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  • 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.
21

Recall of Landmarks in Information Space

Sorrows, Molly 30 September 2005 (has links)
Research on navigation and landmarks in physical space, information space and virtual reality environments indicates that landmarks play an important role in all types of navigation. This dissertation tackles the problem of defining and evaluating the characteristics of landmarks in information space. This work validates a recent theory that three types of characteristics, structural, visual and semantic, are important for effective landmarks. This dissertation applies concepts and techniques from the extensive body of research on physical space navigation to the investigation of landmarks on a web site in the World Wide Web. Data was collected in two experiments to examine characteristics of web pages on the University of Pittsburgh web site. In addition, objective measurements were made to examine the characteristics of web pages with relation to the experimental data. The two experiments examined subjects knowledge, use and evaluation of web pages. This research is unique in research on web navigation in its use of experimental techniques that ask subjects to recall from memory possible navigation paths and URLs. Two measures of landmark quality were used to examine the characteristics of landmarks; one, an algorithm that incorporated objective measures of the structural, visual and semantic characteristics of each web page, and the second, a measure based on the experimental data regarding subjects knowledge and evaluation of the page. Analysis of this data from a web space confirms the tri-partite theory of characteristics of landmarks. Significant positive correlations were found between the objective and subjective landmark measures, indicating that this work is an important step toward the ability to objectively evaluate web pages and web site design in terms of landmarks. This dissertation further suggests that researchers can utilize the characteristics to analyze and improve the design of information spaces, leading to more effective navigation.
22

AUTOMATED FEATURE EXTRACTION AND CONTENT-BASED RETRIEVAL OF PATHOLOGY MICROSCOPIC IMAGES USING K-MEANS CLUSTERING AND CODE RUN-LENGTH PROBABILITY DISTRIBUTION

Zheng, Lei 31 January 2006 (has links)
The dissertation starts with an extensive literature survey on the current issues in content-based image retrieval (CBIR) research, the state-of-the-art theories, methodologies, and implementations, covering topics such as general information retrieval theories, imaging, image feature identification and extraction, feature indexing and multimedia database search, user-system interaction, relevance feedback, and performance evaluation. A general CBIR framework has been proposed with three layers: image document space, feature space, and concept space. The framework emphasizes that while the projection from the image document space to the feature space is algorithmic and unrestricted, the connection between the feature space and the concept space is based on statistics instead of semantics. The scheme favors image features that do not rely on excessive assumptions about image content As an attempt to design a new CBIR methodology following the above framework, k-means clustering color quantization is applied to pathology microscopic images, followed by code run-length probability distribution feature extraction. Kulback-Liebler divergence is used as distance measure for feature comparison. For content-based retrieval, the distance between two images is defined as a function of all individual features. The process is highly automated and the system is capable of working effectively across different tissues without human interference. Possible improvements and future directions have been discussed.
23

Internet QoS market Analysis with peering and usage-sensitive pricing: A game theoretic and simulation approach

Shin, SeungJae 12 June 2003 (has links)
One of the major areas for research and investment related to the Internet is the provision of quality of service (QoS). We remain confident that in the not-to-distance future, QoS will be introduced not only in private networks but in the whole Internet. QoS will bring some new features into the Internet market: (1) vertical product differentiation with BE and QoS, (2) usage-sensitive pricing with metering. In this dissertation, the equilibrium outcomes are analyzed when two rural Internet Access Providers (IAPs) interact with several business and technical strategies such as technology (BE or QoS), pricing scheme (flat-rate pricing or two-part tariff), interconnection (transit or peering) and investment in network capacity. To determine the equilibria, we construct a duopoly game model based on Cournot theory. We calibrate this model to data found in real markets. In this model, we study ten cases with a combination of strategic choices of two IAPs. We use two demand functions: one based on uniform distribution and the other based on empirical distribution which comes from the U.S. General Accounting Office (U.S. GAO) survey for Internet usage. We use a two-stage RNG (Random Number Generator) simulation and a linear regression for the latter. If we consider IAPs with the BE and the flat rate pricing as the current Internet, the equilibrium points of each case in this model suggest a progressive market equilibrium path to the future Internet market. Based on the equilibrium analysis of the game model, we conclude that (1) {QoS, two-part tariff, transit/peering} or {QoS, flat-rate pricing, peering} will be a plausible situation in the future Internet access market, (2) network capacity will still be an important strategy to determine market equilibrium in the future as well as in the current, (3) BE will take a considerable market share in the QoS Internet, and (4) peering arrangements in the QoS Internet will provide a higher social welfare than transit. These implications from the game analysis present an analytical framework for the future Internet policy.
24

