Dissertations / Theses on the topic 'Overlayer'
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Roudgar, Ataollah. "Local reactivity of bimetallic overlayer and cluster systems." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971640084.
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Barnes, Robert David Frazer. "Diffraction gratings as a platform for overlayer detection and representation." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319553.
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Clarke, A. "A wavevector imaging photoelectron spectrometer, with application to a magnetic overlayer system." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233729.
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The work presented in this thesis may be considered in two main parts; firstly a description of the design and operation of a display type photoelectron spectrometer. Secondly a series of experiments investigating the electronic properties of thin epitaxial films (1-5 atomic layers) of cobalt grown on a clean single crystal copper (001) substrate. Conventional angle resolved photoelectron spectrometers of the deflection type are only capable of observing one point in the (E,θ,φ) space at a time. This is often perfectly acceptable if one is concerned with optimal resolution in order to perform accurate band mapping experiments. However certain experiments are essentially impossible, for instance the observation of the emitted photocurrent over all θ,φ at the fermi energy. This is partly because of the time limitations imposed by the necessity to keep the sample atomically clean in the U.H.V. environment. Several previous workers have tackled this problem by designing spectrometers that observe large sections of θ,φ space simultaneously, for a given energy. The first part of this work concerns the design and implementation of a display type spectrometer which embodies some new and quite novel features. Thin epitaxial films of ferromagnetic materials grown on non-magnetic substrates have long been of interest. Partly as a prototypical surface for the investigation of surface magnetism, and partly for the investigation of the changes induced in the magnetic properties as the dimensionality is reduced or as the lattice size is changed. The second part of this thesis concerns experiments using three different spectroscopies on a system of this type, specifically Co on Cu(001). Firstly, a photoemission study using the display spectrometer is presented, observations of the spin-split bands as a function of wavevector parallel to the surface are shown. Secondly an Auger electron study of the growth mode of the epitaxial film, together with a LEED I/V study of the changing lattice strain as a function of film thickness are presented. Although none of these measurements directly probe the magnetism of the films, they provide very necessary information in order to understand their behaviour.
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Anton, Alan Brad Weinberg Henry. "Studies of overlayer vibrational structure and identification of adsorbed reaction intermediates via electron energy loss spectroscopy /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-04032008-110807.
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MORANDI, SARA. "NEW APPROACHES FOR THE DESIGN, SCREENING AND CHARACTERIZATION OF INNOVATIVE SEMICONDUCTOR/OVERLAYER ARCHITECTURES FOR PHOTO-DRIVEN WATER ELECTROLYSIS." Doctoral thesis, Università degli Studi di Milano, 2017. http://hdl.handle.net/2434/484308.
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New approaches for the design, screening and characterization of innovative semiconductor/overlayer architectures for photo-driven water electrolysis
The optimization of environmental protection and remediation and the better exploitation of renewable power sources undoubtedly represent the key issues to lead to the sustainable development of civil and industrial activities. In this context, hydrogen and electricity can be considered as the most promising and as the most adopted energy vector, respectively. The possibility of adopting the former depends on the availability of suitable devices to convert renewable energy into chemical energy. Here, the production of H2 from sunlight, by photoelectrochemical water splitting (PEC-WS), represents one of the most attractive processes giving the possibility of a direct use of sunlight to drive water splitting into molecular hydrogen and oxygen. Notwithstanding the strong interest for PEC‐WS, its development on an industrial scale is hindered by the high costs of core materials and their inadequate efficiency and/or stability. In the last years, a lot of effort has been devoted to the study of different semiconductor/electrocatalyst combinations. In particular, recent studies highlighted the ability of electrocatalyst overlayers of inducing modifications in the semiconductor electron density [1] or of storing the photogenerated holes, thus decreasing the probability of charge recombination [2,3]. This greatly extends the possible candidates for photoelectrocatalysts and requires new efficient screening methods. In this context, scanning electrochemical microscopy (SECM) is an optimal tool for the rapid screening of big libraries of materials [4-8]. In this Ph.D. thesis, innovative approaches for the study of different photoanode architectures are discussed.
In the first part, preliminary results of promising OER electrocatalysts deposited onto Ti sheets are shown. The electrocatalytic activity of the different spots has been studied by SECM using a substrate generation/tip collection (SG-TC) approach, according to which the substrate spots generate molecular oxygen that is reduced at the tip. Since the spots generate O2 all together, the attention was also focused on the application of the double pulse method [9] that allows to address and compare each spot’s activity.
The most performing electrocatalysts were then deposited onto a photoconverter (n-doped semiconductor), to study the photo-electrochemical behaviour of the so-obtained semiconductor/overlayer architecture. The semiconductor chosen for its low-cost, stability and favourable band position was hematite (α-Fe2O3), in the form of nanowires [10]. Various low-cost metal oxides were then deposited onto the same photoconverter layer and screened via SECM, by the double pulse method and under white light irradiation (by means of an optical fibre probe, able to move over the sample under investigation). Considering that the average spot size is of 500 µm, the spot-spot distance (centre-to-centre) is set at 800 µm and the fibre diameter is 200 µm, we can assume that the local illumination addresses only one spot at time during the screening. The SECM rapid evaluation was aimed to select the best semiconductor/overlayer combinations that were then synthesized on lab-scale photoelectrodes and tested with conventional photoelectrochemical characterization methods (CV, EIS, etc.).
As already mentioned, screening of catalysts mostly involve the adoption of generation/collection modes of SECM that use the tip to locally produce one of the reactants or to locally sense the reaction products. Unfortunately, the materials available in the form of microwires useful to produce tips are limited to a short list of metals. For this reason, another part of this thesis was focused on the preparation, characterization and use of cavity-microelectrodes (C-ME) as tips for the SECM [11]. These C-ME tips [12-14] can be filled with a desired finely dispersed material and used as conventional microdisk tip in several SECM configurations.
A third part of the thesis is devoted to the study of stability and performances of different semiconductors, appositely synthesised in the form of amorphous nanoparticles through a different and innovative method. This work was performed during a stay at Professor Joaquin Rodriguez-Lopez laboratories, University of Illinois at Urbana-Champaign (UIUC). The semiconductors under investigation were TiO2, WO3 and BiVO4. These materials were tested at the SECM under white light irradiation, and different conditions were applied to enhance the material photoactivity (Nafion® addition, etc.).
The last part of this thesis discusses the role of different materials for the water oxidation, both deposited onto inert electrodes or semiconductors, using innovative in-situ and operando X-ray absorption (XAS) techniques. These techniques are particularly interesting when combined with electrochemistry, being able to provide information about the oxidation state and surrounding atoms. The techniques were initially applied to conventional, “model” catalysts, like amorphous iridium oxides [15,16] or Pt nanoparticles, and can be in principle extended towards any desired electrochemical or photoelectrochemical system.
[1] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant, PNAS, 109, (2012), 15640-15645.
[2] L. Badia-Bou, E. Mas-Marza, P. Rodenas, E.M. Barea, F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 117, (2013), 3826-3833.
[3] F. Lin, S.W. Boettcher, Nature Materials, 13, (2014), 81-86.
[4] J.L. Fernández, D.A. Walsh, A.J. Bard, J. Am. Chem. Soc., 127, (2005), 357-365.
[5] A. Minguzzi, M.A. Alpuche-Aviles, J. Rodríguez-López, S. Rondinini, A.J. Bard, Anal. Chem., 80, (2008), ,4055-4064.
[6] J. Lee, H. Ye, S. Pan, A.J. Bard, Anal. Chem., 80, (2008), 7445-7450.
[7] H. Ye, H. S. Park, A. J. Bard, J. Phys. Chem. C., 115, (2011), 12464-12470
[8] D. Yuan, L. Xiao, J. Jia, J. Zhang, L. Han, P. Li, B. Mao, D. Zhan, Anal. Chem., 86, (2014), 11972-11976
[9] A. Minguzzi, D. Battistel, J. RodrÍguez-López, A. Vertova, S. Rondinini, A. J. Bard, S. Daniele, J. Phys. Chem. C, 119, (2015), 2941-2947
[10] F. Malara, A. Minguzzi, M. Marelli, S. Morandi, R. Psaro, V. Dal Santo, A. Naldoni, ACS Catalysis, 5, (2015), 5292-5300.
