Comment on "What does the Letelier-Gal'tsov metric describe?"

We show that the Letelier-Gal'tsov (LG) metric describing multiple crossed strings in relative motion does solve the Einstein equations, in spite of the discontinuity uncovered recently by Krasnikov [gr-qc/0502090] provided the strings are straight and moving with constant velocities.Comment: 3 page

The Letelier-Gal'tsov spacetime revisited

Contrary to a recent claim by Anderson ["The Mathematical Theory of Cosmic Strings", I.O.P. Publishing, Bristol 2003], we show that the Letelier-Gal'tsov metric does represent a system of crossed straight infinite cosmic strings moving with arbitrary constant velocities.Comment: 3 page

Diagnostics of seeded RF plasmas: An experimental study related to the gaseous core reactor

Measurements of the temperature profiles in an RF argon plasma were made over magnetic field intensities ranging from 20 amp turns/cm to 80 amp turns/cm. The results were compared with a one-dimensional numerical treatment of the governing equations and with an approximate closed form analytical solution that neglected radiation losses. The average measured temperatures in the plasma compared well with the numerical treatment, though the experimental profile showed less of an off center temperature peak than predicted by theory. This may be a result of the complex turbulent flow pattern present in the experimental torch and not modeled in the numerical treatment. The radiation term cannot be neglected for argon at the power levels investigated. The closed form analytical approximation that neglected radiation led to temperature predictions on the order of 1000 K to 2000 K higher than measured or predicted by the numerical treatment which considered radiation losses

Theoretical calculations of radiant heat transfer properties of particle-seeded gases

Radiant heat transfer properties of particle seeded gases, including absorption and scattering characteristics of carbon, silicon, and tungste

An Exact Conformal Symmetry Ansatz on Kaluza-Klein Reduced TMG

Using a Kaluza-Klein dimensional reduction, and further imposing a conformal Killing symmetry on the reduced metric generated by the dilaton, we show an Ansatz that yields many of the known stationary axisymmetric solutions to TMG.Comment: 20 pages, 1 figure, v3: postprint, added one re

Bounds on the force between black holes

We treat the problem of N interacting, axisymmetric black holes and obtain two relations among physical parameters of the system including the force between the black holes. The first relation involves the total mass, the angular momenta, the distances and the forces between the black holes. The second one relates the angular momentum and area of each black hole with the forces acting on it.Comment: 13 pages, no figure

Killing Vector Fields in Three Dimensions: A Method to Solve Massive Gravity Field Equations

Killing vector fields in three dimensions play important role in the construction of the related spacetime geometry. In this work we show that when a three dimensional geometry admits a Killing vector field then the Ricci tensor of the geometry is determined in terms of the Killing vector field and its scalars. In this way we can generate all products and covariant derivatives at any order of the ricci tensor. Using this property we give ways of solving the field equations of Topologically Massive Gravity (TMG) and New Massive Gravity (NMG) introduced recently. In particular when the scalars of the Killing vector field (timelike, spacelike and null cases) are constants then all three dimensional symmetric tensors of the geometry, the ricci and einstein tensors, their covariant derivatives at all orders, their products of all orders are completely determined by the Killing vector field and the metric. Hence the corresponding three dimensional metrics are strong candidates of solving all higher derivative gravitational field equations in three dimensions.Comment: 25 pages, some changes made and some references added, to be published in Classical and Quantum Gravit

A Service-Oriented Co-Simulation: Holistic Data Center Modelling Using Thermal, Power and Computational Simulations

Holistic modelling of a data center to include both thermodynamics and computational processes has the potential to revolutionize how data centers are designed and managed. Such a model is inherently multi-disciplinary, bringing together the computational elements studied by computer scientists; thermodynamics studied by mechanical engineers; and other aspects in the domain of electrical engineering. This paper proposes the use of the Internet of Simulation to allow engineers to build models of individual complex elements and deploy them as simulation services. These services can then be integrated as simulation system workflows. A proof of concept server simulation is presented, incorporating simulations of CPUs, heat sinks, and fans exposed using the SIMaaS paradigm. The integrated workflow of the server is then exposed as a service (WFaaS) to facilitate the building of an entire virtual data center. Unlike other data center simulations, this approach requires no direct characterisation of the hardware being simulated. Preliminary results are presented showing the effectiveness of the simulation technique and representative behaviour under various simulated cloud workloads. The benefits and future applications of this rapid prototyping approach extend to data center design and data center efficiency research

All stationary axi-symmetric local solutions of topologically massive gravity

We classify all stationary axi-symmetric solutions of topologically massive gravity into Einstein, Schr\"odinger, warped and generic solutions. We construct explicitly all local solutions in the first three sectors and present an algorithm for the numerical construction of all local solutions in the generic sector. The only input for this algorithm is the value of one constant of motion if the solution has an analytic centre, and three constants of motion otherwise. We present several examples, including soliton solutions that asymptote to warped AdS.Comment: 42 pages, 9 figures. v2: Changed potentially confusing labelling of one sector, added references. v3: Minor changes, matches published versio

Time-Symmetric Initial Data for Multi-Body Solutions in Three Dimensions

Time-symmetric initial data for two-body solutions in three dimensional anti-deSitter gravity are found. The spatial geometry has constant negative curvature and is constructed as a quotient of two-dimensional hyperbolic space. Apparent horizons correspond to closed geodesics. In an open universe, it is shown that two black holes cannot exist separately, but are necessarily enclosed by a third horizon. In a closed universe, two separate black holes can exist provided there is an additional image mass.Comment: 12 pages, harvmac macro, minor changes in wordin