Satellite systems around galaxies in hydrodynamic simulations

We investigate the properties of satellite galaxies formed in N -body/SPH simulations of galaxy formation in the ΛCDM cosmology. The simulations include the main physical effects thought to be important in galaxy formation and, in several cases, produce realistic spiral discs. In total, a sample of nine galaxies of luminosity comparable to the Milky Way was obtained. At magnitudes brighter than the resolution limit,   M_V =−12  , the luminosity function of the satellite galaxies in the simulations is in excellent agreement with data for the Local Group. The radial number density profile of the model satellites, as well as their gas fractions also match observations very well. In agreement with previous N -body studies, we find that the satellites tend to be distributed in highly flattened configurations whose major axis is aligned with the major axis of the (generally triaxial) dark halo. In two out of three systems with sufficiently large satellite populations, the satellite system is nearly perpendicular to the plane of the galactic disc, a configuration analogous to that observed in the Milk Way. The discs themselves are perpendicular to the minor axis of their host haloes in the inner parts, and the correlation between the orientation of the galaxy and the shape of the halo persists even out to the virial radius. However, in one case the disc's minor axis ends up, at the virial radius, perpendicular to the minor axis of the halo. The angular momenta of the galaxies and their host halo tend to be well aligned.     

Electron optical investigation of sedimentary dolomites

Transmission electron microscope studies demonstrate a structural distinction between stoichiometric and ancient calcian dolomites of sedimentary origin. A modulated or tweed structure similar in appearance to spinodal microstructures characterizes ancient calcian dolomites, whereas stoichiometric dolomites are homogeneous. Recent calcium-rich dolomites lack a modulated structure, but have a heterogeneous microstructure with high densities of growth defects. Electron and optical diffraction and lattice imaging suggest a fluctuation in interplanar spacing in a coherent lattice. In addition, lattice imaging also reveals discontinuous faults throughout the modulated structure. Ordering and possibly incipient exsolution are suggested, c reflections in SAD patterns of calcian dolomites document a new superstructure in at least part of the lamellar structure and raise questions of different ordering states throughout the structure.The results provide new insight regarding the formation of sedimentary dolomites     

Temperature Response of the 171 Å Passband of the SWAP Imager on PROBA2, with a Comparison to TRACE, SOHO, STEREO, and SDO

We calculated the temperature response of the 171 Å passbands of the Sun Watcher using APS detectors and image Processing (SWAP) instrument onboard the PRoject for OnBoard Autonomy 2 (PROBA2) satellite. These results were compared to the temperature responses of the Extreme Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE), the twin Extreme Ultraviolet Imagers (EUVI) onboard the Solar TErrestrial RElations Observatory (STEREO) A and B spacecraft, and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Multiplying the wavelength-response functions for each instrument by a series of isothermal synthetic spectra and integrating over the range 165?–?195 Å produced temperature-response functions for the six instruments. Each temperature response was then multiplied by sample differential emission-measure functions for four different solar conditions. For any given plasma condition (e.g. quiet Sun, active region), it was found that the overall variation with temperature agreed remarkably well across the six instruments, although the wavelength responses for each instrument have some distinctly different features. Deviations were observed, however, when we compared the response of any one instrument to different solar conditions, particularly for the case of solar flares.     

Laboratory Determination of the Carbon Kinetic Isotope Effects (KIEs) for Reactions of Methyl Halides with Various Nucleophiles in Solution

Large carbon kinetic isotope effects (KIEs) were measured for reactions of methyl bromide (MeBr), methyl chloride (MeCl), and methyl iodide (MeI) with various nucleophiles at 287 and 306 K in aqueous solutions. Rates of reaction of MeBr and MeI with H₂O (neutral hydrolysis) or Cl⁻ (halide substitution) were consistent with previous measurements. Hydrolysis rates increased with increasing temperature or pH (base hydrolysis). KIEs for hydrolysis were 51 ± 6%₀ for MeBr and 38 ± 8%₀ for MeI. Rates of halide substitution increased with increasing temperature and greater reactivity of the attacking nucleophile, with the fastest reaction being that of MeI with Br⁻. KIEs for halide substitution were independent of temperature but varied with the reactant methyl halide and the attacking nucleophile. KIEs were similar for MeBr substitution with Cl⁻ and MeCl substitution with Br⁻ (57 ± 5 and 60 ± 9%₀, respectively). The KIE for halide exchange of MeI was lower overall (33 ± 8%₀) and was greater for substitution with Br⁻ (46 ± 6%₀) than with Cl⁻ (29 ± 6%₀).