Functional Methods and Effective Potentials for Nonlinear Composites

A formulation of variational principles in terms of functional integrals is proposed for any type of local plastic potentials. The minimization problem is reduced to the computation of a path integral. This integral can be used as a starting point for different approximations. As a first application, it is shown how to compute to second-order the weak-disorder perturbative expansion of the effective potentials in random composite. The three-dimensional results of Suquet and Ponte-Casta\~neda (1993) for the plastic dissipation potential with uniform applied tractions are retrieved and extended to any space dimension, taking correlations into account. In addition, the viscoplastic potential is also computed for uniform strain rates.Comment: 20 pages, accepted for publication in JMP

The Effect of the AGN Feedback on the Interstellar Medium of Early-Type Galaxies: 2D Hydrodynamical Simulations of the Low-Rotation Case

We present 2D hydrodynamical simulations for the evolution of early-type galaxies containing central massive black holes (MBHs), starting at age 2 Gyr. The code contains accurate and physically consistent radiative and mechanical AGN wind feedback, with parsec-scale central resolution. Mass input comes from stellar evolution; energy input includes Type Ia and II supernova and stellar heating; star-formation is included. Realistic, axisymmetric dynamical models for the galaxies are built solving the Jeans' equations. The lowest mass models (Mstar = 8 10^{10}Msun) develop global outflows sustained by SNIa's heating, ending with a significantly lower amount of hot gas and new stars. In more massive models, nuclear outbursts last to the present epoch, with large and frequent fluctuations in nuclear emission and from the gas (Lx). Each burst last ~ 10^{7.5} yr, during which (for r < 2-3 kpc) cold, inflowing, and hot, outflowing gas phases coexist. The Lx-T relation for the gas matches that of local galaxies. AGN activity causes positive feedback for star formation. Roughly half of the total mass loss is recycled into new stars (DeltaMstar), just ~ 3% of it is accreted on the MBH, the remainder being ejected from the galaxy. The ratio between the mass of gas expelled to that in to new stars, the load factor, is ~0.6. Rounder galaxies shapes lead to larger final MBH masses, DeltaMstar, and Lx. Almost all the time is spent at very low nuclear luminosities, yet one quarter of the total energy is emitted at an Eddington ratio > 0.1. The duty-cycle of AGN activity approximates 4% (Abridged).Comment: 26 pages, 15 figure, submitted to ApJ. Comments welcom

About the Reaction to ‘Styles of Thought on the Continental Drift Debate’

The article appearing previously in this journal entitled “Styles of Thought on the Continental Drift Debate” (Pellegrini 2019) prompted a response from Weber and Šešelja (2020) which they termed as “a defence of rationalist accounts”. They argue that their self-designated “sophisticated rationalism” explains the closure of the continental-drift debate without being affected by my critiques to rationalist approaches. While ignoring the empirical evidence that shows the complexity of the debate and the necessity to include broader social elements in the analysis (such as scientists denying continental drift even after the plate tectonics theory, others supporting it without being familiarized with the literature), they proclaim to be unconvinced about the analysis of the styles of thought. In order to clarify differences in the approach to the continental-drift historical controversy, I respond here to the criticism my paper drew while discussing the place of rationalism when explaining the acceptance of a theory. I will argue that their distinction between “crude” and “sophisticated” rationalism does not solve the problem of social aspects being left aside by rationalists in view of the acceptance of a theory. I will also argue that in order to understand what leads people to embrace a belief (namely scientists in accepting a theory), the analysis of mere cognitive or epistemic arguments is not enough and it leads to a reductionist explanation as to social behaviour.Fil: Pellegrini, Pablo Ariel. Universidad Nacional de Quilmes. Departamento de Ciencias Sociales. Instituto de Estudios Sociales de la Ciencia y la Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Cooling flows and quasars: II. Detailed models of feedback modulated accretion flows

Most elliptical galaxies contain central black holes (BHs), and most also contain significant amounts of hot gas capable of accreting on to the central BH due to cooling times short compared to the Hubble time. Why therefore do we not see AGNs at the center of most elliptical galaxies rather than in only (at most) a few per cent of them? We propose here the simple idea that feedback from accretion events heats the ambient gas retarding subsequent infall. In this context, we present a class of 1D hydrodynamical evolutionary sequences for the gas flows in elliptical galaxies with a massive central BH. The resulting evolution is characterized by strong oscillations, in which very fast and energetic bursts of the BH are followed by longer periods in which the X-ray galaxy emission comes from the coronal gas. We also allow for departures from spherical symmetry by examining scenarios in which the central engine is either an ADAF or a more conventional accretion disk that is optically thick except for a polar region. In all cases the duty cycle (fraction of the time that the system will be seen as an AGN) is quite small and in the range 10^{-4} - 10^{-3}. Thus, for any reasonable value of the efficiency, the presence of a massive BH at the center of a galaxy seems to be incompatible with the presence of a long-lived cooling flow.Comment: 43 pages, 10 figures. Main additions concern observed Compton temperatures and few extra numerical models. Conclusions unchanged. 1 new table and 3 new figures. Accepted for publication on ApJ (main journal

Non Markovian Quantum Repeated Interactions and Measurements

A non-Markovian model of quantum repeated interactions between a small quantum system and an infinite chain of quantum systems is presented. By adapting and applying usual pro jection operator techniques in this context, discrete versions of the integro-differential and time-convolutioness Master equations for the reduced system are derived. Next, an intuitive and rigorous description of the indirect quantum measurement principle is developed and a discrete non Markovian stochastic Master equation for the open system is obtained. Finally, the question of unravelling in a particular model of non-Markovian quantum interactions is discussed.Comment: 22 page