[11] S. Morandi, A. Minguzzi, Electrochemistry Commumications, 59, (2015), 100-103.
[12] C. Locatelli, A. Miguzzi, A. Vertova, P. Cava, S. Rondinini, Anal. Chem., 83, (2011), 2819-2823
[13] A. Minguzzi, C. Locatelli, G. Cappelletti, C. L. Bianchi, A. Vertova, S. Ardizzone, S. Rondinini, J. Mater. Chem., 22, (2012), 8896-8902
[14] A. Minguzzi, C. Locatelli, O. Lugaresi, A. Vertova, S. Rondinini, Electrochim. Acta, 114, (2013), 637-642
[15] T. Baran, M. Fracchia, A. Vertova, E. Achilli, A. Naldoni, F. Malara, G. Rossi, S. Rondinini, P. Ghigna, A. Minguzzi, F. D’Acapito, Electrochimica Acta, 207, (2016), 16–21
[16] S. Rondinini, A. Minguzzi, E. Achilli, C. Locatelli, G. Agostini, S. Pascarelli, G. Spinolo, A. Vertova, P. Ghigna, Electrochimica Acta, 212, (2016), 247–253
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Andreussi, Oliviero. "Water at Interfaces." Doctoral thesis, Scuola Normale Superiore, 2008. http://hdl.handle.net/11384/85793.
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Law, Yeuk Ting. "Investigation of reaction networks and active sites in ethanol steam reforming reaction over Ni and Co-based catalysts." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00869963.
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Bimetallic catalysts have been widely exploited to improve the performance of various catalytic reactions. Understanding the surface properties and in particular, bimetallic interaction and support effect of the catalytic components is an important step towards rational catalyst design. In this thesis, Ni-Co thin film on polar ZnO single crystal was studied as a model catalyst for ethanol steam reforming reaction. The aim is to provide fundamental understanding of how the surface characteristics of the catalyst influence the mechanism and the efficiency of the reaction. This study focused firstly on the study of the interaction between Ni and Co in oxidative environment using Xray photoelectron spectroscopy (PES). Oxidation of Co is favoured over nickel and the surface is enriched with cobalt oxide. Secondly, Ni-Co thin film supported on polar Zn and O terminated ZnOwas studied by synchrotron based PES. The as deposited layer interacts readily with ZnO and Co is partially oxidized upon deposition, even at room temperature. The interaction of ethanol with Ni- Co/ZnO-Zn was studied by thermal desorption spectroscopy (TDS). Ethanol decomposes in different pathways on Ni and Co, in which C-C bond scission and methane production are favoured on Ni/ZnO-Zn while dehydrogenation is favoured on Co/ZnO-Zn. Finally, Ni-Co powder was studied byin-situ ambient pressure PES under reaction conditions in order to clarify the correspondence between the active state of the catalyst and the reaction activity. The product selectivity on Co catalyst is distinctly different from Ni and Ni-Co. Also, the decomposition of methyl group and the high amount of CO produced over Co is likely to be the cause for its high level of carbon deposition.
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ACHILLI, SIMONA. "Spectral properties of adsorbates on metal surfaces via the embedding method." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10827.
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Adsorbates on metal surfaces have attracted recently the scientific interest both from a fundamental point of view (quantum confinement) and in perspective of application in technology. In particular the electronic properties of such reduced symmetry systems are strictly related to their low dimensionality. An accurate theoretical description of their spectral properties has necessarily to deal with the absence of periodicity that characterizes these systems in one (thin films) or more (adatoms) directions. The embedding method allows to overcome this drawback considering a really infinite system both on vacuum and bulk side. In this thesis the ab initio spectral properties of single adatoms (alkali-metal atom and Ba) on Cu(111) and thin overlayers (K/Cu(111), Bi/Cu(100), O/Fe(100)) are analyzed, also in comparison with experimental results. The capabilities of the theoretical method adopted allow to evidence the role of the substrate band structure on the adsorbates induced electronic states. In particular the aspects related to the resonant charge transfer from the adsorbate's states to the bulk continuum are analyzed. This process represents an elastic decay channel for the surface electronic states and contributes to the elastic lifetime, that we can estimate according to the description of a continuous substrate band structure. The results presented for single adatoms evidence the blockade effect that a surface projected energy gap of the substrate produces on the resonant charge transfer. On the other hand the results relative to the overlayer allows to analyze the complex hybridization mechanism between surface features and substrate states in different points of the surface Brillouin zone.
In addition the theoretical description of the electronic properties of overlayers on metal surfaces is devoted in this thesis also to the simulation of experimental findings, namely STM and STS images and photoemission spectra, showing the predictive character of the theoretical approach used.
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Gerth, Christopher Marc. "Infrared absorption studies of two different types of self-assembled monolayers : alkanethiols deposited from aqueous solution and surface confined polymerization of polymethyl-methacrylate (PMMA) using metal overlayer attenuated total reflectance (ATR) and single bounce germanium attenuated total reflectance (GATR) spectroscopies /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Amft, Tobias Verfasser], Kálmán [Gutachter] Graffi, and Martin [Gutachter] [Mauve. "The Impact of Resource Sharing on Coexisting P2P Overlays and Stacked Overlay Modules / Tobias Amft ; Gutachter: Kalman Graffi, Martin Mauve." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2017. http://d-nb.info/1148066845/34.
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Amft, Tobias [Verfasser], Kálmán Gutachter] Graffi, and Martin [Gutachter] [Mauve. "The Impact of Resource Sharing on Coexisting P2P Overlays and Stacked Overlay Modules / Tobias Amft ; Gutachter: Kalman Graffi, Martin Mauve." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2017. http://d-nb.info/1148066845/34.
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Wearing, Lisa. "Formnation of metallic overlayers on quasicrystalsurfaces." Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502247.
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The main aim of this study is to explore the fundamentals of aperiodicity through the deposition of a single elemental aperiodic overlayer onto a quasicrystal surface. The main difficulty with understanding the effects of aperiodicity on the quasicrystal structure arises due to the chemical complexity associated with the surface, as such structures are only observed in metallic alloys containing two or more elements. The formation of a single element quasicrystalline structure has been achieved through the deposition of Pb on i-AI-Pd-Mn and d-AI-Ni-Co (results of the latter not included). This includes an initial study of the effects of aperiodicity on the electronic properties of the surface and the conclusion that the formation of a pseudogap at the Fermi level is due to the aperiodicity of the quasicrystalline structure and not the chemical complexity of the system. The effects of aperiodicity on the magnetic properties of such a system are not yet known, in particular for a single magnetic species which is ordered aperiodically. For this reason Fe was deposited onto two different quasicrystalline surfaces. They show the formation of such a quasiperiodic magnetic film was not observed, the Fe was in fact aligned periodically along the high symmetry axes of the substrates. This result, along with other work in the same field provides some guidance as to which atoms have the greatest chance of ordering aperiodically. Most of the research within the field involves thin film deposition in ultra high vacuum. This is a costly technique, and if films on quasicrystal surfaces were one day to be exploited by industry then production would be severely limited. It is for this reason that the electrochemical deposition of Cu onto AI-Pd-Mn has been studied. This work provides the starting point for further study into the electrochemical deposition on to the quasicrystal surface and comparison to those studies in Ultra Right Vacuum (URV).
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Capano, Michael Anthony. "X-ray studies of strained overlayers." Thesis, Massachusetts Institute of Technology, 1989. https://hdl.handle.net/1721.1/130223.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989.Includes bibliographical references (leaves 184-188).
by Michael A. Capano.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989.
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Robertson, Robert Scott. "Trusted Mobile Overlays." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2425.
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Sensitive information is increasingly moving online and as data moves further from the control of its owner, there are increased opportunities for it to fall into malicious hands. The Web is comprised of three untrusted components where there is a risk of information compromise: networks, service providers, and clients. This thesis presents Trusted Mobile Overlays: a system that leverages trusted mobile devices to protect users from these untrusted components of the Web, while minimizing deployment difficulties. It presents a high-level design of the system as well as a prototype that implements the design.
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Kronstrand, Alexander, and Andreas Holmqvist. "Overlay Network." Thesis, Linköpings universitet, Informationskodning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119498.
