Hasil untuk "Geography (General)"

David Maibach, Jann Zosso

Balance flux laws of asymptotic symmetries in general relativity provide fully non-perturbative constraint equations on gravitational strain. They have proven useful for constructing numerical gravitational waveforms and for characterizing gravitational memory. As the precision of current and future detectors continues to improve, such constraints become increasingly important for high-precision tests of gravity, including searches for deviations from general relativity. This motivates a systematic understanding of analogous balance laws in theories beyond general relativity. In this work, we investigate the existence and structure of flux laws at null infinity in diffeomorphism-invariant extensions of general relativity. Our analysis is based on the covariant phase space formalism and the definition of conserved quantities, as presented by Wald and Zoupas. For a particularly relevant class of Horndeski theories, we derive a general expression for the flux and formulate the corresponding balance equation via the associated non-conserved charges. We cross-check our general results by comparing them with previous studies of Brans-Dicke gravity. Furthermore, we demonstrate that the employed methods extend straightforwardly to a broader class of diffeomorphism-invariant theories. The null part of the resulting flux laws associated with null memory is compared with and validated against the alternative derivation based on the Isaacson approach to gravitational radiation. Beyond the specific results obtained, this work is intended to serve as a practical guide for computing balance laws in generic diffeomorphism-invariant theories of gravity and paves the way for an in-depth comparison between the Isaacson approach and the covariant phase space formalism.

Vitor Cardoso, Jaime Redondo-Yuste, Ulrich Sperhake et al.

Black holes and gravitational waves are consequences of the nonlinear character of the Einstein equations. Yet, the remarkable properties of General Relativity point to the existence of other effects. Here we uncover new nonlinear facets of gravity. We establish higher harmonic generation, spectral broadening and focusing in the Einstein Klein-Gordon system. In vacuum, we show that scattering of monochromatic waves at quadratic order is weakly sensitive to frequency, at large wavelengths. These aspects can both explain the seemingly smooth behavior of mergers, but also caution us against too simplistic an interpretation of waveforms.

Jackson Stingley

I construct an Einstein-Cartan ekpyrotic model (ECEM): a homogeneous, nearly Friedmann-Lemaître-Robertson-Walker (FLRW) background in Einstein-Cartan (EC) gravity whose spin-torsion sector, modeled phenomenologically as a Weyssenhoff fluid with stiff scaling $\propto a^{-6}$, is coupled to a scalar field with a steep exponential potential that interpolates between a negative ekpyrotic branch and a positive plateau. Extending the Copeland-Liddle-Wands (CLW) scalar-fluid dynamical system to a six-dimensional phase space including shear, curvature, and spin-torsion, I recast the equations in a compact deceleration-parameter form, compute the full Jacobian, and evaluate maximal Lyapunov exponents. Numerical solutions show that the ekpyrotic branch ($w_φ\gg1$) exponentially damps homogeneous shear, while the softened branch ($w_φ<1$) allows $ρ_s$ to overtake the scalar during contraction and trigger a torsion-supported bounce at high but finite densities where the EC spin-torsion term becomes dynamically dominant. Scans in a two-parameter softening plane $(φ_{\rm b},Δ)$ identify a finite region of nonsingular trajectories and quantify the required tuning; in the parameter ranges explored the maximal Lyapunov exponent on the constrained phase space is negative, giving no indication of chaotic behavior in this homogeneous truncation even when the usual curvature mode that destabilizes contracting General Relativity (GR) backgrounds is included. The construction is purely phenomenological and confined to homogeneous backgrounds: it does not address entropy accumulation, the cosmological arrow of time, or a complete cyclic cosmology.

Francesco Bajardi, Daniel Blixt

The primary constraints for general teleparallel quadratic gravity are presented. They provide a basic classification of teleparallel theories from the perspective of the full nonlinear theory and represent the first step towards a full-fledged Hamiltonian analysis. The results are consistent with the limit of metric and symmetric teleparallel quadratic gravity. In the latter case we also present novel results, since symmetric teleparallel theories have only been partially studied so far. Apart from the general results, we also present the special cases of teleparallel theories classically equivalent to general relativity, which differ by a boundary term from the formulation of Einstein and Hilbert. This affects the constraint algebra as the primary constraints involve a mix of torsion and non-metricity, implying that the symmetries of general relativity are realized in a more intricate way compared to the teleparallel case. In this context, a more detailed understanding will provide insights for energy and entropy in gravity, quantum gravity and numerical relativity of this alternative formulation of general relativity. The primary constraints are presented both in the standard formulation and in irreducible parts of torsion and non-metricity. The special role of axial torsion and its connection to the one-parameter of viable new general relativity is confirmed. Furthermore, we find that one of the irreducible parts of non-metricity affects the primary constraint for shift but not lapse.

