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Summary: Weighted compact nonlinear schemes (WCNSs) are a popular family of high‐resolution shock‐capturing schemes for simulating compressible flows, of which the nonlinear interpolation procedure is dominant for the performance. In this work, a simplified weighting strategy is introduced for the nonlinear interpolation procedure. Firstly, an equivalent weighting formulation of WCNS is presented by explicitly including the whole‐point stencil into the set of candidate stencils. Secondly, motivated by the reorganization of WCNS, the WCNS‐CU6 scheme is achieved in a more straightforward way. Thirdly, by introducing a TENO selection procedure in the framework of WCNS‐CU6‐Simplified, a TCNS6‐Simplified scheme is proposed, the resolution of which is comparable with the excellent TENO6 scheme, while the computational cost is much lower. The simplified schemes exhibit more outstanding, at least comparable, fidelity than the original schemes, however, with superior characteristics in terms of efficiency and simplicity. A variety of benchmark test problems are studied to demonstrate the behaviour of the simplified weighting strategy. [ABSTRACT FROM AUTHOR]

Multiscale compressible turbulent flow is widely present in the aerospace field, and the co-existence of shock wave discontinuities and multi-scale turbulence in the flow field poses significant challenges for high-fidelity numerical simulation. To design high-order nonlinear scheme to improve the accuracy of complex turbulence simulation with stable shock wave capture, a weighted compact nonlinear scheme – targeted essentially non-oscillatory (WCNS-T) scheme is developed based on targeted essentially non-oscillatory scheme within the WCNS framework. Also, an improved variant of WCNS-T with smooth scale separation (denoted as WCNS-ST) is proposed from the perspective of both numerical convergence and accuracy. The numerical properties of different nonlinear weights are discussed in classical numerical problems, including spectral properties analysis, and two-dimensional Riemann problem. Then, the newly developed WCNS-ST scheme based on smooth scale separation was used to combine a unified turbulence model called Self-Adaptive Turbulence Eddy Simulation (SATES), which is applied to simulate subsonic flow past a 30P30N airfoil and supersonic base flow. The good convergence and numerical results are obtained using the newly developed WCNS-ST scheme, whereas WCNS-T shows worse convergence. In addition, adaptive dissipation control is further introduced for the WCNS-ST scheme, and the new variant (denoted as WCNS-STA) still shows good residual convergence and predicts more accurate results due to low numerical dissipation. The above results indicate that the proposed smooth scale separation and its WCNS-STA scheme have a good performance in SATES simulations of multiscale flow problems, making it more potential for complex engineering applications. [ABSTRACT FROM AUTHOR]

Based on a 5-point stencil and three 3-point stencils, a nonlinear multi-order weighted method adaptive to 5-3-3-3 stencils for shock capturing is presented in this paper. The form of the weighting function is the same as JS (Jiang–Shu) weighting; however, the smoothness indicator of the 5-point stencil adopts a special design with a higher-order leading term similar to the τ in Z weighting. The design maintains that the nonlinear weights satisfy sufficient conditions for the scheme to avoid degradation even near extreme points. By adjusting the linear weights to a specific value and using the τ in Z weighting, the method can be degraded to Z weighting. Analysis of linear weights shows that they do not affect the accuracy in the smooth region, and they can also adjust the resolution and discontinuity-capturing capability. Numerical tests of different hyperbolic conservation laws are conducted to test the performance of the newly designed nonlinear weights based on the weighted compact nonlinear scheme. The numerical results show that there are no obvious oscillations near the discontinuity, and the resolution of both the discontinuity and smooth regions is better than that of Z weights. [ABSTRACT FROM AUTHOR]

