Ricardo Lopes Coelho

On the Concept of Energy: How Understanding its History can Improve Physics Teaching

Some physicists have pointed out that we do not know what energy is. Many studies have shown that the concept of energy is a problem for teaching. A study of the history of the concept shows that the discoverers of energy did not find anything which is indestructible and transformable but rather that the concept of energy underwent a change of meaning and energy was considered a substance towards the end of the nineteenth century. In distinguishing between the treatment of phenomena and the theories carried out by Mayer and Joule, it can be concluded that they established equivalences between different domains, such as motion and heat, motion and electricity or position and motion. This complies with the interpretation presented in textbooks published about a century ago and enables us to overcome some difficulties with the concept of energy.

On the Definition of Mass in Mechanics: Why Is It So Difficult?

In spite of the concerted efforts of physicists, philosophers, mathematicians, and logicians, no final clarification of the concept of mass has been reached. So concludes Jammer in his book on the history of the concept.1 The Nobel laureate Wilczek called our attention to the problem in his papers on the concepts of the fundamental equation of dynamics.2 In 2005, Roche wrote a paper whose title asks the question “What is mass?”3 Hecht sums up the situation in textbooks in the title of his article “There Is No Really Good Definition of Mass.”4 Where the difficulty in defining mass in classical mechanics lies is the question addressed in the present paper. Before dealing with this topic, it is important to make explicit what the problem consists of, since sometimes people think that there is no problem with mass at all.

Prediction of severe exacerbations and mortality in COPD: the role of exacerbation history and inspiratory capacity/total lung capacity ratio

Background Severe exacerbations and mortality are major outcomes in COPD, and risk factors for these events are actively searched for. Several predictors of mortality have been identified in COPD. The inspiratory capacity/total lung capacity (IC/TLC) ratio has been shown to be a strong predictor of all cause and respiratory mortality in patients with COPD. The major objectives of this study were to analyze which clinical parameters, including lung volumes, were the best predictors of the 5-year cumulative risk of hospital admissions or death and the 5-year risk of exacerbations, in stable COPD patients. Methods This study retrospectively reviewed data from 98 stable COPD patients, consecutively recruited in 2012. Forced expiratory volume in 1 s (FEV1), modified Medical Research Council dyspnea scale, exacerbation history (ExH), Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2011 groups, and lung volumes were reviewed. Five years later, this population was evaluated for cumulative exacerbations, hospital admissions, and mortality. All the population, and GOLD group D separately, were analyzed. Results The cumulative 5-year combined risk of hospital admission or death was significantly predicted by the ExH and the IC/TLC ratio. Analyzing separately group D, FEV1 was the only predictor of this outcome. The frequency of exacerbations in the previous year was the best predictor of future cumulative 5-year risk of subsequent exacerbations, both for the total population and the GOLD D group. Conclusion ExH and IC/TLC ratio were the best predictors of the most severe outcomes in COPD (admissions or mortality), independently of COPD severity. FEV1 was the only predictor of the cumulative 5-year combined risk of hospital admission or death in the GOLD D group. ExH was the best predictor of 5-year cumulative future risk of exacerbations. Besides FEV1 and ExH, the IC/TLC ratio can be a useful predictor of severe outcomes in COPD.

Evaluation of anastomotic diameter in lung transplant: Comparing bronchofibroscopy with multiplanar reconstructed thoracic computed tomography

Introduction: Lung transplant (LT) is therapeutic option for patients (pts) with end-stage lung disease. However it is still associated with many complications, namely airway complications (AC). Recently, a grading system for central AC after lung transplantation was published, known as the MDS classification – corresponding to macroscopic aspect (M), diameter (D) and appearance of the sutures (S) of the anastomosis. Objectives: Compare the anastomosis diameter according to MDS classification assessed with bronchofibroscopy (BF) and multiplanar reconstructed thoracic computed tomography (CT) in a series of pts submitted to LT in our center between Jan/2012 and Dec/2014. Methods: Retrospective analysis of BF reports and correspondent CT images (max 30 days difference). The anastomosis diameter was classified according to MDS classification as D0: normal to fixed reduction up to 33%; D1: malacia greater than 50%; D2: stenosis from 33% to 66% and D3: stenosis greater than 66%. Results: One hundred and thirty exams (performed 15 days to 34 months after LT) were analyzed and the results were as in table 1. No significant correlation between BF and CT results was found. Moreover, when compared to BF (gold standard), the CT sensitivity in the assessment of significant stenosis (D1 – D3) was 17% and specificity 86%. Conclusions: BF remains an indispensable technique in the evaluation of airway complications in LT. However, due to his high specificity, CT can be useful in diagnosing significant stenosis.

On the Concept of Energy

These instructions are intended to provide guidance to authors “It is important to realize that in physics today we have no knowledge of what energy is”, said the Nobel Laureate Richard Feynman in his Lectures. “Nobody knows what energy really is”, one reads in Bergmann and Schaefer’s Experimental Physics (1998). We cannot answer the question of what energy really is, explain Dransfeld et al. (2001). Although everybody has a feeling of what energy is, wrote Cengel and Boles (2002), it is difficult to give a precise definition for it. According to Halliday et al. (2003), it is very difficult to give a simple definition of energy. If we cannot explain in a clear way what energy is, the concept of energy must be a problem in science teaching.