Black holes in a box

The evolution of BHs in "confining boxes" is interesting for a number of reasons, particularly because it mimics some aspects of anti-de Sitter spacetimes. These admit no Cauchy surface and are a simple example of a non-globally hyperbolic spacetime. We are here interested in the potential role that boundary conditions play in the evolution of a BH system. For that, we imprison a binary BH in a box, at which boundary we set mirror-like boundary conditions. © 2010 IOP Publishing Ltd

Simulations of Contrail Optical Properties and Radiative Forcing for Various Crystal Shapes

The aim of this study is to investigate the sensitivity of radiative-forcing computations to various contrail crystal shape models. Contrail optical properties in the shortwave and longwave ranges are derived using a ray-tracing geometric method and the discrete dipole approximation method, respectively. Both methods present good correspondence of the single-scattering albedo and the asymmetry parameter in a transition range (3–8 µm). There are substantial differences in single-scattering properties among 10 crystal models investigated here (e.g., hexagonal columns and plates with different aspect ratios, and spherical particles). The single-scattering albedo and the asymmetry parameter both vary by up to 0.1 among various crystal shapes. The computed single-scattering properties are incorporated in the moderate-resolution atmospheric radiance and transmittance model(MODTRAN) radiative transfer code to simulate solar and infrared fluxes at the top of the atmosphere. Particle shapes have a strong impact on the contrail radiative forcing in both the shortwave and longwave ranges. The differences in the net radiative forcing among optical models reach 50% with respect to the mean model value. The hexagonal-column and hexagonal-plate particles show the smallest net radiative forcing, and the largest forcing is obtained for the spheres. The balance between the shortwave forcing and longwave forcing is highly sensitive with respect to the assumed crystal shape and may even change the sign of the net forcing. The optical depth at which the mean diurnal radiative forcing changes sign from positive to negative varies from 4.5 to 10 for a surface albedo of 0.2 and from 2 to 6.5 for a surface albedo of 0.05. Contrails are probably never that optically thick (except for some aged contrail cirrus), however, and so will not have a cooling effect on climate

Rethinking Assessment: Information Literacy Instruction and the ACRL Framework

Most information literacy instruction (ILI) done in academic libraries today is based on the ACRL’s Information Literacy Competency Standards for Higher Education, but with the replacement of these standards by the new Framework for Information Literacy for Higher Education, there is a need to re-evaluate current teaching strategies and instructional techniques so that they can better serve the Framework’s goals. This paper explores current trends in ILI instruction and in the area of assessment in particular, since ILI assessment provides an opportunity not only to evaluate teaching effectiveness but also to reinforce the learning goals of the new Framework itself. It proposes several ways that assessment strategies can be aligned with the goals of the Framework by using guided group discussion, online discussion platforms, and social media platforms, and proposes further avenues for research in the evaluation of such strategies

Numerical relativity in higher dimensions

We give a status report on our project targeted at performing numerical simulations of a head-on collision of non-spinning black holes in higher dimensional non-compact space-times. These simulations should help us understand black objects in higher dimensions and their stability properties. They are also relevant for the problem of black hole formation and evaporation in particle accelerators and cosmic rays. We use the symmetries of the system to reduce the problem to an effective 3+1 problem, allowing the use of existing numerical codes. As a simple application of the formalism, we present the results for the evolution of a five dimensional single black hole space-time. © 2010 IOP Publishing Ltd

Higher dimensional Numerical Relativity: code comparison

The nonlinear behavior of higher dimensional black hole spacetimes is of interest in several contexts, ranging from an understanding of cosmic censorship to black hole production in high-energy collisions. However, nonlinear numerical evolutions of higher dimensional black hole spacetimes are tremendously complex, involving different diagnostic tools and "dimensional reduction methods". In this work we compare two different successful codes to evolve Einstein's equations in higher dimensions, and show that the results of such different procedures agree to numerical precision, when applied to the collision from rest of two equal-mass black holes. We calculate the total radiated energy to be E/M=9x10^{-4} in five dimensions and E/M=8.1x10^{-4} in six dimensions.Comment: 7 pages, RevTex

Musical Worlds and the Extended Mind

“4E” approaches in cognitive science see mind as embodied, embedded, enacted, and extended. They observe that we routinely “offload” part of our thinking onto body and world. Recently, 4E theorists have turned to music cognition: from work on music perception and musical emotions, to improvisation and music education. I continue this trend. I argue that music — like other tools and technologies — is a beyond-the-head resource that affords offloading. And via this offloading, music can (at least potentially) scaffold various forms of thought, experience, and behavior. To develop this idea, I consider the “material” and “worldmaking” character of music, and I apply these considerations to two cases studies: music as a tool for religious worship, and music as a weapon for torture