Relativistic Positioning Systems: The Emission Coordinates

This paper introduces some general properties of the gravitational metric and the natural basis of vectors and covectors in 4-dimensional emission coordinates. Emission coordinates are a class of space-time coordinates defined and generated by 4 emitters (satellites) broadcasting their proper time by means of electromagnetic signals. They are a constitutive ingredient of the simplest conceivable relativistic positioning systems. Their study is aimed to develop a theory of these positioning systems, based on the framework and concepts of general relativity, as opposed to introducing `relativistic effects' in a classical framework. In particular, we characterize the causal character of the coordinate vectors, covectors and 2-planes, which are of an unusual type. We obtain the inequality conditions for the contravariant metric to be Lorentzian, and the non-trivial and unexpected identities satisfied by the angles formed by each pair of natural vectors. We also prove that the metric can be naturally split in such a way that there appear 2 parameters (scalar functions) dependent exclusively on the trajectory of the emitters, hence independent of the time broadcast, and 4 parameters, one for each emitter, scaling linearly with the time broadcast by the corresponding satellite, hence independent of the others.Comment: 13 pages, 3 figures. Only format changed for a new submission. Submitted to Class. Quantum Gra

Modeling the hydraulic performance of the aeration system in dam bottom outlets using the particle finite element method

Los desagües de fondo juegan un papel fundamental en la seguridad de las presas, ya que permiten controlar el caudal liberado en cada momento, y por tanto el nivel de embalse por debajo del nivel máximo normal. Desde principios del siglo xx se ha observado que para el correcto funcionamiento del desagüe y para evitar daños durante su operación, es conveniente disponer un sistema de aducción de aire aguas abajo de las compuertas, donde pueden aparecer presiones negativas. De otro modo, es frecuente que se produzcan daños por cavitación y vibraciones. Debido a la dificultad para tomar datos o hacer estudios del fenómeno in situ y a escala real, el diseño de los sistemas de aireación se ha realizado tradicionalmente a partir de ensayos en laboratorio con modelos físicos a escala reducida, con cuyos resultados se han obtenido diferentes fórmulas empíricas que estiman el caudal de aire necesario para diseñar el sistema de aducción. En el presente trabajo el problema se estudia mediante modelación numérica, incluyendo la interacción agua-aire. Para ello se utiliza el método de partículas y elementos finitos (PFEM), que había sido previamente aplicado y validado para el análisis del comportamiento de otras estructuras hidráulicas. De este modo se pretenden evitar los efectos de escala inherentes a los ensayos en modelo físico y analizar con más detalle los parámetros fundamentales. Los resultados permiten obtener conclusiones acerca de la influencia de las variables que intervienen.Dam bottom are key elements to control the water surface elevation below the spillway crest level. As a consequence, they are essential in reservoir management, and play a vital role in dam safety. The convenience of installing an aeration system in dam bottom outlets is well known nowadays. Otherwise, damages due to cavitation and vibration are frequently serious, as could be observed in several dams built in the beginning of the 20th century. The intrinsic features of the phenomenon make it hard to analyze either in situ or in full scaled experimental facilities. As a consequence, most of the previous studies have been carried out in small-scale physical models. The results of these works have been used to develop empirical formulas which provide an estimation of the maximum air demand of the aeration system. The progress in the development of numerical methods allows addressing this problem using numerical modeling. The Particle Finite Element Method (PFEM) had been previously applied and validated for the analysis of the performance of other hydraulic structures. In this work, it has been used to simulate air-water interaction in free-flowing gated conduits. The objective is to avoid the scale effects of physical modeling and to study in detail the key parameters. The results clarify the behaviour of the involved fluids (air and water) and provide information about the influence of the main variables that affect their circulation.Peer Reviewe

Governance analysis of two historical MPAs in northern Peru: Isla Lobos de Tierra and Isla Lobos de Afuera

Isla Lobos de Tierra and Isla Lobos de Afuera are two MPAs that show the importance of history in governance. In 2009 they were designated among the Guano Islands, Islets and Capes Reserve System for wildlife conservation and sustainability, after being protected for hundreds of years to manage guano. Since their designation, governance changed on paper, but not de facto. The major driver undermining conservation is fishing, which is enhanced by pressures of the global seafood market and informality (the predominant way of thinking and acting in Peru, transgressive of order and disrespectful of values, norms and institutions). Fish productivity in the Humboldt Current Large Marine Ecosystem is the source of wildlife bounty around these small islands. Few incentives have been initiated to protect it and none looks at directly regulating fisheries. An obstacle is that the Parks Service has no authority to manage marine species. Management effectiveness requires improving cross-jurisdictional coordination with the Vice-Ministry of Fisheries, the Maritime Authority and other relevant entities to develop an integral plan where they all convene on working towards conserving these MPAs. Success will rely on an improved and diligent state participation that deeply understands the social complexities of these environments in order to address informality and potential equity issues. Despite the minimal intervention, the land ecosystem and its species remain relatively protected due to a governance legacy of strict enforcement and fraternal relationships between guardians and artisanal fishers, which highlights the importance of recognising history in conservation

