The application of halide perovskites in memristors

New neuromorphic architectures and memory technologies with low power consumption,scalability and high-speed are in the spotlight due to the von Neumann bottleneck and limitations of Moore’s law.The memristor,a two-terminal synaptic device,shows powerful capabilities in neuromorphic computing and information storage applications.Active materials with high defect migration speed and low defect migration barrier are highly promising for high-performance memristors.Halide perovskite(HP)materials with point defects(such as gaps,vacancies,and inversions)have strong application potential in memristors.In this article,we review recent advances on HP memristors with exceptional performances.First,the working mechanisms of memristors are described.Then,the structures and properties of HPs are explained.Both electrical and photonic HP-based memristors are overviewed and discussed.Different fabrication methods of HP memristor devices and arrays are described and compared.Finally,the challenges in integrating HP memristors with complementary metal oxide semiconductors(CMOS)are briefly discussed.This review can assist in developing HP memristors for the next-generation information technology.

Soft tissue release combined with joint-sparing osteotomy for treatment of cavovarus foot deformity in older children: Analysis of 21 cases

BACKGROUND Cavovarus foot is a common form of foot deformity in children,which is clinically characterized by an abnormal increase of the longitudinal arch of the foot,and it can be simultaneously complicated with forefoot pronation and varus,rearfoot varus,Achilles tendon contracture,or cock-up toe deformity.Muscle force imbalance is the primary cause of such deformity.Many diseases can lead to muscle force imbalance,such as tethered cord syndrome,cerebral palsy,Charcot-Marie-Tooth disease,and trauma.At present,many surgical treatments are available for cavovarus foot.For older children,priority should be given to midfoot osteotomy and fusion.Since complications such as abnormal foot length,foot stiffness,and abnormal gait tend to develop postoperatively,it is important to preserve the joints and correct the deformity as much as possible.Adequate soft tissue release and muscle balance are the keys to correcting the deformity and avoiding its postoperative recurrence.AIM To assess the efficacy of soft tissue release combined with joint-sparing osteotomy in the treatment of cavovarus foot deformity in older children.METHODS The clinical data of 21 older children with cavovarus foot deformity(28 feet)who were treated surgically at the Ninth Department of Orthopedics of Jizhong Energy Xingtai Mining Group General Hospital from November 2014 to July 2017 were retrospectively analyzed.The patients ranged in age from 10 to 14 years old,with an average age of 12.46±1.20 years.Their main clinical manifestations were deformity,pain,and gait abnormality.The patients underwent magnetic resonance imaging of the lumbar spine,electromyographic examination,weightbearing anteroposterior and lateral X-rays of the feet,and the Coleman block test.Surgical procedures including metatarsal fascia release,Achilles tendon or medial gastrocnemius lengthening,"V"-shaped osteotomy on the dorsal side of the metatarsal base,opening medial cuneiform wedge osteotomy,closing cuboid osteotomy,anterior transfer of the posterior tibial tendon,peroneus longus-tobrevis transfer,and calcaneal sliding osteotomy to correct hindfoot varus deformity were performed.After surgery,long leg plaster casts were applied,the plaster casts were removed 6 wk later,Kirschner wires were removed,and functional exercise was initiated.The patients began weight-bearing walk 3 mo after surgery.Therapeutic effects were evaluated using the Wicart grading system,and Meary’s angles and Hibbs’angles were measured based on X-ray images obtained preoperatively and at last follow-up to assess their changes.RESULTS The patients were followed for 6 to 32 mo,with an average follow-up period of 17.68±6.290 mo.Bone healing at the osteotomy site was achieved at 3 mo in all cases.According to the Wicart grading system,very good results were achieved in 18 feet,good in 7,and fair in 3,with a very good/good rate of 89.3%.At last follow-up,mean Meary’s angle was 6.36°±1.810°,and mean Hibbs’angle was 160.21°±4.167°,both of which were significantly improved compared with preoperative values(24.11°±2.948°and 135.86°±5.345°,respectively;P<0.001 for both).No complications such as infection,skin necrosis,or bone nonunion occurred.CONCLUSION Soft tissue release combined with joint-sparing osteotomy has appreciated efficacy in the treatment of cavovarus foot deformity in older children.

Fatigue Crack Initiation and Propagation Dominated by Crystallographic Factors in TiB/near a-Ti

Discontinuously reinforced titanium matrix composites(DRTMCs)with a network structure have been extensively researched due to their superior combination of strength and ductility.However,their fatigue performance has remained unknown.In order to elucidate the fatigue behavior of DRTMCs,a tension-tension fatigue test was performed on a TiB/nearα-Ti composite with network structure.The results showed that the variability of fatigue lifetime increased as the stress level decreased.Fractography analysis indicated that fatigue crack initiation was associated with facet formation,while the subsequent propagation was hindered by the network structure comprising TiB whiskers and silicides.Crystallographic characterization further revealed that facets formed due to a combination of shear and normal stress.The reduction in fatigue lifetime was attributed to an increase in the effective slip length,which was influenced by the orientation of grains near the crack-initiation sites toward basal slip in the life-limiting specimen.Quasi in situ observation suggested that the crack initiation was facilitated by both basal and prismatic slip ofα-Ti as well as fracture of TiBw.Crack propagation was found to be associated with basal and prismatic slip systems with high Schmid factors,regardless of whether the crack was intergranular or intragranular.

Chromatic dispersion manipulation based on metasurface devices in the mid-infrared region

The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth(8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications.

Versatile platform of nonlocal metasurfaces for both spectral and spatial control of lightt waves

Multifunctional nonlocal metasurfaces based on quasi-bound states in the continuum are experimentally demonstrated,which shapes the wavefronts at the resonant wavelengths while have no effect on other wavelengths.By means of cascade and orthogonal perturbations,the nonlocal metasurface devices can be extended to a versatile platform with multifunction.