Microgrid (MG) usually operates in medium/low-voltage systems, where the line impedance parameters are mainly resistive, and traditional P-f / Q-U droop control is no longer applicable. When the ...virtual complex impedance method is adopted, the resistance component of line impedance can be counteracted by a virtual negative resistance. Unfortunately, the improper design of the virtual negative resistance will result in an unstable system due to the problem of line impedance parameter drift and estimation error. According to the line parameters characteristics of the off-grid MG with medium/low voltage, the P-U / Q-f droop control is adopted in this study, where the virtual complex impedance composed of a virtual negative inductance and a virtual resistance is introduced in the control loop. The virtual negative inductance is used to reduce the power coupling caused by the inductive component of the system impedance. The virtual resistance is implemented to enhance the resistive component and adjust the impedance matching degree for raising the accuracy of power sharing. However, the power sharing is still affected by the system hardware parameters; meanwhile, the voltage deviation caused by the droop control and the virtual impedance exists. In this study, a novel voltage stabilization and power sharing control method based on the virtual complex impedance is investigated to achieve accurate power sharing without the impact of hardware parameters variations and to improve the voltage quality. Moreover, the small-signal model of the inverter-based off-grid MG with the proposed controller is established, which can be utilized to analyze the stability and dynamic performance of the system. Meanwhile, the control parameters can be sequentially determined. Analysis shows that the strategy is robust against the line-impedance parameter drift and the estimation error and has a large stability margin and fast dynamic-response speed. Finally, numerical simulations and experimental results are provided to verify the effectiveness of the proposed control method in comparison with traditional frameworks.
Identification of grain shape determining genes can facilitate breeding of rice cultivars with optimal grain shape and appearance quality. Here, we identify GS9 (Grain Shape Gene on Chromosome 9) ...gene by map-based cloning. The gs9 null mutant has slender grains, while overexpression GS9 results in round grains. GS9 encodes a protein without known conserved functional domain. It regulates grain shape by altering cell division. The interaction of GS9 and ovate family proteins OsOFP14 and OsOFP8 is modulated by OsGSK2 kinase, a key regulator of the brassinosteroids signaling pathway. Genetic interaction analysis reveals that GS9 functions independently from other previously identified grain size genes. Introducing the gs9 allele into elite rice cultivars significantly improves grain shape and appearance quality. It suggests potential application of gs9, alone or in combination with other grain size determining genes, in breeding of rice varieties with optimized grain shape.
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•100%, 90.9%, and 78.2% drinkable groundwater in karst, fissured, and granular aquifer.•Groundwater quality in non-urbanized areas was much better than those in other ...areas.•Industrialization, one main driving force for groundwater quality in peri-urban areas.•Urbanization, one main driving force for groundwater quality in fissured aquifers.•Geologic forces control groundwater quality in non-urbanized areas.
Industrialization and urbanization expansion may change the groundwater quality in the Pearl River Delta (PRD). The aims of this study were to evaluate the groundwater quality in various aquifers and areas with different urbanization levels in the PRD, to extract the main impact indicators, and to discuss the driving forces for the groundwater quality. Nearly 400 groundwater samples were collected and 23 indicators were analyzed. In the PRD, 83% groundwater was drinkable (good-quality) by using a fuzzy synthetic evaluation method. Groundwater in karst aquifers was drinkable, and its quality was better than those in granular and fissured aquifers. In the latter two aquifer types, groundwater quality in non-urbanized areas was much better than those in peri-urban and urbanized areas. In granular aquifers, Mn + Fe, I− + Ni + Mn, and Mn + As + I− were the main impact indicators for poor-quality groundwater in urbanized areas, peri-urban areas, and non-urbanized areas, respectively. Correspondingly, reductive dissolution of Fe/Mn (oxy)hydroxides, infiltration of industrial wastewater and reductive dissolution of I− and Mn, and reductive dissolution of Mn, As, and I− were likely responsible for poor-quality groundwater in these areas, respectively. By contrast, in fissured aquifers, NO3−, NO3− + Pb, and I− were the main impact indicators for poor-quality groundwater in urbanized areas, peri-urban areas, and non-urbanized areas, respectively. Correspondingly, infiltration of domestic sewage, infiltration of domestic sewage and industrial wastewater, and mineralization of I-rich organic matter were probably responsible for poor-quality groundwater in these areas, respectively. Industrialization was one of the main driving forces for groundwater quality in granular and fissured aquifers in peri-urban areas, while urbanization was one of the main driving forces for groundwater quality in fissured aquifers in urbanized and peri-urban areas in the PRD.
