Physicists Quantify the 'Coefficient of Inefficiency'

One of the skill one learns as a physicist is to tackle a problem systematically, and to quantify it, if possible, by making an effective, accurate model of the system. This problem doesn't have to be in physics. It can be anything. I mentioned earlier of someone who tried to find the most optimum way to load an airplane, simply because he became curious after observing how an airplane is typically boarded. Well, this is a similar problem.

Three physicists from the University of Vienna examines the efficiency of committees in making a decision in terms of the number of people that makes up the committee.

To understand why, Thurner and fellow physicists Peter Klimek and Rudolf Hanel turned to the British historian C Northcote Parkinson, who studied how the British Navy was once administered. Parkinson, who died in 1993, discovered a strong correlation between a committee’s ability to make a good decision, and its size. In particular, Parkinson found that committees with more than about 20 members are much more ineffectual at making decisions than smaller groups — something he dubbed the “coefficient of inefficiency”.

You can read the preprint of the paper from a link given in that article. It is a clever way to quantify and model this problem. Now if only people who form such committees would pay attention to it.

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Death For Phonons In High-Tc Superconductors?

This is a highly interesting and certainly provocative result.

Remember I posted a while back on the "kink" observed in the angle-resolved photoemission spectra (ARPES) on high-Tc superconductors? There have been a continuing debate since the kink was observed on the origin of this observation. Two leading candidates are the coupling of the charge carrier to a spin fluctuation mode, and a coupling to the phonons.

Now two separate theoretical papers have calculated the coupling to the phonon modes and have arrived at the conclusion that such coupling cannot account for the strength of the kink observed in ARPES spectra.

In recent years, despite mounting experimental evidence against it, some physicists have clung on to this interpretation. But now teams from Germany and the US have performed calculations to suggest that lattice vibrations in cuprates can at best account for just a small fraction of the materials’ superconducting behaviour.
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Manske’s team found that the theoretical energy–momentum relationship produced by these calculations did contain a kink — but about a three to five times smaller than the 2001 observations (Phys. Rev. Lett. 100 137001). This is bad news for physicists who have been hoping phonons can account for all of the behaviour of high-temperature superconductors. “It is embarrassing for people to admit they have worked on something for 20 years if it is not true,” jokes Manske.

Meanwhile, Steven Louie and colleagues at the Univerisity of California in Berkeley have come to a similar conclusion with the cuprate LaSrCuO4. From their calculations, the phonon contribution is almost an order of magnitude too small for the observed kink (Nature 452 975).

This could be rather devastating to the phonon picture. If this is true, the two new results still cannot account for the origin of superconductivity, but at least they have eliminated a red herring. Still, all this could be moot if an earlier report is true about the absence of any kind of "glue" in the mechanism for high-Tc superconductors.

So stay tune. The story is by no means over, and the fat lady hasn't even warmed her vocal cords yet.

Traffic Jams Happen, Get Used to It

I've heard about this research study, but I didn't pay that much attention to it until I saw that they had a video of this effect that was rather neat. It also confirms what I had suspected for a while.

The study was done by a group of Japanese scientists/mathematicians about traffic jams that happened without any bottleneck[1]. In other words, there's no obvious obstacles, such as an on-ramp, or a constrictions, etc. that would be obvious causes for a traffic jam. All they did was increase the traffic density, and at some point, there's some "critical density" in which traffic jams simply occurs because people just don't all drive at the same speed.

What is need is that you can actually this taking place in the video that they have included. I've always suspected this. I drive roughly 31 miles each way to work every day. I sometime get stuck in a couple of slow spots where traffic either slows down or stopped for periods of time. Yet, as you you drive some more, you speed back up again as if nothing has happened, and you don't see any reason why the traffic slowed down. I tend to blame it on slow cars in the left lane, but I had no proof that was the usual cause. Now, I have some evidence to back my haunch! :)

Zz.

[1] Y. Sugiyama et al., New Journal of Physics v.10 p.033001 (2008).

The Science of Tangled Cord

Next time you have to untangled the cords from your electronics, you can at least think of it as a complicated physics process. :)

This news article describes a recent PNAS paper on this very issue.

Knot formation had been studied a lot by mathematicians, but not much by physicists. Smith was worried that the work wouldn't be taken seriously, but it ended up being published in the prestigious Proceedings of the National Academy of Sciences.

