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anonymous

  • one year ago

Carbon dioxide at high enough concentrations is lethal. According to the EPA ( http://www.epa.gov/ozone/snap/fire/co2/co2report.html), exposure to ambient air concentrations greater than 17 % can cause death within one minute. Recall that we constructed the following model for gas exchange in the human lung: ct+1=(1−q)ct+qγ, where q is the fraction of air in the lung that is exchanged for ambient air at each breath, γ is the concentration of chemical in the ambient air, and ct is the concentration of chemical in the lung.

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  1. anonymous
    • one year ago
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    Suppose that the ambient air has a CO2 concentration of 20 % (a concentration sufficient for fire suppression), and that a fire fighter whose oxygen mask has failed is exposed to this air. Suppose that the fire fighter has no CO2 in his lungs and that he exchanges 30 % of the air in his lungs for ambient air at every breath. In the following, you can use γ=0.2 (so that ct is measured as the fraction of the air that is CO2).

  2. anonymous
    • one year ago
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    Now suppose that the fraction of gas exchanged at each breath is only 10 %. What is the concentration in the lung after 4 breaths? so c4 = ? this is where I am stuck!!

  3. anonymous
    • one year ago
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    First off, is this your formula? \[C_t+1=(1-q)C_t+q \gamma\]

  4. anonymous
    • one year ago
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    yes

  5. anonymous
    • one year ago
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    thank you for responding!! :)

  6. anonymous
    • one year ago
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    I found equilibrium which is C^* = 0.2

  7. anonymous
    • one year ago
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    \(q\) is the fraction of air in the lung that is exchanged for ambient air at each breath = 0.3 \(\gamma\) is the concentration of chemical in the ambient air = 0.2 \(C_t\) is the concentration of chemical in the lung = what we're looking for where does the 10% come in?

  8. anonymous
    • one year ago
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    sorry I'm just laying it all out, trying to understand the question

  9. anonymous
    • one year ago
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    the 10% is the next part of the question, so I think they are saying now the fraction of gas exchanged at each breath is only 10 %, whereas before I think it was 20%

  10. anonymous
    • one year ago
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    No not 20%, it was 30% originally

  11. anonymous
    • one year ago
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    "in his lungs and that he exchanges 30 % of the air in his lungs for ambient air at every breath"

  12. anonymous
    • one year ago
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    ok, so it does look like it's asking for \(c_4\), but I'm not seeing where you'd put in the 4

  13. anonymous
    • one year ago
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    I think I have to come up with c1 first, so I have to have a discrete time dynamical system so that I can plug in c1 and do it 4 times to get to c4. Also I am assuming that c0=1 (initial value)

  14. anonymous
    • one year ago
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    ok, so you're supposed to do iterations. that makes sense

  15. anonymous
    • one year ago
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    Is the 1 supposed to be in the subscript?

  16. anonymous
    • one year ago
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    Like this? \[C_1=(1-0.3)(0.2)+(0.3)(0.2)\] And then use this to find \(C_2\)?

  17. anonymous
    • one year ago
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    yes, iteration! I think you are on to something... so for C4 - let me see what I get...

  18. anonymous
    • one year ago
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    so wait shouldn't the 0.2 be 0.1, since the concentration is now 10%?

  19. anonymous
    • one year ago
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    I meant the 0.3 sorry not the 0.2

  20. anonymous
    • one year ago
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    Yes it's 0.1 \(C_{t+1}=(1-q)C_t+q \gamma\) \(C_t\) is the only thing that changes, so the equation is basically \(C_{t+1}=(1 - 0.1)C_t+(0.1)(0.2)\) \(C_{t+1}=0.9C_t+0.02\) Then iterate \(C_{1}=0.9(0.1)+0.02=0.11\) \(C_{2}=0.9(0.11)+0.02=0.119\) \(C_{3}=0.9(0.119)+0.02=0.1271\) \(C_{4}=0.9(0.1271)+0.02=0.13439\) So the concentration after 4 breaths is 13.4%. That's what I'm thinking anyway

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