# FL2013 (0)

Day1: Fort Myers
Day2-5: Marco Islands
Day6-7: Key West
Day8: Miami

# Sirius

《晋书·天文志上》：狼为野将，主侵掠。又说：弧九星，在狼东南，天弓也，主备盗贼，常向於狼。原来天狼和弧矢是二十八宿之一的井宿中的两个星官。

1075年，苏轼时任密州知州。当时北宋与西北的西夏常年征战，北边的辽忙着宫廷政变。原来这是文青苏同学打了两只野兔后豪情万丈YY要杀西夏兵啊。

# How many protons in the universe

What is the probability to create a proton with two kinds of quarks (u and d)?

We know that
1. only protons are stable. Free neutrons (udd) will decay to protons (uud) in 15 minutes.
2. baryons (3-quark configurations) may have different angular momentum (J): 1/2 or 3/2. Protons and neutrons have their higher J companions, while uuu and ddd exist only in J=3/2 due to Pauli exclusion principle. All these four are called Delta particles.
3. anti-quarks form anti-matter, which has the same mass as particles of *ordinary* matter but opposite charge and quantum spin.
4. baryons contain virtual quark-antiquark pairs known as sea quarks, along the valence quarks.

To make life easier, let’s forget these complications for a moment and touch a simple 3-kid problem. What is the probability to find a family with 2 girls among all the families having three children?

You may think as follows. The configurations are {GGG, GGB, GBB, BBB}, where G=girl and B=boy. So the probability (P) = 1/4.

Unfortunately this does not sound right. From our everyday experience, 2-girl families are more common than 3-girl ones!

To correctly calculate the probability, we need to list every configuration with exactly the same possibility. “First girl, then boy, last girl” denotes as GBG, and so on. So the configurations are {GGG, GGB, GBG, BGG, BBG, BGB, GBB,BBB}. Counting{GGB,GBG, BGG} and P=3/8! This means there are 3 times chances for a 3-kid family to have 2 girls than 3 girls. Also notice that when a 2-girl family are expecting, the third kid is equally possible for girl or boy.

Back to the proton problem. The universe was a quark soup right after the big bang.  The *initial* particles were 3/8 protons, 3/8 neutrons, thanks to the insight from the 3-kid problem. The other 2/8 two Delta particles decayed in 10^(-24) seconds to protons. Therefore, the neutron-proton ratio was roughly 3/8:5/8=3:5.

Now comes the part that physics is more than math. When the universe was less than 1 second old, the temperature was so high that the protons and neutrons, with electrons and neutrinos, were in thermal equilibrium and could change one to other freely. The neutron-proton ratio was actually 1:1, before temperature dropped below the neutron-proton mass difference, and froze out at about 1:7. As a result, 7/8 of  the matter in the universe is proton!

Bonus: we can figure out that, based on the neutron-proton ratio, 75% quarks are in hydrogen (1 proton) and 25% helium (2 protons & 2 neutrons) when the big bang nucleosynthesis stopped in about 20 minutes.

# Why the space is three dimensional

Because 4D space is not determinate.

Let’s construct a magic square. “In recreational mathematics, a magic square of order n is an arrangement of n^2 numbers, usually distinct integers, in a square, such that the n numbers in all rows, all columns, and both diagonals sum to the same constant.”

For order 3, only one configuration exists. To sum up 3 rows, 3 columns, and 2 diagonals, we need 8 different combinations. And it is exactly what we can get!  Only 5 appears 4 times so it has to sit in the center. 2/4/6/8 appear 3 times so they are at the corners. 1/3/7/9 appear 2 times and they are at the edges. Then the square is totally determined.

8 3 4
1 5 9
6 7 2

We can always add an arbitrary number to all the numbers in the square, eg,

18 13 14
11 15 19
16 17 12

The story totally changes from 3D to 4D. We only need 10 combinations but there are 86 of them! You should imagine more features or restrictions can be imposed, eg, the sum 34 can be found in each of the quadrants, the center four squares, and the corner squares, and more, just like Albrecht Dürer did 500 years ago!

16  3  2 13
5 10 11  8
9  6  7 12
4 15 14  1

=========

# time management

https://sukye.wordpress.com/2011/06/23/pomodoro-technique-2/

The Now Habit, by Neil Fiore, 2007

replace “I have to” by “I choose to”
replace “I must finish” by “when can I start”
replace “this is so big” by “I can take one small step”
replace “I must be perfect” by “I can be human”
replace “I dont have time to play” by “I must take time to play”
altogether: I choose to start on one small imperfect step knowing I have plenty of time for play.

guilt-free play gives quality work.

plans, action, and solutions are required to direct the energy and complete the work of worrying.

before deciding to go to a recreational activity, take time out for just 30min of work.

# 发现神数9801

1/9801 = 0.00(010203040506070809101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979900)(repeat)

ps1，其实我是看到有人提到1/998001想到的。

ps2，wolframalpha.com 还算错了，漏掉了98。

# openfoam

updated: Aug 15, 2012

1. 安装

2.例子

3.cavity

|– 0
|   |– U
|   `– p
|– constant
|   |– polyMesh
|   |   |– blockMeshDict
|   |   `– boundary
|   `– transportProperties
`– system
|– controlDict
|– fvSchemes
`– fvSolution

4. 计算之前先要画格点，我先单讲在已经有表面几何的情况下，如何用snappyHexMesh来产生mesh。基本参考
http://www.hydroniumion.de/general/snappyhexmesh-tutorial/

|– 0.org
|   |– U
|   |– include
|   |   |– fixedInlet
|   |   |– frontBackUpperPatches
|   |   `– initialConditions
|   |– k
|   |– nut
|   |– omega
|   `– p
|– Allclean
|– Allrun
|– constant
|   |– RASProperties
|   |– polyMesh
|   |   |– blockMeshDict
|   |   `– boundary
|   |– transportProperties
|   `– triSurface
`– system
|– controlDict
|– cuttingPlane
|– decomposeParDict
|– forceCoeffs
|– fvSchemes
|– fvSolution
|– snappyHexMeshDict
`– streamLines

5. snappyHexMeshDict里geometry中的stl换成新的，比如P0935.stl。其他暂时不变。

6. 依次运行blockMesh 和paraFoam &，然后在paraview里打开P0935.stl。

1) transformPoints -translate “(x y z)”来移动框架的中心
2) blockMeshDict里调convertToMeters

7. 运行snappyHexMesh

8.运行solver。
system里的文件做相应的调节。

# 超光速汽车

－－读《Guns, Germs and Steel 》有感