RESUMEN
Immobile water is defined as a firmly bound thin film of water surrounding clay particles that somehow resembles solid features. The characteristics and amount of immobile water depend on pore water chemistry, the type of clay, and the contact area of water with particles. Seepage can occur only when the hydraulic gradient increases sufficiently. To date, no accurate method is available to determine the immobile water content. Therefore, an approach is proposed for direct measurement of the immobile water content, which applies vegetable oil to displace water in saturated compacted clay-rich materials. Under a high hydraulic gradient, the vegetable oil completely displaces the free porewater in the clay-rich materials, and the remaining residual water is assumed to be immobile water. By using carbon tetrachloride (CCl4) as an extracting agent, the oil in the permeated sample was subjected to extraction and distillation, and the total liquid content was determined by the oven-drying method. As a final step, the immobile water content in the sample was calculated. A high-speed centrifugation method was used to determine the immobile water content from the corresponding soil water potential, which accounted for approximately 634.3 kPa. It was found that the immobile water of the clay-rich materials was essentially equal to the bound water. The effective porosity of clay was obtained based on the immobile water content. By comparing the relationship between porosity, effective porosity and hydraulic conductivity, the effective porosity revealed an improved linear relationship with log (k). The test results show the oil seepage method to be useful and reliable for the quantification of the immobile water content of saturated compacted clay-rich materials.
Asunto(s)
Suelo , Agua , Arcilla , Conductividad Eléctrica , Porosidad , Suelo/química , Agua/análisisRESUMEN
At present, plastic concrete is widely used in anti-seepage engineering, and its strength and hydraulic conductivity are important indexes of plastic concrete cutoff walls. The pondus hydrogenii (pH) and electrical conductivity (EC) have an important effect on the strength and hydraulic conductivity of plastic concrete cutoff walls. However, it is not clear why the pH and EC are related to the strength and permeability of these walls. For this reason, plastic concrete composed of sand, cement, water, and bentonite was taken as the research object to study the influence of different mix ratios and curing ages on the unconfined compressive strength and permeability of plastic concrete. The pH and EC of the corresponding mix ratio and curing age were measured. The effects of the pH and EC on the strength and permeability of plastic concrete were studied, and the internal reason was explored from the product type and hydration reaction degree of plastic concrete. Furthermore, the quantitative relationship between pH and EC and the strength and hydraulic conductivity of plastic concrete was established. With increasing cement content, the strength, pH, and EC of plastic concrete increase continuously, while the hydraulic conductivity decreases. With increasing curing age, the strength increases, the hydraulic conductivity decreases, and both the pH and EC show a trend of first increasing and then decreasing. The pH value and electrical conductivity can reflect the product type and hydration reaction degree of plastic concrete, further affecting its strength and hydraulic conductivity. Under different dosage and curing age conditions, the pH showed three stages, namely, 11.7-12.27, 12.27-2.5, and 12.5-12.75, and there is a good power functional relationship among the EC and strength and hydraulic conductivity at each stage.
Asunto(s)
Materiales de Construcción , Plásticos , Fuerza Compresiva , Conductividad Eléctrica , PermeabilidadRESUMEN
OBJECTIVES: To understand medical students' mental health, professional pride, and intention to work in the front-line during coronavirus disease 2019 (COVID-19) pandemic, and provide a reference for psychological intervention. METHODS: We used the depression-anxiety-stress scale and self-designed questionnaire on professional pride, intention to work in the front-line and the extent of family support. Medical students from 4 medical schools in Fujian and Hunan were investigated. Their mental health status, professional pride and first-line work willingness with different characteristics were compared, and the influential factors for professional pride and first-line work willingness were analyzed. RESULTS: A total of 266 valid questionnaires were collected. During the pandemic, there were significant differences in the proportion of depressed students among different college and universities, majors and stages (P<0.05), and the professional pride was significantly different (P<0.001). Medical students with different mental health status showed significant differences in professional pride (P<0.01). Marriage, pressure and extent of family support were the influential factors for their professional pride (P<0.05). The latter two were also influential factors for their intention to work in the front-line (P<0.05). CONCLUSIONS: During the pandemic, students from college and nursing have relatively better mental health and higher professional pride. The professional pride is low in medical students who married, with abnormal stress or low family support. The intention to work in front-line is decreased in students with abnormal stress or low family support.
Asunto(s)
Infecciones por Coronavirus/psicología , Salud Mental , Neumonía Viral/psicología , Estudiantes de Medicina/psicología , Betacoronavirus , COVID-19 , China , Familia , Humanos , Intención , Pandemias , Profesionalismo , SARS-CoV-2 , Apoyo Social , Estrés Psicológico , Encuestas y CuestionariosRESUMEN
OBJECTIVE: To study the changes in serum cortisol levels in adolescents with type 1 diabetes (T1DM) and elevated depressive symptoms. METHODS: Twenty-eight adolescents with T1DM and 31 healthy peers were assessed for depressive symptoms using a depression self-rating scale developed by the Epidemiological Survey Center. Selected subjects were classified into four groups: T1DM with elevated depressive symptoms group (n=15), T1DM without elevated depressive symptoms group (n=13), elevated depressive symptoms without T1DM group (n=15), and normal control group (n=16). Fasting blood samples were collected in the morning, and the levels of serum cortisol were compared among the four groups. The correlations of serum levels of cortisol and glycosylated hemoglobin A1c (HbA1c) with the score of depression self-rating scale were evaluated by Pearson correlation analysis. RESULTS: The fasting serum cortisol levels in the 28 T1DM patients were significantly higher than in the 31 healthy peers (P<0.01). The fasting cortisol levels in the T1DM with elevated depressive symptoms group were significantly higher compared with those in the elevated depressive symptoms without T1DM group and normal control group (P<0.01). In adolescents with T1DM, serum HbA1c level was positively correlated with the score of depression self-rating scale (r=0.481, P=0.010). CONCLUSIONS: The fasting serum cortisol levels in adolescents with T1DM and elevated depressive symptoms are significantly increased, suggesting that the patients with comorbidity of T1DM and depression develop dysfunction of the corticotropin-releasing hormone-adrenocorticotropic hormone-cortisol axis. The elevated depressive symptoms may be associated with a poor control of glucose metabolism.