Crafting divine personae in Julian’s Oration 7

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Metric characterizations II

The present paper is a sequel to our paper "Metric characterization of isometries and of unital operator spaces and systems". We characterize certain common objects in the theory of operator spaces (unitaries, unital operator spaces, operator systems, operator algebras, and so on), in terms which are purely linear-metric, by which we mean that they only use the vector space structure of the space and its matrix norms. In the last part we give some characterizations of operator algebras (which are not linear-metric in our strict sense described in the paper).Comment: Presented at the AMS/SAMS Satellite Conference on Abstract Analysis, University of Pretoria, South Africa, 5-7 December 2011. Revision of 2/24/2012 (Examples after theorem 3.2 added

The Status of Inelastic Dark Matter

In light of recent positive results from the DAMA experiment, as well as new null results from CDMS Soudan, Edelweiss, ZEPLIN-I and CRESST, we reexamine the framework of inelastic dark matter with a standard halo. In this framework, which was originally introduced to reconcile tensions between CDMS and DAMA, dark matter particles can scatter off of nuclei only by making a transition to a nearly degenerate state that is roughly 100 \kev heavier. We find that recent data significantly constrains the parameter space of the framework, but that there are still regions consistent with all experimental results. Due to the enhanced annual modulation and dramatically different energy dependence in this scenario, we emphasize the need for greater information on the dates of data taking, and on the energy distribution of signal and background. We also study the specific case of ``mixed sneutrino'' dark matter, and isolate regions of parameter space which are cosmologically interesting for that particular model. A significant improvement in limits by heavy target experiments such as ZEPLIN or CRESST should be able to confirm or exclude the inelastic dark matter scenario in the near future. Within the mixed sneutrino model, an elastic scattering signature should be seen at upcoming germanium experiments, including future results from CDMS Soudan.Comment: 8 pages, 5 figures; updated to include CRESST results; version to appear in Phys.Rev.

GUT Breaking on the Brane

We present a five-dimensional supersymmetric SU(5) theory in which the gauge symmetry is broken maximally (i.e. at the 5D Planck scale M_*) on the same 4D brane where chiral matter is localized. Masses of the lightest Kaluza-Klein modes for the colored Higgs and X and Y gauge fields are determined by the compactification scale of the fifth dimension, M_C ~ 10^{15} GeV, rather than by M_*. These fields' wave functions are repelled from the GUT-breaking brane, so that proton decay rates are suppressed below experimental limits. Above the compactification scale, the differences between the standard model gauge couplings evolve logarithmically, so that ordinary logarithmic gauge coupling unification is preserved. The maximal breaking of the grand unified group can also lead to other effects, such as O(1) deviations from SU(5) predictions of Yukawa couplings, even in models utilizing the Froggatt-Nielsen mechanism.Comment: 20 pages, 3 figure

Photoionization, Numerical Resolution, and Galaxy Formation

Using cosmological simulations that incorporate gas dynamics and gravitational forces, we investigate the influence of photoionization by a UV radiation background on the formation of galaxies. In our highest resolution simulations, we find that photoionization has essentially no effect on the baryonic mass function of galaxies at $z=2$, down to our resolution limit of 5e9 M_\sun. We do, however, find a strong interplay between the mass resolution of a simulation and the microphysics included in the computation of heating and cooling rates. At low resolution, a photoionizing background can appear to suppress the formation of even relatively massive galaxies. However, when the same initial conditions are evolved with a factor of eight better mass resolution, this effect disappears. Our results demonstrate the need for care in interpreting the results of cosmological simulations that incorporate hydrodynamics and radiation physics. For example, we conclude that a simulation with limited resolution may yield more realistic results if it ignores some relevant physical processes, such as photoionization. At higher resolution, the simulated population of massive galaxies is insensitive to the treatment of photoionization and star formation, but it does depend significantly on the amplitude of the initial density fluctuations. By $z=2$, an $\Omega=1$ cold dark matter model normalized to produce the observed masses of present-day clusters has already formed galaxies with baryon masses exceeding 1e11 M_\sun.Comment: 25 pages, w/ embedded figures. Submitted to ApJ. Also available at http://www-astronomy.mps.ohio-state.edu/~dhw/Docs/preprints.htm

Cosmological Simulations with TreeSPH

We describe numerical methods for incorporating gas dynamics into cosmological simulations and present illustrative applications to the cold dark matter (CDM) scenario. Our evolution code, a version of TreeSPH (Hernquist \& Katz 1989) generalized to handle comoving coordinates and periodic boundary conditions, combines smoothed--particle hydrodynamics (SPH) with the hierarchical tree method for computing gravitational forces. The Lagrangian hydrodynamics approach and individual time steps for gas particles give the algorithm a large dynamic range, which is essential for studies of galaxy formation in a cosmological context. The code incorporates radiative cooling for an optically thin, primordial composition gas in ionization equilibrium with a user-specified ultraviolet background. We adopt a phenomenological prescription for star formation that gradually turns cold, dense, Jeans-unstable gas into collisionless stars, returning supernova feedback energy to the surrounding medium. In CDM simulations, some of the baryons that fall into dark matter potential wells dissipate their acquired thermal energy and condense into clumps with roughly galactic masses. The resulting galaxy population is insensitive to assumptions about star formation; we obtain similar baryonic mass functions and galaxy correlation functions from simulations with star formation and from simulations without star formation in which we identify galaxies directly from the cold, dense gas.Comment: compressed postscript, 38 pages including 6 out of 7 embedded figures. Submitted to ApJ Supplements. Version with all 7 figures available from ftp://bessel.mps.ohio-state.edu/pub/dhw/Preprint

Impact and promise of NASA aeropropulsion technology

The aeropropulsion industry in the U.S. has established an enviable record of leading the world in aeropropulsion for commercial and military aircraft. NASA's aeropropulsion program (primarily conducted through the Lewis Research Center) has significantly contributed to that success through research and technology advances and technology demonstration. Some past NASA contributions to engines in current aircraft are reviewed, and technologies emerging from current research programs for the aircraft of the 1990's are described. Finally, current program thrusts toward improving propulsion systems in the 2000's for subsonic commercial aircraft and higher speed aircraft such as the High-Speed Civil Transport and the National Aerospace Plane are discussed