This paper presents a derivation of the small-signal stability limit of a grid-connected wind farm with M permanent magnet synchronous generators (PMSGs) as determined by the dynamics of phased ...locked loops (PLLs). The stability limit reveals the mechanism whereby the PLLs can destabilize the wind farm in the case of a weak grid connection. Computation of the derived stability limit is simple and obviates the need to establish a parametric model of the wind farm. The stability limit can approximately indicate the potential instability risk collectively posed by the PLLs in the wind farm. Case studies are presented to evaluate the analytical conclusions obtained and the derived small-signal stability limit. Application of the stability limit during the planning and operating stages of a grid-connected wind farm is also demonstrated. Various factors that can affect the stability of the wind farm, and that must be considered during planning and operation, are examined and useful conclusions are obtained. These factors include the length of the transmission line connecting the wind farm to the AC grid, the topology of the wind farm, the wind speed, and its distribution over the wind farm, as well as the parameters of the PLLs.
CRISPR Cas9 in Genome Editing and Beyond Wang, Haifeng; La Russa, Marie; Qi, Lei S
Annual review of biochemistry,
06/2016, Letnik:
85, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Cas9 protein (CRISPR-associated protein 9), derived from type II CRISPR (clustered regularly interspaced short palindromic repeats) bacterial immune systems, is emerging as a powerful tool for ...engineering the genome in diverse organisms. As an RNA-guided DNA endonuclease, Cas9 can be easily programmed to target new sites by altering its guide RNA sequence, and its development as a tool has made sequence-specific gene editing several magnitudes easier. The nuclease-deactivated form of Cas9 further provides a versatile RNA-guided DNA-targeting platform for regulating and imaging the genome, as well as for rewriting the epigenetic status, all in a sequence-specific manner. With all of these advances, we have just begun to explore the possible applications of Cas9 in biomedical research and therapeutics. In this review, we describe the current models of Cas9 function and the structural and biochemical studies that support it. We focus on the applications of Cas9 for genome editing, regulation, and imaging, discuss other possible applications and some technical considerations, and highlight the many advantages that CRISPR Cas9 technology offers.
Aqueous zinc batteries are appealing devices for cost-effective and environmentally sustainable energy storage. However, the zinc metal deposition at the anode strongly influences the battery cycle ...life and performance. To circumvent this issue, here we propose the use of lanthanum nitrate (La(NO
)
) as supporting salt for aqueous zinc sulfate (ZnSO
) electrolyte solutions. Via physicochemical and electrochemical characterizations, we demonstrate that this peculiar electrolyte formulation weakens the electric double layer repulsive force, thus, favouring dense metallic zinc deposits and regulating the charge distribution at the zinc metal|electrolyte interface. When tested in Zn||VS
full coin cell configuration (with cathode mass loading of 16 mg cm
), the electrolyte solution containing the lanthanum ions enables almost 1000 cycles at 1 A g
(after 5 activation cycles at 0.05 A g
) with a stable discharge capacity of about 90 mAh g
and an average cell discharge voltage of ∼0.54 V.
The electrochemical CO2 reduction reaction (CO2RR) is of great importance to tackle the rising CO2 concentration in the atmosphere. The CO2RR can be driven by renewable energy sources, producing ...precious chemicals and fuels, with the implementation of this process largely relying on the development of low‐cost and efficient electrocatalysts. Recently, a range of heterogeneous and potentially low‐cost single‐atom catalysts (SACs) containing non‐precious metals coordinated to earth‐abundant elements have emerged as promising candidates for the CO2RR. Unfortunately, the real catalytically active centers and the key factors that govern the catalytic performance of these SACs remain ambiguous. Here, this ambiguity is addressed by developing a fundamental understanding of the CO2RR‐to‐CO process on SACs, as CO accounts for the major product from CO2RR on SACs. The reaction mechanism, the rate‐determining steps, and the key factors that control the activity and selectivity are analyzed from both experimental and theoretical studies. Then, the synthesis, characterization, and the CO2RR performance of SACs are discussed. Finally, the challenges and future pathways are highlighted in the hope of guiding the design of the SACs to promote and understand the CO2RR on SACs.
Heterogeneous single‐atom catalysts exhibit promising performance for electrochemical CO2 reduction reaction. Various valuable reduction products have been produced on different single‐atom catalysts. In these catalysts, single atomic sites coordinate with heteroatoms, such as N and S, and locate in N‐doped carbon materials, graphene, or metal–organic framework (MOF)‐derived carbon frameworks.
Frequency deviations of power systems caused by grid-connected wind power fluctuations is one of the key factors which restrains the increase of wind penetration level. This paper examines a combined ...wind and hybrid energy storage system (HESS, supercapacitor, and battery) to smooth wind power fluctuations. A fuzzy-based wind-HESS system (FWHS) controller is proposed to suppress the wind power fluctuations. The proposed controller takes full advantage of the complimentary characteristics of the supercapacitor and battery with the supercapacitor and battery in charge of high and middle frequency components of wind fluctuations, respectively. A differential evolution (DE)-based optimal sizing method for HESS systems is introduced to evaluate the minimum capacity of HESS as being limited by grid frequency deviation. The efficiency of the proposed scheme in the paper for wind-HESS system is evaluated by a real Chinese power system.
