Tuesday, July 22, 2014

Big Mystery in the Perseus Cluster

The news about the x-ray emission line seen in the Perseus cluster that can't be explained (yet) by current physics.



The preprint that this video is based on can be found here.

Zz.

Monday, July 21, 2014

Angry Birds Realized In A Classroom Experiment

If you can't get kids/students to be interested in a lesson when you can tie in with a favorite game, then there's nothing more you can do.

This article (which you can get for free) shows the physics and what you will need to do water balloon launcher to teach projectile motion. It includes the air drag factor, since this is done not in the world of Angry Birds, but in real life.

Abstract: A simple, collapsible design for a large water balloon slingshot launcher features a fully adjustable initial velocity vector and a balanced launch platform. The design facilitates quantitative explorations of the dependence of the balloon range and time of flight on the initial speed, launch angle, and projectile mass, in an environment where quadratic air drag is important. Presented are theory and experiments that characterize this drag, and theory and experiments that characterize the nonlinear elastic energy and hysteresis of the latex tubing used in the slingshot. The experiments can be carried out with inexpensive and readily available tools and materials. The launcher provides an engaging way to teach projectile motion and elastic energy to students of a wide variety of ages.

There ya go!

What I like about this one than the common projectile motion demo that occurs in many high school is that there is quite a careful thought being given to the physics. One can do this as simple as one wants to, or ramp up the complexities by including factors that are not normally considered in such situation.

Zz.

Friday, July 18, 2014

The Physics Of A Jumping Articulated Toy

Some time, it is just a pleasure to read about something that isn't too deep, and it is just fun!

This paper on EJP (which is available for free) describes the physics of a jumping kangaroo. The toy makes a complete sommersault as shown in the photo and in the video.

Abstract: We describe the physics of an articulated toy with an internal source of energy provided by a spiral spring. The toy is a funny low cost kangaroo which jumps and rotates. The study consists of mechanical and thermodynamical analyses that make use of the Newton and centre of mass equations, the rotational equations and the first law of thermodynamics. This amazing toy provides a nice demonstrative example of how new physics insights can be brought about when links with thermodynamics are established in the study of mechanical systems.

The authors may want to impart some deeper physical insight into understanding this, which may be true. But I like to take this just on face value. It is just a fun toy and a fun look at how it does what it does.

Zz.

Thursday, July 17, 2014

Three US Dark Matter Projects Get Funding Approval

The US Dept. of Energy and National Science Foundation have jointly approved the funding of three dark matter search projects. These projects were selected based on the recommendation of the P5 panel, which released its report earlier this year.

Two key US federal funding agencies – the Department of Energy's Office of High Energy Physics and the National Science Foundation's Physics Division – have revealed the three "second generation" direct-detection dark-matter experiments that they will support. The agencies' programme will include the Super Cryogenic Dark Matter Search-SNOLAB (SuperCDMS), the LUX-ZEPLIN (LZ) experiment and the next iteration of the Axion Dark Matter eXperiment (ADMX-Gen2). 

Certainly, with High Energy Physics funding in the US being squeezed and shrinking each year, this is the best outcome on funding for the search of dark matter experiments.

Zz.

Tuesday, July 15, 2014

Quantum Criticality Experimentally Confirmed

A new experimental result has confirmed quantitatively the presence of a quantum critical point.

The researchers experimentally confirmed the predicted linear evolution of the gap with the magnetic field, which allowed them to pinpoint the location of the quantum critical point. At the critical field, the observable is expected to display a power-law temperature dependence, another hallmark of quantum criticality, with a characteristic power of -3/4 in this case—precisely what they observed. Even more, a rigorous experimental analysis allowed them to estimate the prefactor to this behavior, which they found to correspond nicely to the theoretically predicted one. And finally, they observed this behavior to persist to as high a temperature as almost half of the exchange coupling, which sets the global energy scale of the problem. This answers an essential question about how far away from the absolute zero temperature quantum criticality reaches or how measurable it really is. The experiment constitutes the first quantitative confirmation of the quantum critical behavior predicted by any of the few existing theories.

Nice! Not surprisingly (at least, not to me), the clearest confirmation of this exotic quantum phenomenon is first found in a condensed matter system.

A few background reading for those who want to have more info on quantum criticality can be found here and here.

Zz.

