Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC composites,ablation experiments under di...Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC composites,ablation experiments under different Laser Energy Density(LAED)and LAG experiments are conducted.Evolution rules and mechanism of physical phase,ablation morphology and crack characteristics caused by laser irradiation are investigated.The forces of LAG and Conventional Grinding(CG)are compared.The results show that ablation surface changes from slight oxidation to obvious material removal with LAED increasing,and ablation depth increases gradually.The ablation products change from submicron SiO_(2)particles to nanoscale particles and floccule.High LAED promotes SiC decomposition and sublimation,which leads to the increase of C element.The SiC phase forms corrugated shape in recast layer and columnar shape in Heat Affected Zone(HAZ)at 56 J/mm^(2).The cold and heat cycle leads to formation of fishbone crack.For ablation specimen under 30 J/mm^(2),the grinding force can be reduced by a maximum of 39%and brittle damage region is reduced.The material removal and microcrack generated will significantly reduce the hardness and improve machinability,which can promote grinding efficiency.展开更多
Background: COVID-19 had become much less virulent but still infectious, and China had loosened controls on its prevention after three years of zero-COVID policy. Nursing students were faced with infection. However, t...Background: COVID-19 had become much less virulent but still infectious, and China had loosened controls on its prevention after three years of zero-COVID policy. Nursing students were faced with infection. However, the symptoms of the vast majority of them were not serious. Objectives: To understand the feelings and thoughts of nursing undergraduates first infected with COVID-19 after implementing the policy of loosening controls on COVID-19 prevention in China. Methods: A semi-structured in-depth interview was adopted to collect data from 19 nursing undergraduates in a nursing school in China in January 2023, which were then analyzed using the Colaizzi analysis method. Results: Two main themes and seven sub-themes were induced: feelings after the diagnosis of being infected (feeling calm by professional confidence, feeling afraid of the consequences of being infected, feeling depressed, feeling relieved/lucky/happy), and thoughts brought by COVID-19 infection (becoming more active in learning, committed to a nursing career, and feeling shaken about becoming a nurse). Conclusions: Schools and hospitals should pay attention to infected nursing students’ mental reactions and changes in study motivation and professional intention. Targeted measures, such as education for epidemic prevention and education for cultivating the professional spirit, should be taken to promote their mental health and reserve their talents for nursing.展开更多
基金funded by the Fundamental Research Funds for the Central Universities,China(Nos.DUT21GF403,DUT22YG210,DUT22LAB117)the High Level Talents Innovation Plan of Dalian,China(No.2020RD02)financial support from the Shenzhen Science and Technology Innovation Commission Project,China(No.JSGG20210420091802007)。
文摘Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC composites,ablation experiments under different Laser Energy Density(LAED)and LAG experiments are conducted.Evolution rules and mechanism of physical phase,ablation morphology and crack characteristics caused by laser irradiation are investigated.The forces of LAG and Conventional Grinding(CG)are compared.The results show that ablation surface changes from slight oxidation to obvious material removal with LAED increasing,and ablation depth increases gradually.The ablation products change from submicron SiO_(2)particles to nanoscale particles and floccule.High LAED promotes SiC decomposition and sublimation,which leads to the increase of C element.The SiC phase forms corrugated shape in recast layer and columnar shape in Heat Affected Zone(HAZ)at 56 J/mm^(2).The cold and heat cycle leads to formation of fishbone crack.For ablation specimen under 30 J/mm^(2),the grinding force can be reduced by a maximum of 39%and brittle damage region is reduced.The material removal and microcrack generated will significantly reduce the hardness and improve machinability,which can promote grinding efficiency.
文摘Background: COVID-19 had become much less virulent but still infectious, and China had loosened controls on its prevention after three years of zero-COVID policy. Nursing students were faced with infection. However, the symptoms of the vast majority of them were not serious. Objectives: To understand the feelings and thoughts of nursing undergraduates first infected with COVID-19 after implementing the policy of loosening controls on COVID-19 prevention in China. Methods: A semi-structured in-depth interview was adopted to collect data from 19 nursing undergraduates in a nursing school in China in January 2023, which were then analyzed using the Colaizzi analysis method. Results: Two main themes and seven sub-themes were induced: feelings after the diagnosis of being infected (feeling calm by professional confidence, feeling afraid of the consequences of being infected, feeling depressed, feeling relieved/lucky/happy), and thoughts brought by COVID-19 infection (becoming more active in learning, committed to a nursing career, and feeling shaken about becoming a nurse). Conclusions: Schools and hospitals should pay attention to infected nursing students’ mental reactions and changes in study motivation and professional intention. Targeted measures, such as education for epidemic prevention and education for cultivating the professional spirit, should be taken to promote their mental health and reserve their talents for nursing.
