Improved engineering solutions for thermal design of artificial ground freezing

La congelación artificial del terreno es un método utilizado en ingeniería civil y minera. Al congelar el terreno, su resistencia aumenta y se impermeabiliza. Cálculos térmicos con cambio de fase son necesarios para diseñar estos trabajos. Estos cálculos se pueden realizar con modelos numéricos o soluciones analíticas. En esta tesis se han investigado los parámetros que influyen en la precisión de los métodos numéricos mediante un análisis de sensibilidad y se han condensado los resultados en un código de buenas prácticas. Además, se ha utilizado un modelo numérico verificado para investigar la precisión de las soluciones analíticas. Se ha concluido que la solución más precisa para el problema de una tubería de congelación es la de Ständer. También se ha ajustado la solución analítica de Sanger & Sayles para una tubería de congelación, que presenta una mejora de precisión significativa. Finalmente, se han utilizado datos experimentales para confirmar las conclusiones.Artificial ground freezing is a method used in civil and mining engineering for ground stabilisation and groundwater cut-off. In order to design these works, thermal calculations with phase change are required, which can be performed by numerical models or analytical solutions. In this thesis, the parameters which influence the accuracy of numerical methods were investigated by means of a sensitivity analysis and the results were condensed in a code of good practice. A verified numerical model was used to investigate the accuracy of analytical solutions. It was concluded that the most accurate solution for the single freeze pipe problem is Ständer’s. Additionally, Sanger & Sayles’ solution for the single freeze pipe has been adjusted, obtaining a significant accuracy improvement. Finally, experimental data were used to confirm the conclusions

An adjusted analytical solution for thermal design in artificial ground freezing

Artificial ground freezing is a widely used, reliable method for excavation in water-bearing ground. The questions posed in the thermal design of ground freezing projects require solving moving boundary (Stefan) problems. Approximate analytical solutions, such as the ones by St¨ ander1 and Sanger and Sayles,2 have been developed for thermal engineering design and are used by practitioners across the industry. For instance, Sanger & Sayles’ solution is widely used for the single-freeze-pipe problem, but it has proven to be of limited accuracy.3 In the present paper, an adjustment to this formula is proposed based on the re-evaluation of their empirical assumption that the ratio between the temperature penetration depth and the phase-change radius equals a constant value of 3 regardless the conditions. A sensitivity study is performed using a verified numerical model as a benchmark to study several problems with different initial and boundary conditions (initial, phase change and freeze pipe temperatures) and thermal properties of the ground (water content, thermal conductivity and heat capacity). This is done for the freezing times of 10 and 365 days, in order to consider the potential change of the ratio with the freezing time. In this way, a calibrated formula is proposed to find appropriate values of this ratio and a suitable adjustment to Sanger & Sayles’ solution is determined. Adjusting Sanger & Sayles’ solution in this manner, a significantly higher and more consistent accuracy is achieved for different boundary and initial conditions. This accuracy improvement was checked for real conditions from an engineering project, which shows that the adjustment can be useful for thermal problems in engineering design of ground freezing

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Selection of contract type in construction contracts: Lump-Sum, Target-cost and Cost-plus contracts

The construction contract is a document which governs the business relationship of Contractor and Employer for the duration of a construction project. However, the selection of the contract type for the project tends to be performed too shallowly. The present thesis aims to analyse how the contract type is chosen among the three paradigmatic contracts considered here: lump-sum contracts, target-cost contracts and cost-plus contracts. The basis of the study is a case study performed on Project X, a large mine construction project in Western Europe. The relevant literature to the subject was reviewed, mainly the principal-agent theory, literature on risk allocation and on contract selection. After identifying several factors which may influence the contract selection in the literature and in a preliminary interview, a survey was conducted to assess their relative influence in general and in particular for the Project X. The survey was responded by a small sample of highly qualified and experienced managers. and was complemented with in-depth interviews with the majority of them. Some research on the project and on contract documents of the NEC standard contract was also performed in order to provide a context of the characteristics of Project X. The findings of the three sources made it possible to confirm the influence on the selection of the contract type of many of the factors proposed. It was possible to shortlist a small number of factors which influenced the most the selection of the contract type for Project X. These were the preferred risk allocation by the parties, the ability to adapt the contract to scope changes, the knowledge of each contract type by the contracting parties, the improvement of the project delivery by the contract type and the aim to enhance cooperation between the parties. Factors not present in previous research were also discovered, such as the different financial costs of the contract types and the requirement of financial information by the funders of the parties. The very different opinions of the respondents to the survey and interviews regarding the selection of the contract type confirm that the parties should consider in more detail that complex process, because by now the parties are not really sure why they are choosing a certain contract type. Further research should be performed in the future to analyse the factors which influenced the contract type selection in other projects. The projects could also be analysed during their whole duration. Other contract types or variants of the three contract types studied in this thesis could also be added to the analysis

Aplicación de las TIC a la enseñanza mediante la Pizarra Digital y los Tablet PC

Se realiza un proyecto de innovación educativa que pretende avanzar hacia la utilización de nuevos recursos tecnológicos en la práctica diaria del proceso de enseñanza-aprendizaje con el fin de renovar las metodologías interactivas en el aula. Desde el C.R.A. 'Manuel Moreno Blanco' de Vitigudino, Salamanca, se realiza un proyecto de innovación para el quinto curso de Educación Primara que se desarrolla en tres fases. La primera fase se centra en el conocimiento y formación en torno a las Pizarras Digitales, de los diferentes modelos existentes y de las posibilidades que ofrece en el aula su manejo. En la segunda fase se conoce y maneja el Software del Modelo Pizarra Digital elegido para el centro escolar. Finalmente en la tercera fase se elabora el CD en el que incluye el material elaborado para cada una de las diferentes áreas del currículo. La utilización de la Pizarra Digital en el proceso de enseñanza-aprendizaje tiene consecuencias positivas para el alumnado: gran motivación e interés, mejor interactividad, rápido y fácil acceso a múltiples recursos, y renovación y actualización pedagógica que implica a todo el centro.Castilla y LeónConsejería de Educación. Dirección General de Universidades e Investigación; Monasterio de Nuestra Señora de Prado, Autovía Puente Colgante s. n.; 47071 Valladolid; +34983411881; +34983411939ES

Effects of pre-operative isolation on postoperative pulmonary complications after elective surgery: an international prospective cohort study an international prospective cohort study

We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care. We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care