Preload-responsive adhesion of microfibre arrays to rough surfaces

Adhesion of bio-inspired microfibre arrays to a rough surface is studied theoretically. The array consists of vertical elastic rods fixed on a rigid backing layer,and the surface is modeled by rigid steps with a normally distributed height. Analytical expressions are obtained for the adhesion forces in both the approach and retraction processes. It is shown that, with the increasing preload, the pull-off force increases at first and then attains a plateau value. The results agree with the previous experiments and are expected helpful in adhesion control of the array in practical applications.

Buckling morphology of glassy nematic films with staggered director field

The photo-induced buckling of axially periodic glassy nematic films with alternating stripped director domains is explored by the F¨oppl-von K′arm′an plate theory along with a modified kinetics approach.The effects of domain widths on the critical light intensity as well as the buckling morphology are examined numerically.It is found that in most cases the buckled film forms regularly aligned dimples and protrusions,but shows large scale bending perpendicular to the periodic axis if the widths of the stripes are nearly the same.In addition,change in light intensity is shown to alter the wavenumber of the buckling pattern.These results are expected helpful to the design of shape-shifting structures with glassy nematic films.

Photo-Activated Snap-Through of Nematic Shallow Spherical Shells

Photo-responsive nematic polymers can transduce light into mechanical work,but the rate is limited by the quasi-static deformation.To enhance the work output,a strat・egy of exploiting photo-triggered snap-through of glassy nematic shallow spherical shells with hemeotropic director alignment is examined here.The criterion for the nonlinear instability is derived analytically by using the modified iteration method.It is shown that,for thin shells of small height and large basal radius,snap-through can be caused by an incident light with moderate irradiation intensity.The phenomenon may inspire some new designs of contactless and ultra-fast actuation devices with high-rate output of mechanical work.

Emergent antisymmetric wrinkling patterns in films on ridged substrates

We report the formation of antisymmetric wrinkling patterns in films on ridged substrates induced by the buckling instability of the substrates via finite element simulations and experiments.Our simulated results reveal that the uniaxial compression along the ridge can trigger both the wrinkling instability of the film and the lateral buckling instability of the ridge.The latter could change the wrinkles from a symmetric pattern to an antisymmetric pattern in a range of film-substrate modulus ratio and aspect ratio of the ridge profile,as validated by the experimental observations.A three-dimensional phase diagram with four buckling patterns,i.e.,sole ridge buckling pattern,antisymmetric wrinkling pattern with different wavelengths from ridge buckling,symmetric wrinkling pattern without ridge buckling,and antisymmetric wrinkling pattern with the same wavelength as ridge buckling,is built with respect to the uniaxial compression,modulus ratio,and aspect ratio.The results not only elucidate how and when the interplay between the wrinkling instability and the ridge instability results in the formation of the antisymmetric wrinkling pattern but also offer a way to generate controllable complex wrinkling patterns.

Surface etching induced ultrathin sandwich structure realizing enhanced photocatalytic activity

Photocatalytic conversion efficiency is limited by serious charge carrier recombination. Efficient carrier separation is usually achieved by elegantly-designed multi-component structures connected by directional electric field. Herein, we developed a twodimensional(2 D) sandwich structure, as a new photocatalytic system, to realize high-efficiency carrier separation. This strategy integrated multifunction into a single structure for the first time, which successfully introduces a stable built-in electric field,realizing high-effective carrier separation. Besides, the carrier concentration is dramatically increased due to dimensional confinement. Benefiting from above synergic advantages, 2 D sandwich photocatalyst achieves the highest nitrogen fixation rate(435 μmol g^(-1) h^(-1)) in inorganic solid photocatalysts under visible light irradiation. We anticipate that 2 D sandwich photocatalyst holds promises for the application and expansion of 2 D materials in photocatalysis research.

Modeling epidemic spread in transportation networks:A review

The emergence of novel infectious diseases has become a serious global problem.Convenient transportation networks lead to rapid mobilization in the context of globalization,which is an important factor underlying the rapid spread of infectious diseases.Transportation systems can cause the transmission of viruses during the epidemic period,but they also support the reopening of economies after the epidemic.Understanding the mechanism of the impact of mobility on the spread of infectious diseases is thus important,as is establishing the risk model of the spread of infectious diseases in transportation networks.In this study,the basic structure and application of various epidemic spread models are reviewed,including mathematical models,statistical models,network-based models,and simulation models.The advantages and limitations of model applications within transportation systems are analyzed,including dynamic characteristics of epidemic transmission and decision supports for management and control.Lastly,research trends and prospects are discussed.It is suggested that there is a need for more in-depth research to examine the mutual feedback mechanism of epidemics and individual behavior,as well as the proposal and evaluation of intervention measures.The findings in this study can help evaluate disease intervention strategies,provide decision supports for transport policy during the epidemic period,and ameliorate the deficiencies of the existing system.

湿度驱动的高性能致动器与传感器:界面工程调控氧化石墨烯与乙基纤维素（英文）

致动器可以将外界环境中的能量直接转换成机械能,在能源应用和智能设备上有着广阔的应用前景.但迄今为止,界面接触强度较低以及湿度响应是制约驱动器发展的瓶颈问题,限制了其实际应用.本文从实验上构建了优化双层膜结构驱动器界面接触的模型,所构建的氧化石墨烯与乙基纤维素双层膜致动器对于环境湿度的变化具有快速可逆的响应性,同时可以驱动压电探测器.此结构模型中,氧化石墨烯与乙基纤维素之间通过化学键结合,成功地构建了机械强度和韧性协同增强的双层膜驱动器.由于氧化石墨烯的优异吸湿特性,同时伴随着明显的体积膨胀,引起双层膜驱动器对于湿度变化超过90度弯曲的响应.同时,构建的压电传感器具有优异可逆性的0.1 V开路电压.我们期望湿度响应驱动器和传感器有望在各种多功能纳米系统中得到应用并能服务于智能设备领域.

Improved phase field model of dislocation intersections

Revealing the long-range elastic interaction and short-range core reaction between intersecting dislocations is crucial to the understanding of dislocation-based strain hardening mechanisms in crystalline solids.Phase field model has shown great potential in modeling dislocation dynamics by both employing the continuum microelasticity theory to describe the elastic interactions and incorporating theγ-surface into the crystalline energy to enable the core reactions.Since the crystalline energy is approximately formulated by linear superposition of interplanar potential of each slip plane in the previous phase field model,it does not fully account for the reactions between dislocations gliding in intersecting slip planes.In this study,an improved phase field model of dislocation intersections is proposed through updating the crystalline energy by coupling the potential of two intersecting planes,and then applied to study the collinear interaction followed by comparison with the previous simulation result using discrete dislocation dynamics.Collinear annihilation captured only in the improved phase field model is found to strongly affect the junction formation and plastic flow in multislip systems.The results indicate that the improvement is essential for phase field model of dislocation intersections.