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Search Results: 1 - 10 of 51549 matches for " Carlos; Rebelo "
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Thermodynamical description of stationary, asymptotically flat solutions with conical singularities
Carlos Herdeiro,Eugen Radu,Carmen Rebelo
Physics , 2010, DOI: 10.1103/PhysRevD.81.104031
Abstract: We examine the thermodynamical properties of a number of asymptotically flat, stationary (but not static) solutions having conical singularities, with both connected and non-connected event horizons, using the thermodynamical description recently proposed in arXiv:0912.3386 [gr-qc]. The examples considered are the double-Kerr solution, the black ring rotating in either S^2 or S^1 and the black Saturn, where the balance condition is not imposed for the latter two solutions. We show that not only the Bekenstein-Hawking area law is recovered from the thermodynamical description but also the thermodynamical angular momentum is the ADM angular momentum. We also analyse the thermodynamical stability and show that, for all these solutions, either the isothermal moment of inertia or the specific heat at constant angular momentum is negative, at any point in parameter space. Therefore, all these solutions are thermodynamically unstable in the grand canonical ensemble.
On the interaction between two Kerr black holes
Carlos A. R. Herdeiro,Carmen Rebelo
Physics , 2008, DOI: 10.1088/1126-6708/2008/10/017
Abstract: The double-Kerr solution is generated using both a Backlund transformation and the Belinskii-Zakharov inverse-scattering technique. We build a dictionary between the parametrisations naturally obtained in the two methods and show their equivalence. We then focus on the asymptotically flat double-Kerr system obeying the axis condition which is Z_2^\phi invariant; for this system there is an exact formula for the force between the two black holes, in terms of their physical quantities and the coordinate distance. We then show that 1) the angular velocity of the two black holes decreases from the usual Kerr value at infinite distance to zero in the touching limit; 2) the extremal limit of the two black holes is given by |J|=cM^2, where c depends on the distance and varies from one to infinity as the distance decreases; 3) for sufficiently large angular momentum the temperature of the black holes attains a maximum at a certain finite coordinate distance. All of these results are interpreted in terms of the dragging effects of the system.
Fontes e conseqüências dos conflitos na rela??o trabalho-família de mulheres-gerentes
Silva,Anielson Barbosa da; Rossetto,Carlos; Rebelo,Luiza;
Revista Portuguesa e Brasileira de Gest?o , 2010,
Abstract: the present research aimed at identifying the sources and consequences of the conflicts in the relation between work-family of the manager women. the methodological approach used was the qualitative one. the research was done with fifteen manager women who work at a financial institution in three brazilian capitals. the data collection was held through semi structured interviews. the interpretative comprehensive results analysis followed the orientation of silva (2005). the study has revealed three sources of conflict: time, behavior and tension. time generates problems in the personal and professional life, interfering more in the family relations than in the professional relations. the conflicts generated by the behavior and by the tension affect us as well as the family relations (kids, spouse and parents) and professional relations (partners, employees and clients). the conflicts in the work-family relation experienced by the women are interconnected and cause harm in their performance and their life quality.
