Real-time decomposition technique for compressive light field display using the multiplex correlations.

How to compress and decompose the high-dimensional light field information in real time is still a challenging task for compressive light field display. Traditional iterative algorithms suffer from slow convergence speed and limited image quality. Therefore, a real-time decomposition technique for compressive light field display using multiplex correlations is proposed. Firstly, the iteration initial value of the algorithm is optimized, by utilizing the spatial correlations of pixel multiplex light fields, which significantly improves the convergence speed and reduces noise. Secondly, the iterative task of high-dimensional matrix in the non-negative matrix factorization (NMF) algorithm is divided into highly parallel linear iterative tasks. A stochastic gradient descent (SGD) optimizer and GPU are used to parallel compress and decompose the light fields. Thirdly, addresses of light field data are reordered using the sign distance field (SDF) transformation in sheared camera frustum space, making the addressing process of compression and decomposition more efficient. A rendering pipeline is constructed that renders the compressive light fields using 3D model data directly. For a light field containing 5 × 5 viewpoints and 1024 × 1024 × 2 pixels, only 2-3 iterations are needed to approach the optimal solution. The decomposition efficiency is increased by 15.24 times. The frame rate of decomposition exceeds 30 frames per second (fps). A compressive light field display system has been built to realize 3D display, verifying the feasibility of the technique.

Molecular Mechanisms of the Generation and Accumulation of Gas at the Interface.

Gas-evolving reactions are widespread in chemical and energy fields. However, the generated gas will accumulate at the interface, which reduces the rate of gas generation. Understanding the microscopic processes of the generation and accumulation of gas at the interface is crucial for improving the efficiency of gas generation. Here, we develop an algorithm to reproduce the process of catalytic gas generation at the molecular scale based on the all-atom molecular dynamics simulations and obtain the quantitative evolution of the gas generation, which agrees well with the experimental results. In addition, we demonstrate that under an external electric field, the generated gas molecules do not accumulate at the electrode surface, which implies that the electric field can significantly increase the rate of the gas generation. The results suggest that the external electric field changes the structure of the water molecules near the electrode surface, making it difficult for gas molecules to accumulate on the electrode surface. Furthermore, it is found that gas desorption from the electrode surface is an entropy-driven process, and its accumulation at the electrode surface depends mainly on the competition between the entropy and the enthalpy of the water molecules under the influence of the electric field. These results provide deep insight into gas generation and inhibition of gas accumulation.

Polarization state evolution of a twisted vector optical field in a strongly nonlocal nonlinear medium.

The evolution of the state of polarization (SoP) in a twisted vector optical field (TVOF) with an astigmatic phase in a strongly nonlocal nonlinear medium (SNNM) is investigated. The effect of an astigmatic phase on the propagation dynamics of the twisted scalar optical field (TSOF) and TVOF during propagation in the SNNM leads to reciprocally periodical evolutions of stretch and shrink, accompanied by the reciprocal transformation of the beam shape between an initial circle shape and threadiness distribution. The TSOF and TVOF rotate along the propagation axis if the beams are anisotropic. In particular, the reciprocal conversions between the linear and circular polarizations occur in the TVOF during propagation, which are strongly related to the initial powers, twisting strength coefficients, and initial beam reshapes. The numerical results confirm the analytical predictions by the moment method for the dynamics of the TSOF and TVOF during propagation in a SNNM. The underlying physics for the polarization evolution of a TVOF in a SNNM are discussed in detail.

The atlas of ACE2 expression in fetal and adult human hearts reveals the potential mechanism of heart-injured patients infected with SARS-CoV-2.

