Multifunctional Chiral 2D Lead Halide Perovskites with Circularly Polarized Photoluminescence and Piezoelectric Energy Harvesting Properties.

Introducing the chiral spacers to two-dimensional (2D) lead halide perovskites (LHPs) enables them to exhibit circularly polarized photoluminescence (CPPL), which could have applications in chiral-optics and spintronics. Despite that a great deal of effort has been made in this field, the reported polarization degree of CPPL at ambient conditions is still very limited, and the integration of multiple functionalities also remains to be explored. Here we report the structures, CPPL, and piezoelectric energy harvesting properties of chiral 2D LHPs, [R-1-(4-bromophenyl)ethylaminium]2PbI4 (R-[BPEA]2PbI4) and [S-1-(4-bromophenyl)ethylaminium]2PbI4 (S-[BPEA]2PbI4). Our results show that these chiral perovskites are direct bandgap semiconductors and exhibit CPPL centered at ∼513 nm with a maximum degree of polarization of up to 11.0% at room temperature. In addition, the unique configurational arrangement of the chiral spacers is found to be able to reduce the interlayer π-π interactions and consequently result in strong electron-phonon coupling. Furthermore, the intrinsic chirality of both R-[BPEA]2PbI4 and S-[BPEA]2PbI4 enables them to be piezoelectric active, and their composite films can be applied to generate voltages and currents up to ∼0.6 V and ∼1.5 µA under periodic impacting with a strength of 2 N, respectively. This work not only reports a high degree of CPPL but also demonstrates piezoelectric energy harvesting behavior for realizing multifunctionalities in chiral 2D LHPs.

Privacy-Preserving Reversible Data Hiding for Medical Images Employing Local Rotation.

As digitalization becomes more common, patients' concerns about the leakage of private information, such as electronic medical record, are increasing, and those concerns motivated this case study of secure covert communication. Therefore, in this paper, a novel reversible data hiding method based on pixel rotation is proposed for medical images. Using pixel rotation, a state mapping model is constructed to represent the payload. More specifically, many intermediate states are derived from an image block, and each of them is used to form a one-to-one mapping relationship with a specific sequence of payload bits. In addition, to ensure the visual quality of stego-medical-images, the payload bits are only concealed in the regular blocks and the other blocks are unchanged. Moreover, the smoother regular image block will be priority to be used to embed the payload to enhance the visual quality of stego-medical-image. The experimental results showed that the stego-medical-images generated by the proposed reversible data hiding method have better visual quality with an average PSNR of 47.0307 dB, which is higher than that provided by some state-of-the-art methods.

Synthesis of Magnetic Ni0.3Mg0.3Zn0.4Fe2O4 Nanoparticles and Their Adsorption Performances of Congo Red.

Magnetic Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles were synthesized by the absolute alcohol combustion method. The morphology, microstructure, and composition of as-prepared Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles were characterized by several techniques: the vibrating sample magnetometer (VSM), the scanning electron microscopy (SEM), the X-ray diffraction (XRD), and the energy dispersive spectroscopy (EDS). The experimental results showed that the calcination temperature and the solvent volume were the crucial factors for the synthesis of the magnetic Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles. The adsorption performance of Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles for congo red (CR) was investigated. The model of pseudo-second-order kinetic was optimal matching for obtaining the parameters of adsorption CR in the initial range of 100-400 mg/L-1, while, the isotherm data of CR onto Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles could conform to the Temkin model owing to the values of the square deviations, which revealed that the adsorption of CR onto Ni0.3Mg0.3Zn0.4Fe2O4 nanoparticles at room temperature was the monolayer and multilayer adsorption mechanism.

A Vision toward Ultimate Optical Out-Coupling for Organic Light-Emitting Diode Displays: 3D Pixel Configuration.

Despite stringent power consumption requirements in many applications, over years organic light-emitting diode (OLED) displays still suffer unsatisfactory energy efficiency due to poor light extraction. Approaches have been reported for OLED light out-coupling, but they in general are not applicable for OLED displays due to difficulties in display image quality and fabrication complexity and compatibility. Thus to date, an effective and feasible light extraction technique that can boost efficiencies and yet keep image quality is still lacking and remains a great challenge. Here, a highly effective and scalable extraction-enhancing OLED display pixel structure is proposed based on embedding the OLED inside a three-dimensional reflective concave structure covered with a patterned high-index filler. It can couple as much internal emission as possible into the filler region and then redirect otherwise confined light for out-coupling. Comprehensive multi-scale optical simulation validates that ultimately high light extraction efficiency approaching ≈80% and excellent viewing characteristics are simultaneously achievable with optimized structures using highly transparent top electrodes. This scheme is scalable and wavelength insensitive, and generally applicable to all red, green, and blue pixels in high-resolution full-color displays. Results of this work are believed to shed light on the development of future generations of advanced OLED displays.

Surface display of active lipase in Pichia pastoris using Sed1 as an anchor protein.

A Pichia pastoris cell-surface display system was constructed using the Sed1 anchor system that has been developed in Saccharomyces cerevisiae. Candida antarctica lipase B (CALB) was used as the model protein and was fused to an anchor that consisted of 338 amino acids of Sed1. The resulting fusion protein CALBSed1 was expressed under the control of the alcohol oxidase 1 promoter (pAOX1). Immunofluorescence microscopy of immunolabeled Pichia pastoris revealed that CALB was displayed on the cell surface. Western blot analysis showed that the fusion protein CALBSed1 was attached covalently to the cell wall and was highly glycosylated. The hydrolytic activity of the displayed CALB was more than 220 U/g dry cells after 120 h of culture. The displayed protein also exhibited a higher degree of thermostability than free CALB.

Display of Candida antarctica lipase B on Pichia pastoris and its application to flavor ester synthesis.

Two alternative cell-surface display systems were developed in Pichia pastoris using the alpha-agglutinin and Flo1p (FS) anchor systems, respectively. Both the anchor cell wall proteins were obtained originally from Saccharomyces cerevisiae. Candida antarctica lipase B (CALB) was displayed functionally on the cell surface of P. pastoris using the anchor proteins alpha-agglutinin and FS. The activity of CALB displayed on P. pastoris was tenfold higher than that of S. cerevisiae. The hydrolytic and synthetic activities of CALB fused with alpha-agglutinin and FS anchored on P. pastoris were investigated. The hydrolytic activities of both lipases displayed on yeast cells surface were more than 200 U/g dry cell after 120 h of culture (200 and 270 U/g dry cell, respectively). However, the synthetic activity of CALB fused with alpha-agglutinin on P. pastoris was threefold higher than that of the FS fusion protein when applied to the synthesis of ethyl caproate. Similarly, the CALB displayed on P. pastoris using alpha-agglutinin had a higher catalytic efficiency with respect to the synthesis of other short-chain flavor esters than that displayed using the FS anchor. Interestingly, for some short-chain esters, the synthetic activity of displaying CALB fused with alpha-agglutinin on P. pastoris was even higher than that of the commercial CALB Novozyme 435.