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One of the most important features observed in real networks is that, as a network's topology evolves so does the network's ability to perform various complex tasks. To explain this, it has also been observed that as a network grows certain subnetworks begin to specialize the function(s) they perform. Here, we introduce a class of models of network growth based on this notion of specialization and show that as a network is specialized using this method its topology becomes increasingly sparse, modular, and hierarchical, each of which are important properties observed in real networks. This procedure is also highly flexible in that a network can be specialized over any subset of its elements. This flexibility allows those studying specific networks the ability to search for mechanisms that describe the growth of these particular networks. As an example, we find that by randomly selecting these elements a network's topology acquires some of the most well-known properties of real networks including the small-world property, disassortativity, power-law like degree distributions, and power-law like clustering coefficients. As far as the authors know, this is the first such class of models that creates an increasingly modular and hierarchical network topology with these properties., Comment: 20 pages, 9 color figures

Throughout the lifetime of the solar system, collisions between small bodies and impacts on the surfaces of small bodies in the Kuiper Belt have occured at speeds of 1.5 - 3 km s-1 (Stern, Astron J 124, 2002), typically at 1-10 km s-1 between Trojan asteroids (Marzari et al. Icarus 119, 1996), and at ~4-8 km s-1 in the asteroid belt (Farinella and Davis, Icarus 97, 1992). Shock effects recorded by minerals composing these bodies are one observable legacy of this evolutionary process, whether they were generated through large collisions, micrometeoroid impacts, or processing during the formation of the solar system. Shock metamorphism has been observed in cometary samples such as those from Comet Wild 2 (Keller et al. Geochim. Cosmochim. Acta 72, 2008; Tomeoka et al. MAPS 43, 2008; Jacobs et al. MAPS 44, 2009) as well as in forsterites and enstatites found in meteorites (McCausland et al. AGU, 2010). To investigate the observable signatures of these processes, we have conducted a suite of impact experiments at NASA Johnson Space Center's Experimental Impact Laboratory (EIL). Target materials included Mg-rich forsterite (olivine), Mg-rich enstatite (orthopyroxene), and antigorite and lizardite (both in the serpentine group of phyllosilicates). Alumina-ceramic spheres were launched at speeds ranging from ~2.0 - 2.6 km s-1 into targets at temperatures from 25degC to -100degC. Recent advancements have been made in cooling targets in the EIL's vertical gun. Liquid nitrogen (LN2) is fed through a unique jacket surrounding the metallic sample container to chill the samples. Real-time values from temperature sensors attached to the sample holder are converted to target temperature through predetermined regression relationships, providing the target temperature at the time of impact with sub-degree accuracy. Fourier Transform Infrared Spectrometer (FTIR) data in the near to mid-IR will be presented, along with trends relating temperature and velocity with impact speeds, and thereby peak shock stresses experienced by the impacted minerals.

A total dose analysis for exposure of electronic parts at the box level is presented for the Hubble Space Telescope. This was done using solid angle sectoring/3-dimensional ray trace and Monte Carlo radiation transport simulations. Results are discussed in terms of parts that are potential total dose concerns.

Comets and asteroids are subjected to extremely cold conditions throughout their lifetimes. During their sojourns in the solar system, they are subjected to collisions at speeds that are easily capable of generating shock waves in their constituent materials. In addition to ices, more common silicate minerals such as olivines and pyroxenes are important components of these objects. The collision-induced shocks could affect the spectral signatures of those mineral components, which could in turn be detected telescopically. We have embarked on a project to determine how impact-generated shock might affect the reflectance spectra and structures of select silicates as both impact speed and target temperature are varied systematically. While the effects of impact speed (in the form of shock stress) on numerous materials have been and continue to be studied, the role of target temperature has received comparatively little attention, presumably because of the operational difficulties it can introduce to experimentation. Our experiments were performed with the vertical gun in the Experimental Impact Laboratory of the Johnson Space Center. A liquid-nitrogen system was plumbed to permit cooling of the target container and its contents under vacuum to temperatures as low as -100 C (173 K). Temperatures were monitored by thermocouples mounted on the outside of the target container. Because those sensors were not in contact with the target material at impact, the measured temperatures are treated as lower limits for the actual values. Peridot (Mg-rich olivine) and enstatite (Mg-rich orthopyroxene) were used as targets, which involved the impact of alumina (Al2O3) spheres at speeds of 2.0 - 2.7 km s(exp -1) and temperatures covering 25 C to -100 C (298 K to 173 K). We have begun collecting and analyzing data in the near to mid-IR with a Fourier-transform infrared spectrometer, and preliminary analyses show that notable differences in absorption-band strength and position occur as functions of both impact speed (peak shock stress) and initial temperature.