Numerous studies have shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect host cells through binding to angiotensin I converting enzyme 2 (ACE2) expressing in various tissues and organs. In this study, we deeply analyzed the single-cell expression profiles of ACE2 in fetal and adult human hearts to explore the potential mechanism of SARS-CoV-2 harming the heart. The molecular docking software was used to simulate the binding of SARS-CoV-2 and its variant spike protein with ACE2. The genes closely related to ACE2 in renin-angiotensin system (RAS) were identified by constructing a protein-protein interaction network. Through the analysis of single-cell transcription profiles at different stages of human embryos, we found that the expression level of ACE2 in ventricular myocytes was increased with embryonic development. The results of single-cell sequencing analysis showed that the expression of ACE2 in ventricular myocytes was upregulated in heart failure induced by dilated cardiomyopathy compared with normal hearts. The upregulation of ACE2 increases the risk of infection with SARS-CoV-2 in fetal and adult human hearts. We also further confirmed the expression of ACE2 and ACE2-related genes in normal and SARS-CoV-2-infected human pluripotent stem cell-derived cardiomyocytes. In addition, the pathway analysis revealed that ACE2 may regulate the differently expressed genes in heart failure through calcium signaling pathway and Wnt signaling pathway.

Perspective clipping and fast rendering of light field images for holographic stereograms using RGBD data.

The production of holographic stereogram (HS) requires a huge amount of light field data. How to efficiently clip and render these image data remains a challenge in the field. This work focuses on the perspective clipping and fast rendering algorithm for light field images using RGBD data without explicit 3D reconstruction. The RGBD data is expanded to RGBDθ data by introducing a light cone for each point, which gives a new degree of freedom for light field image rendering. Using the light cone and perspective coherence, the visibility of 3D image points can be clipped programmatically. Optical imaging effects including mirror imaging and half mirror imaging effects of 3D images can also be rendered with the help of light cones during the light field rendering process. The perspective coherence is also used to accelerate the rendering, which has been shown to be on average 168% faster than traditional DIBR algorithms. A homemade holographic printing system was developed to make the HSs using the rendered light field images. The vivid 3D effects of the HS have validated the effectiveness of the proposed method. It can also be used in holographic dynamic 3D display, augmented reality, virtual reality, and other fields.

Fast rendering and display of light field images with a controllable lighting mechanism.

A fast light field (LF) image rendering method with controllable lighting mechanism is proposed and demonstrated. It solves the issue that previous image-based methods could not render and edit lighting effects for LF images. In contrast to previous methods, light cones and normal maps are defined and used to expand the RGBD images into RGBDNθ data, which gives more degrees of freedom to render LF images. Conjugate cameras are used to capture the RGBDN data, which simultaneously solve the pseudoscopic imaging problem. Perspective coherence is used to accelerate the RGBDNθ-based LF rendering process, which has been shown to be on average 30 times faster than the traditional per-viewpoint rendering (PVR) method. Vivid three-dimensional (3D) images with Lambertian reflection and non-Lambertian reflection effects including specular lighting and compound lighting have been reconstructed in 3D space using a homemade LF display system. The proposed method injects more flexibility into the rendering of LF images and can also be used in holographic display, augmented reality, virtual reality, and other fields.

Simplified retinal 3D projection rendering method and system.

A simplified rendering method and system for retinal 3D projection using view and depth information is proposed and demonstrated. Instead of vertex calculations, image-based techniques, including sub-image shifting, image fusion, and hole filling, combined with the depth information, are used to render the multi-view images in a display space with specific discrete depth coordinates. A set of time-division multiplexing retinal 3D projection systems with dense viewpoints is built. A near-eye display of a 3D scene with complex occlusion relationships is realized using the rendering method and system. The eye box of the retinal projection system is enlarged, and the accommodation response of the eyes is evoked at the same time, which improves the visual experience. Rendering tests are carried out using simple and complex models, which proves the effectiveness of this method. Comparative experiments prove that the proposed retinal projection method can obtain high-performance 3D images comparable to the super multi-view display method while simplifying the rendering process. Additionally, the depth of field of the experimental system can cover most of the vergence accommodation conflict sensitive range of the human eye.

Augmented reality display system using modulated moiré imaging technique.

