Neural View-Interpolation for Sparse Light Field Video

We suggest representing light field (LF) videos as "one-off" neural networks (NN), i.e., a learned mapping from view-plus-time coordinates to high-resolution color values, trained on sparse views. Initially, this sounds like a bad idea for three main reasons: First, a NN LF will likely have less quality than a same-sized pixel basis representation. Second, only few training data, e.g., 9 exemplars per frame are available for sparse LF videos. Third, there is no generalization across LFs, but across view and time instead. Consequently, a network needs to be trained for each LF video. Surprisingly, these problems can turn into substantial advantages: Other than the linear pixel basis, a NN has to come up with a compact, non-linear i.e., more intelligent, explanation of color, conditioned on the sparse view and time coordinates. As observed for many NN however, this representation now is interpolatable: if the image output for sparse view coordinates is plausible, it is for all intermediate, continuous coordinates as well. Our specific network architecture involves a differentiable occlusion-aware warping step, which leads to a compact set of trainable parameters and consequently fast learning and fast execution

A beginner's introduction to Fukaya categories

The goal of these notes is to give a short introduction to Fukaya categories and some of their applications. The first half of the text is devoted to a brief review of Lagrangian Floer (co)homology and product structures. Then we introduce the Fukaya category (informally and without a lot of the necessary technical detail), and briefly discuss algebraic concepts such as exact triangles and generators. Finally, we mention wrapped Fukaya categories and outline a few applications to symplectic topology, mirror symmetry and low-dimensional topology. This text is based on a series of lectures given at a Summer School on Contact and Symplectic Topology at Universit\'e de Nantes in June 2011.Comment: 42 pages, 13 figure

Roles of two successive phase transitions in new spin-Peierls system TiOBr

In this sturdy, we determine the roles of two successive phase transitions in the new spin-Peierls system TiOBr by electron and synchrotron X-ray diffraction analyses. Results show an incommensurate superstructure along the h- and k-directions between Tc1=27K and Tc2=47K, and a twofold superstructure which is related to a spin-Peierls lattice distortion below Tc1. The diffuse scattering observed above Tc2 indicates that a structural correlation develops at a high temperature. We conclude that Tc2 is a second-order lock-in temperature, which is related to the spin-Peierls lattice distortion with the incommensurate structure, and that Tc1 is from incommensurate to commensurate phase transition temperature accompanying the first-order spin-Peierls lattice distortion.Comment: 4 pages, 5 figure

Evolution of 3D Boson Stars with Waveform Extraction

Numerical results from a study of boson stars under nonspherical perturbations using a fully general relativistic 3D code are presented together with the analysis of emitted gravitational radiation. We have constructed a simulation code suitable for the study of scalar fields in space-times of general symmetry by bringing together components for addressing the initial value problem, the full evolution system and the detection and analysis of gravitational waves. Within a series of numerical simulations, we explicitly extract the Zerilli and Newman-Penrose scalar $\Psi_4$ gravitational waveforms when the stars are subjected to different types of perturbations. Boson star systems have rapidly decaying nonradial quasinormal modes and thus the complete gravitational waveform could be extracted for all configurations studied. The gravitational waves emitted from stable, critical, and unstable boson star configurations are analyzed and the numerically observed quasinormal mode frequencies are compared with known linear perturbation results. The superposition of the high frequency nonspherical modes on the lower frequency spherical modes was observed in the metric oscillations when perturbations with radial and nonradial components were applied. The collapse of unstable boson stars to black holes was simulated. The apparent horizons were observed to be slightly nonspherical when initially detected and became spherical as the system evolved. The application of nonradial perturbations proportional to spherical harmonics is observed not to affect the collapse time. An unstable star subjected to a large perturbation was observed to migrate to a stable configuration.Comment: 26 pages, 12 figure

Video Frame Interpolation for High Dynamic Range Sequences Captured with Dual-exposure Sensors

Video frame interpolation (VFI) enables many important applications thatmight involve the temporal domain, such as slow motion playback, or the spatialdomain, such as stop motion sequences. We are focusing on the former task,where one of the key challenges is handling high dynamic range (HDR) scenes inthe presence of complex motion. To this end, we explore possible advantages ofdual-exposure sensors that readily provide sharp short and blurry longexposures that are spatially registered and whose ends are temporally aligned.This way, motion blur registers temporally continuous information on the scenemotion that, combined with the sharp reference, enables more precise motionsampling within a single camera shot. We demonstrate that this facilitates amore complex motion reconstruction in the VFI task, as well as HDR framereconstruction that so far has been considered only for the originally capturedframes, not in-between interpolated frames. We design a neural network trainedin these tasks that clearly outperforms existing solutions. We also propose ametric for scene motion complexity that provides important insights into theperformance of VFI methods at the test time.<br

X-Fields: Implicit Neural View-, Light- and Time-Image Interpolation

We suggest to represent an X-Field -a set of 2D images taken across different view, time or illumination conditions, i.e., video, light field, reflectance fields or combinations thereof-by learning a neural network (NN) to map their view, time or light coordinates to 2D images. Executing this NN at new coordinates results in joint view, time or light interpolation. The key idea to make this workable is a NN that already knows the "basic tricks" of graphics (lighting, 3D projection, occlusion) in a hard-coded and differentiable form. The NN represents the input to that rendering as an implicit map, that for any view, time, or light coordinate and for any pixel can quantify how it will move if view, time or light coordinates change (Jacobian of pixel position with respect to view, time, illumination, etc.). Our X-Field representation is trained for one scene within minutes, leading to a compact set of trainable parameters and hence real-time navigation in view, time and illumination

MUSE-AO view of the starburst-AGN connection: NGC 7130

We present the discovery of a small kinematically decoupled core of 0.2$^{\prime\prime}$ (60 pc) in radius as well as an outflow jet in the archetypical AGN-starburst "composite" galaxy NGC 7130 from integral field data obtained with the adaptive optics-assisted MUSE-NFM instrument on the VLT. Correcting the already good natural seeing at the time of our science verification observations with the four-laser GALACSI AO system, we reach an unprecedented spatial resolution at optical wavelengths of around 0.15$^{\prime\prime}$. We confirm the existence of star-forming knots arranged in a ring of 0.58$^{\prime\prime}$ (185 pc) in radius around the nucleus, previously observed from UV and optical Hubble Space Telescope and CO(6-5) ALMA imaging. We determine the position of the nucleus as the location of a peak in gas velocity dispersion. A plume of material extends towards the NE from the nucleus until at least the edge of our field of view at 2$^{\prime\prime}$ (640 pc) radius which we interpret as an outflow jet originating in the AGN. The plume is not visible morphologically, but is clearly characterised in our data by emission-line ratios characteristic of AGN emission, enhanced gas velocity dispersion, and distinct non-circular gas velocities. Its orientation is roughly perpendicular to the line of nodes of the rotating host galaxy disc. A circumnuclear area of positive and negative velocities of 0.2$^{\prime\prime}$ in radius indicates a tiny inner disc, which can only be seen after combining the integral field spectroscopic capabilities of MUSE with adaptive optics.Comment: Accepted for publication in A&A letter