4,113 research outputs found

    The application of electrochemical impedance spectroscopy for characterizing the degradation of Ni(OH)2/NiOOH electrodes

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    The use of wide-band electrochemical impedance spectroscopy is described for characterizing the degradation of porous Ni(OH)2/NiOOH electrodes in concentrated KOH electrolyte solutions. The impedance spectra are interpreted in terms of a finite electrical transmission line and the changes in the components of the electrical analog are followed as a function of cycle number. The degradation of the capacity of rolled and bonded Ni(OH)2/NiOOH electrodes is caused by rupture of ohmic contacts within the active mass and by restructuring which results in a decrease in the number of active pores

    Mass killings and detection of impacts

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    Highly energetic bolide impacts occur and their flux is known. For larger bodies the energy release is greater than for any other short-term global phenomenon. Such impacts produce or release a large variety of shock induced changes including major atmospheric, sedimentologic, seismic and volcanic events. These events must necessarily leave a variety of records in the stratigraphic column, including mass killings resulting in major changes in population density and reduction or extinction of many taxonomic groups, followed by characteristic patterns of faunal and flora replacement. Of these effects, mass killings, marked by large-scale loss of biomass, are the most easily detected evidence in the field but must be manifest on a near-global scale. Such mass killings that appear to be approximately synchronous and involve disappearance of biomass at a bedding plane in many sedimentologically independent sections globally suggest a common cause and probable synchroneity. Mass killings identify an horizon which may be examined for evidence of cause. Geochemical markers may be ephemeral and absence may not be significant. There appears to be no reason why ongoing phenomena such as climate and sea-level changes are primary causes of anomolous episodic events

    Predicting the steady state thickness of passive films in order to prevent degradations of implant

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    Some implants have approximately a lifetime of 15 years. The femoral stem, for example, should be made of 316L/316LN stainless steel. Fretting corrosion, friction under small displacements, should occur during human gait, due to repeated loadings and un-loadings, between stainless steel and bone for instance. Some experimental investigations of fretting corrosion have been practiced. As well known, metallic alloys and especially stainless steels are covered with a passive film that prevents from the corrosion and degradation. This passive layer of few nanometers, at ambient temperature, is the key of our civilization according to some authors. This work is dedicated to predict the passive layer thicknesses of stainless steel under fretting corrosion with a specific emphasis on the role of proteins. The model is based on the Point Defect Model (micro scale) and an update of the model on the friction process (micro-macro scale). Genetic algorithm was used for finding solution of the problem. The major results are, as expected from experimental results, albumin prevents from degradation at the lowest concentration of chlorides; an incubation time is necessary for degrading the passive film; under fretting corrosion and high concentration of chlorides the passive behavior is annihilated

    Investigating the Relationship between Environment and Active Galactic Nuclei activity at High Redshift

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    This thesis presents an investigation into the relationship between large-scale structure environment and Active Galactic Nuclei (AGN) activity at high redshift. To accomplish this, the environments of AGN are studied from two complementary perspectives. Firstly, various observations of a specific large-scale structure at z = 2.3 are used to assess the level of AGN activity in relation to the field. The main result of this study is that both the emission-line and X-ray selected AGN populations are significantly enhanced; X-ray detected Lyman Alpha Emitters (LAEs), however, are not found to be significantly enhanced. The host galaxy properties of z ~ 1 X-ray sources are then derived and studied in detail. Confirming previous results, X-ray sources are found in optically luminous (MB ~< ‚ąí20.5mag), massive (log(M‚ąó/ M‚äô) ‚Č• 10.5) red and blue hosts. A larger fraction of red/green hosts harbour obscured (log(NH) ‚Č• 22) AGN than blue, with the most obscured sources (log(NH) ‚Č• 23.5) also being more frequently found in red/green host galaxies than blue. The second approach used the 3rd-nearest neighbour measure to study the environment of X-ray hosts at z ~ 1, accounting for their optical colour, luminosity and stellar mass. A main new and important result is that X-ray hosts are found in regions of enhanced density compared to optical galaxies of equivalent mass, which is not due to the observed colour-density relation at z ~ 1. The enhancement is found to be most significant at the reddest colours, brightest luminosities, and highest stellar masses. The results from this thesis show that the dense environments probed in this work generally promote AGN activity. This is probably not due to major mergers, but could be due to an increased probability of minor mergers/interactions and/or milder environmental processes triggering nuclear activity. Alternatively, perhaps there is some other galaxy property (e.g., residing in higher mass haloes) which is conducive to AGN activity

