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Dutch / Nederlands

Diary, April 2010

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Saturday, April 3, 2010

Q Fever

This morning, we got a letter from the government to tell us that Q Fever has been detected at a goat/sheep farm within 5 Km of our home address. The letter did not specify the address, but I did find some map on a web site about Q fever in the Netherlands. In the past three Q Fever has grew into an epidemic in the Netherlands with a growing number of cases each year. On the right it gives a part of the map. The red dot is the location of the farm and the circle around it is the 5 Km circle around it. Our home address is near the blue cross and approxamitely 2 Km away from the infected farm.

De Slegte

This afternoon, I went to bookshop De Slegte and I bought two books. I paid them at 16:18:39. I bought Dune by Frank Herbert, published by New English Library, 1974, ISBN:0450027279. When I saw this, I realized that I never read this book in English. I doubted wheter I should buy the book, because it misspelled 'Arrakis' with 'Arrauis' on the first page. I payed € 4.00. The other book I bought was Buiten is het maandag (Outside it is Monday) by J. Bernlef, ISBN:9021452782. I payed € 5.99 for it.

Wednesday, April 7, 2010


Today, our magnolia started to bloom again. It was a warm and sunny day. By the end of the day many flowers had opened.

Friday, April 9, 2010


Just before I wanted to leave from the office, some colleagues mentioned the movie Avatar. I already had been thinking about whether I should go to this movie this weekend or not. When they mentioned it, I quickly became enthousiastic and after some discussions we decided to go this evening. I biked home, prepared some dinner (consisting of tofu, leek, and eggs), and biked back. I arrived 50 minutes early because we had to collect our reserved tickets. To save my time, I did read some pages of Perfect Rigor. The movie started around 21:25. They also showed the trailer for the next Shrek movie in 3D. I found the movie quite impressive, more than I had expected. Of course, we did discussed some of the 'strange' plot changes and minor glitches in the animation. We also noticed that you get used to the 3D quite quickly and we felt that it was more prominent in the first part of the movie.

The idea of trees communicating, and all the threes on the planet forming a kind of collective 'brain' is interesting. But for organism like a tree, who are stationary, and not being able to move there is not much purpose in developing senses and a neural network. And all the animals having antennae is also weird. Why would the animals develop such an organ. In the later part of the film there also seems to be a lot telepathic communication going on between the 'trees' and the animals.

Wednesday, April 14, 2010

De Slegte: Three books

This afternoon, at 12:10:21, I bought the following three books from De Slegte: The manager of the shop told me that they ready with the reorganisation and that the top floor has been cleared. They are going to use it as a storage area.


I just read the excing news (see Investigational Immune Intervention Slows Brain Shrinkage in Alzheimer's Patients) about some objective effect of Gammagard on the shrinkage of the brain of people with Alzheimer's Disease. At least this is the result of the phase II trial. The phase III trial will soon start. As far as I know it will only be held in the USA and Canada, which means that we could not join this trial.

Saturday, April 17, 2010

Blue sky

Today, we had a perfect blue sky without a single contrails. Not so strange, because there was only one flight in the Netherlands, a test flight with the PH-BGB, a Boeing 737. There was no sign of any ashes in the sky. The test flight also did not encounter any serious problems. I guess that normal flights will be resumed soon. The Eyjafjallajökull is still producing ashes (webcam: eyjafjallajökull frá valahnjúk). It is not clear if and when these arrive in Europe. (See Meteosat 0 degree Dust Central Europe.) If the Katla erupts far more ashes could be produced.

Sunday, April 18, 2010

Going to China

This evening, I have booked our flights to China. After some considerations, we decided that Li-Xia and I will be going to Urumqi from Tuesday, July 13 till Thursday, July 29. We are flying with China Southern (but some of the flights will be done by KLM). Our flight schedule is:

Dusseldorf - Amsterdam     12/07  CZ 7786  18:25   19:20
Amsterdam  - Beijing       12/07  CZ 346   20:55   12:40
Beijing    - Urumqi        13/07  CZ 6908  15:45   19:45

Urumqi     - Beijing       29/07  CZ 6911  08:10   11:45
Beijing    - Amsterdam     29/07  CZ 345   14:20   18:35
Amsterdam  - Dusseldorf    29/07  CZ 7781  21:40   22:30

The reason we are flying from Düsseldorf (Germany) is because this is about 200 euro (per person) cheaper than flying from Amsterdam. We will drive by car to Düsseldorf, which is less than two hours from where we live and park our car there (which will cost about 100 euro). Traveling by train from Enschede to Amsterdam would also cost more than 100 euro.

Tuesday, April 20, 2010


Is it true that after the eruption of the Eyjafjallajökull vulcano, the 'big sister' Katla will explode. The Eyjafjallajökull erupts less frequent than the Katla and according recorded history every time it did erupt the Katla erupted as well. Since yesterday the seismic activity below the Katla has increased and some locals think it might erupt very soon. The eruptions of the Katla are on average more violent and could last for months. One of the possible least serious consequences could be that our trip to China is in danger.


Today, the book Dicionário ee Bandeirantes e Sertanistas do Brasil by Francisco de Assis Carvalho Franco (ISBN:8531900212) arrived in the mail. I bought it through the internet. On July 4, 1995, this book was bought by Boudewijn Büch in Sao Paulo as says a note on the first page of the book. Büch was, besides an author and television personality famous for his documentary still of programs, a bibliophile, who during his life collected about 100.000 books in his library, which he called Bibliotheca Didina et Pinguina. The Dicionário was part of this library. I also own the three volumes of the auction catalogue of this library.