To enhance the depth rendering ability of augmented reality (AR) display systems, a modulated moiré imaging technique is used to render the true three-dimensional (3D) images for AR display systems. 3D images with continuous depth information and large depth of field are rendered and superimposed on the real scene. The proposed AR system consists of a modulated moiré imaging subsystem and an optical combiner. The modulated moiré imaging subsystem employs modulated point light sources, a display device, and a microlens array to generate 3D images. A defocussing equal period moiré imaging structure is used, which gives a chance for the point light sources to modulate the depth position of 3D images continuously. The principles of the imaging system are deduced analytically. A custom-designed transparent off-axis spherical reflective lens is used as an optical combiner to project the 3D images into the real world. An experimental AR system that provides continuous 3D images with depth information ranging from 0.5 to 2.5 m is made to verify the feasibility of the proposed technique.

Plasmonic Enhanced Reactive Oxygen Species Activation on Low-Work-Function Tungsten Nitride for Direct Near-Infrared Driven Photocatalysis.

Realizing near-infrared (NIR) driven photocatalytic reaction is one of the promising strategies to promote the solar energy utilization and photocatalytic efficiencies. However, effective reactive oxygen species (ROS) activation under NIR irradiation remains to be great challenge for nearly all previously reported photocatalysts. Herein, the cubic-phase tungsten nitride (WN) with strong plasmonic NIR absorption and low-work function (≈3.59 eV) is proved to be able to mediate direct ROS activation by both of experimental observation and theoretical simulation. The cubic WN nanocubes (NCs) are synthesized via the hydrothermal-ammonia nitridation process and its NIR-driven photocatalytic properties, including photocatalytic degradation, hydroxylation, and de-esterification, are reported for the first time in this work. The 3D finite element simulation results demonstrate the size dependent and wavelength tuned plasmonic NIR absorption of the WN NCs. The NIR-driven photocatalytic mechanism of WN NCs is proposed based on density functional theory (DFT) calculated electronic structure and facet dependent O2 (or H2 O) molecular activation, radicals scavenging test, spin trapped electron paramagnetic resonance measurements, and ultraviolet photoelectronic spectrum (UPS). Overall, the results in this work pave a way for the application of low-work-function materials as highly reactive NIR photocatalyst.

A study on the effects of mixed organic cations on the structure and properties in lead halide perovskites.

Recently, organic-lead halide perovskites have emerged as strong competitors in photovoltaic and general optoelectronic applications owing to their remarkable characteristics, including high balance hole and electron mobility, strong absorption coefficient and long carrier lifetime. However, the commercial applicability of these materials is hampered by their relative lack of stability compared to established inorganic and organic semiconductors. It has been found that it is possible to tune the properties and stability of the organic-lead halide perovskite materials by site-substitution at A sites of the ABX3 perovskite structure. Here, organic cations (NH4+, HC (NH2)2+, and CH3CH2NH3+) were successfully incorporated in the methylammonium-based perovskite crystal to investigate the role of organic cation size on structure, optical features, thermal stability, and electrical transport properties. Powder X-ray diffraction results indicate that the size of organic cations can not only cause lattice strain by lattice contraction or dilation but also may induce phase transitions by octahedral tilting. Meanwhile, band gaps of these crystals show that organic cations could tune the band gap energy of the perovskites by changing the Pb-I bond angle, which agrees with previous reports. The result of thermogravimetric analysis indicates that thermal stability is related to the probability of HI formation, which is directly related to the acidity of the organic species. These results represent an important step to highlight the role of organic cations in hybrid perovskite materials, which will further benefit the fundamental understanding of materials and device optimization.

Correction: Nanoporous two-dimensional MoS2 membranes for fast saline solution purification.

Correction for 'Nanoporous two-dimensional MoS2 membranes for fast saline solution purification' by Jianlong Kou et al., Phys. Chem. Chem. Phys., 2016, 18, 22210-22216.

