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51.
Digital libraries at a crossroads 总被引:1,自引:1,他引:0
Yannis Ioannidis 《International Journal on Digital Libraries》2005,5(4):255-265
Digital libraries constitute a relatively young scientific field whose life spans roughly the last 10 years. Despite its youth, the field has made a long journey from its initial conception to the present state of the art and has reached a level of maturity that warrants taking stock of its course so far and paving a path for the immediate and long-term future. In this paper, we analyse the recommendations of several activities that were initiated by the DELOS Network of Excellence under the Fifth Framework Programme of the European Commission and demonstrate that there are several issues that arise in similar form in most digital library efforts. We thus conclude that generic digital library management systems that address all these issues in a common fashion can and should be developed, so that future digital library efforts are able to build on such platforms and focus only on the hard issues that specialised functionality raises. 相似文献
52.
Eleonora Papadimitriou Athanasios Theofilatos George Yannis Julien Cestac Sami Kraïem 《Accident; analysis and prevention》2014
Riding a motorcycle under the influence of alcohol is a dangerous activity, especially considering the high vulnerability of motorcyclists. The present research investigates the factors that affect the declared frequency of drink-riding among motorcyclists in Europe and explores regional differences. Data were collected from the SARTRE-4 (Social Attitudes to Road Traffic Risk in Europe) survey, which was conducted in 19 countries. A total sample of 4483 motorcyclists was interviewed by using a face-to-face questionnaire. The data were analyzed by means of multilevel ordered logit models. The results revealed significant regional differences (between Northern, Eastern and Southern European countries) in drink-riding frequencies in Europe. In general, declared drinking and riding were positively associated with gender (males), increased exposure, underestimation of risk, friends’ behaviour, past accidents and alcohol ticket experience. On the other hand, it was negatively associated with underestimation of the amount of alcohol allowed before driving, and support for more severe penalties. 相似文献
53.
Emmanuelle Dupont Jacques J.F. Commandeur Sylvain Lassarre Frits Bijleveld Heike Martensen Constantinos Antoniou Eleonora Papadimitriou George Yannis Elke Hermans Katherine Pérez Elena Santamariña-Rubio Davide Shingo Usami Gabriele Giustiniani 《Accident; analysis and prevention》2014
In this paper a unified methodology is presented for the modelling of the evolution of road safety in 30 European countries. For each country, annual data of the best available exposure indicator and of the number of fatalities were simultaneously analysed with the bivariate latent risk time series model. This model is based on the assumption that the amount of exposure and the number of fatalities are intrinsically related. It captures the dynamic evolution in the fatalities as the product of the dynamic evolution in two latent trends: the trend in the fatality risk and the trend in the exposure to that risk. Before applying the latent risk model to the different countries it was first investigated and tested whether the exposure indicator at hand and the fatalities in each country were in fact related at all. If they were, the latent risk model was applied to that country; if not, a univariate local linear trend model was applied to the fatalities series only, unless the latent risk time series model was found to yield better forecasts than the univariate local linear trend model. In either case, the temporal structure of the unobserved components of the optimal model was established, and structural breaks in the trends related to external events were identified and captured by adding intervention variables to the appropriate components of the model. As a final step, for each country the optimally modelled developments were projected into the future, thus yielding forecasts for the number of fatalities up to and including 2020. 相似文献
54.
Nikos Dimokas Dimitrios Katsaros Leandros Tassiulas Yannis Manolopoulos 《Wireless Networks》2011,17(3):717-737
During the last decade, Wireless Sensor Networks have emerged and matured at such point that they currently support several
applications such as environment control, intelligent buildings, target tracking in battlefields. The vast majority of these
applications require an optimization to the communication among the sensors so as to serve data in short latency and with
minimal energy consumption. Cooperative data caching has been proposed as an effective and efficient technique to achieve
these goals concurrently. The essence of these protocols is the selection of the sensor nodes which will take special roles
in running the caching and request forwarding decisions. This article introduces two new metrics to aid in the selection of
such nodes. Based on these metrics, we propose two new cooperative caching protocols, PCICC and scaPCICC, which are compared against the state-of-the-art competing protocol, namely NICoCa. The proposed solutions are evaluated extensively in an advanced simulation environment and the results confirm that the
proposed caching mechanisms prevail over its competitor. The evaluation attests also that the best policy is always scaPCICC, achieving the shortest latency and the least number of transmitted messages. 相似文献
55.
Ten Benchmark Database Queries for Location-based Services 总被引:4,自引:0,他引:4
56.
Theodoros Tzouramanis Michael Vassilakopoulos Yannis Manolopoulos 《Data & Knowledge Engineering》2004,49(3):1335-286
In this paper we present a performance comparison of access methods for time-evolving regional data. Initially, we briefly review four temporal extensions of the Linear Region Quadtree: the Time-Split Linear Quadtree, the Multiversion Linear Quadtree, the Multiversion Access Structure for Evolving Raster Images and Overlapping Linear Quadtrees. These methods comprise a family of specialized access methods that can efficiently store and manipulate consecutive raster images. A new simpler implementation solution that provides efficient support for spatio-temporal queries referring to the past through these methods, is suggested. An extensive experimental space and time performance comparison of all the above access methods follows. The comparison is made under a common and flexible benchmarking environment in order to choose the best technique depending on the application and on the image characteristics. These experimental results show that in most cases the Overlapping Linear Quadtrees method is the best choice. 相似文献
57.
Nikos Naskas Yannis Papananos 《Analog Integrated Circuits and Signal Processing》2004,41(2-3):109-118
Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB. 相似文献
58.
The context of this paper is the 3D wave propagation simulation with a software based on a ray tracing technique in typical indoor environments. The presented works are complementary to these of the literature which propose the validation of a propagation model in comparison with measurements. Indeed, the presented study consists of a sensitivity analysis of an already validated propagation model. The considered parameters are electromagnetic, geometric and electric; they directly intervene in the two parts of a simulation: the modelling of the wave propagation and of the environment. The aim of this study is to contribute to the setting up of parameterisation rules of a simulation software according to two criteria: the accuracy and the compromise between accuracy and computation time. 相似文献
59.
This article presents a method which optimises the computation time for the prediction of a radio coverage, whatever the propagation model used. The principle consists in reducing the number of application points of the propagation model in relation to a classical technique. The proposed method is based on a multi resolution analysis of measured signals carried out around 2 GHz, and on an electromagnetic analysis of the propagation environment. The performances of the method are evaluated in term of reduction in computation time and of accuracy, in comparaison with the classical technique. 相似文献
60.
Yannis F. Dafalias 《Mechanics of materials : an international journal》1984,3(3):223-233
The basic kinematics and the rate constitutive equations are briefly presented within the framework of a macroscopic formulation of finite plastic transformations for structured media, employing the concept of tensorial structure variables. The key feature is the necessity to provide constitutive relations for the plastic spin according to the proposition of Mandel and Kratochvil. After obtaining these relations for a transversely isotropic medium employing the representation theorems for isotropic second order antisymmetric tensor-valued functions, the role of the plastic spin is illustrated by the analysis of large simple shear for such a medium. 相似文献