Fontes e conseqüências dos conflitos na rela o trabalho-família de mulheres-gerentes Causas y consecuencias de los conflictos en las relaciones trabajo-familia de mujeres directivas Sources and consequences of conflict in the relationship work-family of women managers
Anielson Barbosa da Silva,Carlos Rossetto,Luiza Rebelo
Revista Portuguesa e Brasileira de Gest?o , 2010,
Abstract: Esta pesquisa teve como objetivo identificar as fontes e conseqüências dos conflitos na rela o trabalho-família de mulheres-gerentes. A abordagem metodológica adotada na pesquisa foi a qualitativa. O estudo foi realizado com quinze mulheres-gerentes que atuam em uma institui o financeira em três capitais brasileiras. A coleta dos dados foi realizada por meio de entrevistas semi-estruturadas. A análise compreensiva interpretativa dos resultados seguiu as orienta es de Silva (2005). O estudo revelou a presen a de três fontes de conflito: o tempo , o comportamento e a tens o . O tempo provoca problemas na vida pessoal e profissional, interferindo mais nas rela es em família do que nas rela es profissionais. Os conflitos provocados pelo comportamento e pela tens o afetam tanto a gerente em si, como as rela es familiares (filhos, c njuge e pais) e profissionais (pares, colaboradores e clientes). Os conflitos na rela o trabalho-família vivenciados pelas mulheres est o interconectados e prejudicam o seu desempenho e a sua qualidade de vida. Esta investigación tuvo como objetivo identificar las causas y consecuencias de los conflictos en la relación entre el trabajo y la familia de las mujeres directivas. El enfoque metodológico adoptado en la investigación fue de tipo cualitativo. El estudio se realizó con quince mujeres directivas que trabajan en una institución financiera en tres ciudades brasile as. La recolección de datos se llevó a cabo a través de entrevistas semi-estructuradas. El análisis comprehensivo interpretativo de los resultados siguió las directrices Silva (2005). El estudio reveló la presencia de tres fuentes de conflicto: el tiempo, el comportamiento y la tensión. El tiempo causa problemas en la vida personal y profesional, lo que interfiere en las relaciones familiares más que en las relaciones profesionales. Los conflictos causados por el comportamiento y la tensión afectan tanto a la propia directiva, tales como las relaciones familiares (hijos, cónyuge y padres) y profesionales (compa eros, empleados y clientes). Los conflictos en la relación entre el trabajo y la familia que sufren las mujeres se interconectan y afectan a su rendimiento y calidad de vida. The present research aimed at identifying the sources and consequences of the conflicts in the relation between work-family of the manager women. The methodological approach used was the qualitative one. The research was done with fifteen manager women who work at a financial institution in three Brazilian capitals. The data collection was held through semi structured interviews.
On the backreaction of frame dragging
Carlos A. R. Herdeiro,Carmen Rebelo,Claude M. Warnick
Physics , 2009, DOI: 10.1103/PhysRevD.80.084037
Abstract: The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin j^2>1, which is related to the behaviour of the ring angular velocity. Using the `gravitomagnetic clock effect', for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in both phases, when the central black hole mass increases, for fixed ring mass and angular momentum. A close parallelism between the results for the fat phase and those obtained recently for the double Kerr solution is drawn, considering also a regular black Saturn system with J^{BH}\neq 0.
Dynamical and Thermodynamical Aspects of Interacting Kerr Black Holes
Miguel S. Costa,Carlos A. R. Herdeiro,Carmen Rebelo
Physics , 2009, DOI: 10.1103/PhysRevD.79.123508
Abstract: We consider the asymptotically flat double-Kerr solution for two equal mass black holes with either the same or opposite angular momentum and with a massless strut between them. For fixed angular momentum and mass, the angular velocity of two co-rotating Kerr black holes decreases as they approach one another, from the Kerr value at infinite separation to the value of a single Kerr black hole with twice the mass and the angular momentum at the horizons merging limit. We show that the ratio J/M^2 for extremal co-rotating Kerr black holes varies from unity at infinite separation to two at the merging limit. These results are interpreted in terms of rotational dragging and compared with the case of counter-rotating Kerr black holes. We then analyse the merging of ergo-regions. In the co-rotating case the merger point occurs at an angle of \pi/2, in agreement with recent general arguments. In the counter-rotating case the ergo-regions never merge. We study the horizon geometry for both cases as a function of the distance and provide embedding diagrams. Finally, we study the thermodynamical evolution of the co-rotating double Kerr system, showing that, in the canonical ensemble, it is thermodynamically stable for fast spinning black holes. As for single Kerr black holes the stable and unstable phases are separated by a second order phase transition. We show that for large fixed angular momentum two Kerr black holes reach a minimum distance, before horizon merging has occurred, where the thermodynamical approximation breaks down. We also consider the micro-canonical ensemble to study the maximal energy that can be extracted from the double Kerr system as a function of the separation between the black holes.
