Objective To evaluate viral loads at different stages of disease progression in patients infected with the 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the first four months of the epidemic in Zhejiang province, China. Design Retrospective cohort study. setting A designated hospital for patients with covid-19 in Zhejiang province, China. ParticiPants 96 consecutively admitted patients with laboratory confirmed SARS-CoV-2 infection: 22 with mild disease and 74 with severe disease. Data were collected from 19

This paper reaches a detection system which use for detecting the three-axis consistency of optical collimator basing on equivalent method. Describing the detect principle and calculating the offset of the image of optical path caused by spectroscope via anglicizing of optical system. Meanwhile, it uses zemax to simulate the offset of optical path. After adjusting the structure of the system, the detection system is calibrated by theodolite whose accuracy is 0.5″. The experiment result shows that the measurement error of the optical axis consistency <0.05mrad.

Welding is a main joint way of the alloy constructional steel. However, the welding HAZ is very sensitive to corrosion. In order to increase the corrosion resistance of the welding HAZ without reducing mechanical property of the parts simultaneously, the laser surface remelting was used to treat the welding HAZ in this study. According to the results of the orthogonal test, the optimized processing parameters were obtained. Based on the electrochemical analysis, the corrosion current of 30CrMnSi welding HAZ can be decreased by laser remelting technology. The corrosion resistance of the HAZ can be improved effectively. At the same time, the mechanical property of the treated welding HAZ was better compared with the untreated.

Superalloys have a high tensile strength at elevated temperature, a good stability and reliability in a large range of temperatures. Among these superalloys, GH4169 is widely used as thermal components in the turbojet engine. Traditional welding methods are difficult to adapt to the development of high-tech manufacturing. Laser welding plays an important role in superalloys welding field increasingly for its advantages. In this investigation, superalloy GH4169 plate with a thickness of 1mm was welded utilizing the pulsed laser welding and the mechanical properties of the laser welded joints are analyzed. The maximum tensile strength is 928 Mpa, which is close to the base material tensile strength. The welded joint can meet the requirements of users.

Free damping treatment for a marine life hoist of the helicopter is analyzed in this paper. Based on the pipe structure used in actual life hoist bracket, the complex rigidity method is used to analyze the damping loss factor of the pipe structure. When the temperature is 30°C and the thickness of the damping material is 2.5mm, the damping loss factor of the structure increases by 9.83 times. The damping ratio of the first mode reaches 11.61%. The results indicate that the free damping treatment can obviously increase the damping loss factor and the modal damping ratio of the structure, which can mitigate structural vibration and reduce noise induced by the vibration.