802.11 Markov Channel Modelling

Arauz, Julio Nicolas 28 January 2005 (has links)
In order to understand the behavior of upper layer protocols and to design or fine tune their parameters over wireless networks, it is common to assume that the underlying channel is a flat Rayleigh fading channel. Such channels are commonly modeled as finite state Markov chains. Recently, hidden Markov models have also been employed to characterize these channels. Although Markov models have been widely used to study the performance of communications protocols at the link and transport layers, no validation of their accuracy has been performed against experimental data. These models are not applicable to frequency selective fading channels. Moreover, there are no good models to consider the effects of path loss (average received SNR), the packet size, and transmission rate variations which are significant in IEEE 802.11 wireless local area networks. This research performs validation of Markov models with experimental data and discusses the limitations of the process. In this dissertation, we present different models that have been proposed along with their validity analysis. We use the experimental data with stochastic modeling approaches to characterize the frame losses in IEEE 802.11 wireless LANs. We also characterize the important factor of current wireless LAN technology, the transmission rate variations. New guidelines for the construction of Markov and hidden Markov models for wireless LAN channels are developed and presented along the necessary data to implement them in performance studies. Furthermore we also evaluate the validity of using Markovian models to understand the effects on upper layer protocols such as TCP.
25

ENERGY CONSERVATION FOR WIRELESS AD HOC ROUTING

Hou, Xiaobing 26 July 2006 (has links)
Self-configuring wireless ad hoc networks have attracted considerable attention in the last few years due to their valuable civil and military applications. One aspect of such networks that has been studied insufficiently is the energy efficiency. Energy efficiency is crucial to prolong the network lifetime and thus make the network more survivable. Nodes in wireless ad hoc networks are most likely to be driven by battery and hence operate on an extremely frugal energy budget. Conventional ad hoc routing protocols are focused on handling the mobility instead of energy efficiency. Energy efficient routing strategies proposed in literature either do not take advantage of sleep modes to conserve energy more efficiently, or incur much overhead in terms of control message and computing complexity to schedule sleep modes and thus are not scalable. In this dissertation, a novel strategy is proposed to manage the sleep of the nodes in the network so that energy can be conserved and network connectivity can be kept. The novelty of the strategy is its extreme simplicity. The idea is derived from the results of the percolation theory, typically called gossiping. Gossiping is a convenient and effective approach and has been successfully applied to several areas of the networking. In the proposed work, we will develop a sleep management protocol from gossiping for both static and mobile wireless ad hoc networks. Then the protocol will be extended to the asynchronous network, where nodes manage their own states independently. Analysis and simulations will be conducted to show the correctness, effectiveness and efficiency of the proposed work. The comparison between analytical and simulation results will justify them for each other. We will investigate the most important performance aspects concerning the proposed strategy, including the effect of parameter tuning and the impacts of routing protocols. Furthermore, multiple extensions will be developed to improve the performance and make the proposed strategy apply to different network scenarios.
26