As the second most widely used artificial lift method in petroleum production (and first in produced amount), electrical submersible pump (ESP) maintains or increases flow rate by converting kinetic ...energy to hydraulic pressure of hydrocarbon fluids. To facilitate its optimal working conditions, an ESP has to be operated within a narrow application window. Issues like gas involvement, changing production rate and high oil viscosity, greatly impede ESP boosting pressure. Previous experimental studies showed that the presence of gas would cause ESP hydraulic head degradation. The flow behaviors inside ESPs under gassy conditions, such as pressure surging and gas pockets, further deteriorate ESP pressure boosting ability. Therefore, it is important to know what parameters govern the gas-liquid flow structure inside a rotating ESP and how it can be modeled. This paper presents a comprehensive review on the key factors that affect ESP performance under gassy flow conditions. Furthermore, the empirical and mechanistic models for predicting ESP pressure increment are discussed. The computational fluid dynamics (CFD)-based modeling approach for studying the multiphase flow in a rotating ESP is explained as well. The closure relationships that are critical to both mechanistic and numerical models are reviewed, which are helpful for further development of more accurate models for predicting ESP gas-liquid flow behaviors.
A 3D‐printed digital metamaterial embedded with electromagnets is fabricated. Switching electromagnets between the attaching (1 bit) and detaching (0 bit) modes activates different waveguides in the ...metamaterial. The underlying mechanism is investigated theoretically and experimentally. The hierarchical assemblies of unit cells, mimicking digital bits, allow programmable broadening of the bandgap of the metamaterial.
This paper reviews recent studies in understanding neural-network representations and learning neural networks with interpretable/disentangled middle-layer representations. Although deep neural ...networks have exhibited superior performance in various tasks, interpretability is always Achilles’ heel of deep neural networks. At present, deep neural networks obtain high discrimination power at the cost of a low interpretability of their black-box representations. We believe that high model interpretability may help people break several bottlenecks of deep learning, e.g., learning from a few annotations, learning via human–computer communications at the semantic level, and semantically debugging network representations. We focus on convolutional neural networks (CNNs), and revisit the visualization of CNN representations, methods of diagnosing representations of pre-trained CNNs, approaches for disentangling pre-trained CNN representations, learning of CNNs with disentangled representations, and middle-to-end learning based on model interpretability. Finally, we discuss prospective trends in explainable artificial intelligence.
Background and Purpose
Recent clinical trials report that metformin, an activator of AMP‐activated protein kinase (AMPK) used to treat type 2 diabetes, significantly reduces the risk of stroke by ...actions that are independent of its glucose‐lowering effects. However, the underlying molecular mechanisms are not known. Here, we tested the possibility that acute metformin preconditioning confers neuroprotection by pre‐activation of AMPK‐dependent autophagy in a rat model of permanent middle cerebral artery occlusion (pMCAO).
Experimental Approach
Male Sprague‐Dawley rats were pretreated with either vehicle, an AMPK inhibitor, Compound C, or an autophagy inhibitor, 3‐methyladenine, and were injected with a single dose of metformin (10 mg kg−1, i.p.). Then, AMPK activity and autophagy biomarkers in the brain were assessed. At 24 h after metformin treatment, rats were subjected to pMCAO; infarct volume, neurological deficits and cell apoptosis were evaluated 24 and 96 h later.