Friday, April 23, 2010

Difficult Exact Cover problems

The past days, I have been thinking about ways to construct very difficult Exact Cover problems. The idea is to construct a complex as possible Exact Cover problem that only has one solution. The idea I am working on is to start with the complete graph on n points. A complete graph (with n > 2) has (n-1)!/2 acyclic Hamiltonian cycles. Lets define c as this number. You need ceiling(log2(c)+2) bits to encode these numbers (exclude representation consisting of only zero's and one's). Lets define m as this number plus one, than I think it is possible to construct an Exact Cover with vectors of length nm with n+(n-1)c vectors, such that it only has one solution, and that there are n+(n-1)c over n combinations of vectors to choose the one solution from. The idea is to divide each vector in n segments of length m where each segments represents one point in the graph. First we create n vectors where everytime one of the segments is filled with one's all other positions with zero's. This represents the one solution. Then for each Hamiltonian Path we pick a unique number a bigger than 0 and smaller than 2m-1) such that both a and its complement are not used for any other path. Next we remove an arbitrary edge from the path. For each of the remaining (i,j) edges we create a vector where segment i is filled with the representation of a and segment j is filled with the complement of a. Of course, the columns and the vectors can be scrambled to hide the unique solution. Furthermore, I believe that it is possible to select the unique numbers and the edges that are left out in such a manner that the one's are spread quite uniform over the columns. I also believe it is possible to proof that there is but one solution.

Saturday, April 24, 2010

Difficult Exact Cover problems

I just realized that instead of using Hamiltonian path with a random edge removed for incomplete solutions, it is also possible to use Hamiltonian paths for constructing very difficult Exact Cover problems. A complete graph (with n > 1) has n!/2 acyclic Hamiltonian paths. Although this increases the number of vectors for the incomplete solutions with n, it also increases the size of the vectors, because the value for m also increases.

Sunday, April 25, 2010

Perfect Rigor

This afternoon, I finished reading the book Perfect Rigor by Masha Gessen about Grigory Perelman in which I started reading on April 6, after I received it from where I order it on Sunday, March 28. I found this book a little meager with respect to Perelman. If one would pick five random pages and show it to a stranger, this stranger might not get the idea that this book is about Perelman. I also feel it scarse on biographic details. I do not share the opinion expressed in the the review Nasty and petty book, but great information on The book has increased my doubts with respect to whether Perel man will ever accept the one million dollar price that has been awared to him by the Clay Mathematics Institute.

Wednesday, April 28, 2010

P versus NP

Now that Grigori Perelman has solved one of the seven Millenium Problems from the Clay Mathematics Institute there are still six left. (There is still no sign whether he had made up his mind with respect to accepting the price.) Of these problems the P versus NP problem is the one that I think I understand best. NP is a class of problems for which it is 'easy' to check if a solution is correct. But that does not mean that it is also 'easy' to find a solution. Easy here means that the number of steps required to find a solution (on a Turing machine) is limited by some polynomial function to the size of the problem. A large number of NP problems have been found for which no 'easy' algorithm has been found yet. It also has been proven that many of these problems are basically the same, because they can be mapped upon each other. These are called NP-complete.

Not so long a go, it was proven (see The Complexity of Flood Filling Games) that the Flood-It! game is NP-hard, which means that it is at least NP-complete, but possibly even more complex. Robert Aubrey Hearn deals with the complexity of many games in his PhD thesis Games, Puzzles and Computation.

The NP-complete problem that I have worked on the most is the Exact Cover problem. This made me think about answering the question whether there is an 'easy' algorithm for solving Exact Cover problems. I am very strongly inclined to believe that such an algorith does not exist and that the complexity classes NP and P are not equal. Many computer scientist and complexity expert share this opinion. The problem is that it is very difficult to proof, because you have to show that something does not exists, while there are an almost unlimited number of 'easy' algorithms. Many people already have tried to proof the equality or unequality of NP and P. For more information see The P-versus-NP page by Gerhard J. Woeginger. The paper Faster Solutions for Exact Hitting Set and Exact SAT by Limor Drori and David Peleg, seem to contain some interesting algoritms that shows that Exact Cover problems can be solved in a rather low exponent.

There are some more techniques which point to efficient algorithms for solving NP-complete problems. These are found in:

Thursday, April 29, 2010

Katla earthquake

Yesterday, at 15:28:31 there was an earthquake of magnitude 1.5 (only very minor) at a depth of 5.8 km below the Katla vulcano, which was followed by some hours of increased tremors. In the past weeks there have been many earthquakes around the Eyjafjallajökull vulcano. Is this the first sign that something is hapening below Katla? Or is this one of the normal earthquakes that occur along the fault line such as there has been many in the past weeks. Map with earthquakes in the past 48 hours.

Today, yesterday's earthquake was reclassified as two earthquakes: one 1.0 earthquake at a depth of 7.1 km at 63.695, -19.149 and one 1.5 earthquake at a depth of 0.8 km at 63.668, -19.141. This very interesting because the later earthquake occured above the magna chamber.

Update April 30: Above the 'Katla' tremor page it now says: "Katla is not erupting and there are no indications that Katla is about to erupt. Information on this page is for the Eyjafjallajökull eruption."

This months interesting links

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