Asymptotic stability, ℓ2 gain,boundness analysis,and control synthesis for switched systems: a switching frequency approach

In this paper, several concepts of switching frequency are introduced to analyze the properties and performance of switched systems in infinite as well as finite‐time intervals. The observation is very motivating that different system properties and performances depend on different switching frequencies. Sufficient conditions ensuring asymptotic stability, ?₂ gain performance, and state boundness are derived on the basis of the notions of switching frequency, respectively. Then, on the basis of the analysis results, the control synthesis problems are addressed. LMI‐based design algorithms are proposed to meet different control synthesis requirements. Numerical design examples are provided to demonstrate our results. Copyright © 2011 John Wiley & Sons, Ltd.     

Palynological investigation of some selected species of family Fabaceae from Pakistan,using light and scanning electron microscopy techniques

Pollen morphology of 11 species of family Fabaceae that is, Trifolium alexandrinum, Trifolium resupinatum, Arachis hypogaea, Lathyrus aphaca, Medicago lupulina, Vicia sativa, Lathyrus odoratus, Pongamia pinnata, Melilotus indicus, Medicago polymorpha, Medicago sativa from Pakistan has been investigated by light and scanning electron microscopy. Pollen were generally tricolporate, radially symmetrical, isopolar, elliptic in equatorial view and triangular in polar view under LM. Results showed that pollens were per‐prolate (T. alexandrinum), prolate (T. resupinatum, V. sativa, L. odoratus, Melilotus indicus, M. polymorpha, M. sativa) and sub‐prolate (A. hypogaea, L. aphaca, M. lupulina, P. pinnata). The larger polar/equatorial (P/E) ratio was found in T. alexandrinum (2.26 μm) and the smallest was found in M. lupulina (1.21 μm). The exine of T. resupinatum was 3.00 μm in thickness while others posses smaller exine thickness. The larger pore diameter was found in P. pinnata (16.01 μm) while others have smaller. The length of colpi was larger in Arachis hypogaea (32.24) while others posses smaller. Eight types of surface ornamentation (Psilate, faintly rugulate). Perforate and rugulate to verrucate have been observed under SEM. The pollens were europalynous type. Pollen morphology proved to be useful for the specific delimitation and serve as a tool for the identification and classification of taxa at specific and generic levels and can also be used as a key for the taxonomic features. Diversity in exine sculpture is helpful indicative characters for the isolation of closely related species. Hence, it is clear that both qualitative and quantitative characters of pollen can be useful for differentiating between taxa at specific level.     

Plasmodium species aware based quantification of malaria parasitemia in light microscopy thin blood smear

Malaria is a serious worldwide disease, caused by a bite of a female Anopheles mosquito. The parasite transferred into complex life round in which it is grown and reproduces into the human body. The detection and recognition of Plasmodium species are possible and efficient through a process called staining (Giemsa). The staining process slightly colorizes the red blood cells (RBCs) but highlights Plasmodium parasites, white blood cells and artifacts. Giemsa stains nuclei, chromatin in blue tone and RBCs in pink color. It has been reported in numerous studies that manual microscopy is not a trustworthy screening technique when performed by nonexperts. Malaria parasites host in RBCs when it enters the bloodstream. This paper presents segmentation of Plasmodium parasite from the thin blood smear points on region growing and dynamic convolution based filtering algorithm. After segmentation, malaria parasite classified into four Plasmodium species: Plasmodium falciparum, Plasmodium ovale, Plasmodium vivax, and Plasmodium malaria. The random forest and K‐nearest neighbor are used for classification base on local binary pattern and hue saturation value features. The sensitivity for malaria parasitemia (MP) is 96.75% on training and testing of the proposed approach while specificity is 94.59%. Beside these, the comparisons of the two features are added to the proposed work for classification having sensitivity is 83.60% while having specificity is 94.90% through random forest classifier based on local binary pattern feature.     

