Wave field coding in the spacetime frequency domain

We present a new method for compressing spatio-temporal audio data for reproduction through Wave Field Synthesis. The data is obtained by sampling the sound field in space at equally-spaced points on a straight line, and transformed into the frequency domain using a spatio-temporal lapped trans- form. The two-dimensional spectrum is quantized using a psychoacoustic model derived for spatio-temporal frequen- cies, which estimates the maximum quantization noise power that each frequency can support in order to preserve trans- parency in the decoded signal. On the decoder side, the in- verse lapped transform recovers the spatio-temporal data. In our experimental results, we verified that the bitrate-efficiency can be improved by increasing either the spatial sampling fre- quency or the spatial resolution of the lapped transform

Tomorrow's Metamaterials: Manipulation of Electromagnetic Waves in Space, Time and Spacetime

Metamaterials represent one of the most vibrant fields of modern science and technology. They are generally dispersive structures in the direct and reciprocal space and time domains. Upon this consideration, I overview here a number of metamaterial innovations developed by colleagues and myself in the holistic framework of space and time dispersion engineering. Moreover, I provide some thoughts regarding the future perspectives of the area

Geometric creation of quantum vorticity

We consider superfluidity and quantum vorticity in rotating spacetimes. The system is described by a complex scalar satisfying a nonlinear Klein-Gordon equation. Rotation terms are identified and found to lead to the transfer of angular momentum of the spacetime to the scalar field. The scalar field responds by rotating, physically behaving as a superfluid, through the creation of quantized vortices. We demonstrate the vortex nucleation through numerical simulation.Comment: 10 pages, 1 figure, updated to closely resemble published versio

Non-linear axisymmetric pulsations of rotating relativistic stars in the conformal flatness approximation

We study non-linear axisymmetric pulsations of rotating relativistic stars using a general relativistic hydrodynamics code under the assumption of a conformal flatness. We compare our results to previous simulations where the spacetime dynamics was neglected. The pulsations are studied along various sequences of both uniformly and differentially rotating relativistic polytropes with index N = 1. We identify several modes, including the lowest-order l = 0, 2, and 4 axisymmetric modes, as well as several axisymmetric inertial modes. Differential rotation significantly lowers mode frequencies, increasing prospects for detection by current gravitational wave interferometers. We observe an extended avoided crossing between the l = 0 and l = 4 first overtones, which is important for correctly identifying mode frequencies in case of detection. For uniformly rotating stars near the mass-shedding limit, we confirm the existence of the mass-shedding-induced damping of pulsations, though the effect is not as strong as in the Cowling approximation. We also investigate non-linear harmonics of the linear modes and notice that rotation changes the pulsation frequencies in a way that would allow for various parametric instabilities between two or three modes to take place. We assess the detectability of each obtained mode by current gravitational wave detectors and outline how the empirical relations that have been constructed for gravitational wave asteroseismology could be extended to include the effects of rotation.Comment: 24 pages, 20 figures; minor corrections, added extended discussion and one figure in one subsectio