2,092 research outputs found
Einstein's Field Equations for the Interior of a Uniformly Rotating Stationary Axisymmetric Perfect Fluid
We reduce Einstein's field equations for the interior of a uniformly
rotating, axisymmetric perfect fluid to a system of six second order partial
differential equations for the pressure p the energy density and four
dependent variables.Four of these equations do not depend on p and and
the other two determine p and
Black Hole in a Model with Dilaton and Monopole Fields
We present an exact black hole solution in a model having besides gravity a
dilaton and a monopole field. The solution has three free parameters, one of
which can be identified with the monopole charge, and another with the ADM
mass. The metric is asymptotically flat and has two horizons and irremovable
singularity only at . The dilaton field is singular only at . The
dominant and the strong energy condition are satisfied outside and on the
external horizon. According to a formulation of the no hair conjecture the
solution is "hairy". Also the well know GHS-GM solution is obtained from our
solution for certain values of its parameters.Comment: Selected for Honorable Mention in the Gravity Research Foundation
Essay Competition, 2006, 7 page
Leading birds by their beaks : the response of flocks to external perturbations
Acknowledgments We have benefited from discussions with H Chaté and A Cavagna. We acknowledge support from the Marie Curie Career Integration Grant (CIG) PCIG13-GA-2013-618399. JT also acknowledges support from the SUPA distinguished visitor program and from the National Science Foundation through awards # EF-1137815 and 1006171, and thanks the University of Aberdeen for their hospitality while this work was underway. FG acknowledges support from EPSRC First Grant EP/K018450/1.Peer reviewedPublisher PD
Evolution towards Smart Optical Networking: Where Artificial Intelligence (AI) meets the World of Photonics
Smart optical networks are the next evolution of programmable networking and
programmable automation of optical networks, with human-in-the-loop network
control and management. The paper discusses this evolution and the role of
Artificial Intelligence (AI)
Mechanical Design, Modelling and Control of a Novel Aerial Manipulator
In this paper a novel aerial manipulation system is proposed. The mechanical
structure of the system, the number of thrusters and their geometry will be
derived from technical optimization problems. The aforementioned problems are
defined by taking into consideration the desired actuation forces and torques
applied to the end-effector of the system. The framework of the proposed system
is designed in a CAD Package in order to evaluate the system parameter values.
Following this, the kinematic and dynamic models are developed and an adaptive
backstepping controller is designed aiming to control the exact position and
orientation of the end-effector in the Cartesian space. Finally, the
performance of the system is demonstrated through a simulation study, where a
manipulation task scenario is investigated.Comment: Comments: 8 Pages, 2015 IEEE International Conference on Robotics and
Automation (ICRA '15), Seattle, WA, US
Lumping of Degree-Based Mean Field and Pair Approximation Equations for Multi-State Contact Processes
Contact processes form a large and highly interesting class of dynamic
processes on networks, including epidemic and information spreading. While
devising stochastic models of such processes is relatively easy, analyzing them
is very challenging from a computational point of view, particularly for large
networks appearing in real applications. One strategy to reduce the complexity
of their analysis is to rely on approximations, often in terms of a set of
differential equations capturing the evolution of a random node, distinguishing
nodes with different topological contexts (i.e., different degrees of different
neighborhoods), like degree-based mean field (DBMF), approximate master
equation (AME), or pair approximation (PA). The number of differential
equations so obtained is typically proportional to the maximum degree kmax of
the network, which is much smaller than the size of the master equation of the
underlying stochastic model, yet numerically solving these equations can still
be problematic for large kmax. In this paper, we extend AME and PA, which has
been proposed only for the binary state case, to a multi-state setting and
provide an aggregation procedure that clusters together nodes having similar
degrees, treating those in the same cluster as indistinguishable, thus reducing
the number of equations while preserving an accurate description of global
observables of interest. We also provide an automatic way to build such
equations and to identify a small number of degree clusters that give accurate
results. The method is tested on several case studies, where it shows a high
level of compression and a reduction of computational time of several orders of
magnitude for large networks, with minimal loss in accuracy.Comment: 16 pages with the Appendi
Distance estimation and collision prediction for on-line robotic motion planning
An efficient method for computing the minimum distance and predicting collisions between moving objects is presented. This problem has been incorporated in the framework of an in-line motion planning algorithm to satisfy collision avoidance between a robot and moving objects modeled as convex polyhedra. In the beginning the deterministic problem, where the information about the objects is assumed to be certain is examined. If instead of the Euclidean norm, L(sub 1) or L(sub infinity) norms are used to represent distance, the problem becomes a linear programming problem. The stochastic problem is formulated, where the uncertainty is induced by sensing and the unknown dynamics of the moving obstacles. Two problems are considered: (1) filtering of the minimum distance between the robot and the moving object, at the present time; and (2) prediction of the minimum distance in the future, in order to predict possible collisions with the moving obstacles and estimate the collision time
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