Physics

Imagine diving into the placid surface of a painting by Vermeer, parsing apart Klimt's bejeweled surfaces, or untangling Jackson Pollock's knots of paint. Art historians, collectors, and restoration scholars have long sought to uncover the methods of great painters. Over the past decade, scientists have peered with light beneath the varnished surface of paintings to discover the chemistry of pigments, to identify the authors of unsigned works, or probe the crack depths from damage or age. Now, researchers at the University of Barcelona in Spain have used light at terahertz frequencies to uncover the hidden carbon signature of a painting previously thought to be unsigned. Though unsigned, the painting has been studied by art historians and confirmed to be painted by the Spanish artist Goya in 1771. Such secondary validation made the piece an apropos choice by the researchers, who published their findings May 14, 2013 on the arXiv. "Sacrifice to Vesta" at three different levels of imaging at visible and THz frequencies. Image Credit: http://arxiv.org/abs/1305.3101 Nested between the infrared and microwave regimes, terahertz radiation can travel through materials like plastic or canvas and bounces back slightly differently depending on the chemical composition of each paint color. To analyze the Goya piece, the researchers parsed the painting into 1 millimeter squares and recorded the reflected terahertz wave from each square, obtaining images with millimeter resolution. To analyze the structure of the painting -- essentially how the paint was laid on the canvas -- the researchers looked at the shape of the reflected wave. At each layer of paint, the reflected wave registered a unique bump. This kind of so-called structural data enabled the team to reveal features of the painting hidden beneath layers of paint. Through the structural analysis, the scientists found new textures beneath the painting's veneer. They were able to uncover the thickness of paint strokes, the order of the layers of paint, and even wrinkles in the canvas from pigment deterioration, or mechanical tension on the canvas. Then, at the very bottom of the painting, the team found a signature. Blind to the visible eye, to X-ray, and to infrared analysis, the researchers identified what they believed to be Goya's signature in the image created by the terahertz reflections. The researchers report that the signature was likely written with a pencil. They suggest that, over the years, the top coat of varnish darkened and obscured the carbon signature. They write that the signature might be missing in 2007 X-ray studies of the painting because carbon has a very similar atomic weight to that of the canvas and paint pigments, leaving the X-ray imaging unable to distinguish between the materials. Identifying chemical compositions of paint pigments and other paint media remains an area the researchers hope to explore. In their study, the team found that some pigments reflected terahertz waves more than others. They speculated that these have a higher metallic content leading to higher reflectivity. In the future, the researchers imagine that the creation of a pigment spectroscopy database could enable artists, restorationists, and historians to study the detailed chemical compositions of paintings.

Dianlou Du and Xue Geng In this paper, the relationship between the classical Dicke-Jaynes-Cummings-Gaudin (DJCG) model and the nonlinear Schrodinger (NLS) equation is studied. It is shown that the classical DJCG model is equivalent to a stationary NLS equation. Moreover, the standard NLS equation can be solved by the clas ... [J. Math. Phys. 54, 053510 (2013)] published Fri May 17, 2013.

A new technique for powering medical implants wirelessly could allow them to shrink to sub-millimeter sizes in the future, according to theory and simulations. Published Fri May 17, 2013

When you are buying a car you always look at official miles per gallon figures to find out how much fuel it will use. At the same time, most people have only a vague idea about how much energy their houses consume, even though home energy expenditures often account for a larger share of the household budget.... N.A. McNabb. (2013) Strategies to Achieve Net-Zero Energy Homes: A Framework for Future Guidelines Workshop Summary Report. NIST Special Publication. DOI: 10.6028/NIST.SP.1140 Strategies to Achieve Net-Zero Energy Homes: A Framework for Future Guidelines Workshop Summary Report.

