2D metallic transition-metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, but the batch production remains challenging. Herein, the van der Waals epitaxial growth of monocrystalline, 1T-phase, few-layer metallic VSe2 nanosheets on an atomically flat mica substrate via a ``one-step\''\ chemical vapor deposition method is reported. The thickness of the VSe2 nanosheets is precisely tuned from several nanometers to several tenths of nanometers. More significantly, the 2D VSe2 single crystals are found to present an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 10(6) S m(-1), 1-4 orders of magnitude higher than that of various conductive 2D materials. The thickness-dependent charge-density-wave phase transitions are also examined through low-temperature transport measurements, which reveal that the synthesized 2D metallic 1T-VSe2 nanosheets should serve as good research platforms for the detecting novel many-body states. These results open a new path for the synthesis and property investigations of nanoscale-thickness 2D MTMDs crystals.
East Asia is a densely populated region with a myriad of primary emissions of pollutants such as black carbon (BC) and carbon monoxide (CO). To characterize primary emissions over the eastern coast of China, a series of field campaigns were conducted in 2011, including measurements from a ship cruise, island, and coastal receptor sites. The relationship between BC and CO is presented here for the first ship cruise (C1), the second ship cruise (C2), an island site (Changdao Island, CD), and a coastal site (Wenling, WL). The average BC mass concentrations were 2.43, 2.73, 1.09, 0.94, and 0.77 mu g m(-3) for CD, WL, C1-YS (Yellow Sea), C1-ES (East China Sea), and C2-ES, respectively. For those locations, the average CO mixing ratios were 0.55, 0.48, 0.31, 0.36, and 0.27 ppm. The high loadings of both BC and CO imply severe anthropogenic pollution over the eastern coast of China. Additionally, the linear correlation between BC and CO was regressed for each location. The slopes, i.e., the ratios of Delta BC to Delta CO derived from their relationship, correlated well with the ratios of diesel consumption to gasoline consumption in each province/city, which reveals vehicular emission to be the common source for BC and CO and that there are distinct fuel structures between North and South China. The Delta BC/Delta CO values at coastal sites (Changdao Island and Wenling) were much higher than those over the Yellow Sea and East China Sea, and the correlation coefficients also showed a decreasing trend from the coast to the sea. Therefore, the quantity of Delta BC/Delta CO and the correlation coefficients are possible indicators for the aging and removal of BC.
Microbial methanogenesis in sediment plays a crucial role in CH4 emission from freshwater lake ecosystems. However, knowledge of the layer-depth-related changes of methanogen community structure and activities in freshwater lake sediment is still limited. The present study was conducted to characterize the methanogenesis potential in different sediment-layer depths and the vertical distribution of microbial communities in two freshwater lakes of different trophic status on the Yunnan Plateau (China). Incubation experiments and inhibitor studies were carried out to determine the methanogenesis potential and pathways. 16S rRNA and mcrA genes were used to investigate the abundance and structure of methanogen and archaeal communities, respectively. Hydrogenotrophic methanogenesis was mainly responsible for methane production in sediments of both freshwater lakes. The layer-depth-related changes of methanogenesis potential and the abundance and community structure of methanogens were observed in both Dianchi Lake and Erhai Lake. Archaeal 16S rRNA and mcrA genes displayed a similar abundance change pattern in both lakes, and the relative abundance of methanogens decreased with increasing sediment-layer depth. Archaeal communities differed considerably in Dianchi Lake and Erhai Lake, but methanogen communities showed a slight difference between these two lakes. However, methanogen communities illustrated a remarkable layer-depth-related change. Order Methanomicrobiales was the dominant methanogen group in all sediments, while Methanobacteriales showed a high proportion only in upper layer sediments. The trophic status of the lake might have a notable influence on the depth-related change pattern of methanogenesis activity, while the methanogen community structure was mainly influenced by sediment depth.
The present study investigated the abundance, richness, diversity, and community composition of denitrifiers (based on nirS and nosZ genes) in the stratified water columns and sediments in eutrophic Dianchi Lake and mesotrophic Erhai Lake using quantitative PCR assay and high-throughput sequencing analysis. Both nirS- and nosZ denitrifiers were detected in waters of these two lakes. Surface water showed higher nosZ gene density than bottom water, and Dianchi Lake waters had larger nirS gene abundance than Erhai Lake waters. The abundance of sediment nirS- and nosZ denitrifiers in Dianchi Lake was larger than that in Erhai Lake. nirS richness and diversity and nosZ richness tended to increase with increasing sediment layer depth in both lakes. The distinct structure difference of sediment nirS- and nosZ denitrifier communities was found between in Dianchi Lake and Erhai Lake. These two lakes also differed greatly in water denitrifier community structure. Moreover, phylogenetic analysis indicated the presence of several different groups of nirS- or nosZ denitrifiers in both lakes. The novel nirS denitrifiers were abundant in both Dianchi Lake and Erhai Lake, while most of the obtained nosZ sequences could be affiliated with known genera.
