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排序方式: 共有123条查询结果,搜索用时 15 毫秒
1.
M. Kadja J.S. Anagnostopoulos G.C. Bergeles 《International Communications in Heat and Mass Transfer》1996,23(8):1065-1076
The paper presents a three-dimensional transient numerical model for atmospheric wind flow and industry and/or traffic pollutant dispersion over terrains having a complex topography. The model is based on a finite-volume integration of the equations governing mass, momentum, heat and pollutant transport within the earth's atmospheric boundary layer, using a collocated grid arrangement. The instability provoked by such a formulation was avoided by using a special pressure-velocity coupling. Local refinement of the grid was achieved via a domain decomposition method. The technique of “porosity” used to approximate curved three-dimensional boundaries is incorporated in the procedure thus avoiding the less accurate and more common approximation by a broken surface with segments parallel to the coordinate lines. The method was validated by simulating the flow over the Attica peninsula for which measurements of wind speed and pollutant emissions are available. 相似文献
2.
K. A. Anagnostopoulos S. Mavratzas A. Charalambopoulos D. I. Fotiadis 《Acta Mechanica》2003,161(1-2):39-52
Summary. We consider the acoustic scattering of time-harmonic spherical waves from an eccentric non coaxial spheroidal structure simulating
the kidney-stone system. The proposed analysis is based on the application of the translational addition theorem for spheroidal
wave functions. The resulting theoretical model is frequency-independent. Numerical results concerning the applicability of
our approach are also presented.
Received September 20, 2002 Published online: March 20, 2003 相似文献
3.
4.
We study on the forwarding of quality contextual information in mobile sensor networks (MSNs). Mobile nodes form ad-hoc distributed processing networks that produce accessible and quality-stamped information about the surrounding environment. Due to the dynamic network topology of such networks the context quality indicators seen by the nodes vary over time. A node delays the context forwarding decision until context of better quality is attained. Moreover, nodes have limited resources, thus, they have to balance between energy conservation and quality of context. We propose a time-optimized, distributed decision making model for forwarding context in a MSN based on the theory of optimal stopping. We compare our findings with certain context forwarding schemes found in the literature and pinpoint the advantages of the proposed model. 相似文献
5.
Routis Ioannis Bardaki Cleopatra Dede Georgia Nikolaidou Mara Kamalakis Thomas Anagnostopoulos Dimosthenis 《Software and Systems Modeling》2021,20(6):2089-2109
Software and Systems Modeling - Case Management Model and Notation (CMMN) has been introduced as a graphical modeling language targeting the modeling of human-centric processes. Despite its growing... 相似文献
6.
Marios Anagnostopoulos Georgios Kambourakis Stefanos Gritzalis 《International Journal of Information Security》2016,15(5):455-473
It is without a doubt that botnets pose a growing threat to the Internet, with DDoS attacks of any kind carried out by botnets to be on the rise. Nowadays, botmasters rely on advanced Command and Control (C&C) infrastructures to achieve their goals and most importantly to remain undetected. This work introduces two novel botnet architectures that consist only of mobile devices and evaluates both their impact in terms of DNS amplification and TCP flooding attacks, and their cost pertaining to the maintenance of the C&C channel. The first one puts forward the idea of using a continually changing mobile HTTP proxy in front of the botherder, while the other capitalizes on DNS protocol as a covert channel for coordinating the botnet. That is, for the latter, the messages exchanged among the bots and the herder appear as legitimate DNS transactions. Also, a third architecture is described and assessed, which is basically an optimized variation of the first one. Namely, it utilizes a mixed layout where all the attacking bots are mobile, but the proxy machines are typical PCs not involved in the actual attack. For the DNS amplification attack, which is by nature more powerful, we report an amplification factor that fluctuates between 32.7 and 34.1. Also, regarding the imposed C&C cost, we assert that it is minimal (about 0.25 Mbps) per bot in the worst case happening momentarily when the bot learns about the parameters of the attack. 相似文献
7.
