Hybrid Scene Compression for Visual Localization

Localizing an image wrt. a 3D scene model represents a core task for many computer vision applications. An increasing number of real-world applications of visual localization on mobile devices, e.g., Augmented Reality or autonomous robots such as drones or self-driving cars, demand localization approaches to minimize storage and bandwidth requirements. Compressing the 3D models used for localization thus becomes a practical necessity. In this work, we introduce a new hybrid compression algorithm that uses a given memory limit in a more effective way. Rather than treating all 3D points equally, it represents a small set of points with full appearance information and an additional, larger set of points with compressed information. This enables our approach to obtain a more complete scene representation without increasing the memory requirements, leading to a superior performance compared to previous compression schemes. As part of our contribution, we show how to handle ambiguous matches arising from point compression during RANSAC. Besides outperforming previous compression techniques in terms of pose accuracy under the same memory constraints, our compression scheme itself is also more efficient. Furthermore, the localization rates and accuracy obtained with our approach are comparable to state-of-the-art feature-based methods, while using a small fraction of the memory.Comment: Published at CVPR 201

The Stellar CME-flare relation: What do historic observations reveal?

Solar CMEs and flares have a statistically well defined relation, with more energetic X-ray flares corresponding to faster and more massive CMEs. How this relation extends to more magnetically active stars is a subject of open research. Here, we study the most probable stellar CME candidates associated with flares captured in the literature to date, all of which were observed on magnetically active stars. We use a simple CME model to derive masses and kinetic energies from observed quantities, and transform associated flare data to the GOES 1--8~\AA\ band. Derived CME masses range from $\sim 10^{15}$ to $10^{22}$~g. Associated flare X-ray energies range from $10^{31}$ to $10^{37}$~erg. Stellar CME masses as a function of associated flare energy generally lie along or below the extrapolated mean for solar events. In contrast, CME kinetic energies lie below the analogous solar extrapolation by roughly two orders of magnitude, indicating approximate parity between flare X-ray and CME kinetic energies. These results suggest that the CMEs associated with very energetic flares on active stars are more limited in terms of the ejecta velocity than the ejecta mass, possibly because of the restraining influence of strong overlying magnetic fields and stellar wind drag. Lower CME kinetic energies and velocities present a more optimistic scenario for the effects of CME impacts on exoplanets in close proximity to active stellar hosts.Comment: 23 pages, 3 tables, 4 figures, accepted by Ap

Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU Microscopii

Energetic particles emitted by active stars are likely to propagate in astrospheric magnetized plasma and disrupted by the prior passage of energetic coronal mass ejections (CMEs). We carried out test-particle simulations of ∼GeV protons produced at a variety of distances from the M1Ve star AU Microscopii by coronal flares or traveling shocks. Particles are propagated within a large-scale quiescent three-dimensional magnetic field and stellar wind reconstructed from measured magnetograms, and within the same stellar environment following the passage of a 1036 erg kinetic energy CME. In both cases, magnetic fluctuations with an isotropic power spectrum are overlayed onto the large-scale stellar magnetic field and particle propagation out to the two innnermost confirmed planets is examined. In the quiescent case, the magnetic field concentrates the particles into two regions near the ecliptic plane. After the passage of the CME, the closed field lines remain inflated and the reshuffled magnetic field remains highly compressed, shrinking the scattering mean free path of the particles. In the direction of propagation of the CME lobes the subsequent energetic particle (EP) flux is suppressed. Even for a CME front propagating out of the ecliptic plane, the EP flux along the planetary orbits highly fluctuates and peaks at ∼2-3 orders of magnitude higher than the average solar value at Earth, both in the quiescent and the post-CME cases

Evaluación de patología y vulnerabilidad en edificios patrimoniales de mampostería ubicados en zona de alta sismicidad: un caso de estudio

La Secretaría de Turismo del Gobierno de Mendoza, Argentina, funciona en un edificio de mampostería monumental que data de 1913 ubicado en el microcentro de la Ciudad de Mendoza, que fue originariamente el Jockey Club Mendoza, con detalles arquitectónicos en herrería, vidrio y madera, que aún se conservan, pero hoy presenta patologías estructurales por eventos sísmicos y de mantenimiento por problemas de suelo y pérdidas en instalaciones. Las etapas del trabajo son: un seguimiento de antecedentes históricos, la evaluación de patologías y el estudio de los materiales utilizados, incluido el suelo, y el análisis de las condiciones de seguridad del edificio, previo a la definición definitiva del proyecto arquitectónico que se realiza por concurso público. La metodología utilizada incluye las siguientes etapas: relevamiento, decisiones de emergencia, análisis de las condiciones de conservación del edificio, diagnóstico y criterios sismorresistentes para la propuesta de rehabilitación La capacidad sismorresistente se evalúa de acuerdo a la normativa vigente en la Ciudad de Mendoza de 1987 que establece las pautas de calidad, resistencia y seguridad que deben alcanzar las construcciones que no cumplimentan los reglamentos sismorresistentes y que se deben aplicar obligatoriamente en edificios de uso público. Se analizan distintas propuestas de rehabilitación con técnicas de rehabilitación verificadas en laboratorio para la región, según distintos grados de valoración patrimonial de lo existente. En la propuesta del nuevo “Centro de Interpretación de Mendoza” se deben considerar como determinantes las condiciones del sitio y del suelo en relación a la vulnerabilidad edilicia y a la seguridad estructural, tener especial cuidado en el diseño de instalaciones sanitarias en relación a la vida útil que quiera otorgarse a la construcción y considerar la utilización de técnicas de reparación asociadas a las técnicas constructivas originales de la construcción en mampostería y hormigón armado para optimizar costos y alcanzar los requerimientos normativos.Tópico 6: Patrimonio Urbano de los siglos XVIII al XX. Técnicas de Limpieza y de Conservación

