Cosmological black holes and the direction of time

Macroscopic irreversible processes emerge from fundamental physical laws of reversible character. The source of the local irreversibility seems to be not in the laws themselves but in the initial and boundary conditions of the equations that represent the laws. In this work we propose that the screening of currents by black hole event horizons determines, locally, a preferred direction for the flux of electromagnetic energy. We study the growth of black hole event horizons due to the cosmological expansion and accretion of cosmic microwave background radiation, for different cosmological models. We propose generalized McVittie co-moving metrics and integrate the rate of accretion of cosmic microwave background radiation onto a supermassive black hole over cosmic time. We find that for flat, open, and closed Friedmann cosmological models, the ratio of the total area of the black hole event horizons with respect to the area of a radial co-moving space-like hypersurface always increases. Since accretion of cosmic radiation sets an absolute lower limit to the total matter accreted by black holes, this implies that the causal past and future are not mirror symmetric for any spacetime event. The asymmetry causes a net Poynting flux in the global future direction; the latter is in turn related to the ever increasing thermodynamic entropy. Thus, we expose a connection between four different "time arrows": cosmological, electromagnetic, gravitational, and thermodynamic.Comment: 13 pages, 2 figures in Foundations of Science (2017

El espacio y el tiempo

Preguntas sobre el espacio y el tiempo inquietan los pensamientos del hombre desde hace miles de años. ¿Qué es el espacio? ¿Qué es el tiempo? ¿Vale la pena responder estas preguntas? Presento en este artículo las posturas de algunos pensadores, y mi posición al respecto, con el fin de destacar la importancia de esta área de la Filosofía

Perspectivas epistemológicas no estudo científico e a avaliação clínica das funções executivas

En este artículo se examinan perspectivas epistemológicas que han moldeado e influenciado la búsqueda científica orientada hacia comprender aquello que los neuropsicólogos denominan las "funciones ejecutivas (FE). El término funciones ejecutivas se refiere a aspectos de control de la cognición y la conducta. Las ideas expuestas en este manuscrito presuponen que la orientación epistemológica de una persona determina la manera en la que ella conceptualiza la interacción entre las funciones cerebrales y su entorno físico. Cada una de esas orientaciones conlleva suposiciones acerca del modo como operan las FE y, por ende, el modo como deben ser evaluadas. Hasta fechas recientes esto se había abordado principalmente desde el punto de vista de dos perspectivas teóricas. Una de ellas, la analítica, tiene sus raíces en el movimiento positivista. La otra, también conocida como "ciencia romántica" es sintética, y provee las bases del trabajo científico del muy celebrado neuropsicólogo ruso A.R. Luria. Una tercera perspectiva, formulada en el marco de la "cognición corpórea", ha sido propuesta en los últimos 20 años, y está más estrechamente asociada con los trabajos de Francisco Varela. Se examina aquí, por medio de una revisión reflexiva e integradora de la literatura pertinente, la manera como esas tres perspectivas epistemológicas han influido sobre la investigación y la práctica clínica de la neuropsicología.In this article, epistemological perspectives that have shaped and affected the scientific quest for understanding what neuropsychologists term "executive functions" are reviewed. Executive functions refer to the control functions of cognition and behavior. The underlying thesis of the paper is that one's epistemological orientation determines how one sees the interaction between brain functions and our status in the world. Each different orientation thus carries with it implications with regard to how executive functions operate, as well as how, therefore, one should try to assess them. Until recently, these functions were approached through two primary epistemological points of view. One is analytic, which has its roots in the positivistic movement. The other approach is synthetic, otherwise known as "romantic science", and forms the basis of the work of the prominent Russian neuropsychologist A.R. Luria. A third epistemological perspective, articulated under the umbrella of 'embodied cognition' approaches, has been advanced in the last 20 years, and is associated most closely with the work of Francisco Varela. A review of, and reflection on how these perspectives have affected research and clinical practice in neuropsychology is provided.Neste artigo examinam-se as perspectivas epistemológicas que moldaram e influenciaram a busca científica orientada à compreender aquilo que os neuropsicólogos denominam as "funções executivas (FE). O termo funções executivas se refere a aspectos de controle da cognição e a conduta. As ideias expostas neste manuscrito pressupõem que a orientação epistemológica de uma pessoa determina a maneira em que ela conceitualiza a interação entre as funções cerebrais e seu entorno físico. Cada uma dessas orientações leva a suposições sobre o modo como operam as FE e, portanto, o modo como devem ser avaliadas. Até datas recentes isto havia sido abordado principalmente desde o ponto de vista de duas perspectivas teóricas. Uma delas, a analítica, tem suas raízes no movimento positivista. A outra, também conhecida como "ciência romântica" é sintética, e fornece as bases do trabalho científico do muito celebrado neuropsicólogo russo A.R. Luria. Uma terceira perspectiva, formulada no marco da "cognição corpórea", foi proposta nos últimos 20 anos, e está mais estreitamente associada com os trabalhos de Francisco Varela. Examina-se aqui, através de uma revisão reflexiva e integradora da literatura pertinente, a maneira como essas três perspectivas epistemológicas influíram sobre a pesquisa e a prática da neuropsicologia

Some results on homoclinic and heteroclinic connections in planar systems

Consider a family of planar systems depending on two parameters $(n,b)$ and having at most one limit cycle. Assume that the limit cycle disappears at some homoclinic (or heteroclinic) connection when $\Phi(n,b)=0.$ We present a method that allows to obtain a sequence of explicit algebraic lower and upper bounds for the bifurcation set ${\Phi(n,b)=0}.$ The method is applied to two quadratic families, one of them is the well-known Bogdanov-Takens system. One of the results that we obtain for this system is the bifurcation curve for small values of $n$, given by $b=\frac5 7 n^{1/2}+{72/2401}n- {30024/45294865}n^{3/2}- {2352961656/11108339166925} n^2+O(n^{5/2})$. We obtain the new three terms from purely algebraic calculations, without evaluating Melnikov functions

