Página 1 dos resultados de 21 itens digitais encontrados em 0.005 segundos

An algorithm for ranking quickest simple paths

Pascoal, Marta M. B.; Captivo, M. Eugénia V.; Clímaco, João C. N.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.57%
In this paper, an algorithm for ranking loopless paths in undirected networks, according to the transmission time, is presented. It is shown that the worst-case computational time complexity of the algorithm presented is , which is also the best-known complexity to solve this problem. The worst-case memory complexity is , which improves the existing algorithms. Finally, comparative computational results, with other algorithms for the same problem, are reported.; http://www.sciencedirect.com/science/article/B6VC5-49H1010-2/1/2e3e3bf1d27b1f02e63aa36fe9459417

Internet packet routing: Application of a K-quickest path algorithm

Clímaco, João C. N.; Pascoal, Marta M. B.; Craveirinha, José M. F.; Captivo, M. Eugénia V.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
56.72%
This paper describes a study on the application of an algorithm to rank the K-quickest paths to the routing of data packets in Internet networks. For this purpose an experimental framework was developed by considering two types of random generated networks. To simulate values of the IP packet sizes, a truncated Pareto distribution was defined, having in mind to reflect a key feature of Internet traffic, namely its self-similar stochastic nature. Results concerning the average CPU times of the algorithm for the different sets of experiments will be presented and discussed.; http://www.sciencedirect.com/science/article/B6VCT-4JW124S-B/1/595ef677356cef2b2c795e3eeabee5ef

Computational experiments with a lazy version of a  K  quickest simple path ranking algorithm

Pascoal, M.; Captivo, M.; Clímaco, J.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.16%
Abstract The quickest path problem is related to the classical shortest path problem, but its objective function concerns the transmission time of a given amount of data throughout a path, which involves both cost and capacity. The K-quickest simple paths problem generalises the latter, by looking for a given number K of simple paths in non-decreasing order of transmission time. Two categories of algorithms are known for ranking simple paths according to the transmission time. One is the adaptation of deviation algorithms for ranking shortest simple paths (Pascoal et al. in Comput. Oper. Res. 32(3):509–520, 2005; Rosen et al. in Comput. Oper. Res. 18(6):571–584, 1991), and another is based on ranking shortest simple paths in a sequence of networks with fixed capacity lower bounds (Chen in Inf. Process. Lett. 50:89–92, 1994), and afterwards selecting the K quickest ones. After reviewing the quickest path and the K-quickest simple paths problems we describe a recent algorithm for ranking quickest simple paths (Pascoal et al. in Ann. Oper. Res. 147(1):5–21, 2006). This is a lazy version of Chen’s algorithm, able to interchange the calculation of new simple paths and the output of each k-quickest simple path. Finally...

A comprehensive survey on the quickest path problem

Pascoal, Marta; Captivo, M.; Clímaco, João
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.99%
Abstract This work is a survey on a special minsum-maxmin bicriteria problem, known as the quickest path problem, that can model the transmission of data between two nodes of a network. Moreover, the authors review the problems of ranking the K quickest paths, and the K quickest loopless paths, and compare them in terms of the worst-case complexity order. The classification presented led to the proposal of a new variant of a known K quickest loopless paths algorithm. Finally, applications of quickest path algorithms are mentioned, as well as some comparative empirical results.; http://dx.doi.org/10.1007/s10479-006-0068-x

Virus-Vectored Influenza Virus Vaccines

Tripp, Ralph A.; Tompkins, S. Mark
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 07/08/2014 EN
Relevância na Pesquisa
26.14%
Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans...