Coronal Mass Ejections and Exoplanets: A Numerical Perspective

Coronal mass ejections (CMEs) are more energetic than any other class of solar phenomena. They arise from the rapid release of up to $10^{33}$ erg of magnetic energy mainly in the form of particle acceleration and bulk plasma motion. Their stellar counterparts, presumably involving much larger energies, are expected to play a fundamental role in shaping the environmental conditions around low-mass stars, in some cases perhaps with catastrophic consequences for planetary systems due to processes such as atmospheric erosion and depletion. Despite their importance, the direct observational evidence for stellar CMEs is almost non-existent. In this way, numerical simulations constitute extremely valuable tools to shed some light on eruptive behavior in the stellar regime. Here we review recent results obtained from realistic modeling of CMEs in active stars, highlighting their key role in the interpretation of currently available observational constraints. We include studies performed on M-dwarf stars, focusing on how emerging signatures in different wavelengths related to these events vary as a function of the magnetic properties of the star. Finally, the implications and relevance of these numerical results are discussed in the context of future characterization of host star-exoplanet systems.Comment: 8 pages, 3 figures, Accepted for publication in Astronomical Notes (Astronomische Nachrichten). Based on an invited review talk at the XMM-Newton Science Workshop 2021: "A High-Energy View of Exoplanets and Their Environments

Three-dimensional, Time-dependent MHD Simulation of Disk-Magnetosphere-Stellar Wind Interaction in a T Tauri, Protoplanetary System

We present a three-dimensional, time-dependent, MHD simulation of the short-term interaction between a protoplanetary disk and the stellar corona in a T Tauri system. The simulation includes the stellar magnetic field, self-consistent coronal heating and stellar wind acceleration, and a disk rotating at sub-Keplerian velocity to induce accretion. We find that initially, as the system relaxes from the assumed initial conditions, the inner part of the disk winds around and moves inward and close to the star as expected. However, the self-consistent coronal heating and stellar wind acceleration build up the original state after some time, significantly pushing the disk out beyond $10R_\star$. After this initial relaxation period, we do not find clear evidence of a strong, steady accretion flow funneled along coronal field lines, but only weak, sporadic accretion. We produce synthetic coronal X-ray line emission light curves which show flare-like increases that are not correlated with accretion events nor with heating events. These variations in the line emission flux are the result of compression and expansion due to disk-corona pressure variations. Vertical disk evaporation evolves above and below the disk. However, the disk - stellar wind boundary stays quite stable, and any disk material that reaches the stellar wind region is advected out by the stellar wind.Comment: Accepted to ApJ, 12 pages, 11 figure

Activity dependent feedback inhibition may maintain head direction signals in mouse presubiculum

Orientation in space is represented in specialized brain circuits. Persistent head direction signals are transmitted from anterior thalamus to the presubiculum, but the identity of the presubicular target neurons, their connectivity and function in local microcircuits are unknown. Here, we examine how thalamic afferents recruit presubicular principal neurons and Martinotti interneurons, and the ensuing synaptic interactions between these cells. Pyramidal neuron activation of Martinotti cells in superficial layers is strongly facilitating such that high-frequency head directional stimulation efficiently unmutes synaptic excitation. Martinotti-cell feedback plays a dual role: precisely timed spikes may not inhibit the firing of in-tune head direction cells, while exerting lateral inhibition. Autonomous attractor dynamics emerge from a modelled network implementing wiring motifs and timing sensitive synaptic interactions in the pyramidal - Martinotti-cell feedback loop. This inhibitory microcircuit is therefore tuned to refine and maintain head direction information in the presubiculum

Habitação, saúde e meio ambiente em conflito no Distrito Federal: a Vila Santa Luzia em perspectiva

The article discusses the correlations between housing, environment and health in the Vila Santa Luzia community, Federal District, Brazil. It purports to investigate the perceptions, interpretations and representations of residents and community leaders about such correlations based on health promotion and healthy housing theoretical framework. Data were collected by means of interviews. Results point to a willingness between the parties to reach a satisfactory, reasonable and republican resolution for the conflict in question. In conclusion, the socioenvironmental and health experience of Vila Santa Luzia is relevant and significant, both in empirical and analytical (public policies) terms.Neste artigo discute-se as correlações entre habitação, meio ambiente e saúde na comunidade da Vila Santa Luzia, no Distrito Federal. O objetivo geral do trabalho é conhecer as percepções, interpretações e representações da amostra de um grupo de moradores e líderes comunitários acerca das referidas vinculações. Em termos teóricos, o projeto fundamentou-se no enfoque da promoção da saúde e habitação saudável. Metodologicamente, os dados foram coletados com a técnica da entrevista. O principal resultado alcançado sugere que existe disposição entre as partes para alcançar uma resolução satisfatória, razoável e republicana ao conflito em questão. A conclusão do texto assinala que a experiência socioambiental e sanitária da Vila Santa Luzia é relevante e significativa, quer em termos empíricos, quer em termos analíticos (políticas públicas)