Adaptive Fault Tolerant Control of Multi-time-scale Singularly Perturbed Systems

This paper studies the fault tolerant control, adaptive approach, for linear time-invariant two-time-scale and three-time-scale singularly perturbed systems in presence of actuator faults and external disturbances. First, the full order system will be controlled using ε-dependent control law. The corresponding Lyapunov equation is ill-conditioned due to the presence of slow and fast phenomena. Secondly, a time-scale decomposition of the Lyapunov equation is carried out using singular perturbation method to avoid the numerical stiffness. A composite control law based on local controllers of the slow and fast subsystems is also used to make the control law ε-independent. The designed fault tolerant control guarantees the robust stability of the global closed-loop singularly perturbed system despite loss of effectiveness of actuators. The stability is proved based on the Lyapunov stability theory in the case where the singular perturbation parameter is sufficiently small. A numerical example is provided to illustrate the proposed method.     

Intelligent Open Switch Fault Detection for Power Converter in Wind Energy System

This paper proposes a simple and fast fuzzy logic-based open switch fault detection method for rotor side converter (RSC) in doubly fed induction generator (DFIG) wind turbine system. In the proposed scheme, only the mean values of the three-phase rotor currents are used to identify the power switch in which the open-circuit fault has occurred.

The wind energy conversion system model developed for the design and evaluation of the proposed fault detection technique including three principal controls. the first control ensure the regulation of the electromagnetic torque and the reactive stator power (named Rotor Side Converter (RSC) control), the second regulates the DC-link voltage at the desired level (named Grid Side Converter (GSC) control) and in order to achieve maximum power at any wind speed condition a maximum power point tracking (MPPT) control strategy has been used. The simulation model was developed in MATLAB/Simulink environment. The results show that the proposed fault detection scheme is able to rapidly and effectively identify open switch faults among other fault types in a time less than one period.     

Reusable knowledge in security requirements engineering: a systematic mapping study

Security is a concern that must be taken into consideration starting from the early stages of system development. Over the last two decades, researchers and engineers have developed a considerable number of methods for security requirements engineering. Some of them rely on the (re)use of security knowledge. Despite some existing surveys about security requirements engineering, there is not yet any reference for researchers and practitioners that presents in a systematic way the existing proposals, techniques, and tools related to security knowledge reuse in security requirements engineering. The aim of this paper is to fill this gap by looking into drawing a picture of the literature on knowledge and reuse in security requirements engineering. The questions we address are related to methods, techniques, modeling frameworks, and tools for and by reuse in security requirements engineering. We address these questions through a systematic mapping study. The mapping study was a literature review conducted with the goal of identifying, analyzing, and categorizing state-of-the-art research on our topic. This mapping study analyzes more than thirty approaches, covering 20 years of research in security requirements engineering. The contributions can be summarized as follows: (1) A framework was defined for analyzing and comparing the different proposals as well as categorizing future contributions related to knowledge reuse and security requirements engineering; (2) the different forms of knowledge representation and reuse were identified; and (3) previous surveys were updated. We conclude that most methods should introduce more reusable knowledge to manage security requirements.     

Fast mode decision algorithm for H.264/SVC enhancement layer

Scalable video coding (SVC) has been standardized to extend the capabilities of the H.264 advanced video coding (AVC). The SVC can compress several video sequences of various resolutions as a single bit-stream. In the SVC enhancement layer, for Joint Scalable Video Model (JSVM) software implementation, an exhaustive mode decision process based on the base layer mode predictions is performed to obtain the best mode for each macroblock (MB). This technique may achieve a higher coding efficiency; however, it induces a significant computational complexity in the encoding engine. In order to speedup the SVC encoder, a fast mode decision algorithm was proposed in this paper. In other words, our aim was to decrease the number of candidate modes to reduce the computational complexity and maintain the same level of coding efficiency, this approach used the spatial and temporal correlation between MB situated at the enhancement layer and its co-located MB at the base layer. Our statistical analyses were made using several HD sequences with different motion characteristics. Experimental results show a significant improvement in terms of time encoding which is a major constraint for any real-time implementation. However, this gain is accompanied with an acceptable loss in video quality and a tolerable bit rate increase for most media supports. In fact, our proposed algorithm permits a major improvement that can reach up to 64.9 % in terms of computational effort. This gain will induce an average loss yield to 10.5 or 13.87 % that is comparable to the 13.12 % of the He Li’s algorithm with an acceptable loss in terms of subjective video quality.     

Home ownership policy in Singapore: An assessment

Since independence in 1965, housing conditions in the city‐state of Singapore, with a population of 2.6 million in 1988, have improved considerably. Much of the credit for this must be attributed to the government's policy of building homes for the lower income groups. One objective of the housing policy is 100 per cent home ownership for public housing. In pursuing this policy the political and social aspects are often emphasised. This paper attempts an economic evaluation of the 100 per cent home ownership target. It examines the demand and supply side policies that are employed to achieve the target. In analysing the economic implications of the policy, it is observed that such a policy distorts household expenditure, leads to overconsumption of housing and results in a thinner rental market and constrains tenure choice. These economic losses need to be recognised even while accepting the political and social importance of the policy.     

Some hydrolases in human schistosomiasis with special reference to arylsulfatase B

Among many tested enzymes, lipase was found to be the one most affected by schistosomiasis in human serum, where it is increased eightfold. Arylsulfatases A and B and aspartyl protease displayed a significant decrease in the serum, while other enzymes showed a significant increase. α‐Amylase and Leucine aminopeptidase were significantly increased and arylsulfatase B showed a significant decrease. Arylsulfatase B from a patient's leucocytes did not show either changed kinetic behaviour or temperature‐dependent conformational changes. These results indicate that the diminished activity of this enzyme may be attributed to an opposing mechanism of regulation.     

First-Principles Study of Lattice Dynamics and Thermal Properties of Alkaline-Earth Metal Nitrides CaN,SrN, and BaN

We have performed first-principles calculations to investigate the structural, electronic, magnetic, lattice dynamics, and thermodynamic properties of ferromagnetic alkaline earth metal nitrides CaN, SrN, and BaN in the rocksalt structure using the plane-wave pseudopotential approach to the density functional theory within local density and generalized gradient approximations for the exchange and correlation potential. The linear response to the density functional theory allowed us to calculate the phonon dispersion spectra for these compounds. We reported also the results on thermodynamic properties as a function of temperature calculated by using the quasiharmonic approximation.     

Chemical composition and antimicrobial activity of the essential oils from four Ruta species growing in Algeria

Antimicrobial properties of plants essential oils have been investigated in order to suggest them as potential tools to overcome the microbial drug resistance and the increasing incidence of food borne diseases problems. The aim of this research is to study the antibacterial and antifungal effects of four traditional plants essential oils, Ruta angustifolia, Ruta chalepensis, Ruta graveolens and Ruta tuberculata, against standard bacterial and fungal strains. The chemical compounds of the oils were examined by GC/MS. Results revealed a powerful antifungal activity against filamentous fungi. Aspergillus fumigatus and Cladosporium herbarum are the most sensitive strains to these oils with MIC values less than 3.5 μg ml⁻¹ for certain oils, reaching 7.8 μg ml⁻¹ for other. GC/MS essay exhibited ketones as the most abundant constituent of these oils except for R. tuberculata essential oil which has a completely different composition, monoterpenes alcohols being the most abundant. These compositions explain their potential antifungal activity.