Impacts of travel activity and urbanicity on exposures to ambient oxides of nitrogen and on exposure disparities

Gurram, Sashikanth; Stuart, Amy Lynette; Pinjari, Abdul Rawoof
Fonte: Springer Netherlands Publicador: Springer Netherlands
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
16.14%
Daily exposures to ambient oxides of nitrogen were estimated here for residents of Hillsborough County, FL. The 2009 National Household Travel Survey provided geocoded data on fixed activity locations during each person-day sampled. Routes between activity locations were calculated from transportation network data, assuming the quickest travel path. To estimate daily exposure concentrations for each person-day, the exposure locations were matched with diurnally and spatially varying ambient pollutant concentrations derived from CALPUFF dispersion model results. The social distribution of exposures was analyzed by comparing frequency distributions of grouped daily exposure concentrations and by regression modeling. To investigate exposure error, the activity-based exposure estimates were also compared with estimates derived using residence location alone. The mean daily activity-based exposure concentration for the study sample was 17 μg/m3, with values for individual person-day records ranging from 7.0 to 43 μg/m3. The highest mean exposure concentrations were found for the following groups: black (20 μg/m3), below poverty (18 μg/m3), and urban residence location (22 μg/m3). Urban versus rural residence was associated with the largest increase in exposure concentration in the regression (8.3 μg/m3). Time in nonresidential activities...

Realimentação de relevância via algoritmos genéticos aplicada à recuperação de imagens

Silva, Sérgio Francisco da
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
16.14%
O principal objetivo de um sistema de recuperação de imagens é obter imagens que são o mais similar possível à requisição do usuário, de todas as imagens de uma coleção de referência. Tal objetivo é difícil de ser alcançado devido principalmente à subjetividade do conceito de similaridade entre imagens, visto que uma mesma imagem poder ser interpretada de diferentes maneiras por diferentes pessoas. Na tentativa de resolver este problema os sistemas de recuperação de imagens por conteúdo exploram as características de cor, forma e textura, quase sempre associadas à regiões e usam de mecanismos de realimentação de relevantes para ajustar uma busca aos critérios do usuário. Várias abordagens têm sido usadas em realimentação de relevância entre as quais os algoritmos genéticos têm se tornado bastante populares devido às suas habilidades adaptativas. Neste trabalho apresentamos um sistema de recuperação de imagens com base na similaridade de padrões locais, empregando as características de cor, forma e textura e com realimentação de relevância via algoritmo genético. A tarefa do algoritmo genético é inferir pesos para as características de cor, forma, textura e regiões que melhor ajustam a medida de similaridade entre imagens aos critérios de busca do usuário...

Delaying a convoy

Oh, Dong Hwan
Fonte: Monterey California. Naval Postgraduate School Publicador: Monterey California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xvi, 51 p. : col. ill. ;
Relevância na Pesquisa
26.65%
This thesis studies "the convoy-path interdiction problem" (CPIP) in which an interdictor uses limited resources to attack and disrupt road segments ("arcs") or road intersections ("nodes") in a road network in order to delay an adversary's convoy from reaching its destination. The convoy will move between a known origin node a and destination node b using a "quickest path." We first show how to compute, using an A* search, the convoy's quickest path under the assumptions that the convoy may occupy several arcs simultaneously, each arc may have a different speed limit, and the convoy maintains constant inter-vehicle spacing. The basic model assumes that the convoy moves in a single lane of traffic; an extension handles arcs that may have multiple lanes. Using that algorithm as a subroutine, a decomposition algorithm solves the optimal interdiction problem. Interdiction of a node or arc makes that node or arc impassable. Computational results are presented on grid networks with up to 629 nodes and 2452 arcs with varying levels of interdiction resource. Using Xpress-MP optimization software and a 2 GHz Pentium IV computer, the largest network problem solves in no more than 360 seconds given that at most 4 arcs can be interdicted.

Twenty-Seven Months - Intifada, Closures, and Palestinian Economic Crisis : An Assessment

