具有类roton色散关系的立方对称声学超材料

我们之前的工作表明,声学超材料中的非局部相互作用会导致极不寻常的类roton色散关系,即色散曲线存在局部极小值,与超流体液氦-4类似.然而,这种行为仅限于一个或两个声传播方向.在这里,我们设计了一种三维立方对称声学超材料,沿三个正交方向具有非局部相互作用.有限元计算表明超材料在三个正交方向具有类roton行为,但其行为远非各向同性.有限元结果与半解析模型结果吻合良好.相应的实验正在探索中,由于需要密集而复杂的三维声学管道,实验要求较高.

Selective thermal emission and infrared camouflage based on layered media

Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention.By eliminating thermal radiation differences between the object and the background,it is possible to hide a given object from infrared detection.Infrared camouflage is an important element that increases the survivability of aircraft and missiles,by reducing target susceptibility to infrared guided threats.Herein,a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth,with distinctive advantages of scalability,flexible fabrication,and structural simplicity.The multilayer medium consists of silicon substrate,carbon layer and zinc sulfide film,the optical properties of which are determined by transfer matrix method.By locally changing the thickness of the coating film,the spatial tunability and continuity in thermal emission are demonstrated.A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality.In addition,other functionalities,like thermal illusion and thermal coding,are demonstrated by thickness-engineered multilayer films.

Frequency reconfigurable antenna actuated by inflated triangular structure:Design and analysis

This paper proposes a frequency reconfigurable triangular antenna actuated by an inflated triangular structure.The open path antenna is transformed from an open type to a closed structure by inflating.Inflatable structures are easy to manufacture by fusing 2 inextensible membranes together along a defined pattern of lines.However,the prediction of their deployed shape remains a challenge.To solve the pattern changed problem,guided by geometric analyses and local buckle characteristics,the inflated triangular structure has been designed and verified by experiment and simulation.In the process of transformation of the antenna,the resonant frequency of the antenna is changed because this frequency is determined by the conformational change.The resonant frequency changes from GHz to kHz when the design of initial structure sizes is from millimeter to meter.The measured peak gains,the frequency,and the radiation direction are also reconfigurable by the initial size.Finally,the reconfigurable resonator array is presented,which is coupled to electric fields to absorb all incident radiation.In this work,the changed pattern design by inflating is applied to the antenna design,and its frequency reconfigurability is achieved.Through the electricity performance analysis of the reconfigurable antenna,precise manufacturing will be possible and provide guidance for manufacturing frequency reconfigurable antennas.

一种源自细菌注射系统的可重编程的蛋白质递送工具

Methods of manipulating protein in cells are of great value in research and clinical therapies.Indirect methods,such as plasmid and mRNA transfection,and virus-based delivery,have been important skills of life science and medical researchers.Although extensively applied,these nucleic-acids-based approaches are limited by many shortcomings[1].It is very difficult to precisely manipulate the expression level and timeframe of the objective protein in host cells in these methods.The intracellular stabilities of the plasmids or mRNAs that encode the objective genes are affected by several factors,including gene sequence,three-dimensional structure,host nucleases and their delivery processes.These indirect methods require the host transcriptional and translational systems for protein synthesis.However,the transcription and translation machines are tightly regulated by host signaling.In addition,the immunogenicity of DNAs and viral vectors,and the safety of the lipid nanoparticles for mRNA transfection are obstacles of these indirect methods in many clinical applications[2].In contrast,direct protein delivery with target-cell specificity is more efficient in controlling the quantity and function of the protein of interest.However,due to the hydrophobicity of plasma membrane and high molecular weights of proteins,it remains a great challenge to direct deliver protein into target cells across the intact plasma membrane.

Light weight optimization of stratospheric airship envelope based on reliability analysis

A stratospheric airship is an essential flight vehicle in the aviation field.In this paper,optimal design approach of stratospheric airships is developed to optimize envelope shape considering three failure modes and multidisciplinary analysis models,and could also reduce the mass of a stratospheric airship to be deployed at a specific location.Based on a theoretical analysis,three failure modes of airships including bending wrinkling failure,hoop tearing failure and bending kink failure,are given to describe and illustrate the failure mechanism of stratospheric airships.The results show that the location,length and size of the local uniform load and the large fineness ratio are easier to lead to bending wrinkling failure and bending kink failure.The small fineness ratio and the increasing differential pressure are more prone to cause hoop tearing failure for an airship hull.The failure probability is sensitive to the wind field.From an optimization design,the reliability analysis is essential to be carried out based on the safety of the airship.The solution in this study can provide economical design recommendations.

A novel inflatable rings supported design and buoyancy-weight balance deformation analysis of stratosphere airships

Owing to the unique advantages in flight altitude,dwelling time and wide coverage area,stratospheric airships provide permanent monitoring and surveillance for both civil and military applications.Here we propose a semi-rigid stratosphere airship design with circumferential high-pressure inflatable rings and a longitudinal carbon fiber skeleton supported inside.We perform numerical simulations to analyze the deformation characteristics during the whole ascending and descending process.An equivalent internal gradient pressure model of helium is established based on the capsule shape and buoyancy-weight equilibrium conditions.The implicit dynamic method is used to deal with the large deformation of the airship capsule under a low negative pressure condition.Deformation and load-bearing performance of the airship capsule,inflatable ring,skeleton,and suspension line are obtained under different working conditions.The results show that the airship,supported with the inflatable rings and the suspension lines,effectively maintains the shape and ensures the stiffness during the ascending,dwelling,and descending stages,especially suffering from negative pressure.

Deployment of SMP Miura-ori sheet and its application:Aerodynamic drag and RCS reduction

Origami,such as Miura-ori,is the art of folding two-dimensional materials into complex,elaborate,and multifunctional three-dimensional objects.In this paper,SMP MO sheet are prepared,and the accuracy of deployable process is verified by experiments.The folding and deployable process of SMP MO sheet is divided into 4 stages,and each stage is described in detail.The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0,and this is similar to the theoretical shear equivalent modulus in the Y direction.The effects of various parameters on strain and stress are also explored.The purpose of studying these mechanical characteristics is to provide driving force reference in application;In terms of application,the flow field and electromagnetic characteristics of MO sheet in different directions are studied.The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated.When the dihedral fold angle is about 45°,the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal,which is most beneficial to morphing aircraft.

Pressure-induced instability and its coupled aeroelasticity of inflated pillow

A floating air weapon system(such as airborne floating mines)plays an important role in modern air defense operations.This paper focuses on aeroelastic characteristics of airborne floating mine named inflated pillow.Firstly,the dynamic deployable process of the pillow and characteristics of the local instability of the edge are studied,and the evolution mechanism of wrinkles and kinks is analyzed.Secondly,in the cruising stage,the fluid-structural-thermal coupling analysis is performed on the pillow,and the aeroelastic characteristics are studied.Thirdly,the shapepreserving effect of the inflated pillow during the“negative pressure”slow landing stage is evaluated.It is found that when the wind velocity is higher,the pillow has a collapsed instability(surface extrusion and contact),and when the wind velocity is lower,snap-through instability occurs.Finally,for the collapsed instability,a carbon fiber skeleton is added to discrete the large global collapsed fold into small local folds,thus achieving shape-preserving effect of pillow.For snapthrough instability,the critical internal pressure and different shape evolution under different wind velocity are evaluated.Through the analysis of the mechanical mechanism and control of the structural morphological evolution,it provides theoretical guidance for the application of the curved shell structure in floating air weapon system.