Entropy "floor" and effervescent heating of intracluster gas

Recent X-ray observations of clusters of galaxies have shown that the entropy of the intracluster medium (ICM), even at radii as large as half the virial radius, is higher than that expected from gravitational processes alone. This is thought to be the result of nongravitational processes influencing the physical state of the ICM. In this paper, we investigate whether heating by a central AGN can explain the distribution of excess entropy as a function of radius. The AGN is assumed to inject buoyant bubbles into the ICM, which heat the ambient medium by doing pdV work as they rise and expand. Several authors have suggested that this "effervescent heating" mechanism could allow the central regions of clusters to avoid the ``cooling catastrophe''. Here we study the effect of effervescent heating at large radii. Our calculations show that such a heating mechanism is able to solve the entropy problem. The only free parameters of the model are the time-averaged luminosity and the AGN lifetime. The results are mainly sensitive to the total energy injected into the cluster. Our model predicts that the total energy injected by AGN should be roughly proportional to the cluster mass. The expected correlation is consistent with a linear relation between the mass of the central black hole(s) and the mass of the cluster, which is reminiscent of the Magorrian relation between the black hole and bulge mass.Comment: accepted for Ap

Stochastic modeling of Congress

We analyze the dynamics of growth of the number of congressmen supporting the resolution HR1207 to audit the Federal Reserve. The plot of the total number of co-sponsors as a function of time is of "Devil's staircase" type. The distribution of the numbers of new co-sponsors joining during a particular day (step height) follows a power law. The distribution of the length of intervals between additions of new co-sponsors (step length) also follows a power law. We use a modification of Bak-Tang-Wiesenfeld sandpile model to simulate the dynamics of Congress and obtain a good agreement with the data

Simulation and theory of vibrational phase relaxation in the critical and supercritical nitrogen: Origin of observed anomalies

We present results of extensive computer simulations and theoretical analysis of vibrational phase relaxation of a nitrogen molecule along the critical isochore and also along the gas-liquid coexistence. The simulation includes all the different contributions [atom-atom (AA), vibration-rotation (VR) and resonant transfer] and their cross-correlations. Following Everitt and Skinner, we have included the vibrational coordinate ($q$) dependence of the interatomic potential. It is found that the latter makes an important contribution. The principal important results are: (a) a crossover from a Lorentzian-type to a Gaussian line shape is observed as the critical point is approached along the isochore (from above), (b) the root mean square frequency fluctuation shows nonmonotonic dependence on the temperature along critical isochore, (c) along the coexistence line and the critical isochore the temperature dependent linewidth shows a divergence-like $\lambda$-shape behavior, and (d) the value of the critical exponents along the coexistence and along the isochore are obtained by fitting. The origin of the anomalous temperature dependence of linewidth can be traced to simultaneous occurrence of several factors, (i) the enhancement of negative cross-correlations between AA and VR contributions and (ii) the large density fluctuations as the critical point (CP) is approached. The former makes the decay faster so that local density fluctuations are probed on a femtosecond time scale. A mode coupling theory (MCT) analysis shows the slow decay of the enhanced density fluctuations near critical point. The MCT analysis demonstrates that the large enhancement of VR coupling near CP arises from the non-Gaussian behavior of density fluctuation and this enters through a nonzero value of the triplet direct correlation function.Comment: 35 pages, 15 figures, revtex4 (preprint form

The Eastwood-Singer gauge in Einstein spaces

Electrodynamics in curved spacetime can be studied in the Eastwood--Singer gauge, which has the advantage of respecting the invariance under conformal rescalings of the Maxwell equations. Such a construction is here studied in Einstein spaces, for which the Ricci tensor is proportional to the metric. The classical field equations for the potential are then equivalent to first solving a scalar wave equation with cosmological constant, and then solving a vector wave equation where the inhomogeneous term is obtained from the gradient of the solution of the scalar wave equation. The Eastwood--Singer condition leads to a field equation on the potential which is preserved under gauge transformations provided that the scalar function therein obeys a fourth-order equation where the highest-order term is the wave operator composed with itself. The second-order scalar equation is here solved in de Sitter spacetime, and also the fourth-order equation in a particular case, and these solutions are found to admit an exponential decay at large time provided that square-integrability for positive time is required. Last, the vector wave equation in the Eastwood-Singer gauge is solved explicitly when the potential is taken to depend only on the time variable.Comment: 13 pages. Section 6, with new original calculations, has been added, and the presentation has been improve