Topological Measure Locating the Effective Crossover between Segregation and Integration in a Modular Network

We introduce an easily computable topological measure which locates the effective crossover between segregation and integration in a modular network. Segregation corresponds to the degree of network modularity, while integration is expressed in terms of the algebraic connectivity of an associated hyper-graph. The rigorous treatment of the simplified case of cliques of equal size that are gradually rewired until they become completely merged, allows us to show that this topological crossover can be made to coincide with a dynamical crossover from cluster to global synchronization of a system of coupled phase oscillators. The dynamical crossover is signaled by a peak in the product of the measures of intra-cluster and global synchronization, which we propose as a dynamical measure of complexity. This quantity is much easier to compute than the entropy (of the average frequencies of the oscillators), and displays a behavior which closely mimics that of the dynamical complexity index based on the latter. The proposed toplogical measure simultaneously provides information on the dynamical behavior, sheds light on the interplay between modularity vs total integration and shows how this affects the capability of the network to perform both local and distributed dynamical tasks

Death, dying and informatics: misrepresenting religion on MedLine

BACKGROUND: The globalization of medical science carries for doctors worldwide a correlative duty to deepen their understanding of patients' cultural contexts and religious backgrounds, in order to satisfy each as a unique individual. To become better informed, practitioners may turn to MedLine, but it is unclear whether the information found there is an accurate representation of culture and religion. To test MedLine's representation of this field, we chose the topic of death and dying in the three major monotheistic religions. METHODS: We searched MedLine using PubMed in order to retrieve and thematically analyze full-length scholarly journal papers or case reports dealing with religious traditions and end-of-life care. Our search consisted of a string of words that included the most common denominations of the three religions, the standard heading terms used by the National Reference Center for Bioethics Literature (NRCBL), and the Medical Subject Headings (MeSH) used by the National Library of Medicine. Eligible articles were limited to English-language papers with an abstract. RESULTS: We found that while a bibliographic search in MedLine on this topic produced instant results and some valuable literature, the aggregate reflected a selection bias. American writers were over-represented given the global prevalence of these religious traditions. Denominationally affiliated authors predominated in representing the Christian traditions. The Islamic tradition was under-represented. CONCLUSION: MedLine's capability to identify the most current, reliable and accurate information about purely scientific topics should not be assumed to be the same case when considering the interface of religion, culture and end-of-life care

Positivity and conservation of superenergy tensors

Two essential properties of energy-momentum tensors T_{\mu\nu} are their positivity and conservation. This is mathematically formalized by, respectively, an energy condition, as the dominant energy condition, and the vanishing of their divergence \nabla^\mu T_{\mu\nu}=0. The classical Bel and Bel-Robinson superenergy tensors, generated from the Riemann and Weyl tensors, respectively, are rank-4 tensors. But they share these two properties with energy momentum tensors: the Dominant Property (DP) and the divergence-free property in the absence of sources (vacuum). Senovilla defined a universal algebraic construction which generates a basic superenergy tensor T{A} from any arbitrary tensor A. In this construction the seed tensor A is structured as an r-fold multivector, which can always be done. The most important feature of the basic superenergy tensors is that they satisfy automatically the DP, independently of the generating tensor A. In a previous paper we presented a more compact definition of T{A} using the r-fold Clifford algebra. This form for the superenergy tensors allowed to obtain an easy proof of the DP valid for any dimension. In this paper we include this proof. We explain which new elements appear when we consider the tensor T{A} generated by a non-degree-defined r-fold multivector A and how orthogonal Lorentz transformations and bilinear observables of spinor fields are included as particular cases of superenergy tensors. We find some sufficient conditions for the seed tensor A, which guarantee that the generated tensor T{A} is divergence-free. These sufficient conditions are satisfied by some physical fields, which are presented as examples.Comment: 19 pages, no figures. Language and minor changes. Published versio

A Case Study of the Impact of Bioenergy Development Upon Crop Production, Livestock Feeding, and Water Resource Usage in Kansas

The development of grain-based ethanol production in Kansas has had a marked impact upon the feedgrain and livestock industries of the state. The increased focus on feedgrain production stemming from ethanol development impacts the use and sustainability of Kansas water resources, and has changed the proportional mix of crops grown in the state. The need to handle increased amounts of feedgrains and to transport them to ethanol plants has affected the functional role of local grain elevators as well as the directional flow of grain within the state. The grain trucking industry has been dramatically affected by the increase in demand for moving both feedstock inputs and co-product outputs to and from ethanol plants in the state.Crop Production/Industries, Livestock Production/Industries, Resource /Energy Economics and Policy,

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.Comment: 44 pages, Latex, epsfig, 18 figures, to appear on the Report of the Workshop on Physics at LEP2, CERN 96-01, vol. 1, 199