Optical ranging and vibration sensing based on the lagging propagation phase of structured beams.

Recently, studies have shown that the spatial confinement on waves or photons with beam shaping techniques would modify the propagation speed of optical fields including both group and phase velocities. Particularly, for the monochromatic spatially structured beams, the reduced longitudinal wave vector enables the phase velocity to be superluminal, causing a lagging propagation phase. In this Letter, we propose a novel, to the best of our knowledge, scheme for optical ranging and vibration sensing with the lagging propagation phase of structured beams. We experimentally demonstrate the extraction of displacement from the rotating angles of interfering fringes of superposed Gaussian and higher-order Bessel beams with lagging propagation phase difference. The measuring range is 0.2 m with the limitation of the tested moving stage, but it can be extended to tens of meters in principle. The measuring resolution can reach sub-millimeters, which can be further improved by carefully designing the probe beam and using a finer camera. The results may provide potential applications in position sensing and monitoring.

Lagging propagation phase of spatially structured beams.

The structured beams especially with spatially varying phase distribution have attracted tremendous attention in both physics and engineering. Recently, studies have shown that the transverse spatial confinement of optical fields or photons leads to a modification of the group velocity but the phase velocity of propagating structured beams is revealed insufficiently in the experiments. In this work, we provide the theoretical model and experimental observation of propagation phase of structured beams. The analysis suggests that the spatially structured beams with a definite axial component of wavevector kr carry a so called "lagging propagation phase", which can be considered as a generalized Gouy phase that originally appears within a focal region. Taking the higher-order Bessel beam as an example, the propagation phase difference is demonstrated by mapping to the rotating angle of intensity patterns superposed with different radial and angular phase gradients. Physically, the lagging propagation phase may provide an interpretation for the dynamic evolution of complex structured beams or interfering fringes upon propagation such as the vortex knots or braids. From the application aspect, the lagging propagation phase would facilitate a promising way for structured beams in optical sensing and metrology.

Single-carrier 800-Gb/s self-homodyne coherent transmission of DP-16QAM, DP-32QAM, and DP-64QAM with uncooled DFB laser.

Self-homodyne detection (SHD) is a promising approach to realize high-capacity short-reach optical transmission systems with low cost and low power consumption. We experimentally demonstrate single-carrier net 800-Gb/s SHD transmission with low-cost ∼MHz linewidth distributed feedback (DFB) laser over 2 km, 10 km, 25 km, and 40 km single-mode fiber (SMF) using three different quadrature amplitude modulation (QAM) formats, including 80-Gbaud dual-polarization (DP) 64QAM, 100-Gbaud DP-32QAM, and 120-Gbaud DP-16QAM. Among them, net 800-Gb/s DP-64QAM SHD transmission over 25 km SMF using an uncooled DFB laser with a linewidth of 2.6 MHz is experimentally verified. The detailed experimental performance evaluation of net 800Gb/s SHD system is performed, in which various configurations are considered, such as different laser linewidths, three QAM formats, and different transmission distances. DFB lasers with linewidths of 1 MHz and 2.6 MHz lead to negligible penalty when compared to the same SHD system but using an external cavity laser (ECL) with a linewidth of 26kHz in back-to-back (BTB) case. 80-Gbaud DP-64QAM obtains the highest optical signal-to-noise ratio (OSNR) requirement and the highest bit-error rate (BER) floor but the best tolerance of chromatic dispersion (CD). 120-Gbaud DP-16QAM achieves the lowest OSNR requirement and the lowest BER floor but the worst tolerance of CD. The detailed experimental investigation is conducive to promote the practical application of SHD in different short-reach scenarios.

Direction-discriminated rotational Doppler velocimetry with circularly polarized vortex beams.

The rotational Doppler effect can be exploited in laser rotational Doppler velocimetry to detect the angular velocity of a moving object. Recently, its vectorial counterpart was revealed, which uses vectorial polarization fields and shows the potential to retrieve the full vectorial motion information of a moving object. Here, we further develop the general model for direction-discriminated rotational Doppler velocimetry by considering two optical degrees of freedom (DoFs), i.e., the orbital angular momentum (OAM) and polarization. Analyses indicate that the two optical DoFs of light play different roles in rotational velocity measurement. On the one hand, the OAM DoF enables the detection of the magnitude of rotational velocity; on the other hand, the circular polarization DoF facilitates the determination of the rotation direction by analyzing the relative phase difference between two intensity signals of the superposed light field after two polarizers. We demonstrate an interferometric scheme with two orthogonally circularly polarized beams of opposite OAM for detecting a rotating small object. These demonstrations may provide abundant alternatives for achieving robust Doppler velocimetry in more complicated sensing and metrology applications.

The propagation speed of optical speckle.