World Bank
Fonte: World Bank Publicador: World Bank
Tipo: Economic & Sector Work :: Policy Note; Economic & Sector Work
ENGLISH; EN_US
Relevância na Pesquisa
16.14%
"Twenty-Seven Months - Intifada, Closures and Palestinian Economic Crisis: An Assessment" was prepared as a follow-up to a report published in March 2002 ("Fifteen Months - Intifada, Closures and Palestinian Economic Crisis" report no. 24931). The main objectives of this second Assessment are once again to help donors and the Palestinian Authority (PA) cope with the deep economic crisis in the West Bank and Gaza, as well as to encourage and inform discussion on Palestinian economic issues among the donors, the PA and the Government of Israel. Despite an inevitable preoccupation with short-term emergency issues, the report seeks to preserve a focus on the types of medium-term economic and institutional policies that will return to prominence once the current conflict ceases to dominate the daily lives of Palestinians and Israelis. While any short-term recovery will depend on the lifting of closures, this will not suffice to put the Palestinian economy onto a sustainable growth path. The de facto customs union with Israel formalized under the Paris Protocol makes the Palestinian economy particularly vulnerable to closure. In a structural sense...

Anatomy and efficiency of urban multimodal mobility

Gallotti, Riccardo; Barthelemy, Marc
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 05/11/2014 EN
Relevância na Pesquisa
16.14%
The growth of transportation networks and their increasing interconnections, although positive, has the downside effect of an increasing complexity which make them difficult to use, to assess, and limits their efficiency. On average in the UK, 23% of travel time is lost in connections for trips with more than one mode, and the lack of synchronization decreases very slowly with population size. This lack of synchronization between modes induces differences between the theoretical quickest trip and the ‘time-respecting' path, which takes into account waiting times at interconnection nodes. We analyse here the statistics of these paths on the multilayer, temporal network of the entire, multimodal british public transportation system. We propose a statistical decomposition – the ‘anatomy' – of trips in urban areas, in terms of riding, waiting and walking times, and which shows how the temporal structure of trips varies with distance and allows us to compare different cities. Weaknesses in systems can be either insufficient transportation speed or service frequency, but the key parameter controlling their global efficiency is the total number of stop events per hour for all modes. This analysis suggests the need for better optimization strategies...

Gha rung pa Lha'i rgyal mtshan as a Scholar and Defender of the Jo nang Tradition: a Study of His Lamp That Illuminates The Expanse of Reality with an Annotated Translation and Critical Edition of the Text

Duoji, Nyingcha
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
Relevância na Pesquisa
26.14%
During the fourteenth century, with the rise of Dol po pa Shes rab rgyal mtshan (1292-1361), the gzhan stong philosophical tradition became a source of great controversy in Tibet. Dol po pa taught this new philosophical tradition for the first time to the wider Tibetan intellectual community. As Dol po pa's Jo nang teachings attracted an audience, many other philosophical giants of the day, such as Bu ston Rin chen grub (1290-1364), Red mda' ba Gzhon nu blo gros (1349-1412/13), and their students composed polemical works to refute Jo nang tradition. Lamp that Illuminates the Expanse of Reality was composed in the midst of this controversy to defend the Jo nang point of view. In it, its author, Gha rung pa Lha'i rgyal mtshan (1319-1402/03), attempts to prove that the Jo nang philosophical tradition is the definitive teaching and the quickest path to achieve the Buddhahood.

Quickest Paths in Simulations of Pedestrians

Kretz, Tobias; Grosse, Andree; Hengst, Stefan; Kautzsch, Lukas; Pohlmann, Andrej; Vortisch, Peter
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/07/2011
Relevância na Pesquisa
26.57%
This contribution proposes a method to make agents in a microscopic simulation of pedestrian traffic walk approximately along a path of estimated minimal remaining travel time to their destination. Usually models of pedestrian dynamics are (implicitly) built on the assumption that pedestrians walk along the shortest path. Model elements formulated to make pedestrians locally avoid collisions and intrusion into personal space do not produce motion on quickest paths. Therefore a special model element is needed, if one wants to model and simulate pedestrians for whom travel time matters most (e.g. travelers in a station hall who are late for a train). Here such a model element is proposed, discussed and used within the Social Force Model.; Comment: revised version submitted

