Mechanical properties and microstructure evolution of solidified copper tailings with hydantoin epoxy resin

Based on the strength and microstructure tests,the effects of the hydantoin epoxy resin content and curing time on the mechanical properties and microstructure of copper tailings specimens were studied.The results showed that the strength of the solidified specimens was increased to 20.84 MPa with 30 wt.%addition of hydantoin epoxy resin.When the specimens with 10%hydantoin epoxy resin were cured for 7 and 14 d,the strengths were 6.33 and 6.67 MPa respectively,which met the requirements as foundation filler and building materials.The microscopic tests showed that the agglomeration was enhanced and the porosities of the solidified specimens were reduced with increase in the hydantoin epoxy resin content,which could greatly enhance the strength of solidified specimens.

Comparison of clinical characteristics in patients with coronavirus disease and influenza A in Guangzhou, China

BACKGROUND: This study aims to compare the epidemiological, clinical and laboratory characteristics between patients with coronavirus disease(COVID-19) and influenza A(H1N1), and to develop a differentiating model and a simple scoring system.METHODS: We retrospectively analyzed the data from patients with COVID-19 and H1N1. The logistic regression model based on clinical and laboratory characteristics was constructed to distinguish COVID-19 from H1N1. Scores were assigned to each of independent discrimination factors based on their odds ratios. The performance of the prediction model and scoring system was assessed. RESULTS: A total of 236 patients were recruited, including 20 COVID-19 patients and 216 H1N1 patients. Logistic regression revealed that age >34 years, temperature ≤37.5℃, no sputum or myalgia, lymphocyte ratio ≥20% and creatine kinase-myocardial band isoenzyme(CK-MB) >9.7 U/L were independent differentiating factors for COVID-19. The area under curves(AUCs) of the prediction model and scoring system in differentiating COVID-19 from H1N1 were 0.988 and 0.962, respectively. CONCLUSIONS: There are certain differences in clinical and laboratory features between patients with COVID-19 and H1N1. The simple scoring system may be a useful tool for the early identification of COVID-19 patients from H1N1 patients.

A new preparation technology of structural- gradient materials without a brittle transition zone in a Mn-Si-Cr-B bainitic cast steel

In the present work, a unique gradient cooling heat treatment process(GCHT) for a Mn-Si-Cr-B bainitic cast steel was developed, and microstructure and mechanical properties were examined by OM, SEM, EBSD and a uniaxial tensile test. The results showed that the structural-gradient-material(SGM) with a gradient microstructure from granular bainite to martensite was successfully produced, and it exhibited a good ductility(~13.8%) at one end and an excellent ultimate strength(~1,720 MPa) at the other end. In between the bainite and martensite, a transition region with a superior combination of tensile strength and ductility(1,700 MPa and 11.1%) was obtained, which is different from the normal knowledge of a brittle transition region. Moreover, through changing the gradient of cooling rate, the optimized SGM with a new gradient microstructure from pearlite to martensite showed a more stable structural gradient and an improved ductility(22.8%) at one end. The microstructure variation in the sample was mainly related to the carbon diffusion rate during heat treatment, and the diffusion rate could be controlled by regulating the cooling velocity. Therefore, the SGMs with different gradient microstructures could be designed to meet the needs of different properties. As a result, this work provides a new approach for preparation of the gradient structured steel, which has potential for practical application for dual-property automobile parts.