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## World Population

#### Description:

The number of people in the world is the balance between reproduction and mortality. Reproduction per person is affected by the product of economic assets per person and the number of people, where economic assets are evaluated in emergy units which includes environmental as well as urban assets. Mortality increases by deseases and decreases by economic assets used for health care. This model combines theses factors.

#### Variables:

R = renewable resources remaining unused
F = nonrenewable resource reserves
A = feedback inputs from economic assets
N = feedback inputs from population

#### Equations:

F = -k0*R*F*N*A
R = J/(1 + k1*F*N*A + k2*A)
A = k3*R*F*N*A + k4*R*A - k5*A - k6*A - L0*N^2(1 - k9*A) - L0*N(1 - k9*A)
N = L1(A/N)*N - k7*N(1 - k9*A) - k8*N^2(1 - k9*A)

#### Simulation:

The graph shows the changes of N(blue), F(green) and A(red) over a time period.
Source code: people.java

#### "What if" Experiments:

• What would you change to demonstrate the results of increased medical care? How does this change the long-range population?
• If an epidemic of a disease like AIDS gets worse, how would this change the population prediction? Then, to make things worse, also cut the medical care to zero.