Enhancing integral imaging performance using time-multiplexed convergent backlight.

A method to enhance the performance of an integral imaging system is demonstrated using the time-multiplexed convergent backlight technique. The backlight increases the space bandwidth of the integral imaging system. As a result, the resolution, depth of field, and viewing angle of the integral imaging system are increased simultaneously. The cross-talk noise is also decreased without using any optical barrier. One part of the added space bandwidth comes from the optimized illumination. The other part is converted from the time bandwidth of the system by time-multiplexing. The time-multiplexed convergent backlight modulates the direction of the backlight in time sequence to illuminate the elemental images. Then, the elemental images synthesize the 3D images using a microlens array. An elemental images rendering method using a conjugate pinhole camera and pinhole projector model is designed to dynamically match the illumination direction. The rendering method eliminates the distortion and maximizes the viewing angle and viewing zone. A field programmable gate array (FPGA)-based controller is used to manage and synchronize the time sequence of the backlight and the display devices. Using this technique, high-performance 3D images are realized. Comparison experiments of the integral imaging system using diffused backlight and convergent backlight are performed. The results show the effectiveness of the proposed technique.

Effects of n-butyl amine incorporation on the performance of perovskite light emitting diodes.

The efficiency of perovskite light emitting diodes (PeLEDs) is crucially limited by leakage current and nonradiative recombination. Here we introduce n-butyl amine (BA) to modulate the growth of perovskite films as well as improve the performance of PeLEDs, and investigate in detail the effects of BA incorporation on the structural, optical, and electrical characteristics of perovskite films. The results indicate that BA would terminate the grain surface and inhibit crystal growth, leading to increased radiative recombination. However, BA overload would make the films loose and recreate shunt paths. The electrical detriment of BA overload outweighs its optical benefit. As a result, optimal PeLEDs can be obtained only with moderate BA incorporation.

Bandwidth-enhanced depth priority integral imaging using a band-limited diffusing illumination technique.

The display bandwidth and display mechanism determine the performance of the three-dimensional (3D) display system. In this paper, a bandwidth-enhanced depth priority integral imaging (DPII) technique is proposed. Information transmission efficiency (ITE) defined as the output display bandwidth divided by the input display bandwidth is used to assess the II system. By analyzing the ITE, we find that only a part of the input display bandwidth is used efficiently to present the 3D image in the traditional DPII system. The DPII system sacrifices the ITE for depth enhancement. The low ITE that fundamentally limits the 3D performance of the DPII system is ascribed to the diffusing illumination mechanism of the display system. To enhance the 3D performance, a collimated illumination DPII system as a special case of band-limited diffusing illumination technique has been proposed and demonstrated first. The bandwidth and ITE of such a DPII system are increased. The depth of field (DOF) of the system is doubled. The resolution of the 3D image is increased to the level of the resolution priority II system without sacrificing the viewing angle. A more general case, band-limited illumination DPII system is also demonstrated. By modulating the divergence angle of the illumination system, the 3D image's resolution and DOF can be controlled. The bandwidth and ITE of the DPII system using band-limited illumination are also higher than that of the traditional DPII system. Experiments are presented to prove the bandwidth-enhanced mechanism of the DPII system.

Twin imaging phenomenon of integral imaging.

The imaging principles and phenomena of integral imaging technique have been studied in detail using geometrical optics, wave optics, or light filed theory. However, most of the conclusions are only suit for the integral imaging systems using diffused illumination. In this work, a kind of twin imaging phenomenon and mechanism has been observed in a non-diffused illumination reflective integral imaging system. Interactive twin images including a real and a virtual 3D image of one object can be activated in the system. The imaging phenomenon is similar to the conjugate imaging effect of hologram, but it base on the refraction and reflection instead of diffraction. The imaging characteristics and mechanisms different from traditional integral imaging are deduced analytically. Thin film integral imaging systems with 80µm thickness have also been made to verify the imaging phenomenon. Vivid lighting interactive twin 3D images have been realized using a light-emitting diode (LED) light source. When the LED is moving, the twin 3D images are moving synchronously. This interesting phenomenon shows a good application prospect in interactive 3D display, argument reality, and security authentication.

