• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 54
  • 14
  • 10
  • 7
  • 4
  • 3
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 117
  • 117
  • 44
  • 32
  • 26
  • 19
  • 19
  • 19
  • 15
  • 14
  • 14
  • 13
  • 13
  • 13
  • 12
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Optimisation of the predictive ability of artificial neural network (ANN) models: A comparison of three ANN programs and four classes of training algorithm.

Rowe, Raymond C., Plumb, A.P., York, Peter, Brown, M. January 2005 (has links)
No / The purpose of this study was to determine whether artificial neural network (ANN) programs implementing different backpropagation algorithms and default settings are capable of generating equivalent highly predictive models. Three ANN packages were used: INForm, CAD/Chem and MATLAB. Twenty variants of gradient descent, conjugate gradient, quasi-Newton and Bayesian regularisation algorithms were used to train networks containing a single hidden layer of 3¿12 nodes. All INForm and CAD/Chem models trained satisfactorily for tensile strength, disintegration time and percentage dissolution at 15, 30, 45 and 60 min. Similarly, acceptable training was obtained for MATLAB models using Bayesian regularisation. Training of MATLAB models with other algorithms was erratic. This effect was attributed to a tendency for the MATLAB implementation of the algorithms to attenuate training in local minima of the error surface. Predictive models for tablet capping and friability could not be generated. The most predictive models from each ANN package varied with respect to the optimum network architecture and training algorithm. No significant differences were found in the predictive ability of these models. It is concluded that comparable models are obtainable from different ANN programs provided that both the network architecture and training algorithm are optimised. A broad strategy for optimisation of the predictive ability of an ANN model is proposed.
52

Common Test and Training Range Architecture

Pace, Richard, Walters, Charles E. 11 1900 (has links)
International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / To address the concerns of a declining defense budget, duplicate range capabilities, and applications of new technologies, the Deputy Director, Test Facilities and Resources, Test, Systems Engineering and Evaluation Directorate, Office of the Secretary of Defense (OSD), initiated the Common Test and Training Range Architecture (CTTRA) Workshop project. The development of a common test and training range architecture requires a series of workshops designed to apply the expertise of the test and training ranges and the installed systems test facilities (ISTF) communities to the challenges of architecture development and interface standardization. A common range architecture with standardized interfaces will facilitate asset sharing between the Services, increase the industry-government dual-use potential of OSD's test and training range facilities, and lower the cost of testing. Further, common range interfaces will allow the efficient integration of new instrumentation and simulations at minimum cost. To support development of the CTTRA, there have been three workshops, each expanding the accomplishments of the previous workshop. The first workshop was conducted 20-22 April 1994. The other workshops were held 12-14 October 1994 and 21-24 February 1995. The goals of the workshop process are to: • Develop a common test and training range architecture that supports the requirements of the test, training, and installed systems test facility communities • Identify areas with the potential to yield near-term interface standardization benefits. • Identify potential OSD Central Test and Evaluation Investment Program (CTEIP) projects. Thus far, the workshops have developed a top level and second level candidate CTTRA, identified areas for interface standardization, and established standing working groups responsible for continuing development of CTTRA and selected areas for interface standardization.
53

Packet aggregation for voice over internet protocol on wireless mesh networks

Zulu, Docas Dudu January 2012 (has links)
>Magister Scientiae - MSc / This thesis validates that packet aggregation is a viable technique to increase call ca-pacity for Voice over Internet Protocol over wireless mesh networks. Wireless mesh networks are attractive ways to provide voice services to rural communities. Due to the ad-hoc routing nature of mesh networks, packet loss and delay can reduce voice quality.Even on non-mesh networks, voice quality is reduced by high overhead, associated with the transmission of multiple small packets. Packet aggregation techniques are proven to increase VoIP performance and thus can be deployed in wireless mesh networks. Kernel level packet aggregation was initially implemented and tested on a small mesh network of PCs running Linux, and standard baseline vs. aggregation tests were conducted with a realistic voice tra c pro le in hop-to-hop mode. Modi cations of the kernel were then transferred to either end of a nine node 'mesh potato' network and those tests were conducted with only the end nodes modi ed to perform aggregation duties. Packet ag- gregation increased call capacity expectedly, while quality of service was maintained in both instances, and hop-to-hop aggregation outperformed the end-to-end con guration. However, implementing hop-to-hop in a scalable fashion is prohibitive, due to the extensive kernel level debugging that must be done to achieve the call capacity increase.Therefore, end-to-end call capacity increase is an acceptable compromise for eventual scalable deployment of voice over wireless mesh networks.
54

