Página 19 dos resultados de 2591 itens digitais encontrados em 0.046 segundos

Designing Satellite Communication Networks by Zero-One Quadratic Programming

Helme, Marcia P.; Magnanti, Thomas L.
Fonte: Massachusetts Institute of Technology, Operations Research Center Publicador: Massachusetts Institute of Technology, Operations Research Center
Tipo: Trabalho em Andamento Formato: 2195334 bytes; application/pdf
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In satellite communications networks, distinctive facilities called homing stations perform special transmission functions. Local demand nodes clustered around each homing station communicate with each other via a local switch at the homing station; demand nodes in different clusters communicate with each other via satellite earth stations at the homing stations. Designing such a communication network requires choices on the locations of the earth stations and on the assignments of demand nodes to the local clusters at the earth stations. We formulate this problem as a zero-one quadratic facility location problem and transform it into an equivalent zero-one integer linear program. Computational experience on real data shows that a branch and bound procedure is effective in solving problems with up to forty demand nodes (major cities) and that the solutions that this algorithm finds improve considerably upon management generated solutions. We also show that a greedy add heuristic, as implemented on an IBM PC, consistently generates optimal or near-optimal solutions.

Industrial symbiosis and the successional city : adapting exchange networks to energy constraints

Terway, Timothy M. (Timothy Michael)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 142 p.
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Industrial ecology offers models for hybridizing technology and natural processes, human desires and the capacities of ecosystems in an effort to reconcile the expanding conflicts among them. Industrial symbiosis applies this thinking to the scale of the city and its supporting industrial operations. Case studies of industrial symbiosis, which is the changing of linear, open-loop production to closed-loop systems through the reuse and exchange of waste materials, energy, and knowledge, showcase advantages in waste and energy use reduction within the United States. What are the major limits holding back the widespread development of industrial symbiosis in this country and how can they be overcome? Secondly, what tools can foster its large-scale implementation once the constraints are overcome? Methodologically, the successful study of the future capacity of industrial symbiosis within the American context must address the future consequences of resources that are no longer cheap nor abundant, as well as the current state of their production, distribution, and consumption.; (cont.) The major constraints facing industrial symbiosis in America are: current extremely high subsidies in transport and resource costs, low symbiosis visibility...

An Energy-aware multipath routing extension for heterogeneous Ad hoc networks

Lima Junior, Josias Barbosa de; Kelner, Judith orientadora)
Fonte: Universidade Federal de Pernambuco Publicador: Universidade Federal de Pernambuco
Tipo: Dissertação
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Recentemente, novas técnicas de comunicação surgiram que usam tecnologia sem fio e são capazes de se autoconfigurar. A combinação desses fatores elimina a necessidade de utilizar estruturas cabeadas e configurações pré-definidas. Neste trabalho, o autor desenvolve uma versão simulada, através do simulador de rede “network Simulator 3” (ns-3), do arcabouço “Heterogeneous Technologies Routing” (HTR), que se propõe à interconectar dispositivos em redes heterogêneas ad hoc, estendendo o seu suporte às tecnologias heterogêneas com a adição de dispositivos WiMAX e LTE, propõe uma extensão para fornecer um roteamento baseado em múltiplos caminhos (“Multipath”) e investiga o impacto de modificar os parâmetros de configuração do roteamento no tempo de convergência da rede e consumo de energia. Apesar de um grande número de obras existentes que investigam o impacto da mudança de parâmetros de configuração do roteamento, no meu conhecimento, nenhum deles investiga o impacto destes no tempo de convergência do protocolo e consumo de energia. O “Multipath HTR”, a extensão proposta, oferece vários benefícios como balanceamento de carga, tolerância a falhas, prevenção de “loops” de roteamento...

Information and Communication Technologies and Broad-Based Development : A Partial Review of the Evidence

Grace, Jeremy; Kenny, Charles; Zhen-Wei Qiang, Christine; Liu, Jia; Reynolds, Taylor
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
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Information and communication technologies (ICTs) are increasingly seen as integral to the development process. This paper reviews some of the evidence for the link between telecommunications and the Internet and economic growth, the likely impact of the new ICTs on income inequality and anecdotal evidence regarding the role of the Internet in improving government services and governance. It looks at methods to maximize access to the new ICTs, and improve their development impact both in promoting income generation and the provision of quality services.