Based on one 5-point and two 2-point stencils, a nonlinear weighted scheme adaptive to the weighting of multi-order interpolation candidates for shock capturing is proposed. The JS weight function is adopted. The smoothness indicator of the 5-point stencil is specially designed with a higher-order leading term similar to the reference global smoothness indicator τ in the Z weighting. The design maintains that the nonlinear weights satisfy the sufficient condition for the scheme to avoid degradation at extreme points. The form of the weighting is also simplified, obviously reducing the weighting procedure's computational costs. Inviscid and viscous compressible flow problems are simulated to test the performance of the newly designed nonlinear weights based on the weighted compact nonlinear scheme. The numerical results show no obvious oscillations near the discontinuity, and the resolution of both discontinuities and smooth regions is better than JS, Z, and ZQ weighting. [ABSTRACT FROM AUTHOR]

A novel and effective method for the design of maximum directivity irregular phased arrays is proposed in this article. By decomposing the radiation pattern of irregular arrays (IAs) into the product of subarray pattern and subarray array factor, the principal factor for the reduction of directivity and the appearance of high sidelobes is analyzed. Aimed at maximizing directivity of IAs, a binary quadratic optimization problem (BQOP) is established for the design of subarray tiling configuration, where the directivities at considered scanning angles satisfying given peak sidelobes level (SLL) is maximized. To consider the directivities at all the scanning angles within given scan ranges, a concept of “generalized directivity” is introduced and defined. Meanwhile, it is known that high directivity usually enables to suppress high SLL to a great extent. Therefore, the BQOP is reduced to a simplified binary quadratic problem (SBQP) for the maximization of the “generalized directivity” without the high-dimensional constraint on SLL. The associated complex excitations at subarray level are solved using convex optimization after the subarray tiling configuration is determined. By comparing to the reported state-of-the-art methods, several representative numerical examples are implemented to assess the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An irregular tiled array technique is proposed for the application of massive MIMO systems, where the uniformly spaced antenna array elements are irregularly divided into subarrays fed by only one radio frequency (RF) chain separately. As compared to conventional beamforming architecture, the number of RF chains is reduced to one-half or one-quarter of the original number by using domino-shaped subarrays or tetromino-shaped subarrays, respectively. Two beamforming architectures for such a framework are proposed and a minimum mean square error (MMSE) method is applied to design the layouts of irregular arrays efficiently. In the framework of single-user massive MIMO systems, numerical simulation results show that the proposed architectures outperform conventional beamforming architectures and antenna selection architecture under the same number of RF chains conditions. With saving half of the transceivers, the loss of gain of the state-of-the-art sparsely sampled array is 1.9dB in the broadside and 2.2 dB for scanning to 30° in comparison with reference array (i.e., one transceiver per element). By contrast, there is no loss of gain of domino-shaped irregular array (i.e., one transceiver per two elements) in the broadside as compared to reference array and the loss of gain will be about 1.5dB for scanning to 30°. [ABSTRACT FROM AUTHOR]

Advanced array synthesis problems are usually nonconvex regarding the cost functions, which are rather difficult to solve. A numerical stochastic optimization approach based on the multiagent genetic algorithm (MAGA) is proposed for the synthesis of highly thinned arrays in this article. In particular, two modified techniques are introduced into the traditional MAGA, named as improved MAGA (I‐MAGA), to obtain the balance between exploration and exploitation ability. The proposed approach is utilized in some advanced antenna array synthesis problems, including the synthesis of sum and difference patterns and synthesis of several highly thinned planar arrays with different apertures. Numerical results indicate that the proposed I‐MAGA has an attractive exploration and exploitation ability in the synthesis of highly thinned arrays. Besides, owing to the independent multiagent system, the I‐MAGA is also able to obtain better solutions with a much smaller population size and less computational cost. [ABSTRACT FROM AUTHOR]

An innovative architecture for sparsely excited tightly coupled dipole arrays is proposed, based on the irregular array techniques. In such a framework, an improved maximum-entropy model considering the difference of embedded element patterns is applied to optimize the irregular partition to suppress the grating lobes. Meanwhile, guidelines for the entire design procedure including antenna elements, power dividers, and optimization design of irregular feeding networks are presented. In order to achieve large elevation angle scanning, the differential evolution (DE) algorithm is used to synthesize active pattern and active reflection coefficient simultaneously. Finally, a 192-port prototype operating at 8–12 GHz has been fabricated and measured, where the port spacing is $0.576\lambda _{h}$ ($\lambda _{h}$ is the free-space wavelength at the highest frequency). Numerical and experimental results show that the prototype array is able to achieve the reduction of gain <1 dB for scanning to near broadside and about 2.7 dB for scanning up to 60°, in comparison with that of conventional Taylor arrays. [ABSTRACT FROM AUTHOR]