Prognosis and health monitoring communications quality of service

Unknown Date (has links)
This thesis research was funded by the Southeast National Marine Renewable Energy Center (SNMREC) at Florida Atlantic University. Its objective is the development of Quality of Service (QoS) mechanisms for the wireless communications architecture used by the Prognosis and Health Monitoring (PHM) subsystem. There are numerous technical challenges that the PHM Communications Subsystem tries to solve. Due to ocean platform mobility from waves, currents, and other environmental factors, signal quality can vary significantly. As a result, the wireless link between the electric generator platform and shore systems will have variable quality in terms of data rate, delay, and availability. In addition, the data traffic that flows from generator sensors and PHM applications to the shore systems consists of numerous types of messages that have different QoS demands (e.g. delay) and priority that depends on the message type, user ID, sensor location, and application-dependent parameters. The PHM Communications subsystem must handle effectively high priority messages, such as alarms, alerts, and remote control commands from shore systems. It also performs QoS in the application layer, so it can read the contents of every message to prioritize them. In order to perform QoS in the application layer the PHM subsystem relies on Java Servlet multithreaded technology and different queuing techniques to control message transmission order. Furthermore, it compresses all traffic that comes from the ocean-based electric generator/turbine platform to reduce the load on the wireless link. The PHM Communications subsystem consists of three components: the wireless link, the Link Manager, and the Web Services Network Proxy. We present experimental results for the Web Services Network Proxy and demonstrate the effectiveness of XML data compression and semantic-based message scheduling over a link with variable capacity. / by Timur Tavtilov. / Thesis (M.S.C.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.
55

Loss-free architectures in optical burst switched networks for a reliable and dynamic optical layer / [Architectures sans pertes dans les réseaux optiques avec commutation en rafale pour une couche optique fiable et dynamique]

Coutelen, Thomas 15 June 2010 (has links)
[non communiqué] / For the last three decades, the optical fiber has been a quite systematic response to dimensioning issues in the Internet. Originally restricted to long haul networks, the optical network has gradually descended the network hierarchy to discard the bottlenecks. In the 90's, metropolitan networks became optical. Today, optical fibers are deployed in access networks and reach the users. In a near future, besides wireless access and local area networks, all networks in the network hierarchy may be made of fibers, in order to support current services (HDTV) and the emergence of new applications (3D-TV newly commercialized in USA). The deployment of such greedy applications will initiate an upward upgrade. The first step may be the Metropolitan Area Networks (MANs), not only because of the traffic growth, but also because of the variety of served applications, each with a specific traffic profile. The current optical layer is of mitigated efficiency, dealing with unforeseen events. The lack of reactivity is mainly due to the slow switching devices: any on-line decision of the optical layer is delayed by the configuration of the. devices. When the optical network has been extended in the MANs, a lot of efforts has been deployed to improve the reactivity of the optical layer. The Optical Circuit Switching paradigm (OCS) has been improved but it ultimately relies on off-line configuration of the optical devices. Optical Burst Switching (OBS) can be viewed as a highly flexible evolution of OCS, that operates five order of magnitude faster. Within this 'architecture, the loss-free guaranty can be abandoned in order to improve the reactivity of the optical layer. Indeed, reliability and reactivity appear as antagonists properties and getting closer to either of them mitigates the other. This thesis aims at proposing a solution to achieve reliable transmission over a dynamic optical layer. Focusing on OBS networks, our objective is to solve the contention issue without mitigating the reactivity. After the consideration of contention avoidance mechanisms with routing constraints similar as in OCS networks, we investigate the reactive solutions that intend to solve the contentions. None of the available contention resolution scheme can ensure the 100% efficiency that leads to loss-free transmission. An attractive solution is the recourse to electrical buffering, but it is notoriously disregarded because (1) it may highly impact the delays and (2) loss can occur due to buffer overflows. The efficiency of translucent architectures thus highly depends on the buffer availability, that can be improved by reducing the time spent in the buffers and the contention rate. We show that traffic grooming can highly reduce the emission delay, and consequently the buffer occupancy. In a first architecture, traffic grooming is enabled by a translucent core node architecture, capable to re-aggregate incoming bursts. The re-aggregation is mandatory to "de-groom" the bursts in the core network (i.e., to demultiplex the content of a burst). On the one hand, the re-aggregation highly reduces the loss probability, but on the other hand, it absorbs the benefits of traffic grooming. Finally, dynamic access to re-aggregation for contention resolution, despite the significant reduction of the contention rate, dramatically impacts the end-to-end delay and the memory requirement. We thus propose a second architecture, called CAROBS, that exploits traffic grooming in the optical domain. This framework is fully dynamic and can be used jointly with our translucent architecture that performs re-aggregation. As the (de)grooming operations do not involve re-aggregation, the translucent module can be restricted to contention resolution. As a result, the volume of data submitted to re-aggregation is drastically reduced and loss-free transmission can be reached with the same reactivity, end-to-end delay and memory requirement as a native OBS network
56

