Fate of in-medium heavy quarks via a Lindblad equation

What is the dynamics of heavy quarks and antiquarks in a quark gluon plasma? Can heavy-quark bound states dissociate? Can they (re)combine? These questions are addressed by investigating a Lindblad equation that describes the quantum dynamics of the heavy quarks in a medium. The Lindblad equations for a heavy quark and a heavy quark-antiquark pair are derived from the gauge theory, following a chain of well-defined approximations. In this work the case of an abelian plasma has been considered, but the extension to the non-abelian case is feasible. A one-dimensional simulation of the Lindblad equation is performed to extract information about bound-state dissociation, recombination and quantum decoherence for a heavy quark-antiquark pair. All these phenomena are found to depend strongly on the imaginary part of the inter-quark potential.Comment: 50 pages, 10 figures - added references - corrected typos and added a few comments - added appendix

The relative concentration of visible and dark matter in clusters of galaxies

[Abridged] We consider two clusters (A496 and Coma) that are representative of the two classes of cool-core and non-cool-core clusters. We first refer to a two-component dynamical model that ignores the contribution from the galaxy density distribution and study the condition of hydrostatic equilibrium for the hot intracluster medium (ICM) under the assumption of spherical symmetry, in the presence of dark matter. We model the ICM density distribution in terms of a standard $\beta$-model with $\beta=2/3$, i.e. with a distribution similar to that of a regular isothermal sphere (RIS), and fit the observed X-ray brightness profiles. With the explicit purpose of ignoring cosmological arguments, we na\"ively assume that dark matter, if present, has an analogous density distribution, with the freedom of two different density and length scales. The relative distribution of visible and dark matter is then derived by fitting the temperature data for the ICM under conditions of hydrostatic equilibrium. For both clusters, we find that dark matter is more concentrated with respect to visible matter. We then test whether the conclusion changes significantly when dark matter is taken to be distributed according to cosmologically favored density profiles and when the contribution of the mass contained in galaxies is taken into account. Although the qualitative conclusions remain unchanged, we find that the contribution of galaxies to the mass budget is more important than generally assumed. We also show that, without resorting to additional information on the small scale, it is not possible to tell whether a density cusp is present or absent in these systems. [Abridged]Comment: 13 pages, 3 figures, accepted for publication in Il Nuovo Cimento

On the simulation of interactive non-verbal behaviour in virtual humans

Development of virtual humans has focused mainly in two broad areas - conversational agents and computer game characters. Computer game characters have traditionally been action-oriented - focused on the game-play - and conversational agents have been focused on sensible/intelligent conversation. While virtual humans have incorporated some form of non-verbal behaviour, this has been quite limited and more importantly not connected or connected very loosely with the behaviour of a real human interacting with the virtual human - due to a lack of sensor data and no system to respond to that data. The interactional aspect of non-verbal behaviour is highly important in human-human interactions and previous research has demonstrated that people treat media (and therefore virtual humans) as real people, and so interactive non-verbal behaviour is also important in the development of virtual humans. This paper presents the challenges in creating virtual humans that are non-verbally interactive and drawing corollaries with the development history of control systems in robotics presents some approaches to solving these challenges - specifically using behaviour based systems - and shows how an order of magnitude increase in response time of virtual humans in conversation can be obtained and that the development of rapidly responding non-verbal behaviours can start with just a few behaviours with more behaviours added without difficulty later in development

Heavy quark bound states in a quark-gluon plasma: dissociation and recombination

We present a comprehensive approach to the dynamics of heavy quarks in a quark gluon plasma, including the possibility of bound state formation and dissociation. In this exploratory paper, we restrict ourselves to the case of an Abelian plasma, but the extension of the techniques used to the non Abelian case is straightforward. A chain of well defined approximations leads eventually to a generalized Langevin equation, where the force and the noise terms are determined from a correlation function of the equilibrium plasma, and depend explicitly on the configuration of the heavy quarks. We solve the Langevin equation for various initial conditions, various numbers of heavy quark-antiquark pairs, and various temperatures of the plasma. Results of simulations illustrate various expected phenomena: dissociation of bound states as a result of combined effects of screening of the potential and collisions with the plasma constituent, formation of bound pairs (recombination) that occurs when enough heavy quarks are present in the system

O não-poder do papa em Guilherme de Ockham

Os escritos políticos de Ockham giram ao redor da pergunta a respeito do poder do papa. Como esse poder foi concedido por Cristo, deve-se consultar a Sagrada Escritura para saber o que ela diz a respeito. Mas a exegese bíblica cabe aos teólogos e não aos juristas. Na qualidade de teólogo Ockham afirma que os poderes do papa situam-se na ordem espiritual e mesmo nessa ordem ele não é ilimitado, pois se atém ao que foi concedido expressamente por Cristo e deve respeitar a liberdade dos fiéi

The mass accretion rate of galaxy clusters: a measurable quantity

We explore the possibility of measuring the mass accretion rate (MAR) of galaxy clusters from their mass profiles beyond the virial radius $R_{200}$. We derive the accretion rate from the mass of a spherical shell whose inner radius is $2R_{200}$, whose thickness changes with redshift, and whose infall velocity is assumed to be equal to the mean infall velocity of the spherical shells of dark matter halos extracted from $N$-body simulations. This approximation is rather crude in hierarchical clustering scenarios where both smooth accretion and aggregation of smaller dark matter halos contribute to the mass accretion of clusters.Nevertheless, in the redshift range $z=[0,2]$, our prescription returns an average MAR within $20-40 \%$ of the average rate derived from the merger trees of dark matter halos extracted from $N$-body simulations. The MAR of galaxy clusters has been the topic of numerous detailed numerical and theoretical investigations, but so far it has remained inaccessible to measurements in the real universe. Since the measurement of the mass profile of clusters beyond their virial radius can be performed with the caustic technique applied to dense redshift surveys of the cluster outer regions, our result suggests that measuring the mean MAR of a sample of galaxy clusters is actually feasible. We thus provide a new potential observational test of the cosmological and structure formation models.Comment: 11 pages, 7 figures, 5 tables, minor text modifications to match the published version, typos correcte

Genome-wide transcriptomics analysis identifies sox7 and sox18 as specifically regulated by gata4 in cardiomyogenesis

This work was supported by British Heart Foundation (BHF Project Grant no PG/13/23/30080 to B.A.A and S.H.), Biotechnology and Biological Sciences Research Council (BB/M001695/1 to S.H.) and the University of Aberdeen (for A.T.L). Acknowledgements We’re grateful to Ms Yvonne Turnbull and Ms Kate Watt for technical assistance and lab management. We would like to thank Professor Cedric Blanpain and Dr Xionghui Li from Université Libre de Bruxelles for providing training of ES cell manipulation and Mesp1/Gata4 cell lines. We are grateful to Professor Todd Evans from Weill Cornell Medical College for generously providing iGata ES cell lines. We also would like to thank Professor Aaron Zorn and Scott Rankin for providing Xsox18 plasmid.Peer reviewedPublisher PD