The Quantum Quartet

I made some drawings recently. For no particular purpose, really, other than to distract myself.

And here is the joker:

Books in E major

Look! Listen! I've made a music video for your smooth start into the weekend:



I finally realized I won't be able to do any painting till the girls are old enough to not try to lick on the brushes. So, I was looking for a new hobby and that is my first try. I made a series of mistakes that I'll try to learn from.

Stefan and I needed three attempts to throw the books down. First, a book hit the camera stand. At second try, I lost my glasses and had to laugh. Third, I realized belatedly that I had moved the camera and cut off my own head. I then decided it will do, after all I don't want to win an Oscar. I also had a small disagreement with the video editing software and accidentally didn't save the file, so no more editing on that one. Stefan kindly said that the brightness correction of the camera which overreacted to passing clouds "adds drama."

In case you wondered, we had cushions on the floor and the books fell softly. For all I can tell they were not seriously injured.

Anyway, the biggest shortcoming is that I can't actually sing. Worse, I noticed somewhat belatedly that I particularly can't sing anything below the middle C. Somewhat surprisingly so, because I always thought my voice is rather deep for a woman. After two weeks or so of practice, I finally managed to hit the C#5 (at 2:04 min). Luckily our downstairs neighbor is on vacation and the upstairs neighbor doesn't hear well.

3 hours after uploading the video to YouTube I got a message saying they suspect a copyright violation, if I could please provide documentation that I have permission to use the song. A quite dramatic shift in procedure there.

Below the lyrics. I promise the next one won't be quite as serious ;o)

[Intro]
What do you know?

[Verse 1]
You know it all
So many things I do not understand
You know it all
The wrong and the right
You like to talk
So many items I had marked all read
Right or wrong
Hard to decide

[Verse 2]
I see the world
Neatly filtered for my Daily Me
I have it all
Too much and too fast
No need to see
So many things I do not want to see
We have it all
No time to ask

[Chorus 1]
What do you know?
I would appreciate some input here
What do you know?
Your conclusions are not clear to me
What do you know?
I could recommend some books to you
What do you know
We got a long way to go

[Verse 3]
Is it too much for you to watch
Is it finally enough
Do you follow, do you share
Do you listen, do you care
We know it all
So many things that we simply take for such
Who do you trust
And do you dare

[Repeat Chorus 1] 

[Interlude]
What do you know? I don't know.
What do you know? I don't know.

[Chorus 2]
What do you know?
The facts are not consistent with your claim
What do you know?
The assumptions that were used are not the same
What do you know?
I could recommend some books to you
What do you know
We got a long way to go

CERNland

Do you recognize the place?



It's the lawn in front of the CERN Cafeteria!

This lovely scene is the backdrop of a picture puzzle, and just one small part of CERNland, a cute interactive site for young kids to explore a bit about CERN, the place, the people working there, the experiments, and the physics background.

Thanks for the link, Sabine, it's really great (... OK, the sound is a bit tedious, to my ears at least, but that's what the volume control is good for).

Enjoy!

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Gallery of Fluid Motion

The motion of fluids can be surprising, beautiful, and sometimes just funny to watch. At its annual meetings, the Division of Fluid Dynamics of the American Physical Society organizes exhibits with stunning photographs and videos of fluid. Each year, awards are assigned to "photographs and videos [that] illustrate both experimental and numerical investigations of a wide variety of flow phenomena. Judged by a distinguished international panel of referees, winning entries were selected based upon criteria of scientific merit, originality, and artistry/aesthetic appeal."

Here is a winning entry from the Gallery of Fluid Motion 2008, chosen from the exhibition at the Annual Meeting of the APS Division of Fluid Dynamics in Salt Lake City last November (click on the still to get to the movie, requires some patience and Quicktime):

"BLACK HOLE" NUCLEATION IN A SPLASH OF MILK, by Laurent Courbin, James C. Bird, Andrew Belmonte, and Howard A. Stone: This video shows the impact dynamics of a millimeter-size drop of milk onto a superhydrophobic substrate that is spinning at a constant rate. (explanation as PDF file).