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Nowadays, optical fiber is widely used in several areas, especially in communication networking. The main reason is that optical fiber has low attenuation and high bandwidth. However, the switching functionality is performed in the electrical domain (inside the router), thus we have transmission delays in the network lanes. In this study we explore the possibility of developing a hardware “plug-in” that can be connected in parallel with routers of the network enabling the router with “plug-in” to let it bypass time-critical traffic. We researched different switching techniques for optical fibers and realized it would be an expensive endeavor to create one for a large number of wavelength/connections, thus, we scaled it down to prove the concept “plug-in” where we use fiber optical switches and Mux/Demuxes for our design. With our chosen optical components, we were able to bypass the routers (layer 3 switches) in our test environment and switch between different users to chose which one has the direct link. The conclusion can be drawn that it is possible to create such a “plug-in” which could be used by ISPs, to provide a faster lane to consumers with less modification of existing networks.
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Myers, Colin Stephen. "Navigating networks using overlays." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5055/.
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This thesis contributes a novel approach to navigation tasks in large graphs. Graph visualization is the problem of representing the structure of a mathematical graph G = (V,E), V a set of vertices (or nodes) and E ⊆V ×V a set of edges. My work is concerned with the node-link representation of graphs and I use the term network to distinguish this external representation from the underlying mathematical structure. Networks are an intuitive representation of a set of elements and the relationships between them, and are known to be effective for analysis tasks involving following paths between nodes. I define navigation as the task of identifying and following such a path in display space. Unfortunately the utility of a network diminishes as the density of edges increases and edge-crossings make navigation taxing. A well-explored approach to this problem is to find a perspicuous layout of the nodes. While this improves the readability of individual nodes and edges it may also require a compromise: to be easily understood the overall arrangement of the network should also correspond with the user’s internal mental model of the domain, a property referred to as congruence. Other solutions distort the display space or use multiple-scaled-views to promote comprehension of local details while retaining awareness of the global context, but often lack direct support for navigation of the network topology beyond the local context. This thesis contributes a model of visual graph analysis that brings together recent advances in cartographic representation, diagram comprehension, and graph visualization, leading to a greater understanding of network navigation bottlenecks in terms of the degree of correspondence between the external graph representation, and the user’s ‘mental map’. Motivated by this model I present a new approach to graph visualization that separates concerns of navigation from those of depiction with the aim of improving correspondence between the internal and external representations. I describe the design and realization of an interface for network navigation inspired by the new approach within a pipeline-based architecture, and provide a reflective evaluation of the implementation.
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Andersen, David G. (David Godbe) 1975. "Resilient overlay networks." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86657.
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Fraiwan, Mohammad Amin. "Overlay networks monitoring." [Ames, Iowa : Iowa State University], 2008.
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Yiu, Wai-Pun. "Secure overlay multicast /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?COMP%202004%20YIU.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 71-77). Also available in electronic version. Access restricted to campus users.
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Jemander, Thorbjörn. "STM studies of overlayers on semiconductor or insulator surfaces /." Linköping : Univ, 2001. http://www.bibl.liu.se/liupubl/disp/disp2001/tek686s.pdf.
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Poulston, Stephen. "Structure and properties of metallic overlayers on Ru(100)." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338256.
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Sanders, Paul John. "Reinforced asphalt overlays for pavements." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/12221/.
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The maintenance of road pavements in England has become a costly necessity, due largely to the large volume of commercial vehicles using the roads which cause pavements to deteriorate quickly, and makes their repair more difficult to carry out. These roadworks incur not only direct works costs, but also indirect costs from factors such as congestion, motor accidents and pollution. There is obviously a need for cost-effective maintenance that minimises the occurrence and duration of these disruptions. To strengthen pavements bituminous overlays are often used, but may crack prematurely when placed over a layer with discontinuities such as cracks or joints, or deform excessively under wheel loading. The problem of 'reflective cracking' is widespread and reduces the life of maintenance treatments considerably. To increase the time before cracking appears on the surface of a pavement, a (more expensive) thicker overlay may be used, but this can lead to problems with property thresholds and bridge clearance. One possible option of reducing the thickness of overlays by making them more resistant against cracking and deformation, is to place a layer-of reinforcement within or at the bottom of the overlay. Although this approach has been used occasionally to reinforce overlays, over 40 years or so, it is not favoured with many road authorities, as the results of these treatments are difficult to anticipate, and may not be cost effective. This thesis describes an investigation into the effect of reinforcing thin bituminous overlays to identify key factors that significantly influence their performance. By identifying these factors, optimum use of reinforced asphalt should be possible, and thus maintenance of the road network made more cost effective. The investigation was principally carried out in the laboratory using beam tests, shear box tests, tensile tests on reinforcement and large-scale wheel tracking tests. 2-D Finite Element Analysis was used in the analysis of test results. Results show that properly constructed reinforced overlays can be between two or three times more resistant to cracking, and have less than half the permanent deformation of unreinforced materials.
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Latif, L. "Node selection in distributed overlays." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1389944/.
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With the proliferation of latency aware services such as live video streaming, Internetbased financial trading and the popularity of distributed overlays such as BitTorrent there is a growing need for latency-aware distributed overlays. To make such overlays viable, efficient resource discovery services are needed. Anycast is a routing protocol that sends packets to nodes that are a member of a particular group, with the work presented the Anycast protocol in the distributed overlay domain. Structured and unstructured distributed networks have become a popular way to disseminate data without the need for a fixed infrastructure, however there is a need to provide quality of service (QoS). To meet the demands of applications, an overlay needs to maintain accurate Anycast group membership data, locality information and have minimal protocol overhead. Three protocols are proposed to meet these goals. The Distributed Overlay Anycast Table (DOAT) brings the notion of locality to a structured overlay, while introducing Bloom filters as an efficient data structure to present an overlay that can accurately return a node that is participating in a particular group. The Gossip Overlay Anycast Table (GOAT) is a scalable location-aware unstructured overlay that can provide the probabilistic Anycast routing. Through the use of an efficient discovery protocol and the use of Bloom filters, GOAT is able to provide the advantages of a structured overlay, while mitigating the performance issues typically found in unstructured overlays. The N-casting overlay is an unstructured overlay with the ability to send queries to multiple members of an group, uses a hierarchical decomposition of the Internet and an elegant data structure that offers predictable compression of overlay membership. N-casting shows that unstructured overlays can be scalable and sustain high performance in environments that exhibit realistic membership churn. DOAT, GOAT and N-casting present viable services that implemented at the application layer provide location aware node discovery in QoS-enabled applications.
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Fonseca, Pedro. "Search Strategies in Unstructured Overlays." Master's thesis, Department of Informatics, University of Lisbon, 2008. http://hdl.handle.net/10451/13892.
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Unstructured peer-to-peer networks have a low maintenance cost, high resilience and tolerance to the continuous arrival and departure of nodes. In these networks search is usually performed by flooding, which generates a high number of duplicate messages. To improve scalability, unstructured overlays evolved to a two-tiered architecture where regular nodes rely on special nodes to locate resources, called supernodes or superpeers, thus reducing the scope of flooding based searches. While this approach takes advantage of node heterogeneity, it makes the overlay less resilient to accidental and malicious faults, and less attractive to users concerned with the consumption of their resources and who may not desire to commit additional resources that are required by nodes selected as superpeers. Another point of concern is churn, defined as the constant entry and departure of nodes. Churn affects both structured and unstructured overlay networks and, in order to build resilient search protocols, it must be taken into account. This dissertation proposes a novel search algorithm, called FASE, which combines a replication policy and a search space division technique to achieve low hop counts using a small number of messages, on unstructured overlays with non-hierarquical topologies. The problem of churn is mitigated by a distributed monitoring algorithm designed with FASE in mind. Simulation results validate FASE efficiency when compared to other search algorithms for peer-to-peer networks. The evaluation of the distributed monitoring algorithm shows that it maintains FASE performance when subjected to churn
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Qazi, Sameer Hashmat Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Scalable resilient overlay networks." Awarded By:University of New South Wales. Electrical Engineering & Telecommunications, 2009. http://handle.unsw.edu.au/1959.4/44536.
