Ascent from the lunar surface

Ascent from lunar surface problem with solution by variational calculu

A Universal Temperature Profile for Galaxy Clusters

We investigate the predicted present-day temperature profiles of the hot, X-ray emitting gas in galaxy clusters for two cosmological models - a current best-guess LCDM model and standard cold dark matter (SCDM). Our numerically-simulated "catalogs" of clusters are derived from high-resolution (15/h kpc) simulations which make use of a sophisticated, Eulerian-based, Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which are essential for correctly modelling cluster temperatures. We show that the temperature structure on Mpc-scales is highly complex and non-isothermal. However, the temperature profiles of the simulated LCDM and SCDM clusters are remarkably similar and drop-off as $T +AFw-propto (1+-r/a_x)^{-+AFw-delta}$ where $a_x +AFw-sim r_{vir}/1.5$ and $+AFw-delta +AFw-sim 1.6$. This decrease is in good agreement with the observational results of Markevitch et al.(1998) but diverges, primarily in the innermost regions, from their fit which assumes a polytropic equation of state. Our result is also in good agreement with a recent sample of clusters observed by BeppoSAX though there is some indication of missing physics at small radii ($r<0.2 r_{vir}$). We discuss the interpretation of our results and make predictions for new x-ray observations that will extend to larger radii than previously possible. Finally, we show that, for $r>0.2 r_{vir}$, our universal temperature profile is consistent with our most recent simulations which include both radiative cooling and supernovae feedback.Comment: 8 pages, 6 figures, accepted for publication in ApJ, full-page version of Fig. 2 at http://www.cita.utoronto.ca/+AH4-cloken/PAPERS/UTP/f2.ep

Climate Change Geoengineering: Philosophical Perspectives, Legal Issues, and Governance Frameworks

The international community is not taking the action necessary to avert dangerous increases in greenhouse gases. Facing a potentially bleak future, the question that confronts humanity is whether the best of bad alternatives may be to counter global warming through human-engineered climate interventions. In this book, eleven prominent authorities on climate change consider the legal, policy, and philosophical issues presented by geoengineering. The book asks: When, if ever, are decisions to embark on potentially risky climate modification projects justified? If such decisions can be justified, in a world without a central governing authority, who should authorize such projects and by what moral and legal right? If states or private actors undertake geoengineering ventures absent the blessing of the international community, what recourse do the rest of us have

Far infrared properties of the rare-earth scandate DyScO3

We present reflectance measurements in the infrared region on a single crystal the rare earth scandate DyScO3. Measurements performed between room temperature and 10 K allow to determine the frequency of the infrared-active phonons, never investigated experimentally, and to get information on their temperature dependence. A comparison with the phonon peak frequency resulting from ab-initio computations is also provided. We finally report detailed data on the frequency dependence of the complex refractive index of DyScO3 in the terahertz region, which is important in the analysis of terahertz measurements on thin films deposited on DyScO3

A Comparison of Radio and X-Ray Morphologies of Four Clusters of Galaxies Containing Radio Halos

Clusters of galaxies may contain cluster-wide, centrally located, diffuse radio sources, called halos. They have been found to show morphologies similar to those of the X-ray emission. To quantify this qualitative statement we performed a point-to-point comparison of the radio and the X-ray emission for four clusters of galaxies containing radio halos: Coma, Abell 2255, Abell 2319, Abell 2744. Our study leads to a linear relation between the radio and the X-ray surface brightness in two clusters, namely Abell 2255 and Abell 2744. In Coma and A2319 the radio and the X-ray brightnesses seem to be related with a sub-linear power law. Implications of these findings within simple radio halo formation models are briefly discussed.Comment: 9 pages, 13 .ps figures, accepted by A&

The flywheel effect: Ionospheric currents after a geomagnetic storm

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95263/1/grl5685.pd

Investigating Possible Synergies in Intermodal Operations With Truck and Rail

As the trucking industry continues to examine ways to provide better service at lower cost, many companies are more heavily utilizing intermodal (IM) strategies between truck and rail, especially for those loads that are relatively non-critical in terms of delivery time requirements and that have longer lengths of haul. As IM business grows, supporting dray infrastructure naturally develops around IM rail yards. What is unknown is whether it is best to have a dedicated set of drivers performing dray operations or if efficiency and cost savings can result when utilizing a joint driving fleet to concurrently support IM and traditionally dispatched truckload freight transportation. This paper describes a set of experiments utilizing a comprehensive discrete-event system simulation model and historical data from J.B. Hunt Transport to determine whether or not operating synergies exist when IM dray operations are integrated with local, regional, and long-haul trucking operations. Performance metrics of interest to drivers, customers, and trucking companies are utilized to ensure that the research addresses issues of importance to all constituencies. The results show that there is a trade-off between different performance variables when combining operations, but that generally speaking synergies do exist when considering the needs of professional drivers. Results are more mixed with respect to the needs of carriers and customers, but the authors reach the conclusion that the positive aspects of combining OTR and IM dispatching activities outweigh the negative. Because the evaluative simulation model itself is considered to be a major contribution, it is also described in some detail herein