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This article presents a new three-phase five-level converter topology with a single dc source. The proposed topology combines the features of the conventional flying capacitor multicell and diode-clamped multilevel topologies. An important advantage of the proposed topology is the reduced volt-ampere, and hence, the volume, of the flying capacitors in its structure while keeping the same voltage blocking capability for semiconductor switches. The appropriate modulation strategy along with the flying capacitor voltage balancing technique is presented. To show the advantages of the proposed converter, different performance criteria such as switch count and rating, volt-ampere of flying capacitors, component cost, losses, and switching frequency are compared with some existing five-level topologies with a single dc source and the same voltage rating of switches. The results indicate that the proposed structure is superior to other five-level converters from different standpoints of the performance criteria. Simulation results are shown to verify the converter operation and its performance. The validity of the theoretical analysis is verified by experimentation on a scaled-down prototype system. [ABSTRACT FROM AUTHOR]

BACKGROUND Potentiometric detections based on ion‐selective electrodes offer the advantages of simplicity, speed, and low cost over other electrochemical methods. In this work, the preparation of a novel carbon‐paste electrochemical sensor containing the synthesized N‐(1‐(4‐bromophenyl)‐3‐oxo‐3‐phenylpropyl)acetamide is described. Multi‐walled carbon nanotubes (MWCNTs) were incorporated into the electrode composition to promote electron transfer reactions. The modified carbon paste electrode was evaluated as a selective sensor for the detection of chromium (III). RESULTS: The prepared sensor showed nearly stable potentials in the pH range of 4.0–6.5, with a fast response time (<15 s). At the optimum conditions, the potentiometric method exhibited a linear response toward Cr(III) concentration in the range of 5.0 × 10−7 to 1.0 × 10−3 mol L−1 with a Nernstian slope of 19.5 ± 0.1 mV per decade and a detection limit of 3.1 × 10−7 mol L−1. CONCLUSION: The proposed sensor possesses the advantages of good selectivity to Cr(III) and an improved detection limit compared to the results of some other studies. Better selectivity can be attributed to the ability of the ionophore to form a stable chelate with Cr(III) ions. The new Cr(III) sensor showed excellent stability over 8 weeks and its response time was comparable to other previously reported chromium ion‐selective electrodes (ISEs). The simple, fast, and cheap synthesis method of ionophore provided other advantages for this study. The modified electrode was also used as a sensor for the end‐point detection in the potentiometric titration of Cr(III) against ethylenediaminetetra acetic acid (EDTA). © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Multisource inverters (MSIs) as a new approach for the integration of the energy and the power sources in electric vehicle applications have gained considerable attraction. Such structures offer the active control of the dc sources without using any dc/dc converters or magnetic elements, which reduces the weight, and the volume of the power electronics interface between the sources and the load. Moreover, high power density and improved efficiency due to the elimination of the magnetics are the other significant features of an MSI. This article proposes a novel three-phase MSI for integration and active control of a high-voltage dc source and a low-voltage dc source. The proposed MSI structure employs a smaller number of semiconductor devices at the current path in various operating modes in comparison to the previously published counterparts, which results in an improved efficiency operation. Performance of the proposed MSI using a modified space vector modulation technique for all possible operating modes is verified through simulations and experiments on a laboratory prototype [ABSTRACT FROM AUTHOR]

The space vector modulation (SVM) scheme is popularly implemented in multilevel converters. However, in flying capacitor-based (FC-based) multilevel converters, it becomes extremely challenging to implement due to the redundancy in phase voltage levels. The intrinsic property of line voltage redundancy of SVM in addition to the phase voltage redundancy of FC-based converters results in considerably increased computational complexity and storage requirements. In fact, one of the most important concerns about FC-based converters is the voltage control of the FCs. This article proposes a generalized decoupled SVM scheme for the FC-based multilevel converters, including the classic flying capacitor multicell (FCM) converters, which is less computationally complex. For balancing the FC voltages, an overall priority index is employed to determine the switching state with the best balancing characteristics. The proposed decoupled SVM scheme along with the capacitor voltage balancing scheme can be implemented intuitively and simply for all FC-based multilevel converters. The simulation results of a five-level FCM converter show the effectiveness of the proposed method in the regulation of FC voltages. Moreover, the proposed voltage balancing method is robust to static load and transient conditions. Also, experimental results demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes a four-level single flying capacitor converter (4L-SFCC) topology along with a new modulation technique. The proposed four-level single flying capacitor converter (4L-SFCC) topology has only one flying capacitor in each phase. This results in no redundant switching states associated with each voltage levels, and thus conventional modulation techniques cannot fulfill the capacitor voltage balancing requirement. Therefore, a new modulation technique is also proposed in this article in which the average capacitor current is set to zero during each sampling time, resulting in no net capacitor voltage change and hence voltage balancing during each sampling period. The proposed modulation scheme does not significantly increase the switching frequency and has equal switching frequency for all semiconductor switches, which is an advantage in terms of equalized switching losses. Simulation results are used to further evaluate the performance of the proposed converter. A laboratory-type experimental setup is used to validate the theoretical results. [ABSTRACT FROM AUTHOR]

