Design and Analysis of Spatial Modulation Based Orthogonal Time Frequency Space System

In this paper,we design a spatial modulation based orthogonal time frequency space(SMOTFS)system to achieve improved transmission reliability and meet the high transmission rate and highspeed demands of future mobile communications,which fully utilizes the characteristics of spatial modulation(SM)and orthogonal time frequency space(OTFS)transmission.The detailed system design and signal processing of the SM-OTFS system have been presented.The closed-form expressions of the average symbol error rate(ASER)and average bit error rate(ABER)of the SM-OTFS system have been derived over the delay-Doppler channel with the help of the union bounding technique and moment-generating function(MGF).Meanwhile,the system complexity has been evaluated.Numerical results verify the correctness of the theoretical ASER and ABER analysis of the SM-OTFS system in the high signal-to-noise ratio(SNR)regions and also show that the SM-OTFS system outperforms the traditional SM based orthogonal frequency division multiplexing(SM-OFDM)system with limited complexity increase under mobile conditions,especially in high mobility scenarios.

生物可降解地膜的研究进展

地膜在现代化农业中已经得到了广泛的应用,但由于传统塑料地膜在土壤中难以降解而导致"白色污染",破坏土壤结构,减小土壤肥力,影响农业的可持续发展,而推广生物可降解地膜是解决这一问题的有效途径。本文综述了生物可降解地膜的种类、性能及其应用。

聚乳酸改性及其在包装材料中的应用

聚乳酸(PLA)是一种具有高强度、高模量、透明性、生物降解性和生物相容性的生物基热塑性聚酯,已发展成为具有一定竞争力的商业化材料,并有望在包装领域逐步替代传统的石油基聚合物。然而,PLA的应用却受其本身固有的结晶速率慢、结晶度低和脆性大等缺点的限制。近年来,研究人员做了大量工作以解决PLA的上述技术瓶颈。本文综述了PLA在成核结晶与增韧改性领域的研究进展以及PLA在包装材料中的应用。

Hierarchical graphene@MXene composite foam modified with flower-shaped FeS for efficient and broadband electromagnetic absorption

Developing high-performance broadband microwave absorption material becomes an urgent concern in the field of electromagnetic protection.In this work,an ultralight magnetic composite foam was con-structed by electrostatic self-assembly of MXene on the surface of graphene skeletons,and subsequent hydrothermal anchoring of flower-shaped FeS clusters.Under the synergistic effect of MXene coating in-creasing conductive loss and FeS clusters improving magnetic loss,the rational construction of hierarchi-cal impedance structure in foam can effectively promote the entrance and consumption of more incident electromagnetic waves.The minimum reflection loss(RL min)reaches-47.17 dB at a thickness of 4.78 mm,and the corresponding effective absorption bandwidth(EAB)is up to 6.15 GHz.More importantly,the microwave absorption performance of composite foam can be further optimized by controlling the load-ing of MXene and thermal treatment at a low temperature.The maximum of EAB for GMF-300 can be extended to an unprecedented value of 11.20 GHz(covering 6.10-17.30 GHz).

Ultrathin,flexible,and oxidation-resistant MXene/graphene porous films for efficient electromagnetic interference shielding

Designing and fabricating efficient electromagnetic interference(EMI)shielding materials becomes a significant and urgent concern.Hence,a novel ultrathin,flexible,and oxidation-resistant MXene-based graphene(M-rGX)porous film is successfully fabricated by electrostatic self-assembly between MXene and graphene oxide(GO)nanosheets,and subsequently thermal annealing under hydrogen-argon atmosphere.The rapid breakaway of functional groups on GO and MXene sheets induces formation of porous conductive network in film,thereby facilitating efficient shielding for incident electromagnetic waves.The optimal absolute shielding effectiveness(SSE/t)value of 76,422 dB·cm2·g−1 can be achieved at a thinner thickness of 15μm.More importantly,the effective removal of functional groups on MXene conspicuously improves the oxidation resistance of the film,endowing it with an excellent durability(12 months)in EMI shielding performance.