Quickest Path Queries on Transportation Network

Shawi, Radwa El; Gudmundsson, Joachim; Levcopoulos, Christos
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.84%
This paper considers the problem of finding a quickest path between two points in the Euclidean plane in the presence of a transportation network. A transportation network consists of a planar network where each road (edge) has an individual speed. A traveller may enter and exit the network at any point on the roads. Along any road the traveller moves with a fixed speed depending on the road, and outside the network the traveller moves at unit speed in any direction. We give an exact algorithm for the basic version of the problem: given a transportation network of total complexity n in the Euclidean plane, a source point s and a destination point t, and the quickest path between s and t. We also show how the transportation network can be preprocessed in time O(n^2 log n) into a data structure of size O(n^2) such that (1 + \epsilon)-approximate cheapest path cost queries between any two points in the plane can be answered in time O(1\epsilon^4 log n).; Comment: 16 pages, 7 figures

The use of dynamic distance potential fields for pedestrian flow around corners

Kretz, Tobias
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2009
Relevância na Pesquisa
26.65%
This contribution investigates situations in pedestrian dynamics, where trying to walk the shortest path leads to largely different results than trying to walk the quickest path. A heuristic one-shot method to model the influence of the will to walk the quickest path is introduced.; Comment: Prepared and Accepted for "First International Conference on Evacuation Modeling and Management" (ICEM 09)

Hamiltonian Graphs and the Traveling Salesman Problem

Mehendale, Dhananjay P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
16.29%
A new characterization of Hamiltonian graphs using f-cutset matrix is proposed. A new exact polynomial time algorithm for the traveling salesman problem (TSP) based on this new characterization is developed. We then define so called ordered weighted adjacency list for given weighted complete graph and proceed to the main result of the paper, namely, the exact algorithm based on utilization of ordered weighted adjacency list and the simple properties that any path or circuit must satisfy. This algorithm performs checking of sub-lists, containing (p-1) entries (edge pairs) for paths and p entries (edge pairs) for circuits, chosen from ordered adjacency list in a well defined sequence to determine exactly the shortest Hamiltonian path and shortest Hamiltonian circuit in a weighted complete graph of p vertices. The procedure has intrinsic advantage of landing on the desired solution in quickest possible time and even in worst case in polynomial time. A new characterization of shortest Hamiltonian tour for a weighted complete graph satisfying triangle inequality (i.e. for tours passing through every city on a realistic map of cities where cities can be taken as points on a Euclidean plane) is also proposed. Finally, we discuss a novel classical algorithm for unstructured search and its effect on any of the NP-Complete problems.; Comment: 30 pages. Section 2.7 is added to discuss a new algorithm for unstructured search

Modelling dynamic route choice of pedestrians to assess the criticality of building evacuation

Wagoum, A. U. Kemloh; Seyfried, A.; Holl, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/03/2011
Relevância na Pesquisa
26.84%
This paper presents an event-driven way finding algorithm for pedestrians in an evacuation scenario, which operates on a graph-based structure. The motivation of each pedestrian is to leave the facility. The events used to redirect pedestrians include the identification of a jam situation and/or identification of a better route than the current. This study considers two types of pedestrians: familiar and unfamiliar with the facility. Four strategies are modelled to cover those groups. The modelled strategies are the shortest path (local and global); They are combined with a quickest path approach, which is based on an observation principle. In the quickest path approach, pedestrians take their decisions based on the observed environment and are routed dynamically in the network using an appropriate cost benefit analysis function. The dynamic modelling of route choice with different strategies and types of pedestrians considers the manifold of in uences which appears in the real system and raises questions about the criticality of an evacuation process. To address this question criteria are elaborated. The criteria we focus on in this contribution are the evacuation time, the individual times spent in jam, the jam size evolution and the overall jam size itself. The in uences of the different strategies on those evaluation criteria are investigated. The sensibility of the system to disturbances (e.g. broken escape route) is also analysed. Keywords: pedestrian dynamics...

