No abstract

V itamin D is important at all life stages, but attaining adequate vitamin D during pregnancy may be especially important for the health of both mother and child. Vitamin D inadequacy during pregnancy has been associated with preeclampsia, the leading cause of maternal morbidity in Canada. 1,2 Poor vitamin D status during pregnancy may also adversely affect calcium homeostasis and skeletal mineralization in the unborn child. Rickets, which still occurs in Canada, is found almost exclusively in breastfed infants born to vitamin D-deficient mothers. 3 In addition, a lack of vitamin D in utero or in early life may increase the risk of type 1 diabetes, 4 asthma, 5 and low bone mass 6 later in life. Circulating 25 hydroxyvitamin D (25OHD) is the best indicator of vitamin D status as it represents vitamin D obtained from both UV skin synthesis and dietary sources. 7,8 The optimal 25OHD concentration in pregnancy is not known with certainty. In 2010, the Institute of Medicine recommended that maintaining a serum 25OHD concentration of approximately 50 nmol/L is desirable in all life-stage groups. 9 In 2007, the Canadian Pediatric Society adopted a 25OHD serum concentration of >75 nmol/L as "sufficient" for pregnant and lactating women, and infants. 10 Low 25OHD concentrations have been reported in pregnant women in several countries, 11,12 yet there are few studies of pregnant women in Canada. Factors that might predispose Canadian women to poor vitamin D status include living at high latitude, low vitamin D intakes from food, and for some individuals, darker skin pigmentation. Very few Canadian women of reproductive age achieve the Recommended Dietary Allowance of vitamin D intake of 600 IU. 9 However, over 80% of pregnant women consume a multivitamin supplement at some point during pregnancy. 13 It is unclear whether the amount of vitamin D provided in prenatal supplements, typically 400 IU, is sufficient to achieve optimal 25OHD concentrations. Given the widening spectrum of adverse maternal and child outcomes associated with a lack of vitamin D during pregnancy and the paucity of Canadian data, we measured 25OHD concentrations in an ethnically diverse sample of pregnant women living in Vancouver. We also explored the determinants of 25OHD concentration such as season, ethnicity and skin colour, as well as dietary and supplement intake of vitamin D.

No abstract

It is well known that children’s academic performances are affected by both their family backgrounds and contextual or structural factors such as the urban–rural difference and regional variation. This article evaluates the relative importance of family background versus structural factors in determining children’s academic achievements across three different societies: China, the United States of America, and Germany, analyzing data from five large-scale, high-quality, and nationally representative data sets. The results reveal two main findings: (a) family socioeconomic status exerts much stronger positive effects on children’s academic achievement in the USA and Germany than in China; and (b) structural factors (such as those measured by location and urban/rural residence) play much smaller roles in the USA and Germany than in China.

High-speed rail (HSR) systems potentially provide a more efficient way of door-to-door transportation than airplane. However, they also pose unprecedented challenges in delivering seamless Internet service for on-board passengers. In this paper, we conduct a large-scale active-passive measurement study of TCP performance over LTE on HSR. Our measurement targets the HSR routes in China operating at above 300 km/h. We performed extensive data collection through both controlled setting and passive monitoring, obtaining 1732.9 GB data collected over 135719 km of trips. Leveraging such a unique dataset, we measure important performance metrics such as TCP goodput, latency, loss rate, as well as key characteristics of TCP flows, application breakdown, and users' behaviors. We further quantitatively study the impact of frequent cellular handover on HSR networking performance, and conduct in-depth examination of the performance of two widely deployed transport-layer protocols: TCP CUBIC and TCP BBR. Our findings reveal the performance of today's commercial HSR networks "in the wild", as well as identify several performance inefficiencies, which motivate us to design a simple yet effective congestion control algorithm based on BBR to further boost the throughput by up to 36.5%. They together highlight the need to develop dedicated protocol mechanisms that are friendly to extreme mobility. * This work is a pre-print version to appear at MobiCom 2019. † J.Wang, Y.Zheng and Y. Ni are the co-primary student authors.