Event-Based Motion Segmentation by Motion Compensation

In contrast to traditional cameras, whose pixels have a common exposure time, event-based cameras are novel bio-inspired sensors whose pixels work independently and asynchronously output intensity changes (called "events"), with microsecond resolution. Since events are caused by the apparent motion of objects, event-based cameras sample visual information based on the scene dynamics and are, therefore, a more natural fit than traditional cameras to acquire motion, especially at high speeds, where traditional cameras suffer from motion blur. However, distinguishing between events caused by different moving objects and by the camera's ego-motion is a challenging task. We present the first per-event segmentation method for splitting a scene into independently moving objects. Our method jointly estimates the event-object associations (i.e., segmentation) and the motion parameters of the objects (or the background) by maximization of an objective function, which builds upon recent results on event-based motion-compensation. We provide a thorough evaluation of our method on a public dataset, outperforming the state-of-the-art by as much as 10%. We also show the first quantitative evaluation of a segmentation algorithm for event cameras, yielding around 90% accuracy at 4 pixels relative displacement.Comment: When viewed in Acrobat Reader, several of the figures animate. Video: https://youtu.be/0q6ap_OSBA

Processes endure, whereas events occur

In this essay, we aim to help clarify the nature of so-called 'occurrences' by attributing distinct modes of existence and persistence to processes and events. In doing so, we break with the perdurantism claimed by DOLCE’s authors and we distance ourselves from mereological analyzes like those recently conducted by Guarino to distinguish between 'processes' and 'episodes'. In line with the works of Stout and Galton, we first bring closer (physical) processes and objects in their way of enduring by proposing for processes a notion of dynamic presence (contrasting with a static presence for objects). Then, on the events side, we attribute to them the status of abstract entities by identifying them with objects of thought (by individual and collective subjects), and this allows us to distinguish for themselves between existence and occurrence. We therefore identify them with psychological (or even social) endurants, which may contingently occur

Detectability of Oort cloud objects using Kepler

The size distribution and total mass of objects in the Oort Cloud have important implications to the theory of planets formation, including the properties of, and the processes taking place in the early solar system. We discuss the potential of space missions like Kepler and CoRoT, designed to discover transiting exo-planets, to detect Oort Cloud, Kuiper Belt and main belt objects by occultations of background stars. Relying on published dynamical estimates of the content of the Oort Cloud, we find that Kepler's main program is expected to detect between 0 and ~100 occultation events by deca-kilometer-sized Oort Cloud objects. The occultations rate depends on the mass of the Oort cloud, the distance to its "inner edge", and the size distribution of its objects. In contrast, Kepler is unlikely to find occultations by Kuiper Belt or main belt asteroids, mainly due to the fact that it is observing a high ecliptic latitude field. Occultations by Solar System objects will appear as a photometric deviation in a single measurement, implying that the information regarding the time scale and light-curve shape of each event is lost. We present statistical methods that have the potential to verify the authenticity of occultation events by Solar System objects, to estimate the distance to the occulting population, and to constrain their size distribution. Our results are useful for planning of future space-based exo-planet searches in a way that will maximize the probability of detecting solar system objects, without hampering the main science goals.Comment: Submitted to ApJL, 5 pages, 1 figur

Binary Encounters With Supermassive Black Holes: Zero-Eccentricity LISA Events

Current simulations of the rate at which stellar-mass compact objects merge with supermassive black holes (called extreme mass ratio inspirals, or EMRIs) focus on two-body capture by emission of gravitational radiation. The gravitational wave signal of such events will likely involve a significant eccentricity in the sensitivity range of the Laser Interferometer Space Antenna (LISA). We show that tidal separation of stellar-mass compact object binaries by supermassive black holes will instead produce events whose eccentricity is nearly zero in the LISA band. Compared to two-body capture events, tidal separations have a high cross section and result in orbits that have a large pericenter and small apocenter. Therefore, the rate of interactions per binary is high and the resulting systems are very unlikely to be perturbed by other stars into nearly radial plunges. Depending on the fraction of compact objects that are in binaries within a few parsecs of the center, the rate of low-eccentricity LISA events could be comparable to or larger than the rate of high-eccentricity events.Comment: Final accepted version: ApJ Letters 2005, 631, L11