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The Internet has scaled massively over the past 15 years to extend to billions of users. These users increasingly require extensive applications and capabilities from the Internet, such as Quality of Service (QoS) optimized paths between end hosts. When default Internet paths may not meet their requirements adequately, there is a need to facilitate the discovery of such QoS optimized paths. Fortunately, even though the route offered by the Internet may not work (to the required level of performance), often there exist alternate routes that do work. When the direct Internet path between two Internet hosts for instance is sub-optimal (according to specific user defined criterion), there is a possibility that the direct paths of both to a third host may not be suffering from the same problem owing to path disjointness. Overlay Networks facilitate the discovery of such composite alternate paths through third party hosts. To discover such alternate paths, overlay hosts regularly monitor both Internet path quality and choose better alternate paths via other hosts. Such measurements are costly and pose scalability problems for large overlay networks. This thesis asserts and shows that these overheads could be lowered substantially if the network layer path information between overlay hosts could be obtained, which facilitates selection of disjoint paths. This thesis further demonstrates that obtaining such network layer path information is very challenging. As opposed to the path monitoring which only requires cooperation of overlay hosts, disjoint path selection depends on the accuracy of information about the underlay, which is out of the domain of control of the overlay and so may contain inaccuracies. This thesis investigates how such information could be gleaned at different granularities for optimal tradeoffs between spatial and/or temporal methods for selection of alternate paths. The main contributions of this thesis are: (i) investigation of scalable techniques to facilitate alternate path computation using network layer path information; (ii) a review of the realistic performance gains achievable using such alternate paths; and (iii) investigation of techniques for revealing the presence of incorrect network layer path information, proposal of new techniques for its removal.
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Srivastava, Manoj. "SECURITY OVERLAY FOR RMI." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20011106-220340.
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Distributed object computing refers to allowing objects to be distributed across a network. These objects may be distributed across a number of different computers and across networks.This thesis presents a popular distributed object architecture, Remote Method Invocation (RMI). As RMI works on a Java framework, it provides the same features Java provides. Its portability, ability to transport objects as a whole, and power to connect to existing as well as legacy systems makes a strong choice amongst other competing technologies. Needless to say, the transport of objects across systems brings along with it the necessity for a strong security framework.The Secure Sockets Layer (SSL) is a widely popular protocol that currently provides the secure framework RMI needs. Most e-commerce applications these days run over SSL. However, SSL may not the right choice for every application requiring a security backbone. The motivation behind this thesis lies in this thought. The Secure Remote Password Protocol (SRP) provides a secure, simple and fast approach for providing client authentication. An attempt has been made to build a new infrastructure using SRP. The infrastructure that has been developed can provide authentication and privacy, as well as maintain message integrity. One such application domain is mobile computing. In this era where data is required to be accessible from anywhere and everywhere, mobile computing is a growing area. Again, due to the use of mobile agents in this area, security plays an important role. The security mechanism provided needs to be fast and simple and at the same time provide strong security. The new security overlay developed has been proposed as a possible solution.
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Berns, Andrew David. "Self-stabilizing overlay networks." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3431.
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Today's distributed systems exist on a scale that was unimaginable only a few decades ago. Distributed systems now can consist of thousands or even millions of computers spread across the entire world. These large systems are often organized into overlay networks - networks composed of virtual links, with each virtual link realized by one or more physical links. Self-stabilizing overlay networks promise that, starting from any weakly-connected configuration, the correct network topology is always built. This area of research is young, and prior examples of self-stabilizing overlay networks have either been for simple topologies, or involved complex algorithms that were difficult to verify and extend. We address these limitations in this thesis.
First, we present the Transitive Closure Framework, a generic framework to transform any locally-checkable overlay network into a self-stabilizing network. This simple framework has a running time which is at most a logarithmic number of rounds more than optimal, and in fact is optimal for a particular class of overlay networks. We also prove the only known non-trivial lower bound on the convergence time of any self-stabilizing overlay network. To allow fast and efficient repairs for local faults, we extend the Transitive Closure Framework to the Local Repair Framework. We demonstrate this framework by implementing an efficient algorithm for node joins in the Skip+ graph.
Next, we present the Avatar network, which is a generic locally checkable overlay network capable of simulating many other overlay networks. We design a self-stabilizing algorithm for a binary search tree embedded onto the Avatar network, and prove this algorithm requires only a polylogarithmic number of rounds to converge and limits degree increases to within a polylogarithmic factor of optimal. This algorithm is the first to achieve such efficiency, and its modular design makes it easy to extend. Finally, we introduce a technique called network scaffolding, which builds other overlay network topologies using the Avatar network.
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Ng, May Ling. "Characterization and Functionalization of 2D Overlayers Adsorbed on Transition Metals." Doctoral thesis, Uppsala universitet, Yt- och gränsskiktsvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-130342.
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Two-dimensional layered materials, namely monolayer hexagonal boron nitride and graphene were grown by CVD on various transition metals. The physical and chemical properties of these systems were characterized systematically using synchrotron-based spectroscopic techniques, scanning tunneling microscopy and low energy electron diffraction. It is learned that the overlayer–substrate interaction is caused by the overlayer π–substrate d band hybridization. The physical properties of these overlayers depend on the strength of interaction and the degree of lattice matching at the interface. The strength of interaction between the boron nitride and graphene overlayers and the transition metal substrates is increasing from Pt(111)–Ir(111)–Rh(111)–Ru(0001). For overlayers adsorbed on Rh and Ru, the interplay between these two parameters can result in corrugation of the overlayer, i.e. a surface with bonding and non-bonding areas. The amplitude of corrugation is increasing with the strength of interfacial interaction. The corrugated BN overlayer (BN nanomesh) was used as a template for the growth of two-dimensional and highly dispersive Au nanoparticles. In addition, the inert BN nanomesh was used as a substrate for the deposition of pentacene molecules that conform to the corrugated surface while preserving the herringbone crystal structure. The coadsorption of oxygen and Co clusters on the nanomesh was investigated. Oxygen was utilized to lower the Co surface energy, i.e. to prevent Co agglomeration. It is observed that the smaller Co clusters intercalate through the BN overlayer upon soft annealing. Beside the surface structure, the substrate induced surface reactivity of the MG overlayer was employed to promote the hydrogenation of graphene on Pt, Ir and Ni. The graphene layer adsorbed on Pt and Ir shows higher H uptake than MG/Ni. Furthermore the uptake increases with the size of the bonded graphene. The small H uptake for MG/Ni was attributed to the electron localization in the C-Ni bonds.
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Nicklin, Christopher L. "Electronic and structural properties of ultra-thin rare earth overlayers." Thesis, University of Leicester, 1993. http://hdl.handle.net/2381/35750.
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Photoelectron spectroscopy, low energy electron diffraction (LEED), Auger electron spectroscopy (AES), secondary electron emission crystal current (SEECC) and work function change measurements have been used to correlate the electronic and geometric structures of well characterised overlayers of Tm and Gd on Mo(110) and Ag(001). Tm deposited on Mo(110) is shown to form two ordered structures with (10x2) and c(8x4) symmetry before a hexagonal monolayer is formed. Mixed valence, caused by low co-ordinated adatoms, has been observed for sub-monolayer coverages of this system at room temperature. Tm alloys with Ag(001) at room temperature and above, and is found to be trivalent. At 130K the diffusion is inhibited and low co-ordinated atoms are again found to be the cause of mixed valence. Resonant photoemission measurements of thick, mixed valent Tm layers at the 4d-4f absorption threshold indicate that the 4d hole, caused by three strong absorption processes, decays in all cases by direct recombination. Strong enhancement of the trivalent 5s and 5p photoemission are noted for the lowest energy absorption peak and the second two peaks result in enhanced trivalent 4f features. There is also evidence of divalent 4f level enhancement. Gd grows on Mo(110) in a layer by layer mode, and forms six different sub-monolayer structures. The symmetry of the overlayers is similar to Gd/W(110) but with an extra (4x2) phase occurring. The initial growth is characterised by a constant ordering in the [001] direction and gradual contraction in the [110] direction, before isotropic growth of hexagonally based structures. The 3d-4f absorption process for thick Gd layers, reveals two strong peaks due to absorption from the 3d3/2 and 3d5/2 electron energy levels. The 3d hole decays by direct recombination leading to enhanced photoemission features, although a significant Auger intensity is observed on the high energy sides of the absorption peaks.