And here, a winning entry from the Gallery of Fluid Motion 2007 (Bee's absolute favourite):

CREEPING, WALKING AND JUMPING DROP by A. Renaudin, E. Galopin, V. Thomy, C. Druon, and F. Zoueshtiagh: This video shows the movement of a deionized water drop provoked by surface acoustic waves. (explanation as PDF file)

Don't be put off by the lengthy, silent-picture style explanations of the experimental setup at the beginning of the clips.

To see the amazing behavior of these drops rewards a little patience - enjoy!

German Citizenship Test

As previously mentioned, Germany has introduced a citizen test for immigrants. Spiegel Online now has the full version with 33 questions:

TAKE THE CITIZENSHIP TEST
Are You Smart Enough to Be German?

I got 32 right, I failed on the colors in the state flag of North Rhine-Westphalia. Outcome:

"Well done! You would have no problem getting a German passport."

I'm relieved to hear. Particularly nice the question:

Which of the following do Germans traditionally do at Easter?



• Leave pumpkins in front of the door
• Decorate a fir tree
• Paint eggs
• Let off fireworks

Hint: if you follow this blog, you know the answer.

They left out however some of the really important questions, here are my suggestions:

1. Besides being a citizen of Frankfurt, what is a 'Frankfurter'



• A: A bakery
• B: A sausage
• C: A flat tire
• D: A drink mixed of beer and lemonade

2. If a German says he will meet you at three-quarter eight (dreiviertel Acht), what does he mean?



• A: 8:45
• B: 8:15
• C: 7:45
• D: Any time between three quarter to and after eight, ie 7:15 - 8:45

3. What did the crowd chant on Nov. 9th '89 at the Brandenburg Gate?



• A: Lasst uns rein - Let us in
• B: Lasst uns raus - Let us out
• C: Wir sind der Staat - We are the state
• D: Wir sind das Volk - We are the people

4. If a Bavarian tells you to "Grüss Gott" - "Say hello to God", he means



• A: Thank you
• B: Hello
• C: Piss off
• D: I died and went to heaven

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(Answers: 1 - B, 2 - I don't know!, 3 - D, 4 - B)

PS to Canada Day

After you could recently test whether you qualify to be German, for Canada Day the Globe and Mail offers a similar questionaire "What's the score, eh?" to see whether you'd make a good Canadian/American. I scored 6/10 for both Canadian and American (mostly guessing though). Have fun!

Science Mugs

On Friday I came across Corie Lok's blog who announces the "Nerdiest Science Mug Competition" and offers a DNA strand with the names of faculty members. Brian Clegg adds a global warming mug, and Bob O'Hara contributes a mug from the Metapopulation Research Group (website). I can't quite keep up with so much nerdiness, but I found my mug from the String Pheno 2004 in my husband's kitchen. Here it is:



Looks like a black hole but if one fills in hot coffee it reveals...



A Calabi-Yau manifold. (Seems to be essentially the same picture as this.) And here is the backside, just for completeness.




My favourite mug is actually my PI mug, black and stylish.

So what's your nerdy mug? (Blogger doesn't allow images in the comments but you can leave links.)

Vampire Devices

This press release from the White House is almost seven years old, but I think it is worthwhile to mention that the President of the United States explained he does not wish to break basic laws of Nature like conservation of energy, and therefore wants to support vampire slayers.

"The President will challenge American businesses, both in their manufacturing decisions and in their purchasing decisions, to look to the vampire slayer as a means of conserving energy and saving money."

"Conserve your energy. That's the message I'm sending to Congress today," stated president Bush.

Sorry, couldn't resist. And yes, of course I'm all for energy saving, so stop laughing, it burns calories.

Flying Over Mars

Next Sunday, on May 25, the Phoenix Mars Mission is supposed to land on Mars.

