A NUMERICAL STUDY OF INDENTATION WITH SMALL SPHERICAL INDENTERS

The finite element method for the conventional theory of mechanism-based strain gradient plasticity is used to study the indentation size effect. For small indenters （e.g., radii on the order of 10μm）, the maximum allowable geometrically necessary dislocation （GND） density is introduced to cap the GND density such that the latter does not become unrealistically high. The numerical results agree well with the indentation hardness data of iridium. The GND density is much larger than the density of statistically stored dislocations （SSD） underneath the indenter, but this trend reverses away from the indenter. As the indentation depth （or equivalently, contact radius） increases, the GND density decreases but the SSD density increases.

Mechanics of bioinspired imaging systems

Imaging systems in nature have attracted a lot of research interest due to their superior optical and imaging characteristics, Recent advancements in materials science, mechanics, and stretchable electronics have led to successful development of bioinspired cameras that resemble the structures and functions of biological light-sensing organs. In this review, we discuss some recent progresses in mechanics of bioinspired imaging systems, including tunable hemispherical eyeball camera and artificial compound eye camera. The mechanics models and results reviewed in this article can provide efficient tools for design and optimization of such systems, as well as other related optoelectronic systems that combine rigid elements with soft substrates.

Metal and organo-catalysed asymmetric hydroaminomethylation of styrenes

A new protocol that enables asymmetric hydroaminomethylation of styrenes to afford chiral amines has been developed. Catalysed by an Rh-phosphine species and a chiral phosphoric acid, styrenes are converted into β-chiral amines with good enantioselectivities under syngas in the presence of an amine and Hantzsch ester. The reaction involves two key steps, hydroformylation and reductive amination, with the former catalysed by the Rh species whilst the latter by the phosphoric acid.

甲醇为氢源:Rhodacycle催化α,β-不饱和酮化学选择性转移加氢反应（英文）

甲醇是一种安全、经济、易处理的氢源,然而它很少用于转移加氢反应中.本文以甲醇为氢源,报道了一种环金属化铑配合物, Rhodacycle,催化α,β-不饱和酮的高度化学选择性加氢反应.在回流甲醇中反应很短的时间,将各种查尔酮、苯乙烯基甲基酮和乙烯基甲基酮(包括空间要求大的酮)还原为饱和酮,无需惰性气体保护,也未观察到羰基部分的还原.该催化反应为α,β-不饱和酮化合物中烯键的还原提供了一种简便、操作安全的方法.

Buckling of thin gel strip under swelling

The buckling of thin gel film has attracted much attention due to its applications in the design of three- dimensional structure from two-dimensional template. We have established an analytical model to study the swelling-induced buckling of a thin gel strip with one edge clamped and the others free. The closed-form solutions for the amplitude and wavelength of the buckled shape are obtained by energy minimization of the total potential energy. The analytical results agree well with finite element analysis based on the inhomogeneous gel theory without any parameter fitting. The model provides a route to study complex postbuckling behaviors of thin gel films and guidelines to design the buckled configuration quantitatively by controlling the swelling ratio.

Optical Micro/Nano Fibers Enabled Smart Textiles for Human-Machine Interface

Wearable human-machine interface(HMI)is an advanced technology that has a wide range of applications from robotics to augmented/virtual reality(AR/VR).In this study,an optically driven wearable human-interactive smart textile is proposed by integrating a polydimethylsiloxane(PDMS)patch embedded with optical micro/nanofibers(MNF)array with a piece of textiles.Enabled by the highly sensitive pressure dependent bending loss of MNF,the smart textile shows high sensitivity(65.5 kPa^(−1))and fast response(25 ms)for touch sensing.Benefiting from the warp and weft structure of the textile,the optical smart textile can feel slight finger slip along the MNF.Furthermore,machine learning is utilized to classify the touch manners,achieving a recognition accuracy as high as 98.1%.As a proof-of-concept,a remote-control robotic hand and a smart interactive doll are demonstrated based on the optical smart textile.This optical smart textile represents an ideal HMI for AR/VR and robotics applications.