This paper presents an efficient procedure for overcoming the deficiency of weighted essentially non-oscillatory schemes near discontinuities. Through a thorough incorporation of smoothness indicators into the weights definition, up to ninth-order accurate multistep methods are devised, providing weighted essentially non-oscillatory schemes with enhanced order of convergence at transition points from smooth regions to a discontinuity, while maintaining stability and the essentially non-oscillatory behavior. We also provide a detailed analysis of the resolution power and show that the solution enhancements of the new method at smooth regions come from their ability to render smoothness indicators closer to uniformity. The new scheme exhibits similar fidelity as other multistep schemes; however, with superior characteristics in terms of robustness and efficiency, as no logical statements or mapping function is needed. Extensions to higher orders of accuracy present no extra complexity. Numerical solutions of linear advection problems and nonlinear hyperbolic conservation laws are used to demonstrate the scheme's improved behavior for shock-capturing problems. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background: Myocardial necrosis caused by myocardial ischemia-reperfusion (MI/R) in diabetic patients is prominently aggravated and can cause oxidative stress. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a redox-sensing transcription factor that protects against myocardial ischemia/reperfusion injury (MIRI). However, the mechanism of action of Nrf2 in resveratrol-pretreated cardiomyocytes is complex. We assumed that adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)/p38 mitogen-activated protein kinases (p38)/Nrf2 might be involved in resveratrol alleviating MIRI in diabetic rats as an endogenous protective mechanism., Methods: A total of 50 type 2 diabetes mellitus (T2DM) rat models were randomly divided into 5 groups (n=10 in each group): sham group; MI/R group; AMPK inhibitor compound C + myocardial ischemia-reperfusion (C + MI/R) group; resveratrol + myocardial ischemia-reperfusion (RSV + MI/R) group; and resveratrol + AMPK inhibitor compound C + myocardium ischemia-reperfusion group (RSV + C + MI/R) group. Rats were fed a high fat diet, and the T2DM models were established by intraperitoneal injection of 1% streptozotocin (STZ). The MIRI models were established by ligating the left anterior descending coronary artery for 30 minutes followed by reperfusion for 120 minutes. The size of myocardial infarction was measured. Serum samples were collected to measure the concentrations of creatine kinase-MB (CK-MB). The levels of lactate dehydrogenase (LDH), glutathione (GSH), and superoxide dismutase (SOD) in myocardial tissues were determined. Immunofluorescence analysis of translocase of outer mitochondrial membrane 20 (TOMM20) was performed to observe the pathological changes in myocardial tissues. The protein expressions of AMPK, p-AMPK, p38, p-p38, Nrf2, and heme oxygenase 1 (HO-1) were determined by western blotting., Results: Compared with the sham group, the expressions of AMPK, p38, Nrf2, and HO-1 in the myocardium were significantly increased in the MI/R group. Compared with the MI/R group, the RSV + MI/R group had a significantly lower oxidative stress level, milder myocardial injury, increased expressions of AMPK, Nrf2, and HO-1, and lower expression of p38. The protein expressions of Nrf2 and HO-1 were partially inhibited in the RSV + C + MI/R group., Conclusions: Resveratrol can inhibit oxidative stress and alleviate MIRI by activating the AMPK/p38/Nrf2 signaling pathway. Meanwhile, AMPK/p38/Nrf2 is also an endogenous antioxidant stress pathway that protects against stress., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://atm.amegroups.com/article/view/10.21037/atm-22-3789/coif). All authors report that this study was supported by the National Natural Science Foundation of China general program (No. 81860345). The authors have no other conflicts of interest to declare., (2022 Annals of Translational Medicine. All rights reserved.)