In the meantime, here is fancy animation of a flight over the Columbia Hills on Mars, via the Astronomy Picture of the Day:



The animation, by Doug Ellison, Randolph Kirk (USGS), MSSS / MER / NASA, combines real topographical data from the Mars Reconnaissance Orbiter with information about the Spirit Mars Rover, making its appearance at 1:45 in the movie...

More about the Mars Exploration Rovers (MER) Spirit and Opportunity and Phoenix at the Planetary Society. The Planetary Society Weblog also has links to QuickTime versions of the movie.


Tags: Mars, Spirit, Phoenix

Fun with Magnets

Last week, my brother had started to tidy up a cupboard at our parent's place where we had stored away toys and other stuff from our childhood. In between chemistry and electronics kits, he dug out a small orange box I had completely forgotten about, but which I had loved when I was a small boy: A kit with a few magnets.

There was a magnet with a grip that can be used to lift coins and paper clips, two funny plastic spheres with bar magnets hidden inside, and two rings of magnetic material. The only thing missing was the little jar with iron filings to map out magnetic field lines - but I remember that my mother once had removed it from the kit, because she had become fed up with this stuff ending up either distributed all over the kitchen or sticking to the magnets.




These ring magnets were especially fascinating because one of them could be made hovering above the other on a pole, and oscillate along the pole when dropped.

The most surprising effect I could create with the oscillating magnets I had discovered by chance: I could use the magnets to switch off our new, remote-controlled TV set. Physics was cool!

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Here are more Cool Experiments with Magnets. Unfortunately, understanding the origin of the "itinerant ferromagnetism" of the classical permanent magnets, iron, cobalt, and nickel, is not that easy, but interesting nevertheless.

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Backboard

See the full photo here. Submitted by somebody called Alexis to Incredimazing, filed under the title How to Reform the US Educational System.

Let Me Entertain You

Spring finally arrived in Waterloo. Within a couple of days, the temperature rose by 15°C. The meters-high snow mountains in the yards and parking lots were slow with melting, and during the last days I could see the Canadians in T-shirts, shorts and flip-flops walking around the remaining snow piles. Meadows are little more than brownish mud, and there isn't yet a single leaf on the trees.

Some fun things I came across recently

• Another take on the future of the cellphone:
  
  
  
  [Thanks to Thomas]



• As a PS on the previous post on 'Models and Theories', I recommend this documentation of an experiment to test the hypothesis that one can't nail jelly to the wall. I'd say they should have paid more attention to the temperature dependence.



• You might want to check out this amazing collection of photos, which are the finalists for the Sony World Photography Award 2008.



• Quotation of the week:
  
  
  "And I find it kind of funny
  I find it kind of sad
  The dreams in which I'm dying
  Are the best I've ever had
  I find it hard to tell you
  'Cos I find it hard to take
  When people run in circles
  It's a very, very
  Mad World"
  
  
  ~Tears For Fears
  
  

The Elastic Mind

If you have some time to kill this weekend, browse the websites of the exhibition

"Design and the Elastic Mind"

in realitas at the MoMA in NYC, through May 12. According to the blurb: "The exhibition highlights designers’ ability to grasp momentous changes in technology, science, and history." It also explains "elasticity" is "the product of adaptability plus acceleration," thereby documenting a marvelous understanding of basic mathematics. But let us see how designers grasp the momentous changes.

There are for example the "Accessories for Lonely Men" by Noam Tora, electronic devices "designed to alleviate loneliness by simulating the—sometimes annoying—traces that one’s companion would normally leave behind", like the "Sheet Thief, which winds the bedclothes up on the other side of the bed while you’re sleeping".

James Auger and Jimmy Loizeau envision the "AfterLife Microbial Fuel Cell", which is "charged by the decomposed gastric acids of a dead loved one, can be engraved with an epitaph and can power a full range of electronic products", like for example a vibrator, as they suggest.