AGN heating, thermal conduction and Sunyaev-Zeldovich effect in galaxy groups and clusters

(abridged) We investigate in detail the role of active galactic nuclei on the physical state of the gas in galaxy groups and clusters, and the implications for anisotropy in the CMB from Sunyaev-Zeldovich effect. We include the effect of thermal conduction, and find that the resulting profiles of temperature and entropy are consistent with observations. Unlike previously proposed models, our model predicts that isentropic cores are not an inevitable consequence of preheating. The model also reproduces the observational trend for the density profiles to flatten in lower mass systems. We deduce the energy E_agn required to explain the entropy observations as a function of mass of groups and clusters M_cl and show that E_agn is proportional to M_cl^alpha with alpha~1.5. We demonstrate that the entropy measurements, in conjunction with our model, can be translated into constraints on the cluster--black hole mass relation. The inferred relation is nonlinear and has the form M_bh\propto M_cl^alpha. This scaling is an analog and extension of a similar relation between the black hole mass and the galactic halo mass that holds on smaller scales. We show that the central decrement of the CMB temperature is reduced due to the enhanced entropy of the ICM, and that the decrement predicted from the plausible range of energy input from the AGN is consistent with available data of SZ decrement. We show that AGN heating, combined with the observational constraints on entropy, leads to suppression of higher multipole moments in the angular power spectrum and we find that this effect is stronger than previously thought.Comment: accepted for publication in The Astrophysical Journa

Non-full rank bound entangled states satisfying the range criterion

A systematic method for generating bound entangled states in any bipartite system, with ranks ranging from five to full rank, is presented. These states are constructed by mixing separable states with UPB (Unextendible Product Basis) - generated PPT bound entangled states. A subset of this class of PPT bound entangled states, having less than full rank, is shown to satisfy the range criterion [Phys. Lett. A, vol. 232 (1997) 333].Comment: 6 pages, Latex. Minor corrections and additions. More references added. Accepted for publication in Phys. Rev.

Threshold Error Penalty for Fault Tolerant Computation with Nearest Neighbour Communication

The error threshold for fault tolerant quantum computation with concatenated encoding of qubits is penalized by internal communication overhead. Many quantum computation proposals rely on nearest-neighbour communication, which requires excess gate operations. For a qubit stripe with a width of L+1 physical qubits implementing L levels of concatenation, we find that the error threshold of 2.1x10^-5 without any communication burden is reduced to 1.2x10^-7 when gate errors are the dominant source of error. This ~175X penalty in error threshold translates to an ~13X penalty in the amplitude and timing of gate operation control pulses.Comment: minor correctio

Spinor two-point functions and Peierls bracket in de Sitter space

This paper studies spinor two-point functions for spin-1/2 and spin-3/2 fields in maximally symmetric spaces such as de Sitter spacetime, by using intrinsic geometric objects. The Feynman, positive- and negative-frequency Green functions are then obtained for these cases, from which we eventually display the supercommutator and the Peierls bracket under such a setting in two-component-spinor language.Comment: 22 pages, Latex. In the final version, the presentation has been improve

On the complete analytic structure of the massive gravitino propagator in four-dimensional de Sitter space

With the help of the general theory of the Heun equation, this paper completes previous work by the authors and other groups on the explicit representation of the massive gravitino propagator in four-dimensional de Sitter space. As a result of our original contribution, all weight functions which multiply the geometric invariants in the gravitino propagator are expressed through Heun functions, and the resulting plots are displayed and discussed after resorting to a suitable truncation in the series expansion of the Heun function. It turns out that there exist two ranges of values of the independent variable in which the weight functions can be divided into dominating and sub-dominating family.Comment: 21 pages, 9 figures. The presentation has been further improve

UOLO - automatic object detection and segmentation in biomedical images

We propose UOLO, a novel framework for the simultaneous detection and segmentation of structures of interest in medical images. UOLO consists of an object segmentation module which intermediate abstract representations are processed and used as input for object detection. The resulting system is optimized simultaneously for detecting a class of objects and segmenting an optionally different class of structures. UOLO is trained on a set of bounding boxes enclosing the objects to detect, as well as pixel-wise segmentation information, when available. A new loss function is devised, taking into account whether a reference segmentation is accessible for each training image, in order to suitably backpropagate the error. We validate UOLO on the task of simultaneous optic disc (OD) detection, fovea detection, and OD segmentation from retinal images, achieving state-of-the-art performance on public datasets.Comment: Publised on DLMIA 2018. Licensed under the Creative Commons CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0