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The real-time rendering of large-scale terrain scenes has been a challenge and is a popular research topic in the fields of 3D games and virtual reality. To fully utilize GPU features, this paper proposes a real-time rendering algorithm for large-scale regular grid terrain based on GPU Tessellation. The CPU processes a coarse-grained quadtree to generate terrain patches and then passes the patches to the GPU after view culling. Then, the GPU refines the terrain by using GPU Tessellation and displacement mapping. The most important advantage of our method is that during the tessellation stage, a new rule that the distance, screen space projection error and variance of the height, as the standard of terrain roughness, is designed. During the tessellation stage, the distance, screen space projection error and variance of the height, as the standard of terrain roughness, are considered. The experimental results show that our algorithm can greatly reduce the CPU processing time and main memory space requirement, and fully utilize the new features of the GPU; In conclusion, the proposed approach can render large-scale terrain with high-precision in real-time.

Path tracing can generate realistic images based on virtual 3D scene models, but the images are prone to be noisy. To solve this problem, we developed a novel denoising algorithm framework. Firstly, according to the relative mean square error of the noisy pixels, we introduced a progressive adaptive sampling strategy to optimize the distribution of samples. Next, to enhance the quality of the final reconstructed images, we designed an improved bilateral filtering algorithm with use of the gradient feature to obtain the noise-free images. Experimental results demonstrate that our framework outperforms the state-of-the-art path tracing denoising methods in terms of the visual quality, numerical error , and time cost.

In order to evaluate the quality of computer-generated stereoscopic images further accurately, we propose a new quality assessment metric based on the human visual system (HVS) modeling and machine-learning algorithm. First, we consider the existence of binocular rivalry to generate a cyclopean image of the asymmetrically distorted part that can be masked. Furthermore, we can get a pair of cyclopean images, decompose the reference and distorted images with RGB-YUV color channels respectively. We respectively calculate the edge and texture features of the 3-channel color map to obtain 6 pairs of color feature maps, then calculate the color feature difference values of each pair of feature maps. Finally, we use the support vector regression (SVR) for 6 color feature difference values to be calculated, the final quality value can be obtained. It can be seen from the experimental results that our algorithm has better performance and more accurate calculations than existing algorithms.

With the rapid development of image acquisition technology, video stabilization becomes increasingly important. The gyroscope-based video stabilization methods obtain camera motion path through gyroscope, which can avoid the poor image quality affecting the video stabilization effect. However, the camera motion path obtained by the gyroscope is in the gyroscope coordinate system, and there is a rotation relationship between the gyroscope coordinate system and the camera coordinate system. Therefore, a self-calibration method of gyroscope and camera in video stabilization is proposed. By collecting the video sequence with rich features, the camera motion is estimated according to the image information. At the same time, the camera motion in the gyroscope coordinate system is obtained by using the gyroscope data, and the rotation relationship between two coordinate systems is obtained by optimizing the minimum distance between the paths in two coordinate systems. The experimental results show that the proposed method can improve the video stabilization accuracy, and is more flexible.

Background As reported, 27-93 % of pregnant women take at least one drug during pregnancy. However, drug exposure during pregnancy still lacks sufficient foetal safety evidence of human origin. It is urgent to fill the knowledge gap about medication safety during pregnancy for optimization of maternal disease treatment and pregnancy drug consultation. Methods and analysis The China Teratology Birth Cohort (CTBC) was established in 2019 and is a hospital-based open-ended prospective cohort study with the aim of assessing drug safety during pregnancy. Pregnant women who set up the pregnancy health records in the first trimester or who seek drug consultation regardless of gestational age in the member hospitals are recruited. Enrolled pregnant women need to be investigated four times, namely, 6–14 and 24–28 weeks of gestational age, before discharge after hospital delivery, and 28–42 days after birth. Maternal medication exposure during pregnancy is the focus of the CTBC. For drugs, information on the type, name, and route of medication; start and end time of medication; single dose; frequency of medication; dosage form; manufacturer; and reason for medication is collected. The adverse pregnancy outcomes collected in the study include birth defects, stillbirth, spontaneous abortion, preterm birth, post-term birth, low birth weight, macrosomia, small for gestational age, large for gestational age and low Apgar score. CTBC uses an electronic questionnaire for data collection and a cloud system for data management. Biological samples are collected if informed consents are obtained. Multi-level logistic regression, mixed-effect negative binomial distribution regression and spline function regression are used to explore the effect of drugs on the occurrence of birth defects. Discussion The findings of the study will assist in further understanding the risk of birth defects and other adverse pregnancy outcomes associated with maternal drug exposure and developing the optimal treatment plans and drug counselling for pregnant women. Trial registration This study was approved by the Research Ethics Committee of the West China Second Hospital of Sichuan University and registered at the Chinese Clinical Trial Registry (http://www.chictr.org.cn/index.aspx, registration number ChiCTR1900022569).

We present the modified-Bessel-superposed Gaussian (MBSG) orbital-angular-momentum (OAM) modes, which can evolve into a field featuring a tailored Gaussian amplitude profile after propagating to a target receiving plane. Analytical expressions for the MBSG OAM modes at a source plane are developed in both the space and wavevector domains. The space- and wavevector-domain representations of the MBSG OAM modes at the source plane are found to share a mathematically formal similarity. We propose to utilize this appealing property for designing a Fourier-transform-based approach to forming the MBSG OAM modes at the source plane. Unlike other commonly reported OAM modes, the receiving-plane field of MBSG OAM modes always exhibits a customized non-ring-shaped Gaussian intensity pattern. This behavior can be exploited, e.g., to benefit the projective phase-flattening OAM measurement and to reduce the turbulence-induced OAM-mode scattering in relevant practical applications.