Thursday, July 10, 2014

Stephen Hawking By The Numbers

It's strange that someone, or some organization, would keep such a statistics, but here they are. I found a website that compiled a bunch of "interesting" stats about the life of Stephen Hawking so far.

1 Word Per Minute

The rate at which Hawking currently communicates by moving his cheek muscles to express one letter at a time.

1,000

The number of hours that Hawking estimates he spent studying in three years at the University of Oxford, where he found the course work “ridiculously easy.”

21 

The age at which Hawking begin to experience the symptoms of ALS.

2

The number of wives Hawking has had.

1984 

The year Hawking completed A Brief History of Time, his first work for the general public, which he wrote to help pay for his three children’s education expenses.

1990

The year that Hawking left his first wife, Jane, for one of his nurses, Elaine Mason, whom he later married and divorced.

237

The record number of weeks A Brief History of Time stayed on the Sunday Times’ bestseller list.

10 million

The number of books Hawking has sold (“I have sold more books on physics than Madonna has on sex,” he bragged).

25 seconds

How long Hawking escaped gravity and the confines of his wheelchair in 2007 when he became the first person with a disability to fly on one of the zero gravity flights offered by Zero Gravity Corp., a space tourism company.

2011

The year that Hawking pronounced (a) that “philosophy is dead” at Google’s Zeitgeist Conference and (b) that heaven is a “fairy story” for people afraid of death.

The media and public fascination on Hawking continues....

Zz.

Tuesday, July 08, 2014

Physicist Untangles The Mystery Of Tangled Earbuds

Does it really take a physicist to actually "solve" this?

If you have earbuds, or in-ear headphones, you know that sooner or later, they get tangled up. It appears that a visiting physicist in Aston University in Birmingham, England has a mathematical theory on how it happens, and proposes a way to store the darn thing without it tangling.

Matthews’ years of study suggest that clipping the two earbuds together, then attaching them to the end near the audio jack to form a loop, will cause a tenfold reduction in knot formation. 

“First, by forming the loop you've effectively reduced the length of string able to explore the 3D space by 50 per cent, which makes a big difference.” Matthews said. “Second, you've also eliminated the two ends, which are the prime movers of knot formation.” 

Unfortunately, as is a common practice in the popular media, they didn't cite source or if this has been published, or submitted for publication. Heaven forbid, a reader of their website would actually want to look it up and study this closer than beyond their superficial reporting.

Addendum. The Daily Mail has a bit more to say about this than the above website.

Zz.

Monday, July 07, 2014

Topological Insulators

In case you missed it and are interested in this area, this is a review article, which happens to be a chapter in a book, on "Topological Insulators, Topological Crystalline Insulators, and Topological Kondo Insulators". This is not meant for non-experts because it reviews the current understanding of this family of material.

Zz.

Friday, July 04, 2014

Quantum Physics In Your Daily Lives

I initially thought that this Newsweek article was reporting something new that had been discovered in quantum mechanics that had some serious applications. But it turns out that it was more of an article that quite clearly described all the practical advances that came out of QM.

At the most basic, almost everything we do is grounded in quantum physics—matter (all of it) is a collection of quantum particles, while light, electricity and magnetism are all quantum phenomena. At the next level are the quantum technologies we humans built without being aware of the physics that made them possible. When Swan and Edison produced electric lightbulbs, they didn’t know that light generated from a heated filament is a quantum process—they ended up implicitly drawing on quantum physics without even knowing it.
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It only takes a few minutes analyzing a smartphone to realize the pervasiveness of quantum technology. To start, quantum physics is required to construct any solid-state electronics—every chip inside your iPhone is packed full of quantum devices like transistors and has to be designed to encompass the peculiar quantum behavior of electrons. On top of that, your phone has a computer, display, touch interface, digital camera, light-emitting diode and global positioning system receiver—each developed as a result of our understanding of the field.

As I've always tried to convey, physics is more than just the LHC and string theory. It is also your iPhone, your MRI, your GPS, etc. A lot of people often hear about the exotic properties and consequences of QM without realizing that it works, and that they are using it! So this is a good article to give anyone who is ignorant about this.

Zz.

Thursday, July 03, 2014

Why She Won't Be Studying Physics At The A-Level

This is an essay by a very articulate young lady in the UK (assuming that what was written is true) on why she won't continue to study physics for her A-Level exams.. While it may be towards the UK educational system, I can't help thinking that this is more common than we think.

