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排序方式: 共有7480条查询结果,搜索用时 15 毫秒
71.
Jun Pan Li Na Quan Yongbiao Zhao Wei Peng Banavoth Murali Smritakshi P. Sarmah Mingjian Yuan Lutfan Sinatra Noktan M. Alyami Jiakai Liu Emre Yassitepe Zhenyu Yang Oleksandr Voznyy Riccardo Comin Mohamed N. Hedhili Omar F. Mohammed Zheng Hong Lu Dong Ha Kim Edward H. Sargent Osman M. Bakr 《Advanced materials (Deerfield Beach, Fla.)》2016,28(39):8718-8725
72.
Mohamed Amine Ouamri Reem Alkanhel Cedric Gueguen Manal Abdullah Alohali Sherif S. M. Ghoneim 《计算机、材料和连续体(英文)》2023,74(1):453-467
With the rapid development of emerging 5G and beyond (B5G), Unmanned Aerial Vehicles (UAVs) are increasingly important to improve the performance of dense cellular networks. As a conventional metric, coverage probability has been widely studied in communication systems due to the increasing density of users and complexity of the heterogeneous environment. In recent years, stochastic geometry has attracted more attention as a mathematical tool for modeling mobile network systems. In this paper, an analytical approach to the coverage probability analysis of UAV-assisted cellular networks with imperfect beam alignment has been proposed. An assumption was considered that all users are distributed according to Poisson Cluster Process (PCP) around base stations, in particular, Thomas Cluster Process (TCP). Using this model, the impact of beam alignment errors on the coverage probability was investigated. Initially, the Probability Density Function (PDF) of directional antenna gain between the user and its serving base station was obtained. Then, association probability with each tier was achieved. A tractable expression was derived for coverage probability in both Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) condition links. Numerical results demonstrated that at low UAVs altitude, beam alignment errors significantly degrade coverage performance. Moreover, for a small cluster size, alignment errors do not necessarily affect the coverage performance. 相似文献
73.
Mohamed Rabhi Anis Ben Abdessalem Laurent Saintis Bruno Castanier Rodrigue Sohoin 《Quality and Reliability Engineering International》2023,39(3):1058-1082
Accelerated life testing (ALT) is widely used in high-reliability product estimation to get relevant information about an item's performance and its failure mechanisms. To analyse the observed ALT data, reliability practitioners need to select a suitable accelerated life model based on the nature of the stress and the physics involved. A statistical model consists of (i) a lifetime distribution that represents the scatter in product life and (ii) a relationship between life and stress. In practice, several accelerated life models could be used for the same failure mode and the choice of the best model is far from trivial. For this reason, an efficient selection procedure to discriminate between a set of competing accelerated life models is of great importance for practitioners. In this paper, accelerated life model selection is approached by using the Approximate Bayesian Computation (ABC) method and a likelihood-based approach for comparison purposes. To demonstrate the efficiency of the ABC method in calibrating and selecting accelerated life model, an extensive Monte Carlo simulation study is carried out using different distances to measure the discrepancy between the empirical and simulated times of failure data. Then, the ABC algorithm is applied to real accelerated fatigue life data in order to select the most likely model among five plausible models. It has been demonstrated that the ABC method outperforms the likelihood-based approach in terms of reliability predictions mainly at lower percentiles particularly useful in reliability engineering and risk assessment applications. Moreover, it has shown that ABC could mitigate the effects of model misspecification through an appropriate choice of the distance function. 相似文献
74.
Mohamed Fahim Hassan Mohamed Zribi Hamed M. K. Alazemi 《International Journal of Control, Automation and Systems》2011,9(2):237-248
This paper proposes an optimal recursive estimator to estimate the states of a stochastic discrete time linear dynamic system
when the states of the system are constrained with inequality constraints. The case when the constraints are strictly satisfied
is treated independently from the case when some of the constraints are violated. For the first case, the well known Kalman
filter estimator is used. In the second case, an algorithm which uses a series of successive orthogonalizations on the measurement
subspaces is employed to obtain the optimal estimate. It is shown that the proposed estimator has several attractive properties
such that it is an unbiased estimator. More importantly, compared to other estimator found in the literature, the proposed
estimator needs less computational efforts, is numerically more stable and it leads to a smaller variance. To show the effectiveness
of the proposed estimator, several simulation results are presented and discussed. 相似文献
75.