A group of British guys 'designs' a cellphone that delivers electric shocks if the person using it speaks too loudly and "disturb[s] others with their intrusive conversations".

A group of Australians wants to see pigs fly.

On the more serious side, there is James King, who considers the possibility that it will become possible to "grow edible meat in a laboratory from sample cells." Young Hyun, who presents a 3d visualization tool for directed graphs (called 'Walrus', for reasons that elude me), and Michael Burton who puts forward his Nanotopia, in which he argues that the advances in nanoscience might widen the gap between rich and poor: "While the upper classes might make the most of advances in bodily aesthetics and invent new cosmetic rituals, such as beguilingly long eyelashes, the poor might transform their bodies into farms “to cultivate desirable clinical and pharmaceutical products,” including stem cells developed from adipose (fat) tissue."

The website itself is a bit annoying, not only does it load a long time and is wider than the screen which makes vertical and horizontal scrolling necessary, it also beeps (I can't stand this). The color of links visited doesn't change, marked text isn't highlighted (one can copy and paste nevertheless, one just doesn't know exactly what), and the back button doesn't work, so you will have to use the 'Return' link. For even better readability I would recommend that next time they chose the text-color to be black on black ground, that would be optimally cool.

Nevertheless, it's fun, so check it out. A nice weekend to all of you!

Lost in Translation

Ever wondered what happens if you use an algorithm to translate a text back and forth to French, German, Italian, Portuguese, and Spanish? You can to this with the super-babelizer Lost in Translation. As an example, here is the translation of the first paragraph of 0801.3471 (for no specific reason).

The original:

Classical General Relativity in more than four spacetime dimensions has been the subject of increasing attention in recent years. Among the reasons why it should be interesting to study this extension of Einstein’s theory, and in particular its black hole solutions, we may mention that

• String theory contains gravity and requires more than four dimensions. In fact, the first successful statistical counting of black hole entropy in string theory was performed for a fivedimensional black hole. This example provides the best laboratory for the microscopic string theory of black holes.


• The AdS/CFT correspondence relates the properties of a d-dimensional black hole with those of a quantum field theory in d − 1 dimensions.


• The production of higher-dimensional black holes in future colliders becomes a conceivable possibility in scenarios involving large extra dimensions and TeV-scale gravity.


• As mathematical objects, black hole spacetimes are among the most important Lorentzian Ricci-flat manifolds in any dimension.

And the translation:

Traditional general of relativity in more than four masses of that the time of the space was the subject of the increase attention these the slipped years. To the relations of transformation, so that he had that to being interesting, to this extension of the theory of Einstein to study and in the detail of the relative solutions to perforate black color, that we can we mentioned this

• The theory of the series of the characters will count the force of the gravity and it more has the necessity of the one of mass four. They executed the first guessed right statistical client of the entropy of the black color that really perforates in the theory of the series of the characters the end to perforate the black color of the fivedimensional. This better example releases the laboratory available for the microscopic theory of the series of the characters of the black color of the perforations.


• The correspondence of AdS/CFT connects the characteristics of a D dimensional schwarzen that the sacadores with those with a theory of the zone of the section of the time in the D without mass 1.


• The production of the perforations that the high-dimensional-black color in her the future transforms of colliders inside the great possibilities imaginable ones into the writing of the suggestion adds of the film and in the fairs of TeV the force of the gravity.


• As matemati of the messages those we belong spacetimes of the black color that the sacadores to the tubes the greatest piece of the important Stocherkaehne I gave curly Lorentzian in each possible measurement.

I hope that clarifies everything.

Makes me wonder why there is no requirement these translation maps be invertible.

Hazardous Quantum Mechanics

Quantum mechanics is hazardous - make sure to wear a lab coat and protective goggles when handling delicate formulas!

(Found under the heading "Research" at academics.com, the online job market for higher-education professionals who are aiming to develop their career in Germany, Austria or Switzerland. I wonder what the operators of the web site know and think about their target group?)

