Notes on SYSTEMS AND MODELS

Outline the concepts and characteristics of systems

• Holistically – together or viewed as a whole
• A system consists of different parts and relationships which are interrelated through the transfer of energy and matter
• A holistic approach is to understand the way systems operate.
• Systems consist of:
  • Storage
  • Flows
  • Processes
  • Feedback mechanisms that maintain stability and equilibrium.
• System Diagrams consist of:
• Boxes that show storages
• Arrows that show flows

The systems concept on a range of scales

• An ecosystem is the biological community of organisms and environment they inhabit.
• Local scale is an ecosystems with inputs, outputs, and stores. (Ex: forest)
• Global Scale is the ecosystems in the the world that have similar climatic conditions called biomes. (Ex: tundra, desert, rain forest, etc.)
• Water, soil, rock, atmosphere, and the living component called the biosphere.

Open, closed, and isolated systems

• These 3 types of systems are depending on the flow of energy between the system and its surrounding.
  • Open Systems
  • Matter and energy are exchanging in the system.
  • Organic so it must interact with its surrounding to obtain food and to remove waste
  • Closed Systems
  • Only energy is exchanged
  • Isolated Systems
  • Neither energy not matter is exchanged

Laws of thermodynamics and environmental systems

• Heat can be converted to other forms when there is a temperature difference.
• Thermodynamics are the behavior of energy in systems.
  • First law or law of conservation of energy - Energy can neither created nor destroyed, but it can only changed its forms. Heat is released because of the inability to transfer the energy.
  • Second law states that the end of the process, the available energy is less usable than the available at the beginning of the process.
  • As there is less energy, there is higher entropy
  • Matter can be recycled within the system.

The nature of equilibria

• Open systems are in the state of equilibrium which means that if there is any
  changes in the system, there is no sudden changes.
  • A steady-state equilibrium – There is the stability in inputs and outputs in the system. If there is any change to a stable system results, it will return to the original equilibrium.
  • Static equilibrium – There is no inputs and outputs of energy or matter. So there's no changes in the system.
  • Stable and unstable equilibrium – It's stable if the system returns to the original state after the disturbance. On the other hand, it's unstable if the system doesn't return to its original equilibrium.

Positive and negative feedback

• Systems require feedback mechanisms to return to the original state.
  • Positive feedback (Instability) – An increase in size of the system's outputs can change the state of the system away from its original equilibrium.
  • Negative feedback (Stability) – Reduce the outputs and it maintains the steady-state equilibrium.

Transfers and transformation processes (Both types use energy)

• A transfer is when the movement doesn't involve a change of state/form. → Use less energy and more efficient.
• A transformation is when the movement does involve a change of state/form. → New end product.

Flows and storage

• Basically, flows are inputs and outputs in the forms of energy and matter. It sometimes stores in the form of stocks.

Models and flows of storage

• A model shows the structure of a system.
• Biomass is all the living things in the ecosystem.

Evaluation of models

• The models can be represented by computer models or diagrams or whatever that can represent the real system.
• For example, the complex computer simulations (examine about the climate).
  • The advantages of these models are:
    • Simplify the complex systems.
    • They can change the inputs and they don't need to wait to see the outcomes for real events.
    • They can share the results to public.
  • The disadvantages of those models are:
    • The result might not be accurate.
    • Different people have different interpretations.
    • They can use the same data in many different forms of models.
    • The results depend on the people who use them.
    • A good model can be looked from the data.