Glass fibers with clay nanocomposite coating: Improved barrier resistance in alkaline environment

Coatings made from neat vinyl ester and nanoclay reinforced vinyl ester composites are applied onto individual glass fibers as well as rovings to evaluate their barrier resistance against alkali and moisture attack. The fibers coated with clay nanocomposites present a significantly less damage caused by the diffusing alkali ions, giving rise to a much higher residual tensile strength after aging than the fibers without coating or those with a neat polymer coating. The static fatigue test performed on individual fibers verifies the advantage of using nanoclay composite to retard the corrosion process under the combined stress and alkaline environment. Similar beneficial effects of incorporating nanoclay on residual strength are identified for impregnated fiber bundles. The above observations confirm the excellent barrier characteristics of intercalated/exfoliated nanoclay in polymer that are applied in composite structures on both the microscopic and macroscopic scales.     

Structural stability of silver under single-chamber solid oxide fuel cell conditions

In the present study, structural stability of silver under single-chamber conditions has been examined. Micro-tubular cells made of conventional solid oxide fuel cell materials (Ni-YSZ/YSZ/LSM) with silver paste and silver current-collecting wires (for both electrodes) were prepared. The cells were operated with methane/air mixture of 25/60 mL min⁻¹, furnace temperature of 750 °C, and at an operating voltage of 0.5 V. The results showed increasing porosity in the current-collecting silver wire with time, leading to rupture, finally. It is postulated that the porosity formation could be due to the formation of silver oxide which is highly unstable (volatile) at operating temperature considered in this study. Furthermore, vaporization and melting of silver due to cell overheating under mixed-reactant conditions is expected. Based on experimental evidences, it is concluded that silver may not be a good choice to be employed under the above specified operating conditions, as it lacks long-term structural stability.     

Tailoring of chiroptical properties of substituted polyanilines by controlling steric hindrance

Optically active polyorthoanisidine, polyorthotoluidine, polyorthoethylaniline and polyorthochloroaniline were synthesized with chemical polymerization of corresponding monomers in aqueous medium by using d- or l-camphorsulfonic acid (d- or l-CSA) as chiral dopant, ammonium persulfate as oxidant, and diaminodiphenylamine as initiator. By circular dichroism spectroscopic measurements, it was found that PANI exhibited generally a reversed chirality in comparison with the used chiral dopant, but the substituted PANIs had the same one as the chiral dopant. This revealed that the substituent at ortho position caused helical inversion of conformation in comparison with the parent PANI. Such effect was further confirmed by the influence of the copolymerization of aniline and its derivatives on the chirality of the copolymers. The effect of the substituent on the chirality of the copolymers was increased with the increase of the steric hindrance of the ortho substituent. A mechanism was proposed to explain the effects of steric hindrance on the chirality of PANIs. The clarified relationship between the steric hindrance and the chirality of the polymer can enable us to tailor the chiroptical properties of functional polymer materials for future application.     

Economic production quantity model with a shifting production rate

Typical models for determining the economic production quantity (EPQ) assume perfect product quality and perfect production processes. Deteriorating processes may affect production systems in several ways. They may decrease the quality of the items produced, cause production stoppage and breakdowns and/or reduce the production rate due to production process inefficiency. The purpose of this paper is to present an EPQ model that incorporates the effect of shifts in production rate on lot sizing decisions due to speed losses. The cycle starts with a certain production rate and after a random time, the production rate shifts to a lower value. A mathematical model to determine the optimal production policy under these conditions is developed and analyzed. Numerical examples are presented for illustrative purposes.     

Compressive sensing based high-resolution passive bistatic radar

Passive bistatic radar (PBR) systems using different communication signals can only offer low-resolution target detection due to their inherent low bandwidth. In this paper, compressive sensing (CS) is applied to multichannel FM and GSM PBR to achieve improved range-Doppler resolutions and avoid some limitations of classical multiband PBR processing. In CS context, block-structured time-domain dictionary which is formed from multichannel signals suffers from coherence when fine range resolution is employed. To overcome such a pitfall, this work first transforms the dictionary to spectral domain where only the most important spectral components are retained. Principle component analysis followed by a whitening method are then applied to this spectrally transformed data in order to reduce the dimensionality of problem, thereby reducing the dictionary size and most importantly fulfilling the required condition of dictionary incoherence for better CS-based recovery. Two different block-structured dictionary formations are tested. The performance of the recovery of spatially close targets, in both FM and GSM PBR setups, are reported.