Polarization quaternion DOA estimation based on vector MISC array

This paper examines the direction of arrival(DOA)estimation for polarized signals impinging on a sparse vector sensor array which is based on the maximum interelement spacing constraint(MISC).The vector array effectively utilizes the polarization domain information of incident signals,and the quaternion model is adopted for signals polarization characteristic maintenance and computational burden reduction.The features of MISC arrays are crucial to the mutual coupling effects reduction and higher degrees of freedom(DOFs).The quaternion data model based on vector MISC arrays is established,which extends the scalar MISC array into the vector MISC array.Based on the model,a quaternion multiple signal classification(MUSIC)algorithm based on vector MISC arrays is proposed for DOA estimation.The algorithm combines the advantages of the quaternion model and the vector MISC array to enhance the DOA estimation performance.Analytical simulations are performed to certify the capability of the algorithm.

Quantitative law of diffusion induced fracture

Through dimension analysis, an almost analytical model for the maximum diffusion induced stress（DIS）and critical temperature（or concentration） difference at which cracks begin to initiate in the diffusion process is developed. It interestingly predicts that the spacing of diffusioninduced cracks is constant, independent of the thickness of specimen and the temperature difference. These conclusions are validated by our thermal shock experiments on alumina plates. Furthermore, the proposed model can interpret observed hierarchical crack patterns for high temperature jump cases, and a three-stage relation between the residual strength and the temperature difference. The prediction for crack spacing can guide the biomimetic thermal-shockfailure proof design, in which the hard platelets smaller than the predicted diffusion induced by constant crack-spacing are embedded in a soft matrix, and, therefore, no fracture will happen. This may guide the design of the thermal protection system and the lithium ion battery. Finally we present the maximum normalized DISes for various geometry and boundary conditions by single-variable curves for the stressindependent diffusion process and two-variable contour plots for the stress-dependent diffusion process, which can provideengineers and materialists a simple and easy way to quickly evaluate the reliability of related materials and devices.

From Mechanically Interlocked Structures to Host-Guest Chemistry Based on Twisted Dimeric Architectures by Adjusting Space Constraints

Mechanically interlocked molecules(MIMs)and host–guest chemistry have received great attention in the past few decades.However,it remains challenging to design architectures with mechanically interlocked features and construct cavities for guest molecule recognition using similar building blocks.In this study,we designed and constructed a series of novel twisted supramolecular structures by assembling various multitopic terpyridine(tpy)ligands with the same diameter and Zn(II)ions.The obtained complexes exhibited evolutional architectures and showed distinctively different space-constraint effects.Specifically,the assembled dimer SA,SB,and SBH displayed mechanically interlocked phenomena,including[2]catenane and[3]catenane,with an increase in concentration.However,no interlocked structures were observed in complexes SC and SCH constructed by hexatopic tpy ligands due to the significant space constraints.The single-crystal data of complex SCH further proved significant space constraints and illustrated the formation of a relatively closed cavity,which showed excellent host–guest properties for different calixarenes,especially high affinity for calix[6]arene.

Cooperative game penetration guidance for multiple hypersonic vehicles under safety critical framework

The rapid development of the anti-missile weapon technology brings new challenges to the cooperative penetration strategy solution and the guidance law design for Hypersonic Vehicles(HVs).This paper studies the coordinated game penetration guidance problem for multiple hypersonic vehicles faced with space threat areas.A scheme for seeking cooperative game penetration guidance strategy under safety critical control framework is presented.In this scheme,a multiHV cooperative game model is proposed in a minimum optimization form which can simplify the solving process and accelerate the computing speed.Then,a second-order control barrier function is developed to transform the implicit nonlinear constraints of the proposed model into linear ones.In order to obtain better performance of guidance strategy,a composite guidance law under the safety critical control framework is presented to allocate guidance strategies appropriately in the whole process.It is shown that the proposed scheme can guarantee successful penetration while avoiding threat areas.Finally,a comparative simulation with a two-on-three game is conducted to verify the effectiveness of the proposed method.