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Geometric parameters play a crucial role in determining the characteristics of metasurfaces, whereas studying the effect of each geometric parameter on the simulation results is a difficult and challenging problem. In this paper, we propose a framework to investigate the dynamic relationship between geometric parameters and transmission, which is based on multifractal detrended cross-correlation analysis (MF-DCCA) and light gradient boosting machine (LightGBM). The MF-DCCA algorithm analyzes the cross-correlation between the two columns of data, while the LightGBM model is used to solve machine learning regression problems. We found that the cross-correlation between geometric parameters and transmission is multifractal, with long-range correlation and generally fat-tailed as the source of multifractality. The regression coefficient (R2) of LightGBM model for predicting transmission is 0.984. This study not only provides a reference for the importance of geometric parameters in metasurface simulation but also provides a tool for feature screening in forward and inverse design. [ABSTRACT FROM AUTHOR]

Spherical geometry, adaptive optics, and highly dense network of neurons bridging the eye with the visual cortex, are the primary features of human eyes which enable wide field-of-view (FoV), low aberration, excellent adaptivity, and preprocessing of perceived visual information. Therefore, fabricating spherical artificial eyes has garnered enormous scientific interest. However, fusing color vision, in-device preprocessing and optical adaptivity into spherical artificial eyes has always been a tremendous challenge. Herein, we demonstrate a bionic eye comprising tunable liquid crystal optics, and a hemispherical neuromorphic retina with filter-free color vision, enabled by wavelength dependent bidirectional synaptic photo-response in a metal-oxide nanotube/perovskite nanowire hybrid structure. Moreover, by tuning the color selectivity with bias, the device can reconstruct full color images. This work demonstrates a unique approach to address the color vision and optical adaptivity issues associated with artificial eyes that can bring them to a new level approaching their biological counterparts. Designing full-color spherical artificial eyes remains a challenge. Here, Long et al. report a bionic eye where each pixel on the hemispherical retina can recognize different colors based on the unique bidirectional photo response; with optical adaptivity and neuromorphic preprocessing ability [ABSTRACT FROM AUTHOR]

The emergence of metamaterials has brought a revolutionary way to manipulate the behavior of light on the nanoscale. However, there are still many problems in design process, such as time-consuming and many-to-one mapping. Here, we demonstrate the forward and inverse design of plasmonic metamaterial absorbers based on Light gradient boosting machine (LightGBM) and Extreme Gradient Boosting (XGBoost). The inverse framework can use the input reflection value to design the metamaterial parameter structure. The experimental results show that XGBoost has better performance in forward and inverse design (Forward-R2: 0.956; Inverse-R2: 0.967). The framework is suitable for designing metamaterials on demand, and it can be used in zoom imaging, metamaterial absorbers, metamaterial filters, and other fields. [ABSTRACT FROM AUTHOR]

Halide perovskites are enticing candidates for highly efficient planar light-emitting diodes (LEDs) with commercial potential in displays and lighting. However, it remains a challenge for conventional solution fabrication processes to fabricate large-scale or non-planar LEDs due to the non-uniformity of perovskite films in conjunction with material stability issues. Here large-area highly uniform arrays of crystalline perovskite quantum wires are grown with emission spectra covering the whole visible range. Photoluminescence quantum yield of up to 92% and 5,644 hours as the time for photoluminescence to degrade down to its 50% of the initial value under ambient conditions are achieved for MAPbBr3 quantum wires. LEDs based on these quantum wires on rigid and flexible planar substrates are fabricated up to a four-inch wafer size and also unique three-dimensional spherical LEDs with outstanding uniformity are reported. The results suggest that the approach developed here can be generalized to other unconventional three-dimensional LEDs in the future. The use of perovskite quantum-wire light emitters results in high-quality planar and spherical light-emitting diodes. [ABSTRACT FROM AUTHOR]

Exploring the locality stereotype with respect to CEO's trustworthiness, we find that firms whose CEOs are from more reputable hometowns have a higher likelihood of stock price crashes, indicating the presence of a CEO "Trust Exploitation" effect, i.e. a high-trust identity does not guarantee managerial ethics; to the contrary, it could tempt CEOs to abuse outsiders' trust, camouflage their misconducts and conceal adverse information more severely. The effect of CEO's perceived trustworthiness on tail risk of stock price remains robust when controlling for the region-level trust of firm's headquarters, and in 2SLS regression with an instrumental variable. Further, CEO's "Trust Exploitation" effect is more prominent among firms with lower disclosure quality, higher capital market pressure and higher CEO incentives. Our findings highlight an unexplored imperfection of individual-level trustworthiness as a reliable substitute for formal monitoring devices in terms of improving stock market stability. [ABSTRACT FROM AUTHOR]