Productivity, factor accumulation and social networks: theory and evidence

Grafton, R. Quentin; Kompas, Tom; Owen, P. Dorian
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Working/Technical Paper Formato: 729328 bytes; 352 bytes; application/pdf; application/octet-stream
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The paper analyzes how social barriers to communication affect economy-wide productivity and factor accumulation. Using a dynamic model of an economy that includes a reproducible capital stock (physical or human) and effective labor, a negative relationship is shown to exist between social barriers to communication and total factor productivity (TFP), per capita consumption and reproducible capital. Robust estimates obtained from cross-country data are consistent with the models predictions. The theory and empirical results help explain cross-country differences in TFP, the high productivity performance of leading industrialized countries and how productivity catch up may be initiated.; no

Tunneled data transmission over wireless sensor networks

Yow, Thiam Poh
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado
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A technique for terminal communication through transmission links established across a wireless sensor network is developed and tested. Using protocols established for conventional wireless communication networks as a guiding principle, different methodologies for link management, and segmentation and reassembly of information are explored. A protocol for sensor network encapsulation was designed and implemented across a network of terminals and wireless sensor motes. The study concludes with a discussion of the capabilities and limitations of this technique supported by results obtained through experiments under various scenarios.

Tecnologias digitais no jardim de infância : comunicação, aprendizagem e desenvolvimento profissional docente; Digital technologies in kindergarten : communication, learning and teacher professional development

Faria, Ádila
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 04/07/2014 Português
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Tese de doutoramento em Estudos da Criança (ramo do conhecimento em Tecnologias de Informação e Comunicação); A evolução da sociedade digital provocou tal impacto no modo como atualmente se concebe e organiza globalmente o mundo que se considera que, na sociedade do conhecimento, a Educação é indissociável das Tecnologias de Informação e Comunicação. Neste contexto, este estudo visa compreender de que forma podem diversos recursos digitais contribuir para o a aprendizagem e para o desenvolvimento integral das crianças do jardim de infância; analisa também o contributos da rede social NING da janela do meu jardim para a interação com os encarregados de educação, educadores, professores, investigadores e para o desenvolvimento profissional docente. O quadro teórico e metodológico deste estudo alicerça-se numa revisão sistemática da literatura, que aporta subsídios teóricos fundamentais para que se pudessem compreender e aprofundar no estado da arte relativamente a esta temática em causa. A investigação realizada inscreve-se num paradigma de investigação qualitativa tendo-se optado pelo estudo de caso. Foram utilizadas diferentes técnicas de recolha de dados, predominantemente qualitativos. A análise foi feita através da análise de conteúdo com apoio do NVivo. Os resultados do presente estudo evidenciam a importância da integração das tecnologias digitais em contexto de jardim de infância...

STARR-DCS: Spatio-temporal adaptation of random replication for data-centric storage

Cuevas, Ángel; Urueña, Manuel; De Veciana, Gustavo; Yadav, Aditya
Fonte: Association for Computing Machinery Publicador: Association for Computing Machinery
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article
Publicado em /11/2013 Português
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This article presents a novel framework for data-centric storage (DCS) in a wireless sensor and actor network (WSAN) that employs a randomly selected set of data replication nodes, which also change over time. This enables reductions in the average network traffic and energy consumption by adapting the number of replicas to applications' traffic, while balancing energy burdens by varying their locations. To that end, we propose and validate a simple model to determine the optimal number of replicas, in terms of minimizing average traffic/energy consumption, based on measurements of applications' production and consumption traffic. Simple mechanisms are proposed to decide when the current set of replication nodes should be changed, to enable new applications and nodes to efficiently bootstrap into a working WSAN, to recover from failing nodes, and to adapt to changing conditions. Extensive simulations demonstrate that our approach can extend a WSAN's lifetime by at least 60%, and up to a factor of 10× depending on the lifetime criterion being considered. The feasibility of the proposed framework has been validated in a prototype with 20 resource-constrained motes, and the results obtained via simulation for large WSANs have been also corroborated in that prototype.; ; The research leading to these results has been partially funded by the Spanish MEC under the CRAMNET project (TEC2012-38362-C03-01) and the FIERRO project (TEC 2010- 12250-E)...

