Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel.

This study aims to investigate in situ the three-dimensional (3D) morphology and distribution of primary carbides (PCs) in electro-slag remelting (ESR) forged 30Cr3Ni3Mo2V steel. A facile non-aqueous electrolytic etching method was applied to prepare 3D PCs on the matrix. The morphology, composition, and element concentrations of PCs were characterized using a combination of optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and electron back-scattered diffusion (EBSD). The precipitation, type, and composition of PCs in the same steel were also simulated using Thermo-Calc software Version 2015a. The results indicate that PC is rich in Nb, which is a potential heterogeneous nucleating agent. Both the size and number of PCs increase from the edge to the center of the ingot. The large-sized PCs present three dominant types of morphology, which vary in different regions, i.e., a bulky type dominates in the edge region, a lamellar type dominates in the middle region, and a stripy type dominates in the core region. The results of EBSD analysis show that the orientation of PCs with different morphologies is different and that more nanosized V-rich type carbides are precipitated on the matrix. The thermodynamic calculations show that MC precipitates from the liquid phase when the solid phase fraction is greater than 0.985 and that the MC-type carbides are rich in Nb, which agrees well with the experimental results.

[Water intake of primary and middle school students in four cities of China].

OBJECTIVE: To investigate total intake of drinking water of primary and middle school students in four cities of China, and to provide scientific evidence for developing standard of intake of drinking water for primary and middle school students in China. METHODS: A total of 5914 primary and middle school students were selected from Beijing, Shanghai, Chengdu and Guangzhou using multi-stage random sampling method and 5868 subjects completed the survey. The information on the amounts of daily drinking water was recorded for seven consecutive days using a 24 hour measurement. The amounts of daily drinking water among different cities and ages and between boys and girls or urban and rural were analyzed. RESULTS: The average daily total drinking water of subjects was (1089 ± 540) ml, with significant differences among the four cities ((1165 ± 549), (1126 ± 544), (866 ± 421), (1185 ± 568) ml in Beijing, Shanghai, Chengdu and Guangzhou, respectively; F = 114.28, P < 0.05). The average daily drinking water was significantly higher in boys (1157 ± 575) ml than in girls (1026 ± 498) ml (Z = 8.88, P < 0.05), and in urban (1185 ± 578) ml than in rural (991 ± 480) ml (Z = 13.94, P < 0.05). The difference among different ages was statistically significant (F = 91.53, P < 0.05) with ascending order in 7 - 10, 11 - 13 and 14 - 17 years old ((953 ± 483), (1134 ± 551) and (1170 ± 557) ml respectively). CONCLUSION: The daily consumption of total drinking water is different in primary and middle school students among different cities, regions, genders and ages.

[Study on human case of avian influenza in Guangzhou 2006 without causing human-to-human transmission among close contacts].

UNLABELLED: Study on human case of avian influenza in Guangzhou 2006 without causing human-to-human transmission OBJECTIVE: To explore the possibility of transmission from a human case of avian influenza to his close contacts. METHODS: Close contacts of the human case of avian influenza in Guangzhou 2006 were found out according to the definition and methods publicized by the Ministry of Health, People's Republic of China. Epidemiological investigation and medical observation were carried out. Serum antibodies were tested in some of the close contacts. RESULTS: The avian influenza patient had never left Guangzhou in the month prior to disease onset. No contact history with dead or diseased poultry was found. A total of 56 close contacts, including his girl friend, relatives, friends and medical staff who had taken care of him, were brought under medical observation for 7 days but none of them showed signs of infection. CONCLUSION: Unlike SARS, direct contact with patient contracted with avian influenza at the end of incubation period and in the stage of illness through flying droplets, saliva, mucous membrane and skin injuries will not lead to human-to-human transmission, indicating the virus' ability to pass from human to human is limited.