Mutually complementary bases are crucial to secure quantum key distribution (QKD). By aiming at free-space QKD with use of spatially structured photons, the effect of turbulence on the mutual unbiasedness of two complementary bases relevant to photonic orbital-angular-momentum (OAM) modes is modeled theoretically, with novel insightful expressions and physical explanations yielded. For two complementary bases constructed from Laguerre-Gaussian (LG) modes with a fixed radial index of zero, it is shown that the superposed joint-two-LG-mode (JTLGM) correlation function plays a fundamental role in determining the turbulence-induced mutual-unbiasedness decay. The mutual information between the sent and detected photonic states is used as a metric to quantify the degree of turbulence-induced mutual-unbiasedness decay. It is found that the degree of turbulence-induced mutual-unbiasedness decay depends on the scaled atmospheric coherence width, anisotropy of turbulence and contents of the complementary bases, and it can become non-negligible in certain cases.

Inter-symbol interference (ISI) is one of the key problems that seriously limit the transmission data rate in optical communication system. To eliminate ISI and further improve the system performance, we design a specific cascade finite impulse response-least mean square (FIR-LMS) equalizer. To the best of our knowledge, it is the first time this kind of equalizer is employed for high-speed indoor free-space optical wireless (OW) communication system. After LD driver printed circuit board (PCB) validated the design, a special miniaturized and inexpensive LD, and a spatial photodetector are employed at the transmitter and receiver, respectively. Based on these, we experimentally investigate the scheme of 4-pulse amplitude modulation (4-PAM) optical signal combined with cascade FIR-LMS adaptive equalizer in an indoor free-space OW communication system. The convergence performance between LMS and FIR-LMS is compared, the bit error rate (BER) performances of FIR, LMS and FIR-LMS equalizer at different propagation distances are also demonstrated. With the utility of the proposed equalizer, the OW communication system can successfully achieve the bit rate 10 Gbit/s transmission over 500 cm indoor free-space link distance. The BER significantly below the 7 % forward error correction (FEC) limit of 3 . 8 × 1 0 − 3 , which is lower than LMS by more than an order of magnitude.

To estimate the prevalence of violent discipline at home against young children, and to explore the potential association between violent discipline at home and multifaceted health risks in children. A community-based cross-sectional survey was conducted in twenty rural counties of weight provinces in western China. The information about child neglect and socio-demographic factors, exposure to different forms of violent discipline at home and four health outcomes was collected by face-to-face interview. Before analysis, the included interviews were weighted by the double-weighted comprehensive weighting. The proportion of children reported by primary caregivers to have experienced different forms of violent discipline by gender were calculated. To adjust the clustering effect of the survey design, two-level univariate and multivariate logistic regression models were constructed to evaluate the potential association between a child’s exposure to violent discipline at home and risk of suffering from diarrhea, fever, cough and injury. A total of 3,682 weighted interviews were finally included in the analysis. The prevalence of any violent discipline, psychological aggression, any physical punishment and severe physical punishment were 76.4%, 57.5%, 68.3% and 14.1%, respectively. In multivariate analysis, after adjusting for clustering, there was still a positive association between a child’s exposure to psychological aggression and risk of diarrhea (adjusted OR: 1.47, 95%CI: 1.14-1.90) and injury (adjusted OR: 1.95, 95%CI: 1.36-2.80); a child’s exposure to any physical punishment and risk of diarrhea (adjusted OR: 1.36, 95%CI: 1.04-1.77), cough (adjusted OR: 1.37, 95%CI: 1.14-1.66), and injury (adjusted OR: 2.05, 95%CI: 1.37-3.06); and a child’s exposure to severe physical punishment and risk of injury (adjusted OR: 2.07, 95%CI: 1.41-3.05). Considering that using violent discipline at home is prevalent in rural western China, and it could threaten young children’s health, effective measures to prevent young children from violent discipline are urgently needed.

We propose a video stabilization algorithm based on the rotation of a virtual sphere. Unlike traditional video stabilization algorithms relying on two-dimensional motion models or reconstruction of (3D) camera motions, the proposed virtual sphere model stabilizes video by projecting each frame onto the sphere and performing corrective rotations. Specifically, matching feature points between two adjacent frames are first projected onto two virtual spheres to obtain pairs of spherical points. Then, the rotation matrix between the previous and current frame is calculated. The resulting 3D rotation matrix sequence is used to represent the camera motion, and it is smoothed using the geodesic distance on a Riemannian manifold. Finally, the difference between the smoothed and original path allows obtaining the rotation matrix that causes camera jitter, and the virtual spheres are rotated reversely to suppress jitter. Experimental results show that the proposed algorithm can effectively reduce random jitter, outperforming state-of-the-art methods.

