Closed-Loop Control of Transonic Buffet Using Active Shock Control Bump

At transonic flight conditions, the buffet caused by the shockwave/boundary-layer interaction can degrade aircraft performance and even threaten their safety. In this paper, a closed-loop control using an active shock control bump (SCB) has been proposed to suppress the buffet on a supercritical airfoil flying at transonic speeds. A closed-loop control law is designed by using the lift coefficient as the feedback signal and using the bump height as the control variable. The unsteady numerical simulations show that the buffet can be effectively suppressed by an optimal combination of the parameters of the control law, namely the gain and the delay time. Furthermore, the buffet control effectiveness is still acceptably constrained by a prescribed maximum bump height, which is believed to be practically important. In addition to being able to achieve both wave drag reduction and buffet alleviation, the active SCB is less sensitive to the parameters of the control law and has a shorter response time in comparison with the reference active trailing edge flap

Understanding the Effect of Stepwise Irrigation on Liquid Holdup and Hysteresis Behavior of Unsaturated Ore Heap

Liquid is a crucial medium to contain soluble oxygen, valuable metal ions, and bacteria in unsaturated heap leaching. Liquid retention behavior is the first critical issue to be considered to efficiently extract low-grade minerals or wastes. In this study, the residual liquid holdup of an unsaturated packed bed was quantitatively discussed by liquid holdup (θ), residual liquid holdup (θresidual), relative liquid holdup (θ′), and relative porosity (n*) using the designed measuring device. The detailed liquid holdup and the hysteresis behavior under stepwise irrigation are indicated and discussed herein. The results show that relative porosity of the packed bed was negatively related to particle size, and intra-particle porosity was more developed in the −4.0 + 2.0 mm packed bed. The higher liquid retention of the unsaturated packed bed could be obtained by using stepwise irrigation (incrementally improved from 0.001 to 0.1 mm/s) instead of uniform irrigation (0.1 mm/s). It could be explained in that some of the immobile liquid could not flow out of the unsaturated packed bed, and this historical irrigation could have accelerated formation of flow paths. The θ was sensitive to superficial flow rate (or irrigation rate) in that it obviously increased if a higher superficial flow rate (u) was introduced, however, the θresidual was commonly affected by n* and θ′. Moreover, the liquid hysteresis easily performed under stepwise irrigation condition, where θ and θresidual were larger at u of the decreasing flow rate stage (DFRS) instead of u of the increasing flow rate stage (IFRS). These findings effectively quantify the liquid retention and the hysteresis behavior of ore heap, and the stepwise irrigation provides potential possibility to adjust liquid retention conditions

The growth kinetic behaviors of the intermetallics at W/Co interface under the current of spark plasma sintering

The interdiffusion behaviors of elements at the W/Co interface under the application of current during SPS were investigated. It is found that Co _7 W _6 and Co _3 W are formed at the W/Co bonding interface. The growth of the Co _3 W layer is apparently improved by the high current during SPS. The growth rate constant of the Co _3 W layer undercurrent is 1.73–3.03 times faster than that without current. The research shows that the growth rate is increased with the current density. The growth activation energy of the Co _3 W layer is calculated to be 229.51 ± 27 kJ mol ^−1 undercurrent, which is smaller than that without current (279.38 ± 11 kJ mol ^−1 ). Moreover, the growth activation energy of the Co _3 W layer is decreased with the increase of the current density. The mechanism of current-improved growth of the Co _3 W layer is suggested to be the fact that the current lowers the nucleation barrier of intermetallic layer, which accordingly promotes chemical reactions

Uniaxial Negative Thermal Expansion, Negative Linear Compressibility, and Negative Poisson's Ratio Induced by Specific Topology in Zn[Au(CN)(2)](2)

The well-known idea of "structure determines properties" can be understood profoundly in the case of hexagonal zinc dicyanometalate. Using density functional theory (DFT) calculations, we show the uniaxial negative thermal expansion (NTE) and negative linear compressibility (NLC) properties of Zn[Au(CN)(2)](2). The temperature dependence of phonon frequencies within the quasi harmonic approximation (QHA) is investigated. The abnormal phonon hardening (frequency increase on heating) is detected in the ranges of 0-225, 320-345, and 410-430 cm(-1), which can be indicative of the unusual physical properties of Zn[Au(CN)(2)](2). Due to the significance of low-energy phonon frequencies in Zn[Au(CN)(2)](2), in this work, the corresponding vibrational mode of the lowest-frequency optical phonon at the zone center is analyzed. The specific topology of a springlike framework that will produce the effects of a compressed spring on heating and an extended spring under hydrostatic pressure is identified and leads to the coexistence of uniaxial-NTE and NLC behaviors in Zn[Au(CN)(2)](2). The. distinguishing phonon group velocity along the a axis and c axis facilitates different responses for both the axes under temperature and hydrostatic pressure field. Through an analysis and visualization of the spatial dependence of elastic tensors, it is found that a negative Poisson's ratio (NPR) is presented in all projection planes due to the specific topology