10 effects you should have heard of

1. The Photoelectric Effect
   
   Light falling on a metal plate can lead to emission of electrons, called the "photoelectric effect". Experiments show, for this to happen the frequency of the light needs to be above a threshold depending on the material. This finding was explained in 1905 by Albert Einstein who suggested that the light should be thought of as quanta whose energy is proportional to the frequency of the light, the constant of proportionality being Planck's constant. Einstein received the Nobel Prize in 1921 "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."
   
   Recommended reading: Our post on the Photoelectric Effect and the Nobel Prize speech from 1921.
   



2. The Casimir Effect
   
   This effect was first predicted by Hendrik Casimir who explained that as a consequence of quantum field theory, boundary conditions that can for example be set by conducting (uncharged!) plates, can result in measurable forces. This Casimir force is very weak and can be measured only at very small distances.
   
   Recommended reading: Our post on the Casimir Effect and R. Jaffe's The Casimir Effect and the Quantum Vacuum.
   



3. The Doppler Effect
   
   The Doppler effect, named after Christian Doppler, is the change in frequency of a wave when the source moves relative to the observer. The most common example is that of an approaching ambulance, where the pitch of the signal is higher when it moves towards you than when it moves away from you. This does not only happen for sound waves, but also for light and leads to red- or blueshifts respectively.
   
   Recommended reading: The Physics Classroom Tutorial.
   



4. The Hall Effect
   
   Electrons in a conducting plate that is brought into a magnetic field are subject to the Lorentz force. If the plate is oriented perpendicular to the magnetic field, a voltage can be measured between opposing ends of the plate which can be used to determine the strength of the magnetic field. First proposed by Edwin Hall, this voltage is called the Hall voltage, and the effect is called the Hall effect. If the plate is very thin, the temperature low, and the magnetic field very strong, a quantization of the conductivity can be measured, which is also known as the quantum Hall effect.
   
   Recommended reading: Our post on The Quantum Hall Effect.
   



5. The Meissner-Ochsenfeld Effect
   
   The Meissner-Ochsenfeld effect, discovered by Walther Meissner and his postdoc Robert Ochsenfeld in 1933, is the expulsion of a magnetic field from a superconductor. Most spectacularly, this can be used to let magnets levitate above superconductors since their field lines can not enter the superconductor. I assure you this has absolutely nothing to do with Yogic flying.
   
   Recommended watching: Amazing Physics on YouTube.
   



6. The Butterfly Effect
   
   

   "A legendary butterfly flapping its wings in Rio changes the weather in Chicago. (I have lived in Chicago and personally suspect that nothing can change the weather there.) It always appears to be the same butterfly whenever anyone tells of this example. One would think it possible to imagine, by a vast conceptual leap, some other example. Maybe a moth in Omaha, perhaps, or a starling in Sheboygan. Whatever winged creature is responsible, the point is that any small change in a chaotic system can, and typically does, have large and amplifying effects. Thus this sensitivity implies that the detailed initial conditions - how fast, at what angle, and precisely how the starling flapped its wings - would have to be known to infinite precision to predict the result."

   
   
   ~ Stuart Kauffman, At Home in the Universe.
   
   



7. The Hawking Effect
   
   Based on a semi-classical treatment of quantum fields in a black hole geometry, Stephen Hawking showed in 1975 that black holes emit thermal radiation with a temperature inverse to the black hole's mass. This emission process of the black hole is called the Hawking Effect. This result has lead to a great progress in understanding the physics of black holes, and is still subject of research.
   
   Recommended reading: Black Hole Thermodynamics by David Harrison and P.K. Townsend's lecture notes on Black Holes.
   



8. The Zeeman Effect/Stark Effect
   
   In the presence of a magnetic field, energy levels of electrons in atomic orbits that are usually degenerated (i.e. equal) can obtain different values, depending on their quantum number. As a consequence, spectral lines corresponding to transitions between these energy levels can split into several lines in the presence of a static magnetic field. This effect is named after the Dutch physicist Pieter Zeeman, who was awarded the 1902 physics Nobel prize for its discovery. The Zeeman effect is an important tool to measure magnetic fields in astronomy. For some historical reasons, the plain vanilla pattern of line splitting is called the Anomalous Zeeman effect.
   