Background The influence of the safety and security of environments on early childhood development (ECD) has been under-explored. Although housing might be linked to ECD by affecting a child’s health and a parent’s ability to provide adequate care, only a few studies have examined this factor. We hypothesized that housing environment is associated with ECD in sub-Saharan Africa (SSA). Methods and findings From 92,433 children aged 36 to 59 months who participated in Multiple Indicator Cluster Survey (MICS) in 20 SSA countries, 88,271 were tested for cognitive and social–emotional development using the Early Childhood Development Index (ECDI) questionnaire and were thus included in this cross-sectional analysis. Children’s mean age was 47.2 months, and 49.8% were girls. Children were considered developmentally on track in a certain domain if they failed no more than 1 ECDI item in that domain. In each country, we used conditional logistic regression models to estimate the association between improved housing (housing with finished building materials, improved drinking water, improved sanitation facilities, and sufficient living area) and children’s cognitive and social–emotional development, accounting for contextual effects and socioeconomic factors. Estimates from each country were pooled using random-effects meta-analyses. Subgroup analyses were conducted by the child’s gender, maternal education, and household wealth quintiles. On-track cognitive development was associated with improved housing (odds ratio [OR] = 1.15, 95% CI 1.06 to 1.24, p < 0.001), improved drinking water (OR = 1.07, 95% CI 1.00 to 1.14, p = 0.046), improved sanitation facilities (OR = 1.15, 95% CI 1.03 to 1.28, p = 0.014), and sufficient living area (OR = 1.06, 95% CI 1.01 to 1.10, p = 0.018). On-track social–emotional development was associated with improved housing only in girls (OR = 1.14, 95% CI 1.04 to 1.25, p = 0.006). The main limitations of this study included the cross-sectional nature of the datasets and the use of the ECDI, which lacks sensitivity to measure ECD outcomes. Conclusions In this study, we observed that improved housing was associated with on-track cognitive development and with on-track social–emotional development in girls. These findings suggest that housing improvement in SSA may be associated not only with benefits for children’s physical health but also with broader aspects of healthy child development., In a cross-sectional analysis of nationally representative survey data from 20 countries, Yaqing Gao and colleagues investigate associations between housing environment and cognitive and social development in children., Author summary Why was this study done? Sub-Saharan Africa (SSA) had the largest number of children (29.4 million) with low cognitive and/or social–emotional development worldwide in 2010. Housing might be linked to early childhood development (ECD) by affecting a child’s health and a parent’s ability to provide adequate care but is neglected in public health, especially in low- and middle-income countries (LMIC). What did the researchers do and find? We tested the hypothesis that improved housing is associated with on-track development in 2 ECD domains (cognitive and social–emotional). We analyzed data from 88,271 children aged 36 to 59 months in 20 SSA countries collected from nationally representative surveys conducted between 2010 and 2019. Improved housing was associated with 15% higher odds of being developmentally on track in the cognitive domain. Overall, improved housing was associated with on-track social–emotional development in girls but not boys. What do these findings mean? Housing improvement in SSA may be associated not only with benefits for children’s physical health but also with broader aspects of healthy child development. Future work to establish a causal link between housing and ECD and to assess its underlying mechanisms is crucial for the designing of cost-effective ECD interventions in SSA.

Early intervention of gestational diabetes mellitus (GDM) is effective in reducing pregnancy disorders. Fetal growth, measured by routine ultrasound scan a few weeks earlier before GDM diagnosis, might be useful to identify women at high risk of GDM. In the study, generalized estimating equations were applied to examine the associations between ultrasonic indicators of abnormal fetal growth at 22&ndash, 24 weeks and the risk of subsequent GDM diagnosis. Of 44,179 deliveries, 8324 (18.8%) were diagnosed with GDM between 24 and 28 weeks. At 22&ndash, 24 weeks, fetal head circumference (HC) &lt, 10th, fetal femur length (FL) &lt, 10th, and estimated fetal weight (EFW) &lt, 10th percentile were associated with 13% to 17% increased risks of maternal GDM diagnosis. Small fetal size appeared to be especially predictive of GDM among women who were parous. Fetal growth in the highest decile of abdominal circumference (AC), HC, FL and EFW was not associated with risk of subsequent GDM. The observed mean difference in fetal size across gestation by GDM was small, there was less than 1 mm difference for AC, HC, and FL, and less than 5 g for EFW before 24 weeks. Despite similar mean fetal growth among women who were and were not later diagnosed with GDM, mothers with fetuses in the lowest decile of HC, FL and EFW at 22&ndash, 24 weeks tended to have higher risk of GDM.

The practicability of Nyquist wavelength-division-multiplexed (WDM) channels with optical Sinc-shaped pulses is greatly limited by phase noise and power flatness of the WDM sources. We insert uniform and coherent lines around each line of flat electro-optic frequency combs to generate 5 Nyquist-WDM channels with high quality. The normalized root-mean-square error (NRMSE) of optical Sinc-shaped pulses for the 5 channels can be between 1.23%–1.96%. The optical signal-to-noise ratios (OSNRs) of optical Nyquist pulses have a 7 dB improvement by reducing optical linewidth of electro-optic combs. Further, the high OSNR of Nyquist-WDM channels can bring benefits to transmission performance in high spectral efficiency Nyquist-WDM communication system.

We experimentally demonstrate an optimization of wide-spectral mode-locking fiber laser carriers by the introduction of continuous light stable pulse scheme with fiber dispersion management. The bandwidth of the optimized supercontinuum and the fluctuation between pulses have been significantly improved, and the fluctuation between pulses has been reduced by nearly 60%. After 1km of simulated atmospheric transmission, it is found that the optimized eye diagram has obvious eye opening. The signal to noise ratio increased by 6.84dB. And this optimization scheme is easy to integrate into the communication light source. It can be an adaptive scheme for free space optical communication in the foreseeable future.

We experimentally demonstrated a free space optical (FSO) transmission system with a pulse seedded wide-spectrum partially coherent beams (PCB) in a tunable turbulent channel. With 4Gbit/s on-off keying (OOK) modulation, the FSO transmission characters of the wide-spectrum laser are analyzed. The transmission link with the pulse seeded PCB shows the receive power fluctuation of 0.278dBm, receive SNR of 10.56dB, and the receive sensitivity of −34.8dBm, which is well beyond the performance of coherent beams (CB) and non-seeded PCB.

We propose a framework for cloud mobile virtual reality (VR) applications on smart phone web browsers. It combines cloud rendering and panoramic stereo imaging technology to realize interactive high-quality 3D scene display on smart phones. The images of the VR 3D scenes are transmitted in the manner of video stream, and the interactive data is processed by the proposed anti-jitter algorithm (AJA). A web-side lightweight rendering approach is also realized in our framework. Use of our framework can both reduce the computational cost of displaying VR 3D scenes on smart phones, meanwhile eliminating the need of installing plug-ins or dedicated APPs. Our framework can interactively display VR 3D scenes on a smart phone web browser and provide satisfactory immersive experience for observers with the help of VR glasses.

Monte Carlo rendering image denoising is different from natural image denoising. The auxiliary information can be used to reconstruct the image. However, ordinary convolutional networks cannot handle MC noise well, and it is difficult to establish a suitable model between noise, auxiliary information and the original image. In this paper we addresses the above issues, propose a Monte Carlo image denoising network based on deep neural network, construct a residual aggregation module, add dense connections, and extract image detail features. Combining the three most commonly used auxiliary information (depth, normal, and reflectivity) helps the network accurately restore the image. The experimental results show that the algorithm proposed in this paper can adapt to various typical scenes and effectively reduce the noise of rendered images.

