Indoor Wireless RF Energy Transfer for Powering Wireless Sensors

For powering wireless sensors in buildings, rechargeable batteries may be used. These batteries will be recharged remotely by dedicated RF sources. Far-field RF energy transport is known to suffer from path loss and therefore the RF power available on the rectifying antenna or rectenna will be very low. As a consequence, the RF-to-DC conversion efficiency of the rectenna will also be very low. By optimizing not only the subsystems of a rectenna but also taking the propagation channel into account and using the channel information for adapting the transmit antenna radiation pattern, the RF energy transport efficiency will be improved. The rectenna optimization, channel modeling and design of a transmit antenna are discussed

Gravitational vacuum polarization III: Energy conditions in the (1+1) Schwarzschild spacetime

Building on a pair of earlier papers, I investigate the various point-wise and averaged energy conditions for the quantum stress-energy tensor corresponding to a conformally-coupled massless scalar field in the in the (1+1)-dimensional Schwarzschild spacetime. Because the stress-energy tensors are analytically known, I can get exact results for the Hartle--Hawking, Boulware, and Unruh vacua. This exactly solvable model serves as a useful sanity check on my (3+1)-dimensional investigations wherein I had to resort to a mixture of analytic approximations and numerical techniques. Key results in (1+1) dimensions are: (1) NEC is satisfied outside the event horizon for the Hartle--Hawking vacuum, and violated for the Boulware and Unruh vacua. (2) DEC is violated everywhere in the spacetime (for any quantum state, not just the standard vacuum states).Comment: 7 pages, ReV_Te

Buchdahl-like transformations for perfect fluid spheres

In two previous articles [Phys. Rev. D71 (2005) 124307 (gr-qc/0503007), and gr-qc/0607001] we have discussed several "algorithmic" techniques that permit one (in a purely mechanical way) to generate large classes of general relativistic static perfect fluid spheres. Working in Schwarzschild curvature coordinates, we used these algorithmic ideas to prove several "solution-generating theorems" of varying levels of complexity. In the present article we consider the situation in other coordinate systems: In particular, in general diagonal coordinates we shall generalize our previous theorems, in isotropic coordinates we shall encounter a variant of the so-called "Buchdahl transformation", while in other coordinate systems (such as Gaussian polar coordinates, Synge isothermal coordinates, and Buchdahl coordinates) we shall find a number of more complex "Buchdahl-like transformations" and "solution-generating theorems" that may be used to investigate and classify the general relativistic static perfect fluid sphere. Finally by returning to general diagonal coordinates and making a suitable ansatz for the functional form of the metric components we place the Buchdahl transformation in its most general possible setting.Comment: 23 page

Is Transparency to No Avail? Committee Decision-Making, Pre-Meetings, and Credible Deals

Transparent decision-making processes are widely regarded as a prerequisite for the working of a representative democracy. It facilitates accountability, and citizens may suspect that decisions, if taken behind closed doors, do not promote their interests. Why else the secrecy? We provide a model of committee decision-making that explains the public.s demand for transparency, and committee members. aversion to it. In line with case study evidence, we show how pressures to become transparent induce committee members to organize pre-meetings away from the public eye. Outcomes of pre-meetings, deals, are less determined, more anarchic, than those of formal meetings, but within bounds. We characterize deals that are self-enforcing in the formal meeting.Committee decision-making, reputational concerns, transparency, pre-meetings, deliberation, self-enforcing deals, coalitions

Decision Making and Learning in a Globalizing World

Decision-makers can benefit from the experience of others with solutions to common problems. If a best practice exists, the challenge is to recognize it and to ensure its diffusion. Information about different solutions is often dispersed, and decision-makers may be reluctant to switch for reputational reasons. We study how (i) the assignment of decision rights (who decides on the solutions.implementation?) and (ii) globalization (who knows what about solutions adopted in other places?) in.uence both the quality of the information on locally adopted solutions that decision-makers exchange and the quality of the solutions that are actually being used next.centralization, decentralization, learning, cheap talk, reputational concerns, globalization, health care consensus panels, EU Open Method of Coordination

Generating perfect fluid spheres in general relativity

Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star -- a static spherically symmetric blob of fluid with position-independent density -- the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres.Comment: 18 pages, 4 tables, 4 figure

Effective 4D propagation of a charged scalar particle in Visser brane world

In this work we extend an analysis due to Visser of the effective propagation of a neutral scalar particle on a brane world scenario which is a particular solution of the five dimensional Einstein-Maxwell equations with cosmological constant having an electric field pointing in the extra spatial dimension. We determine the dispersion relations of a charged scalar particle to first order in a perturbative analysis around those of the neutral particle. Since depending on whether the particle is charged or not the dispersion relations change, we could collect bulk information, namely the presence of the electric field, by studying the 4D dynamics of the particles.Comment: 12 pages, 5 figure

Energy management of three-dimensional minimum-time intercept

A real-time computer algorithm to control and optimize aircraft flight profiles is described and applied to a three-dimensional minimum-time intercept mission