Kaluza-Klein Formalism of General Spacetimes

I describe the Kaluza-Klein approach to general relativity of 4-dimensional spacetimes. This approach is based on the (2,2)-fibration of a generic 4-dimensional spacetime, which is viewed as a local product of a (1+1)-dimensional base manifold and a 2-dimensional fibre space. It is shown that the metric coefficients can be decomposed into sets of fields, which transform as a tensor field, gauge fields, and scalar fields with respect to the infinite dimensional group of the diffeomorphisms of the 2-dimensional fibre space. I discuss a few applications of this formalism.Comment: RevTex, no figure

General relativity on a null surface: Hamiltonian formulation in the teleparallel geometry

The Hamiltonian formulation of general relativity on a null surface is established in the teleparallel geometry. No particular gauge conditons on the tetrads are imposed, such as the time gauge condition. By means of a 3+1 decomposition the resulting Hamiltonian arises as a completely constrained system. However, it is structurally different from the the standard Arnowitt-Deser-Misner (ADM) type formulation. In this geometrical framework the basic field quantities are tetrads that transform under the global SO(3,1) and the torsion tensor.Comment: 15 pages, Latex, no figures, to appear in the Gen. Rel. Gra

Social Feedback as a Creative Process

Arguably one of the most important activities of a university is to provide environments where students develop the wide variety of social and intellectual skills necessary for giving and receiving feedback. We are not talking here about the kinds of activity typically associated with the term “feedback” — such as that which occurs through individual course evaluation questionnaires or more universal systems such as the National Student Survey, but the profoundly creative and human act of giving and receiving feedback in order to validate, challenge and inspire. So as to emphasise we are talking about this kind of feedback, we coin the term “creative feedback” to distinguish it from the pre-conceived rather dreary compliance-inflected notions of feedback and set out in this paper to characterise its qualities. In order to ground and motivate our definition and use of “creative feedback” we take a historical look at the two concepts of creativity/creative and feedback. Our intention is to use this rich history to motivate both the choice of these two words, and the reason to bring them together. In doing so we wish to emphasise the characteristics of an educational philosophy underpinned by social interaction. By describing those qualities necessary to characterise creative feedback this paper sets out an educational philosophy for how schools, communities and universities could develop their learning environments. What we present here serves not only as a manifesto for designing learning environments generally, but as a driver for designing technologies to support online social learning, as captured in the concept of social Moocs [70]. Technology not only provides us with new opportunities to support such learning but also to investigate and evidence the way in which we learn and the most effective learning environments

Motivation-based selection of negotiation partners

Negotiation is key to resolving conflicts, allocating resources and establishing cooperation in systems of self interested agents. Often, an agent may have to select between different potential negotiation partners, and identifying which offers the best chance of a successful negotiation is a challenging task. However, poor selection of partners can result in failure or in inefficient outcomes. To that end, this paper describes a motivation-based mechanism to evaluate and select between negotiation candidates. This is achieved by a twofold process: first, acceptable candidates are identified using motivation-based thresholds on objective scoring measures; second, the importance of issues is considered, and expected performance measures are evaluated accordingly. The mechanism is described and empirically evaluated

Weaving a fabric of socially aware agents

The expansion of web-enabled social interaction has shed light on social aspects of intelligence that have not been typically studied within the AI paradigm so far. In this context, our aim is to understand what constitutes intelligent social behaviour and to build computational systems that support it. We argue that social intelligence involves socially aware, autonomous individuals that agree on how to accomplish a common endeavour, and then enact such agreements. In particular, we provide a framework with the essential elements for such agreements to be achieved and executed by individuals that meet in an open environment. Such framework sets the foundations to build a computational infrastructure that enables socially aware autonomy.This work has been supported by the projects EVE(TIN2009-14702-C02-01) and AT (CSD2007-0022)Peer Reviewe

Quasi-Local Conservation Equations in General Relativity

A set of exact quasi-local conservation equations is derived from the Einstein's equations using the first-order Kaluza-Klein formalism of general relativity in the (2,2)-splitting of 4-dimensional spacetime. These equations are interpreted as quasi-local energy, momentum, and angular momentum conservation equations. In the asymptotic region of asymptotically flat spacetimes, it is shown that the quasi-local energy and energy-flux integral reduce to the Bondi energy and energy-flux, respectively. In spherically symmetric spacetimes, the quasi-local energy becomes the Misner-Sharp energy. Moreover, on the event horizon of a general dynamical black hole, the quasi-local energy conservation equation coincides with the conservation equation studied by Thorne {\it et al}. We discuss the remaining quasi-local conservation equations briefly.Comment: RevTex, 8 pages, a final version to appear in Phys. Lett.

Creative Feedback: a manifesto for social learning

Arguably one of the most important activities of a university is to provide environments where students develop the wide variety of social and intellectual skills necessary for giving and receiving feedback. We are not talking here about the kinds of activity typically associated with the term “feedback” -such as that which occurs through individual course evaluation questionnaires or more universal systems such as the National Student Survey, but the profoundly creative and human act of giving and receiving feedback in order validate, challenge and inspire. So as to emphasise we are talking about this kind of feedback, we coin the term “creative feedback” to distinguish it from the pre-conceived rather dreary compliance-inflected notions of feedback and set out in this paper to characterise its qualities. In order to ground and motivate our definition and use of “creative feedback” we take a historical look at the two concepts of creativity/creative and feedback. Our intention is to use this rich history to motivate both the choice two words, and the reason to bring them together. In doing so we wish to emphasise the characteristics of an educational philosophy underpinned by social interaction. By describing those qualities necessary to characterise creative feedback this paper sets out an educational philosophy for how schools, communities and universities could develop their learning environments. What we present here serves not only as a manifesto for designing learning environments generally but as a driver for designing technologies to support online social learning. Technology not only provides us with new opportunities to support such learning but also to investigate and evidence the way in which we learn and the most effective learning environments

Negotiation in Multi-Agent Systems

In systems composed of multiple autonomous agents, negotiation is a key form of interaction that enables groups of agents to arrive at a mutual agreement regarding some belief, goal or plan, for example. Particularly because the agents are autonomous and cannot be assumed to be benevolent, agents must influence others to convince them to act in certain ways, and negotiation is thus critical for managing such inter-agent dependencies. The process of negotiation may be of many different forms, such as auctions, protocols in the style of the contract net, and argumentation, but it is unclear just how sophisticated the agents or the protocols for interaction must be for successful negotiation in different contexts. All these issues were raised in the panel session on negotiation

Normative agent reasoning in dynamic societies

Several innovative software applications such as those required by ambient intelligence, the semantic grid, e-commerce and e-marketing, can be viewed as open societies of heterogeneous and self-interested agents in which social order is achieved through norms. For agents to participate in these kinds of societies, it is enough that they are able to represent and fulfill norms, and to recognise the authority of certain agents. However, to voluntarily be part of a society or to voluntarily leave it, other characteristics of agents are needed. To find these characteristics we observe that on the one hand, autonomous agents have their own goals and, sometimes, they act on behalf of others whose goals must be satisfied. On the other, we observe that by being members, agents must comply with some norms that can be in clear conflict with their goals. Consequently, agents must evaluate the positive or negative effects of norms on their goals before making a decision concerning their social behaviour. Providing a model of autonomous agents that undertake this kind of norm reasoning is the aim of this paper