The Tuskegee Syphilis Study: Access and Control over Controversial Records

Whorley, Tywanna 06 October 2006 (has links)
As the nations archives, the National Archives and Records Administration (NARA) preserves and provides access to records that document how our government conducts business on behalf of the American peoplepast and present. For the American citizen, NARA provides a form of accountability through the records within its custody which affect the nations collective memory. A plethora of these records, however, contain evidence of the federal governments misconduct in episodes in American history which affected public trust. The Tuskegee Syphilis Study records are a prime example of records within the custody of NARA that continue to have a lasting affect on public trust in the federal government. Even though NARA disclosed administrative records that document the governments role in the study, the Tuskegee Syphilis Study records continue to challenge the institution on a variety of archival issues such as access, privacy, collective memory, and accountability. Through historical case study methodology, this study examines the National Archives and Records Administrations administrative role in maintaining and providing access to the Tuskegee Syphilis Study records, especially the restricted information. The effect of the changing social context on NARAs recordkeeping practices of the Tuskegee Syphilis Study records is also explored.
27

Integrating Protein Data Resources through Semantic Web Services

Liu, Xiong 30 January 2007 (has links)
Understanding the function of every protein is one major objective of bioinformatics. Currently, a large amount of information (e.g., sequence, structure and dynamics) is being produced by experiments and predictions that are associated with protein function. Integrating these diverse data about protein sequence, structure, dynamics and other protein features allows further exploration and establishment of the relationships between protein sequence, structure, dynamics and function, and thereby controlling the function of target proteins. However, information integration in protein data resources faces challenges at technology level for interfacing heterogeneous data formats and standards and at application level for semantic interpretation of dissimilar data and queries. In this research, a semantic web services infrastructure, called Web Services for Protein data resources (WSP), for flexible and user-oriented integration of protein data resources, is proposed. This infrastructure includes a method for modeling protein web services, a service publication algorithm, an efficient service discovery (matching) algorithm, and an optimal service chaining algorithm. Rather than relying on syntactic matching, the matching algorithm discovers services based on their similarity to the requested service. Therefore, users can locate services that semantically match their data requirements even if they are syntactically distinctive. Furthermore, WSP supports a workflow-based approach for service integration. The chaining algorithm is used to select and chain services, based on the criteria of service accuracy and data interoperability. The algorithm generates a web services workflow which automatically integrates the results from individual services. A number of experiments are conducted to evaluate the performance of the matching algorithm. The results reveal that the algorithm can discover services with reasonable performance. Also, a composite service, which integrates protein dynamics and conservation, is experimented using the WSP infrastructure.
28

An Overlay Architecture for Personalized Object Access and Sharing in a Peer-to-Peer Environment

Sangpachatanaruk, Chatree 30 January 2007 (has links)
Due to its exponential growth and decentralized nature, the Internet has evolved into a chaotic repository, making it difficult for users to discover and access resources of interest to them. As a result, users have to deal with the problem of information overload. The Semantic Web's emergence provides Internet users with the ability to associate explicit, self-described semantics with resources. This ability will facilitate in turn the development of ontology-based resource discovery tools to help users retrieve information in an efficient manner. However, it is widely believed that the Semantic Web of the future will be a complex web of smaller ontologies, mostly created by various groups of web users who share a similar interest, referred to as a Community of Interest. This thesis proposes a solution to the information overload problem using a user driven framework, referred to as a Personalized Web, that allows individual users to organize themselves into Communities of Interests based on ontologies agreed upon by all community members. Within this framework, users can define and augment their personalized views of the Internet by associating specific properties and attributes to resources and defining constraint-functions and rules that govern the interpretation of the semantics associated with the resources. Such views can then be used to capture the user's interests and integrate these views into a user-defined Personalized Web. As a proof of concept, a Personalized Web architecture that employs ontology-based semantics and a structured Peer-to-Peer overlay network to provide a foundation of semantically-based resource indexing and advertising is developed. In order to investigate mechanisms that support the resource advertising and retrieval of the Personalized Web architecture, three agent-driven advertising and retrieval schemes, the Aggressive scheme, the Crawler-based scheme, and the Minimum-Cover-Rule scheme, were implemented and evaluated in both stable and churn environments. In addition to the development of a Personalized Web architecture that deals with typical web resources, this thesis used a case study to explore the potential of the Personalized Web architecture to support future web service workflow applications. The results of this investigation demonstrated that the architecture can support the automation of service discovery, negotiation, and invocation, allowing service consumers to actualize a personalized web service workflow. Further investigation will be required to improve the performance of the automation and allow it to be performed in a secure and robust manner. In order to support the next generation Internet, further exploration will be needed for the development of a Personalized Web that includes ubiquitous and pervasive resources.
29