Interfacial materials play a critical role in photoelectric conversion properties as well as the anomalous hysteresis phenomenon of the perovskite solar tells (PSCs), In this article, a water-soluble polythiophene PTEBS was employed as a cathode interfacial, material for PSCs. Efficient energy level aligning and improved film morphology Were obtained due to an ultrathin coating of PTEBS. Better ohmic contact :between the perovskite layer and the cathode also benefits the charge transport and extraction of the device. Moreover, less charge accumulation at the interface weakens the polarization of the perovskite resulting in a relatively quick response of the modified device. The ITO/PTEBS/CH3NH3PbI3/spiro-MeOTAD/Au cells by an all low-temperature process achieved power conversion efficiencies of up to 15.4% without apparent hysteresis effect. Consequently, the utilization of this water-soluble polythiophene is a practical approach for the fabrication of highly efficient, large-area, and low-cost PSCs and compatible with low:temperature solution process, roll-to-roll manufacture, and flexible application.
BACKGROUND: Raised blood pressure is an important risk factor for cardiovascular diseases and chronic kidney disease. We estimated worldwide trends in mean systolic and mean diastolic blood pressure, and the prevalence of, and number of people with, raised blood pressure, defined as systolic blood pressure of 140 mm Hg or higher or diastolic blood pressure of 90 mm Hg or higher. METHODS: For this analysis, we pooled national, subnational, or community population-based studies that had measured blood pressure in adults aged 18 years and older. We used a Bayesian hierarchical model to estimate trends from 1975 to 2015 in mean systolic and mean diastolic blood pressure, and the prevalence of raised blood pressure for 200 countries. We calculated the contributions of changes in prevalence versus population growth and ageing to the increase in the number of adults with raised blood pressure. FINDINGS: We pooled 1479 studies that had measured the blood pressures of 19.1 million adults. Global age-standardised mean systolic blood pressure in 2015 was 127.0 mm Hg (95% credible interval 125.7-128.3) in men and 122.3 mm Hg (121.0-123.6) in women; age-standardised mean diastolic blood pressure was 78.7 mm Hg (77.9-79.5) for men and 76.7 mm Hg (75.9-77.6) for women. Global age-standardised prevalence of raised blood pressure was 24.1% (21.4-27.1) in men and 20.1% (17.8-22.5) in women in 2015. Mean systolic and mean diastolic blood pressure decreased substantially from 1975 to 2015 in high-income western and Asia Pacific countries, moving these countries from having some of the highest worldwide blood pressure in 1975 to the lowest in 2015. Mean blood pressure also decreased in women in central and eastern Europe, Latin America and the Caribbean, and, more recently, central Asia, Middle East, and north Africa, but the estimated trends in these super-regions had larger uncertainty than in high-income super-regions. By contrast, mean blood pressure might have increased in east and southeast Asia, south Asia, Oceania, and sub-Saharan Africa. In 2015, central and eastern Europe, sub-Saharan Africa, and south Asia had the highest blood pressure levels. Prevalence of raised blood pressure decreased in high-income and some middle-income countries; it remained unchanged elsewhere. The number of adults with raised blood pressure increased from 594 million in 1975 to 1.13 billion in 2015, with the increase largely in low-income and middle-income countries. The global increase in the number of adults with raised blood pressure is a net effect of increase due to population growth and ageing, and decrease due to declining age-specific prevalence. INTERPRETATION: During the past four decades, the highest worldwide blood pressure levels have shifted from high-income countries to low-income countries in south Asia and sub-Saharan Africa due to opposite trends, while blood pressure has been persistently high in central and eastern Europe. FUNDING: Wellcome Trust.