Elena Pajarón, Alicia López, Joaquín Castelo et al.

Los robles eurosiberianos tienen una escasa y no bien conocida área de distribución en el Sistema Central oriental. Dado que consideramos que el conocimiento preciso de la Corología es una herramienta fundamental para el adecuado manejo y conservación forestal, se ha realizado un estudio pormenorizado de su presencia en este territorio. Éste se ha basado en la recopilación de información bibliográfica y procedente de bases de datos botánicas y forestales y, también, aportando nuevos datos procedentes de las prospecciones de campo realizadas entre los años 2000 y 2015, que incluyen la ubicación, extensión y características de individuos, rodales o bosques. Toda esta información se ha sometido a procesos de homogeneización y sistematización, pues procedía de distintas fuentes con diferente estructura, calidad y grado de detalle. Se han determinado 231 cuadrículas UTM de 1x1 km distintas en las que está presente de manera natural alguno de los taxones que integran el grupo, entre las que 157 cuadrículas se indican por primera vez. Además, se han seleccionado y analizado 30 poblaciones, entre las más numerosas, con mayor probabilidad de reclutamiento y persistencia en el tiempo, comprobando una mayor presencia de estos robles en la Sierra de Ayllón, siendo sus representaciones cada vez más reducidas y aisladas hacia el oeste.

Minghao Xia, Sijie Gao

Tolman proposed that the proper temper $T$ of a static self-gravitating fluid in thermodynamic equilibrium satisfies the relation $χT=constant$, where $χ$ is the redshift factor of the spacetime. The Tolman law has been proven for radiation in stationary spacetimes and for perfect fluids in stationary, asymototically flat and axisymmetric spacetimes. It is unclear whether the proof can be extended to more general cases. In this paper, we prove that under some reasonable conditions, the Tolman law always holds for a perfect fluid in a stationary spacetime. The key assumption in our proof is that the particle number density $n$ can not be determined by the energy density $ρ$ and pressure $p$ via the equations of state. This is true for many known fluids with the equation of state $p=p(ρ)$. Then, by requiring that the total entropy of the fluid is an extremum for the variation of $n$ with a fixed metric, we prove the Tolman law. In our proof, only the conservations of stress energy and the total particle number are used, and no field equations are involved. Our work suggests that the Tolman law holds for a generic perfect fluid in a stationary spacetime, even beyond general relativity.

D. Hobson, M. Harty, S. R. Tracy et al.

<p>The management of agricultural soils during crop establishment can affect root development due to changes in the soil structure. This paper assesses the influence of tillage depth (250 mm, 100 mm, and zero tillage) and traffic management (conventional tyre pressure, low tyre pressure, and no traffic) on wheat root system architecture during winter wheat (<i>Triticum aestivum</i> L.) tillering and flowering growth stages (GS) at a long-term tillage trial site. The study revealed that zero-tillage systems increased crop yield through significantly greater root biomass (<span class="inline-formula"><i>P</i><i>&lt;</i>0.001</span>), root length density, and deeper seminal rooting analysed using X-ray computed tomography (CT) (<span class="inline-formula"><i>P</i><i>&lt;</i>0.001</span>) compared with trafficked treatments. In general, conventional-pressure traffic had a significant negative influence on the crop yield (<span class="inline-formula"><i>P</i><i>&lt;</i>0.01</span>), root development (0.001), bulk density (<span class="inline-formula"><i>P</i><i>&lt;</i>0.05</span>), and total soil porosity (<span class="inline-formula"><i>P</i><i>&lt;</i>0.05</span>) of deep- and shallow-tillage conventional-pressure systems compared with no-traffic zero- and deep-tillage systems. Visual improvements in soil structure under zero-tillage conditions may have improved crop rooting in zero-tillage treatments through vertical pore fissures (biopores), enhancing water uptake during the crop flowering period. This study highlights the increasing implications of soil structural damage on root system architecture created by machinery traffic in crop production. Although the tillage method was less important, the constricted root systems were more pronounced in conventional-pressure shallow-tillage and deep-tillage systems, emphasizing the importance of using controlled-traffic farming methods to improve soil management and reduce the trafficked areas of agricultural fields.</p>

Danilo Đokić, Bojan Matkovski, Žana Jurjević et al.