    Social Justice in Outdoor Experiential Education: A Literature Analysis of K-12 Outdoor Education Programs in the United States

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    Historically, the field of outdoor experiential education (OEE) has been exclusionary and has primarily served white middle- and upper-middle class male populations. Scholars have called for research on how to address issues of social justice in the field for decades, and leaders are finally making steps toward becoming more inclusive. Through a secondary analysis of empirical studies on OEE, this paper examines how the field has modified its focus towards minority populations in K-12 OEE programs in the United States and provides recommendations for practitioners of OEE. There is evidence of an increase in studies on how OEE is perceived by minorities and how its impacts have affected different communities over the last 40 years. The understanding of attitudes and perceptions of OEE has changed with the introduction of new concepts regarding health and wellbeing tied to outdoor experiences as well as social justice

    Crisis in the Wilderness

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    All experiential education programs involve the potential for students to experience a crisis far from the secure environment of campus and home. Students engaging in these programs are therefore required to carry medical and travel insurance and to complete the waiver of liability forms particular to their college or university. Even as they gather this documentation, honors directors sending students to or leading such programs hold their breath and hope that they will never need to use the emergency contact information. This has been our collective hope during the past four years that we have offered Partners in the Parks (PITP) experiential learning adventures. As University of Alaska Fairbanks physics professor and honors director Channon Price‚ÄĒcoordinator of the latest expedition‚ÄĒgathered the documents, he was keenly aware that the remote Alaskan wilderness of Denali National Park and Preserve would be a difficult environment in which to manage a student crisis

    Galactic spheroid structure from subluminous stars

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    Galactic halo subdwarfs and white dwarfs are locally very scarce and many of their character¬≠istics are hence poorly understood. As the most common members of the spheroid, however, they are crucial to the understanding of our own and other galaxies, able to yield key informa¬≠tion about the shape, formation, chemical history and dark matter of the spheroid, as well as providing clues about the processes of stellar evolution.Wide-field photographic data spanning observations taken over long time baselines, such as those available from the SuperCOSMOS Sky Survey (SSS), are unparalleled in their ability to identify large numbers of these dwarf spheroid stars through their large space motions. How¬≠ever, the ‚ÄúAchilles Heel‚ÄĚ of photographic astronomy in studies such as this is poor photometry: a problem which can now be circumvented - whilst retaining the astrometric information of the photographic data - with the advent of large-scale, deep CCD surveys with accurate photometry such as the Sloan Digital Sky Survey (SDSS). In this thesis I show that the combination of these two types of dataset brings vast numbers of locally-rare dwarf spheroid stars into the observa¬≠tional reach of astronomers, yielding reliable samples many times larger than have previously been available solely from photographic data.Using SSS data coupled with the SDSS archive I identify a sample of ~2600 candidate subdwarfs through strict selection criteria. This forms one of the largest and most reliable samples of subdwarfs known, and enables accurate determination of luminosity functions along many different lines of sight. I derive the subdwarf luminosity function with unprecedented accuracy to M y ¬£ 12.5, finding good agreement with recent local estimates but discrepancy with results for the more distant spheroid. This provides further evidence that the inner and outer parts of the stellar halo cannot be described by a single density distribution. I also use the data to show that the form of the inner spheroid density profile within distances of 2.5 kpc is closely matched by a power law with an index of a = ‚ÄĒ3.15 ¬Ī 0.3. Whilst this study is unable to provide further constraints on Galactic structure at present, development of these methods and results have the potential to yield much more information on the formation and evolution of the Galaxy

    Exploring library leadership technology decision-making and support through the use case of the Institutional Repository

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    Academic and research libraries are dependent on a wide range of technology and systems to manage access and storage of digital research materials and collections. Given the high level of costs and staff needed to support these systems, the factors that influence library leadership in their decision-making process to support or adopt new technologies is important. To understand the dynamics involved with this decision-making process, this study specifically examined influencing factors that academic library leaders use in their decisions to support or adopt institutional repository (IR) systems. A mixed method research study using a quantitative research survey instrument, adapted from the Technology Acceptance Model (TAM), followed by semi-structured interviews was used in this study. The data collected from this research reveal that library leaders place a significant emphasis on the factors of the perceived need, reliability, and perceived usefulness. Building on these factors, interviews with senior library leaders revealed that the influencing factor of costs or ability to fund a system was a constant presence in their decision-making rubric. Using these findings, it is anticipated that those seeking support and funding for new and ongoing library technology systems, will be able to present proposals in alignment with the factors that influence the library leadership making the decisions
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