The conventional buck-boost converter has the advantages of simple structure, low cost, and the capability to achieve both voltage step-up and down. However, due to the negative impacts of the parasitic parameters of the device, the voltage conversion gain of the conventional buck-boost converter is greatly limited. A low-voltage stress buck-boost converter with a high voltage conversion gain based on a coat circuit is proposed in this paper to address the problem. Similar to a coat that can enhance human's resistance to cold weather, by adding the proposed coat circuit to the conventional buck-boost converter, not only the range for the voltage conversion can be extended, but also the voltage stresses of the semiconductor components are effectively reduced. In this work, comprehensive analysis on the working principles and performance characteristics of the coat converter are provided. Experimental results are obtained and analyzed to validate of the theoretical analysis based on a 300W closed-loop prototype platform.INDEX TERMS Buck-boost, coat circuits, high voltage conversion gain, voltage stress.

The percentage of elderly people in the world is increasing at an unprecedented pace; so it is in China, which has the world's largest population and a high ratio of the seniors (aged 60 and above) to working-age adults. The growing elderly population is presenting a major social challenge. Accordingly, it is not only imperative as a national strategic demand but also promises great scientific values to understand the biological process of aging, explore the mystery of healthy aging, delay the aging process, and treat the age-related diseases. This Perspective summarizes past and present advances of the basic and translational aging research in China and offers perspectives on future endeavors in this area. Based on a national survey conducted by the National Bureau of Statistics, China's elderly population (aged 60 and above) had reached 249 million by the end of 2018, making up about 17.9% of the total population; those aged 65 and above totaled 167 million, accounting for 11.9% of the total population. The 2013 "China Aging Development Report" pointed out that the severity of the aging problems in China was unprecedented. Population aging is accompanied by increased prevalence of various age-related chronic diseases. The cost of healthcare for the elderlies is imposing a heavy financial burden both on the elderlies and their families as well as on society as a whole. It is of great social significance to achieve healthy aging to reduce medical expenses and increase productive engagement of elderly population. The history of aging research in China can be traced back to early 1980s, Chinese scientists began to decode aging. Prof. Tanjun Tong's team discovered the relationship between P16 and telomeres, unraveled the molecular mechanisms by which P16 regulates cellular senescence, and identified genetic indicators and quantitative indices for estimating the "age" of human cells, including telomere length, cell proliferative capacity, senescence-associated βgalactosidase activity, advanced glycation end products, DNA damage repair ability, DNA methylation degree, mitochondrial DNA deletion, and α-2-macroglobulin protein level

Background Maternal vitamin D deficiency has been a worldwide concern in recent years. However the epidemiological data of vitamin D deficiency among large group of Chinese pregnant women is limited. This study is to evaluate the prevalence of vitamin D deficiency among pregnant women in Shanghai, China and to analyze the association of vitamin D status with some pregnancy outcomes (gestational diabetes and low birth weight). Methods A total of 34,417 pregnant women in Shanghai were included in this study from January 2014 to December 2017, and the serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured at 16th week of gestation by electrochemiluminescence assay. Seventy five grams of glucose was used to conduct oral glucose tolerance test during 24-28th week of gestational in all enrolled persons and the birth weight of newborns was recorded. Results The median serum 25(OH) D concentration in the pregnant women during 4 years was 42.87 nmol/L (32.88–51.90 nmol/L). 9.9% of the population were severe vitamin D deficient [25(OH)D < 25 nmol/L], 60.1% were deficient [25 nmol/L ≤ 25(OH)D < 50 nmol/L], 28.4% were insufficient [50 nmol/L ≤ 25(OH)D < 75 nmol/L] and only 1.6% of the enrolled population reached the level of adequate [25(OH)D ≥ 75 nmol/L]. Serum 25(OH) D concentrations showed significant difference among seasons with the highest level in winter and the lowest level in summer. Women with advanced maternal age were more likely to have better vitamin D status compared with younger women. The 25(OH) D levels were significantly different among 2014–2017. The year of 2017 had the highest 25(OH) D level with the median serum concentration reaching 47.80 nmol/L (41.00–55.00 nmol/L), while the lowest appeared in 2016 which has median 25(OH) D concentration at 38.87 nmol/L (28.76–49.97 nmol/L). No relations were found between the 25(OH) D status and the rate of gestational diabetes or low birth weight of newborns. Conclusion Pregnant women in Shanghai were generally deficient in vitamin D status and the level of vitamin D was related to season and age. No evidence showed vitamin D deficiency in pregnant women contributes to the rate of gestational diabetes or low birth weight of newborns in this study. These results suggest that most of the pregnant women may need vitamin D supplementation to achieve adequate vitamin D level.