A fully configurable virtual laboratory of classical mechanics

Dissertação de mestrado em Computer ScienceNowadays many mathematical applications allow the user to introduce its own equations in the system and also observe through different possibilities the desired results. Regarding physics, an extended range of virtual laboratories allow the user to accomplish virtual physics experiments. These virtual laboratories consist in predefined scenarios where the user can change the value of the physics variables and then visualise the changes accomplished. Other virtual laboratories uses a physics engine allowing the user to create its own scenarios. However, the physical behaviour of the objects is hardcoded since it results strictly on the physics equations used internally by the physics engine. This dissertation pretends to investigate how far and with what degree of scientific rigor it is possible to associate the idea of the user introducing its own equations with the idea of accomplishing virtual experiments of physics. As a proof of concept, this dissertation focus on a specific area of mechanics: the dynamic of rigid bodies. The result of this research is a virtual laboratory completely different relatively the others. Our system has no knowledge about physics. Even the most general laws of physics such as the Newton’s second law are not known by the system. To the system, any equation introduced is considered just as one more equation without any particular meaning associated to it. The same happens for any physics entity. For example, if the gravitational acceleration is introduced by the user, to the system it is just another attribute of the world. Taking into account the dynamics of rigid bodies, an object can be identified as being, at any time, in one of three different states. These are: when a object is not in contact with any other, when an object collides with another object and they immediately separate, and when two objects remain in contact over time. The user must specify all the equations that drive each of these three states. Using its geometrical knowledge, the engine determines at any time in which state an object is. Also, the system provides all the relevant geometrical information. For instance, in a collision between two objects, the point and the two normals vectors of the collision are provided. The graphical simulations reflects strictly on the equations introduced. Therefore, if the equations to solve a collision between two objects does not reflect the real underlying physics of the situation, it is possible that the objects simply ends-up penetrating each other. All the relevant numerical information about an experience can be processed through different forms. In fact, the user can request plots of variables, the graphical application of vectors on objects, and even the tracing of the variables at a specific event

Hyponatraemia and changes in natraemia during hospitalization for acute heart failure and associations with in-hospital and long-term outcomes - from the ESC HFA EORP Heart Failure Long-Term Registry

Aims: To comprehensively assess hyponatraemia in acute heart failure (AHF) regarding prevalence, associations, hospital course, and post-discharge outcomes. Methods and results: Of 8,298 patients in the ESC-HF Long-Term Registry hospitalized for AHF with any ejection fraction, 20% presented with hyponatraemia (serum sodium <135 mmol/L). Independent predictors included lower systolic blood pressure, estimated glomerular filtration rate (eGFR) and haemoglobin, along with diabetes, hepatic disease, use of thiazide diuretics, mineralocorticoid receptor antagonists, digoxin, higher doses of loop diuretics, and non-use of angiotensin-converting-enzyme inhibitors/angiotensin receptor blockers and beta-blockers. In-hospital death occurred in 3.3%. The prevalence of hyponatraemia and in-hospital mortality with different combinations were: 9% hyponatraemia both at admission and discharge (hyponatraemia Yes/Yes, in-hospital mortality 6.9%), 11% Yes/No (in-hospital mortality 4.9%), 8% No/Yes (in-hospital mortality 4.7%), and 72% No/No (in-hospital mortality 2.4%). Correction of hyponatraemia was associated with improvement in eGFR. In-hospital development of hyponatraemia was associated with greater diuretic use and worsening eGFR but also more effective decongestion. Among hospital survivors, 12-month mortality was 19% and adjusted hazard ratios were for hyponatraemia Yes/Yes 1.60 (1.35-1.89), Yes/No 1.35 (1.14-1.59), and No/Yes 1.18 (0.96-1.45). For death or HF hospitalization they were 1.38 (1.21-1.58), 1.17 (1.02-1.33), and 1.09 (0.93-1.27), respectively. Conclusion: Among patients with AHF, 20% had hyponatraemia at admission, which was associated with more advanced HF and normalized in half of patients during hospitalization. Admission hyponatraemia (possibly dilutional), especially if it did not resolve, was associated with worse in-hospital and post-discharge outcomes. Hyponatraemia developing during hospitalization (possibly depletional) was associated with lower risk. This article is protected by copyright. All rights reserved