To me, GCSE physics seemed out of touch compared with the stem cells and glucoregulation we were studying in biology. I could see the practical reasons for studying biology, but I found physics hard to relate to my everyday life.

All too often, the link from theory to human application was missing from the physics syllabus, making me wonder when I would ever need to calculate the half-life of a radioactive sample or describe the retrograde motion of Mars outside of the exam hall.

When I used to teach intro physics, at almost every new topics that we were about to start, I spend a few minutes just giving the students an overall picture of what it is, what we will be doing, where such knowledge is applied, and why we are going to study it. It isn't very long, but I know a few students had commented that they like being given the "big picture" and were able to know how things fit in. As physicists, and educators, we often  forget that students do not usually get the big picture, and that it is difficult for them to see how trying to find the electric field inside a conducting sphere would matter, or finding the exact angle of a projectile to hit a monkey when it jumped off a tree. We should spend some time explaining and justifying to the students why they are being made to learn these things, and what are the potential benefits of doing such exercises. It may not always get them to enjoy doing it, but at the very least, they understand that we do not ask them to do this for no rational reason.

Teaching someone to use a screw driver, or a drill, without telling that person what that screw driver and that drill can be used for, or that the skill in being able to efficiently used a screw driver and a drill might be of some benefit, will diminish the interest in learning how to use those tools. And obviously, in this case, it might even turn some student off from learning it entirely. I just wish that this student would have opened more advanced text in physics where many relevant applications and connections have been made to real-world issues. Even the infamous Halliday/Resnick text now devotes ample space to such description. And certain, Muller's text "Physics for Future Presidents" amplifies the importance of having a population that is knowledgeable in basic physics and can make analytical decisions on many important issues.

There are things we can do, as educators, to rectify the problem stated in this article. We do not have to wait for some school board, or examination board, to wake up and realize the shortcoming of the education system.

Zz.

Wednesday, July 02, 2014

Many-Body Quantum Fluctuations In Residual Resistivity Of Metals

As a condensed matter physicist by training, the issue of charge transport in matter has always been a topic that I encounter often, especially when I was doing my postdoc many, many years ago. While the physics of charge transport in metals, under "ordinary" situations, can be adequately described by the Drude model, resulting in, for example, the beloved Ohm's Law, there are many other situations where such a simplistic model just doesn't work. And in those situations, that is where the physics gets very interesting and can be quite complicated.

The factors that influences charge transport in matter depends very much on how a charge carrier scatters. So the scattering rate determines the properties of resistivity/conductivity, etc. In a metal, there several types of scattering: electron-phonon scattering, electron-impurity scattering, and electron-electron scattering.[1] The dominant term that has a strong temperature dependence is the electron-phonon scattering, which is the primary mechanism that determines the resistivity of a metal. The electron-electron scattering has a weaker temperature dependence, while the electron-impurity scattering is mostly temperature independent.

What this means is that, as we lower the temperature, at some point, the electron-phonon scattering "freezes out", and no electron-phonon scattering contributes to the resistivity. The resistivity will then be a function of predominantly the electron-electron contribution. As the temperature approaches 0 K, one will notice indication that the resistivity will not be zero. This is the residual resistivity, whereby even at 0 K, there will still be a net resistivity of the material that is due to electron-impurity scattering. Note that this "impurity" need not be foreign atoms that are not part of the material. It can also be crystal defects and deformation that interrupts the long-range order of the crystal structure of the metals. The charge carriers can scatter off these defects as well.

That is how we were taught in solid state courses. we often deal with charge transport using the Boltzmann transport equation, and treating this within the Drude model The full quantum mechanical treatment, via the Kubo formulation, is a BEAST, and often unsolvable.

But now, along comes a new theoretical treatment of charge transport in metals, using DFT, that arrived at a rather unexpected result.[2] The new treatment showed that there is a strong contribution to the electron-impurity scattering due to the electron-electron many-body effects. The electron-impurity scattering is not as simple as we thought. They showed how well this new explanation matches the residual resistivity measured for aluminum.

This is another example where, something that we know very well and for a long time, can often reveal new physics and information when it is examined at the very edge of the boundary of our knowledge. We subject many of our ideas to the extreme case (in this case, very close to 0K) to see how well they work in those situations. It is one of the ways we expand the boundary of our knowledge.

Zz.

[1] see http://arxiv.org/abs/cond-mat/9904449
[2] http://physics.aps.org/articles/v7/70