Background Underweight, overweight, and obesity in childhood and adolescence are associated with adverse health consequences throughout the life-course. Our aim was to estimate worldwide trends in mean body-mass index (BMI) and a comprehensive set of BMI categories that cover underweight to obesity in children and adolescents, and to compare trends with those of adults. Methods We pooled 2416 population-based studies with measurements of height and weight on 128.9 million participants aged 5 years and older, including 31.5 million aged 5-19 years. We used a Bayesian hierarchical model to estimate trends from 1975 to 2016 in 200 countries for mean BMI and for prevalence of BMI in the following categories for children and adolescents aged 5-19 years: more than 2 SD below the median of the WHO growth reference for children and adolescents (referred to as moderate and severe underweight hereafter), 2 SD to more than 1 SD below the median (mild underweight), 1 SD below the median to 1 SD above the median (healthy weight), more than 1 SD to 2 SD above the median (overweight but not obese), and more than 2 SD above the median (obesity). Findings Regional change in age-standardised mean BMI in girls from 1975 to 2016 ranged from virtually no change (-0.01 kg/m (2) per decade; 95% credible interval -0.42 to 0.39, posterior probability [PP] of the observed decrease being a true decrease= 0.5098) in eastern Europe to an increase of 1.00 kg/m(2) per decade (0.69-1.35, PP> 0.9999) in central Latin America and an increase of 0.95 kg/m (2) per decade (0.64-1.25, PP> 0.9999) in Polynesia and Micronesia. The range for boys was from a non-significant increase of 0.09 kg/m(2) per decade (-0.33 to 0.49, PP= 0.6926) in eastern Europe to an increase of 0.77 kg/m (2) per decade (0.50-1.06, PP> 0.9999) in Polynesia and Micronesia. Trends in mean BMI have recently flattened in northwestern Europe and the high-income English-speaking and Asia-Pacific regions for both sexes, southwestern Europe for boys, and central and Andean Latin America for girls. By contrast, the rise in BMI has accelerated in east and south Asia for both sexes, and southeast Asia for boys. Global age-standardised prevalence of obesity increased from 0.7% (0.4-1.2) in 1975 to 5.6% (4.8-6.5) in 2016 in girls, and from 0.9% (0.5-1.3) in 1975 to 7.8% (6.7-9.1) in 2016 in boys; the prevalence of moderate and severe underweight decreased from 9.2% (6.0-12.9) in 1975 to 8.4% (6.8-10.1) in 2016 in girls and from 14.8% (10.4-19.5) in 1975 to 12.4% (10.3-14.5) in 2016 in boys. Prevalence of moderate and severe underweight was highest in India, at 22.7% (16.7-29.6) among girls and 30.7% (23.5-38.0) among boys. Prevalence of obesity was more than 30% in girls in Nauru, the Cook Islands, and Palau; and boys in the Cook Islands, Nauru, Palau, Niue, and American Samoa in 2016. Prevalence of obesity was about 20% or more in several countries in Polynesia and Micronesia, the Middle East and north Africa, the Caribbean, and the USA. In 2016, 75 (44-117) million girls and 117 (70-178) million boys worldwide were moderately or severely underweight. In the same year, 50 (24-89) million girls and 74 (39-125) million boys worldwide were obese. Interpretation The rising trends in children's and adolescents' BMI have plateaued in many high-income countries, albeit at high levels, but have accelerated in parts of Asia, with trends no longer correlated with those of adults.
Existing scholarship on the rise of China and Chinese foreign policy has largely neglected to explain one puzzling phenomenon—although China’s network position in the global economic system has become more similar to that of developed countries, China continues to set its foreign policy from the perspective of a developing country. By analysing the relationship between the environmental possibilities and China’s intentional strategy, this article argues that the sharp contrast between China’s positions in the international political and economic systems reflects China’s ‘network strategy of embedded rise’. There are two mechanisms that go in opposite directions and jointly determine China’s foreign policy location in the international political spectrum. The first, called the ‘structural alienation effect’, is that wherein divergence in the centre-periphery positions in the global economic network increases the heterogeneity of two countries’ preferences, attitudes, and incentives, and in turn weakens alignment of their foreign policies. However, this structural effect is moderated by the second mechanism, namely, the ‘strategic affinity effect’. China’s strategy of assuming the role of a ‘broker’ to connect developing countries at the periphery of the international political and economic networks with developed countries at the centre achieves high ‘betweenness’ centrality, and so increases its social capital and influence in international politics. This article tests the proposed theory of China’s network strategy of embedded rise through hierarchical models that use global trade network centrality data and the United Nations General Assembly (UNGA) votes of 161 developing countries from 1994 to 2012. Our findings show that the globalized world both constrains and enables China’s great power status.
