The virialization shock around an X-ray cluster primarily heats the ions, since they carry most of the kinetic energy of the infalling gas. Subsequently, the ions share their thermal energy with the electrons through Coulomb collisions. We quantify the expected temperature difference between the electrons and ions as a function of radius and time, based on a spherical self-similar model for the accretion of gas by a cluster in an Ω = 1, h 50 = 1 universe. Clusters with X-ray temperatures T x = 4-10 × 10 7 K, show noticeable differences between their electron and ion temperatures at radii ∼ > 2Mpc. High resolution spectroscopy with future X-ray satellites such as Astro E may be able to determine the ion temperature in intracluster gas from the width of its X-ray emission lines, and compare it to the electron temperature as inferred from the free-free emission spectrum. Any difference between these temperatures can be used to date the period of time that has passed since the infalling gas joined the cluster.

X-ray and Sunyaev-Zeldovich effect observations can be combined to measure the distance to clusters of galaxies. If the intracluster gas distribution is not spherical, but elongated by a factor of Z along the line of sight, the inferred distance is increased by Z, and H0 is decreased by the same factor. Averaging the inferred value of H0 over a sufficiently large sample of clusters can reduce any systematic bias due to cluster shapes, provided the clusters are selected without any preferred orientation. Even so, elongation contributes significantly to the variance in the measured distances and in the inferred value of H0. With the addition of gravitational lensing observations, it is possible to infer the three-dimensional shape of clusters, provided the gas is in hydrostatic equilibrium. We demonstrate a specific method for finding the shape and correcting the measured distances to individual clusters. To test this method, we apply it to artificial observations of simple model clusters. We recover the true distances to each of our clusters without detectable bias, and with statistical errors due to measurement uncertainties of 4 to 6%.Comment: submitted to ApJ. 35 pages, 4 figures Replaced with revised version (34 pages, 3 figures), including the general case of triaxial clusters with arbitrary orientation, as re-submitted to Ap

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A gas cell apparatus to measure charge exchange cross sections for charge state- and energy-resolved ion beams with neutrals is described. The design features a short well-defined interaction region required for beams of multicharged ions with high cross sections. Our method includes measuring the beam transmission at four different neutral pressures and extracting the cross section from the slope of a beam loss vs pressure plot. The design and procedure were tested for Ar interacting with neutral Ar gas over the incident ion energy range of 1.0-5.0 keV. The charge exchange cross sections agree well with previous complementary measurement techniques.

In this paper we describe VoiceCode, a system for programming-by-voice. With VoiceCode, programmers can dictate code in an easy to pronounce syntax, which the system translates to native syntax in the current programming language. We illustrate how this approach addresses most of the usability issues for programming-by-voice.