Concept of a system

Before diseussing the strueture of a eontrol system it is neeessary to define what is meant by a system. Systems mean different things to different people and ean inelude purely physieal systems sueh as the maehine table of a Computer Numerieally Controlled (CNC) maehine tool or alternatively the proeedures neeessary for the purehase of raw materials together with the eontrol of inventory in a Material Requirements Planning (MRP) system. 

However, all systems have eertain things in eommon. They all, for example, require inputs and outputs to be speeified. In the ease of the CNC maehine tool maehine table, the input might be the power to the drive motor, and the outputs might be the position, veloeity and aeeeleration of the table. For the MRP system inputs would inelude sales orders and sales foreeasts (ineorporated in a master 

In control engineering, the way in which the system outputs respond in changes to the system inputs (i.e. the system response) is very important. The control system design engineer will attempt to evaluate the system response by determining a mathematical model for the system. Knowledge of the system inputs, together with the mathematical model, will allow the system outputs to be calculated. 

It is conventional to refer to the system being controlled as the plant, and this, as with other elements, is represented by a block diagram. Some inputs, the engineer will have direct control over, and can be used to control the plant outputs. These are known as control inputs. There are other inputs over which the engineer has no control, and these will tend to deflect the plant outputs from their desired values. These are called disturbance inputs. 

Forward Velocity Heading Ship Motion (roll, pitch, heave) 

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In addition to the general concept of a system, we define different types of systems. An isolated system is one that is surrounded by an envelope of such nature that no interaction whatsoever can take place between the system and the surroundings. The system is completely isolated from the surroundings. A closed system is one in which no matter is allowed to transfer across the boundary that is, no matter can enter or leave the system. In contrast to a closed system we have an open system, in which matter can be transferred across the boundary, so that the mass of a system may be varied. (Flow systems are also open systems, but are excluded in this definition because only equilibrium systems are considered in this book.)... 

So what is the consensus According to the survey conducted by Genome Technology in May 2004, some 90% of respondents listed the following requirements as critical to realizing the practical concept of a systems biology ... 

The proportioning of premixed liquids leads to longer phases of output loss when the concentration is altered because the vaporizer must be emptied and reflUed each time. Therefore the volumes between the liquid tank and the pump need to be considered when estimating the response time of the system. This volume Hrst must be displaced before the new mixture can reach the vaporizer. The concept of a system in which all substances are emitted via one dosing track is suitable for experiments in which concentrations need not be changed in rapid succession. 

We must remember, however, that concepts of a system and of an object are relative. A wing of an airplane may be considered a subsystem when the entire plane is considered as a system, but it can also be seen as a supersystem for its subsystems. Also, each system is a part of a larger system. A house is a part of a subdivision, a subdivision is a part of a town, a town is a part of a metropolitan area, and so on. We must decide what part of our reality will be considered as a system and what in any given case will become a supersystem, a system, and subsystems. 

Kohn and Sham presented the concept of a system with non-interacting electrons, subject to some wonder external field VQ(r) (instead of that of the nuclei), such that the resulting density p remains identical to the exact ground-state density distribution pQ. This fictitious system of electrons plays a very important role in the DFT. 

The concept of a system approach to training of construction specialists in the field of engineering geology includes the following algorithm of learning process. 

The concept of a system, subsystem, and element is relative and depends on the degree of analysis for example, we can take the entire human body as a system, and the heart, the arms, the liver, and so forth as the elements. Alternatively, we can consider these elements as subsystems and analyze them with respect to smaller elements (or subsystems) and so on. 

The redox status of an aqueous system is described by the concentrations of the oxidized and reduced chemical species of all components in the chemical system (Scott Morgan 1990). Because of the slowness of oxidation-reduction reactions, natural rock-water systems are often not in redox equilibrium and thus the concept of a system Eh or pE becomes meaningless. Intensity factors such as Eh or pE are not very useful descriptors of the redox state of the system, but capacity factors which reflect the total concentration of redox-sensitive species may be better and more conservative measures of redox state. 

All of these definitions are proper and have their area of applicability, some wider, some more narrow their differences only point out that the concept of a system and its application to engineering is not entirely straight-forward. But while there is nothing wrong with any of these definitions, they are all completely utilitarian... 

In the two preceding sections we have seen that, whether we are considering the thought process or the formation of sentences, the entities we are using or processing refer either to a physical object or to an abstract concept. The question of whether these abstract entities have any real existence (e.g. as in Plato s ideas) or not has been and still is a central one in philosophy, and because we already suspect that the concept of a system will be an entity of the abstract kind, this question could be very relevant to our present quest to place the system concept within the framework of philosophy. However, we shall adopt a point of view put forward by Rudolf Carnap, which effectively allows us to sidestep the question for our purposes. 

In this chapter, we present elements of classical mechanics and quantum mechanics that will prove useful in connecting microscopic and macroscopic thermodynamics. We introduce the concept of a system s phase space as a crucial one in statistical thermodynamics. 

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