Human eyes possess exceptional image-sensing characteristics such as an extremely wide field of view, high resolution and sensitivity with low aberration1. Biomimetic eyes with such characteristics are highly desirable, especially in robotics and visual prostheses. However, the spherical shape and the retina of the biological eye pose an enormous fabrication challenge for biomimetic devices2,3. Here we present an electrochemical eye with a hemispherical retina made of a high-density array of nanowires mimicking the photoreceptors on a human retina. The device design has a high degree of structural similarity to a human eye with the potential to achieve high imaging resolution when individual nanowires are electrically addressed. Additionally, we demonstrate the image-sensing function of our biomimetic device by reconstructing the optical patterns projected onto the device. This work may lead to biomimetic photosensing devices that could find use in a wide spectrum of technological applications. A biomimetic electrochemical eye is presented that has a hemispherical retina made from a high-density array of perovskite nanowires that are sensitive to light, mimicking the photoreceptors of a biological retina. [ABSTRACT FROM AUTHOR]

Preimplantation genetic diagnosis (PGD) has gained widespread application in clinical medicine and hence the health of PGD offspring needs to be systematically assessed. Given the critical role of the stress response in growth and health, assessments of the development and function of the stress system might help to clarify the health outcomes of PGD. In this study, we constructed a PGD-conceived mouse model and used naturally conceived mice as controls; we used this model to evaluate the potential effect of PGD procedures on the stress system of the offspring. Serum and tissues of stress organs, namely the hypothalamus, locus coeruleus and adrenal gland, were collected from 5-week-old mice in the basal state or after cold stress. The serum levels of stress-related hormones and the structural and functional indices of the stress organs were then examined. In the basal state, ultrastructural abnormalities and low expression of genes involved in steroid hormone synthesis were found in the adrenals of the PGD mice, which had low corticosterone and high epinephrine levels compared with those of control mice. After acute cold stress, the PGD mice continued to show structural and glucocorticoid secretion abnormalities resulting in a late response to the environmental change. Thus, our study indicates that PGD manipulations affect adrenal development, result in structural and functional abnormalities of the adrenals in the offspring and influence their reactivity and adaptability to cold stress. [ABSTRACT FROM AUTHOR]

Metal halide perovskite has emerged as a promising material for light-emitting diodes. In the past, the performance of devices has been improved mainly by optimizing the active and charge injection layers. However, the large refractive index difference among different materials limits the overall light extraction. Herein, we fabricate efficient methylammonium lead bromide light-emitting diodes on nanophotonic substrates with an optimal device external quantum efficiency of 17.5% which is around twice of the record for the planar device based on this material system. Furthermore, optical modelling shows that a high light extraction efficiency of 73.6% can be achieved as a result of a two-step light extraction process involving nanodome light couplers and nanowire optical antennas on the nanophotonic substrate. These results suggest that utilization of nanophotonic structures can be an effective approach to achieve high performance perovskite light-emitting diodes. The rapid development of halide perovskite light-emitting diodes mainly relies on the optimization of the active layer and charge injection layers. Here Zhang et al. incorporate three-dimensional nanophotonic substrates to enhance light out-coupling and achieve high external quantum efficiency of 17.5%. [ABSTRACT FROM AUTHOR]

Organometallic trihalide perovskites are promising materials for photovoltaic applications, which have demonstrated a rapid rise in photovoltaic performance in a short period of time. We report a facile one-step method to fabricate planar heterojunction perovskite solar cells by chemical vapor deposition (CVD), with a solar power conversion efficiency of up to 11.1%. We performed a systematic optimization of CVD parameters such as temperature and growth time to obtain high quality films of CH3NH3PbI3 and CH3NH3PbI3-xClx perovskite. Scanning electron microscopy and time resolved photoluminescence data showed that the perovskite films have a large grain size of more than 1 micrometer, and carrier life-times of 10 ns and 120 ns for CH3NH3PbI3 and CH3NH3PbI3-xClx, respectively. This is the first demonstration of a highly efficient perovskite solar cell using one step CVD and there is likely room for significant improvement of device efficiency. [ABSTRACT FROM AUTHOR]

Competing Interests: The authors declare no conflict of interest.