Black-hole kicks from numerical-relativity surrogate models

Binary black holes radiate linear momentum in gravitational waves as they merge. Recoils imparted to the black-hole remnant can reach thousands of km/s, thus ejecting black holes from their host galaxies. We exploit recent advances in gravitational waveform modeling to quickly and reliably extract recoils imparted to generic, precessing, black hole binaries. Our procedure uses a numerical-relativity surrogate model to obtain the gravitational waveform given a set of binary parameters, then from this waveform we directly integrate the gravitational-wave linear momentum flux. This entirely bypasses the need of fitting formulae which are typically used to model black-hole recoils in astrophysical contexts. We provide a thorough exploration of the black-hole kick phenomenology in the parameter space, summarizing and extending previous numerical results on the topic. Our extraction procedure is made publicly available as a module for the Python programming language named SURRKICK. Kick evaluations take ~0.1s on a standard off-the-shelf machine, thus making our code ideal to be ported to large-scale astrophysical studies.Comment: More: https://davidegerosa.com/surrkick - Source: https://github.com/dgerosa/surrkick - pypi: https://pypi.python.org/pypi/surrkick - Published in PR

The Federal Administrative Court Proposal: An Examination of General Principals

Simulations of relativistic hydrodynamics often need both high accuracy and robust shock-handling properties. The discontinuous Galerkin method combines these features—a high order of convergence in regions where the solution is smooth and shock-capturing properties for regions where it is not—with geometric flexibility and is therefore well suited to solve the partial differential equations describing astrophysical scenarios. We present here evolutions of a general-relativistic neutron star with the discontinuous Galerkin method. In these simulations, we simultaneously evolve the spacetime geometry and the matter on the same computational grid, which we conform to the spherical geometry of the problem. To verify the correctness of our implementation, we perform standard convergence and shock tests. We then show results for evolving, in three dimensions, a Kerr black hole; a neutron star in the Cowling approximation (holding the spacetime metric fixed); and, finally, a neutron star where the spacetime and matter are both dynamical. The evolutions show long-term stability, good accuracy, and an improved rate of convergence versus a comparable-resolution finite-volume method

Les déclarations d’impôts personnels des Québécois pour l’année 1985 : qui les complète et à quel coût?

Ce texte examine les choix des contribuables du Québec, soit des individus ayant déposé des déclarations d’impôt sur le revenu pour 1985, qu’ils aient ou non payé de l’impôt, quant à la façon de compléter leurs déclarations d’impôt sur le revenu des particuliers et les coûts encourus à cette fin. Nous y utilisons des données recueillies par sondage à notre demande auprès d’un échantillon de 447 contribuables. Nos principaux résultats sont que les contribuables susceptibles d’être plus aptes à compléter eux-mêmes leurs déclarations d'impôt le font eux-mêmes, malgré le fait que la valeur de leur temps soit plus élevée, que les contribuables faisant face à une situation fiscale plus complexe sont moins susceptibles de compléter eux-mêmes leur rapport d’impôt et que les contribuables québécois ont des comportements et encourent des coûts similaires à ceux du Canada et, lorsque la comparaison est possible, à ceux des États-Unis.This paper examines the 1985 Québec taxpayers' choice as to how they completed their personal income tax returns, and quantifies the compliance costs thus incurred. The data used therein were collected at our request by surveying a représentative sample of 447 taxpayers. Our main results are: 1 ) taxpayers more capable of completing their own returns do so even though the value of their time is higher; 2) taxpayers faced with a more complex tax situation are less likely to prepare their own returns; and 3) Québec taxpayers have similar behaviors and costs to those of Canadians and, when the comparison is feasible, Americans as well

High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants

We present accurate fits for the remnant properties of generically precessing binary black holes, trained on large banks of numerical-relativity simulations. We use Gaussian process regression to interpolate the remnant mass, spin, and recoil velocity in the 7-dimensional parameter space of precessing black-hole binaries with mass ratios $q\leq2$, and spin magnitudes $\chi_1,\chi_2\leq0.8$. For precessing systems, our errors in estimating the remnant mass, spin magnitude, and kick magnitude are lower than those of existing fitting formulae by at least an order of magnitude (improvement is also reported in the extrapolated region at high mass ratios and spins). In addition, we also model the remnant spin and kick directions. Being trained directly on precessing simulations, our fits are free from ambiguities regarding the initial frequency at which precessing quantities are defined. We also construct a model for remnant properties of aligned-spin systems with mass ratios $q\leq8$, and spin magnitudes $\chi_1,\chi_2\leq0.8$. As a byproduct, we also provide error estimates for all fitted quantities, which can be consistently incorporated into current and future gravitational-wave parameter-estimation analyses. Our model(s) are made publicly available through a fast and easy-to-use Python module called surfinBH.Comment: 6+5 pages. Matches PRL version. Python implementation available at https://pypi.org/project/surfinBH

Growth response and water relations of three-year-old planted black spruce and jack pine seedlings in site prepared lichen woodlands

