Failure of morphology of (0 deg)8 graphite/epoxy as influenced by environments and processing

Optical and scanning electron microscopy were used to investigate the failure morphology of graphite/epoxy specimens which had been tested until tensile failure. Failure morphology was studied as a function of the quality control variables of specimen preparation technique, prepreg batch, and cure condition, and also as a function of the environmental parameters of temperature and moisture content. Defective specimens were found to exhibit a low energy failure morphology. Poor specimen edge preparation and one batch of prepreg when tested at elevated temperature or moisture content also exhibited energy failure morphology. Postcuring had no effect on strength but did slightly alter failure morphology. Temperature or moisture appeared to decrease flaw sensitivity and thus increase strength; however, moisture also appeared to increase interfacial debonding between filament and matrix. When combined moisture and temperature increased interfacial debonding and made the epoxy matrix more prone to fracture

An assembly to provide a time reference for the JPL Network Operations Control Center, Real-Time

A device is described which provides the value of date coordinated universal time (date UTC) to the JPL Network Operations Control Center, Real Time (NOCC-RT) facility. The NOCC-RT is the real time portion of the NOCC upgrade task. The time scale is generated in the NOCC-RT clock processor; however, there is a continuous reference to UTC, as realized by the National Institute of Standards and Technology and transmitted by Earth orbiting satellites. An important functional design requirement is the 99.9 pct. availability

Starburst and AGN activity in ultraluminous infrared galaxies

(Abridged) We examine the power source of 41 local Ultraluminous Infrared Galaxies using archival infrared and optical photometry. We fit the observed Spectral Energy Distributions (SEDs) with starburst and AGN components; each component being drawn from a family of templates. We find all of the sample require a starburst, whereas only half require an AGN. In 90% of the sample the starburst provides over half the IR emission, with a mean fractional luminosity of 82%. When combined with other galaxy samples we find that starburst and AGN luminosities correlate over 6 decades in IR luminosity suggesting that a common factor governs both luminosities, plausibly the gas masses in the nuclear regions. We find that the mid-IR 7.7 micron line-continuum ratio is no indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that this ratio is not a reliable diagnostic of the power source in ULIRGs. We propose that the scatter in the radio-IR correlation in ULIRGs is due to a skewed starburst IMF and/or relic relativistic electrons from a previous starburst, rather than contamination from an obscured AGN. We show that most ULIRGs undergo multiple starbursts during their lifetime, and by inference that mergers between more than two galaxies may be common amongst ULIRGs. Our results support the evolutionary model for ULIRGs proposed by Farrah et al 2001, where they can follow many different evolutionary paths of starburst and AGN activity in transforming merging spiral galaxies into elliptical galaxies, but that most do not go through an optical QSO phase. The lower level of AGN activity in our local sample than in z~1 HLIRGs implies that the two samples are distinct populations. We postulate that different galaxy formation processes at high-z are responsible for this difference.Comment: 24 pages, 8 figures. Accepted for publication in MNRA

Filter media expansion during backwash: The effect of biological activity

Close observation at a number of South African water treatment plants has shown that media losses during backwashing are excessive – much higher than anticipated. The only likely reasons for this phenomenon are either that insufficient freeboard was provided by the designer or that the mechanical behaviour of the media gradually changes after being placed in the filters. A number of media tests confirmed that the biological fraction of the specific deposit on the filter media (after backwashing) is relatively high – about 50% of the total specific deposit. This led to the hypothesis that the combination of high nutrient concentrations in surface waters, coupled with elevated water temperatures, stimulate biofilm formation on the media grains. These films, in turn, somehowaffect the mechanical behaviour of the media bed expansion and backwash. This paper reviews the Dharmarajah bed expansion model (as the most advanced model for media expansion to date) and presents evidence that it predicts the expansion of clean, ovendried media reasonably well. It further shows that media from filters which have been in operation for a while, expand significantly more than predicted by the Dharmarajah model. This finding has major implications for filter design, and suggestions are made on how to adapt design procedures for what is now believed to be the formation of biofilm on media grains. Water SA Vol. 30 (5) 2005: pp.51-5