Some applications require real-time analysis of trajectory data. But the direct release of the original trajectory to a third party for analysis will threaten the privacy of the trajectory subject. So the protection of trajectory privacy published dynamically is important. In this paper, a Mincer algorithm is proposed, which realizes the dynamic publishing of trajectories through the Translocation policy of trajectory points. The algorithm is low delay and reduces the information loss. The effectiveness of the algorithm and the usefulness of the published data are verified by experiments.

Optical spatial-mode reception has a physical nature quite different from that of the traditional optical power-in-the-bucket (PIB) reception. The former belongs to coherent reception scheme while the latter pertains to incoherent reception scheme. Under weak-turbulence conditions, the statistical correlation between turbulence-impacted optical signals collected by a pair of adjacent spatial-mode receivers is mathematically formulated in terms of a new theoretical framework that takes into account the distinctive nature of the spatial-mode reception. The aperture Fresnel number, coherence Fresnel number, separation Fresnel number and mode Fresnel number are identified as fundamental determinative parameters in evaluation of the correlation coefficient. With the help of the obtained formulations, two analytical asymptotic formulae for the correlation coefficient are further derived under the conditions that the aperture Fresnel number is much smaller than the coherence Fresnel number and separation Fresnel number, respectively. Despite the use of asymptotic approximations in the theoretical derivation, it is found that the two asymptotic formulae indeed have utility in many situations of practical interest to us. Furthermore, Monte-Carlo-simulation-based calculations are carried out to examine the accuracy of employing the two asymptotic formulae to approximate the correlation coefficient. It is shown that the ranges of applicability of these two asymptotic formulae are mainly determined by the coherence Fresnel number and the ratio of the separation Fresnel number to the aperture Fresnel number, basically irrespective of the mode Fresnel number.

In the past few decades, anti-aliasing method has been widely investigated in the field of computer graphics. Compared with the traditional anti-aliasing method, the anti-aliasing method with temporal coherence can avoid the computational cost of rendering additional samples. However, most of the existing temporal coherence anti-aliasing methods have limitations in performing anti-aliasing of specular materials. In this paper, we propose an optimized anti-aliasing method based on virtual hit point, which can avoid sampling error of specular surface. We use ray-tracing pipeline to render the image and display the results. Experimental results show that our method can achieve anti-aliasing effect with real-time performance.

To improve the performance of cloud-based rendering systems, it not only requires a good load balancing algorithm, but also needs less cost for data transfer. This paper proposes an internal data compression method in the cloud, which reduces the cost of data transfer between worker nodes on the basis of Hadoop distributed framework. In this method, the coordinate system transformation and simple vector addition are used to reduce the storage space of each pixel's primary ray-object intersection point and unit normal vector. We implemented the experiment of data transfer in a Hadoop ray tracing cluster with gigabit switch. First, we compared the cost under different types of data transfer. Secondly, we measured the execution time of the compression method. Finally, we analyze the reason for the error between the decompressed data and the origin data. The results show that the cost of data transfer in our method is approximately 66% of that of the three-dimensional coordinate representation method, and the calculation error is less than 10-6. Thus, our proposed method can effectively improve the transfer efficiency of cloud-based rendering system.

The instantaneous transmission coefficient, i.e., instantaneous transmittance, of a turbulent optical orbital-angular-momentum (OAM) channel is mathematically formulated as a weighted integration and is found to range between 0 and 1. Common probability distribution models for optical irradiance fluctuations with a support from 0 to ∞ are not strictly proper for statistical description of the fluctuating transmission coefficient. The novel dual Johnson S B distribution is proposed to model the statistical behavior of the fluctuating transmission coefficient. Its applicability is verified by making comparisons between the histograms of transmission-coefficient samples generated by Monte Carlo simulations and the corresponding fitted probability density functions; the values for its four independent control parameters under different conditions are obtained by the fit of the dual Johnson S B distribution to relevant simulated transmission-coefficient samples. It is found that each of the four independent control parameters of the dual Johnson S B distribution can be considered as a function of three quantities, viz., the OAM index, the Fried’s atmospheric coherence width, and the ratio of the root-mean-square (RMS) OAM-beam radius to the Fried’s atmospheric coherence width. The results demonstrate that the statistical distribution of the fluctuating transmission coefficient depends less on the first two quantities than on the last one. Finding a model for direct mapping from these three quantities to the four control parameters of the dual Johnson S B distribution deserves future study.

In comparison with the generation of monoscopic images, the time cost of rendering stereoscopic images is doubled. When generating stereoscopic images by computer algorithms, it is desirable to save the computational expense by decreasing the image resolution, without degrading the visual perceptual quality of the images. In this work, to evaluate the perceptual visual quality of computer-generated stereoscopic images (CGSIs), a data set consisting of stereoscopic images created with different horizontal and vertical resolutions was constructed. First, a series of subjective experiments for the analysis of various perceptual situations was conducted. The experimental results show that when the original image resolution was reduced by half, the image difference was not perceptible. In addition, based on full-reference (FR) and no-reference (NR) image quality measurement (IQM), a combined FR-and-NR CGSIQA model was established to predict perceptual quality. We perform weighting calculations for different combinations of FR and NR. The experimental results show that the proposed model significantly outperforms all the classical models.

