Indirect Sliding Mode Control for DC-DC SEPIC Converters

This article presents an indirect sliding mode control (SMC) for single-ended primary-inductor converters (SEPIC). Unlike the conventional SMC methods, the proposed SMC method employs a sliding surface function based on the input current error only. The use of such sliding surface function not only simplifies the implementation but also reduces the cost of implementation. It is shown that the output voltage control can be achieved indirectly. The input current reference is generated by a proportional-integral (PI) regulator. The existence condition and the region of the closed-loop system are determined for all possibilities of the PI gains. The performance of the proposed SMC method is investigated on a laboratory prototype converter, operated in buck and boost modes, in terms of the voltage regulation ability under abrupt changes in the input voltage and load resistance. Simulation and experimental results are presented and discussed

An Effective Model Predictive Control Method With Self-Balanced Capacitor Voltages for Single-Phase Three-Level Shunt Active Filters

This paper presents an effective model predictive control (MPC) method for single-phase three-level T-type inverter-based shunt active power filters (SAPFs). The SAPF using T-type inverter topology has not been reported in the literature yet. Contrary to most of the existing MPC methods, the proposed MPC method eliminates the need for using weighting factor and additional constraints required for balancing dc capacitor voltages in the cost function. The design of cost function is based on the energy function. Since the factor used in the formulation of the energy function does not have any adverse influence on the performance of the system, the cost function becomes weighting factor free. The weighting factor free based MPC brings simplicity in the practical implementation. The effectiveness of the proposed MPC method has been investigated in steady-state as well as dynamic transients caused by load changes. The theoretical considerations are verified through experimental studies performed on a 3 kVA system

The Real Time Implementation of a Chaotic System’s Synchronization for Secure Communication

The chaotic systems are preferred in secure communication systems as well as used in many different implementation areas. Real time chaos synchronization is also required for secure communication systems. In this study, the Master–Slave synchronization of chaotic Chen system was performed on a real time implementation for the secure communication systems. Active control method was used in the design of controller required for the realization of synchronization. The successful realization of the Master-Slave synchronization of the Chen system by using the controller designed on MATLAB/Simulink was shown by the obtained simulation results. Moreover, by using analogue outputs of NI-DAQ card, the Master-Slave synchronization of the Chen system was obtained and secure communication was achieved on a real time basis under LabVIEW environment

Settling velocity of microplastic particles having regular and irregular shapes

The settling velocities of 66 microplastic particle groups, having both regular (58) and irregular (eight) shapes, are measured experimentally. Regular shapes considered include: spheres, cylinders, disks, square plates, cubes, other cuboids (square and rectangular prisms), tetrahedrons, and fibers. The experiments generally consider Reynolds numbers greater than 102, extending the predominant range covered by previous studies. The present data is combined with an extensive data set from the literature, and the settling velocities are systematically analyzed on a shape-by-shape basis. Novel parameterizations and predictive drag coefficient formulations are developed for both regular and irregular particle shapes, properly accounting for preferential settling orientation. These are shown to be more accurate than the best existing predictive formulation from the literature. The developed method for predicting the settling velocity of irregularly-shaped microplastic particles is demonstrated to be equally well suited for natural sediments in the Appendix

Microplastic retention in marine vegetation canopies under breaking irregular waves

The present study provides indications and underlying drivers of wave-induced transport and retention potential of microplastic particles (MP) in marine vegetation canopies having different densities. The anthropogenic occurrence of MP in coastal waters is well documented in the recent literature. It is acknowledged that coastal vegetation can serve as a sink for MP due to its energy dissipating features, which can mimic a novel ecosystem service. While the transport behavior of MP in vegetation has previously been investigated to some extent for stationary flow conditions, fundamental investigations for unsteady surf zone flow conditions under irregular waves are still lacking. Herein, we demonstrate by means of hydraulic model tests that a vegetation's retention potential of MP in waves increases with the vegetation shoot density, the MP settling velocity and decreasing wave energy. It is found that particles migrating by traction (predominantly in contact with the bed) are trapped in the wake regions around a canopy, whereas suspended particles are able to pass vegetated areas more easily. Very dense canopies can also promote the passage of MP with diameters larger than the plant spacing, as the canopies then show characteristics of a solid sill and avoid particle penetration. The particle migration ability through a marine vegetation canopy is quantified, and the key drivers are described by an empirical expression based on the particle settling velocity, the canopy length and density. The findings of this study may contribute to improved prediction and assessment of MP accumulation hotspots in vegetated coastal areas and, thus, may help in tracing MP sinks. Such knowledge can be considered a prerequisite to develope methods or new technologies to recover plastic pollutants and rehabilitate valuable coastal environments

