I learned bookkeeping on Khan Academy with the two types of accounting: accrual basis and cash accounting. Assets, liabilities and equity words entered my head, currently busy with some Khan brain teasers.
And I managed to solve all currently published exercises on Khan Academy (129/129) :-) Kudos to my TI-89 which helped me out so many times! However, the unknown and legendary Black Hole badges aren't yet in my journeyer backpack... And to earn them, it is currently impossible because... the answer is ... hidden in Kahn's source code. Check badges/point_badges.py and exercise_completion_count_badges.py to unveil the secret...
Fabian Bellard's scientific web calculator is very powerful! I discovered it today while reading an advogato entry on him!
My academic career was a failure, but fortunately my khanacademic career is skyroketing :-). These days, I watched videos on Thermodynamics (in Chemistry section). I had a deep look at the Carnot Cycle, at adjabatic and isothermic processes and at the entropy definition, and the Maxwell's demon was lurking all the time.
I watched videos in history from French revolution, through Napoleon's rise and until his fall, and I felt sympathetic with people in the Haitian revolution and was scared by the dishonest debt they had to pay until 1947! In my previous history courses I had a more theoretical approach to the French revolution: we discussed in deep all Illuministic theories, but I completeley missed the stuff going on in Europe in 1789-1815. In the end, the Swiss constitution was enforced by Napoleon... I wonder how I could visit London and Paris without knowing what I do now... I practiced with exercises on the Academy site, too. To date, I watched 124 videos and solved 104 exercices. My goal is to earn at least one of the two unknown Black Hole badges!
As my one and one half year old daughter is learning by imitation, I decided to do the same! I equipped myself with an Aiptek 10000U (for about 130 Swiss francs) and bought Screenvideorecorder for another 40 bucks. I then created a tutorial video on how to compute the gamma factor of special relativity. English, audio and overall handling are experimental! (what else would you expect from dangermouse? ;-)
Excel SUMIFS function
It adds the cells in a range (range: Two or more cells on a sheet. The cells in a range can be adjacent or nonadjacent.) that meet multiple criteria. For example, if you want to sum the numbers in the range A1:A20 only if the corresponding numbers in B1:B20 are greater than zero (0) and the corresponding numbers in C1:C20 are less than 10, you can use the following formula:
=SUMIFS(A1:A20, B1:B20, ">0", C1:C20, "<10")
I recently saw SUMIFS used as an extended VLOOKUP with more than one cell which needed to match.
There is an interplanetary internet, and there may exist an internet between civilizations running at tachyonic speed. This time I ventured into
It starts with configuring the DNS servers with ones published at the OpenNIC project. You need to configure both primary and secondary DNS. Configuring only the primary DNS does not work, as the algorithm always chooses the DNS entry with lower network latency. After configuration, you still are able to surf on the usual Internet, but you also opened a little door to domains like .geek, .bbs and .telnet.
On the wiki of OpenNiC there are very few links, and in the beginning I was disappointed of such few links. Then I learnt of the specular search engine http://grep.geek. By searching for keywords like Blog or Chat you get to view some of the most accurate blogs and interesting chatrooms, especially for people who like to code.
Pioneer Anomaly solved with heat model
Pioneer space probes are the farthest human made objects from the Earth. In a previous post I explained how to connect to the JPL server via telnet and get their current distance from Earth.
Pioneer space probes feel an additional force towards the sun in the order of magnitude of about a_pioneer ~= H*c, which is also the one predicted by Modified Newton Dynamics theories to empirically explain the flat shape of radial velocity curves observed in galaxies. Currently, the the best theories to explain the galactic radial velocity anomaly are ones that look at the Universe at as inhomogeneous sponge. I hope the dark matters theories will be then finally wiped out, as to me they look as a revival of the theories on ether used before Einstein to explain the Michelson-Morley experiment. Also to have so much dark and heavy things passing through my body without interfering with it does not make me feel confortable at all. Springtime is time to give a compete cleanup to the Universe, it's needed once in a while :-)
The GPU project was looking for a solution of the Pioneer Anomaly. It ported source code from the Orsa Project made by Pasquale Tricarico from C to Delphi and experimented a bit with special physics without further success. It was not possible to replicate the linear shift of the signal received from the Jet Propulsion Laboratory dued to the pioneer anomalous acceleration towards the sun.
There is now an article here, that explains how the anomaly can be explained with 1970s computer graphics (basically a more advanced heat model as the one presented in the original Anderson et al. paper about the anomaly). The paper with the heat model explanation is on Arxiv and awaits confirmation from other scientific teams.
How seismic waves tell us about the inner Earth core
The GPU project was also experimenting with seismic sensors. Nanobit built one (picture) and I also built one with a 3D accelerometer on top of a coil. This series of 6 videos on seismic waves by Khan Academy explain very well the types of seismic waves, why Secondary waves travel only into solids (and in pudding :-), the curved path of refracted waves due to the density differences, the S-Wave shadow zone beginning from 105 degrees, and the P-Wave shadow zones. The seismic waves indirectly tell us how the inner Earth core is made, even if none of us digged that deep. Humankind only scratched the surface of Earth!
