Water waves overtopping over barriers

A numerical and experimental analysis of the wave overtopping over emerged and submerged structures, is presented. An original model is used in order to simulate three-dimensional free surface flows. The model is based on the numerical solution of the motion equations expressed in an integral form in time-dependent curvilinear coordinates. A non-intrusive and continuous-in-space image analysis technique, which is able to properly identify the free surface even in very shallow waters or breaking waves, is adopted for the experimental tests. Numerical and experimental results are compared, for several wave and water depth conditions

Observation of shock waves in a large Bose-Einstein condensate

We observe the formation of shock waves in a Bose-Einstein condensate containing a large number of sodium atoms. The shock wave is initiated with a repulsive, blue-detuned light barrier, intersecting the BEC, after which two shock fronts appear. We observe breaking of these waves when the size of these waves approaches the healing length of the condensate. At this time, the wave front splits into two parts and clear fringes appear. The experiment is modeled using an effective 1D Gross-Pitaevskii-like equation and gives excellent quantitative agreement with the experiment, even though matter waves with wavelengths two orders of magnitude smaller than the healing length are present. In these experiments, no significant heating or particle loss is observed.Comment: 7 pages, 7 figure

How to find real-world applications for compressive sensing

The potential of compressive sensing (CS) has spurred great interest in the research community and is a fast growing area of research. However, research translating CS theory into practical hardware and demonstrating clear and significant benefits with this hardware over current, conventional imaging techniques has been limited. This article helps researchers to find those niche applications where the CS approach provides substantial gain over conventional approaches by articulating lessons learned in finding one such application; sea skimming missile detection. As a proof of concept, it is demonstrated that a simplified CS missile detection architecture and algorithm provides comparable results to the conventional imaging approach but using a smaller FPA. The primary message is that all of the excitement surrounding CS is necessary and appropriate for encouraging our creativity but we all must also take off our "rose colored glasses" and critically judge our ideas, methods and results relative to conventional imaging approaches.Comment: 10 page

New Exclusion Limits for the Search of Scalar and Pseudoscalar Axion-Like Particles from "Light Shining Through a Wall"

Physics beyond the Standard Model predicts the possible existence of new particles that can be searched at the low energy frontier in the sub-eV range. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles", such as axion or Axion-Like Particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. In 2014, this experiment has been run with an outstanding sensitivity, using an 18.5 W continuous wave laser emitting in the green at the single wavelength of 532 nm. No regenerated photons have been detected after the wall, pushing the limits for the existence of axions and ALPs down to an unprecedented level for such a type of laboratory experiment. The di-photon couplings of possible pseudo-scalar and scalar ALPs can be constrained in the nearly massless limit to be less than $3.5\cdot 10^{-8}$ GeV$^{-1}$ and $3.2\cdot 10^{-8}$ GeV$^{-1}$, respectively, at 95% Confidence Level.Comment: 6 pages, 6 figure

A Cosmic Microwave Background feature consistent with a cosmic texture

The Cosmic Microwave Background provides our most ancient image of the Universe and our best tool for studying its early evolution. Theories of high energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent, 5 degree radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry breaking energy scale to be phi_0 ~ 8.7 x 10^(15) GeV. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment.Comment: Accepted by Science. Published electronically via Science Express on 25 October 2007, http://www.sciencemag.org/cgi/content/abstract/114869

First results from the OSQAR photon regeneration experiment: No light shining through a wall

A new method to amplify the photon-axion conversions in magnetic field is proposed using a buffer gas at a specific pressure. As a first result, new bounds for mass and coupling constant for purely laboratory experiments aiming to detect any hypothetical scalars and pseudo-scalars which can couple to photons were obtained at 95% confidence level, excluding the PVLAS result newly disclaimed.Comment: 4 pages, 5 figure