Coding metasurfaces for diffusion scattering of electromagnetic (EM) waves are important for stealth applications and have recently attracted researchers in physics and engineering communities. Typically, the available design approaches of coding metasurfaces lack a coding sequence design formula and sometimes cannot simultaneously ensure uniform diffusion and low reflected power intensity without extensive computational optimization. To the authors' best knowledge, the diffusion and radar-cross-section reduction (RCSR) of 2D axicon metasurfaces for cloaking and stealth applications have not been explored before. This article presents a single-layer coding metasurface design that exhibits an axicon phase mask on its aperture for efficient diffusion of EM-waves and RCSR of metallic objects. The proposed approach is robust and ensures greater than 10 dB of RCSR for normal incidence and a wide-range of off-normal incident angles. Theoretical calculations, numerical simulations, and experimental validations of the proposed axicon coding metasurface demonstrate that the 10 dB RCSR covers the frequency range of 15 to 35 GHz (fractional bandwidth is 80%) under normal incidence. Under off-normal incidence, the RCSR and the diffusive scattering behavior are preserved up to 60° regardless of the polarization of the far-field incident radar wave. Compared to other available approaches, the presented design approach is fast, robust, and can achieve more uniform diffusive scattering patterns with remarkable RCSR, which makes it very attractive for potential stealth applications.
An experimental investigation on the spatial distribution of knock events in a turbocharged spark-ignition engine for hybrid vehicle applications was conducted by using a multichannel fiber optic method. The knock positions were detected under different conditions to investigate the influence of crucial engine design and operating parameters on the knock characteristics including the spatial distribution in the combustion chamber and its relationship to knock intensity. The measured data reveal that the spatial distribution in the engine with a port fuel injection (PFI) system is mainly located on the exhaust side with insignificant influence of engine speed and load, which is attributed to the elevated thermal load around the exhaust valves. However, the knock events under gasoline direct-injection (DI) conditions were found to occur in more scattered locations with more occurring on the engine front-end and rear-end sides. These results indicate that the in-cylinder fuel-air mixing process may have a significant impact on the knock occurrence spots under DI conditions. The knock positions of the engine with different excessive air ratios, injection timings, and intake-valve timings were also detected, indicating that engine operating parameters have complex influences on the knock-region distribution in a DI engine. In addition, experiments were also carried out in two different cylinders to verify the cylinder-to-cylinder variations in knock regions which may be caused by the engine cooling design. Furthermore, no apparent correlations were observed between the knock position and the knock intensity by analysis of the experimental data.
In this paper, a residual cut square antenna array is designed based on a broadband all-metal cavity slot antenna with filtering performance for aerial reconnaissance radar. The proposed antenna element consists of a metal cavity with radiation slots and a metal matching block. The antenna element obtains a wide operating bandwidth through the multiple resonant modes of the cavity and slots. Simulation results show that the impedance bandwidth (S11<-10 dB) of the antenna element is operating from 7.83 GHz to 12.41 GHz with a relative bandwidth of 45%. It also has good filtering characteristics with more than 20-dB stop-band rejection, which suppresses unwanted interference and helps to achieve a good electromagnetic compatibility (EMC) design. A 2×16 antenna array was designed to verify the performance of beam scanning for Cosecant square.
Study status on shearer mining in thin seams in the world is introduced. Base on the geological conditions of instable and soft thin-seam with hard roof in Caoyao Coal Mine of Yima Coal Group, China, and combined with related parameters of strata behaviors at coal faces, the paper concludes that the strata control on the thin-seam coal face is comparatively easy in line with the criteria for classification on strata stability of gently-inclined coal faces in China. Hydraulic supports of two-prop shielding with rated effective resistance of 2400kN can be employed in thin seam coal faces. Basic requirements for coordination equipments of shearer are summed up while mining thin seams. According to successful experiences of extracting thin seams in similar geological conditions in China, the scheme of feasibility coordination equipments of shearer is optimized in thin seams with thickness of 0.8-1.4m and 1.1-1.9m, respectively. The conclusions will provide a reference value for Caoyao Coal Mine on carrying out mechanized mining of the mine, improving safety production capability, and prolonging the mine life.
Four-point bend test and numerical simulation method were used to investigate the crack tip stress and strain field and ductile to brittle transition behavior of pure Al interlayer,which was constrained by LY12 alloy at both sides through explosive bond method,under different strength mismatch ratio after heat treatment at different temperatures.The results show that the increase of strength mismatch ratio at interfaces has an obvious effect on the triaxial tensile stress and its distribution,and the increase of stress triaxiality has a dominant role in the ductile to brittle transition of Al interlayer.Cleavage will initiate at crack-tip of the Al interlayer under critical stress triaxiality and maximum tensile stress.
Abstract Protein folding is subject to the effects of solvation environment. A variety of organic solvents are used as additives for in vitro refolding of denatured proteins. Examination of the solvent effects on protein folding could be of fundamental importance to understand the molecular interactions in determining protein structure. This article investigated the folding of α-helix and β-hairpin structures in water and the solutions of two representative refolding additives (methanol (MeOH) and 1-Ethyl-3-methylimidazolium chloride (EMIM-Cl) ionic liquid) using REMD simulations. For both α-helix and β-hairpin in MeOH/water solution or α-helix in EMIM-Cl/water solution, the transient structures along the folding pathway are consistent with the counterparts in water but the relative statistical weights are changed, leading to the decrease in the overall folding free energy barrier. Accordingly, MeOH promotes the folding of both α-helix and β-hairpin but EMIM-Cl ionic liquid only promotes the folding of α-helix, consistent with experimental observations. The present study reveals for the first time the trivial effects on folding route but significant effects on folding thermodynamics from MeOH and EMIM-Cl, explaining the function of protein refolding additives and testifying the validity of the folding mechanism revealed by in vitro protein folding study using refolding additives.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)