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This study determined the rate of secondary infection among contacts of individuals with confirmed coronavirus disease 2019 (COVID-19) in Hangzhou according to the type of contacts, the intensity of contacts, and their relationship with the index patient. This is a retrospective cohort study. The analysis used the data of 2994 contacts of 144 individuals with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The contacts were categorized according to the information source, type of contact, location, intensity of contact, and relationship with the index patient. The incidence of infection differed significantly according to contact type. Of the contacts, 186 (6.2%) developed symptoms, and 71 (2.4%) had confirmed SARS-CoV-2 infection. The main symptoms were cough and fever. Compared with those who had brief contact with the index case, those who had dined with the index case had 2.6 times higher risk of acquiring infection; those who had shared transport with, had visited, or had contact with the index case in a medical institution had 3.6 times higher risk of acquiring infection; and household contacts had 41.7 times higher risk of acquiring infection. Family members had 31.6 times higher risk of acquiring infection than healthcare providers or other patients exposed to an index case. The form and frequency of contact are the main factors affecting the risk of infection among contacts of individuals with COVID-19. Centralized isolation and observation of close contacts of individuals with confirmed SARS-CoV-2 infection, in addition to population-based control measures, can reduce the risk of secondary infections and curb the spread of the infection. • The incidence of infection differed significantly according to contact type. • Contact form and frequency are important to the risk of COVID-19. • Centralized isolation and observation of contacts curbed the spread of the infection. [ABSTRACT FROM AUTHOR]

Abstract: Large carbon isotope fluctuations have been systematically reported for Ediacaran carbonate rocks, the meaning of which remains controversial. In order to better understand the mechanisms behind such variations, we present new paired δ 13C data on carbonates (δ 13Ccarb) and their associated organic matter (δ 13Corg) from a shelf-margin section (Yangjiaping) of the Doushantuo Formation. In this section, the Doushantuo Formation starts with cap dolostones presenting δ 13Ccarb values around −5‰ and δ 13Corg values between −30.3 and −27.6‰. Up-section, phased variations in δ 13Ccarb and δ 13Corg describe positive and negative excursions, while their difference (Δ13Cdol–org = δ 13Ccarb − δ 13Corg) remains around +29.2‰. These new data allow the first reconstruction of lateral variations of δ 13Ccarb, δ 13Corg and Δ13Ccarb–org for a shelf-to-basin cross-section of the Yangtze platform (South China) after integration with results reported previously for two other sections. Across the Yangtze platform, the isotope signals reveal strong lateral heterogeneities, with complex variations of δ 13Ccarb and Δ13Cdol–org in the inner-shelf section, phased variations in the shelf-margin section with positive δ 13Ccarb and Δ13Cdol–org close to 29‰, and dominantly negative δ 13Ccarb with δ 13Corg as low as −35‰ in the basin. These variations are incompatible with the idea that the δ 13Ccarb can systematically be used as a proxy of ocean surface waters. Assuming that δ 13Ccarb are acquired in bottom waters and/or upper sediments, we show that the heterogeneous δ 13Ccarb and Δ13Cdol–org are compatible with a stratified water column composed of up to three layers: (i) an oxic surface layer, where dissolved inorganic carbon (DIC) is probably in isotope equilibrium with the atmosphere; (ii) an intermediate euxinic layer with a lower δ 13CDIC due to organic matter oxidation by ongoing sulphate reduction; (iii) a bottom euxinic layer that seems to be restricted to the inner-shelf lagoonal facies, lacking sulphate, containing methane and with a higher δ 13CDIC due to DIC production by methanogenesis. If our model holds true, it suggests that not only negative but also positive Ediacaran carbon isotope excursions may reflect ocean stratification, the positive excursion possibly recording a sulphate-free methanogenic layer at the bottom of restricted basins. [Copyright &y& Elsevier]

Based on wave measurements lasting four and a half years, wave characteristics in a lagoon of the South China Sea are discussed in this paper. The significant wave height (H s), mean periods (T z) and wind speed (W s) are mostly smaller than 1 m, 6 s and 15 m/s, respectively. Based on the monthly average H s , there exists a transition season between winter and summer in the first half of the year. Waves of the transition season are very small, which is helpful for fishing and tourism. To characterize the seasonal cycle of wind and waves, a monsoon index based on the H s and the wind direction (W d) is proposed. It is verified by the monthly average air temperature. Finally, waves of winter (monsoon indexes < -0.25) are studied in detail. It shows that most of these waves come from the north, and are driven by the northeast monsoon and the cold-air from the mainland of China. Besides, locally generated fetch waves are common in winter. These waves can be identified by the Gaussian kernel clustering method. The relationship between peak energy density S (f p) and g −1/2 H s 5/2 is also verified for these waves. • A transition season between winter and summer in the first half of the year has been found. • A monsoon index based on the Hs and the wind direction is proposed to characterize the seasonal cycle of wind and waves. • It is found that waves of winter are mostly locally generated fetch waves. [ABSTRACT FROM AUTHOR]