Radiation from a D-dimensional collision of shock waves: first order perturbation theory
Carlos Herdeiro,Marco O. P. Sampaio,Carmen Rebelo
Physics , 2011, DOI: 10.1007/JHEP07(2011)121
Abstract: We study the spacetime obtained by superimposing two equal Aichelburg-Sexl shock waves in D dimensions traveling, head-on, in opposite directions. Considering the collision in a boosted frame, one shock becomes stronger than the other, and a perturbative framework to compute the metric in the future of the collision is setup. The geometry is given, in first order perturbation theory, as an integral solution, in terms of initial data on the null surface where the strong shock has support. We then extract the radiation emitted in the collision by using a D-dimensional generalisation of the Landau-Lifschitz pseudo-tensor and compute the percentage of the initial centre of mass energy epsilon emitted as gravitational waves. In D=4 we find epsilon=25.0%, in agreement with the result of D'Eath and Payne. As D increases, this percentage increases monotonically, reaching 40.0% in D=10. Our result is always within the bound obtained from apparent horizons by Penrose, in D=4, yielding 29.3%, and Eardley and Giddings, in D> 4, which also increases monotonically with dimension, reaching 41.2% in D=10. We also present the wave forms and provide a physical interpretation for the observed peaks, in terms of the null generators of the shocks.
Radiation from a D-dimensional collision of shock waves: higher order set up and perturbation theory validity
Flávio S. Coelho,Carlos Herdeiro,Carmen Rebelo,Marco Sampaio
Physics , 2012, DOI: 10.1103/PhysRevD.87.084034
Abstract: The collision of two D-dimensional, ultra-relativistic particles, described in General Relativity as Aichelberg-Sexl shock waves, is inelastic. In first order perturbation theory, the fraction of the initial centre of mass energy radiated away was recently shown to be 1/2 - 1/D. Here, we extend the formalism to higher orders in perturbation theory, and derive a general expression to extract the inelasticity, valid non-perturbatively, based on the Bondi mass loss formula. Then, to clarify why perturbation theory captures relevant physics of a strong field process in this problem, we provide one variation of the problem where the perturbative framework breaks down: the collision of ultra-relativistic charged particles. The addition of charge, and the associated repulsive nature of the source, originates an extra radiation burst, which we argue to be an artifact of the perturbative framework, veiling the relevant physics.
Urgency/Emergency Health Processes' Modelling: A Case Study
Carlos Santos,Armindo Rebelo,Carla Ferreira,José Tribolet
Computer Science , 2011,
Abstract: The growing complexity and sophistication of the organizational information systems, and hospital ones particularly, render difficult their comprehension and, consequently, the implementation of control mechanisms that may assure, at all times, the auditability of the above mentioned systems, without having to use models. This paper, framed in a wider investigation, aims to describe the application of techniques and methodologies, in the sphere of action of Organizational Engineering, in the modelling of business processes developed in the main Operating Theatre of the Coimbra's University Hospital Emergency Service, as a support for the implementation of an information system architecture, using for that purpose the CEO framework, developed and suggested by the Centre for Organizational Engineering (CEO), based on the UML language.
Identification of the Risk Related to a Process on Hospital Emergency Service: a Case Study
Carlos Santos,Armindo Rebelo,Carla Ferreira,José Tribolet
Computer Science , 2011,
Abstract: This paper, framed in a vast investigation, describes the application of techniques and methodologies in Organizational Engineering connected to the associated risk to the processes developed in an Emergency Service of an important Portuguese Hospital. The transactions performed in an emergency service and the consequent risk identification (negative behaviour associated to those transactions) is done based on static and dynamic models, developed during the business modelling. Any non-trivial system is better portrayed trough a small number of reasonably independent models. From this point of view it is important to look at the systems from a "micro" perspective, which allows us to analyse the system at the transaction level. All processes have some associated risk (inherent risk). Its identification will be decisive for future analysis and for the consequent decision over the need, or not, to study internal control mechanisms. This decision will depend on the risk level that the organization considers acceptable.
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