This article presents a simple yet effective capacitor voltage balancing method for a five-level nested neutral point clamped (NNPC) converter. The NNPC has been recently developed for medium-voltage high-power applications and has interesting features. This hybrid topology has three flying capacitors in each leg. Like other flying capacitor-based topologies, it is necessary to regulate and balance the voltage of the flying capacitors in an NNPC converter to certain values. In this article, a new approach is proposed to accomplish this task. The proposed regulation technique employs line current direction and voltage deviation of flying capacitors to achieve regulation. The charging/discharging status of flying capacitors with respect to different switching states is used to define a priority index. This index is eventually used to select the proper switching state. A detailed investigation is presented to determine the best switching state for each level of the output voltage. The proposed method does not need any cost function and is very intuitive and simple to implement. Using simulations, the amplitude of the flying capacitor voltage ripple is measured, which shows reduction under all operating conditions. The feasibility and performance of the proposed method are confirmed by using a laboratory-type experimental setup. [ABSTRACT FROM AUTHOR]

Several fundamental problems that arise in optimization and computer science can be cast as follows: Given vectors v1, . . ., vm È Rd and a constraint family B \subseteq 2[m], find a set S ÈB that maximizes the squared volume of the simplex spanned by the vectors in S. A motivating example is the ubiquitous data-summarization problem in machine learning and information retrieval where one is given a collection of feature vectors that represent data such as documents or images. The volume of a collection of vectors is used as a measure of their diversity, and partition or matroid constraints over [m] are imposed in order to ensure resource or fairness constraints. Even with a simple cardinality constraint (B = ([m] r), the problem becomes NP-hard and has received much attention starting with a result by Khachiyan [J. Complexity, 11 (1995) pp. 138--153] who gave an rO(r) approximation algorithm for a special case of this problem. Recently, Nikolov and Singh [Proceedings of the Forty-eighth Annual ACM Symposium on Theory of Computing, 2016, pp. 192-- 201] presented a convex program and showed how it can be used to estimate the value of the most diverse set when there are multiple cardinality constraints (i.e., when \scrB corresponds to a partition matroid). Their proof of the integrality gap of the convex program relied on an inequality by Gurvits [Proceedings of the Thirty-eighth Annual ACM Symposium on Theory of Computing, ACM, 2006, pp. 417--426], and was recently extended to regular matroids [Straszak and Vishnoi, Proceedings of the Forty-ninth ACM SIGACT Symposium on Theory of Computing, 2017, pp. 370--383] and [Anaris and Gharan, Proceedings of the Forty-ninth Annual SIGACT Symposium on Theory of Computing, 2017, pp. 384--396] and general matroids [Anari, Gharan, and Vinzant, Proceedings of the Fifty-ninth IEEE Annual Symposium on Foundations of Computer Science, 2018, pp. 35-- 46]. The question of whether these estimation algorithms can be converted into the more useful approximation algorithms--that also output a set--remained open. The main contribution of this paper is to give the first approximation algorithms for both partition and regular matroids. We present novel formulations for the subdeterminant maximization problem, for these matroids; this reduces them to the problem of finding a point that maximizes the absolute value of a nonconvex function over a Cartesian product of probability simplices. The technical core of our results is a new anti-concentration inequality for dependent random variables that arise from these functions, which allows us to relate the optimal value of these nonconvex functions to their value at a random point. Unlike prior work on the constrained subdeterminant maximization problem, our proofs do not rely on real-stability or convexity and could be of independent interest both in algorithms and complexity where anti-concentration phenomena have recently been deployed. [ABSTRACT FROM AUTHOR]