A DIVERSE BAND-AWARE DYNAMIC SPECTRUM ACCESS ARCHITECTURE FOR CONNECTIVITY IN RURAL COMMUNITIES

Shah, Vijay K. 01 January 2019 (has links)
Ubiquitous connectivity plays an important role in improving the quality of life in terms of economic development, health and well being, social justice and equity, as well as in providing new educational opportunities. However, rural communities which account for 46% of the world's population lacks access to proper connectivity to avail such societal benefits, creating a huge "digital divide" between the urban and rural areas. A primary reason is that the Information and Communication Technologies (ICT) providers have less incentives to invest in rural areas due to lack of promising revenue returns. Existing research and industrial attempts in providing connectivity to rural communities suffer from severe drawbacks, such as expensive wireless spectrum licenses and infrastructures, under- and over-provisioning of spectrum resources while handling heterogeneous traffic, lack of novel wireless technologies tailored to the unique challenges and requirements of rural communities (e.g., agricultural fields). Leveraging the recent advances in Dynamic Spectrum Access (DSA) technologies like wide band spectrum analyzers and spectrum access systems, and multi-radio access technologies (multi-RAT), this dissertation proposes a novel Diverse Band-aware DSA (d-DSA) network architecture, that addresses the drawbacks of existing standard and DSA wireless solutions, and extends ubiquitous connectivity to rural communities; a step forward in the direction of the societal and economic improvements in rural communities, and hence, narrowing the "digital divide" between the rural and urban societies. According to this paradigm, a certain wireless device is equipped with software defined radios (SDRs) that are capable of accessing multiple (un)licensed spectrum bands, such as, TV, LTE, GSM, CBRS, ISM, and possibly futuristic mmWaves. In order to fully exploit the potential of the d-DSA paradigm, while meeting heterogeneous traffic demands that may be generated in rural communities, we design efficient routing strategies and optimization techniques, which are based on a variety of tools such as graph modeling, integer linear programming, dynamic programming, and heuristic design. Our results on realistic traces in a large variety of rural scenarios show that the proposed techniques are able to meet the heterogeneous traffic requirements of rural applications, while ensuring energy efficiency and robustness of the architecture for providing connectivity to rural communities.
57

Network capacity sharing with QoS as a financial derivative pricing problem : algorithms and network design

Rasmusson, Lars January 2002 (has links)
A design of anautomatic network capacity markets, oftenreferred to as a bandwidth market, is presented. Three topicsare investigated. First, a network model is proposed. Theproposed model is based upon a trisection of the participantroles into network users, network owners, and market middlemen.The network capacity is defined in a way that allows it to betraded, and to have a well defined price. The network devicesare modeled as core nodes, access nodes, and border nodes.Requirements on these are given. It is shown how theirfunctionalities can be implemented in a network. Second, asimulated capacity market is presented, and a statisticalmethod for estimating the price dynamics in the market isproposed. A method for pricing network services based on sharedcapacity is proposed, in which the price of a service isequivalent to that of a financial derivative contract on anumber of simple capacity shares.Third, protocols for theinteraction between the participants are proposed. The marketparticipants need to commit to contracts with an auditableprotocol with a small overhead. The proposed protocol is basedon a public key infrastructure and on known protocols for multiparty contract signing. The proposed model allows networkcapacity to be traded in a manner that utilizes the networkeciently. A new feature of this market model, compared to othernetwork capacity markets, is that the prices are not controlledby the network owners. It is the end-users who, by middlemen,trade capacity among each-other. Therefore, financial, ratherthan control theoretic, methods are used for the pricing ofcapacity. <b>Keywords:</b>Computer network architecture, bandwidthtrading, inter-domain Quality-of-Service, pricing,combinatorial allocation, financial derivative pricing,stochastic modeling
58

ASPIRE: Adaptive Service Provider Infrastructure for VANETs

Koulakezian, Agop 25 August 2011 (has links)
User desire for ubiquitous applications on-board a vehicle motivates the necessity for Network Mobility (NEMO) solutions for Vehicular Ad-Hoc Networks (VANETs). Due to the dynamic topology of VANETs, this approach incurs excessive infrastructure cost to maintain stable connectivity and support these applications. Our solution to this problem is focused on a novel NEMO-based Network Architecture where vehicles are the main network infrastructure. Within this Architecture, we present a Network Criticality-based clustering algorithm, which adapts to mobility changes to form stable self-organizing clusters of vehicles and dynamically builds on vehicle clusters to form more stable Mobile Networks. Simulation results show that the proposed method provides more stable clusters, lower handoffs and better connectivity compared to popular density-based vehicle clustering methods. In addition, they confirm the validity of the proposed Network Architecture. The proposed method is also robust to channel error and exhibits better performance when the heterogeneity of vehicles is exploited.
59

