Collective Interview on the History of Town Meetings

As illustrated in the introduction, the special issue ends with a ‘collective interview’ to some distinguished scholars that have given an important contribution to the study of New England Town Meetings. The collective interview has been realized by submitting three questions to our interviewees, who responded individually in written. The text of the answers has not been edited, if not minimally. However, the editors have broken up longer individual answers in shorter parts. These have been subsequently rearranged in an effort to provide, as much as possible, a fluid structure and a degree of interaction among the different perspectives provided by our interviewees on similar issues. The final version of this interview has been edited and approved by all interviewees

LOX/GOX mechanical impact tester assessment

The performances of three existing high pressure oxygen mechanical impact test systems were tested at two different test sites. The systems from one test site were fabricated from the same design drawing, whereas the system tested at the other site was of different design. Energy delivered to the test sample for each test system was evaluated and compared. Results were compared to the reaction rates obtained

Metal Cooling in Simulations of Cosmic Structure Formation

The addition of metals to any gas can significantly alter its evolution by increasing the rate of radiative cooling. In star-forming environments, enhanced cooling can potentially lead to fragmentation and the formation of low-mass stars, where metal-free gas-clouds have been shown not to fragment. Adding metal cooling to numerical simulations has traditionally required a choice between speed and accuracy. We introduce a method that uses the sophisticated chemical network of the photoionization software, Cloudy, to include radiative cooling from a complete set of metals up to atomic number 30 (Zn) that can be used with large-scale three-dimensional hydrodynamic simulations. Our method is valid over an extremely large temperature range (10 K < T < 10^8 K), up to hydrogen number densities of 10^12 cm^-3. At this density, a sphere of 1 Msun has a radius of roughly 40 AU. We implement our method in the adaptive mesh refinement (AMR) hydrodynamic/N-body code, Enzo. Using cooling rates generated with this method, we study the physical conditions that led to the transition from Population III to Population II star formation. While C, O, Fe, and Si have been previously shown to make the strongest contribution to the cooling in low-metallicity gas, we find that up to 40% of the metal cooling comes from fine-structure emission by S, when solar abundance patterns are present. At metallicities, Z > 10^-4 Zsun, regions of density and temperature exist where gas is both thermally unstable and has a cooling time less than its dynamical time. We identify these doubly unstable regions as the most inducive to fragmentation. At high redshifts, the CMB inhibits efficient cooling at low temperatures and, thus, reduces the size of the doubly unstable regions, making fragmentation more difficult.Comment: 19 pages, 12 figures, significant revision, including new figure

The use of imaging systems to monitor shoreline dynamics

The development of imaging systems is nowadays established as one of the most powerful and reliable tools for monitoring beach morphodynamics. Two different techniques for shoreline detection are presented here and, in one case, applied to the study of beach width oscillations on a sandy beach (Pauanui Beach, New Zealand). Results indicate that images can provide datasets whose length and sample interval are accurate enough to resolve inter-annual and seasonal oscillations, and long-term trends. Similarly, imaging systems can be extremely useful in determining the statistics of rip current occurrence. Further improvements in accuracy and reliability are expected with the recent introduction of digital systems

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

The X-ray surface brightness distribution from diffuse gas

We use simulations to predict the X-ray surface brightness distribution arising from hot, cosmologically distributed diffuse gas. The distribution is computed for two bands: 0.5-2 keV and 0.1-0.4 keV, using a cosmological-constant dominated cosmology that fits many other observations. We examine a number of numerical issues such as resolution, simulation volume and pixel size and show that the predicted mean background is sensitive to resolution such that higher resolution systematically increases the mean predicted background. Although this means that we can compute only lower bounds to the predicted level, these bounds are already quite restrictive. Since the observed extra-galactic X-ray background is mostly accounted for by compact sources, the amount of the observed background attributable to diffuse gas is tightly constrained. We show that without physical processes in addition to those included in the simulations (such as radiative cooling or non-gravitational heating), both bands exceed observational limits. In order to examine the effect of non-gravitational heating we explore a simple modeling of energy injection and show that substantial amounts of heating are required (i.e. 5 keV per particle when averaged over all baryons). Finally, we also compute the distribution of surface brightness on the sky and show that it has a well-resolved characteristic shape. This shape is substantially modified by non-gravitational heating and can be used as a probe of such energy injection.Comment: 11 pages, 11 figures, submitted to Ap