Classical Mechanics

This chapter applies our reasoning about structure in physics to two formulations of classical mechanics, Lagrangian and Newtonian mechanics, that are generally taken to be completely equivalent. It argues that these two formulations differ in both the type and amount of structure presupposed by their dynamical laws, as revealed by the invariances of the equations representing the laws as well as the theories’ statespace structures. This suggests that these are not fully equivalent theories: they differ in dynamical structure. There are also various metaphysical differences between them. The chapter goes on to argue that the minimize-structure rule tells us to choose one over the other. Along the way, the idea that preferred or natural coordinate systems indicate underlying structure is discussed.

PROBLEMS OF CONSTRUCTION OF ASYNCHRONOUS ELECTRIC DRIVES WITH STATE OBSERVERS

This paper considers the problems of constructing asynchronous electric drives with state observers and the latest advances in the field of sensorless alternating current drives. The main areas of application of asynchronous electric drives with state observers are determined. A vector sensorless control system using coordinate converters from a natural coordinate system to a stationary and rotating one and a state observer based on a mathematical model of a motor in a two-phase stationary coordinate system was used as a basic one when considering the structures of modern asynchronous electric drives. The main types of flow and speed observers of asynchronous electric drives are considered for the tasks of constructing a high-quality asynchronous electric drive with vector control without using sensors. The problem was formulated for further modernization of control systems based on an electric drive with a flow and speed observer.

A Measure of Whole-Brain White Matter Topography

The unprecedentedly high-quality large-scale brain imaging datasets, from such as the Human Connectome Project (HCP) and UK-Biobank, provide a unique opportunity for measuring the white matter topography of the human brain. By leveraging the multi-shell diffusion MRI data from the original young adult HCP, we systematically develop a reliable measure of the whole-brain white matter topography, and we coin it topographic vector. As the main result, we find that the three most dominant dimensions of the topographic vectors strongly and linearly correlate with the coordinates of the corresponding streamlines of the whole-brain tractograms. Our results support the earlier prescient hypothesis that brain development follows a “base-plan” established by three (main) chemotactic gradients of early embryogenesis, and they implicate that the whole brain white matter tracts can be represented by vectors of a natural coordinate system.

Multi-body coupling dynamic research of carrier-based aircraft catapult launch based on natural coordinate method

There is an increasing demand for predicting the dynamic behaviours of carrier-based aircrafts(CBAs) during catapult launch. This paper presents a maximal parameterised dynamic model of the launch process from a new perspective, and conducts a detailed study of its mechanical behaviours. Based on the topological analysis of the multi-body catapult launch system, the natural coordinate method is adopted to establish a comprehensive model including steam catapult, landing gears, ship motion, aerodynamic and multi-body modules. The predictive capability of the model is demonstrated by presenting the CBA launch dynamic properties under different conditions. First, effects of steam flow area rate and the coupling carrier movement in different directions on catapult performance are discussed. Second, the take-off characteristics as well as the initial catapult attitude are analysed. Then, by investigating Lagrange multipliers, the loads of torque arms, holdback bar and launch bar are compared. Finally, the loads of buffer struts and tyres during launch are also discussed. The results show that it is reasonable to keep the steam flow area increasing in a linear way, but the opening velocity needs to be strictly controlled. When the CBA departs from the deck, the possible sink of the bow is the major threat to the take-off safety, the larger the sink is, the more dangerous the flight becomes. The upwash at the bow may be the primary reason of stall and cannot be ignored. The model established is reliable with capacities of capturing the coupled behaviours between different sub-modules as well as the load change of each component in detail. The natural coordinate method proves to be efficient and accurate, which should be given more attention.