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Snow
This morning, when I went outside, I noticed the
first snow flakes. Soon they
became more and I noticed that they stayed on the
ground. But when the sun came out, it quickly disappeared.
Around noon, there where some big snow flakes falling
from the sky, but they did not really stay on the ground.
In the evening, between seven and eight there was some
substantial snow, but again, it did not stay everywhere
on the ground. It quickly disappeared when the snow
turned into rain.
Snow!
This morning, while I was still in bed, Annabel shouted:
"It is snowing outside". She even
opened the blinds and curtains to show me while I was still
laying in bed. The snowing stopped around 10 o'clock when
there was about 2 cm of snow.
Divisibility sequences
Earlier this week, I was contacted by Richard Guy again with
respect to the sequences in my one mathematical paper.
He is still working on the subject of divisibility sequences.
He asked me if I had some proof of some the sequences
being divisibility sequences. I tried to find a definition
for with Google, but only found references to papers. When
I told this, he replied with: "A divisibility sequence
is simply a sequence {a(n)} with the property that a(m) divides
a(n) whenever m divides n." Furthermore he stated that
although they are easy to define, they are not so easy
to prove.
De Slegte
This evening, when I was visiting bookshop De Slegte I noticed one of the shop-assistants
moving around books. When I asked him about this, he told
me headquarters had ordered them to reorganize the shop
and close the third floor. On the first floor there are only
new books that are no longer being sold by normal prices.
On the second floor there are only second hand books. On the
third floor there are some second hand books and some new
books. In some way I can understand the idea to close that
floor, but on the otherhand it means that the total number of
books in the shop will be reduced, which, I think, is bad.
But if they are going to have some sale of the books that they
have to put away, then maybe it is good. I wonder what they
are going to do with the third floor. It would not surprise
me if they are simply going to close it for the public and
use it as a storage area. We will see.
De Slegte: Three books for five
This afternoon at 14:04:23, I bought three books from
De Slegte for five Euro.
I only wanted to buy one book. The books are:
- Dertien (Black Swan Green) by David Mitchell
- Isabelle by Annette Kobak
- Anna, Hanna en Johanna door Marianne Fredriksson.
Perfect Rigor
I was thinking about buying the book Perfect Rigor: A Genius
and the Mathematical Breakthrough of the Century by Masha Gessen
about Grigori Perelman but started
to doubt when I read the review Nasty and petty book, but great information on Amazon.com,
which states that Gessen wrote the book as if she hates her subject with
a passion. Gessen argues that Perelman is crazy, where crazy means that
a person has an internally consistent view of the world that is entirely
different from the view most people consider normal. The author of the
review however argues that Perelman is not crazy at all but that all his
seemingly strange decisions can be explained by his very high ethical
standards by which he is living. It looks like Gessen did not really
understand Perelman.
De Slegte: Two books
This afternoon at 17:02:23, I bought two books from
De Slegte The books are:
- Isabelle Eberhardt: Brieven, dagboeken en verhalen for €nbsp;3.00.
- Aandacht voor Anna (ISBN 97-890-71227-189) for € 7.50.
Grigori Perelman
Yesterday, the Clay Mathematics Institute
made the announcement that
the first Clay Mathematics
Institute Millennium Prize will be awarded to Dr. Grigori Perelman for the resolution of the Poincaré Conjecture. This really great news, especially when you
know that Perelman did not meet the official requirement that the proof should
be published in a peer-reviewed journal. Perelman did not give a detailed
proof, but roughly sketched how the conjecture (or actually the more
general Thurston's geometrization conjecture). He did this in the three
ArXiv papers:
The entropy formula
for the Ricci flow and its geometric applications (November 11, 2002),
Ricci flow with
surgery on three-manifolds (March 10, 2003), and
Finite extinction time for
the solutions to the Ricci flow on certain three-manifolds (July 17, 2003).
Furthermore, in April 2003, he explained his proof in a number of lectures
give at the Massachusetts Institute of Technology. Various others went
to give detailed proves. At first Huai-Dong Cao and Xi-Ping Zhu claimed that they had proven the conjecture, but later they
played this down in a revised version their paper called Hamilton-Perelman's Proof of the Poincaré Conjecture and the Geometrization
Conjecture.
The fact that Cao and Zhu at first claimed to have proven the conjecture,
which was supported by Gang Tian
among others, and that other mathematicians did not raise their voice about
this, made Perelman decided to withdraw from mathematics and to live a
reclusive life.
I am happy that the Clays Mathematics Institute did award him this price of
one milion dollar, and I hope that Perelman will accept the price, but I am
afraid that he will not do so, just like he rejected the Fields Medal.
Perelman turned down price
It seems that Dr. Grigori Perelman
has turned down the Clay Mathematics
Institute Millennium Prize with the words: "I have all I want."
Knowing that turned down the Fields Medal some years ago, this was to
be expected, but still I think it is quite sad that this genius is
lost. It is about eight years ago that he published his 'proof'. Not
much later he abandoned mathematics because of the controversy around
this proof. He could have tackled some more hard mathematical problems
in his life time. At least he will not be forgotten in the centuries to
come.
Update, Wednesday, March 24: An article on Life.ru states that Perelman still has not made up
his mind whether to accept the price or not.
This evening, I noticed that Google Earth
has applied a recalibration of the position of the images for some parts
of the Netherlands. Around Enschede the images are shifted about 10 meters.
This means that all the tracks that I have made in the past year now
appear on the wrong place. I do not know what I should think about this.
I guess that they did this with a purpose, but on the otherhand it destroys
all the tracks I have created in the past year. Of course, I could write
a program to correct the coordinates, but that would be a lot of work,
also because the recalibration is not uniform over the whole country.
In some places of the country there is no recalibration at all. In some
other locations it is a few meters in a different direction. How long
would it take me to construct an accurate map of all the recalibrations
that have been applied. It is also likely that these recalibrations
occur at certain strict borders. In the past years I have often come
along places where the arial pictures where not stitched correctly and
where I was forced to make a 'jump' in the track. It is possible that
some of these 'jumps' are now removed.
Perfect Rigor
I changed my mind with respect to buying the book Perfect Rigor
about the life of Grigori Perelman,
and ordered the book from bol.com. On
22:04:55 I received an email confirming my order.
Two rainbows
This afternoon, we saw some rain fall from some clouds at the horizon.
When the cloud came closer it even developed a roll shape. (See
this picture). After is
passed over, I realized that there might be a rainbow, and indeed, when we looked out of the window on the
otherside there was a full double rainbow (around 18:20). See the
picture displayed on the right. About half an hour later, when I went
home another wide cloud was moving over, and while I biked along the
Kanaalstraat (between 18:54 and 19:02), I saw a single complete
rainbow on the left. I did not see anything of a double rainbow. Maybe
this was related to the fact that the raindrops where much smaller
than with the first rainbow.
This months interesting links
Movements
KMZ file of movements (incomplete).
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Wednesday, March 31, 2010