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Murukesvan, Abhinash. "Distributed Overlays in Wireless Sensor Networks." Thesis, KTH, Kommunikationssystem, CoS, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92202.
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This thesis investigates two architectures and compares their suitability for selective application and user differentiation in sensor networks. A hierarchical architecture consisting of more capable cluster heads surrounded by weaker nodes is compared to a flat architecture of equally powerful nodes. In both architectures there exists a logical overlay network that connects the nodes, depending on the application and user. Furthermore, a broadcast encryption scheme is proposed to aid in distributing keys to nodes for secure communication and to maintain these restricted groups.applikation och användar differentiering i trådlösa sensor nätverk. En hierarkisk arkitekturbestående av kraftfullare sensor noder omgiven av mindre kraftfulla sensor noder jämförsmed en platt arkitektur bestående av lika kraftfulla sensor noder. I båda arkitekturer existerarett logiskt lager ovanpå stacken som kopplar noder beroende på applikation och användare,helt oberoende av geografisk placering. Utöver det, bör en nyckel management schema användas till att distribuera nycklar tillnoderna för säker kommunikation och att bibehålla dessa slutna grupper.
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Masuku, Crispen. "Tensile relaxation of bonded concrete overlays." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/12109.
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Includes abstract.Includes bibliographical references (leaves 131-135).
Restrained shrinkage in bonded concrete overlays can cause stress build up, cracking and even debonding. Tensile relaxation is the main mechanism of stress relief in concrete overlays. This results in less possibility of cracking and debonding. The research described in this study presents an analytical method of analysis. This method is based on tests performed to assess tensile relaxation in concretes subjected to restraint. Although this study is limited in scope, it serves as an introduction to the topic and contributes a valuable bank of results obtained. In this study, commercial repair mortar (Sika® Rep LW), 0.45 and 0.65 w/c ratio custom-made mixes were investigated. Uniaxial tensile strength, tensile elastic modulus, shrinkage and tensile relaxation tests were done on dog-bone concrete mortar specimens.
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Gustafsson, Maria. "Läshastighet på datorskärm med färgade overlays." Thesis, Linnéuniversitetet, Institutionen för medicin och optometri (MEO), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-65546.
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Syfte: Att undersöka läshastigheten på datorskärm och om den kan förbättras med hjälp av färgade overlays, samt om det finns någon skillnad i läshastighet på utskrivet papper och datorskärm. Metod: Deltagarna (n=30) fick läsa ett Wilkins rate of reading test översatt till svenska, där antalet ord som hann läsas upp högt under en minut jämfördes då de läste på papper utan overlay och på datorskärm med och utan overlay. Studien gjordes på studenter mellan 18-31 år. Resultat: Den här studien visar att det inte finns någon signifikant skillnad i läshastighet mellan läsning på utskrivet papper och datorskärm (p=0,508). Deltagarna läste 1,6 ± 13,3 ord mer/min på datorskärm än på papper. En signifikant skillnad kan däremot ses mellan läsning på datorskärm med och utan färgat overlay (p=0,008). Läshastigheten ökade med 4,7 ± 9,1 ord/min med färgat overlay. Slutsats: Läshastigheten på papper och datorskärm är ungefär densamma. Man kan öka läshastigheten på datorskärm genom att placera ett färgat overlay över texten.Purpose: To investigate reading speed on a computer screen and if it can be improved by using coloured overlays, and also if there is any difference in reading speed on printed paper and computer screen. Methods: The participants (n=30) read a Wilkins rate of reading test translated into Swedish, where the number of words read out loud in one minute was compared when reading on a paper without overlay and on a computer screen with and without an overlay. This study was performed on students aged 18-31 years. Results: This study shows that there is no significant difference in reading speed between reading on a printed paper and on a computer screen (p=0.508). The participants read 1.6 ± 13.3 words/min more on the computer screen than on the paper. A significant difference however was found in reading on a computer screen with and without coloured overlay (p=0.008). The reading speed increased with 4.7 ± 9.1 words/min with a coloured overlay. Conclusions: The reading speed on paper is similar to the reading speed on computer screen. The reading speed on the computer screen can be increased by placing a coloured overlay in front of the text.
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Sun, Zhenhua. "Evaluation of concrete bridge deck overlays." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3630.
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Thesis (M.S.)--West Virginia University, 2004.Title from document title page. Document formatted into pages; contains xiii, 101 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 97-101).
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Wagh, Prasad J. "DiffServ overlay multicast for videoconferencing." Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/4301.
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Thesis (M.S.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (January 10 , 2007) Includes bibliographical references.
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Wu, Xiao. "SIP on an Overlay Network." Thesis, KTH, Kommunikationssystem, CoS, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91491.
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With the development of mobile (specifically: wide area cellular telephony) technology, users’ requirements have changed from the basic voice service based on circuit switch technology to a desire for high speed packet based data transmission services. Voice over IP (VoIP), a packet based service, is gaining increasing attention due to its high performance and low cost. However, VoIP does not work well in every situation. Today Network address translation (NAT) traversal has become the main obstruction for future VoIP deployment. In this thesis we analyze and compare the existing NAT traversal solutions. Following this, we introduce a VoIP over IPSec (VOIPSec) solution (i.e., a VoIP over IPSec virtual private network (VPN) scheme) and an extended VOIPSec solution mechanism. These two solutions were tested and compared to measure their performance in comparison to a version of the same Session Initiation Protocol (SIP) user agent running without IPSec. In the proposed VOIPSec solution, the IPSec VPN tunnel connects each of the SIP clients to a SIP server, thus making all of the potential SIP participants reachable, i.e., solving the NAT traversal problem. All SIP signaling and media traffic for VoIP calls are transmitted through this prior established tunnel. This VPN tunnel provides the desired universal means for VoIP traffic to traverse NAT equipment. Additionally, the IPSec VPN also guarantees the security of VoIP calls at the IP level. In order to improve the security level of media streams for the VOIPSec solution, we deployed and evaluated an extended VOIPSec solution which provides end-to-end protection of the real time media traffic. In this extended VOIPSec solution, we used SRTP instead of RTP to carry the media content. This extended method was shown to provide all of the advantages of VOIPSec and SRTP without any additional delay for the media traffic (as compared to the VoIPSec solution). Note that the solution proposed in this thesis may be of limited practical importance in the future as more NATs become VoIP capable; but the solution is currently essential for facilitating the increasing deployment of VoIP systems in practice. For VoIP calls that do not need end-to-end security, we recommend the use of the VOIPSec solution as a means to solve the NAT traversal problem and to protect traffic at the IP level. When application to application security is not needed we prefer the VOIPSec solution to the extended VOIPSec solution for the following reasons: (1) our test results show that the time for call setup for the extended VOIPSec solution is twice time the time needed for the VOIPSec solution and the extended VOIPSec solution requires the use of user agents that support SRTP. While, the VOIPSec solution does not require a special user agent and all VoIP clients in the market are compatible with this solution. However, when more SIP user agents add support for SRTP, the extended VOIPSec solution will be applicable for users of these SIP user agents.Med utvecklingen av mobil (specifikt: wide area cellulär telefoni)-teknik, har användarnas krav ändras från den grundläggande röst-tjänst som bygger på krets kopplad teknik till att vilja ha hög-hastighets paket baserade dataöverföringstjänster. Voice over IP (VoIP) som vinner allt mer uppmärksamhet på grund av sin höga prestanda och låga kostnader är en paket baserad telefon tjänst. Däremot fungerar VoIP inte bra i alla situationer. Network address translation (NAT) har blivit det största hinder för en framtida användning av VoIP. I denna avhandling analyserar vi och jämför nuvarande NAT lösningar. Efter detta inför vi en VoIP över IPSec (VOIPSec) lösning (dvs. ett VoIP över IPSec Virtual Private Network (VPN) system) och en utvidgad VOIPSec lösnings mekanism. Dessa två lösningar testas och jämfördes för att mäta prestationer i förhållande till en version av samma SIP User Agent som körs utan IPSec. I den föreslagna lösningen VOIPSec ansluter IPSec en VPN-tunnel till varje SIP-klient och SIP-server, vilket gör att alla de potentiella SIP deltagarna kan nås, dvs eventuella NAT problem löses. All SIP-signalering och media trafik för VoIP-samtal överförs via denna etablerade tunnel. Denna VPN-tunnel ger allmänna medel för VoIP-trafik att passera NAT utrustningen. Dessutom ger IPSec VPN också garanterad säkerheten för VoIP-samtal på IP-nivå. För att förbättra skyddsnivån för mediaströmmar med VOIPSec, skapade vi och utvärderade en utsträckt VOIPSec lösning som innehåller end-to-end skydd av realtids media trafik. I denna utökade VOIPSec lösning, använde vi SRTP stället för RTP för att bära medieinnehåll. Denna utvidgade metod visade sig ge alla fördelar VOIPSec och SRTP kunde erbjuda utan ytterligare dröjsmål för media trafiken (jämfört med VoIPSec lösningen). Observera att den lösning som föreslås i denna avhandling kan vara av begränsad praktisk betydelse i framtiden då fler NAT lösningar blir VoIP kapabla, men lösningen är idag nödvändigt för att underlätta den ökande användningen av VoIP-system i praktiken. För VoIP-samtal som inte behöver end to end säkerhet rekommenderar vi användning av VOIPSec lösningen som ett sätt att lösa NAT problem och för att skydda trafiken på IP-nivå. När end to end säkerhet inte behövs föredrar vi VOIPSec lösningen av följande skäl: (1) våra testresultat visar att tiden för samtal inställning för det förlängda VOIPSec lösningen är dubbelt den tid som krävs för VOIPSec lösningen och den utökade VOIPSec lösningen kräver användning av användarprogram som stödjer SRTP. Medan VOIPSec lösningen inte kräver en speciell användar agent och alla VoIP-klienter på marknaden är kompatibla med denna lösning. Men när fler SIP användaragenter får stöd för SRTP, kommer den förlängda VOIPSec lösning tillämpas för användare av dessa SIP användarprogram.
