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This paper presents a method for the control design of five-level DCC converters based on mixed-integer optimization and machine learning. The resulting controller is computationally simple and can be easily implemented on low-resource control hardware using simple nested "if-else" statements. The optimization problem is recalled from previous work by modifying the cost function to further enhance the dynamic performance. Additionally, and in contrast to previous works, the online implementation accomplished in this paper allows the system to cover a wider range of operating points. For this, the optimization problem is solved offline for several operating conditions, and the results are gathered into a dataset to train classification and regression trees (CARTs), which are later used online. Due to the generalization capability of the CARTs, a more flexible and less resource-intensive implementation is achieved which is capable of operating at points outside the ones considered in the training dataset. The resulting control strategy is compared in simulation and experiments with several alternative approaches found in the literature. This approach can be extended to other power converter topologies, allowing the implementation of optimized modulations. • Modulation of five-level DCC as a mixed-integer optimization problem. • Achievement of wider range of operating points. • Classification and regression trees used for implementation of optimization problem. • Guidelines for robust implementation of such tress. • In-detail comparison with existing approaches both in simulation and experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Small Ni 1−x Mn x Co 2 O 4 nanoparticles were synthesized by low-temperature gel combustion. • All the nanoparticles revealed strong catalytic performance in 4-nitrophenol reduction. • The catalytic performance of Ni 0.5 Mn 0.5 Co 2 O 4 nanoparticles was superior to NiCo 2 O 4 and MnCo 2 O 4 nanoparticles. • >90 % of 4-nitrophenol could be reduced in 12 min. • The anomalous catalytic behaviors of the nanostructures in repeated cycles were explained. Developing efficient catalysts is one of the challenging tasks for protecting our environment from contamination. Here we present the synthesis of Ni 1−x Mn x Co 2 O 4 , noble-metal free multimetallic oxide nanoparticles of 9.5–25.0 nm average sizes by a low-temperature gel combustion method and their utilization as catalysts for rapid reduction of 4-nitrophenol (4-NP) to aminophenol (AP). Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and vibrating sample magnetometry were used for the characterization of the nanostructures. All the nanostructures revealed strong catalytic performance in the reduction of 4-NP, and the performance of Ni 0.5 Mn 0.5 Co 2 O 4 nanoparticles was superior (>90 % reduction in 12 min) to that of NiCo 2 O 4 and MnCo 2 O 4 nanoparticles. While the 4-NP reduction process followed a pseudo-first-order kinetics for all the catalysts, the reduction efficiency of the samples manifested a complex trend from cycle to cycle. The anomalous catalytic behavior of the nanostructures in 4-NP degradation has been explained. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ge beyond x ∼ 0.4 in kesterite Cu 2 ZnSn 1-x Ge x S 4 causes the formation of secondary phases. • We could eliminate those secondary phases by an acid etching process. • The acid etching process does not affect the size and morphology of the nanostructures. • The phase pure kesterite films manifest high conductivity and enhanced hole concentration. Hole-transporting materials are very important for achieving high efficiency in perovskite solar cells. Thin films made of Cu 2 ZnSn 1-x Ge x S 4 have attracted the attention of researchers due to their potential as hole-transporting layers. However, defects and impurities define their effectiveness in solar cells. In this work, we present a facile wet chemical approach to remove the ZnS and Cu 8 GeS 6 impurities from small (∼11 nm) Cu 2 ZnSn 1-x Ge x S 4 (x = 0.0 to 0.7) nanoparticles synthesized by a hydrothermal process. The wet chemical process converted the nanostructures Cu-rich Zn-poor from their initial Zn-rich Cu-poor stoichiometry. Moreover, the bandgap energies of the nanostructures were reduced by about 0.1 eV after chemical treatment due to change the oxidation state of Cu from Cu1+ to Cu2+. The kesterite films prepared by spin coating of chemically treated nanoparticle inks revealed enhanced electrical conductivity and hole concentration in comparison to the films prepared using untreated nanoparticle inks. While the highest hole concentration of about 6.52x1018 cm−3 was obtained for the films made of Cu 2 ZnSn 1-x Ge x S 4 nanoparticles with the highest x value (x = 0.7), the highest hole mobility (18.9 cm2V−1s−1) was achieved for x = 0.3. The effects of secondary phase elimination on carrier concentration and mobility variation have been discussed. [ABSTRACT FROM AUTHOR]