With the development of handheld video capturing devices, video stabilization becomes increasingly important. The gyroscope-based video stabilization methods perform promising ability, since they can return more reliable three-dimensional (3D) camera rotation estimation, especially when there are many moving objects in scenes or there are serious motion blur or illumination changes. However, the gyroscope-based methods depend on the camera intrinsic parameters to execute video stabilization. Therefore, a self-calibrated spherical video stabilization method was proposed. It builds a virtual sphere, of which the spherical radius is calibrated automatically, and then projects each frame of the video to the sphere. Through the inverse rotation of the spherical image according to the rotation jitter component, the dependence on the camera intrinsic parameters is relaxed. The experimental results showed that the proposed method does not need to calibrate the camera and it can suppress the camera jitter by binding the gyroscope on the camera. Moreover, compared with other state-of-the-art methods, the proposed method can improve the peak signal-to-noise ratio, the structural similarity metric, the cropping ratio, the distortion score, and the stability score.

Recently, deep learning-based approaches have led to dramatic improvements for Monte Carlo rendering at the low sampling rate. Most of these approaches are aimed at path tracing. However, they are not suitable for photon mapping. In this paper, we develop a novel accelerate stochastic progressive photon mapping approaches with neural network. First, our framework utilizes the particle-based rendering and focuses on photon density estimation. We train a neural network to predict a kernel function to aggregate photon contributions at shading point. Then we construct a estimation images with the prediction network. During experiments, we could find that there are spike pixels and noises in estimation images sometimes. So we present the improved denoising network to post-process the estimation images. Finally, we can obtain the high-quality reconstructions of complex global illumination effects like caustics with an order of magnitude fewer photons compared with previous photon mapping methods. Besides, our denoising network can reduce most multi-scale noises on both low-frequency and high-frequency areas while preserving more illumination details, especially caustics, compared with other state-of-the-art learning-based denoising methods.

In order to better evaluate the relationship between reciprocity and time delay of the fiber receiving system in the atmospheric turbulence channel, a time-domain signal generation mathematical model is proposed for the first time. A numerical solution of Johnson SB probability density distribution (PDF) in time-domain is creatively given for evaluating the reciprocity of both communication ends, which relates to the normalized fluctuation variance of the light intensity and the Greenwood frequency. An experiment is then carried out for verifying the time-domain signal generation model and measuring reciprocity. It shows that the excellent fitting accuracy of Johnson SB PDF signal generation model is first experimentally verified. It also indicates that the system reciprocity is improved by 10% after eliminating the system time delay. Meanwhile, the relationship between time delay and reciprocity under different atmospheric environments are analyzed and the relationship between time delay and system reciprocity at different Greenwood frequencies are discussed. This work provides a time parameter reference for the design of adaptive system and free-space optical (FSO) communication system.

Load balancing determines the performance of the sort-first rendering clusters. A dynamic load balancing algorithm based on per-pixel rendering cost is proposed. Firstly, a 3D scene is rendered by ray tracing. At the same time, the number of intersection points between rays and scene objects in a pixel is obtained. Then, a rendering-cost map is created according to these numbers in a frame. Based on the render history, the rendering-cost map in a previous frame is used to estimate the real distribution of the ray tracing rendering cost in a future frame. Finally, a load assignment strategy is proposed to make rendering cost more uniform among rendering nodes. The experimental results show that the proposed algorithm can render continuously the next frame by subdividing future frames in advance. It is better than the compared algorithm in terms of load balancing and frame rate.

Virtual binocular stereoscopic camera models that can be used in generation of stereoscopic images or videos of virtual 3D scenes by use of computer graphics techniques are presented and analyzed in detail. It is found that the paralleloptical-axis model is most appropriate for synthesizing stereoscopic images or videos of virtual 3D scenes. Mathematical formulae for calculating the camera position and ‘lookat’ position of both the left and right virtual cameras therein are developed. Light-source visibility filtering with a depth variation constraint is proposed to speed up the ray-tracing-based soft shadow rendering of virtual 3D scenes and meanwhile to eliminate the drawback of generating fake shadows associated with the original light-source visibility filtering method; dual light-source visibility filtering scheme is suggested to make shadows reflected in a mirror surface correctly feature penumbra. The stereoscopic video experimentally generated by use of our method shows pleasing visual realism and impressive stereoscopic effects.

Common randomness arising from turbulence-induced signal fading in reciprocal optical wireless channels is a beneficial resource that can be used to generate secret keys shared by two legitimate parties. The concept of optical wireless channels using common-transverse-spatial-mode coupling (CTSMC) that can maintain perfect fading reciprocity in atmospheric turbulence is first developed in a general manner. Subsequently, by performing Monte Carlo simulations, the Johnson SB probability distribution is demonstrated to be appropriate for statistical description of turbulence-induced signal fading in an optical wireless channel constructed by use of two identical CTSMC transceivers, and the nature of correlation between signal fadings detected by two contiguous reception spatial modes is further quantitatively characterized, revealing that rapid spatial decorrelation between signal fadings observed by a legitimate party and an eavesdropper holds for scenarios of practical interest. Finally, the information theoretic capacity for generating secret keys from CTSMC-based optical wireless channels is theoretically formulated and quantitatively examined under different conditions, manifesting that the turbulence strength and average electrical signal-to-noise ratio have a noticeable combined impact on the secret key capacity, especially in the far-field case.

In this paper, an OTDM communication system based on pulse width compression of supercontinuum (SC) is proposed. A dispersion-shifted fiber (DSF) was used to narrow the pulse width and generate a SC with partial coherence property. The coherence length and attenuation of the atmospheric channel is adjustable so that the effect of atmospheric turbulence on FSO could be easily observed. We also compare the scintillation index between the wide-spectral carriers and narrow-spectral carriers of the 1km OTDM FSO link. Verifying the feasibility of wide-spectral FSO communication link through atmospheric turbulence to reduce scintillation index can be achieved.

In this paper, we experimentally realized mixed space transmission of laser beam and microwave signal which is generated by two laser beams beating using optical heterodyne method. And the hybrid RF/FSO system is confirmed to be stable and of prior performance.