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Junkert, Levi Daniel. "The grid overlay system model." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/junkert/JunkertL0509.pdf.
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The grid overlay system model is a new technique for forming a grid computing model for research computing. In this method we construct a grid that is dynamically allocated from a set of resources in a unique and progressive manner. This new system model allows for construction of virtual environments for execution of applications on many diverse shared resources. The system can dynamically scale to create a range of resources from a single machine to a virtual cluster of machines. This model provides a virtual container that can run legacy and customized software in an emulated environment or directly on the host's hardware through virtualization. Using this model on current consumer hardware allows for a unique blend of software containment with dynamic resource allocation. Our model, in combination with commercial off the shelf (COTS) hardware and software, is able to create a large grid system with multiple combinations of hardware and software environments. In our model we propose a unique set of abstraction layers for systems. The combination of our model with current consumer hardware and software provides a unique design principle for addressing grid implementation, hardware reusability, operating system deployment and implementation, virtualization in the grid, and user control techniques. This provides a robust and simple framework that allows for the construction of computational research solutions in which performance can be traded for flexibility, and vice versa. Our model can be applied to computational research grids, service oriented grids, and even scales to collections of mobile or embedded system grids.
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Tam, W. S. "Pavement evaluation and overlay design." Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378746.
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Rashid, Lezan. "Overlay welding of FeCrAl alloys." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-44345.
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In this master thesis different overlay welding methods suitable for boiler application has been investigated. The purpose of this project is to define advantages and disadvantages for each overlay welding methods and suggest some evaluation criteria on some commercial and experimental alloys aimed for overlay welding material. Many components in a boiler are made of low alloy steel and the atmosphere in the furnace region can be very complex; therefore many different types of corrosion can occur. Weld overlay is a process where one or multiple layers of corrosion resistant material are applied to a base material. The two overlay welding methods investigated in this study were Tungsten Inert Gas welding and Metal Inert/Active Gas welding. Tests were performed with FeCrAl alloys (Kanthal A, Kanthal D and some experimental alloys). FeCrAl alloys in general are ferritic iron-based steels with a typical concentration of 20-23 wt. % chromium and ~5 wt.% aluminum. Different overlay welding evaluation was made; visual examination, dye penetrant inspection, macro/micro examination, side bend test and short term corrosion test (~50hours). Conclusion of this thesis is that MIG welding is a more productive method than TIG, but more defects such cracks and lack of fusion can be produced for MIG welding. These defects can be “fixed” if welding parameters is optimized. If repairing a certain place TIG welding is a better option. A conclusion about number of layers; one layer with MIG welding is almost as thick as three layers with TIG welding with welding wire Ø 1mm. Three welding evaluation that is really important is visual examination, dye penetrant testing and corrosion test in order to choose which overlay welding method is suitable in boiler application.I detta examensarbete har olika påsvetsningsmetoder som är lämpliga för en pannapplikation undersökts. Syftet med denna studie var att undersöka både för- och nackdelar med påsvetsningsmetoderna och föreslå några utvärderingskriterier på vissa kommersiella och experimentella legeringar som lämpar sig för påsvetsningsmaterial. Många komponenter i en panna är tillverkade av låg legerat stål och miljön där förbränningen sker kan vara väldigt komplex, därför kan det ske korrosion. Påsvetsning är en process där ett eller flera skikt av ett mer korrosionsbeständigt material appliceras på ett basmaterial. De två olika svetsmetoderna som undersöktes i denna studie var TIG-svetsning och MIG-svetsning. Testerna utfördes med FeCrAl legeringar (Kanthal A, Kanthal D och vissa experimentella legeringar). FeCrAl legeringar är i allmänhet ferritiska järnbaserade stål med 20-23% krom och ~5% aluminium. De utvärderingsmetoderna som undersöktes var: visuell undersökning, penetrantprovning, makro/ mikroundersökning, sidobockprovning och korttidskorrosionstest (~50 timmar). Slutsatsen av detta examensarbete är att MIG-svetsning är en mer produktiv metod än TIG, men fler defekter såsom bindfel och sprickor uppkom för MIG-svetsning. Dessa defekter kan ”fixas” genom optimering av svetsparametrar. Om man bara ska reparera ett specifikt område är TIG-svetsning ett bättre alternativ. En slutsats om antal lager är att ett lager med MIG-svetsning är nästan lika tjockt som tre lager med TIG-svetsning med Ø 1mm svetstråd. Tre svetsutvärderingar som är viktiga är visuell undersökning, penetrantprovning och korrosionstest för att välja vilken påsvetsmetod som är lämpligast i pannapplikation.
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Miao, Jun. "Load balance in overlay multicast /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?COMP%202004%20MIAO.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 59-62). Also available in electronic version. Access restricted to campus users.
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Payberah, Amir H. "Distributed Optimization of P2P Media Delivery Overlays." Licentiate thesis, KTH, Programvaru- och datorsystem, SCS, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33287.
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Media streaming over the Internet is becoming increasingly popular. Currently, most media is delivered using global content-delivery networks, providing a scalable and robust client-server model. However, content delivery infrastructures are expensive. One approach to reduce the cost of media delivery is to use peer-to-peer (P2P) overlay networks, where nodes share responsibility for delivering the media to one another. The main challenges in P2P media streaming using overlay networks include: (i) nodes should receive the stream with respect to certain timing constraints, (ii) the overlay should adapt to the changes in the network, e.g., varying bandwidth capacity and join/failure of nodes, (iii) nodes should be intentivized to contribute and share their resources, and (iv) nodes should be able to establish connectivity to the other nodes behind NATs. In this work, we meet these requirements by presenting P2P solutions for live media streaming, as well as proposing a distributed NAT traversal solution. First of all, we introduce a distributed market model to construct an approximately minimal height multiple-tree streaming overlay for content delivery, in gradienTv. In this system, we assume all the nodes are cooperative and execute the protocol. However, in reality, there may exist some opportunistic nodes, free-riders, that take advantage of the system, without contributing to content distribution. To overcome this problem, we extend our market model in Sepidar to be effective in deterring free-riders. However, gradienTv and Sepidar are tree-based solutions, which are fragile in high churn and failure scenarios. We present a solution to this problem in GLive that provides a more robust overlay by replacing the tree structure with a mesh. We show in simulation, that the mesh-based overlay outperforms the multiple-tree overlay. Moreover, we compare the performance of all our systems with the state-of-the-art NewCoolstreaming, and observe that they provide better playback continuity and lower playback latency than that of NewCoolstreaming under a variety of experimental scenarios. Although our distributed market model can be run against a random sample of nodes, we improve its convergence time by executing it against a sample of nodes taken from the Gradient overlay. The Gradient overlay organizes nodes in a topology using a local utility value at each node, such that nodes are ordered in descending utility values away from a core of the highest utility nodes. The evaluations show that the streaming overlays converge faster when our market model works on top of the Gradient overlay. We use a gossip-based peer sampling service in our streaming systems to provide each node with a small list of live nodes. However, in the Internet, where a high percentage of nodes are behind NATs, existing gossiping protocols break down. To solve this problem, we present Gozar , a NAT-friendly gossip-based peer sampling service that: (i) provides uniform random samples in the presence of NATs, and (ii) enables direct connectivity to sampled nodes using a fully distributed NAT traversal service. We compare Gozar with the state-of-the-art NAT-friendly gossip-based peer sampling service, Nylon, and show that only Gozar supports one-hop NAT traversal, and its overhead is roughly half of Nylon’s. QC 20110517
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Khelghatdoust, Mansour. "Gossip based peer sampling in social overlays." Thesis, KTH, Kommunikationsnät, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-144278.