That the speed of light in vacuum is constant is a cornerstone of modern physics. However, recent experiments have shown that when the light field is confined in the transverse plane, the observed propagation speed of the light is reduced. This effect is a consequence of the transverse structure which reduces the component of wavevector of the light in the direction of propagation, thereby modifying both the phase and group velocity. Here, we consider the case of optical speckle, which has a random transverse distribution and is ubiquitous with scales ranging from the microscopic to the astronomical. We numerically investigate the plane-to-plane propagation speed of the optical speckle by using the method of angular spectrum analysis. For a general diffuser with Gaussian scattering over an angular range of 5°, we calculate the slowing of the propagation speed of the optical speckle to be on the order of 1% of the free-space speed, resulting in a significantly higher temporal delay compared to the Bessel and Laguerre-Gaussian beams considered previously. Our results have implications for studying optical speckle in both laboratory and astronomical settings.

Long-Term Consumption of Green Tea Can Reduce the Degree of Depression in Postmenopausal Women by Increasing Estradiol.

Postmenopausal women face a higher risk of depression due to a combination of social and physiological factors. As a beverage rich in a variety of bioactive substances, green tea has significant effects on metabolism, inflammation and endocrine, and may reduce the risk of depression, but few studies have looked at the effects of green tea on postmenopausal women. Therefore, we designed this study to investigate the effects of long-term green tea consumption on inflammation, endocrine and depression levels in postmenopausal women. We investigated a tea-producing village and eventually included 386 postmenopausal women, both in the tea drinking and control groups. The results showed that there were significant differences in the degree of insomnia, degree of depression, BMI, SII and estradiol between the two groups. And, green tea consumption may reduce the risk of depression through the mediating pathway of sleep, SII and estradiol. In summary, long-term green tea consumption can reduce the risk of depression in postmenopausal women by reducing inflammation and increasing estradiol. This kind of living habit deserves further promotion.

Design, Analysis, and Real-Time Simulation of a 3D Soft Robotic Snake.

Snakes are a remarkable source of inspiration for mobile search-and-rescue robots. Their unique slender body structure and multiple modes of locomotion are well-suited to movement in narrow passages and other difficult terrain. The design, manufacturing, modeling, and control techniques of soft robotics make it possible to imitate the structure, mechanical properties, and locomotion gaits of snakes, opening up new possibilities in robotics research. Building on our track record of contributions in this area, this article presents a soft robotic snake made of modules that can actively deform in three-dimensional (3D) and rigorously studies its performance under a range of conditions, including gait parameters, number of modules, and differences in the environment. A soft 3D-printed wave spring sheath is developed to support the robot modules, increasing the snake's performance in climbing steps threefold. Finally, we introduce a simulator and a numerical model to provide a real-time simulation of the soft robotic snake. With the help of the real-time simulator, it is possible to develop and test new locomotion gaits for the soft robotic snake within a short period of time, compared with experimental trial and error. As a result, the soft robotic snake presented in this article is able to locomote on different surfaces, perform different bioinspired and custom gaits, and climb over steps.

People with passive sleep delay have more severe depression and sleep problems than those with active sleep delays-a cross-sectional study after the COVID-19 pandemic.

Objective: This study was designed to investigate the effect of different types of sleep delay in depression and sleep characteristics after the pandemic. Meanwhile, risk factors for depression were also explored. Methods: The survey was conducted in Wuhan from March 1 to May 30, 2021, and participants were recruited through a snowball process. A total of 1,583 people with sleep delays responded to the invitation, of which 1,296 were enrolled. Participants filled out a questionnaire including social demographics, sleep characteristics, Social Support Rating Scale (SSRS), Pittsburgh Sleep Quality Index (PSQI) and Patient Health Questionnaire-9 (PHQ-9). Results: There were no significant differences in sex, social support and level of education between the two types of sleep delay (p = 0.961, p = 0.110, p = 0.090), but the average age of the passive sleep delay group was higher (p = 0.015). And most people with active sleep delay were caused by the use of electronic devices (73.6%), while most people with passive sleep delay were caused by work or study tasks (73.2%), with a significant difference between the two groups (p < 0.001). People who actively delayed sleep had more regular sleep (p < 0.001), better sleep quality and longer sleep duration (p < 0.001, p < 0.001). In addition, although they delayed sleep more frequently (p < 0.001), they had significantly lower depression degree than people who passively delayed sleep (p < 0.001). Conclusions: Passive sleep delays, usually caused by work or study, has higher levels of depression and more adverse sleep behaviors than active sleep delay. The findings help further understand the effects of delayed sleep and provide insight for people with delayed sleep to evaluate their own condition. Future studies are required to standardize and accurately classify sleep delay and further explore it.

Remote Measurement of the Angular Velocity Vector Based on Vectorial Doppler Effect Using Air-Core Optical Fiber.

