An accurate Newtonian description of particle motion around a Schwarzschild black hole

A generalized Newtonian potential is derived from the geodesic motion of test particles in Schwarzschild spacetime. This potential reproduces several relativistic features with higher accuracy than commonly used pseudo-Newtonian approaches. The new potential reproduces the exact location of the marginally stable, marginally bound, and photon circular orbits, as well as the exact radial dependence of the binding energy and the angular momentum of these orbits. Moreover, it reproduces the orbital and epicyclic angular frequencies to better than 6%. In addition, the spatial projections of general trajectories coincide with their relativistic counterparts, while the time evolution of parabolic-like trajectories and the pericentre advance of elliptical-like trajectories are both reproduced exactly. We apply this approach to a standard thin accretion disc and find that the efficiency of energy extraction agrees to within 3% with the exact relativistic value, while the energy flux per unit area as a function of radius is reproduced everywhere to better than 7%. As a further astrophysical application we implement the new approach within a smoothed particle hydrodynamics code and study the tidal disruption of a main-sequence star by a supermassive black hole. The results obtained are in very good agreement with previous relativistic simulations of tidal disruptions in Schwarzschild spacetime. The equations of motion derived from this potential can be implemented easily within existing Newtonian hydrodynamics codes with hardly any additional computational effort.Comment: 11 pages, 8 figures, minor corrections to match version accepted for publication in MNRA

An analytic toy model for relativistic accretion in Kerr spacetime

We present a relativistic model for the stationary axisymmetric accretion flow of a rotating cloud of non-interacting particles falling onto a Kerr black hole. Based on a ballistic approximation, streamlines are described analytically in terms of timelike geodesics, while a simple numerical scheme is introduced for calculating the density field. A novel approach is presented for describing all of the possible types of orbit by means of a single analytic expression. This model is a useful tool for highlighting purely relativistic signatures in the accretion flow dynamics coming from a strong gravitational field with frame-dragging. In particular, we explore the coupling due to this between the spin of the black hole and the angular momentum of the infalling matter. Moreover, we demonstrate how this analytic solution may be used for benchmarking general relativistic numerical hydrodynamics codes by comparing it against results of smoothed particle hydrodynamics simulations for a collapsar-like setup. These simulations are performed first for a ballistic flow (with zero pressure) and then for a hydrodynamical one where we measure the effects of pressure gradients on the infall, thus exploring the extent of applicability of the ballistic approximation.Comment: 15 pages, 8 figures, references and minor changes added to match version accepted for publication in MNRA

IDENTIFICACIÓN MORFOLÓGICA, FISIOLÓGICA Y MOLECULAR DE LEVADURAS DEL GÉNERO SACCHAROMYCES PARA LA ELABORACIÓN DE CERVEZA

We  sought  to  recognize  key  patterns  to identifying morphologically, physiologically and molecularly yeasts of the genus Sac-charomyces through bibliographic search in  databases  (FEMS:  Yeast  research, PMC-NCBI  and  Google  academic).  Beer  is a non-distilled, frothy alcoholic beverage resulting from a fermentation process using yeasts. Yeasts are unicellular microscopic organisms belong to the Eukarya domain and  there  are  classified  within  the  Fungi kingdom. The knowledge of yeasts is im-portant in the food industry because of the ability to convert carbohydrates into etha-nol and CO2 through the process of alco-holic fermentation. Yeasts can be morpho-logically,  physiologically  and  molecularly identified by PCR techniques, low molecu-lar weight RNA (LMW-RNA), microsatellite analysis, Length polymorphism in the res-triction fragments of rDNA / rRNA (RFLP)Se  busco  reconocer  pautas  clave  al  mo-mento de identificar morfológica, fisiológi-ca y molecularmente levaduras del género Saccharomyces para  la  elaboración  de  cerveza  mediante  la  búsqueda  bibliográfica en bases de datos (FEMS: Yeast re-search, PMC-NCBI y Google académico). La  cerveza  es  una  bebida  alcohólica  no destilada, espumosa, resultante de un pro-ceso  de  fermentación  usando  levaduras.  Las  levaduras  como  organismos  micros-cópicos unicelulares son pertenecientes al dominio Eukarya y están clasificadas dentro del reino Fungi. El conocimiento de las levaduras es importante en la industria de los alimentos por la capacidad que poseen de  convertir  carbohidratos  en  etanol  y CO2 mediante el proceso de fermentación alcohólica. Las levaduras pueden identificarse de forma morfológica, fisiológica y molecular por medio de técnicas de PCR, ARN de bajo peso molecular (LMW-RNA), análisis de microsatélites, Polimorfismo de longitud  en  los  fragmentos  de  restricción  del ADNr/ARNr(RFLP)

Isolated Fe(III)-O Sites Catalyze the Hydrogenation of Acetylene in Ethylene Flows under Front-End Industrial Conditions

[EN] The search for simple, earth-abundant, cheap, and nontoxic metal catalysts able to perform industrial hydrogenations is a topic of interest, transversal to many catalytic processes. Here, we show that isolated FeIII¿O sites on solids are able to dissociate and chemoselectively transfer H2 to acetylene in an industrial process. For that, a novel, robust, and highly crystalline metal¿organic framework (MOF), embedding FeIII¿OH2 single sites within its pores, was prepared in multigram scale and used as an efficient catalyst for the hydrogenation of 1% acetylene in ethylene streams under front-end conditions. Cutting-edge X-ray crystallography allowed the resolution of the crystal structure and snapshotted the single-atom nature of the catalytic FeIII¿O site. Translation of the active site concept to even more robust and inexpensive titania and zirconia supports enabled the industrially relevant hydrogenation of acetylene with similar activity to the Pd-catalyzed process.This work was supported by the MINECO (Spain) (Projects CTQ2016-75671-P, CTQ2014-56312-P, CTQ2014-55178-R, and Excellence Units "Severo Ochoa" and "Maria de Maeztu" SEV-2016-0683 and MDM-2015-0538) and the Ministero dell'Istruzione, dell'Universita e della Ricerca (Italy) (FFABR 2017). M.M. thanks the mineco for a predoctoral contract. Thanks are also extended to the Ramon y Cajal Program (E.P.) and the "Suprograma atraccio de talent-contractes postdoctorals de la Universitat de Valencia" (J.F.-S.). A.L.-P. and J.F.S. also thank fBBVA for the concession of a young investigator grants.Tejeda-Serrano, M.; Mon, M.; Ross, B.; Gonell-Gómez, F.; Ferrando-Soria, J.; Corma Canós, A.; Leyva Perez, A.... (2018). Isolated Fe(III)-O Sites Catalyze the Hydrogenation of Acetylene in Ethylene Flows under Front-End Industrial Conditions. Journal of the American Chemical Society. 140(28):8827-8832. https://doi.org/10.1021/jacs.8b04669S882788321402