Practice of Water Ecological Restoration of Large Urban Eutrophication Lake——A case of study of Donghu Lake, Wuhan

Submerged macrophytes are the main components of lake ecosystems, and restoration of submerged macrophyte community is an important part of restoring lake ecosystems. Taking Water Ecological Restoration Projects in Wuhan Donghu Lake as an example, Combined with the current situation of the Donghu Lake environment, the submerged phytoremediation area, the restoration species of each sub-lake and the submerged plant configuration plan were determined. The planting of submerged macrophyte adopts the process of “selecting the area - removing debris and repelling fish ecologically - improving the substrate - setting the line planting”. Since the project was implemented , the submerged macrophyte grow well, the coverage of plants reaches more than 70%, and the transparency can reach more than 120cm, which meets the design requirements basically

The preferential growth behaviors of the intermetallics at the W/Co interface during spark plasma sintering

The strong electric current in spark plasma sintering (SPS) often gives sintered materials unique microstructures. In the present study, it is found that the Co3W grains formed at the W/Co bonding interface preferentially grow along [2 1 ¯ 1 ¯0] (or its equivalent orientations) in the current direction during SPS, which is significantly different from that without current. We propose that the resistance anisotropy of grains under electromigration leads to anisotropic atomic diffusion, inducing the preferential growth of grains under current. This work may provide an approach and a theoretical foundation for the preparation of materials exhibiting directional growth

Changes in volatile compounds of fermented minced pepper during natural and inoculated fermentation process based on headspace–gas chromatography–ion mobility spectrometry

Abstract Changes in volatile compounds of fermented minced pepper (FMP) during natural fermentation (NF) and inoculated fermentation (IF) process were analyzed by the headspace–gas chromatography–ion mobility spectrometry (HS‐GC‐IMS). A total of 53 volatile compounds were identified, including 12 esters, 17 aldehydes, 13 alcohols, four ketones, three furans, two acids, one pyrazine, and one ether. Generally, fermentation time played an important role in volatile compounds of FMP. It was found that most esters, aldehydes, and alcohols obviously decreased with the increase in fermentation time, including isoamyl hexanoate, methyl octanoate, gamma‐butyrolactone, phenylacetaldehyde, methional, and E‐2‐hexenol. Only a few volatile compounds increased, especially for 2‐methylbutanoic acid, 2‐methylpropionic acid, linalool, ethanol, and ethyl acetate. However, no significant difference in volatile compounds was found between NF and IF samples at the same fermentation time. In addition, the fermentation process in all samples was well discriminated as three stages (0 days; 6 day; and 12, 18, and 24 days), and all volatile compounds were divided into two categories (increase and decrease) based on principal component analysis and heat map

Hierarchical and ultrathin copper nanosheets synthesized via galvanic replacement for selective electrocatalytic carbon dioxide conversion to carbon monoxide

Electrochemical conversion of carbon dioxide (CO2) to desirable products with high selectivity and efficiency remains critical challenges in balancing carbon cycle for sustainable society. Herein, we demonstrate the hierarchical porous architectures assembled by ultrathin copper (Cu) nanosheets (NS) via a simple galvanic replacement method for the improved selectivity of CO2 conversion with a large current density. Specifically, the optimized hierarchical Cu electrodes achieve high selectivity and activity to convert CO2 into CO, showing a Faradaic efficiency (FE) of 74.1%, record-high partial current density of 23.0 mA cm−2, and turnover frequency of 0.092 s-1 for CO product as well as FE of 24.8% for H2 at potential of -1.0 V vs RHE. The onset potential for the CO2 conversion is -0.29 V vs RHE. Theoretical calculations indicate that the abundant vacancy defects exposed on ultrathin Cu nanosheets can accelerate the initial kinetics of CO formation during the CO2 conversion process. As demonstrated by experimental and computational analyses, the unique hierarchical architecture of integrated Cu electrode contributes the outstanding electrocatalytic performance due to the rapid mass and electrons transport as well as the abundant active sites and associated intrinsic activity.This work is financially supported by National 1000 Young Talents Program of China. The Fundamental Research Funds for the Central Universities (2018KFYXKJC044, 2018KFYYXJJ121, 2017KFXKJC002, 2017KFYXJJ164) and the Innovation Foundation of Shenzhen Government (JCYJ20160408173202143) are also acknowledged. H. S. Park acknowledges financial support from the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning of the Korean Government (NRF-2015R1A1A1A05027727). The authors also acknowledge the support of the Analytical and Testing Center of Huazhong University of Science and Technology for XRD, SEM, TEM and AFM measurements