This paper focuses on a possible connection between food security and the migrant crisis that began in 2015, which had a tremendous impact on the European Union as well as on the Mediterranean area. The goal of this paper is to determine if there is a correlation between the number of migrants and the levels of food security in both their homeland countries and destination countries. The Promethee method was used to attempt to answer this question. Unfortunately, the analysis is limited due to lack of data for certain countries concerning food security caused by current poor political situations. Nevertheless, the results showed that the best-ranked countries by food security are mostly EU countries. These countries do not have issues with food security, especially in comparison to countries in the Middle East. Also, countries with a high level of food security and political stability have the highest influx of migrants, which suggests there is also an economic motivation for migration. Finally, the analysis confirmed a strong correlation between countries’ achieved level of food security and the number of migrants.

Joana Tereza Vaz de Moura, Paulo Cesar Ramos

A aprovação do Estatuto da Igualdade Racial, em 2010, representou um avanço no debate das questões raciais no Brasil. As narrativas usadas pelo movimento negro tiveram um papel estratégico nesse processo. Nesse artigo, examinamos as narrativas através das quais o movimento negro se legitimou como um ator político legítimo. Buscamos contribuir para a literatura dos movimentos sociais trazendo as narrativas como estratégias essenciais para pautar demandas e atingir resultados na sua relação com o Poder Público. Utilizamos como fontes de informação entrevistas com representantes do movimento negro e documentos disponíveis. O estudo mostra que os ativistas operaram dentro dos limites discursivos do campo político e aproveitaram as oportunidades políticas sinalizadas pelo Estado, reconhecendo-os e legitimando-os como agentes políticos. Enfatizamos também, as circunstâncias que possibilitaram a unificação de um discurso e a concertação para uma narrativa para que os negros se tornassem protagonistas nesse debate.

Petar Mitrić

In this paper we review the canonical analysis of constrained systems and apply it in the case of teleparallel equivalent of general relativity and teleparallel gravity. For each of them we find all the Poisson brackets, generators of gauge symmetries, as well as the number of degrees of freedom.

Katarzyna Lisek

Analiza treści jest metodą szeroko wykorzystywaną nie tylko w naukach społecznych, ale też studiach humanistycznych. Automatyzacja oraz wsparcie komputerowe tej metody cieszy się dużym zainteresowaniem badaczy w Polsce i na świecie. Nowe perspektywy dla rozwoju tej dziedziny może otworzyć crowdsourcing, to jest metoda wirtualnej współpracy, do której zapraszani są liczni, anonimowi użytkownicy nowych technologii. Pierwsze próby wykorzystania tego fenomenu w nauce zakończyły się powodzeniem zarówno w obrębie nauk ścisłych, jak i humanistycznych. Rozpoznanie możliwości używania crowdsourcingu w analizie treści wymaga jednak dalszych testów i poszukiwań. Celem artykułu jest przedstawienie próby użycia pilotażowego narzędzia do crowdsourcingowego kodowania treści oraz refleksja na temat potencjału i ograniczeń tego podejścia. Przedstawiona zostanie krótka charakterystyka zjawiska crowdsourcingu, jego zastosowanie w nauce oraz opis proponowanego narzędzia. Podsumowanie artykułu stanowi analiza szans oraz słabości, które crowdsourcing może oferować dla rozwoju tej metody.

Thomas C. Bachlechner

We provide a novel, concise and self-contained evaluation of true- and false vacuum decay rates in general relativity. We insist on general covariance and choose observable boundary conditions, which yields the well known false-vacuum decay rate and a new true-vacuum decay rate that differs significantly from prior work. The rates of true- and false vacuum decays are identical in general relativity. The second variation of the action has a negative mode for all parameters. Our findings imply a new perspective on cosmological initial conditions and the ultimate fate of our universe.

