyond the core disciplines represented here, principally anthropology and geography. Key concluding themes related to the ambivalent nature of ‘faith’, connections over place and time, and the contested nature of community. Implicit in terms like ‘faith’, ‘community’, and ‘life course’ are larger interwoven narratives of space, time, place, corporeality, and emotion. The authors found that understanding how places, communities, and faiths differ and intersect requires an understanding of social relatedness and boundaries

Overcharging a Black Hole and Cosmic Censorship

We show that, contrary to a widespread belief, one can overcharge a near extremal Reissner-Nordstrom black hole by throwing in a charged particle, as long as the backreaction effects may be considered negligible. Furthermore, we find that we can make the particle's classical radius, mass, and charge, as well as the relative size of the backreaction terms arbitrarily small, by adjusting the parameters corresponding to the particle appropriately. This suggests that the question of cosmic censorship is still not wholly resolved even in this simple scenario. We contrast this with attempting to overcharge a black hole with a charged imploding shell, where we find that cosmic censorship is upheld. We also briefly comment on a number of possible extensions.Comment: 26 pages, 3 figures, LaTe

Authenticated Key Distribution: When the Coupon Collector is Your Enemy

We introduce new authenticated key exchange protocols which on the one hand do not resort to standard public key setups with corresponding assumptions of computationally hard problems, but on the other hand, are more efficient than distributing symmetric keys among the participants. To this end, we rely on a trusted central authority distributing key material whose size is independent of the total number of users, and which allows the users to obtain shared secret keys. We analyze the security of our construction, taking into account various attack models. Importantly, only symmetric primitives are needed in the protocol making it an alternative to quantum-safe key exchange protocols which rely on hardness assumptions