Set-membership filtering for generator dynamic state estimation with delayed measurements

In this paper, the set-membership filtering problem is investigated for the dynamic state estimation (DSE) of the synchronous generator with delayed measurements. The process noise and measurement noise are assumed to be unknown, bounded and confined to a specified ellipsoidal set. The measurement delay is modeled by a special matrix composed of a delay-driven variable taking values of 1 or 0. Taking into explicit consideration the estimation uncertainty due to the linearization, the constrained Quasi-Newton method is adopted to minimize the linearization errors. The aim of this paper is to design a set-membership filter capable of confining the state estimate of the system to a certain ellipsoidal region, and the ellipsoidal set including all possible states is obtained by the convex optimization approach. Finally, the proposed algorithm is verified on a single machine infinite bus system to further demonstrate its effectiveness

Mechanochemistry: An Efficient Way to Recycle Thermoset Polyurethanes

A recycling process of waste thermosetting polyurethane plastics was proposed based on the mechanochemical method, aiming at the three-dimensional network cross-linking structure of thermosetting polyurethane. Orthogonal experimental design was adopted to select three factors of crushing speed, crushing time, and feed amount to determine the best crushing parameters. Then, the waste polyurethane insulation boards were crushed and degraded by the mechanism of regenerative forming with the adjustable speed test machine. Accordingly, the recycled powder was obtained. Finally, nine kinds of polyurethane recycled composite plates were prepared by hot pressing process. The degradation effect of thermosetting polyurethane was analyzed by Fourier transform infrared spectroscopy, scanning electron microscope, and X-ray diffraction. Moreover, the mechanical properties and thermal insulation properties of recycled composite plates were tested and analyzed. The results show that the network cross-linking molecular structure of waste thermosetting polyurethane plastics is destroyed by the effect of mechanochemical action, and methyl and aldehyde groups are decomposed. Therefore, a recycled powder with strong reactivity and plasticity is generated, which improves the activity regeneration ability. After adding thermoplastic resin, the mechanical properties and formability of recycled composite plates are enhanced, with maximum tensile strength up to 9.913 MPa. Correspondingly, the thermal insulation performance of plates is reduced. However, the minimum thermal conductivity can also reach 0.056 W/m·K. This study provides an effective method for the recycling of thermosetting polyurethane plastics

Origins of Selective C(sp²)–H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical–Experimental Study

The strategy using N,N-bidentate directing groups is a promising way to achieve selective C­(sp²)–H activation inaccessible by that of monodentate directing groups. Herein, through theoretical calculations, we present a rationale behind this strategy, which deciphers its key roles in C–H activation promoted by Ni, Pd, Ru, and Cu. The calculations reveal two key points: (a) Between the two coordination sites of the N,N-bidentate directing group, the proximal one influences more the C–H activation barrier Δ<i>G</i>^‡, whereas the distal site affects more the free energy change Δ<i>G</i> relevant to the substrate coordination. (b) Enlarging/shrinking the chelation ring can exert different effects on the reactivity, depending on the metal identity and the ring size. Importantly, our computational results are in full agreement with previous experimental findings concerning reactivity. Furthermore, a prediction about the unprecedented reactivity from our theory is confirmed by our experiments, lending more credence to the rationale and insights gained in this study

Mn-Catalyzed Three-Component Reactions of Imines/Nitriles, Grignard Reagents, and Tetrahydrofuran: An Expedient Access to 1,5-Amino/Keto Alcohols

An expedient Mn-catalyzed three-component synthesis of 1,5-amino/keto alcohols from Grignard reagents, imines/nitriles, and tetrahydrofuran (THF) is described, which deviates from the classic Grignard addition to imines/nitriles in THF solvent. THF is split and “sewn” in an unprecedented manner in the reaction, leading to the formation of two geminal C–C bonds via C–H and C–O cleavage. Mechanistic experiments and DFT calculations reveal radical and organo-Mn intermediates in the catalytic cycle and the α-arylative ring-opening of THF as the key reaction step

Morphology Evolution and Degradation of CsPbBr₃ Nanocrystals under Blue Light-Emitting Diode Illumination

Under illumination of light-emitting diode (LED) or sunlight, the green color of all-inorganic CsPbBr₃ perovskite nanocrystals (CPB-NCs) often quickly changes to yellow, followed by large photoluminescence (PL) loss. To figure out what is happening on CPB-NCs during the color change process, the morphology, structure, and PL evolutions are systematically investigated by varying the influence factors of illumination, moisture, oxygen, and temperature. We find that the yellow color is mainly originated from the large CPB crystals formed in the illumination process. With maximized isolation of oxygen for the sandwiched film or the uncovered film stored in nitrogen, the color change can be dramatically slowed down whether there is water vapor or not. Under dark condition, the PL emissions are not significantly influenced by the varied relative humidity (RH) levels and temperatures up to 60 °C. Under the precondition of oxygen or air, color change and PL loss become more obvious when increasing the illumination power or RH level, and the large-sized cubic CPB crystals are further evolved into the oval-shaped crystals. We confirm that oxygen is the crucial factor to drive the color change, which has the strong synergistic effect with the illumination and moisture for the degradation of the CPB film. Meanwhile, the surface decomposition and the increased charge trap states occurred in the formed large CPB crystals play important roles for the PL loss