Developing a Fly-Away-Kit (FLAK) to support Hastily Formed Networks (HFN) for Humanitarian Assistance and Disaster Relief)

Lancaster, David D.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xvi,71 p. : ill. (some col.), map ;
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This research discusses developing a FLy-Away-Kit (FLAK) to support the forming of Hastily Formed Networks (HFNs) in remote areas in support of Humanitarian Assistance and Disaster Relief (HA/DR) operations. The initial focus will be on the requirements, situation, area of operations and mission. Different definitions and perspectives emerge when an individual mentions HFNs, HA/DR and Complex Humanitarian Disasters (CHDs). It is the author's intention to define and describe both a HFN and a CHD, in order to justify the need for the FLAK. This process will also define the requirements for the FLAK as well as facilitate processes for ensuring those requirements are met. The personnel responding to the attacks of September 11, 2001 and the December 26, 2004 Southeast Asia Tsunami suffered Command and Control (C2) and information challenges. Even more challenges are being currently addressed by Homeland Defense, Maritime Domain Awareness, and Non-Governmental Organizations (NGOs) abroad. From the top down, levels of administration are developing new plans, procedures, and organizations that will improve the security and communication processes of our nation. A global, broadband, rapidly deployable network node complete with Internet reachback...

Message passing versus distributed shared memory on networks of workstations

Lu, Honghui
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 51 p.; application/pdf
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We compared the message passing library Parallel Virtual Machine (PVM) with the distributed shared memory system TreadMarks, on networks of workstations. We presented the performance of nine applications, including Water and Barnes-Hut from the SPLASH benchmarks; 3-D FFT, Integer Sort and Embarrassingly Parallel from the NAS benchmarks; ILINK, a widely used genetic analysis program; and SOR, TSP, and QuickSort. TreadMarks performed nearly identical to PVM on computation bound programs, such as the Water simulation of 1728 molecules. For most of the other applications, including ILINK, TreadMarks performed within 75% of PVM with 8 processes. The separation of synchronization and data transfer, and additional messages to request updates for data in the invalidate-based shared-memory protocol were two of the reasons for TreadMarks's lower performance. TreadMarks also suffered from extra data communication due to false sharing. Moreover, PVM benefited from the ability to aggregate scattered data in a single message.

The Adversarial Noise Threshold for Distributed Protocols

Hoza, William M.; Schulman, Leonard J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We consider the problem of implementing distributed protocols, despite adversarial channel errors, on synchronous-messaging networks with arbitrary topology. In our first result we show that any $n$-party $T$-round protocol on an undirected communication network $G$ can be compiled into a robust simulation protocol on a sparse ($\mathcal{O}(n)$ edges) subnetwork so that the simulation tolerates an adversarial error rate of $\Omega\left(\frac{1}{n}\right)$; the simulation has a round complexity of $\mathcal{O}\left(\frac{m \log n}{n} T\right)$, where $m$ is the number of edges in $G$. (So the simulation is work-preserving up to a $\log$ factor.) The adversary's error rate is within a constant factor of optimal. Given the error rate, the round complexity blowup is within a factor of $\mathcal{O}(k \log n)$ of optimal, where $k$ is the edge connectivity of $G$. We also determine that the maximum tolerable error rate on directed communication networks is $\Theta(1/s)$ where $s$ is the number of edges in a minimum equivalent digraph. Next we investigate adversarial per-edge error rates, where the adversary is given an error budget on each edge of the network. We determine the exact limit for tolerable per-edge error rates on an arbitrary directed graph. However...

Modeling, Performance Analysis and Comparison of Two Level Single Chain Pointer Forwarding Strategy For Location Management in Wireless Mobile Communication

Kant, Chhaya Ravi; Arun, P.; Prakash, Nupur
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/09/2006 Português
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Global wireless networks enable mobile users to communicate regardless of their locations. Location management is an important part of the emerging wireless and mobile technology. A Personal Communication System (PCS) network must have an efficient way to keep track of the mobile users to deliver services effectively. Global System for Mobile Communication (GSM) is a commonly accepted standard for mobility management of mobile users. Location management involves location tracking, and location information storage. Location management requires mobile users to register at various registration areas whenever they are on the move. The registration process may cause excessive signaling traffic and long service delays. To improve the efficiency of location tracking and avoid call set up delays, several strategies such as local anchor scheme, per-user caching scheme and several pointer forwarding schemes have been proposed in the past. In this paper, we propose a new "Two Level Single Chain Pointer Forwarding (TLSCP) Strategy" in which a two level hierarchy of level-1 and level-2 forwarding pointers reduced to single chain length are used. Organizing the pointers in a two level hierarchy and further restricting the pointer chain lengths at both the levels to single chain localizes the network signaling traffic and reduces the call set up delays. To justify the effectiveness of our proposed strategy...