76.
We present two new classifiers for two-class classification problems using a new Beta-SVM kernel transformation and an iterative
algorithm to concurrently select the support vectors for a support vector machine (SVM) and the hidden units for a single
hidden layer neural network to achieve a better generalization performance. To construct the classifiers, the contributing
data points are chosen on the basis of a thresholding scheme of the outputs of a single perceptron trained using all training
data samples. The chosen support vectors are used to construct a new SVM classifier that we call Beta-SVN. The number of chosen
support vectors is used to determine the structure of the hidden layer in a single hidden layer neural network that we call
Beta-NN. The Beta-SVN and Beta-NN structures produced by our method outperformed other commonly used classifiers when tested
on a 2-dimensional non-linearly separable data set. 相似文献
77.
Yacine Rebahi Mohamed Nassar Thomas Magedanz Olivier FestorAuthor vitae 《Information Security Technical Report》2011,16(1):12-19
The migration from circuit-switched networks to packet-switched networks necessitates the investigation of related issues such as service delivery, QoS, security, and service fraud and misuse. The latter can be seen as a combination of accounting and security aspects. In traditional telecommunication networks, fraud accounts for annual losses at an average of 3%–5% of the operators’ revenue and still increasing at a rate of more than 10% yearly. It is also expected that in VoIP networks, the situation will be worse due to the lack of strong built-in security mechanisms, and the use of open standards. This paper discusses the fraud problem in VoIP networks and evaluates the related available solutions. 相似文献
78.
Maher El��Arbi Mohamed Koubaa Maha Charfeddine Chokri Ben Amar 《Multimedia Tools and Applications》2011,55(3):579-600
In this paper, we propose a video watermarking algorithm which embeds different parts of a single watermark into different shots of a video under the wavelet domain. Based on a Motion Activity Analysis, different regions of the original video are separated into perceptually distinct categories according to motion information and region complexity. Thus, the localizations of the watermark are adjusted adaptively in accordance with the human visual system and signal characteristics, which makes them perceptually invisible and less vulnerable to automated removal. In addition, contrary to traditional methods where the watermark remains at a fixed position on the screen, the watermark moves along with moving objects and thus motion artefacts can be avoid. The multi-frame based extraction strategy ensures that the watermark can be correctly recovered from a very short segment of video. Individual frames extracted from the video also contain watermark information. Experimental results show that the inserted watermark is not only less perceptible but also robust against common video processing attacks. 相似文献
79.
In this paper, we present a new sufficient condition for absolute stability of Lure system with two additive time-varying delay components. This criterion is expressed as a set of linear matrix inequalities (LMIs), which can be readily tested by using standard numerical software. We use this new criterion to stabilize a class of nonlinear time-delay systems. Some numerical examples are given to illustrate the applicability of the results using standard numerical software. 相似文献
80.
We address the verification problem of networks of communicating pushdown systems modeling communicating parallel programs with procedure calls. Processes in such networks can read the control state of the other processes according to a given communication structure (specifying the observability rights between processes). The reachability problem of such models is undecidable in general. First, we define a class of networks that effectively preserves recognizability (hence, its reachability problem is decidable). Then, we consider networks where the communication structure can change dynamically during the execution according to a phase graph. The reachability problem for these dynamic networks being undecidable in general, we define a subclass for which it becomes decidable. Then, we consider reachability when the switches in the communication structures are bounded. We show that this problem is undecidable even for one switch. We define a natural class of models for which this problem is decidable. This class can be used in the definition of an efficient semi-decision procedure for the analysis of the general model of dynamic networks. Our techniques allowed to find bugs in two versions of a Windows NT Bluetooth driver. 相似文献