Learning the periodic table of the elements
The Fukushima accident made me courious of chemistry, and I sorted out an old periodic table of the chemical elements I was using in school. It has a list of the radioctive elements and their half decay time. I then realized that I did not understand anymore why the table was organized in this way. To be honest, I never understood it! I then took time to watch the introductory course on Chemistry by Khan Academy. The first ten videos explained me much more in detail how the periodic table works. In particular, I can do electronic configurations which was never taught in my chemistry course, and I understand a bit why metals are placed in the 'd' configuration. Metals and salts I already knew from before. And the f configuration at the bottom is for the heavier elements, which in principle should be moved between earth alcali and transitive metals, for the electronic configuration process.
IRC chat primer
I use on Gentoo weechat-curses as IRC chat terminal (emerge -av weechat-curses to install it).
Some topics in maths I did not knew or refreshed with Khan Academy are: Laplace Transforms, Convolution Theorem, Dirac Delta function, Taylor Theorem, Implicit differentation, insights in Chain rule, Conic Sections (foci of Ellipse, Hyperbola, and Parabola with Directrix), partial fraction expansion, l'Hôpital rule, surface integrals... I also learned a bit finance on forward contracts, futures and the margin mechanism I can use on the job. Sal, you are great!
Useful git hints
These git hints are taken from the Linux Magazine, article "Git in der Praxis".
git config --global user.name Danger Mouse git config --global user.email firstname.lastname@example.org
git config --global color.diff auto git config --global color.status auto git config --global color.branch auto
cd myproject git init git add . git commit
git commit -a -m "these are the changes" git push
git branch Refactor #switch to branch git checkout Refactor #back to master git checkout master
git checkout -b Refactor
git checkout master git merge Refactor
git tag -a "Tag_1.3.6" -m "new tag at version 1.3.6"
# on branch Refactor git commit git checkout master git pull git checkout Refactor git rebase master # repair conflicts git commit git format-patch master --stdout > mybugfix-patch.diff
I am also trying to understand a bit of this book:
The book is centered around Möbius transformations and Schottky circles. Möbius transformations
f(z) := (az+b)/(cz+d)are visualized as compositons of affine projections (az+b) and of projections on the Riemann's sphere 1/(cz+d) of the complex plane. They are at the ground of Beltrami disk (on page 379) and represent a non-euclidean geometry for which the parallel postulate is not valid. Schottky circles are generated by two Möbius maps which project one circle a into a circle A and another circle b into a circle B. With a breadth-first or depth first algorithm all set of reduced words (e.g AbBb reduces to Ab) are generated, and interesting pictures come out. Like the glowing gasket by Apollonius, invented in 220 BC, which is also the best way to pack as many tangent circles as possible (apollonian packing). The most famous fractal (Mandelbrot's apple) shortly appears at page 291.
When installing Debian Squeeze, the partition with Windows XP was not recognized. Normally I adjust /boot/grub/menu.lst but this time the file was missing.
os-prober grub-updatedid it....
As "scientist of information", you might find these tricks with M$ tools useful:
Creating SQL statements out of an Excel table with
=CONCATENATE("INSERT INTO tbdata(id, name, address) VALUES(";A1;"'";A2;"'";"'";A3;"'";");");
Or an update:
=CONCATENATE("UPDATE tbdata SET name='";A1;"');");
Lookup table in Excel
=VLOOKUP(C3;$L2:$O$25;3;FALSE);This formula looks up for the value in C3 in the table $L$2:$O$25 and returns values in the 3 column where C3 was found. It's a vertical lookup.
Importing Excel tables into access With File->Import->LInk External Table it is possible to import Excel tables into Access and then with SQL queries to extract data from them. However, I learnt that there is a limitation in the complexity of queries you can launch. I always switch from 'Design view' into 'SQL view' when creating queries.
For the interoperability of the Deltasql project, I setup a MS SQL server 2008 instance...
Installing SQL server
Downloading and installing it is easy, but at the end you need to assign a port to it, else the thing won't work. Might sound simple, but I assumed this step was automated by the install procedure. At best, you install it without touching defaults and as last step tweak it to open say port 2345 on TCP/IP protocol. Only after this step, you'll be able to connect with SQL Server Management studio client.
I still think that Oracle and Postgres are the high end of the database offer. However, I see once again how Microsoft is eating more and more of the lower segment. I know many little companies (10-30 employees) which now use some accounting solution based on SQL server. Still, sometimes at work I am puzzled and wonder if the transaction integrity of SQL server is always guaranteed, when under heavy load...
Tips to install Gentoo
I used an old CD to reinstall the latest Gentoo on andromeda, but failed due to some kernel issue with udev after several tries. I then decide to install Debian Squeeze, as I did not want to recompile everything on this old toaster (1GHz, 512 RAM) :-) As side effect I learned that it is always best to use the latest image of Gentoo install CD to get it running 8-)
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
Keep up with the latest Advogato features by reading the Advogato status blog.
If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!