A controllable water signal transistor.

We performed molecular dynamics simulations to study the regulating ability of water chains confined in a Y-shaped nanochannel. It was shown that a signal at the molecular level could be controlled by two other charge-induced signals when the water chains were confined in a Y-shaped nanochannel, demonstrating promising applications as water signal transistors in nanosignal systems. The mechanism of a water signal transistor is similar to a signal logic device. This remarkable ability to control the water signal is attributed to the strong dipole-ordering of the water chains in the nanochannel. The controllable water signal process of the Y-shaped nanochannel provides opportunities for future application in the design of molecular-scale signal devices.

Nanoporous two-dimensional MoS2 membranes for fast saline solution purification.

Finding a membrane with both high permeability and high salt rejection is very important for saline solution purification. Here, we report the performance of molybdenum disulfide (MoS2) membranes with nanoscale pores for saline solution purification via all-atom molecular dynamics simulations. It was found that the nanoporous two-dimensional MoS2 membrane can impede salt ions, while allowing highly efficient permeation of water molecules. By engineering the appropriate sizes of the nanopores within two-dimensional MoS2 membranes, their water permeability can be tens of times as high as that of conventional reverse osmosis membranes, while still maintaining a high salt rejection rate. These remarkable water permeability and salt rejection properties of the nanoporous monolayer MoS2 membranes are attributed to the formation of single chain hydrogen bonds, which link the water molecules within the nanopores and those at the immediate exteriors of the nanopores, causing significant reduction in the resistance of water molecules passing through the nanopores, which are small enough for any salt ions to pass through. Therefore such nanoporous monolayer MoS2 membranes have great potential for saline solution purification.

A transition between bistable ice when coupling electric field and nanoconfinement.

The effects of an electric field on the phase behavior of water confined inside a nanoscale space were studied using molecular dynamics simulations. It was found that the diffusion coefficient of water reaches its maximum when value of the surfaces' charge is at the threshold, qc = 0.5e. This unexpected phenomenon was attributed to the intermediate state between two stable ice states induced by nanoconfinement and the electric field generated by charged surfaces, respectively. Our finding is helpful to understand electromelting and electrofreezing of water under nanoconfinement with the electric field.

Electricity resonance-induced fast transport of water through nanochannels.

We performed molecular dynamics simulations to study water permeation through a single-walled carbon nanotube with electrical interference. It was found that the water net flux across the nanochannel is greatly affected by the external electrical interference, with the maximal net flux occurred at an electrical interference frequency of 16670 GHz being about nine times as high as the net flux at the low or high frequency range of (<1000 GHz or >80,000 GHz). The above phenomena can be attributed to the breakage of hydrogen bonds as the electrical interference frequency approaches to the inherent resonant frequency of hydrogen bonds. The new mechanism of regulating water flux across nanochannels revealed in this study provides an insight into the water transportation through biological water channels and has tremendous potential in the design of high-flux nanofluidic systems.

Electromanipulating water flow in nanochannels.

In sharp contrast to the prevailing view that a stationary charge outside a nanochannel impedes water permeation across the nanochannel, molecular dynamics simulations show that a vibrational charge outside the nanochannel can promote water flux. In the vibrational charge system, a decrease in the distance between the charge and the nanochannel leads to an increase in the water net flux, which is contrary to that of the fixed-charge system. The increase in net water flux is the result of the vibrational charge-induced disruption of hydrogen bonds when the net water flux is strongly affected by the vibrational frequency of the charge. In particular, the net flux is reaches a maximum when the vibrational frequency matches the inherent frequency of hydrogen bond inside the nanochannel. This electromanipulating transport phenomenon provides an important new mechanism of water transport confined in nanochannels.