R. P. Martinez-y-Romero, H. N. Nunez-Yepez, and A. L. Salas-Brito The classical 2D dynamics of a particle moving under an inverse square potential, k/r, is analysed. We show that such problem is an example of a geometric system since its negative energy orbits are equivalent to free motion on a certain hypersurface. We then solve in momentum space, the correspondi ... [J. Math. Phys. 54, 053509 (2013)] published Fri May 17, 2013.

Simple and cheap technique could be used in medical imaging

An artist honors the science and people of the CMS collaboration. There’s a new splash of color at Point Five, the home of CMS detector on the Large Hadron Collider. Five vivid banners drape the gray walls of the complex, lending the warehouse a cathedral-like atmosphere. Arranged in a line, they pull the viewer’s gaze from panel to panel to land on a true-to-scale photo of the detector itself, magnificently displayed on the back wall.

Dimensionally reduced scientist.“Science is the only news,” Steward Brand wrote. My reading of this sentence is that science, the exploration of nature and natural law, is the ultimate source of inspiration. Developing a model and studying its properties can be like discovering a new world, and the discoveries that are the most fascinating are the ones that are surprising and unintuitive. Probability amplitudes and wavefunctions are examples of such surprising and unintuitive properties, examples that are now a century old and that have changed the way we think about the world. Holography is a more recent example. And, gathering momentum in the quantum gravity community right now, is dimensional reduction. Dimensional reduction means that on short distances the dimension of space-time decreases. To quantify what this means one has to be very careful with defining “dimension.” The way we normally think about the dimension of space is to picture how lines spread out from a point. How quickly the lines dilute into their environment tells us something about the spheres we can draw around the point. The dimension of these spheres can be used to define the “Hausdorff dimension” of a space. The faster the lines dilute with distance, the larger the Hausdorff dimension.The notion of dimension that is relevant for the effect of dimensional reduction is not the Hausdorff dimension, but instead the “spectral dimension.” The spectral dimension can be found by first getting rid of the Lorentzian signature and going to Euclidean space. And then to watch a random walker who starts at one point, and measure the probability for him to return to that point. The smaller the average return probability, the higher the probability he’ll get lost, and the higher the number of dimensions. One can define the spectral dimension from the average return probability.Normally, for a flat, classical space, both notions of dimension are identical. However, there have been several approaches toward quantum geometry that found that the spectral dimension at short distances goes down from four to two. The return probability for short walks is larger than expected. One says that the spectral dimension “runs”, meaning it depends on the distance at which space-time is probed. Surprising. Unintuitive. This strange behavior was first found in Causal Dynamical Triangulations (hep-th/0505113), where one does a numerical simulation of an actual random walk in Euclidean space. But in other approaches one does not need a numerical simulation; it is possible to study the spectral dimension analytically as follows.The behavior of the random walk is governed by a differential equation, the diffusion equation, in which there enters the metric of the background space-time. In approaches to quantum gravity in which the metric is quantized, it is then the expectation value of the operator that the metric has become which enters the diffusion equation. From the diffusion equation one calculates the return probability for the random walk.This way, one can then infer the spectral dimension also in Asymptotically Safe Gravity (hep-th/0508202). Interestingly, one finds the same drop from four to two spectral dimensions. Yet another indication comes from Loop Quantum Gravity, where the scaling of the area operator with length changes at short distances. It is somewhat questionable whether the notion of a metric makes sense at all in this regime, but if one nevertheless constructs the diffusion equation from this scaling, one again finds that the spectral dimension drops from four to two (0812.2214). And Horava-Lifshitz gravity is maybe the best studied case where one finds dimensional reduction (0902.3657).Surprising. Unintuitive. It is difficult to interpret this behavior. Maybe a good way to picture it, as Calcagni, Eichhorn and Saueressig suggested, is to think of the quantum fluctuations of space-time hindering a particle’s random walk and slowing it down. It wouldn’t have to be t

