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51.
This paper introduces an approach to effectively exploit incremental SAT in order to search for multiple equivalence-preserving transformations of combinational circuits. Typical applications, such as redundancy removal with observability and external care conditions, adequate abstractions and other optimizations used in a state-of-the-art SAT-based model checker, can reap benefits from the proposed strategies. Our techniques exploit SAT incrementality, by iteratively refining the set of candidate transformations with a counter-example driven analysis, until an unsatisfiable point is reached. The key point of our technique is the ability to address satisfiable instances first, where SAT solvers are generally much faster than with unsatisfiable runs. We also discuss partitioning and problem reduction issues, that are fundamental in order to provide a scalable approach. Experimental results show the effectiveness of the proposed strategies.  相似文献   
52.
The design of standard communications and security mechanisms for resource‐constrained sensing applications and devices may provide an important contribution for its integration with the Internet and consequently towards the realization of what we nowadays identify as the Internet of Things. This vision will only be realizable if appropriate security mechanisms are available, and in this context we target the design and experimental evaluation of security mechanisms for communications at the network‐layer with sensing devices (smart objects) using the standard IPv6 protocol. Our work proposes and evaluates the usage of new compressed security headers for the network layer with smart objects. We implement and evaluate what is, as far as we know, the first proposal of security at the network layer experimentally evaluated using the TinyOS operating system and its networking stack. As we verify in the course of our evaluation study, various scenarios employing network‐layer secure communications involving smart objects are feasible, particularly when security mechanisms are designed to benefit from cross‐layer interactions that allow the optimization of expensive cryptographic operations. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
53.
The adsorptive properties of the isoreticular series [Ni8(OH)4(H2O)2(BDP_X)6] (H2BDP_X = 1,4‐bis(pyrazol‐4‐yl)benzene‐4‐X with X = H (1), OH (2), NH2 (3)) can be enhanced by postsynthetic treatment with an excess of KOH in ethanol. In the case of X = H, NH2, this treatment leads to partial removal of the organic linkers, deprotonation of coordinated water molecules and introduction of extraframework cations, giving rise to materials of K[Ni8(OH)5(EtO)‐(H2O)2(BDP_X)5.5] (1@KOH, 3@KOH) formulation, in which the original framework topology is maintained. By contrast, the same treatment with KOH in the [Ni8(OH)4(H2O)2(BDP_OH)6] (2) system, enclosing the more acidic phenol residues, leads to a new material containing a larger fraction of missing linker defects and extra‐framework cations as well as phenolate residues, giving rise to the material K3[Ni8(OH)3(EtO)(H2O)6(BDP_O)5] (2@KOH), which also conserves the original face cubic centered (fcu) topology. It is noteworthy that the introduction of missing linker defects leads to a higher accessible pore volume with a concomitant increased adsorption capacity. Moreover, the creation of coordinatively unsaturated metal centers, charge gradients, and phenolate nucleophilic sites in 2@KOH gives rise to a boosting of CO2 capture features with increased adsorption heat and adsorption capacity, as proven by the measurement of pulse gas chromatography and breakthrough curve measurements of simulated flue gas.  相似文献   
54.
Monitoring speech quality in Voice over IP (VoIP) networks is important to ensure a minimal acceptable level of speech quality for IP calls running through a managed network. Information such as packet loss, codec type, jitter, end‐to‐end delay and overall speech quality enables the network manager to verify and accurately tune parameters in order to adjust network problems. The present article proposes the deployment of a monitoring architecture that collects, stores and displays speech quality information about concluded voice calls. This architecture is based on our proposed MIB (Management Information Base) VOIPQOS, deployed for speech quality monitoring purposes. Currently, the architecture is totally implemented, but under adjustment and validation tests. In the future, the VOIPQOS MIB can be expanded to automatically analyze collected data and control VoIP clients and network parameters for tuning the overall speech quality of ongoing calls. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
55.
This paper presents two techniques for DC model parameter extraction for a Gallium Arsenide (GaAs) based MEtal Semiconductor Field Effect Transistor (MESFET) device. The proposed methods uses Particle Swarm Optimization (PSO) and Quantum Particle Swarm Optimization (QPSO) methods for optimizing the difference between measured data and simulated data. Simulated data are obtained by using four different popular DC models. These techniques avoid complex computational steps involved in traditional parameter extraction techniques. The performance comparison in terms of quality of solution and execution time of classical PSO and QPSO to extract the model parameters are presented. The validity of this approach is verified by comparing the simulated and measured results of a fabricated GaAs MESFET device with gate length of 0.7 μm and gate width of 600 μm (4 × 150). Simulation results indicate that both the technique based on PSO and QPSO accurately extracts the model parameters of MESFET.  相似文献   
56.