   A related effect, the splitting of spectral lines in strong electric fields, is called the Stark Effect, after Johannes Stark.
   
   Recommended reading: HyperPhysics on the Zeeman effect and the Sodium doublet.
   



9. The Mikheyev-Smirnov-Wolfenstein Effect
   
   The Mikheyev-Smirnov-Wolfenstein effect, commonly called MSW effect, is an in-medium modification of neutrino oscillation that can for example take place in the sun or the earth. It it a resonance effect that depends on the density of the medium and can significantly effect the conversion of one flavor into another. The effect is named after Stanislav Mikheyev, Alexei Smirnov and Lincoln Wolfenstein.
   
   Recommended reading: The MSW effect and Solar Neutrinos.
   



10. The Sunyaev-Zel'dovich Effect
    
    The Sunyaev-Zel'dovich effect, first described by Rashid Sunyaev and Yakov Zel'dovich, is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which some of the energy of the electrons is transferred to the low energy CMB photons. Observed distortions of the cosmic microwave background spectrum are used to detect the density perturbations of the universe. Dense clusters of galaxies have been observed with use of this effect.
    
    Recommended reading: Max Planck Society press release Crafoord Prize 2008 awarded to Rashid Sunyaev and The Sunyaev-Zel'dovich effect by Mark Birkinshaw.
    



11. Bonus: The Pauli Effect
    
    Named after the Austrian theoretical physicist Wolfgang Pauli, the Pauli Effect is well known to every student of physics. It describes a spontaneous failure of technical equipment in the presence of theoretical physicists, who should therefore never be allowed on the vacuum pumps, lasers or oscilloscopes.
    
    Recommended reading: Our post Happy Birthday Wolfgang Pauli.

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TAGS: PHYSICS, EFFECTS

How the Easter Bunny gets its Eggs

As every child in Germany knows, before and around Easter, hares are extemely busy, because they have to colour thousands of eggs and to hide them carefully in the gardens and woods, often together with chocolate eggs and chocolate bunnies.



Spoiler warning: Plot and/or ending details follow.

I do not remember at which age I become aware that the eggs my brother and I went searching on Easter morning had actually been coloured by my father the night before. But colouring eggs has been a traditional thing to do ever since in our family the night before Easter.

You just start by hard-boiling a dozen of eggs for about 8 to 10 minutes - best use a large pot, and give plenty of salt in the water to avoid premature breaking of the shells. While the eggs are boiling, prepare cans with the colourant. The dye my father has always been using comes in small tablets, which are dissolved in a mixture of hot water and vinegar.


The boiled eggs are put, still hot, in the colour bath, and let there for about five minutes each. There are several other methods to colour eggs, for example with "natural" colourants from plants, or with colourants for use with cold water. But, as a long experience shows, this procedure really works best and gives the most satisfactory results.


Once the eggs are coloured, you can rub them with some bacon rind to give them a nice, shiny finsish. Voilà!

All that remains to do: hide them! But try to make sure that you will find them again before next Easter.

Happy Easter!

Experimental Traffic Jams

You may have already come across this nice movie of a large-scale physics experiment:


From Traffic jams without bottlenecks—experimental evidence for the physical mechanism of the formation of a jam by Yuki Sugiyama et al., New J. Phys. 10 (2008) 033001 (including movies).

If ever you have been driving on a crowded highway, chances are high that you have taken part in a similar "experiment", just that no one has captured it on film and put it on YouTube. This happened to me last Monday on my way to work: First, I got stuck in a traffic jam at the merging of three lanes into two - no wonder in rush-hour traffic. But then there was a second full stop, a few kilometres down the road, and for no obvious reason at all - no construction site, no junction, no accident... it was the classical phantom traffic jam.