Ana Mª Domínguez-Quintero

Elias Rodrigues da Cunha, Vitor Matheus Bacani, Lucy Ribeiro Ayach

O presente trabalho objetivou analisar a fragilidade ambiental da bacia hidrográfica do córrego Indaiá/MS, utilizando técnicas de geoprocessamento. Os procedimentos técnicos científicos empregados consistiram na aplicação da proposta metodológica elaborada por Ross (1994) e na adaptação da metodologia proposta por Crepani et al. (2001) com uso de Sistema de Informação Geográfica (SIG). Os resultados mostraram quatro níveis de fragilidade: baixa, média, alta e muito alta, ocupando 4,44%, 42,10%, 53% e 0,31% da área da bacia, respectivamente. Conclui-se que a bacia do córrego Indaiá apresenta um predomínio de baixo e médio grau de fragilidade potencial, entretanto quando considerado o fator antrópico tem-se um predomínio de alta fragilidade ambiental, indicando estado de alerta em relação à intensifcação da ocupação, sobretudo nas áreas onde se encontram instalados os atuais assentamentos rurais.

Tatsuya Narikawa, Hideyuki Tagoshi

We discuss the potential of the advanced ground-based gravitational-wave detectors such as LIGO, Virgo, and KAGRA to detect generic deviations of gravitational waveforms from the predictions of general relativity. We use the parameterized post-Einsteinian formalism to characterize the deviations, and assess what magnitude of deviations are detectable by using an approximate decision scheme based on Bayesian statistics. We find that there exist detectable regions of the parameterized post-Einsteinian parameters for different binary masses from the observation of a single gravitational wave event. The regions are not excluded by currently existing binary pulsar observations for the parameterized post-Einsteinian parameters at higher post-Newtonian order. We also find that neglect of orbital eccentricity or tidal deformation effects do not cause a significant bias on the detectable region of generic deviations from general relativity.

Aleksandar Mikovic, Marko Vojinovic

We give a brief review of the problem of quantum gravity. After the discussion of the nonrenormalizability of general relativity, we briefly mention the main research directions which aim to resolve this problem. Our attention then focuses on the approach of Loop Quantum Gravity, specifically spinfoam models. These models have some issues concerning the semiclassical limit and coupling of matter fields. The recent developments in category theory provide us with the necessary formalism to introduce a new action for general relativity and perform covariant quantization so that the issues of spinfoam models are successfully resolved.

Sergio Serulnikov

The article explores the relationship between global approaches and historical biography. It contends that the so-called transnational, connected or crossed history raises questions of heuristic and hermeneutic interest for biographical inquires. Whereas the biography, like microhistory in general, focuses on the link between the history of an individual and a culture, between the micro and the macro, global approaches seek to articulate various spatial scales of analysis. Their goal is to reconstruct connections and transferences among different societies by looking at discrete historical events, including personal trajectories. The second part of the essay applies these insights to the case of Ignacio Flores, a late Spanish colonial magistrate. Born in Quito to a prominent Creole family, Flores was educated in Europe and developed his political career in the Upper Peru region. It is argued that that his personal journey, which took him from the political and intellectual circles in the metropolis, to his appointment as first Intendant of Charcas, and his removal and arrest shortly afterward, can only be understood by examining the intertwinement of his European cultural identity, his adscription to the putative Spanish nation, his creole origins, and his political alignments in the local conflicts.

Aydee Hurtado Garcés y Carmen Ramos Carv

Resumen

E. A. Panidi

Due to continuous improvement and cheapening of remote sensing technologies the remote sensing methods being increasingly utilized to solve problems of research, monitoring and management of the territories, natural environment, transport and society. Remote sensing data are characterized by significant volumes in general, even compared with other types of spatial data. And improving of the technologies of remote sensing data production leads to more and more significant growth of these volumes. In this context the one of most important tasks of working with remote sensing data is the development of methods for automating of the data processing and analysis, as well as ways of data and processing results storing. The cloud computing technologies and Web solutions that base on such technologies and implement data access and working with the data in the Web, are used in recent years to solve both of the problems. One of such Web-based solutions are geoportals that aggregate access ways to distributed spatial data and processing tools. In current interpretation the geoportal, as a special case of Web-GIS, should not only provide users with spatial data and metadata access but also with the processing tools that allow to solve a wide range of tasks, from displaying to analysis. However, the technologies of spatial data processing and analysis tools are the least developed and standardized at this time. The only WPS (Web Processing Service) international standard specifies how to create spatial data processing Web services. This paper deals with some issues of creating Web services for the spatial data processing (geoprocessing) explored by the author and his colleagues.

Glover Ja