No-horizon theorem for spacetimes with spacelike G1 isometry groups

We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike $G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on ${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent horizons. Given any (3+1) spacetime with spacelike translational isometry, the no-horizon condition can be readily tested without the need for dimensional reduction. This provides thus a useful and encompassing apparent horizon test for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence towards the validity of the hoop conjecture, and signals possible violations of strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra

Cosmic homogeneity: a spectroscopic and model-independent measurement

Cosmology relies on the Cosmological Principle, i.e., the hypothesis that the Universe is homogeneous and isotropic on large scales. This implies in particular that the counts of galaxies should approach a homogeneous scaling with volume at sufficiently large scales. Testing homogeneity is crucial to obtain a correct interpretation of the physical assumptions underlying the current cosmic acceleration and structure formation of the Universe. In this Letter, we use the Baryon Oscillation Spectroscopic Survey to make the first spectroscopic and model-independent measurements of the angular homogeneity scale $\theta_{\rm h}$. Applying four statistical estimators, we show that the angular distribution of galaxies in the range 0.46 < z < 0.62 is consistent with homogeneity at large scales, and that $\theta_{\rm h}$ varies with redshift, indicating a smoother Universe in the past. These results are in agreement with the foundations of the standard cosmological paradigm.Comment: 5 pages, 2 figures, Version accepted by MNRA

Experimental and theoretical evidences for the ice regime in planar artificial spin ices

In this work, we explore a kind of geometrical effect in the thermodynamics of artificial spin ices (ASI). In general, such artificial materials are athermal. Here, We demonstrate that geometrically driven dynamics in ASI can open up the panorama of exploring distinct ground states and thermally magnetic monopole excitations. It is shown that a particular ASI lattice will provide a richer thermodynamics with nanomagnet spins experiencing less restriction to flip precisely in a kind of rhombic lattice. This can be observed by analysis of only three types of rectangular artificial spin ices (RASI). Denoting the horizontal and vertical lattice spacings by a and b, respectively, then, a RASI material can be described by its aspect ratio $\gamma$=a/b. The rhombic lattice emerges when $\gamma$=$\sqrt{3}$. So, by comparing the impact of thermal effects on the spin flips in these three appropriate different RASI arrays, it is possible to find a system very close to the ice regime

Scaling limits of a tagged particle in the exclusion process with variable diffusion coefficient

We prove a law of large numbers and a central limit theorem for a tagged particle in a symmetric simple exclusion process in the one-dimensional lattice with variable diffusion coefficient. The scaling limits are obtained from a similar result for the current through -1/2 for a zero-range process with bond disorder. For the CLT, we prove convergence to a fractional Brownian motion of Hurst exponent 1/4.Comment: 9 page

Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse

We study the occurrence, visibility, and curvature strength of singularities in dust-containing Szekeres spacetimes (which possess no Killing vectors) with a positive cosmological constant. We find that such singularities can be locally naked, Tipler strong, and develop from a non-zero-measure set of regular initial data. When examined along timelike geodesics, the singularity's curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for publication in Class. Quantum Gra

Tendências Seculares na Mortalidade por Doenças Cerebrovasculares em Portugal: 1902-2012

Introduction: Cerebrovascular diseases (CVD) are one of the main causes of death in Portugal. Research on the epidemiologic history might help to understand the phenomenon and guide intervention strategies. Objectives: (1) Describe historic trends in mortality. (2) Estimate the impact of demographic variations on the registered number of cases. Methods: (1) We calculated rates, specific and standardized, for deaths registered as CVD (ICD-10: I60-I69, G45; ICD8/9: 430-438; ICD-6/7: 330-334) by sex (1902-2012) and by sex and age groups (1913-2012). We used Join point analysis to identify statistically significant changes in standardized death rates, and multivariate regression models, Poisson and negative binomial, controlling for demographic dynamics and time trend, from 1913 to 2012. (2) We calculated the contribution of demographic variations using the application RiskDiff. (3) We evaluated if changes in coding rules might have been a source of bias. Data source: National Institute of Statistics. Results: (1) We gathered the longest and most discriminated mortality series from CVD in Portugal with data since the beginning of nationwide collection. Mortality increases exponentially with age and is higher in men. (2) We observed significant variations in age-standardized time trends (1913-1933: APC 2.0%; 1933-1955: APC -0.9%; 1955-1974: 2.9%; 1974- 1996: -2.4%; 1996-2012: -6.5%). (3) Population ageing exerted a significant pressure to increase the number of deaths, particularly in the second half of the twentieth century. However, this effect was counterweighted by protective factors. Conclusion: CVD mortality in Portugal is particularly expressive when compared to other European countries, although significant gains have been observed in the last decades. Population ageing combined with a transition between the morbid and mortality dimensions changed the public health paradigm.Introdução: As doenças cerebrovasculares (DCV) são uma das principais causas de morte em Portugal. O estudo da história epidemiológica deste fenómeno contribui para a sua compreensão e ajuda a orientar estratégias de intervenção. Objetivos: (1) Descrever tendências históricas na mortalidade. (2) Estimar o impacto das variações demográficas no número de casos registado. Métodos: (1) Calculámos taxas, específicas e padronizadas, para as mortes registadas como resultantes de DCV (CID-10: I60-I69, G45; ICD-8/9: 430-438; ICD-6/7: 330-334) por sexo (1902-2012) e por sexo e grupos etários (1913- 2012). Utilizámos Joinpoint-analysis para identificar variações estatisticamente significativas na tendência temporal e modelos multivariados de regressão, Poisson e binomial negativo, controlando dinâmicas demográficas e tendências temporais, constrangidos à população exposta, de 1913 a 2012. (2) Aferimos o peso relativo de variações demográficas recorrendo à aplicação RiskDiff. (3) Avaliámos se as interrupções na continuidade das séries definidas por alterações nos critérios de codificação da causa de morte podem ter constituído factores confundentes. Fontes dos dados: Instituto Nacional de Estatística. Resultados: (1) Elencámos a mais longa e discriminada série de mortalidade por DCV em Portugal com dados desde que há registo com abrangência nacional. A mortalidade aumenta exponencialmente com a idade e é superior nos homens. (2) Observámos variações significativas na direcção e amplitude da tendência temporal das taxas padronizadas (1913-1933: APC 2,0%; 1933-1955: APC -0,9%; 1955-1974: 2,9%; 1974-1996: -2,4%; 1996-2012: -6,5%). (3) O envelhecimento demográfico exerceu uma pressão significativa para o aumento no número de casos particularmente na segunda metade do século XX. No entanto este efeito foi neutralizado por factores protectores. Conclusão: Em Portugal a DCV é particularmente expressiva quando comparada com outros países da Europa embora se tenham observado ganhos significativos nas últimas décadas. O envelhecimento demográfico combinado com uma eventual transição relativa entre as dimensões morbil e de mortalidade proporcionaram uma mudança no paradigma de saúde pública.info:eu-repo/semantics/publishedVersio