Satellite networks are better alternatives to terrestrial networks because of their global coverage. Different satellite networks like GEO, MEO, and LEO can be used for the purpose of global communication. Especially, LEO satellites are more suitable for communication because of their lower propagation delays and fewer power consumptions. However, the high speed of LEO satellites is a big issue which leads to frequent cell and satellite handovers. Many techniques have been proposed to deal with satellite handover, but most of proposed techniques did not consider the situation when “the required channels are more than available channels” which causes more delays, terminations, and blocking. To handle this situation, we proposed a fuzzy C-mean cluster-based handover technique to improve the QoS of the network during handover. In the proposed technique, users (waiting for handover in a queue) are divided into clusters based on their geographic locations. Cluster heads are selected from each cluster and they act as the relay between their members and the satellite. During handover, only cluster heads reserve the channels in upcoming satellite and perform handover with their members. The experimental results prove that the proposed technique helps to reduce the handover failure, terminations, and number of waiting users, as well as it also improves the utility of network.

For a long time, Shanghai, as an international megacity, requires high reliability and strict environmental protection. The demand for improving resource allocation efficiency through market means has always been there. In order to make market mechanism play a part in the optimal allocation of power resources better, promote the power resources to help each other, and promote the reform of power generation plan, Shanghai needs to combine the balance of power, electricity market, power supply structure and the actual situation of the direct purchase of electricity for the research of the implementation scheme of the priority power generation right of Shanghai power grid. In this paper, according to the current electricity supply and demand of Shanghai power grid, the priority order of power generation in Shanghai power grid and the corresponding priority generation strategy are analyzed. Four calculation methods of coal fired unit priority power generation are put forward.

Two distinct methods based on which two different quadratic-form expressions for the two-source spherical wave structure function (WSF) can be derived are reviewed. The validity of closed-form expressions for the beam-wave cross-spectral density function (CSDF) due to generalized atmospheric turbulence featuring an arbitrary spectral index ranging from 3 to 4, developed based on the quadratic two-source spherical WSFs, is examined in detail. New formulations for the conditions under which the said closed-form expressions for the beam-wave CSDF are strictly valid are developed and several novel interesting findings are elucidated. In particular, the closed-form beam-wave CSDF derived based on the small-separation asymptotic two-source spherical WSF can be considered a rigorous asymptotic solution under the strong-turbulence condition only when the separation distance between the two observation points is much smaller than the inner scale of turbulence; moreover it is also a rigorous asymptotic solution when a certain relation among the initial beam radius, initial transverse coherence width and inner scale holds, regardless of the turbulence strength and spectral index. On the other hand, the accuracy of the closed-form beam-wave CSDF derived based on the large-separation-approximation two-source spherical WSF depends on the spectral index, and a spectral index closer to 4 results in better accuracy.

Expressions for the correlation coefficient between light-flux fluctuations of two waves counter-propagating along a common path in weak turbulence are developed. Only the aperture and inner-scale Fresnel parameters are needed for evaluation of the correlation coefficient if the turbulence spectrum has no path dependence, and of the path weighting functions for the cross-covariance and variances of normalized light-flux fluctuations if the turbulence spectrum is dependent on path locations. Under the condition that atmospheric turbulence is statistically homogeneous over a path, although good correlation between light-flux fluctuations of two counter-propagating spherical waves may be achieved for a relatively small aperture Fresnel parameter or relatively large inner-scale Fresnel parameter, the correlation coefficient between light-flux fluctuations of two counter-propagating plane waves is always lower than 1 obviously. When the aperture Fresnel parameter becomes larger than the inner-scale Fresnel parameter, the inner scale of turbulence tends to play an unimportant role in determining the correlation coefficient.

Expressions for both the temporal first- and second-order intensity moments of pulsed Gaussian-beam waves passing through generalized atmospheric turbulence are derived under the near- and far-field approximations, respectively. With the help of these expressions, the time-dependent scintillation behavior of optical pulses during propagation in generalized atmospheric turbulence is examined by numerical calculations. The effects that the spectral index of the spatial power spectrum of refractive-index fluctuations has on the temporal dependence of pulse scintillations are analyzed under the condition that the generalized plane-wave Rytov variance is specified as a constant for various spectral indices. It is shown that both the near- and far-field scintillations of an optical pulse are less dependent on time as the spectral index becomes smaller, indicating that there does exist a significant difference between the time-dependent scintillation behavior of an optical pulse in non-Kolmogorov turbulence and that in the Kolmogorov one. The obtained results are helpful for understanding the time-dependent scintillations of optical pulses propagating in generalized atmospheric turbulence and hence are useful for practical applications.

Expressions for the average intensity of both phase-locked and non-phase-locked Airy array beams propagating through atmospheric turbulence are derived based on the extended Huygens–Fresnel principle. The evolution of the average intensity distribution of both phase-locked and non-phase-locked Airy array beams during propagation in atmospheric turbulence is examined by numerical examples and is compared with that in free space. It is found that both phase-locked and non-phase-locked Airy array beams can have the “self-focusing” capability which is impacted by the beamlet-combination type, turbulence strength and Airy-beamlet parameters. It is also shown that when the atmospheric turbulence is strong enough, the differences between the propagation properties of phase-locked Airy array beams and those of non-phase-locked ones become unobservable; this is different from the free-space propagation cases. The obtained results are helpful for understanding the propagation properties of Airy array beams in atmospheric turbulence and hence useful for practical applications.