Cation exchange polymeric matrices are widely used in water treatment protocols to reduce the mineral content of hard waters, even for human consumption. However, they are not antibacterial and flowing bacteria can be trapped in their structures and proliferate, thus acting as microbial contamination sources. Here, Ag@Co‐nanoparticles (Ag@Co‐NPs) with a low‐cost superparamagnetic Co0‐core and an antibacterial Ag‐shell are synthesized on granulated cation exchange polymeric matrices under soft reaction conditions. The presence of these NPs provides the final nanocomposite (NC) with additional functionalities (superparamagnetism and antibacterial activity) making it ideal for water purification applications. Ag@Co‐NPs are synthesized in situ on four cation exchange polymeric matrices containing either strong (sulfonic) or weak (carboxylic) acid functional groups homogeneously distributed (C‐type) or concentrated on an external shell (SST‐type) by the intermatrix synthesis (IMS) method. The NCs are characterized (metal content, NP size and distribution, metal oxidative state, and metal release) and evaluated for water purification applications.  相似文献   
57.
The aim of our study is to obtain theoretical limits for the gain that can be expected when using handover prediction and to determine the sensitivity of the system performance against different parameters. We apply an average-reward reinforcement learning approach based on afterstates to the design of optimal admission control policies in mobile multimedia cellular networks where predictive information related to the occurrence of future handovers is available. We consider a type of predictor that labels active mobile terminals in the cell neighborhood a fixed amount of time before handovers are predicted to occur, which we call the anticipation time. The admission controller exploits this information to reserve resources efficiently. We show that there exists an optimum value for the anticipation time at which the highest performance gain is obtained. Although the optimum anticipation time depends on system parameters, we find that its value changes very little when the system parameters vary within a reasonable range. We also find that, in terms of system performance, deploying prediction is always advantageous when compared to a system without prediction, even when the system parameters are estimated with poor precision.  相似文献   
58.
The amount of data generated by computer systems in Online Distance Learning (ODL) contains rich information. One example of this information we define as the Learner Learning Trail (LLT), which is the sequence of interactions between the students and the virtual environment. Another example is the Learner Learning Style (LLS), which is associated with the student behavior and choices during the learning process. This information can be used to identify learner behavior and learning style. We perceived, after the study of related literature, that the research field of learner diagnosis for ODL does not apply the conjoint use of LLT and LLS. In this article, we propose a model capable of integrating data generated from the behavior of students in ODL with cognitive aspects of them, such as their Learning Styles, by crossing LLT with LLS. We also propose the CPAD method (Collect, Preprocessing, Analysis, Diagnosis), which is implemented by collecting the raw data regarding learning activities, preprocessing the data into structured time sequences, analyzing the sequences regarding the learning styles and using this analysis to diagnose the learner behavior. We selected the dropout to investigate, once the dropout rate in ODL is a real problem in universities around the world. In addition, the dropout is a student decision which can be associated with previous students behaviors. We performed a study with 202 learners to evaluate if learning styles are capable of explaining aspects of the student behavior. The results suggest that Sequential/Global learning style dimension is more capable of explaining the dropout than the other dimensions. Also, we performed four classification experiments to verify how the dimensions of Felder-Silverman Learning Style Model influence the learner diagnosis. We perceived that the Sequential/Global dimension could provide a higher accuracy average with lower variation independently of the diagnosis technique.  相似文献   
59.
Signals and Noise in Evoked Brain Potentials   总被引:2,自引:0,他引:2  
Event-related brain potentials measured with scalp electrodes are always corrupted by unrelated electrical discharges occurring in the brain. These unrelated electrical discharges, generally referred to as noise, have temporal and spectral characteristics similar to evoked potential waveforms, and they greatly increase the difficulty of detecting and estimating the parameters of the evoked potential waveforms themselves. This problem has been analyzed by computing the probability distributions for measured amplitudes and latencies of ERP components measured in the presence of the ongoing EEG. The analytical results have been verified over a wide range of signal-to-noise ratios by computer simulation. Comparisons of theoretical results to measured data indicate that the latency variations found experimentally greatly exceed what would be expected if they were due only to additive noise. It may be concluded, therefore, that the single ERP is not a signal whose components are deterministically related to the stimulus, but is made up of components that shift significantly in both amplitude and latency from one stimulus application to the next. Using the expressions developed in the paper, it is possible to separate the contributions to the variance due to interference from the ongoing EEG and that inherent in the ERP.  相似文献   
60.
We study arcs of diffeomorphisms (ft) in manifolds of dimension greater than or equal to three bifurcating via non-critical saddle-node cycles. We construct an open set j of such arcs for which, after the bifurcation, every diffeomorphism j does not satisfy Axiom A. We also exhibit an open subset j' of j such that after the bifurcation every diffeomorphism has a partially hyperbolic set of saddle-type which is persistent, locally maximal and transitive. As a consequence, we get a submanifold of codimension-1 of diffeomorphisms with a saddle-node that locally separates the set of Morse-Smale systems from the diffeomorphisms with a partially hyperbolic transitive set.  相似文献   
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