ASPIRE: Adaptive Service Provider Infrastructure for VANETs

Koulakezian, Agop 25 August 2011 (has links)
User desire for ubiquitous applications on-board a vehicle motivates the necessity for Network Mobility (NEMO) solutions for Vehicular Ad-Hoc Networks (VANETs). Due to the dynamic topology of VANETs, this approach incurs excessive infrastructure cost to maintain stable connectivity and support these applications. Our solution to this problem is focused on a novel NEMO-based Network Architecture where vehicles are the main network infrastructure. Within this Architecture, we present a Network Criticality-based clustering algorithm, which adapts to mobility changes to form stable self-organizing clusters of vehicles and dynamically builds on vehicle clusters to form more stable Mobile Networks. Simulation results show that the proposed method provides more stable clusters, lower handoffs and better connectivity compared to popular density-based vehicle clustering methods. In addition, they confirm the validity of the proposed Network Architecture. The proposed method is also robust to channel error and exhibits better performance when the heterogeneity of vehicles is exploited.
60

Emergent structure formation of the actin cytoskeleton / Emergente Strukturbildung des Aktin-Zytoskeletts

Huber, Florian 23 July 2012 (has links) (PDF)
Anders als menschengemachte Maschinen verfügen Zellen über keinen festgeschriebenen Bauplan und die Positionen einzelner Elemente sind häufig nicht genau festgelegt, da die Moleküle diffusiven Zufallsbewegungen unterworfen sind. Darüber hinaus sind einzelne Bauteile auch nicht auf eine einzelne Funktion festgelegt, sondern können parallel in verschiedene Prozesse einbezogen sein. Basierend auf Selbstorganisation und Selbstassemblierung muß die Organisation von Anordnung und Funktion einer lebenden Zelle also bereits in ihren einzelnen Komponenten inhärent enthalten sein. Die intrazelluläre Organisation wird zum großen Teil durch ein internes Biopolymergerüst reguliert, das Zytoskelett. Biopolymer-Netzwerke und –Fasern durchdringen die gesamte Zelle und sind verantworlich für mechanische Integrität und die funktionale Architektur. Unzählige essentielle biologische Prozesse hängen direkt von einem funktionierenden Zytoskelett ab. Die vorliegende Arbeit zielt auf ein besser Verständnis und den Nachbau zweier verschiedener funktionaler Module lebender Zellen anhand stark reduzierter Modellsysteme. Als zentrales Element wurde Aktin gewählt, da dieses Biopolymer eine herausragende Rolle in nahezu allen eukaryotischen Zellen spielt. Mit dem ersten Modellsystem wird der bewegliche Aktin-Polymerfilm an der Vorderkante migrierender Zellen betrachtet. Die wichtigsten Elemente dieser hochdynamischen Netzwerke sind bereits bekannt und wurden in dieser Arbeit benutzt um ein experimentelles Modellsystem zu etablieren. Vor allem aber lieferten detailierte Computersimulationen und ein mathematisches Modell neue Erkenntnisse über grundlegende Organisationsprinzipien dieser Aktinnetzwerke. Damit war es nicht nur möglich, experimentelle Daten erfolgreich zu reproduzieren, sondern das Entstehen von Substrukturen und deren Charakteristika auf proteinunabhängige, generelle Mechanismen zurückzuführen. Das zweite studierte System betrachtet die Selbstassemblierung von Aktinnetzwerken durch entropische Kräfte. Aktinfilamente aggregieren hierbei durch Kondensation multivalenter Ionen oder durch Volumenausschluss hochkonzentrierter inerter Polymere. Ein neu entwickelter Experimentalaufbau bietet die Möglichkeit in gut definierten zellähnlichen Volumina, Konvektionseinflüsse zu umgehen und Aggregationseffekte gezielt einzuschalten. Hierbei wurden neuartige, regelmäßige Netzwerkstrukturen entdeckt, die bislang nur im Zusammenhang mit molekularen Motoren bekannt waren. Es konnte ferner gezeigt werden, dass die Physik der Flüssigkristalle entscheidend zu weiteren Variationen dieser Netzwerke beiträgt. Dabei wird ersichtlich, dass entstehende Netzwerke in ihrer Architektur direkt die zuvor herrschenden Anisotropien der Filamentlösung widerspiegeln.

Page generated in 0.0764 seconds