Background Reducing anaemia is an important component of children's health. Studies have shown that different media can provide information about safe health practices. However, it is uncertain how amenable ethnic minority parents are to receiving information about health care in China. We aimed to determine the use of media by Chinese parents in rural, under-served regions, and to inform technology-based interventions in diverse populations. Methods In this cross-sectional study, we used findings from a survey done in 2016, which covered 26 rural counties in 11 central and western provinces of China. We collected data from children aged 0–59 months and we included data from children aged 6–23 months in our analysis. 24 different ethnic groups were reported and ethnicity was categorised as either Han or other minority groups (Tibetan, Yi, Hui, Uygur, Kazak, Miao, Dong, Naxi, Lisu, Tujia, Bai, Buyi, Dai, Dongxiang, Gelao, Kirgiz, Mongolian, Pumi, She, Tu, Wa, Xibo, Zhuang). Five forms of media (television, radio, computer, mobile phone and internet) were studied. We designed the survey and collected the first-hand data from caregivers with children. We obtained all survey information from a structured questionnaire based on the Multiple Indicator Cluster Surveys questionnaire, and each child's haemoglobin concentration was measured by trained staff using a capillary blood sample and a calibrated, automated analyser (HemoCue 201, HemoCue, Angelholm, Sweden. Anaemia was defined as a haemoglobin concentration less than 110 g/L, adjusted for altitude of residence for children aged 6–23 months, based on WHO diagnostic criteria for anaemia. Data were anoymised. We used χ2 testing to determine whether there were differences in media access and useage according to ethnicity. We used Poisson regression to investigate demographic characteristics and media access and useage associated with anaemia. Findings We assessed data from 2711 children aged 6–23 months. The overall prevalence of anaemia in surveyed areas was 73·0% (95% CI 71·4–74·7; appendix ). Most caregivers had access to a television (n=2581, 95·2%) or mobile phone (n=2638, 97·3%), of whom 1730 (63·8%) used it access the internet. Compared with Han groups, media access was less prevalent among all ethnic groups, especially among the Yi. After adjusting for potential confounders, and by contrast with children from the Han minority, we found that Yi children were at 1·20 times greater risk, and Tibetan children at 1·39 times greater risk of anaemia. Additionally, children were more likely to have anaemia if their caregivers never connected to the internet via a computer (adjusted risk ratio 1·11, 95% CI 1·04–1·18), never connected to the internet via a mobile phone (1·07,1·01–1·13), or never connected to the internet (1·08, 1·02–1·14). Interpretation Anaemia is a serious public health problem in children aged 6–23 months in central and western China. There is broad access and use of television and mobile phone technology among Chinese caregivers, but disparities in media use exist among different ethnicities. To reduce the prevalence of anaemia in ethnic minorities, further efforts are needed to address anaemia-relevant health-care information, by means of television, short message services, or internet. Funding UNICEF China

The spatiotemporal coherence properties of broadband Gaussian Schell-model (GSM) beams with different spectral bandwidths propagating through atmospheric turbulence are numerically calculated and analyzed. The results show that although the spatial coherence properties of an intermediate-broadband GSM beam almost do not depend on the spectral bandwidth, those of its ultra-broadband counterpart do. The temporal coherence of an ultra-broadband GSM beam not only has radial dependence in the observation plane, but also varies with the increasing propagation distance; however, the same behavior does not hold for an intermediate-broadband GSM beam of which the temporal coherence remains nearly invariable as the radial distance of the observation point or propagation distance changes.

With the development in the field of three dimensional application and the hologram, it is necessary to go beyond the conventional interaction practices with machines, especially with computers. In contrast to conventional two dimensional interaction practices, we propose a novel human-to-machine three dimensional interaction practice which enables advanced interaction capabilities: pure direct 3D input capability, touch-free controlling capability and simultaneous multi-user interaction capability. The framework facilitates 360° 3D rotation and horizontal left and right swipe gestures. The experiment results emphasize that the framework observes and outputs the user input rotation with decent accuracy, and precisely recognizes the user inputted swipe gestures. The framework is easy to adopt. It works the same under different conditions and can be integrated easily to existing applications.

Numerical simulations are used to investigate the statistical properties of the instantaneous difference in the received powers between the two ends of a bidirectional optical wireless communication (OWC) link through atmospheric turbulence. The probability density estimates of the instantaneous difference between the received powers at the two link ends are obtained with various receiver aperture sizes being considered. It is found that asymmetry of turbulence profiles with respect to the path midpoint may incur obvious difference in the received powers between the two link ends. When atmospheric turbulence is distributed uniformly over the propagation path, the probability of the received powers at the two link ends being the same is nontrivial; however, it gets lower as the turbulence becomes stronger. A large enough receiver aperture may result in negligible difference between the received powers at the two link ends.

We characterize the performance of the optical signal propagation model of multi-level pulse amplitude modulation (M-PAM) based on avalanche photodiode (APD) detector in the free-space link for the first time. When the number of photons absorbed by the active surface of the APD is large enough, the bit error rate (BER) performance relationship of the systems based on the signal intensity and the photon characteristics are depicted. We use the Gamma-Gamma (G-G) channel model to analysis the communication systems with joint parameter constraints, and demonstrate the atmospheric turbulence intensity, link lengths, optical wavelength, symbol transmission rate, temperature of APD and pointing errors (PEs) impact on the system average bit error rate (ABER) performance. Moreover, the relationship between signal-to-noise-ratio (SNR) and ABER rate is given. The numerical results show that the 4-PAM free-space optical (FSO) communication is suitable for medium-to-weak turbulence, and the high gain of APD can mitigate the influence of ABER. The best detection condition of the 4-PAM optical signal is at least 20 dB SNR, when the ABER is under the 7% forward error correction (FEC) limit of 3.8 × 10-3. This work provides a reference for parameter designing and evaluating in M-PAM FSO communication systems.

In this paper, the design and cost analysis of a real-time, geographical information system (GIS) based management system for hazardous waste transportation are described. The implementation of such a system can effectively prevent illegal dumping and perform emergency responses during the transportation of hazardous wastes. A case study was conducted in Guangzhou, China to build a small-scale, real-time management system for waste transportation. Two alternatives were evaluated in terms of system capability and cost structure. Alternative I was the building of a complete real-time monitoring and management system in a governing agency; whereas alternative II was the combination of the existing management framework with a commercial Telematics service to achieve the desired level of monitoring and management. The technological framework under consideration included locating transportation vehicles using a global positioning system (GPS), exchanging vehicle location data via the Internet and Intranet, managing hazardous waste transportation using a government management system and responding to emergencies during transportation. Analysis of the cost structure showed that alternative II lowered the capital and operation cost by 38 and 56% in comparison with alternative I. It is demonstrated that efficient management can be achieved through integration of the existing technological components with additional cost benefits being achieved by streamlined software interfacing.