The combined effects of ocean acidification and ultraviolet radiation (UVR) have been studied in the kelps Alaria esculenta and Saccharina latissima from Kongsfjorden (Svalbard), two major components of the Arctic macroalgal community, in order to assess their potential to thrive in a changing environment. Overall results revealed synergistic effects, however with a different amplitude in the respective species. Changes in growth, internal N, C:N ratio, pigments, optimum quantum yield (Fv/Fm) and electron transport rates (ETR) following CO 2 enrichment and/or UVR were generally more pronounced in S. latissima than in A. esculenta . The highest growth rates were recorded under simultaneous CO 2 enrichment and UVR in both species. UVR-mediated changes in pigment content were partially prevented under elevated CO 2 in both species. Similarly, UVR led to increased photosynthetic efficiency (α) and ETR only if CO 2 was not elevated in A. esculenta and even under high CO 2 in S. latissima . Increased CO 2 did not inhibit external carbonic anhydrase (eCA) activity in the short-term but in the mid-term, indicating a control through acclimation of photosynthesis rather than a direct inhibition of eCA by CO 2 . The higher benefit of simultaneous CO 2 enrichment and UVR for S. latissima respect to A. esculenta seems to involve higher C and N assimilation efficiency, as well as higher ETR, despite a more sensitive Fv/Fm. The differential responses shown by these two species indicate that ongoing ocean acidification and UVR could potentially change the dominance at lower depths (4–6 m), which will eventually drive changes at the community level in the Arctic coastal ecosystem. These results support an existing consideration of S. latissima as a winner species in the global change scenario. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the problems associated with the dc-link capacitor voltages of the three-level neutral-point-clamped power converter: the imbalance of the capacitor voltages as well as the presence of an ac-voltage low-frequency oscillation in the dc link of the converter. In order to cope with them, a mathematical analysis of the capacitor voltage difference dynamics, based on a direct average continuous model, is carried out, considering a singular perturbation approach. The analysis leads to a final expression where a sinusoidal disturbance appears explicitly. Consequently, the two problems can be handled together using the ordinary formulation of a problem of regulating the output of a system subject to sinusoidal disturbances, applying classical control theory to design the controller. In this way, the controller is designed including the disturbance estimate provided by a Luenberger observer to asymptotically cancel the disturbance, while also keeping the capacitor voltages balanced. Experiments for a synchronous three-level neutral-point-clamped converter prototype are carried out to evaluate the performance and usefulness of the converter working as a grid-connected inverter under the proposed control law. [Copyright &y& Elsevier]

[Display omitted] • Kesterite CZTS and CZTGS nanoparticles are synthesize by low-temperature hydrothermal process. • Substitution of 30% Sn by Ge in the kesterite lattice does not induce any impurity phase. • Ge incorporation in kesterite lattice increases the concentration of (V Cu + Zn Cu) defect complex. • Incorporation of Ge in kesterite lattice decreases [2Cu Zn + Sn Zn ] defect concentration. • Formation of V Cu enhances carrier concentration and conductivity of kesterite nanoparticles. Phase pure Cu 2 ZnSnS 4 (CZTS) and Cu 2 ZnSn 0.7 Ge 0.3 S 4 (CZTGS) kesterite nanoparticles of 10–35 nm size range were fabricated through a low-temperature hydrothermal process. Morphology, structure, and structural phase of the nanoparticles were determined utilizing field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectroscopy. Electrical transport behaviors of the pelletized nanostructures were studied in a physical properties measurement system (PPMS) in the 100–320 K temperature range. Obtained results indicate that both the CZTS and CZTGS nanostructures have p-type conductivity, with high room temperature hole concentration and carrier mobility. Substitution of 30% Sn by Ge enhances the electrical conductivity of CZTS about four times. While the room temperature hole mobility in the kesterite nanostructures reduces to about 60%, the hole concentration increases about one order on Ge incorporation. The limited substitution of Sn atoms by Ge does not affect the position of acceptor levels in the electronic band gap of the kesterite nanostructures. However, it increases the concentration of Cu Zn and Zn Cu antisite defects and affects the transition temperature where the electrical transport of kesterite nanostructures changes from lattice scattering controlled to defect scattering controlled conduction. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel control strategy for a nonlinear boost inverter is proposed. The idea is based on generating an autonomous oscillator that does not need an external reference signal. This aim is achieved by using energy-shaping methodology with a suitable Hamiltonian function which defines the desired system behavior. A phase controller is added to the control law in order to achieve 180°-synchronization between both parts of the circuit as well as synchronize the voltage output with a pre-specified signal, e.g. synchronization with the electrical grid. An adaptive control is designed for dealing with the common problem of unknown load. In order to analyze the stability of the full system, singular perturbation approach is used. The resulting control is tested by means of simulations. [ABSTRACT FROM AUTHOR]

