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# Systems - What is a system SYSTEMS& SYSTEM MODELING A...

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Unformatted text preview: What is a system? SYSTEMS & SYSTEM MODELING A system is a set of objects (elements) together with the elements) relationships between the objects and between their attributes. (Hall and Fagen, Fagen, 1956) What is a system? Definitions Objects Set Attributes (characteristics) Relationship Boundary? What is a model? A Model is widely defined as any simplification of reality Why do we use models? Do models need to be capable of generating a prediction? Models e.g., hardware (physical), conceptual, theoretical, mathematical, numerical etc. System & Model Categories Systems may be categorized in several different ways: Functional categories Structural categories Functional Categories Some functional categories are: Isolated System Closed System Open System 1 Functional Categories An Isolated System: Boundaries are not crossed by energy or matter Examples? A Closed System: Boundaries may be crossed by energy, but NOT by matter. energy, matter. Examples? Functional Categories An Open system: Boundaries may be crossed by both energy and matter. matter. Examples? System Feedback Information Feedback Pathways: Feedback loops Feedback information is the control or the guide for further system operations in an open system. system. System Feedback Negative Feedback Self regulation A tendency to absorb/dampen out impacts Example? (The saucer example) Positive Feedback Instability A tendency to continue/magnify impacts Example? (The inverted saucer example) Structural Categories Some structural categories are: Morphological System Cascading System Process-response or ProcessProcessProcessform System (reflecting increasing degrees of complexity) Structural Categories Morphological System Identified in terms of its internal geometry. A simple earth science example: Cliff, free face, or scarp, plus a talus 2 Structural Categories Cascading System A set of subsystems, linked by a cascade (flow) (flow) of energy and/or matter with inputs and outputs. Structural Categories Process-Response ProcessSystem: System: Focus on axis! (+) (-) (-) (+) Process - Response Models We will spend most of our time looking at process-response models, i.e., processsimplified ideas about how the surface of the earth changes in response to the processes acting upon it. Plus a similar perspective on human populations, as well as how people and the Earth's surface Earth' interact. The latter two are always more complicated than the first alone. Equilibrium Concept Input & Output Input = Output? Input Output? Input > Output Input < Output How does a system respond? Simple Equilibrium Concepts Equilibrium is not a single concept and many disciplines have their own concept, and especially their own metric, e.g., economists use money flows while earth scientists are likely to be interested in energy or mass flows. Various Kinds of Equilibrium Static: A truly static situation Example? 3 Various Kinds of Equilibrium Stable: Self regulation (Negative Feedback) Various Kinds of Equilibrium Unstable: Positive Feedback Equilibrium 2 Equilibrium 1 Various Kinds of Equilibrium Metastable: Threshold concept Metastable: Various Kinds of Equilibrium Steady-state: Oscillations & fluctuations, Steadybut no trend. Equilibrium 2 Equilibrium 1 Various Kinds of Equilibrium Dynamic Metastable: Dynamic + metastable Metastable: 4 ...
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