Neighborhood-Based Topology Recognition in Sensor Networks

Fekete, Sandor P.; Kroeller, Alexander; Pfisterer, Dennis; Fischer, Stefan; Buschmann, Carsten
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/05/2004 Português
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We consider a crucial aspect of self-organization of a sensor network consisting of a large set of simple sensor nodes with no location hardware and only very limited communication range. After having been distributed randomly in a given two-dimensional region, the nodes are required to develop a sense for the environment, based on a limited amount of local communication. We describe algorithmic approaches for determining the structure of boundary nodes of the region, and the topology of the region. We also develop methods for determining the outside boundary, the distance to the closest boundary for each point, the Voronoi diagram of the different boundaries, and the geometric thickness of the network. Our methods rely on a number of natural assumptions that are present in densely distributed sets of nodes, and make use of a combination of stochastics, topology, and geometry. Evaluation requires only a limited number of simple local computations.; Comment: 14 pages, 6 figures, Latex, to appear in Workshop on Algorithms Aspects of Sensor Networks (ALGOSENSORS 2004)

Organizational structure and communication networks in a university environment

Mathiesen, Joachim; Jamtveit, Bjørn; Sneppen, Kim
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/06/2010 Português
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The ``six degrees of separation" between any two individuals on Earth has become emblematic of the 'small world' theme, even though the information conveyed via a chain of human encounters decays very rapidly with increasing chain length, and diffusion of information via this process may be very inefficient in large human organizations. The information flow on a communication network in a large organization, the University of Oslo, has been studied by analyzing e-mail records. The records allow for quantification of communication intensity across organizational levels and between organizational units (referred to as ``modules"). We find that the number of e-mails messages within modules scales with module size to the power of $1.29\pm .06$, and the frequency of communication between individuals decays exponentially with the number of links required upwards in the organizational hierarchy before they are connected. Our data also indicates that the number of messages sent by administrative units is proportional to the number of individuals at lower levels in the administrative hierarchy, and the ``divergence of information" within modules is associated with this linear relationship. The observed scaling is consistent with a hierarchical system in which individuals far apart in the organization interact little with each other and receive a disproportionate number of messages from higher levels in the administrative hierarchy.; Comment: 9 pages...

Efficient Construction of Dominating Set in Wireless Networks

Xu, Xiaohua; Li, Xiang-Yang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/08/2012 Português
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Considering a communication topology of a wireless network modeled by a graph where an edge exists between two nodes if they are within each other's communication range. A subset $U$ of nodes is a dominating set if each node is either in $U$ or adjacent to some node in $U$. Assume each node has a disparate communication range and is associated with a positive weight, we present a randomized algorithm to find a min-weight dominating set. Considering any orientation of the graph where an arc $\overrightarrow{uv}$ exists if the node $v$ lies in $u$'s communication range. A subset $U$ of nodes is a strongly dominating set if every node except $U$ has both in-neighbor(s) and out-neighbor(s) in $U$. We present a polynomial-time algorithm to find a strongly dominating set of size at most $(2+\epsilon)$ times of the optimum. We also investigate another related problem called $K$-Coverage. Given are a set ${\cal D}$ of disks with positive weight and a set ${\cal P}$ of nodes. Assume all input nodes lie below a horizontal line $l$ and all input disks lie above this line $l$ in the plane. The objective is to find a min-weight subset ${\cal D}'\subseteq {\cal D}$ of disks such that each node is covered at least $K$ disks in ${\cal D}'$. We propose a novel two-approximation algorithm for this problem.; Comment: 8 pages...

Reconstruction of Aggregation Tree in spite of Faulty Nodes in Wireless Sensor Networks

Sharma, Punit; Mandal, Partha Sarathi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/10/2010 Português
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Recent advances in wireless sensor networks (WSNs) have led to many new promissing applications. However data communication between nodes consumes a large portion of the total energy of WSNs. Consequently efficient data aggregation technique can help greatly to reduce power consumption. Data aggregation has emerged as a basic approach in WSNs in order to reduce the number of transmissions of sensor nodes over {\it aggregation tree} and hence minimizing the overall power consumption in the network. If a sensor node fails during data aggregation then the aggregation tree is disconnected. Hence the WSNs rely on in-network aggregation for efficiency but a single faulty node can severely influence the outcome by contributing an arbitrary partial aggregate value. In this paper we have presented a distributed algorithm that reconstruct the aggregation tree from the initial aggregation tree excluding the faulty sensor node. This is a synchronous model that is completed in several rounds. Our proposed scheme can handle multiple number of faulty nodes as well.; Comment: this is a 5 page paper. this paper has been submitted to WCSN 2010