A fuzzy logic controller saturates outside the universe of discourse region. This saturation gives rise to a universal nonlinearity for this type of controller. In this paper, the effects of this nonlinearity are analyzed for the most usual fuzzy controllers: PD and PI fuzzy controllers. It is shown that due to this saturation some pathological behaviors such as oscillations or unstable limit cycles can occur. The methodology employed in the analysis is based on the describing function, which is determined for PD and PI fuzzy controllers. One example illustrates the relevance of the proposed methodology. [Copyright &y& Elsevier]

Changes in the accumulation of cAMP levels were measured by the isotope dilution assay using protein kinase A in the lichen Evernia prunastri at varying light conditions. cAMP levels decreased following exposure to low irradiance (20 μmol quanta m−2 s−1, and below the compensation point for photosynthesis) of red light (600–710-nm wave length) and increased by 50% after far-red light illumination (15 μmol quanta m−2 s−1, 710–800-nm wavelength). Far-red partially reverted the effect of red light when the former was supplied after the latter. cAMP increased to its maximum level under high irradiance supplied by a non-photomorphogenic yellow light source (400 μmol quanta m−2 s−1, reaching photosynthetic saturation). The addition of small quantities of red and far-red light, however, had profound restricting effects on cAMP accumulation. The addition of inhibitors of electron transport chains did not promote any significant change in cAMP levels in any of the treatments, indicating that cAMP accumulation could not depend on ATP synthesis. We propose that the response of cAMP accumulation at low irradiance comprises the activation of a morphogenic pathway through a red/far-red photoreceptor. In addition, at high irradiance the response would occur most likely through photosystems II and I acting as sensors of light quantity, that can be strongly modified by the red/far-red photomorphogenic system. Thus, cAMP would be involved in sensing the overall light environment. [Copyright &y& Elsevier]

The appearance of self-sustained oscillations in high performance AC drives, and in particular, in induction motors whose speed is regulated with the industry standard field-oriented control, is a well-documented but little understood phenomenon. It is well known that the oscillations may be quenched by returning the outer-loop PI speed control, but no precise rules to carry out this task, which may be time consuming, are known. In this paper, we show that these oscillations may arise due to the existence of Hopf bifurcations. Some simple rules for selecting the gains of the PI controller are obtained as a result of our analysis. [Copyright &y& Elsevier]

• Modulation of five-level DCC formulated as a mixed-integer optimization problem. • Optimization: Reduction on commutations number and balancing task fulfillment. • Off-line computation and look-up table implementation. • Guidelines for robust implementation of resulted look-up table. • Steady-state enhancement for distortion improvement. In power converters, the modulation stage commands the switching devices to drive the converter outputs to the voltage required by the inner controllers in order to achieve their objectives. However, in multilevel converters, the modulation may be in charge of an additional goal since it also has to tackle with the capacitor voltage balancing issue. This paper formulates the modulation of multilevel three-phase power converters, specifically five-level diode-clamped converters (DCC), as a mixed-integer linear optimization problem. In this paper, it is shown that the presented optimization problem can deal with the capacitor voltage balance at the same time that the number of commutations is minimized. The problem is solved offline and its solution is stored in a lookup table to be used during normal operation. Then, an online procedure to obtain the levels that modulate each phase from the lookup table is given. Comparisons with model predictive control, space-vector-based algorithms and other modulation approaches are presented in simulations. Several experimental results are presented showing the feasibility of this approach with changes in the operating conditions. [ABSTRACT FROM AUTHOR]

