Reference Phase Stabilizer for Distributed Underwater Sonar Systems.

An optical fiber is a promising approach for data and clock transmission in distributed underwater sonar systems. However, synchronization is a critical challenge in distributed sonar systems, which mandates accurate clock synchronization down to a sub degree. Potential phase misalignment is caused by fiber length variations. In this paper, we propose a fiber-based phase stabilizer method to achieve accurate clock synchronization among sensor nodes. We use fiber-based feedback loop between sensor nodes and central station unit to monitor phase variations. Subsequently, we leverage phase shifters symmetrically arranged on the forward lane and feedback lane to compensate real-time phase variation and maintain high-precision synchronization. Besides, an ambiguity eliminator circuit is designed to remove the clock's cyclic ambiguity. Both analysis and experimental results suggest that the proposed phase stabilizer can achieve 10 MHz reference clock synchronization within 0.4 degree. We also analyze the impact of the reference clock's phase error on the system range detection accuracy, which indicates that the proposed phase stabilizer can greatly improve detection accuracy of sonar systems.

A Fast Calibration Method for Phased Arrays by Using the Graph Coloring Theory.

Phased array radars are able to provide highly accurate airplane surveillance and tracking performance if they are properly calibrated. However, the ambient temperature variation and device aging could greatly deteriorate their performance. Currently, performing a calibration over a large-scale phased array with thousands of antennas is time-consuming. To facilitate the process, we propose a fast calibration method for phased arrays with omnidirectional radiation patterns based on the graph coloring theory. This method transforms the calibration problem into a coloring problem that aims at minimizing the number of used colors. By reusing the calibration time slots spatially, more than one omnidirectional antenna can perform calibration simultaneously. The simulation proves this method can prominently reduce total calibration time and recover the radiation pattern from amplitude and phase errors and noise. It is worth noting that the total calibration time consumed by the proposed method remains constant and is negligible compared with other calibration methods.

Effect of Caregiver's Mental Health on Early Childhood Development across Different Rural Communities in China.

Previous research has found that there are high rates of developmental delays among infants and toddlers in rural areas of China. Caregiver mental health problems might be one significant predictor of developmental delays among infants and toddlers, as has been found in other areas of the world. One way that the mental health of caregivers could affect early childhood development is through its effect on parenting practices. In this study, we used data from four major subpopulations of rural China to measure the correlation of caregiver mental health problems with the developmental outcomes of infants and toddlers. To do so, the study used the Bayley Scales of Infant Development III (BSID III) to examine the rates of developmental delays among 2514 rural infants/toddlers aged 6⁻30 months old. The results of the testing demonstrate that 48% of the sample's infants/toddlers have cognitive delays; 52% have language delays; 53% have social-emotional delays; and 30% have motor delays. The data collection team also assessed caregiver mental health by using the Depression Anxiety Stress Scales (DASS-21) questionnaire. According to the findings, 39% of caregivers in the sample have symptoms of at least one kind of mental health problem (depression, anxiety, or stress). We also found that most caregivers do not engage in positive parenting practices, while a significant share of caregivers engage in negative parenting practices. The statistical analysis found that showing signs of mental health problems is significantly and negatively associated with infant/toddler developmental outcomes. The study also found that caregivers who show signs of mental health problems are significantly less likely to engage in interactive parenting practices. The study confirms that society needs to pay more attention to caregiver mental health problems in order to improve infant/toddler developmental outcomes in rural China and increase human capital accumulation in China as a whole.