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Cooperative spectrum sensing is regarded as the foundation and a key stage of cognitive radio networks. The node allocation strategy during the spectrum detection process was directly determined by the results of joint spectrum sensing. Various methods for allocating cognitive terminals to enhance the efficiency and fairness of spectrum sensing were introduced. Aiming at the perceptual efficiency of different sub-bands, an indicator called the inefficient transmission parameter (ITP) was proposed to evaluate communication performance, and a closed-form expression solution to the perceptual efficiency optimization problem was provided. The designed scenarios included terminal pairs with the same frequencies having different perceptual properties and the same perceptual properties. For the perceived fairness among different sub-bands, two allocation algorithms were proposed: the arcuate allocation algorithm and the class division allocation algorithm. Fairness between sub-bands was measured by evaluating the worst perceived performance in the sub-band. In order to be applicable to actual scenarios, the frequency band property parameter was added to enhance fairness. This parameter was taken into account the priority and anti-interference ability of the main user using different frequency bands. Simulation results show that the proposed strategy significantly improves ITP in cognitive radio networks, especially when sub-band utilization is different, and the proposed arcuate allocation algorithm significantly improves the perceived fairness of the system.

Mg-based porous materials have broad application prospect in biomedical field.In order to improve the corrosion resistance of porous Mg-Al alloy in human body fluid，porous Mg-Al alloy was prepared by powder metallurgy，and Y2O3 with different contents (0，0.2%，0.4%，0.6%) was added to modify the Mg-Al alloy.The effects of Y2 O3 content on the porosity，pore morphology，microstructure，compressive strength and corrosion resistance of porous Mg-Al alloy in Hank's biomimetic solution were investigated by means of metallographic microscope，XRD，SEM，universal testing machine and electrochemical workstation.Results showed that the porosity of porous Mg-Al alloy prepared by powder metallurgy was about 39%，and the powder metallurgy method could accurately control the pore morphology and size of porous Mg-Al alloy.Moreover，porous Mg-Al alloy was mainly composed of Mg and the second phase Al12Mg17.The addition of Y2O3 could refine the grains of porous Mg-Al alloy，homogenize the grain size，distribute the second phase more evenly，and improve the compressive strength of porous Mg-Al alloy and its corrosion resistance in Hank's bionic solution.When the content of Y2O3 was 0.4%，the compressive strength of porous Mg-Al alloy was 46.4 MPa，and the corrosion rate in Hank's biomimetic solution was 0.887 44 mm/a.

As an important strengthening phase in Al-Mg-Fe alloy, the elastic and ductile–brittle characteristics of Al13Fe4 intermetallics hold prime significance in ascertaining the mechanical properties and potential application of Al-Mg-Fe alloys. In this study, multialloying of Co, Cu, Cr, Mn, and Ni has been adopted for tuning the mechanical characteristics of the Al13Fe4 phase; their effects on mechanical features and electronic structure of the Al13Fe4 phase have been scrutinized systematically by first-principles calculations employing the density functional theory. The replacement of Fe with M (M = Co, Cu, Cr, Mn, and Ni) is energetically advantageous at 0 K, as evidenced by the negative cohesive energy and mixing enthalpy of all Al13(Fe,M)4 phases. Cu and Ni, on the contrary, have a detrimental impact on Al13Fe4′s modulus and hardness due to the evolution of chemical bonding strength. Co, Cr, and Mn are thus, interesting candidate elements. In the light of B/G and Poisson's ratio (σ) criteria, Al13Fe4, Al13(Fe,Cu)4, and Al13(Fe,Ni)4 have superior ductility; however, Al13(Fe,Co), Al13(Fe,Mn), and Al13(Fe,Cr)4 tend to be brittle materials. Calculation-based findings show that Co, Cr, and Mn are appropriate alloying elements for enhancing fracture toughness, whereas Mn reduces Al13Fe4′s elastic anisotropy. The electronic structure assessment found that the mechanical properties of the intermetallics are predominantly influenced by the Al-M bonds when the alloying element M replaced Fe. [ABSTRACT FROM AUTHOR]

As a carrier of stealth technology and electromagnetic protection, microwave absorbing materials have received extensive attention from researchers. Herein, a biomass porous C/FexOy composite was prepared by heat treatment of almond shell layers dipped in different concentrations of iron nitrate solution at 600 °C, 800 °C, and 1000 °C, respectively. The composite material was examined and found to have good microwave absorption properties and multi-loss synergistic effects. When the ferric nitrate concentration is 22.3%, and the heat treatment temperature is 800 °C, the minimum reflection loss can be obtained as − 31.8 dB with a thickness of 2.5 mm. The frequency bandwidth with a reflection loss of less than − 10 dB is 4.80 GHz when the absorber thickness is 2 mm. Therefore, almond wood porous biomass carbon exhibits strong microwave absorbing properties and has great application potential in military and civilian fields. [ABSTRACT FROM AUTHOR]