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Performance of many P2P systems depends on the ability to construct a ran- dom overlay network among the nodes. Current state-of-the-art techniques for constructing random overlays have an implicit requirement that any two nodes in the system should always be able to communicate and establish a link be- tween them. However, this is not the case in some of the environments where distributed systems are required to be deployed, e.g, Decentralized Online So- cial Networks, Wireless networks, or networks with limited connectivity because of NATs/firewalls, etc. In such restricted networks, every node is able to com- municate with only a predefined set of nodes and thus, the existing solutions for constructing random overlays are not applicable.In this thesis we propose a gossip based peer sampling service capable of running on top of such restricted networks and producing an on-the-fly random overlay. The service provides ev- ery participating node with a set of uniform random nodes from the network, as well as efficient routing paths for reaching those nodes via the restricted net- work. We perform extensive experiments on four real-world networks and show that the resulting overlays rapidly converge to random overlays. The results also exhibit that the constructed random overlays have self healing behaviour under churn and catastrophic failures.
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Libarikian, Ari Levon 1978. "Robustness of bus overlays in optical networks." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16850.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 53-56).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Local area networks (LANs) nowadays use optical fiber as the medium of communication. This fiber is used to connect a collection of electro-optic nodes which form network clouds. A network cloud is a distribution network that connects several external nodes to the backbone, and often takes the form of a star or tree. Optical stars and trees have expensive and inefficient recovery schemes, and as a result, are not attractive options when designing networks. In order to solve this problem, we introduce a virtual topology that makes use of the robustness that is inherently present in a metropolitan area network (MAN) or wide area network (WAN) (long haul network). The virtual topology uses a folded bus scheme and includes some of the elements of the real topology (architecture). By optically bypassing some of the router/switch nodes in the physical architecture, the virtual topology yields better recovery performance and more efficient systems (with respect to cost related to bandwidth and recoverability). We present a bus overlay which uses simple access nodes and is robust to single failures. Our architecture allows the use of existing optical backbone infrastructure. We consider a linear folded bus architecture and introduce a T-shaped folded bus. Although buses are generally not able to recover from failures, we propose a loopback approach. Our approach allows optical bypass of some routers during normal operation, thus reducing the load on routers, but makes use of routers in case of failures. We analyze the behavior of our linear and T-shaped systems under average use and failure conditions. We show that certain simple characteristics of the traffic matrix give meaningful performance characterization. We show that our architecture provides solutions which limit loads on the router.
by Ari Levon Libarikian.
S.M.
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Bamforth, Miren. "Electrical design of structurally tunable skin overlays." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119543.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 94-98).
Current on-skin interfaces focus on enabling electronic circuitry and display-like output on top of the skin, but to the best of our knowledge interfaces for tuning the texture or stiffness of the skin itself are unexplored. We present SkinMorph, a second skin layer that alters its texture and color due to attached electronic control circuitry. Modular electrical design of the system includes a bare-bones processor board with three optional, interchangeable, stackable peripheral modules: a programming and debugging module, a Bluetooth module, and an accelerometer module. The modular circuits in tandem with customizable silicone injection molds allow for adaptation to a variety of applications, resulting in a system which affords some physical protection via tuning the skin overlay characteristics on various areas of the body. Particular attention is paid to on-skin challenges such as electrical and heat safety, miniaturization of circuit components, and skin-safe material choices. The entire system including battery, control board and peripherals, and tunable skin overlay can be mounted on the body without a wired tether impeding the user.
by Miren Bamforth.
M. Eng.
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Stevens, Robert James. "Polyester Polymer Concrete for Bridge Deck Overlays." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8143.
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The objectives of this research were to 1) compile a synthesis of information about polyester polymer concrete (PPC) from the literature; 2) conduct a scanning tour to observe PPC construction, inspect in-service PPC overlays, and discuss topics related to PPC; 3) revise the existing Utah Department of Transportation (UDOT) PPC specification; 4) document a PPC field demonstration project; and 5) perform laboratory characterization of the material properties of field-mixed PPC. The scope of the research included a scanning tour, field testing, and laboratory experimentation. The objectives of the scanning tour included observation of a PPC overlay placement, inspection of existing overlays, and discussion of selected topics related to PPC. The scanning tour comprised a 3-day visit to California. Items related to material properties, mixture and overlay design, laboratory testing, and construction and field testing were investigated. Several recommendations relevant to Utah bridge deck preservation practice were developed based on the findings and then incorporated into a revised UDOT PPC specification. The objective of the field testing was to evaluate specific aspects of construction, quality assurance, and performance of PPC overlays on concrete bridge decks. The scope of the project included testing of a PPC test section overlay and three PPC bridge deck overlays during and after construction. Hardness tests were performed on the test section placements, and hardness, skid resistance, impact-echo, impedance, and resin content determination tests were performed on each of the bridge deck overlays. The field testing yielded valuable information about PPC overlays. Recommendations regarding hardness testing, skid resistance testing, patching, and surface preparation were developed based on the findings. The objectives of the laboratory experimentation were to characterize several material properties of field-mixed PPC sampled from actual bridge deck overlay placements in Utah and compare them to properties of laboratory-mixed PPC reported in the literature. Laboratory testing was conducted on a typical PPC mixture. Properties that were measured include density, modulus of elasticity, coefficient of thermal expansion, hardness, unconfined compressive strength, splitting tensile strength, rapid chloride permeability, and resin content. Measured properties were consistent with typical ranges cited in the literature.
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Payberah, Amir. "Distributed Optimization of P2P Media Delivery Overlays." Licentiate thesis, SICS, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ri:diva-23989.