This paper is treated with optimum energy management in a DC/AC Microgrid (MG) containing hybrid power sources to supply the load within cost minimization. In this hybrid electrical networks, energy sources are exploited as DC and AC manner, in which the Independent System Operator (ISO) should provide a practical coordination between them in order to procure the demand load optimally. This paper presents a framework that all available resources are formulated mathematically in hybrid microgrid with full constraints along with Demand Response (DR) programs implementation. The network under consideration can operate both in grid-tied and autonomous modes to manage power exchanging. Uncertainty and intermittent of Photovoltaic (PV) with Maximum Power Point Tracker (MPPT) equipped, Wind Turbine (WT), Energy Storage Systems (ESS) and DR programs are also considered to achieve the optimal control and operation. The ESSs are capable to connect both DC and AC links and the State of Charge (SOC) is maintained within permissible range. The proposed DG control framework and operation scheduling has facilitated the energy management of renewables using dynamic programing approach. A 24-hour time horizon simulation and discussion through three scenarios verified on a IEEE 33 bus distribution network, is done to represent the effectiveness of proposed energy management strategy to keep the whole hybrid grid stable. [ABSTRACT FROM AUTHOR]

This paper presents a generalized topology for multilevel converters based on flying capacitor multicell structure. The proposed topology consists of two modular high-frequency (HF) and low-frequency (LF) sections or cells. The HF cells consist of flying capacitors and semiconductor switches operating at carrier frequency. The LF cells consist of dc sources and semiconductor switches operating at line frequency and its multiples. The proposed topology can be implemented with arbitrary number HF and LF cells. An important advantage of the proposed topology is its reduced components when compared to other multilevel converter topologies in the same family. Another interesting feature is the relatively low blocking voltage requirement for HF switches, making it an attractive choice for high-power applications. A modulating algorithm is devised to generate the gating pulses for the HF and LF cells using phase-shifted carrier-based pulsewidth modulation. As a particular case, the operation of a 25-level topology is explained by the help of illustrating waveforms. A comprehensive comparative study is presented to illustrate the advantages of the proposed topology in terms of the number of components and other performance criteria. Various simulations are carried out to verify the operation of the proposed topology at different operating conditions. The theoretical analysis is experimentally verified using a scaled-down laboratory setup. [ABSTRACT FROM AUTHOR]

This paper presents a new six-level flying capacitor based (FC-based) multilevel converter with one dc source and the capability of operating in all power factors and modulation indexes. Multilevel converters with one dc voltage source are attractive in many applications as they do not need rather expensive and bulky multiwinding input transformer connection at the dc side. On the other hand, not all classic multilevel converters with one dc source can produce any desirable number of output voltage levels at all power factors and/or modulation indexes. In this paper, a hybrid structure is proposed in which six voltage levels can be realized at the ac terminals. The modulation technique and the control strategy for the FC voltage balancing are presented. To show the advantages of the proposed converter, different performance criteria, such as switch count and rating, the size of capacitors, switching frequency, and power losses, are compared with other existing six-level topologies. The results indicate that the proposed structure is superior to other six-level converters from different standpoints. Simulation results are used to further evaluate the performance of the proposed converter. A laboratory-type experimental setup is used to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Theoretical investigations based on density functional theory have been carried out to understand the underlying interactions between the chitosan monomer and several types of hexagonal monolayers consisting of pristine and defected graphene and boron-nitride nanosheets. Based on the obtained results, it was found that the type of the interaction for all the systems is of non-covalent nature and the chitosan monomer physically interacts with the surface of mentioned nanostructures. The interaction strength was evaluated by calculating the adsorption energies for the considered systems and it was found that the adsorption of chitosan monomer accompanies by the release of about −0.67 and −0.66 eV energy for pristine graphene and h-BN monolayer, respectively. The role of structural defect has also been considered by embedding a Stone-Wales defect within the structure of mentioned monolayers and it was found that the introduced defect enhances the interactions between the chitosan monomer and nanostructures. The role of dispersion interactions has also been taken into account and it was found that these long-range interactions play the dominating role in the attachment of chitosan monomer onto the graphene sheet, while having strong contribution together with the electrostatic interactions for the stabilization of chitosan onto the surface of h-BN monolayer. For all the cases, the adsorption of chitosan monomer did not change the inherent electronic properties of the nanostructures based on the results of charge transfer analysis and energy gap calculations. The findings of the present work would be very useful in future investigations to explore the potential applications of these hybrid materials in materials science and bio-related fields. [ABSTRACT FROM AUTHOR]

This paper presents a new multicell topology based on flying capacitor (FC) structure suitable for multilevel converters. The proposed topology employs the concept of phase-shifted carrier pulse width modulation (PWM) with modified modulating signals to generate appropriate PWM signals. The modulation strategy along with all possible switching states are explained. The implementation of the proposed PWM technique is shown by the help of illustrating waveforms. To show the advantages of the proposed structure, different performance criteria are compared with other FC multicell (FCM) structures. Simulation results are used to further evaluate the potential merits of the proposed topology. It is shown that the proposed structure is superior to other FCM-based structures from different standpoints. Specifically, it reduces the number of high-frequency switches, the number of FCs, and at the same time improves the quality of output voltage. A laboratory-type experimental setup is used to validate the modulation strategy and other theoretical findings. [ABSTRACT FROM AUTHOR]

