Detecting Gravitational Waves by Twisted Light - Dipole Interaction of Photons and Gravitational Waves

Motivated by the next generation of gravitational wave (GW) detectors, we study the wave mechanics of a twisted light beam in the GW perturbed spacetime. We found a new gravitational dipole interaction of photons and gravitational waves. Physically, this interaction is due to coupling between the angular momentum of twisted light and the GW polarizations. We demonstrate that for the higher-order Laguerre-Gauss (LG) modes, this coupling effect makes photons undergoing dipole transitions between different orbital-angular-momentum(OAM) eigenstates, and leads to some measurable optical features in the 2-D intensity pattern. It offers an alternative way to realize precision measurements of the gravitational waves, and enables us to extract more information about the physical properties of gravitational waves than the current interferometry. With a well-designed optical setup, this dipole interaction is expected to be justified in laboratories.Comment: 4 pages, 2 figure

Disentangling Object Motion and Occlusion for Unsupervised Multi-frame Monocular Depth

Conventional self-supervised monocular depth prediction methods are based on a static environment assumption, which leads to accuracy degradation in dynamic scenes due to the mismatch and occlusion problems introduced by object motions. Existing dynamic-object-focused methods only partially solved the mismatch problem at the training loss level. In this paper, we accordingly propose a novel multi-frame monocular depth prediction method to solve these problems at both the prediction and supervision loss levels. Our method, called DynamicDepth, is a new framework trained via a self-supervised cycle consistent learning scheme. A Dynamic Object Motion Disentanglement (DOMD) module is proposed to disentangle object motions to solve the mismatch problem. Moreover, novel occlusion-aware Cost Volume and Re-projection Loss are designed to alleviate the occlusion effects of object motions. Extensive analyses and experiments on the Cityscapes and KITTI datasets show that our method significantly outperforms the state-of-the-art monocular depth prediction methods, especially in the areas of dynamic objects. Our code will be made publicly available

Experimental and theoretical analysis of microstructural evolution and deformation behaviors of CuW composites during equal channel angular pressing

CuW composites were synthesized using an equal channel angular pressing (ECAP) technique. Microstructural evolution during sintering process was investigated using both optical microscopy and transmission electron microscopy (TEM), and their deformation mechanisms were studied using finite element analysis (FEA). Results showed severe plastic deformation of the CuW composites and effective refinement of W grains after the ECAP process. TEM observation revealed that the ECAP process resulted in lamellar bands with high densities dislocations inside the composites. Effects of extrusion temperature and extrusion angles on stress-strain relationship and sizes of deformation zones after the ECAP process were investigated both theoretically and experimentally. When the extrusion angle was 90°, a maximum equivalent stress of ~1001 MPa was obtained when the extrusion test was done at room temperature of 22 °C, and this value was lower than compression strength of the CuW composites (1105.43 MPa). The maximum equivalent strains were varied between 0.5 and 0.7. However, when the extrusion temperature was increased to 550 °C and further to 900 °C, the maximum equivalent stresses were decreased sharply, with readings of 311 MPa and 68 MPa, respectively. When the extrusion angle was increased to 135°, the maximum equivalent stresses were found to be 716.9 MPa, 208 MPa, and 32 MPa for the samples extruded at temperatures of 22 °C, 550 °C and 900 °C, respectively. Simultaneously, the maximum equivalent strains were decreased to 0.2–0.4. Furthermore, results showed that the maximum equivalent stress was located on the sample's external surface and the stress values were gradually decreased from the surface to the center of samples, and the magnitudes of plastic deformation zones at the surface were much larger than those at the central part of the sintered samples. FEA simulation results were in good agreements with experimentally measured ones

An ideal mass assignment scheme for measuring the Power Spectrum with FFTs

In measuring the power spectrum of the distribution of large numbers of dark matter particles in simulations, or galaxies in observations, one has to use Fast Fourier Transforms (FFT) for calculational efficiency. However, because of the required mass assignment onto grid points in this method, the measured power spectrum \la |\delta^f(k)|^2\ra obtained with an FFT is not the true power spectrum $P(k)$ but instead one that is convolved with a window function $|W(\vec k)|^2$ in Fourier space. In a recent paper, Jing (2005) proposed an elegant algorithm to deconvolve the sampling effects of the window function and to extract the true power spectrum, and tests using N-body simulations show that this algorithm works very well for the three most commonly used mass assignment functions, i.e., the Nearest Grid Point (NGP), the Cloud In Cell (CIC) and the Triangular Shaped Cloud (TSC) methods. In this paper, rather than trying to deconvolve the sampling effects of the window function, we propose to select a particular function in performing the mass assignment that can minimize these effects. An ideal window function should fulfill the following criteria: (i) compact top-hat like support in Fourier space to minimize the sampling effects; (ii) compact support in real space to allow a fast and computationally feasible mass assignment onto grids. We find that the scale functions of Daubechies wavelet transformations are good candidates for such a purpose. Our tests using data from the Millennium Simulation show that the true power spectrum of dark matter can be accurately measured at a level better than 2% up to $k=0.7k_N$, without applying any deconvolution processes. The new scheme is especially valuable for measurements of higher order statistics, e.g. the bi-spectrum,........Comment: 17 pages, 3 figures, Accepted for publication in ApJ,Matches the accepte