Key Results
A single dose of metformin significantly activated AMPK and induced autophagy in the brain. The enhanced autophagic activity was inhibited by Compound C pretreatment. Furthermore, acute metformin preconditioning significantly reduced infarct volume, neurological deficits and cell apoptosis during a subsequent focal cerebral ischaemia. The neuroprotection mediated by metformin preconditioning was fully abolished by Compound C and partially inhibited by 3‐methyladenine.
Conclusions and Implications
These results provide the first evidence that acute metformin preconditioning induces autophagy by activation of brain AMPK, which confers neuroprotection against subsequent cerebral ischaemia. This suggests that metformin, a well‐known hypoglycaemic drug, may have a practical clinical use for stroke prevention.
Although plasma catalysis is gaining increasing interest for various environmental applications, the underlying mechanisms are still far from understood. For instance, it is not yet clear whether and ...how plasma streamers can propagate in catalyst pores, and what is the minimum pore size to make this happen. As this is crucial information to ensure good plasma-catalyst interaction, we study here the mechanism of plasma streamer propagation in a catalyst pore, by means of a two-dimensional particle-in-cell/Monte Carlo collision model, for various pore diameters in the nm-range to m-range. The so-called Debye length is an important criterion for plasma penetration into catalyst pores, i.e. a plasma streamer can penetrate into pores when their diameter is larger than the Debye length. The Debye length is typically in the order of a few 100 nm up to 1 m at the conditions under study, depending on electron density and temperature in the plasma streamer. For pores in the range of ∼50 nm, plasma can thus only penetrate to some extent and at very short times, i.e. at the beginning of a micro-discharge, before the actual plasma streamer reaches the catalyst surface and a sheath is formed in front of the surface. We can make plasma streamers penetrate into smaller pores (down to ca. 500 nm at the conditions under study) by increasing the applied voltage, which yields a higher plasma density, and thus reduces the Debye length. Our simulations also reveal that the plasma streamers induce surface charging of the catalyst pore sidewalls, causing discharge enhancement inside the pore, depending on pore diameter and depth.
Pathogenesis of liver cirrhosis Zhou, Wen-Ce; Zhang, Quan-Bao; Qiao, Liang
World journal of gastroenterology : WJG,
06/2014, Letnik:
20, Številka:
23
Journal Article
Odprti dostop
Liver cirrhosis is the final pathological result of various chronic liver diseases,and fibrosis is the precursor of cirrhosis.Many types of cells,cytokines and miRNAs are involved in the initiation ...and progression of liver fibrosis and cirrhosis.Activation of hepatic stellate cells(HSCs)is a pivotal event in fibrosis.Defenestration and capillarization of liver sinusoidal endothelial cells are major contributing factors to hepatic dysfunction in liver cirrhosis.Activated Kupffer cells destroy hepatocytes and stimulate the activation of HSCs.Repeated cycles of apoptosis and regeneration of hepatocytes contribute to pathogenesis of cirrhosis.At the molecular level,many cytokines are involved in mediation of signaling pathways that regulate activation of HSCs and fibrogenesis.Recently,miRNAs as a post-transcriptional regulator have been found to play a key role in fibrosis and cirrhosis.Robust animal models of liver fibrosis and cirrhosis,as well as the recently identified critical cellular and molecular factors involved in the development of liver fibrosis and cirrhosis will facilitate the development of more effective therapeutic approaches for these conditions.
Complex fabrication process and expensive materials have restricted the development of smart three-dimensional (3D) lightweight structures, which are expected to possess self-shaping, self-folding ...and self-unfolding performances. Here we present a simple approach to fabricate smart lightweight structures by triggering shape transformation from thin printed composite sheets. The release of the internal strain in printed polymer materials enables the printed composite sheet to keep flat under heating and transform into a designed 3D configuration when cooled down to room temperature. The 3D lightweight structure can be switched between flat and 3D configuration under appropriate thermal stimuli. Our work exploits uniform internal strain in printed materials as a controllable tool to fabricate smart 3D lightweight structures, opening an avenue for possible applications in engineering fields.
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