Properties of Very Luminous Galaxies

Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has shown that very luminous galaxies are much more strongly clustered than fainter galaxies. In fact, the amplitude of the correlation function of very luminous galaxies ($L > L^*$) asymptotically approaches that of $R \ge 0$ clusters. In this paper we investigate the properties of the most luminous galaxies, with blue absolute magnitude $M_B \le -21$. We find that: 1) the population mix is comparable to that in other ranges of absolute magnitudes; 2) only a small fraction are located in bona fide clusters; 3) the bright galaxy-cluster cross-correlation function is significantly higher on large scales than that measured for fainter galaxies; 4) the correlation length of galaxies brighter than \MB $\sim -20.0$, expressed as a function of the mean interparticle distance, appears to follow the universal dimensionless correlation function found for clusters and radio galaxies; 5) a large fraction of the bright galaxies are in interacting pairs, others show evidence for tidal distortions, while some appear to be surrounded by faint satellite galaxies. We conclude that very luminous optical galaxies differ from the normal population of galaxies both in the clustering and other respects. We speculate that this population is highly biased tracers of mass, being associated to dark halos with masses more comparable to clusters than typical loose groups.Comment: 29 pages (6 figures) + 2 tables; paper with all figures and images available at http://boas5.bo.astro.it/~cappi/papers.html; The Astronomical Journal, in pres

X-ray properties expected from AGN feedback in elliptical galaxies

The ISM evolution of elliptical galaxies experiencing feedback from accretion onto a central black hole was studied recently with high-resolution 1D hydrodynamical simulations including radiative heating and pressure effects, a RIAF-like radiative efficiency, mechanical input from AGN winds, and accretion-driven starbursts. Here we focus on the observational properties of the models in the X-ray band (nuclear luminosity; hot ISM luminosity and temperature; temperature and brightness profiles during quiescence and during outbursts). The nuclear bursts last for ~10^7 yr, with a duty-cycle of a few X (10^-3-10^-2); the present epoch bolometric nuclear emission is very sub-Eddington. The ISM thermal luminosity \lx oscillates in phase with the nuclear one; this helps reproduce statistically the observed large \lx variation. In quiescence the temperature profile has a negative gradient; thanks to past outbursts, the brightness profile lacks the steep shape typical of inflowing models. Outbursts produce disturbances in these profiles. Most significantly, a hot bubble from shocked hot gas is inflated at the galaxy center; the bubble would be conical in shape, and show radio emission. The ISM resumes a smooth appearance on a time-scale of ~200 Myr; the duty-cycle of perturbances in the ISM is of the order of 5-10%. From the present analysis, additional input physics is important in the ISM-black hole coevolution, to fully account for the properties of real galaxies, as a confining external medium and a jet. The jet will reduce further the mass available for accretion (and then the Eddington ratio $l$), and may help, together with an external pressure, to produce flat or positive temperature gradient profiles (observed in high density environments). Alternatively, $l$ can be reduced if the switch from high to low radiative efficiency takes place at a larger $l$ than routinely assumed.Comment: 40 pages, submitted to Ap

Energy Consumption Minimization Problem In A Railway Network

EWGT 2016 - 19th EURO Working Group on Transportation Meeting, Istanbul, TURQUIE, 05-/09/2016 - 07/09/2016; When train operations are perturbed, a new working timetable needs to be computed in real-time. In the literature, several algorithms have been proposed for optimizing this computation. This optimization usually does not consider energy consumption. However, minimizing energy consumption is a central issue both from the environmental and economic perspective. In this paper, we address the real-time problem of minimizing the energy consumption. The energy consumption depends on driving regimes used by the train drivers. Hence, we focus on the decision of the appropriate driving regimes throughout each train's travel along a given infrastructure. A model and solution approach for this problem are provided. We show a proof of concept on the applicability of this solution approach on a simple test case

The Hot Interstellar Medium in Normal Elliptical Galaxies III: The Thermal Structure of the Gas

This is the third paper in a series analyzing X-ray emission from the hot interstellar medium in a sample of 54 normal elliptical galaxies observed by Chandra, focusing on 36 galaxies with sufficient signal to compute radial temperature profiles. We distinguish four qualitatively different types of profile: positive gradient (outwardly rising), negative gradients (falling), quasi-isothermal (flat) and hybrid (falling at small radii, then rising). We measure the mean logarithmic temperature gradients in two radial regions: from 0--2 $J$-band effective radii $R_J$ (excluding the central point source), and from 2--$4R_J$. We find the outer gradient to be uncorrelated with intrinsic host galaxy properties, but strongly influenced by the environment: galaxies in low-density environments tend to show negative outer gradients, while those in high-density environments show positive outer gradients, suggesting influence of circumgalactic hot gas. The inner temperature gradient is unaffected by the environment but strongly correlated with intrinsic host galaxy characteristics: negative inner gradients are more common for smaller, optically faint, low radio-luminosity galaxies, whereas positive gradients are found in bright galaxies with stronger radio sources. There is no evidence for bimodality in the distribution of inner or outer gradients. We propose three scenarios to explain the inner temperature gradients: (1) Weak AGN heat the ISM locally, higher-luminosity AGN heat the system globally through jets inflating cavities at larger radii; (2) The onset of negative inner gradients indicates a declining importance of AGN heating relative to other sources, such as compressional heating or supernovae; (3) The variety of temperature profiles are snapshots of different stages of a time-dependent flow.Comment: 18 pages, emulateapj, 55 figures (36 online-only figures included in astro-ph version), submitted to Ap