"The way that you get a knot is the string has to bend back on itself, coil back on itself," Smith said. As a string or cord tumbles, the end of it has a 50 percent chance of weaving to the left or the right of the coils, and under or over the coils, sort of like random braiding, Smith said.

The exact citation for this paper (which none of these popular newspapers ever give) is:

Dorian M. Raymer and Douglas E. Smith, PNAS v.104, p.16432 (2007).

Don't get all tied up with it.

:)

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When Superconductivity Became Clear (to Some)

I mentioned last October (2007) of the conference being held at UIUC to commemorate the 50th Anniversary of the BCS Theory of Superconductivity. Well now the NY Times has an article related to that, and includes a delightful anecdotal history on how Bardeen recruited Cooper to come to UIUC to work on the superconductivity problem. I think most people are not aware that some of the giants in physics at that time had tried to solve the superconductivity problem and failed!

After wrapping up special and general relativity, Albert Einstein tried, and failed, to devise a theory of superconductivity. Werner Heisenberg, the physicist who came up with the Heisenberg uncertainty principle, struggled with the problem, as did other pioneers of quantum mechanics like Niels Bohr and Wolfgang Pauli. Felix Bloch, another thwarted theorist, jokingly concluded: Every theory of superconductivity can be disproved.

You seldom hear in any of Einstein biography of him dabbling in trying to solve this.

This is a terrific story. Don't miss it.

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The Physics Behind Four Amazing Demonstrations

Skeptical Enquirer has listed 4 amazing demonstrations and gave each one of them a plausible and reasonable physical explanation. This should be quite handy if you ever encounter anyone using any of them as "proof" of some supernatural phenomenon.

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Schrodinger's Kittens Enter The Classical World

This is a rather fascinating angle on the quantum to classical transition. The traditional explanation on the cause of the difference between quantum world and the classical world is the onset of decoherence, where the system interacts with its environment. That interaction with the large degree of freedom causes the emergence of our familiar classical world. We have seen several experiments that showed that the onset of such decoherence gave us back the familiar classical description. In fact, it has been shown that even with just ONE interaction, a single-particle system can quickly lose its quantum coherence.

However, a new theoretical research has taken a different angle. Two physicists in Austria has published a paper[1] showing that the emergence of classical observation can be also be obtained without having any decoherence effect, but rather due to the "coarse-grained" measurement that we make. A review of this work was reported in Nature Daily News (the link may be available for a limited time and may require registration and/or subscription).

Johannes Kofler and Časlav Brukner of the University of Vienna and the Institute of Quantum Optics and Quantum Information, also in Vienna, say that the emergence of the 'classical' laws of physics, deduced by the likes of Galileo and Newton, from quantum rules happens not as objects get bigger, but because of the ways we measure these objects. If we could make every measurement with as much precision as we liked, there would be no classical world at all, they say.

We know that "size" isn't the issue here, especially with the recent SQUID experiments of Delft and Stony Brook. However, the conventional thinking is that the larger the size, the more difficult it is to maintain coherence of all the parts of the system. What the new approach here has tried to explain is that with the larger size, the precision of our measurement also tends to get worse. Unfortunately, their proposal to measure and detect the quantum effects on large system appears to be rather daunting, if not almost-impossible.

Kofler says that we should be able to see this transition between classical and quantum behaviour. The transition would be curious: classical behaviour would be punctuated by occasional quantum jumps, so that, say, the compass needle would mostly rotate smoothly, but sometimes jump instantaneously.

But watching such quantum jumps between life and death for Schrödinger’s cat would require that we be able to measure precisely an impractically large number of quantum states. For a 'cat' containing 1020 quantum particles, say, we would need to be able to tell the difference between 1010 states – too many to be feasible.

Still, I wouldn't put it past some experimentalists coming up with an ingenious way to test this.

Zz.

[1] J. Kofler and C. Brukner, Phys. Rev. Lett. v.99, p.180403 (2007).

Do Classical Laws Arise From Quantum Laws?

This is a timely subject, since the issue of "decoherence", and how far quantum laws can be extrapolated into our classical world seems to be the topic of discussion on here (see comments from the last few blog entries).

Physicists from Austria have formulated a theoretical scenario in which QM laws are the underlying physical description of the classical world that we see today.

“Our motivation is to understand how the classical world comes out of quantum physics,” Kofler says. “The established approach in research is decoherence where one has to take into account the complexity of systems and interactions with environment.” It is interaction with the environment that brings decoherence into play, destroying quantum coherences and making it impossible to observe quantum phenomena. “We believe we found a process complementary to decoherence which can explain the quantum-to-classical transition.”

