Physics

RT @astronautdotcom: Massive Moon Meteor Explosion Was Visible to Naked Eye

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.

-Scientific studies done with the “PAPER” array, one of the world-class scientific instruments in South Africa’s Karoo Radio Astronomy Reserve, is producing ground-breaking science and spectacular cosmic images, resulting in several important articles in top astronomy journals. -The first scientific paper based on observations performed with South Africa’s new KAT-7 radio telescope, has been accepted for publication by the prestigious journal Monthly Notices of the Royal Astronomy Society. “This is a significant milestone for South Africa’s SKA project, proving that our engineers are able to deliver a cutting-edge scientific instrument, and that our scientists are able to use it for frontier science,” says Derek Hanekom, South Africa’s Minister of Science and Technology. “It bodes well for the delivery of our 64-dish MeerKAT telescope, currently under construction in the Karoo, and for our ability to play a key role in building and commissioning thousands of SKA antennas over the next ten years.”... SKA SA Project Office. (2013) Ground-breaking science and spectacular cosmic images from the PAPER instrument in the Karoo. SKA Africa . info:/

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