Experimental investigation on the nearshore transport of buoyant microplastic particles

This paper presents experimental measurements of beaching times for buoyant microplastic particles released, both in the pre-breaking region and within the surf zone. The beaching times are used to quantify cross-shore Lagrangian transport velocities of the microplastics. Prior to breaking the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity, regardless of particle characteristics. In the surf zone the Lagrangian velocities of the microplastics increase and become closer to the wave celerity. Furthermore, it is demonstrated that particles having low Dean numbers (dimensionless fall velocity) are transported at higher mean velocities, as they have a larger tendency to be at the free-surface relative to particles with higher Dean numbers. An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles, valid for both non-breaking and breaking irregular waves. The expression matches the present experiments well, in addition to two prior studies

Role of Adipokines and Hormones of Obesity in Childhood Asthma

Purpose: The aim of this study was to evaluate serum levels of leptin, ghrelin, and adiponectin in obese and non-obese children with asthma and in healthy non-asthmatic children, and analyze their relationships with clinical outcomes. Methods: This study enrolled 40 obese and 51 non-obese children with asthma and 20 healthy children. Body mass index and serum leptin, ghrelin, and adiponectin levels were determined in all children. Asthma symptom scores and lung function test results were recorded for subjects with asthma. Results: Serum leptin levels (11.8 +/- 7.9, 5.3 +/- 6.8, and 2.1 +/- 2.4 ng/mL in the obese asthmatic, non-obese asthmatic, and control groups, respectively) and adiponectin levels (12,586.2 +/- 3,724.1; 18,089.3 +/- 6,452.3; and 20,297.5 +/- 3,680.7 ng/mL, respectively) differed significantly among the groups (P<0.001 for all). Mean ghrelin levels were 196.1 +/- 96.8 and 311.9 +/- 352.8 pg/mL in the obese and non-obese asthmatic groups, respectively, and 348.8 +/- 146.4 pg/mL in the control group (P=0.001). The asthma symptom score was significantly higher in the obese children with asthma than in the non-obese children with asthma (P<0.001). Leptin and adiponectin levels were correlated with the asthma symptom score in non-obese children with asthma (r=0.34 and r=-0.62, respectively). Conclusions: Obesity leads to more severe asthma symptoms in children. Moreover, leptin, adiponectin, and ghrelin may play important roles in the inflammatory pathogenesis of asthma and obesity co-morbidity

Trends in distance education research: A content analysis of journals 2009-2013

This study intends to explore the current trends in the field of distance education research during the period of 2009-2013. The trends were identified by an extensive review of seven peer reviewed scholarly journals: The American Journal of Distance Education (AJDE), Distance Education (DE), The European Journal of Open, Distance and e-Learning (EURODL), The Journal of Distance Education (JDE), The Journal of Online Learning and Technology (JOLT), Open Learning: The Journal of Open, Distance and e-Learning (OL) and The International Review of Research in Open and Distributed Learning (IRRODL). A total of 861 research articles was reviewed. Mainly content analysis was employed to be able to analyze the current research. Also, a social network analysis (SNA) was used to interpret the interrelationship between keywords indicated in these articles. Themes were developed and the content of the articles in the selected journals were coded according to categories derived from earlier studies. The results were interpreted using descriptive analysis (frequencies) and social network analysis. The reporting of the results were organized into the following categories: research areas, theoretical and conceptual frameworks, variables, methods, models, strategies, data collection and analysis methods, and the participants. The study also identified the most commonly used keywords, and the most frequently cited authors and studies in distance education. The findings obtained in this study may be useful in the exploration of potential research areas and identification of neglected areas in the field of distance education