In these days is ongoing LHCP 2013 (First Large Hadron Collider Physics Conference) and CMS data seem to point significantly toward new physics. Their measurements on the production modes for WW and ZZ are agreeing with my recent computations (see here) and overall are deviating slightly from Standard Model expectations giving Note that Standard Model is alive and […]... Marco Frasca. (2013) Revisiting the Higgs sector of the Standard Model. arXiv. arXiv: 1303.3158v1 Marco Frasca. (2010) Mass generation and supersymmetry. arXiv. arXiv: 1007.5275v2 T. G. Steele, & Zhi-Wei Wang. (2013) Is Radiative Electroweak Symmetry Breaking Consistent with a 125 GeV Higgs Mass?. Physical Review Letters, 151601. arXiv: 1209.5416v3 Krzysztof A. Meissner, & Hermann Nicolai. (2006) Conformal Symmetry and the Standard Model. Phys.Lett.B648:312-317,2007. arXiv: hep-th/0612165v4

Physics Phun in the Phorthcoming Physical Review What do gabby gazelles, mosh pits and jumping shampoo jets have in common? They're all covered in upcoming Physical Review papers. (This image is a mash up of pictures from Wikimedia Commons. Details and rights info are here, here and here.) Week after week, the American Physical Society journals are chock full of some of the most important physics papers published anywhere. Importance, of course, doesn't necessarily make something interesting to anyone outside the field. Every once in a while, though, we get a handful of papers that are significant enough to get into the Physical Review journals, including the flagship Physical Review Letters, as well as appealing to people who don't necessarily spend their days hunkered down in a lab or scribbling away on an equation-covered blackboard. After a quick glance at papers currently accepted for eventual publication in the Physical Review, I've found three that I can't wait to read. Topping my list is a look at the surprisingly simply collective motions that take place in mosh pits. In case you've never been in one, a mosh pit is usually an area near the stage during a concert where the most rabid fans can enjoy the show while being slammed around by dozens of other equally rabid fans. We covered this very research before, when it was being presented at the 2013 APS annual meeting in Baltimore, and it's worth checking out our older piece if you want to see how a crowd of crazy kids is like a flock of birds or a swirling gas. The interesting thing to me is that many people I spoke to back in March thought the research was nothing but a frivolous distraction for a few grad students who really should have been concentrating on their dissertations, not hanging out with hoards of death metal moshers. With the study soon to appear in the world's greatest physics journal, I wonder who's laughing now? I'm nearly as eager to read about a simulation of Mongolian Gazelles as they wander the steppes of Eastern Mongolia in search of food and, apparently, hollering to each other to "Come and get it!" I had never heard of Mongolian Gazelles before, and hadn't realized that gazelles of any type made noises, much less called other gazelles to dinner. That means in simply reading one abstract, I've already learned three entirely new things! I can't wait to see the actual paper to find out what other gazelle-related wonders it may contain. The third forthcoming paper I stumbled across had me worried for a bit. It seems that shampoo can sometimes leap out of your hand as you're pouring it from the bottle in preparation to wash your hair. It's not something I've ever experienced, although it makes my eyes water in anticipation of an unprovoked shampoo attack the next time I take a shower. While it's new to me, I've learned that the phenomenon is well known, and is called the Kaye effect. Check out the video below for some eye-endangering examples. The new twist, in the paper soon to be published in Physical Review E, is that these jets of soap don't occur for the reason usually given. In the past, most people who studied the effect assumed it had something to do with the fact that shampoo doesn't flow like normal (so-called Newtonian) fluids. Not so, it turns out. As the researchers say in their abstract, " . . . we show unambiguously that the jet slides on a lubricating air layer." Now that we know the truth, I can only assume that a solution (other than wearing protective goggles to bathe, as I plan to do tomorrow) can't be far behind. One possibility that comes to mind, assuming they're right about the lubricating air, is to shower in an evacuated vacuum chamber. No air, obviously, means no bouncing soap jets. NASA could probably work that out with some sort of pressure suit arrangement. Getting access to your hair through the helmet is going to be tough. But hey, they put a man on the moon, and are currently work