Enabling Large-Scale Peer-to-Peer Stored Video Streaming Service with QoS Support

Okuda, Masaru 30 January 2007 (has links)
This research aims to enable a large-scale, high-volume, peer-to-peer, stored-video streaming service over the Internet, such as on-line DVD rentals. P2P allows a group of dynamically organized users to cooperatively support content discovery and distribution services without needing to employ a central server. P2P has the potential to overcome the scalability issue associated with client-server based video distribution networks; however, it brings a new set of challenges. This research addresses the following five technical challenges associated with the distribution of streaming video over the P2P network: 1) allow users with limited transmit bandwidth capacity to become contributing sources, 2) support the advertisement and discovery of time-changing and time-bounded video frame availability, 3) Minimize the impact of distribution source losses during video playback, 4) incorporate user mobility information in the selection of distribution sources, and 5) design a streaming network architecture that enables above functionalities. To meet the above requirements, we propose a video distribution network model based on a hybrid architecture between client-server and P2P. In this model, a video is divided into a sequence of small segments and each user executes a scheduling algorithm to determine the order, the timing, and the rate of segment retrievals from other users. The model also employs an advertisement and discovery scheme which incorporates parameters of the scheduling algorithm to allow users to share their life-time of video segment availability information in one advertisement and one query. An accompanying QoS scheme allows reduction in the number of video playback interruptions while one or more distribution sources depart from the service prematurely. The simulation study shows that the proposed model and associated schemes greatly alleviate the bandwidth requirement of the video distribution server, especially when the number of participating users grows large. As much as 90% of load reduction was observed in some experiments when compared to a traditional client-server based video distribution service. A significant reduction is also observed in the number of video presentation interruptions when the proposed QoS scheme is incorporated in the distribution process while certain percentages of distribution sources depart from the service unexpectedly.
30

THE EFFECT OF INTERACTIONS BETWEEN PROTOCOLS AND PHYSICAL TOPOLOGIES ON THE LIFETIME OF WIRELESS SENSOR NETWORKS

Yupho, Debdhanit 29 June 2007 (has links)
Wireless sensor networks enable monitoring and control applications such weather sensing, target tracking, medical monitoring, road monitoring, and airport lighting. Additionally, these applications require long term and robust sensing, and therefore require sensor networks to have long system lifetime. However, sensor devices are typically battery operated. The design of long lifetime networks requires efficient sensor node circuits, architectures, algorithms, and protocols. In this research, we observed that most protocols turn on sensor radios to listen or receive data then make a decision whether or not to relay it. To conserve energy, sensor nodes should consider not listening or receiving the data when not necessary by turning off the radio. We employ a cross layer scheme to target at the network layer issues. We propose a simple, scalable, and energy efficient forwarding scheme, which is called Gossip-based Sleep Protocol (GSP). Our proposed GSP protocol is designed for large low-cost wireless sensor networks with low complexity to reduce the energy cost for every node as much as possible. The analysis shows that allowing some nodes to remain in sleep mode improves energy efficiency and extends network lifetime without data loss in the topologies such as square grid, rectangular grid, random grid, lattice topology, and star topology. Additionally, GSP distributes energy consumption over the entire network because the nodes go to sleep in a fully random fashion and the traffic forwarding continuously via the same path can be avoided.

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