Diffusion Monte Carlo study of two-dimensional liquid 4^4He

The ground-state properties of two-dimensional liquid $^4$He at zero temperature are studied by means of a quadratic diffusion Monte Carlo method. As interatomic potential we use a revised version of the HFDHE2 Aziz potential which is expected to give a better description of the interaction between helium atoms. The equation of state is determined with great accuracy over a wide range of densities in the liquid phase from the spinodal point up to the freezing density. The spinodal decomposition density is estimated and other properties of the liquid, such as radial distribution function, static form factor, momentum distribution and density dependence of the condensate fraction are all presented.Comment: 19 pages, RevTex 3.0, 7 figures available upon reques

Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks

We present new, high angular resolution (~0.22") MERLIN observations of neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially resolved HI absorption is detected against the morphologically complex and extended 21-cm radio continuum emission, consistent with two counterrotating disks of neutral hydrogen, with a small bridge of gas connecting the two. We propose a merger model in which the two nuclei represent the galaxy cores which have survived the initial encounter and are now in the final stages of merging, similar to conclusions drawn from previous CO studies (Sakamoto, Scoville & Yun 1999). However, we suggest that instead of being coplanar with the main CO disk (in which the eastern nucleus is embedded), the western nucleus lies above it and, as suggested by bridge of HI connecting the two nuclei, will soon complete its final merger with the main disk. We suggest that the collection of radio supernovae (RSN) detected in VLBA studies in the more compact western nucleus represent the second burst of star formation associated with this final merger stage and that free-free absorption due to ionised gas in the bulge-like component can account for the observed RSN distribution. (Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in Ap

Integrating trap-neuter-return campaigns into a social framework: developing long-term positive behaviour change towards unowned cats in urban areas

Cat management is often discussed in terms of population reduction, with trap-neuter-return (TNR) campaigns commonly organized to manage unowned urban cat populations. However, long-term effectiveness is only possible if positive neutering practices are continued by local residents. Here we discuss how implementing TNR within a wider framework of social engagement has the potential to tackle cat overpopulation and instill long-term positive behavior change toward them. We demonstrate how community engagement pre-TNR can help establish a baseline of the attitudes, knowledge and behavior concerning cats. Using a case study, we explore whether this information can be linked with positive intended behavior based on intentions to arrange for neutering of unowned cats. Structural equation modeling indicated that negative attitudes toward cats and reduced knowledge around neutering reduced the likelihood of positive intended behavior. This result was underpinned by the indirect effects of perceptions of unowned cats and reduced understanding of their needs. Utilizing these results alongside an understanding of the values and motivation of the community allows for tailored and targeted education and intervention. In turn, this addresses the underlying knowledge gaps and perceptions regarding cat welfare. This framework can help address the challenge of cat management because it: (1) takes an integrative approach to identifying the motivations of communities to take responsibility for unowned cats; (2) changes the structure of the social environment, encouraging positive neutering practices for unowned cats. In turn this improves the impact and longevity of TNR campaigns whilst promoting positive welfare change for unowned and owned cats; and (3) appreciates that opinions are likely to vary hugely between areas, therefore providing an adaptable community level approach

Excitations in confined helium

We design models for helium in matrices like aerogel, Vycor or Geltech from a manifestly microscopic point of view. For that purpose, we calculate the dynamic structure function of 4He on Si substrates and between two Si walls as a function of energy, momentum transfer, and the scattering angle. The angle--averaged results are in good agreement with the neutron scattering data; the remaining differences can be attributed to the simplified model used here for the complex pore structure of the materials. A focus of the present work is the detailed identification of coexisting layer modes and bulk--like excitations, and, in the case of thick films, ripplon excitations. Involving essentially two--dimensional motion of atoms, the layer modes are sensitive to the scattering angle.Comment: Phys. Rev. B (2003, in press