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authorbnewbold <>2016-06-11 17:23:36 -0400
committerbnewbold <>2016-06-11 17:23:36 -0400
commit2f79265986a185e79b14e0ddf113ecf355da830f (patch)
tree03efd4cfc63b30f1a43463886279cb112710b59c /misc
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?".