This publisher's note corrects a typo in the title in Opt. Lett.38, 1887 (2013)OPLEDP0146-959210.1364/OL.38.001887.

The mean-square angle-of-arrival (AOA) difference between two counter-propagating spherical waves in atmospheric turbulence is theoretically formulated. Closed-form expressions for the path weighting functions are obtained. It is found that the diffraction and refraction effects of turbulent cells make negative and positive contributions to the mean-square AOA difference, respectively, and the turbulent cells located at the midpoint of the propagation path have no contributions to the mean-square AOA difference. If the mean-square AOA difference is separated into the refraction and diffraction parts, the refraction part always dominates the diffraction one, and the ratio of the diffraction part to the refraction one is never larger than 0.5 for any turbulence spectrum. Based on the expressions for the mean-square AOA difference, formulae for the correlation coefficient between the angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are derived. Numerical calculations are carried out by considering that the turbulence spectrum has no path dependence. It is shown that the mean-square AOA difference always approximates to the variance of AOA fluctuations. It is found that the correlation coefficient between the angles of arrival in the x or y direction of two counter-propagating spherical waves ranges from 0.46 to 0.5, implying that the instantaneous angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are far from being perfectly correlated even when the turbulence spectrum does not vary along the path.

The on-axis two-frequency mutual coherence function (MCF) for beam waves propagating along a horizontal path in strong anisotropic atmospheric turbulence is theoretically formulated by making use of the extended Huygens-Fresnel principle. Based on this formulation, a new closed-form expression for the mean square temporal width of Gaussian-beam-wave pulses passing horizontally through strong anisotropic atmospheric turbulence is developed. With the help of this expression, the increments of mean square temporal pulse width due to strong anisotropic atmospheric turbulence under various conditions are further calculated. Results show that the increment of mean square temporal pulse width due to strong anisotropic atmospheric turbulence is basically proportional to the effective anisotropic factor in most situations of interest, with the possible exception of cases in which both the Fresnel ratio and spectral index become relatively small; increasing the effective anisotropic factor can reduce the number of the said exceptions; the turbulence-induced increment of mean square temporal pulse width enlarges as the spectral index increases with a fixed value of the nondimensional turbulence-strength parameter. It is also illustrated that a significant enlargement in the turbulence-induced increment of mean square temporal pulse width occurs by changing the Fresnel ratio from a large to a tiny value if both the effective anisotropic factor and spectral index are relatively small.

Based on partially coherent polarized light transmission characteristics of the atmosphere, an intensity expression of completely coherent flashing light is derived from Andrews scale modulation method. According to the generalized Huygens-Fresnel principle and Rytov theory, the phase fluctuation structure function is obtained on condition that the refractive index profile in the atmosphere meet Von Karman spectrum, then get the arrival Angle fluctuation variance. Through the RMS beam width of gaussian beams in turbulent atmosphere, deviation angle formula of fully coherent gaussian beams in turbulence atmosphere is attained, then get the RMS beam width of partially coherent and derivation angle expression of GSM beam in turbulent atmosphere. Combined with transmission properties of radial polarized laser beam, cross spectral density matrix of partially coherent radially polarized light can be gained by using generalized huygens-fresnel principle. And light intensity and polarization after transmission can be known according to the unity of coherence and polarization theory. On the basis of the analysis model and numerical simulation, the simulation results show that: the light spot caused by atmospheric turbulence of partially coherent polarization will be superior to completely polarized light.Taking advantage of this feature, designed a new wireless suppression technology of atmospheric turbulence, that is the optimization criterion of initial degree of coherent light beam. The optimal initial degree of coherent light beam will change along with the change of atmospheric turbulence conditions,make control the beam’s initial degree of coherence to realize the initial degree of coherence of light beam in real time and dynamic control. A spatial phase screen before emission aperture of fully coherent light is to generate the partially coherent light, liquid crystal spatial light modulator is is a preferable way to realize the dynamic random phase. Finally look future of the application research of partially coherent light.

Build theory model of intensity scintilla characteristics of laser atmospheric transmission. Under the analysis of the model, focus on theory model simulation of effect model simulation of laser transmission characteristics. And simulation results show that: the laser scintilla caused by atmospheric turbulence increased with the transmission distance and turbulence intensity increased; The longer wavelengths of light intensity, the smaller intensity scintilla; The plane waves of laser scintilla is smaller than spherical wave and so on. Finally research of the laser transmission characteristics in the atmosphere is prospected.

The changes in the radial content of orbital-angular-momentum (OAM) photonic states described by Laguerre-Gaussian (LG) modes with a radial index of zero, suffering from turbulence-induced distortions, are explored by numerical simulations. For a single-photon field with a given LG mode propagating through weak-to-strong atmospheric turbulence, both the average LG and OAM mode densities are dependent only on two nondimensional parameters, i.e., the Fresnel ratio and coherence-width-to-beam-radius (CWBR) ratio. It is found that atmospheric turbulence causes the radially-adjacent-mode mixing, besides the azimuthally-adjacent-mode mixing, in the propagated photonic states; the former is relatively slighter than the latter. With the same Fresnel ratio, the probabilities that a photon can be found in the zero-index radial mode of intended OAM states in terms of the relative turbulence strength behave very similarly; a smaller Fresnel ratio leads to a slower decrease in the probabilities as the relative turbulence strength increases. A photon can be found in various radial modes with approximately equal probability when the relative turbulence strength turns great enough. The use of a single-mode fiber in OAM measurements can result in photon loss and hence alter the observed transition probability between various OAM states. The bit error probability in OAM-based free-space optical communication systems that transmit photonic modes belonging to the same orthogonal LG basis may depend on what digit is sent.