Single optical microfiber enabled tactile sensor for simultaneous temperature and pressure measurement

The ability to sense heat and touch is essential for healthcare,robotics,and human–machine interfaces.By taking advantage of the engineerable waveguiding properties,we design and fabricate a flexible optical microfiber sensor for simultaneous temperature and pressure measurement based on theoretical calculation.The sensor exhibits a high temperature sensitivity of 1.2 nm/℃ by measuring the shift of a high-order mode cutoff wavelength in the short-wavelength range.In the case of pressure sensing,the sensor shows a sensitivity of 4.5%per kilopascal with a fast temporal frequency response of 1000 Hz owing to the strong evanescent wave guided outside the microfiber.The cross talk is negligible because the temperature and pressure signals are measured at different wavelengths based on different mechanisms.The properties of fast temporal response,high temperature,and pressure sensitivity enable the sensor for real-time skin temperature and wrist pulse measurements,which is critical to the accurate analysis of pulse waveforms.We believe the sensor will have great potential in wearable optical devices ranging from healthcare to humanoid robots.

Stretchable,Rehealable,Recyclable,and Reconfigurable Integrated Strain Sensor for Joint Motion and Respiration Monitoring

Cutting-edge technologies of stretchable,skin-mountable,and wearable electronics have attracted tremendous attention recently due to their very wide applications and promising performances.One direction of particular interest is to investigate novel properties in stretchable electronics by exploring multifunctional materials.Here,we report an integrated strain sensing system that is highly stretchable,rehealable,fully recyclable,and reconfigurable.This system consists of dynamic covalent thermoset polyimine as the moldable substrate and encapsulation,eutectic liquid metal alloy as the strain sensing unit and interconnects,and off-the-shelf chip components for measuring and magnifying functions.The device can be attached on different parts of the human body for accurately monitoring joint motion and respiration.Such a strain sensing system provides a reliable,economical,and ecofriendly solution to wearable technologies,with wide applications in health care,prosthetics,robotics,and biomedical devices.

Confined thin film wrinkling on shape memory polymer with hybrid surface morphologies

With appropriate stimuli,such as heat,humidity,or magnetic field,shape memory polymers(SMPs)can recover to their original shapes from temporary,programmed states.Using thermal responsive SMPs as substrates,we demonstrate a simple method to realize hybrid surface morphologies through confined thin film wrinkling in localized areas.The bilayer system was fabricated by depositing a layer of aluminum thin?lm on top of a SMP substrate programmed with a tensile strain.After the system was heated by a heating wire,hybrid wrinkling patterns were formed in a confined circular area around the heat source,with an inner spoke pattern and an outer ring pattern.Wrinkling patterns showed good symmetry,and the size of the wrinkling area can be tuned by controlling the heat input.This study o?ers a simple but effective approach to fabricate hybrid morphological features in micro-scale.With appropriate stimuli,such as heat,humidity,or magnetic field,shape memory polymers(SMPs)can recover to their original shapes from temporary,programmed states.Using thermal responsive SMPs as substrates,we demonstrate a simple method to realize hybrid surface morphologies through confined thin film wrinkling in localized areas.The bilayer system was fabricated by depositing a layer of aluminum thin?lm on top of a SMP substrate programmed with a tensile strain.After the system was heated by a heating wire,hybrid wrinkling patterns were formed in a confined circular area around the heat source,with an inner spoke pattern and an outer ring pattern.Wrinkling patterns showed good symmetry,and the size of the wrinkling area can be tuned by controlling the heat input.This study offers a simple but effective approach to fabricate hybrid morphological features in micro-scale.

Cobalt-catalyzed asymmetric hydrogenation of ketones:A remarkable additive effect on enantioselectivity

A chiral cobalt pincer complex,when combined with an achiral electron-rich mono-phosphine ligand,catalyzes efficient asymmetric hydrogenation of a wide range of aryl ketones,affording chiral alcohols with high yields and moderate to excellent enantioselectivities(29 examples,up to 93%ee).Notably,the achiral mono-phosphine ligand shows a remarkable effect on the enantioselectivity of the reaction.