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Media streaming over the Internet is becoming increasingly popular. Currently, most media is delivered using global content-delivery networks, providing a scalable and robust client-server model. However, content delivery infrastructures are expensive. One approach to reduce the cost of media delivery is to use peer-to-peer (P2P) overlay networks, where nodes share responsibility for delivering the media to one another. The main challenges in P2P media streaming using overlay networks include: (i) nodes should receive the stream with respect to certain timing constraints, (ii) the overlay should adapt to the changes in the network, e.g., varying bandwidth capacity and join/failure of nodes, (iii) nodes should be intentivized to contribute and share their resources, and (iv) nodes should be able to establish connectivity to the other nodes behind NATs. In this work, we meet these requirements by presenting P2P solutions for live media streaming, as well as proposing a distributed NAT traversal solution. First of all, we introduce a distributed market model to construct an approximately minimal height multiple-tree streaming overlay for content delivery, in gradienTv. In this system, we assume all the nodes are cooperative and execute the protocol. However, in reality, there may exist some opportunistic nodes, free-riders, that take advantage of the system, without contributing to content distribution. To overcome this problem, we extend our market model in Sepidar to be effective in deterring free-riders. However, gradienTv and Sepidar are tree-based solutions, which are fragile in high churn and failure scenarios. We present a solution to this problem in GLive that provides a more robust overlay by replacing the tree structure with a mesh. We show in simulation, that the mesh-based overlay outperforms the multiple-tree overlay. Moreover, we compare the performance of all our systems with the state-of-the-art NewCoolstreaming, and observe that they provide better playback continuity and lower playback latency than that of NewCoolstreaming under a variety of experimental scenarios. Although our distributed market model can be run against a random sample of nodes, we improve its convergence time by executing it against a sample of nodes taken from the Gradient overlay. The Gradient overlay organizes nodes in a topology using a local utility value at each node, such that nodes are ordered in descending utility values away from a core of the highest utility nodes. The evaluations show that the streaming overlays converge faster when our market model works on top of the Gradient overlay. We use a gossip-based peer sampling service in our streaming systems to provide each node with a small list of live nodes. However, in the Internet, where a high percentage of nodes are behind NATs, existing gossiping protocols break down. To solve this problem, we present Gozar, a NAT-friendly gossip-based peer sampling service that: (i) provides uniform random samples in the presence of NATs, and (ii) enables direct connectivity to sampled nodes using a fully distributed NAT traversal service. We compare Gozar with the state-of-the-art NAT-friendly gossip-based peer sampling service, Nylon, and show that only Gozar supports one-hop NAT traversal, and its overhead is roughly half of Nylon’s.REST
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Patel, Prakash Shashikant. "Diffusion problems and degradation of bearing overlays." Thesis, London Metropolitan University, 1989. http://repository.londonmet.ac.uk/3192/.
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The corrosion and degradation of Pb-Sn bearing overlays Is a bilateral process . During service, the lubricant becomes corrosive due to the breakdown of inhibitors with subsequent oxidation occurring at operating temperatures (120-170[degrees]). ...
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Cakmak, Mehmet. "Theoretical studies of structural and electronic properties of overlayers on semiconductor surfaces." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286574.
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Phan, Minh Son. "Dynamic response function and the theory of spin waves in metallic overlayers." Thesis, City, University of London, 1989. http://openaccess.city.ac.uk/20133/.
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A general recursion method (method of adlayers) for calculating the exact Green function in an arbitrary overlayer is developed. The method as presented applies to an s-band tight-binding Hamiltonian with hopping between nearest-neighbours only. The general.isation of the method to a multi-orbital band structure is described. The overlayer we consider is deposited above the (100) surface of a simple cubic semi-infinite nonmagnetic metallic substrate occupying the half-space z < O. The aim of the present thesis is twofold: firstly, the ground state of a ferromagnetic overlayer is investigated. In particular, the local densities of states (LOOS) of an overlayer are calculated using the method of adlayers. The method of adlayers is very simple, computationally stable and extremely accurate. The numerical results for the LOOS and the Hartree-Fock (HF) occupation numbers of a single-adlayer and a seven-adlayer overlayer are presented. The surface and bulk DOSs for an overlayer of seven atomic planes are compared. The presence of an adlayer may induce surface states if a strong enough perturbation occurs at the surface. Such surface states are automatically included in our method of adlayers. Secondly, spin waves in a transition metal overlayer are investigated within the framework of the itinerant theory of magnetism. The overlayer is modelled by a single-orbital tight-binding band with a strong intra-atomic repulsion U (one band Hubbard model). All the matrix elements of the HF dynamic unenhanced susceptibility in the overlayer are computed from the HF one-electron Green functions. Spin waves are then poles of the full dynamic enhanced susceptibility which is determined in the random phase approximation (RPA). It is demonstrated that a very high accuracy in solving the HF ground state is needed to determine correctly spin wave modes. When this requirement is fulfilled, the Goldstone theorem at zero wavevector and zero frequency is very well satisfied. Numerical results for the spin wave spectra of a single-adlayer are presented for a range of values of U. Spin wave energies for a single-adlayer, for an unsupported layer and the exchange stiffness constant 0 of an unsupported layer are compared. Finally, all the computed spin wave branches of an overlayer of seven atomic planes are presented and discussed. The disappearance of spin waves in the Stoner continuum is illustrated and the possibility that a surface spin wave mode might occur is briefly discussed.
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Castillo, Barrero Rafael. "Platinium based catalysts for the PROX reaction. Influence of the carbon overlayers." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC292.
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Dans la technologie à l'hydrogène, l'oxydation préférentielle du CO en excès d'hydrogène (réaction PrOx) est un processus important pour l'obtention d'hydrogène sans CO pour les piles à combustible à membrane échangeuse de protons (PEMFC). Les catalyseurs à base de PtCu sont l’un des systèmes les plus étudiés pour les dispositifs mobiles en raison de leur bilan d’activité / sélectivité élevé et de leurs propriétés chimiques et mécaniques appropriées pour les procédures de démarrage / arrêt dans les conditions de fonctionnement des processeurs de combustible.Récemment, l'utilisation de catalyseurs bimétalliques Pt-Cu avec une activité et une sélectivité excellentes vis-à-vis de l'oxydation du CO a été rapportée pour la réaction PrOx. Cependant, la nature des phases actives et le rôle des deux métaux au cours de la réaction ne sont pas clairement démontrés.Pour comprendre ce système, il est nécessaire de créer un catalyseur modèle qui facilite l’étude. Ainsi, des nanoparticules d'alliage bimétallique Pt-Cu bien définies ont été synthétisées et étudiées par des techniques d'Operando permettant de comprendre les modifications électroniques de surface de l'interface solide-gaz du catalyseur modèle mentionné ci-dessus dans des conditions de réaction PrOx.Dans ce travail, la composition et la nature des espèces présentes à la surface du catalyseur dans des conditions de réaction bien contrôlées ont été étudiées, en particulier du point de vue de la dynamique de surface, des transitions structurelles et des effets possibles de l’atmosphère de réaction et des couches superposées adsorbées sur la surface. composition superficielle et structure de l'alliageIn the Hydrogen technology, the preferential oxidation of CO in excess of hydrogen (PrOx reaction) is an important process for obtaining CO-free hydrogen for proton exchange membrane fuel cells (PEMFCs). PtCu based catalysts are one of the most studied systems for mobile devices because of their high activity/selectivity balance and their appropriate chemical and mechanical properties for the start-up/shut-down procedures during fuel processors operation conditions.Recently, the use of Pt-Cu bimetallic catalysts with excellent activity and selectivity towards CO oxidation was reported for PrOx reaction. However, there are not clear evidences off the nature of the active phases and the role of both metals during the reaction.To understand this system it is necessary to create a model catalyst which facilitates the study. Thus, well-defined Pt-Cu bimetallic alloy nanoparticles were synthetized and studied by Operando techniques allowing the comprehension of the surface electronic modifications in the solid-gas interface of the above mentioned model catalyst under PrOx reaction conditions.In this work, the composition and nature of the species present on the catalyst surface upon well-controlled reaction conditions were studied, in particular from the point of view of surface dynamics, structural transitions and the possible effects of reaction atmosphere and adsorbed overlayers on the surface composition and structure of the alloy
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Mastour, Eshgh Somayeh Sadat. "Distributed Reinforcement Learning for Overlay Networks." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92131.
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In this thesis, we study Collaborative Reinforcement Learning (CRL) in the context of Information Retrieval in unstructured distributed systems. Collaborative reinforcement learning is an extension to reinforcement learning to support multiple agents that both share value functions and cooperate to solve tasks. Specifically, we propose and develop an algorithm for searching in peer to peer systems by using collaborative reinforcement learning. We present a search technique that achieve higher performance than currently available techniques, but is straightforward and practical enough to be easily incorporated into existing systems. Theapproach is profitable because reinforcement learning methods search for good behaviors gradually during the lifetime of the learning peer. However, we must overcome the challenges due to the fundamental partial observability inherent in distributed systems which have highly dynamic nature and changes in their configuration are common practice. Also, we undertake a performance study of the effects that some environment parameters, such as the number of peers, network traffic bandwidth, and partial behavioral knowledge from previous experience, have on the speed and reliability of learning. In the process, we show how CRL can be used to establish and maintain autonomic properties of decentralized distributed systems. This thesis is an empirical study of collaborative reinforcement learning. However, our results contribute to the broader understanding of learning strategies and design of different search policies in distributed systems. Our experimental results confirm the performance improvement of CRL in heterogeneous overlay networks over standard techniques such as random walking.