Operator context scanning to support high segmentation rates for real time license plate recognition
Ioannis Giannoukos Author Vitae Christos-Nikolaos Anagnostopoulos Author VitaeAuthor Vitae Eleftherios Kayafas Author Vitae 《Pattern recognition》2010,43(11):3866-3878
Introducing high definition videos and images in object recognition has provided new possibilities in the field of intelligent image processing and pattern recognition. However, due to the large amount of information that needs to be processed, the computational costs are high, making the HD systems slow. To this end, a novel algorithm applied to sliding window analysis, namely Operator Context Scanning (OCS), is proposed and tested on the license plate detection module of a License Plate Recognition (LPR) system. In the LPR system, the OCS algorithm is applied on the Sliding Concentric Windows pixel operator and has been found to improve the LPR system’s performance in terms of speed by rapidly scanning input images focusing only on regions of interest, while at the same time it does not reduce the system effectiveness. Additionally, a novel characteristic is presented, namely, the context of the image based on a sliding windows operator. This characteristic helps to quickly categorize the environmental conditions upon which the input image was taken. The algorithm is tested on a data set that includes images of various resolutions, acquired under a variety of environmental conditions. 相似文献
8.
We formulate the portfolio selection as a tri-objective optimization problem so as to find tradeoffs between risk, return and the number of securities in the portfolio. Furthermore, quantity and class constraints are introduced into the model in order to limit the proportion of the portfolio invested in assets with common characteristics and to avoid very small holdings. Since the proposed portfolio selection model involves mixed integer decision variables and multiple objectives finding the exact efficient frontier may be very hard. Nevertheless, finding a good approximation of the efficient surface which provides the investor with a diverse set of portfolios capturing all possible tradeoffs between the objectives within limited computational time is usually acceptable. We experiment with the current state of the art evolutionary multiobjective optimization techniques, namely the Non-dominated Sorting Genetic Algorithm II (NSGA-II), Pareto Envelope-based Selection Algorithm (PESA) and Strength Pareto Evolutionary Algorithm 2 (SPEA2), for solving the mixed-integer multiobjective optimization problem and provide a performance comparison among them using metrics proposed by the community. 相似文献
9.
We consider the problem of efficiently sampling Web search engine query results. In turn, using a small random sample instead
of the full set of results leads to efficient approximate algorithms for several applications, such as:
We present and analyze efficient algorithms for obtaining uniform random samples applicable to any search engine that is based
on posting lists and document-at-a-time evaluation. (To our knowledge, all popular Web search engines, for example, Google,
Yahoo Search, MSN Search, Ask, belong to this class.) Furthermore, our algorithm can be modified to follow the modern object-oriented
approach whereby posting lists are viewed as streams equipped with a next method, and the next method for Boolean and other complex queries is built from the next method for primitive terms. In our case we show how to construct a basic sample-next(p) method that samples term posting lists with probability p, and show how to construct sample-next(p) methods for Boolean operators (AND, OR, WAND) from primitive methods. Finally, we test the efficiency and quality of our approach on both synthetic and real-world data.
A preliminary version of this work has appeared in [3].
Work performed while A. Anagnostopoulos and A.Z. Broder were at IBM T. J. Watson Research Center. 相似文献
• | Determining the set of categories in a given taxonomy spanned by the search results; |
• | Finding the range of metadata values associated with the result set in order to enable “multi-faceted search”; |
• | Estimating the size of the result set; |
• | Data mining associations to the query terms. |
10.
Ghaith Rabadi Georgios C. Anagnostopoulos Mansooreh Mollaghasemi 《The International Journal of Advanced Manufacturing Technology》2007,32(3-4):326-335
This paper addresses the single machine early/tardy problem with unrestricted common due date and sequence-dependent setup
times. Two algorithms are introduced to reach near-optimum solutions: the SAPT, a heuristic tailored for the problem, and
a simulated annealing (SA) algorithm. It will be shown that SA provides solutions with slightly better quality; however, SAPT
requires much less computational time. SAPT-SA is a hybrid heuristic that combines both approaches to obtain high quality
solutions with low computational cost. Solutions provided by the three algorithms were compared to optimal solutions for problems
with up to 25 jobs and to each other for larger problems. 相似文献