Black spruce-lichen woodlands are low tree density stands within the closed crown, North American boreal forest that represent a diverging post-fire type of black spruce forest. As natural densification of lichen woodlands has never been observed, afforestation remains the only way of shifting these stands to closed canopy stands. The objective of the study was to evaluate site preparation effects on growth and water relations of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) seedlings in black spruce-lichen woodlands (LW), compared to managed black spruce-feathermoss stands (BSFM). Site preparation treatments in LW were no preparation (LWno), patch scarification (LWps), and disk scarification (LWds). The operationally managed BSFM stands stood for the control. Results from the third growing season indicate that soil water availability in intact or lightly prepared patch scarified LW is a limiting variable for seedling growth for both black spruce and jack pine seedlings. However, once LW are prepared with disk scarification, this planting check factor is significantly reduced, to the point of being equal to BSFM in terms of water availability and seedling water relations. The significant seedling growth difference, in favor of BSFM, might be a consequence of the lower level of pre-plantation disturbance in LW, compared to BSFM. Our results also suggest that jack pine, through higher water stress tolerance, could constitute a wise silvicultural choice over black spruce, especially with LW established on coarse drought-prone material

Perspective écophysiologique de l'envahissement des éricacées dans le sous-domaine de la pessière noire à mousses de l'Est du Québec

Les arbustes éricacées sont réputés pour nuire à la croissance de l’épinette noire (Picea mariana (Mill.) [B.S.P.]) par une forte compétition pour les ressources. L’ouverture de la voûte forestière par la coupe peut intensifier cette compétition et mener à l’envahissement des plantes éricacées. L’objectif de ce projet de recherche était d’expliquer, par l’évaluation de la réponse des traits fonctionnels, le potentiel d’envahissement des éricacées et la stagnation de la croissance de la régénération naturelle d’épinette noire après coupe dans le domaine de la pessière noire à mousses de l’est. Le premier volet de la thèse démontre que le thé du Labrador (Rhododendron groenlandicum [Oeder] Kron & Judd) s’acclimate rapidement à l’augmentation de lumière causée par la coupe, spécialement dans les coupes les plus intenses, par des modifications physiolgiques. De son côté, les traits morphologiques de l’épinette noire n’ont pas répondu au changement d’environement créé par la coupe, indicant soit une absence ou un délai d’acclimatation. La deuxième expérience terrain a permis de constater que la photosynthèse de l’épinette noire était influencée négativement par la présence des plantes éricacées sur le parterre de coupe, et ce, peu importe la qualité de la station étudiée. Cette réduction du taux de photosynthèse serait attribuable à la plus faible disponibilité en azote minéral dans les parcelles témoin résultant d’une forte compétition souterraine des plantes éricacées pour les ressources nutritives du sol. Une troisième expérience en serre a démontré que la masse foliaire par unité de surface (LMA) du Rhododendron et du Kalmia a diminué avec l’ombrage. L’épinette noire a montré une taux d’absorption et un taux d’absorption spécifique supérieurs à des niveaux d’azote plus élevés comparativement aux éricacées. La plasiticité envers la lumière fut supérieure pour le Kalmia (sauf pour la LMA) et celle envers l’addition d’azote fut supérieure pour le Rhododendron et l’épinette suggérant que la plasticité des traits est en accord avec le statut successionnel des espèces.Ericaceous shrubs are known to impair black spruce (Picea mariana (Mill.) [B.S.P.]) growth by creating a strong competition for below and aboveground resources. Opening of the forest canopy with harvest can intensify this competition and lead to enroachment of ericaceous shrub. Our objective was to explain, through evaluation response of functional traits, ericaceous potential enroachment after logging and stagnant growth of black spruce advance regeneration in the Quebec’s eastern black spruce-feathermoss sub-domain. The first chapter demonstrated the rapid acclimation of bog Labrador tea (Rhododendron groenlandicum [Oeder] Kron & Judd) to higher light availability created by logging, especially in the more intense treatements, through a modification of both physiological leaf traits. On the other hand, black spruce leaf traits did not respond to changes in environement associated with logging; this may indicate either an absence or a delay in acclimation. In a second field experiment, black spruce photosynthetic rate was negatively influenced by ericaceous shrub presence on the cutting area, regardless of the site fertility quality. The lower photosynthesis rate of black spruce, when associated with ericaceous shrubs, could be resulting of a lower mineral soil nitrogen availability created by a greater belowground competition for ressources form the ericaceous shrubs. A third experiment under greenhouse conditions showed that Rhododendron and Kalmia leaf mass per unit of area (LMA) was reduced by shading, but was similar for black spruce. There were few differences in trait response to N addition among species. Black spruce showed higher absorption rate and specific absorption rate at higher N levels, compared to the two ericads. Plasticity to light was higher for Kalmia (except for LMA) and plasticity for nitrogen addition was higher for Rhododendron black spruce suggesting that trait plasticity is in accordance with successional status of these species