Credence cues of pork are more important than consumers' culinary skills to boost their purchasing intention

The role of consumers' culinary skills on purchasing cues of pork, with emphasis on niche demands (outdoor husbandry and/or certified organic), was assessed in cross-country regions of Spain (Catalonia and Aragon) and Portugal (North). A sample of 974 respondents answered an on-line survey with questions regarding consumer purchasing habits, product involvement and intrinsic and credence attributes. They also chose between two contrasting boneless pork loins and express willingness to pay (WTP) for different product scenarios with different pig farm facilities and for organic pork standards. Two optimal segments were identified based on food-related habits: ‘uninvolved’ and ‘innovative cook lovers’, both similarly balanced across socio-demographics, score for credence attributes or consumer involvement dimensions. Overall mean WTP premium across countries was 11.8% for marbled pork, 20.0% for outdoor pork and 24.3% for organic logo stamp. Credence cues of pork claiming health issues (absence of antibiotics and hormone residues) rather than consumers' culinary skills defined the WTP for niche pork in these regions

Botryosphaeriaceae species associated with diseased loquat trees in Italy and description of Diplodia rosacearum sp. nov

[EN] Loquat (Eriobotrya japonica) is a fruit tree cultivated in several countries in the Mediterranean region. A survey of a loquat orchard in Sicily ( Italy) revealed the presence of plants showing dieback symptoms and cankers with wedge-shaped necrotic sectors. Fungi from the genera Diplodia and Neofusicoccum were isolated from symptomatic plants. On the basis of morphological characters and DNA sequence data four species were identified, Neofusicoccum parvum, N. vitifusiforme, Diplodia seriata and a novel Diplodia species, which is here described as D. rosacearum sp. nov. Inoculation trials of loquat plants cv Sanfilipparo showed that N. parvum, D. seriata and D. rosacearum were pathogenic to this host. Although variability was observed between isolates, N. parvum and D. rosacearum were the most aggressive species.This research was supported by Servizio VII Fitosanitario Forestale del Dipartimento Regionale, Azienda Regionale Foreste Demaniali. Artur Alves acknowledges financing by European Funds through COMPETE and by National Funds through the Portuguese Foundation for Science and Technology (FCT) to the research unit CESAM (UID/AMB/50017/2013 - POCI-01-0145-FEDER-007638) and himself (FCT Investigator Programme - IF/00835/2013), and support by the Contributi avvio e sviluppo collaborazioni internazionali (CORI-2014), Visiting Professor Programme at the University of Palermo, Italy. The authors thank Dr. Giuseppe Lo Giudice for allowing carrying out the surveys in his loquat field.Giambra, S.; Piazza, G.; Alves, A.; Mondello, V.; Berbegal Martinez, M.; Armengol Fortí, J.; Burruano, S. (2016). Botryosphaeriaceae species associated with diseased loquat trees in Italy and description of Diplodia rosacearum sp. nov. Mycosphere (Online). 7(7):978-989. https://doi.org/10.5943/mycosphere/si/1b/9S9789897

The Case for Quantum Key Distribution

Quantum key distribution (QKD) promises secure key agreement by using quantum mechanical systems. We argue that QKD will be an important part of future cryptographic infrastructures. It can provide long-term confidentiality for encrypted information without reliance on computational assumptions. Although QKD still requires authentication to prevent man-in-the-middle attacks, it can make use of either information-theoretically secure symmetric key authentication or computationally secure public key authentication: even when using public key authentication, we argue that QKD still offers stronger security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009 Workshop on Quantum and Classical Information Security; version 2 minor content revision

Some properties of the k-dimensional Lyness' map

This paper is devoted to study some properties of the k-dimensional Lyness' map. Our main result presentes a rational vector field that gives a Lie symmetry for F. This vector field is used, for k less or equal to 5 to give information about the nature of the invariant sets under F. When k is odd, we also present a new (as far as we know) first integral for F^2 which allows to deduce in a very simple way several properties of the dynamical system generated by F. In particular for this case we prove that, except on a given codimension one algebraic set, none of the positive initial conditions can be a periodic point of odd period.Comment: 22 pages; 3 figure

Ameliorating the Courant-Friedrichs-Lewy condition in spherical coordinates: A double FFT filter method for general relativistic MHD in dynamical spacetimes

Numerical simulations of merging compact objects and their remnants form the theoretical foundation for gravitational wave and multi-messenger astronomy. While Cartesian-coordinate-based adaptive mesh refinement is commonly used for simulations, spherical-like coordinates are more suitable for nearly spherical remnants and azimuthal flows due to lower numerical dissipation in the evolution of fluid angular momentum, as well as requiring fewer numbers of computational cells. However, the use of spherical coordinates to numerically solve hyperbolic partial differential equations can result in severe Courant-Friedrichs-Lewy (CFL) stability condition timestep limitations, which can make simulations prohibitively expensive. This paper addresses this issue for the numerical solution of coupled spacetime and general relativistic magnetohydrodynamics evolutions by introducing a double FFT filter and implementing it within the fully MPI-parallelized SphericalNR framework in the Einstein Toolkit. We demonstrate the effectiveness and robustness of the filtering algorithm by applying it to a number of challenging code tests, and show that it passes these tests effectively, demonstrating convergence while also increasing the timestep significantly compared to unfiltered simulations.Comment: 15 pages, 13 figures, revtex4-