The article focuses on the discovery and improvement of multi-component reactions (MCRs) with recyclable catalysts. Topics include the economic and environmental importance of the design and preparation of recyclable catalysts, the production of magnetic nanoparticles, and the availability of fourteen acidic hydro-gens, high thermal stability and high hydrolytic stability found in Preyssler heteropoly acid.

A dichloromethane membrane system incorporated with benzyl bis(thiosemicarbazone)(LH2)as carrier is introduced for the selective transport of Cu(II) ion from an aqueous source solution containing Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Pb(II) metal cations to a receiving aqueous phase. The optimum transport conditions were established by studding the composition of receiving phase, time of transport, stirring rate, pH of source phase, presence of fatty acid in the membrane as a phase modifier, type and concentration of surfactant, and concentration of mineral acid in the receiving phase, carrier concentration, and temperature. A kinetic model was also used to describe the Cu(II) ion transport behavior, assuming that it obeys the kinetic laws of two consecutive irreversible first-order processes. Under the optimal conditions, 43% of the initial concentration of Cu(II) ion from the aqueous source phase was extracted into the receiving phase through the bulk liquid membrane. [ABSTRACT FROM AUTHOR]

The capacity for multiterminal secret-key agreement inspires a natural generalization of Shannon’s mutual information from two random variables to multiple random variables. Under a general source model without helpers, the capacity is shown to be equal to the normalized divergence from the joint distribution of the random sources to the product of marginal distributions minimized over partitions of the random sources. The mathematical underpinnings are the works on co-intersecting submodular functions and the principle lattices of partitions of the Dilworth truncation. We clarify the connection to these works and enrich them with information-theoretic interpretations and properties that are useful in solving other related problems in information theory as well as machine learning. [ABSTRACT FROM AUTHOR]

For the first time, a new water stable Brønsted acidic ionic liquid based on Keggin heteroployacid (HPA) was used as environmentally benign catalytic medium in the esterfication of salicylic acid with aliphatic alcohols, CnH2n+1OH (n = 1-5) and benzylic alcohols, RC6H4CH2OH (R = H, NO2, OCH3). This ionic liquid (IL) afforded excellent yield in both thermal conditions and microwave irradiation. Maximum yields were observed under microwave irradiation. Different reaction runs were conducted by varying the reaction parameters such as molar ratio of reactants, weight of the IL, and reaction period in order to optimize the reaction. The IL was easily recovered and reused many times. No significant loss in catalytic activity was observed on recycling. [ABSTRACT FROM AUTHOR]

A long-standing open question in information theory is to characterize the unicast capacity of a wireless relay network. The difficulty arises due to the complex signal interactions induced in the network, since the wireless channel inherently broadcasts the signals and there is interference among transmissions. Recently, Avestimehr et al. [2007b] proposed a linear deterministic model that takes into account the shared nature of wireless channels, focusing on the signal interactions rather than the background noise. They generalized the min-cut max-flow theorem for graphs to networks of deterministic channels and proved that the capacity can be achieved using information theoretical tools. They showed that the value of the minimum cut is in this case the minimum rank of all the adjacency matrices describing source-destination cuts. In this article, we develop a polynomial-time algorithm that discovers the relay encoding strategy to achieve the min-cut value in linear deterministic (wireless) networks, for the case of a unicast connection. Our algorithm crucially uses a notion of linear independence between channels to calculate the capacity in polynomial time. Moreover, we can achieve the capacity by using very simple one-symbol processing at the intermediate nodes, thereby constructively yielding finite-length strategies that achieve the unicast capacity of the linear deterministic (wireless) relay network. [ABSTRACT FROM AUTHOR]

In this paper, a new topology for cascaded multilevel converter based on submultilevel converter units and full-bridge converters is proposed. The proposed topology significantly reduces the number of dc voltage sources, switches, IGBTs, and power diodes as the number of output voltage levels increases. Also, an algorithm to determine dc voltage sources magnitudes is proposed. To synthesize maximum levels at the output voltage, the proposed topology is optimized for various objectives, such as the minimization of the number of switches, gate driver circuits and capacitors, and blocking voltage on switches. The analytical analyses of the power losses of the proposed converter are also presented. The operation and performance of the proposed multilevel converter have been evaluated with the experimental results of a single-phase 125-level prototype converter. [ABSTRACT FROM PUBLISHER]