Constructing Optimal Highways

Ahn, Hee-Kap; Alt, Helmut; Asano, Tetsuo; Bae, Sang Won; Brass, Peter; Cheong, Otfried; Knauer, Christian; Na, Hyeon-Suk; Shin, Chan-Su; Wolff, Alexander
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/03/2007
Relevância na Pesquisa
26.14%
For two points $p$ and $q$ in the plane, a straight line $h$, called a highway, and a real $v>1$, we define the \emph{travel time} (also known as the \emph{city distance}) from $p$ and $q$ to be the time needed to traverse a quickest path from $p$ to $q$, where the distance is measured with speed $v$ on $h$ and with speed 1 in the underlying metric elsewhere. Given a set $S$ of $n$ points in the plane and a highway speed $v$, we consider the problem of finding a \emph{highway} that minimizes the maximum travel time over all pairs of points in $S$. If the orientation of the highway is fixed, the optimal highway can be computed in linear time, both for the $L_1$- and the Euclidean metric as the underlying metric. If arbitrary orientations are allowed, then the optimal highway can be computed in $O(n^{2} \log n)$ time. We also consider the problem of computing an optimal pair of highways, one being horizontal, one vertical.; Comment: 13 pages, 9 figures, preliminary version appeared at CATS'07

Pedestrian Traffic: on the Quickest Path

Kretz, Tobias
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/01/2009
Relevância na Pesquisa
36.73%
When a large group of pedestrians moves around a corner, most pedestrians do not follow the shortest path, which is to stay as close as possible to the inner wall, but try to minimize the travel time. For this they accept to move on a longer path with some distance to the corner, to avoid large densities and by this succeed in maintaining a comparatively high speed. In many models of pedestrian dynamics the basic rule of motion is often either "move as far as possible toward the destination" or - reformulated - "of all coordinates accessible in this time step move to the one with the smallest distance to the destination". Atop of this rule modifications are placed to make the motion more realistic. These modifications usually focus on local behavior and neglect long-ranged effects. Compared to real pedestrians this leads to agents in a simulation valuing the shortest path a lot better than the quickest. So, in a situation as the movement of a large crowd around a corner, one needs an additional element in a model of pedestrian dynamics that makes the agents deviate from the rule of the shortest path. In this work it is shown, how this can be achieved by using a flood fill dynamic potential field method, where during the filling process the value of a field cell is not increased by 1...

Applications of the Dynamic Distance Potential Field Method

Kretz, Tobias
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/11/2009
Relevância na Pesquisa
26.14%
Recently the dynamic distance potential field (DDPF) was introduced as a computationally efficient method to make agents in a simulation of pedestrians move rather on the quickest path than the shortest. It can be considered to be an estimated-remaining-journey-time-based one-shot dynamic assignment method for pedestrian route choice on the operational level of dynamics. In this contribution the method is shortly introduced and the effect of the method on RiMEA's test case 11 is investigated.; Comment: Accepted as contribution to "Traffic and Granular Flow 09" proceedings. This is a slightly extended version

Brownian motion and multidimensional decision making

Lange, Rutger-Jan
Fonte: University of Cambridge; Judge Business School; King's College; Electricity Policy Research Group (EPRG) Publicador: University of Cambridge; Judge Business School; King's College; Electricity Policy Research Group (EPRG)
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
16.29%
This thesis consists of three self-contained parts, each with its own abstract, body, references and page numbering. Part I, "Potential theory, path integrals and the Laplacian of the indicator", finds the transition density of absorbed or reflected Brownian motion in a d-dimensional domain as a Feynman-Kac functional involving the Laplacian of the indicator, thereby relating the hitherto unrelated fields of classical potential theory and path integrals. Part II, "The problem of alternatives", considers parallel investment in alternative technologies or drugs developed over time, where there can be only one winner. Parallel investment accelerates the search for the winner, and increases the winner's expected performance, but is also costly. To determine which candidates show sufficient performance and/or promise, we find an integral equation for the boundary of the optimal continuation region. Part III, "Optimal support for renewable deployment", considers the role of government subsidies for renewable technologies. Rapidly diminishing subsidies are cheaper for taxpayers, but could prematurely kill otherwise successful technologies. By contrast, high subsidies are not only expensive but can also prop up uneconomical technologies. To analyse this trade-off we present a new model for technology learning that makes capacity expansion endogenous. There are two reasons for this standalone structure. First...