La 1-x Sr x MnO 3 perovskites are of enormous current interest due to their superior magnetoresistance and application as cathode material for solid oxide fuel cells. However, practical applications of these perovskites critically depend on size, composition, and concentration of La3+ vacancies at their surfaces. Here we present the fabrication of size controlled (90–255 nm average size), highly crystalline La 1-x Sr x MnO 3 (x = 0, 0.3, 0.5, and 1) nanoparticles, simply by ball-milling of metal acetylacetonate precursors in NaCl and subsequent air-annealing. The size of the nanoparticles increased in the order LaMnO 3+ δ < La 0.7 Sr 0.3 MnO 3 ≈ La 0.5 Sr 0.5 MnO 3 < SrMnO 3. While LaMnO 3+δ particles remain well dispersed, a fraction of particles containing Sr remains partially inter-connected after air-annealing (900 °C). A change in site symmetry of the Mn3+-O 6 octahedron promoted by the Jahn-Teller distortion of LaMnO 3+δ lattice was detected. Substitution of La3+ ions by Sr2+ increases the ferromagnetic interaction in La 1-x Sr x MnO 3 (x = 0, 0.3, 0.5) nanostructures, increasing their Curie temperature and magnetization (M s) progressively. Effect of particle dispersion due to Sr2+ incorporation on the lattice and magnetic behavior of the nanostructures is discussed considering the Jahn-Teller distortion and La3+ vacancy induced Mn3+ ion oxidation (to Mn4+) in the lattice. Image 1 • La 1-x Sr x MnO 3 perovskite nanoparticles of 90–255 nm av. Size range were fabricated by ball-milling. • Presence of Na+ ion at surface promotes the dispersion of LaMnO 3+δ nanoparticles. • Particle dispersion modifies the T irr of La 1-x Sr x MnO 3 nanostructures. • Substitution of La3+ by Sr2+ in La 1-x Sr x MnO 3 increases their T Curie and M s. • Jahn-Teller distortion and La3+ vacancy induced Mn3+ oxidation affect their magnetic behavior. [ABSTRACT FROM AUTHOR]

This article revisits the modeling of the grid-connected neutral point-clamped converter as a time-varying nonlinear hybrid dynamical system. As a result, an embedded control law that guarantees stability and fulfills the control objectives, namely dc-link voltage regulation, power-to-grid energy exchange and capacitor voltage balancing, is proposed. In addition, a rigorous study of stability is carried out without depending on an averaged model and considering the hybrid dynamical character of the system. Moreover, the hybrid control guarantees a minimum dwell time. This approach could be extended to other topologies or control laws in the search for rigorous stability guarantee The algorithm is evaluated and tested experimentally, verifying the feasibility of the approach. This process involves adapting the algorithm to be programmed in a FPGA as well as some further modifications to improve the steady-state performance. The experimental results are performed under several reference changes and perturbations to prove the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract: Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly active memberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects. [Copyright &y& Elsevier]

Multilevel converters are nowadays an enabling key in the integration of electric power into the grid as they introduce less distortion and, thus, they are more compliant with the grid standards, among other benefits. A well-known topology is the three-level Neutral-Point-Clamped whose control requires to deal with the capacitors voltage unbalance. This paper presents a modulation approach where the injection of a common component in the modulated voltage is studied in order to achieve such voltage balance. An optimization problem that, apart from the voltage balance, aims the lowest number of commutations and can be solved very efficiently with up to five computations of the cost function is formulated. The main advantages of the proposed modulation strategy are its simplicity and its flexibility, since it is also valid for unbalanced grid conditions and, with little added complexity, for low (and even zero) power factor conditions. Simulation results under unbalanced grid conditions are provided in order to show its validity under this scenario. The strategy is evaluated and compared with a space-vector-based approach in an experimental setup, yielding similar total harmonic current distortion, a 30% reduction in the number of commutations, and better voltage balance performance for lower power factor conditions. • A modulation approach for capacitors balance in NPC converters is proposed. • The advantages are simplicity and validity for unbalanced-grid-voltage conditions. • The number of commutations is optimized. • An enhancement is proposed to work under low-power-factor conditions. • Experimental comparison with virtual space vector is performed. [ABSTRACT FROM AUTHOR]