# 2020(S08) Lecture:week 10

(Difference between revisions)
 Revision as of 16:00, 12 April 2008 (view source)← Previous diff Revision as of 17:14, 12 April 2008 (view source) (→Challenge 1: Reliable materials/use)Next diff → Line 9: Line 9: modified from a lesson described in Henry Petroski’s book, [http://www.amazon.com/Engineer-Human-Failure-Successful-Design/dp/0679734163 To Engineer is Human] modified from a lesson described in Henry Petroski’s book, [http://www.amazon.com/Engineer-Human-Failure-Successful-Design/dp/0679734163 To Engineer is Human] - Boxes of paper clips don’t usually come with “ a money back guarantee” since nearly everyone in the world who uses standard paperclips finds them reliably able to hold a few pieces of paper together. But bend the paperclip wide a few times and it’s likely to break. How many times will that be? We’ll do a quick experiment to find out. Each of you will bend a paperclip back and forth until it breaks and we’ll plot the data on a histogram. + Boxes of paper clips don’t usually come with “ a money back guarantee” since nearly everyone in the world who uses paperclips finds them a reliable way to hold a few pieces of paper together. But bend the paperclip wide a few times and it’s likely to break. How many times will that be? We’ll do a quick experiment to find out. Each of you will bend a paperclip back and forth until it breaks and we’ll plot the data on a histogram.
- [[Image:Bends2break.png|600px]] + [[Image:BendFreq.png|600px]]
Line 19: Line 19: - Mapping these ideas to your project + ===Mapping these ideas to your project=== This paperclip challenge spotlights two modes of system failure, namely This paperclip challenge spotlights two modes of system failure, namely # fatigue of the materials that comprise the device and # fatigue of the materials that comprise the device and - # application of uncharacteristic forces. When thinking about biotechnologies, what is akin to “material fatigue”? What situations might be considered uncharacteristic? Take [http://openwetware.org/wiki/IGEM:MIT/2007 the Eau d’coli project from the MIT 2007 iGEM team.] These bacterial cells were designed to smell like bananas when they reach stationary phase. + # application of uncharacteristic forces.
As you've seen these affect each paperclip to differing degrees. When thinking about biotechnologies, what is akin to “material fatigue”? What situations might be considered uncharacteristic? How cell to cell differences can be taken into account is touched on in the next challenge but here let's apply material and use variations to [http://openwetware.org/wiki/IGEM:MIT/2007 the Eau d’coli project] from the MIT 2007 iGEM team. Recall, these bacterial cells were designed to smell like bananas when they reach stationary phase. +
+ [[Image:BBa_J45200.png|600px]] +
+ #In your groups imagine at least two ways that the genetic material in this system might "fatigue" and how you'd know. + #Next define at least two environmental conditions that would derail the system and decide how likely these conditions are. + ==Challenge 2: Reliable performance== ==Challenge 2: Reliable performance== ==Challenge 3: Reliable sources== ==Challenge 3: Reliable sources==

## Revision as of 17:14, 12 April 2008

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# Week 10 Tuesday

Accidents waiting to happen

Not all engineers are pessimists but since good designs anticipate failure modes, many engineers must at least consider Murphy’s Law (what can go wrong will go wrong) as they flesh out the details of their designs. Like Daedalus’ wax wings flown too close to the sun, even designs that work well have limits and breaking points. If an engineered object is to work reliably, then the designers will have to carefully examine its multiple points of failure, including the three that today’s challenges address: extreme forces, performance variations, and human fallibility.

## Challenge 1: Reliable materials/use

modified from a lesson described in Henry Petroski’s book, To Engineer is Human

Boxes of paper clips don’t usually come with “ a money back guarantee” since nearly everyone in the world who uses paperclips finds them a reliable way to hold a few pieces of paper together. But bend the paperclip wide a few times and it’s likely to break. How many times will that be? We’ll do a quick experiment to find out. Each of you will bend a paperclip back and forth until it breaks and we’ll plot the data on a histogram.

Did all the paperclips break after the same number of bends? If so, why? If not, why not?
Reason 1:
Reason 2:

### Mapping these ideas to your project

This paperclip challenge spotlights two modes of system failure, namely

1. fatigue of the materials that comprise the device and
2. application of uncharacteristic forces.
As you've seen these affect each paperclip to differing degrees. When thinking about biotechnologies, what is akin to “material fatigue”? What situations might be considered uncharacteristic? How cell to cell differences can be taken into account is touched on in the next challenge but here let's apply material and use variations to the Eau d’coli project from the MIT 2007 iGEM team. Recall, these bacterial cells were designed to smell like bananas when they reach stationary phase.

1. In your groups imagine at least two ways that the genetic material in this system might "fatigue" and how you'd know.
2. Next define at least two environmental conditions that would derail the system and decide how likely these conditions are.

# Week 10 Thursday

==Challenge: Ownership and Sharing==