This kind of annoying phenomenon occurs on roads with a steady traffic flow if the distances between cars become too small: As soon as a car slows down a bit for whatever reason, the following car must break also, and so on. And because drivers are humans and have a reaction time, they break ever later, and ever stronger, and at one point, they come to a full stop. This stop then moves "upstream", in the opposite direction of the traffic flow - it's a shockwave-like phenomenon that has been intensively studied by German physicists since the 1990s.

But it seems that no one so far has checked the models that describe the phantom jams in a controlled fashion, and so, the Japanese guys have set up an experiment: Take 22 cars, put them on a road, and tell the drivers to go on at a constant speed. As so often in physics, periodic boundary conditions are a useful trick to simulate a much larger system - the cars are driving on a circular track. It doesn't take long before the shockwave develops.

Here is a chart, taken from the paper, that shows the evolution of the flow of the cars:



The horizontal axis shows distance along the circular track, the vertical axis indicates time. The lines trace the paths of each of the 22 cars. The flatter the line, the higher the speed, and a vertical segment of the line means halt. One can see how a perturbation of the steady flow set in after just 40 seconds around metre 150 of the track. At closer inpection, the culprit seems to be a car that was a bit slower than the others for a while. Speeding up (the kink in the orange circle) doesn't help - the following cars have to break, and the phantom traffic jam can't be avoided anymore. The plot shows nicely how the perturbation - the zone of zero velocity (aka the jam) - travels at constant speed in the direction opposite to the traffic flow.

Too bad - phantom traffic jams just happen, it's all physics...

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• The short paper about this experiment by the Japanese group (Traffic jams without bottlenecks—experimental evidence for the physical mechanism of the formation of a jam, New J. Phys. 10 (2008) 033001) is available as open access. The text is understandable also to non-physicists! And there is a second movie, showing a bird's eye perspective of the developing crisis.


• Modern understanding of phantom traffic jams started with the papers Cluster effect in initially homogeneous traffic flow by B. S. Kerner and P. Konhäuser, Phys. Rev. E 48 (1993) R2335 - R2338, and A cellular automaton model for freeway traffic by Kai Nagel and Michael Schreckenberg, J. Phys. I France 2 (1992) 2221-2229. A detailed review is Traffic and Related Self-Driven Many-Particle Systems by Dirk Helbing, Reviews of Modern Physics 73 (2001) 1067-1141, cond-mat/0012229.


• Here is a collection of great Java applets which show the emergence of phantom jams in simulations (by Martin Treiber, Technical University Dresden).

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TAGS: physics, traffic jam, self-organization

PI day Captcha

From Quantum Random Bit Generator Service via mathlog and wiskundemeisjes.

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Captcha: "Completely Automated Public Turing test to tell Computers and Humans Apart".

PI Day, recycled.

Lunar Eclipse from Mauna Kea

Skies over Frankfurt had been covered with thick rainclouds two weeks ago, and so I had missed the Lunar Eclipse of February 20/21. But never mind - here is a photo of that event, the most awesome photo of a Lunar Eclipse I have ever seen:


Astronomy Picture of the Day, 2008 March 1; Credits & Copyright: Alex Mukensnable.

The photo was taken from top of Mauna Kea, Hawaii, in the evening of February 20, local time. The total eclipse of the Moon was already over. The Sun was just setting in the West, casting the shadow of the volvano on the haze of the Eastern horizon. And there, the Moon was rising, just leaving the shadow of the Earth. Indeed, the shadow of the Earth is a disk, "fixed" below the shadow of the tip of Mauna Kea, which at this very moment actually is just a small bump at the border of this disk. And can see the outline of this shadow, because it still covers large parts of the the Moon, some 400,000 kilometres away.

The photo is part of a most amazing video Alex Mukensnable has made of this special Moonrise on February 20 - check it out!

Thanks to The Ridger from thegreenbelt for the link!