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Number of results: 9
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Abstract

Abstract In this paper, we investigate the global uniform practical exponential stability for a class of uncertain Takagi-Sugeno fuzzy systems. The uncertainties are supposed uniformly to be bounded by some known integrable functions to obtain an exponential convergence toward a neighborhood of the origin. Therefore, we use common quadratic Lyapunov function (CQLF) and parallel distributed compensation (PDC) controller techniques to show the global uniform practical exponential stability of the closed-loop system. Numeric simulations are given to validate the proposed approach.
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Abstract

This work presents a simulation of the response of packets of microbubbles in an ultrasonic pulse-echo scan line. Rayleigh-Plesset equation has been used to predict the echo from numerically obtained radial dynamics of microbubbles. Varying the number of scattering microbubbles on the pulse wave form has been discussed. To improve microbubble-specific imaging at high frequencies, the subharmonic and second harmonic signals from individual microbubbles as well as microbubbles packets were simulated as a function of size and pressure. Two different modes of harmonic generation have been distinguished. The strength and bandwidth of the subharmonic component in the scattering spectrum of microbubbles is greater than that of the second harmonic. The pressure spectra provide quantitative and detailed information on the dynamic behaviour of ultrasound contrast agent microbubbles packet.
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Abstract

In this work, an approach to the design of broadband thickness-mode piezoelectric transducer is pre- sented. In this approach, simulation of discrete time model of the impulse response of matched and backed piezoelectric transducer is used to design high sensitivity, broad bandwidth, and short-duration impulse response transducers. The effect of matching the performance of transmitting and receiving air backed PZT-5A transducer working into water load is studied. The optimum acoustical characteristics of the quarter wavelength matching layers are determined by a compromise between sensitivity and pulse duration. The thickness of bonding layers is smaller than that of the quarter wavelength matching layers so that they do not change the resonance peak significantly. Our calculations show that the −3 dB air backed transducer bandwidth can be improved considerably by using quarter wavelength matching layers. The computer model developed in this work to predict the behavior of multilayer structures driven by a transient waveform agrees well with measured results. Furthermore, the advantage of this this model over other approaches is that the time signal for optimum set of matching layers can be predicted rapidly
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Abstract

Early blight disease caused by Alternaria sp. is one of the most devastating diseases of Solanaceous crops widely distributed in Sudan. The aim of this study was to determine the genetic variation among different Alternaria isolates recovered from different Solanaceae crops showing typical symptoms of early blight disease. Infected leaves of tomato, potato, eggplant and pepper were collected from different geographical zones in Sudan. The recovered fungal isolates were identified to the genus level based on cultural and morphological characteristics. Five representative isolates were sent to the CABI Bioscience, U.K. for confirmation. The genetic relationship among the isolates was determined using the amplified fragments length polymorphism (AFLP) technique and the generated data were used to create similarity matrices using the PAST 3.01 software package. Dendrograms were constructed based on Jaccard’s similarity coefficients. A total of 70 fungal isolates was recovered from the tested plants and all of them showed morphological characteristics typical of Alternaria spp. The conidia appeared in multiple-branched chains with spore sizes in the range of 2.38−13.09 μm × 12.30−43.63 μm. Therefore, the isolates were identified as Alternaria alternata (Fr.) Keissl. The identification was then confirmed by CABI.AFLPbased dendrogram which revealed five clusters with a significant cophenetic correlation coefficient (r = 0.834) between the dendrogram and the original similarity matrix irrespective of their geographical origins. Eighteen (75%) of the Alternaria isolated from tomato leaves were clustered together in cluster I and five isolates formed two separate clusters, viz. cluster IV (T-Kh5 and T-H1) and cluster V (T-H4 and T-Med2). The remaining isolate, T-Am5, grouped with one of the potato isolates in cluster III. The other isolates which were recovered from potato, pepper and eggplants were all separated from the tomato isolates in the largest cluster.
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Abstract

AbstractThis paper covers work intended to study the interplay of sedimentary dynamics and climatic variability over the last two millennia within Tunisia’s sebkha Souassi. Based on the Visual Core Description, and magnetic susceptibility, we date the core from sebkha Souassi to the last two millennia. Genetic grain-size distribution then provided a basis for the identification of six climatic stages, i.e. the Warming Present (WP), the Late Little Ice Age (Late LIA), the Early Little Ice Age (ELIA), the Medieval Climatic Anomaly (MCA), the Dark Ages (DA), and the Roman Warm Period (RWP). The WP stretches across the uppermost 3 cm, with a high grey scale indicating a dry climate. The Late LIA is located between 3 and 7 cm, and the ELIA between 7 and 28 cm. Intermediate values for GS indicate that this stage may be classified as moderate. The MCA spanning from 28 to 40 cm is marked by a sharp decrease in GS indicative of a wet period. The DA appear along the part between 40 and 79 cm, a shift from light to dark sediments being recorded. The RWP in turn appears between 79 and 114 cm. Based on the grain-size distribution, two low-frequency cycles were identified, indicating radical global changes in climatic conditions, differential tectonics and groundwater fluctuations. High-frequency cycles in turn attest to local modifications of climatic conditions.
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