Ultralight and ordered lamellar polyimide-based graphene foams with efficient broadband electromagnetic absorption

The development of high-performance microwave absorption materials with strong absorption capacity and broad bandwidth is highly desirable in the field of electromagnetic pollution protection.Herein,ultralight polyimide-based graphene foam with ordered lamellar structure is precisely designed and controllably constructed by bidirectional freezing process.More lamellar interfaces formed inside the foam per unit volume effectively facilitate the layer-by-layer dissipation for the vertical incident electromagnetic waves,thereby endowing the foam with efficient broadband electromagnetic absorption performance.More importantly,electromagnetic absorption performance can be controllably adjusted by optimizing impedance distribution and microstructure of skeletons.As a result,the optimized foam with an ultralow density of 9.10 mg/cm^(3)presents a minimum reflection loss value of-61.29 dB at 9.25 GHz and an effective absorption bandwidth of 5.51 GHz(7.06-12.57 GHz,covering the whole X band) when the thickness is 4.75 mm.

Compressible and Lightweight MXene/Carbon Nanofiber Aerogel with “Layer‑Strut” Bracing Microscopic Architecture for Efficient Energy Storage

Two-dimensional MXene has recently captured widespread research attention in energy storage and conversion fields due to its high conductivity,large specific surface area,and remarkable electro-activity.However,its performance is still hindered by severe self-restacking of MXene flakes.Herein,conductive Ti_(3)C_(2)T_(x)/carbon nanofiber(CNF)composite aerogel with typical“layer-strut”bracing 3D microscopic architecture has been fabricated via synergistic assembly and freeze-drying process.In virtu of the strong interfacial interaction between polymeric precursor nanofibers and MXene mono-layers,gelation capability and 3D formability of Ti_(3)C_(2)T_(x) is greatly reinforced,as resulted Ti_(3)C_(2)T_(x)/CNF aerogels possess a highly ordered microporous structure with interlayered CNF penetrating between large size MXene lamellae.This special configuration guarantees the stability and pliability of the composite aerogels.Furthermore,the 3D form interconnected conductive network and the parallell alignment of the pores allow free electrical carriers motion and ion migration.As a result,the prepared Ti_(3)C_(2)T_(x)/CNF aerogel-based electrode exhibits an exceptional gravimetric specific capacitance of 268 F g^(−1) at a current density of 0.5 A g^(−1) and an excellent cycling stability of 8000 cylcles,and the assembled symmetric supercapacitor,delivers a high energy density of 3.425 W h kg^(−1) at 6000 W kg^(−1).This work offers a new route for the rational construction of 3D MXene assembly for advanced energy storage materials.

Bio-renewable polymers based on lignin-derived phenol monomers:Synthesis,applications,and perspectives

In recent decades,the continuous depletion of fossil fuels and the increasingly serious environmental issue have aroused wide attention on the development of biopolymers based on renewable biomass.Lignin is the second most abundant organic bio-based macromolecule second to cellulose,and it can be widely found in plants.Furthermore,various phenol derivatives can be obtained by their depolymerization processes.The development of bio-renewable polymeric materials originating from lignin-derivative phenol monomers,such as vanillin,syringaldehyde,eugenol,vanillyl alcohol,vanillic acid,and ferulic acid,will not only valorize the bio-sourced materials but also effectively reduce petroleum resource consumption and mitigate the environmental pollution.Therefore,an updated overview of the synthesis processes of these bio-based polymers developed in the past decade,which includes both thermosets and thermoplastics such as epoxy,phenolic,polyimine,polybenzoxazine,polyurethane,and polyesters,are elucidated.In addition,the applications of these bio-based polymers and their composites in flame-retarded materials,degradable and reprocessable materials,dielectric materials,optoelectronic materials,as well as smart responsive materials are also intensively discussed.In line with the gradual development of synthesis technologies,we believe that derivatives of lignin will turn into one of the most promising materials to be considered for the preparation of high-performance and functional bio-based polymer materials.