A new evolutionary algorithm known as the shuffled frog leaping algorithm is presented in this paper, to solve the unit commitment (UC) problem. This integer-coded algorithm has been developed to minimize the total energy dispatch cost over the scheduling horizon while all of the constraints should be satisfied. In addition, minimum up/down-time constraints have been directly coded not using the penalty function method. The proposed algorithm has been applied to ten up to 100 generating units, considering one-day and seven-day scheduling periods. The most important merit of the proposed method is its high convergence speed. The simulation results of the proposed algorithm have been compared with the results of algorithms such as Lagrangian relaxation, genetic algorithm, particle swarm optimization, and bacterial foraging. The comparison results testify to the efficiency of the proposed method. [ABSTRACT FROM PUBLISHER]

We develop new algebraic algorithms for scalar and vector network coding. In vector network coding, the source multicasts information by transmitting vectors of length L, while intermediate nodes process and combine their incoming packets by multiplying them with L\,\times\,L coding matrices that play a similar role as coding coefficients in scalar coding. We start our work by extending the algebraic framework developed for multicasting over graphs by Koetter and Medard to include operations over matrices; we build on this generalized framework, to provide a new approach for both scalar and vector code design which attempts to minimize the employed field size and employed vector length, while selecting the coding operations. Our algorithms also lead as a special case to network code designs that employ structured matrices. [ABSTRACT FROM AUTHOR]

Optimal power sharing between parallel inverters and the demand load in microgrids is challenging and particularly critical for power grids in islanding operation. This paper introduces a novel control approach for managing parallel distributed power sources in the presence of variable load in islanding regime. The proposed scheme is based on the modified sliding mode control (MSMC) which is combined with the optimal Riccati control method to achieve convergence at the slip level with higher accuracy. The mathematical principles of the network equations are derived and its stability is obtained using the Lyapunov function. The MSMC simulation results are discussed in relation to the conventional droop method, while the laboratory evaluation was carried out to characterize its dynamic and static response. The results show that the proposed scheme control is able to manage the distributed power generation for static and dynamic load scenarios, and as such, guarantying microgrid frequency stability. [ABSTRACT FROM AUTHOR]

Biologically active substituted dihydropyrano[2,3-c]pyrazole derivatives (IV) are obtained by a simple, green, and efficient four-component reaction of various benzaldehydes (II), ethyl acetoacetate (I), malononitrile (III), and hydrazine hydrate using an acidic ionic liquid as catalyst. [ABSTRACT FROM AUTHOR]

In this paper, we use generalized incremental predictive control (GIPC) to stabilize attitude of satellite. We compare Generalized Predictive Control (GPC) with GIPC algorithm and present that GIPC has better performance. The three-axis attitude control systems are activated in pulse mode. Consequently, a modulation of the torque command is compelling in order to avoid high non-linear control action. This work considers the Pulse-Width Pulse-Frequency modulator (PWPF) is composed of a Schmitt trigger, a first order filter, and a feedback loop. PWPF modulator has several advantages over classical bang-bang controllers such as close to linear operation, high accuracy, and reduced propellant consumption. [ABSTRACT FROM AUTHOR]

A new procedure is presented for the determination of low concentrations of lead and cadmium in water samples. Ligand assisted pseudo-stir bar hollow fiber solid/liquid phase microextraction using sol-gel sorbent reinforced with carbon nanotubes was combined with differential pulse anodic stripping voltammetry for simultaneous determination of cadmium and lead in tap water, and Darongar river water samples. In the present work, differential pulse anodic stripping voltammetry (DPASV) using a hanging mercury drop electrode (HMDE) was used in order to determine the ultra trace level of lead and cadmium ions in real samples. This method is based on accumulation of lead and cadmium ions on the electrode using different ligands; Quinolin-8-ol, 5,7-diiodo quinoline-8-ol, 4,5-diphenyl-1H-imidazole-2(3H)-one and 2-{[2-(2-Hydroxy-ethylamino)-ethylamino]-methyl}-phenol as the complexing agent. The optimized conditions were obtained. The relationship between the peak current versus concentration was linear over the range of 0.05-500 ng mL(-1) for Cd (II) and Pb (II). The limits of detection for lead and cadmium were 0.015 ng mL(-1) and 0.012 ng mL(-1), respectively. Under the optimized conditions, the pre-concentration factors are 2440 and 3710 for Cd (II) and Pb (II) in 5 mL of water sample, respectively.