The exact reference to the paper is as follows:

Johannes Kofler and Časlav Brukner, "Classical World Arising out of Quantum Physics under the Restriction of Coarse-Grained Measurements", Phys. Rev. Lett. 99, 180403 (2007).

Again, many people who don't understand this think that QM phenomena can be easily extrapolated, and used in mystical ways to explain human behavior, our world, etc. They can't! QM phenomena are not easy to find. If it is, we would have seen it already and won't have to wait till about 100 years ago in human civilization to formulate it! And not only that, QM effects are difficult to maintain because a system can interact so easily with its environment, destroying the coherence that is necessary to preserve such quantum phenomena.

So stop it already!

:)

Zz.

The Kondo Effect

I was 'trolling' around the 'net looking for a few articles when I came across this article on the Kondo effect. This is where the resistivity of a certain type metal, as you lower the temperature, suddenly shoots up, which is not what is expected. This phenomenon was discovered in the 1930's, and was explained by Jun Kondo in the 1960's.

What is fascinating here is that this is, as far as I know, the first example of an "asymptotic freedom" in nature that was discovered. This, of course, was waaaaay before the same type of description was applied to the strong interaction in elementary particles. It reinforces my view earlier that there are many aspects of condensed matter physics that actually are extremely important and "fundamental". Peter Higgs, in fact, clearly confesses to getting his idea about the Higgs mechanism out of condensed matter. So these are just a few of the examples where this field actually has a huge and significant contribution to fundamental knowledge. It isn't just an "applied physics" field, even though it is responsible for the understanding of properties of materials that we use.

I just wish many students that are going "ga-ga" over String theory and particle physics would realize this.

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Scientists Discover Possible Cosmic Defect, Remnant From Big Bang

Scientists may have discovered "texture", cosmic defects in the vacuum structure that is a remnant of the Big Bang.

“Our work investigates the exciting possibility that the cold spot is due to the presence of a cosmic texture; some current particle physics theories predict textures to be produced as the universe evolves, but they had never been observed. Somewhat to our surprise, we found that the cold spot, and in fact the cosmic microwave background radiation over the whole sky, is indeed consistent with such a texture model. Although the current data are not yet compelling, we suggest future observations that should be able to test our hypothesis definitively. If the cold spot is indeed proven to be a texture it will completely change our view of how the universe evolved following the Big Bang.”

If this is true, another consequence of the Big Bang is verified.

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Mpemba Effect

I first read about the Mpemba effect when I was reading through Jearl Walker's fun book "The Flying Circus of Physics". This is the effect where warm water freezes faster than cold water. It was thought to be simply an old wives tale, but this effect turns out to be real.

What amazes me is the amount of published work that has resulted in trying to come up with a qualitative and quantitative explanation of this effect. In fact, one just appeared on the e-print ArXiv this morning, which was the impetus for me to report on this effect.

So these 3 preprints (some may have been published) should provide quite a fascinating description of this intriguing effect.

http://arxiv.org/abs/0704.1381
http://arxiv.org/abs/physics/0604224
http://arxiv.org/abs/physics/0512262

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Superluminal Tunneling?

There have been claims made now and then of an apparent superluminal signal occuring in quantum tunneling process. Of course, quacks like to jump all over something like this and going off into their own laa-laa land to come up with their outlandish theories.

However, the issue isn't as simple, and in fact, could be explained via re-examining on what actually is being timed during tunneling. Several publications have dealt with such a thing. See the list below:

H. Winful, PRL v.90, p.023901 (2003)
M. Buttiker and S. Washburn, Nature v.422, p.271 (2003)

The most recent comprehensive treatment of this issue was published by H. Winful, where he again expanded upon his PRL paper and explained away the apparent superluminal paradox in various tunneling phenomena.

H. Winful, Phys. Rep. v.436, p.1 (2006).

Of course, this may not sit well with some people, and I'm sure there will be a lot more being discussed about this. However, the point here is that claims of superluminal tunneling is far from convincing.

Zz.

More on Schrodinger Cat

I pointed out earlier of several references regarding the new development and results related to the Schrodinger Cat-type phenomenon. I left out Leggett's article in Physics World from a while back after the Stony Brook/Delft experiments were reported. So if you haven't read it yet, here it is.

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