Online Distributed Optimization on Dynamic Networks

Hosseini, Saghar; Chapman, Airlie; Mesbahi, Mehran
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/12/2014 Português
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This paper presents a distributed optimization scheme over a network of agents in the presence of cost uncertainties and over switching communication topologies. Inspired by recent advances in distributed convex optimization, we propose a distributed algorithm based on a dual sub-gradient averaging. The objective of this algorithm is to minimize a cost function cooperatively. Furthermore, the algorithm changes the weights on the communication links in the network to adapt to varying reliability of neighboring agents. A convergence rate analysis as a function of the underlying network topology is then presented, followed by simulation results for representative classes of sensor networks.; Comment: Submitted to The IEEE Transactions on Automatic Control, 2014

Simultaneous Event Execution in Heterogeneous Wireless Sensor Networks

Baumgartner, Tobias; Fekete, Sandor P.; Hellmann, Winfried; Kroeller, Alexander
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/09/2010 Português
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We present a synchronization algorithm to let nodes in a sensor network simultaneously execute a task at a given point in time. In contrast to other time synchronization algorithms we do not provide a global time basis that is shared on all nodes. Instead, any node in the network can spontaneously initiate a process that allows the simultaneous execution of arbitrary tasks. We show that our approach is beneficial in scenarios where a global time is not needed, as it requires little communication compared with other time synchronization algorithms. We also show that our algorithm works in heterogeneous systems where the hardware provides highly varying clock accuracy. Moreover, heterogeneity does not only affect the hardware, but also the communication channels. We deal with different connection types---from highly unreliable and fluctuating wireless channels to reliable and fast wired connections.; Comment: 6 pages, 5 figures, 3 tables, to appear in Journal of Networks

Joint Optimization of Area Spectral Efficiency and Delay Over PPP Interfered Ad-hoc Networks

Chun, Young Jin; Omri, Aymen; Hasna, Mazen O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/08/2015 Português
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Due to the increasing demand on user data rates, future wireless communication networks require higher spectral efficiency. To reach higher spectral efficiencies, wireless network technologies collaborate and construct a seamless interconnection between multiple tiers of architectures at the cost of increased co-channel interference. To evaluate the performance of the co-channel transmission based communication, we propose a new metric for area spectral efficiency (ASE) of interference limited Ad-hoc network by assuming that the nodes are randomly distributed according to a Poisson point processes (PPP). We introduce a utility function, U = ASE/delay and derive the optimal ALOHA transmission probability p and the SIR threshold \tau that jointly maximize the ASE and minimize the local delay. Finally numerical results has been conducted to confirm that the joint optimization based on the U metric achieves a significant performance gain compared to conventional systems.; Comment: Accepted for publication, IEEE Communications Letters

Cryptographic techniques for mobile ad-hoc networks

Daza, Vanesa; Herranz, Javier; Morillo, Paz; Ràfols, Carla
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 180053 bytes; application/pdf
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13 pages.-- Printed version published on Dec 19, 2007.; In this paper, we propose some cryptographic techniques to securely set up a mobile ad-hoc network. The process is fully self-managed by the nodes, without any trusted party. New nodes can join the network and are able to obtain the same capabilities as initial nodes; further, each node can obtain a pair of secret/public keys to secure and authenticate its communication. Two additional features of our system are that it allows to implement threshold operations (signature or decryption) involving subgroups of nodes in the network and that any subgroup with a small number of nodes (between 2 and 6) can obtain a common secret key without any communication after the set up phase.; The work of the two first authors was partially supported by Spanish Ministry of Education and Science, under projects SEG2004-04352-C04-01 (“PROPRIETAS”) and CONSOLIDER CSD2007-00004 (“ARES”). The work of the first author was also supported by the Government of Catalonia under grant 2005 SGR 00446 and by the UNESCO Chair in Data Privacy. This author is solely responsible for the view expressed in this paper, which does not necessarily reflect the position of UNESCO nor commits that organization. The work of the two last authors was partially supported by Spanish Ministry of Education and Science...