Rotational Doppler effect has made tremendous development in both theoretical and applied research over the last decade. Different from the inertial thinking of focusing on the scalar field dominated by helical phase light, we have revealed a vectorial Doppler effect in our previous work, which is based on the spatially variant polarized light fields to simultaneously acquire the speed and direction of a target. Here, further, we propose a method to construct a flexible and robust velocimeter based on that novel effect by employing an air-core fiber with kilometer-length scale for remotely measuring the vectorial information of angular velocity in situ. In addition, we experimentally substantiate that the measurement system still has commendable accuracy in determining the direction of movement even when the air-core fiber is interfered by the external environment. The demonstrations prove the potential of vectorial Doppler effect in practical scenarios and remote measurements.

Vectorial Doppler metrology.

The Doppler effect is a universal wave phenomenon that has spurred a myriad of applications. In early manifestations, it was implemented by interference with a reference wave to infer linear velocities along the direction of motion, and more recently lateral and angular velocities using scalar phase structured light. A consequence of the scalar wave approach is that it is technically challenging to directly deduce the motion direction of moving targets. Here we overcome this challenge using vectorially structured light with spatially variant polarization, allowing the velocity and motion direction of a moving particle to be fully determined. Using what we call a vectorial Doppler effect, we conduct a proof of principle experiment and successfully measure the rotational velocity (magnitude and direction) of a moving isotropic particle. The instantaneous position of the moving particle is also tracked under the conditions of knowing its starting position and continuous tracking. Additionally, we discuss its applicability to anisotropic particle detection, and show its potential to distinguish the rotation and spin of the anisotropic particle and measure its rotational velocity and spin speed (magnitude and direction). Our demonstration opens the path to vectorial Doppler metrology for detection of universal motion vectors with vectorially structured light.

Motion Planning and Iterative Learning Control of a Modular Soft Robotic Snake.

Snake robotics is an important research topic with a wide range of applications, including inspection in confined spaces, search-and-rescue, and disaster response. Snake robots are well-suited to these applications because of their versatility and adaptability to unstructured and constrained environments. In this paper, we introduce a soft pneumatic robotic snake that can imitate the capabilities of biological snakes, its soft body can provide flexibility and adaptability to the environment. This paper combines soft mobile robot modeling, proprioceptive feedback control, and motion planning to pave the way for functional soft robotic snake autonomy. We propose a pressure-operated soft robotic snake with a high degree of modularity that makes use of customized embedded flexible curvature sensing. On this platform, we introduce the use of iterative learning control using feedback from the on-board curvature sensors to enable the snake to automatically correct its gait for superior locomotion. We also present a motion planning and trajectory tracking algorithm using an adaptive bounding box, which allows for efficient motion planning that still takes into account the kinematic state of the soft robotic snake. We test this algorithm experimentally, and demonstrate its performance in obstacle avoidance scenarios.

Percutaneous pinning versus volar locking plate internal fixation for unstable distal radius fractures: a meta-analysis.

This meta-analysis compared outcomes between percutaneous pinning/wiring and open reduction internal fixation (ORIF) with locking plates for treatment of unstable distal radius fractures. Medline, Cochrane, EMBASE, and Google Scholar were searched through December 30, 2015. Twenty randomised controlled trials (RCTs) and non-randomised two-arm studies were included. Outcomes included scores of Disabilities of the Arms, Shoulders and Hands (DASH), visual analogue scale (VAS) pain, and patient rated wrist evaluation (PRWE) score, as well as range of motion (ROM) and complication incidence. ORIF/plating was associated with lower DASH scores but longer procedure time, while there was no difference between the two methods with respect to VAS pain score and PRWE score. The overall incidence of complications, including complex regional pain syndrome, was higher with pinning/wiring, though the incidence of carpal tunnel syndrome and nerve defects was not different. Supination and grip strength were better with ORIF. Radiographically, ulnar variation was greater with pinning/wiring. These results suggest that ORIF/plating is the preferred method of managing unstable distal radius fractures. LEVEL OF EVIDENCE: II.

Rapid thermal annealing and crystallization mechanisms study of silicon nanocrystal in silicon carbide matrix.

In this paper, a positive effect of rapid thermal annealing (RTA) technique has been researched and compared with conventional furnace annealing for Si nanocrystalline in silicon carbide (SiC) matrix system. Amorphous Si-rich SiC layer has been deposited by co-sputtering in different Si concentrations (50 to approximately 80 v%). Si nanocrystals (Si-NC) containing different grain sizes have been fabricated within the SiC matrix under two different annealing conditions: furnace annealing and RTA both at 1,100°C. HRTEM image clearly reveals both Si and SiC-NC formed in the films. Much better "degree of crystallization" of Si-NC can be achieved in RTA than furnace annealing from the research of GIXRD and Raman analysis, especially in high-Si-concentration situation. Differences from the two annealing procedures and the crystallization mechanism have been discussed based on the experimental results.