Super-energy tensor for space-times with vanishing scalar curvature

A four-index tensor is constructed with terms both quadratic in the Riemann tensor and linear in its second derivatives, which has zero divergence for space-times with vanishing scalar curvature. This tensor reduces in vacuum to the Bel-Robinson tensor. Furthermore, the completely timelike component referred to any observer is positive, and zero if and only if the space-time is flat (excluding some unphysical space-times). We also show that this tensor is the unique that can be constructed with these properties. Such a tensor does not exist for general gravitational fields. Finally, we study this tensor in several examples: the Friedmann-Lema\^{\i}tre-Robertson-Walker space-times filled with radiation, the plane-fronted gravitational waves, and the Vaidya radiating metric.Comment: 13 pages, LaTeX 2.09. To be published in Journal of Mathematical Physic

Extreme objects with arbitrary large mass, or density, and arbitrary size

We consider a generalization of the interior Schwarzschild solution that we match to the exterior one to build global C^1 models that can have arbitrary large mass, or density, with arbitrary size. This is possible because of a new insight into the problem of localizing the center of symmetry of the models and the use of principal transformations to understand the structure of space.Comment: 20 pages, 6 figures. Fixed one reference. Added a new equatio

Public versus private water delivery, remunicipalization and water tariffs

Evidence regarding the drivers and the effects of remunicipalization remains in short supply. In this paper we exploit existing analyses of earlier historical phases of the remunicipalization of water delivery services to disentangle the role played by a range of different factors – most notably overpricing and corruption under private ownership – in the decision to remunicipalize these services. Additionally, we discuss what the effects of remunicipalization might be in the light of the, as yet, somewhat sketchy evidence. In the specific case of water tariffs, our analysis casts some doubt on whether the initial price reductions introduced following remunicipalization are sustainable over time

Ergodicity Breaking in a Deterministic Dynamical System

The concept of weak ergodicity breaking is defined and studied in the context of deterministic dynamics. We show that weak ergodicity breaking describes a weakly chaotic dynamical system: a nonlinear map which generates subdiffusion deterministically. In the non-ergodic phase non-trivial distribution of the fraction of occupation times is obtained. The visitation fraction remains uniform even in the non-ergodic phase. In this sense the non-ergodicity is quantified, leading to a statistical mechanical description of the system even though it is not ergodic.Comment: 11 pages, 4 figure

Beyond government size: Types of government intervention and corruption

Evidence on the relationship between government size and corruption is mixed, and might be misleading, as government size is usually measured by fiscal size. The core hypothesis in this research is that the type of government intervention in the economy – rather than the size of government – is a key explanatory factor for corruption. The empirical analysis disentangles the effects of the two main government tools for intervention: fiscal and regulatory. The main result is that fiscal burden does not present any significant relationship with corruption. In contrast, a consistent and significant positive association is found between regulatory burden and corruption. Furthermore, legal origins and democratic experience contribute to explaining differences in corruption. [Correction added on 22 April 2021, after first online publication: In the Abstract, the word ‘quality’ has been replaced with ‘burden’.

Myopic PPPs: Risk allocation and hidden liabilities for taxpayers and users

Drawing on evidence from three case studies, we show how the State's Financial Liability has worked in assigning risk in large PPP contracts in Spain. Project failure and the concessionaires' bankruptcy have resulted in the government having to assume heavy financial obligations, which have ultimately been absorbed by taxpayers and users. In contrast, Spain's leading construction companies, which were also major investors in the concessionaires, have been able to minimize their risk. Myopic PPPs have been entered into based on the transference of liabilities to taxpayers and users, and the, consequent, minimization of risks for the main private investors

Grid-scale Fluctuations and Forecast Error in Wind Power

The fluctuations in wind power entering an electrical grid (Irish grid) were analyzed and found to exhibit correlated fluctuations with a self-similar structure, a signature of large-scale correlations in atmospheric turbulence. The statistical structure of temporal correlations for fluctuations in generated and forecast time series was used to quantify two types of forecast error: a timescale error ($e_{\tau}$) that quantifies the deviations between the high frequency components of the forecast and the generated time series, and a scaling error ($e_{\zeta}$) that quantifies the degree to which the models fail to predict temporal correlations in the fluctuations of the generated power. With no $a$ $priori$ knowledge of the forecast models, we suggest a simple memory kernel that reduces both the timescale error ($e_{\tau}$) and the scaling error ($e_{\zeta}$)

Intelligent Decision Support Capabilities for a Law Enforcement GIS

Most GIS systems process huge amounts of data but lack the capability to produce useful knowledge and actionable information. Unless GIS information generates a Bayesian update (a surprise or information that decision makers cannot anticipate), this GIS remains weak and a simple storage of dead data. Furthermore, even if this GIS stores valuable data, it still remains weak if it lacks the ability to generate the decision support that users need. This work in progress aims at adding decision support capabilities to a standard law enforcement GIS in terms of two main features: 1) visual decision support at the functional management and control levels in remote locations of police stations protecting their urban zones, and 2) evidence-based decision support at the strategic management level in the police department protecting the conurbation constituting the urban zones under its jurisdiction. The visual decision aids employ dynamic choropleth maps that are revised on a monthly basis. The evidence-based decision process is provided using Dempster and Shafer theory. While some of the tools are primarily used by police departments to devise effective policing strategies, police chiefs supervising the police stations can also locally benefit from adopting them. This study provides a numerical example to demonstrate the working of the proposed decision aids

Stochastic Ergodicity Breaking: a Random Walk Approach

The continuous time random walk (CTRW) model exhibits a non-ergodic phase when the average waiting time diverges. Using an analytical approach for the non-biased and the uniformly biased CTRWs, and numerical simulations for the CTRW in a potential field, we obtain the non-ergodic properties of the random walk which show strong deviations from Boltzmann--Gibbs theory. We derive the distribution function of occupation times in a bounded region of space which, in the ergodic phase recovers the Boltzmann--Gibbs theory, while in the non-ergodic phase yields a generalized non-ergodic statistical law.Comment: 5 pages, 3 figure

Electromagnetic radiation produces frame dragging

It is shown that for a generic electrovacuum spacetime, electromagnetic radiation produces vorticity of worldlines of observers in a Bondi--Sachs frame. Such an effect (and the ensuing gyroscope precession with respect to the lattice) which is a reminiscence of generation of vorticity by gravitational radiation, may be linked to the nonvanishing of components of the Poynting and the super--Poynting vectors on the planes othogonal to the vorticity vector. The possible observational relevance of such an effect is commented.Comment: 8 pages RevTex 4-1; updated version to appear in Physical Review