53,565 research outputs found
Recent progress on the notion of global hyperbolicity
Global hyperbolicity is a central concept in Mathematical Relativity. Here,
we review the different approaches to this concept explaining both, classical
approaches and recent results. The former includes Cauchy hypersurfaces, naked
singularities, and the space of the causal curves connecting two events. The
latter includes structural results on globally hyperbolic spacetimes, their
embeddability in Lorentz-Minkowski, and the recently revised notions of both,
causal and conformal boundaries. Moreover, two criteria for checking global
hyperbolicity are reviewed. The first one applies to general splitting
spacetimes. The second one characterizes accurately global hyperbolicity and
spacelike Cauchy hypersurfaces for standard stationary spacetimes, in terms of
a naturally associated Finsler metric.Comment: 18 pages, 1 figure. Extended and updated contribution to the meeting
"New Developments in Lorentzian Geometry" Berlin, Nov. 200
Optimizing Engagement Simulations Through the Advanced Framework for Simulation, Integration, and Modeling (AFSIM) Software
The ability to effectively model and simulate military missions holds the potential to save lives, money, and resources for the United States. The Advanced Framework for Simulation, Integration, and Modeling (AFSIM) software is a tool used to rapidly simulate and model new technologies and mission level scenarios. In this thesis, our objective is to integrate a closed loop optimization routine with AFSIM to identify an effective objective function to assess optimal inputs for engagement scenarios. Given the many factors which impact a mission level engagement, we developed a tool which interfaces with AFSIM to observe the effects from multiple inputs in an engagement scenario. Our tool operates under the assumption that simulation results have met an acceptable convergence threshold. The objective function evaluates the effectiveness and associated cost with a scenario using a genetic algorithm and a particle swarm optimization algorithm. From this, a statistical analysis was performed to assess risk from the distribution of effectiveness and cost at each point. The method allows an optimal set of inputs to be selected for a desired result from the selected engagement scenario.No embargoAcademic Major: Mechanical Engineerin
Collaborative Consent: harnessing the strengths of the Internet for consent in the online environment
Consent in the online environment is a crucial issue at this stage of the development of the Internet, and at the same time, in practice it is generally dealt with only on a superficial level. However, while the Internet offers significant challenges in terms of consent, it also provides unparalleled opportunities, which, if grasped, could enable a new level of consent, particularly where consent is required for services such as behavioural advertising systems. Through an examination of the failure of Phorm, the paper introduces a new concept, 'collaborative consent', treating consent not as a discrete, one-off decision but as a collaborative and communicative process, an ongoing relationship between the individual and the enterprise. The Internet provides a medium for immediate and interactive communication that could allow information to be given and choices to be made in real time - a first step to real, informed consent in the online world
The fallout from the McAlpine saga threatens the role of Twitter in public life
The fallout from the McAlpine saga has led to increasing fears that legal action will have a ‘chilling effect’ on the microblogging platform. Paul Bernal argues that Twitter provides something quite special for the media and that it should be nurtured. It’s possible a defence may develop naturally from the legal processes McAlpine’s team bring about but, if not, we ought to work to develop it
Smoothness of time functions and the metric splitting of globally hyperbolic spacetimes
The folk questions in Lorentzian Geometry, which concerns the smoothness of
time functions and slicings by Cauchy hypersurfaces, are solved by giving
simple proofs of: (a) any globally hyperbolic spacetime admits a smooth
time function whose levels are spacelike Cauchy hyperfurfaces and, thus,
also a smooth global splitting , , (b) if a spacetime admits a (continuous) time
function (i.e., it is stably causal) then it admits a smooth (time)
function with timelike gradient on all .Comment: 9 pages, Latex, to appear in Commun. Math. Phys. Some comments on
time functions and stably causal spacetimes are incorporated, and referred to
gr-qc/0411143 for further detail
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