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authorbnewbold <>2016-06-11 17:23:36 -0400
committerbnewbold <>2016-06-11 17:23:36 -0400
commit2f79265986a185e79b14e0ddf113ecf355da830f (patch)
tree03efd4cfc63b30f1a43463886279cb112710b59c /tmp
parent556b3c33daa7a41550cb2bbe23d333ba39414be0 (diff)
move some decent pages over to misc folder
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-SCUBA Diving
-Self Contained Underwater Breathing Apparatus
-SCUBA stands for "Self-Contained Underwater Breathing Apparatus".
-One of the primary organization regulating recreational SCUBA diving is
-PADI (the Professional Association of Diving Instructors).
-:BCD: The buoyancy control device is basically an inflatable live vest
- that you can inflate using the regulator (or by mouth) to control
- your buoyancy. Your buoyancy changes as you use up air (tank gets
- lighter for same volume displaced), inhale/exhale, swim in water
- of different temperature or salinity, or change depth: increased
- pressure compresses any flexible air pockets, including the BCD
- itself, neoprene foam, or a dry-suit.
- Most BCDs have their own pressure hoses coming from the first stage
- regulator that supply air.
- Sometimes there is only one vent valve, which has to be at the
- highest orientation or air will not vent out of the bladders.
-:Tank: Most tanks are made of steel or aluminum and can store compressed
- air of up to 3000psi. They are stored at pressure to prevent moisture
- from leaking in. There is a valve built into the tank itself that
- usually gets taken apart and repaired every two years. Tanks
- can last for decades even with heavy use; they are pressure tested
- for fatigue and leaks.
-:Regulator: The first-stage regulator is connected to the tank and steps
- the pressure down to about 250psi above the surrounding/ambient
- pressure. Hoses carry air at this mid-level pressure to the second
- stage regulator/mouthpiece, which steps the pressure down to
- about what is in your lungs. Depending on the regulator they can
- be stiff (you have to suck a bit to get air, but then it rushes
- in with force) or very natural feeling (air comes very smoothly
- on inhalation and doesn't press into your lungs).
-:Alternate: These days almost everybody carries a second regulator mouthpiece
- for emergencies. These are always on and ready to breath from,
- but usually stiffer so they don't free-flow as often.
-:Dive Computer:
- A dive computer monitors time and depth to give you an accurate picture
- of how much excess nitrogen is in a diver's bloodstream. By
- continuously integrating they usually "give more time at depth" than
- hand calculations using tables (which err towards safety).
-:Dry Suit: A dry suit is a sealed and air tight, keeping the diver's skin dry.
- Extra insulation is needed to give warmth underneath. Some dry
- suits are made of compressed neoprene.
- A dry suit has to be constantly adjusted with tank air just like
- the BCD to maintain inflation and buoyancy.
-:Wet Suit: Wet suits work on the principle of holding water against the skin:
- a diver's body warms this water and stays cozy as long as water
- flow is restricted enough. Even little bit too much flow through
- wrist or ankle openings can be very cold.
-A PADI Open Water Diving course gives a recommended limit of 20m/60ft.
-A "deep dive adventure course" gives a recommended limit of 30m/100ft,
-and additional experience gives a limit of 40m/130ft.
-With careful decompression stops and enriched compressed air (higher oxygen
-content) it's possible to reach depths of hundreds of meters. Sometimes
-commercial divers will dive for many hours using surface supplied air,
-then live at the surface in a compression chamber overnight between dives
-to stay at the same pressure [*]_.
-I'm pretty sure `Jacques Cousteau`_ invented the aqualung, which is the basis
-for modern diving, but I'll have to check.
-.. _Jacques Cousteau: /k/jacquescousteau/
-After a regular no-decompression dive, wait at least 12
-hours before flying (or going to high altitude, eg over 300m).
-.. [*] Need a citation, heard this word of mouth
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-* Kay Sage (1898-1963), American Surrealist Painter
-* Yves Tanguy (1900-1955), French Surrealist Painter
-* Hans Bellmer (1902-1975), French. "Die Puppe" series (dolls)
-* Francis Picabia (1879-1953) French Painter
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-Newcomb's Dialemma
-Newcomb's paradox was thought up by a researcher named Newcomb; it was first
-explored and written up by Robert Nozick in the 1969 paper
-"Newcomb's Problem and Two principles of Choice".
-The Situation
-As narrated by an all knowing "predictor"::
- I am going to give you a choice. It is important to know that I really
- pretty much know what you are going to do. I have been watching their whole
- life and am additionally an immortal being; i've been doing this a long
- time and always guess correctly. It's also important to know that I am
- unbiased and don't care which decision you make, I have nothing to gain
- either way.
- Here are two boxes: a large and a small. The small has a 10 shekel coin
- in it (show everybody). The large one may or may not have a thousand
- shekels in it; you don't know. Your choice is to either take only the
- large box or to take both the large and small boxes. The twist is that
- I already knew which decision you will make and decided whether or not
- to put the $1000 in the large box or not based on that knowledge.
- If I knew you would "two box", then I left the large box empty. If I knew
- you would "one box" then I filled it.
-Dominance Mindset
-Regardless of what decision was made previously, and whether or not there
-is anything in the large box, the person is better off taking both boxes;
-either they will get just $10 (better than none) or $1010 (better
-than $1000). So two-box.
-Trusting Mindset
-The predictor is pretty much always right so we can just ignore the
-possibility that they are wrong. In this case, choosing to one-box
-implies that the Predictor knew you would and you get $1000;
-choosing to two-box implies that the predictor knew you would and you
-only get $10.
-The predictor doesn't even have to be perfectly accurate; say they are
-If you one-box, your expected value is $900.
-If you two-box, your expected value is $110.
-It's disputed whether this is a paradox, and there are many deeper arguments
-that I don't have time to go into here. Ultimately, I am a one-boxer
-though this is something of a minority position.
-The person who taught me this paradox, Professor Augustin Rayo, a
-two-boxer, then had this to add. He was talking with his one-boxing friend
-and accused her of letting irrationality undermine her logic: she is so
-optimistic that if a statement S is unprovable, but it would be nicer if S
-was true than false, then she pretens that S is proven. So basically, even
-though there is no rationalization, she will accept a statement "just
-because it would be nice", and this isn't how logic works. To which she
-replied "but wouldn't it be nice if it was?".