A series of AlxTiZrNbHf refractory high entropy alloys (RHEAs) were prepared to investigate the mechanical and wear properties. Despite the different crystal structures of each constituent, the RHEAs ...exhibited body centered cubic (BCC) phase structures as revealed by X-ray diffraction and transmission electron microscopy. Along with the primary BCC phase, another ordered BCC phase appeared in AlTiZrNbHf, being supported by a high negative mixing enthalpy (<−16.28 kJ-mol−1) and a low valence electron concentration (< 4.04). The improved mechanical properties and wear resistance by the Al addition are ascribed to severe lattice distortion and second phase strengthening. These findings highlight significant alterations in the microstructure, mechanical and wear properties with the Al addition, which are beneficial to the design of alloys for wear applications.
•Refractory high entropy alloys AlxTiZrNbHf has been prepared using Arc Melting technique.•Mechanical properties have been significantly improved with the higher amounts of Al in the alloys.•Friction coefficient, alloys microstructure and wear properties strongly affected with the variations of Al contents in AlxTiZrNbHf.
Proper disposal of spent lithium-ion batteries is beneficial for the resource recycling and pollution elimination. Full liberation of electrode materials, including the liberation between electrode ...material and current collector (copper/aluminum foils) and the liberation among electrode material particles, is the pivotal precondition for improving the recovery efficiency of electrode materials. In this article, authors attempt to carry out a summary of current technologies used in the liberation of electrode materials derived from spent lithium-ion batteries. However, specialized studies about the liberation of electrode materials are insufficient at present. This research clearly shows that: (1) Organic binder must be removed so as to improve the liberation and metallurgy efficiency of electrode materials; (2) A collaboration of varied technologies is the necessary process to achieve high liberation efficiency between electrode materials and copper/aluminum foils; (3) Pyrolysis may be a recommended technology for removal of organic binder because part of pyrolysis products can be recovered. Finally, an alternative recycling flowchart of spent LIBs is proposed.
Display omitted
•Review different technologies for the liberation of electrode materials from foils•Identify the necessity of removing organic binders for recycling of spent LIBs•Summary main problems in the recycling process of spent LIBs•Suggest alternative flowchart for the recovery of electrode materials
The upgrading of plastic waste is one of the grand challenges for the 21st century owing to its disruptive impact on the environment. Here, we show the first example of the upgrading of various ...aromatic plastic wastes with C−O and/or C−C linkages to arenes (75–85 % yield) via catalytic hydrogenolysis over a Ru/Nb2O5 catalyst. This catalyst not only allows the selective conversion of single‐component aromatic plastic, and more importantly, enables the simultaneous conversion of a mixture of aromatic plastic to arenes. The excellent performance is attributed to unique features including: (1) the small sized Ru clusters on Nb2O5, which prevent the adsorption of aromatic ring and its hydrogenation; (2) the strong oxygen affinity of NbOx species for C−O bond activation and Brønsted acid sites for C−C bond activation. This study offers a catalytic path to integrate aromatic plastic waste back into the supply chain of plastic production under the context of circular economy.
While plastic waste upcycling has attracted increasing worldwide concern, catalytic routes capable to convert a mixture of plastics selectively and effectively into useful chemicals remain exceedingly rare. Here, we report a salient example of the catalytic upgrading of various aromatic plastic waste to simple arenes in high yield via the selective cleavage of interunit C−O and C−C linkages.
A vast amount of text data is recorded in the forms of repair verbatim in railway maintenance sectors. Efficient text mining of such maintenance data plays an important role in detecting anomalies ...and improving fault diagnosis efficiency. However, unstructured verbatim, high-dimensional data, and imbalanced fault class distribution pose challenges for feature selections and fault diagnosis. We propose a bilevel feature extraction-based text mining that integrates features extracted at both syntax and semantic levels with the aim to improve the fault classification performance. We first perform an improved X 2 statistics-based feature selection at the syntax level to overcome the learning difficulty caused by an imbalanced data set. Then, we perform a prior latent Dirichlet allocation-based feature selection at the semantic level to reduce the data set into a low-dimensional topic space. Finally, we fuse fault features derived from both syntax and semantic levels via serial fusion. The proposed method uses fault features at different levels and enhances the precision of fault diagnosis for all fault classes, particularly minority ones. Its performance has been validated by using a railway maintenance data set collected from 2008 to 2014 by a railway corporation. It outperforms traditional approaches.
During the last decade, tidal stream and wave energy technologies have made significant progress. A number of large-scale prototypes have been deployed around the world. In this article, the recent ...development in some western countries and China is presented. Taken as the representatives from European and American continent, UK, Portugal and US are chosen to compare with China in resource assessment, research& development, and policy aspects. With an analysis of similarities and differences, the major elements that have great effect on development of ocean energy industry are concluded, and some suggestions are given to improve the development of tidal stream and wave energy technology.
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