1,869 research outputs found
The closet non-Gaussianity of anisotropic Gaussian fluctuations
In this paper we explore the connection between anisotropic Gaussian
fluctuations and isotropic non-Gaussian fluctuations. We first set up a large
angle framework for characterizing non-Gaussian fluctuations: large angle
non-Gaussian spectra. We then consider anisotropic Gaussian fluctuations in two
different situations. Firstly we look at anisotropic space-times and propose a
prescription for superimposed Gaussian fluctuations; we argue against
accidental symmetry in the fluctuations and that therefore the fluctuations
should be anisotropic. We show how these fluctuations display previously known
non-Gaussian effects both in the angular power spectrum and in non-Gaussian
spectra. Secondly we consider the anisotropic Grischuk-Zel'dovich effect. We
construct a flat space time with anisotropic, non-trivial topology and show how
Gaussian fluctuations in such a space-time look non-Gaussian. In particular we
show how non-Gaussian spectra may probe superhorizon anisotropy
Evidence for non-Gaussianity in the COBE DMR Four Year Sky Maps
We introduce and study the distribution of an estimator for the normalized
bispectrum of the Cosmic Microwave Background (CMB) anisotropy. We use it to
construct a goodness of fit statistic to test the coadded 53 and 90 GHz
COBE-DMR 4 year maps for non-Gaussianity. Our results indicate that Gaussianity
is ruled out at the confidence level in excess of 98%. This value is a lower
bound, given all the investigated systematics. The dominant non-Gaussian
contribution is found near the multipole of order . Our attempts to
explain this effect as caused by the diffuse foreground emission from the
Galaxy have failed. We conclude that unless there exists a microwave foreground
emission which spatially correlates neither with the DIRBE nor Haslam maps, the
cosmological CMB anisotropy is genuinely non-Gaussian.Comment: 16 pages, 3 figs uses aasms4.tex, revised and accepted to Ap. J. Let
Where is the COBE maps' non-Gaussianity?
We review our recent claim that there is evidence of non-Gaussianity in the 4
Year COBE DMR data. We present some new results concerning the effect of the
galactic cut upon the non-Gaussian signal. These findings imply a localization
of the non-Gaussian signal on the Northern galactic hemisphere.Comment: Proceedings of COSMO98 Asiloma
Non-Gaussian Spectra
Gaussian cosmic microwave background skies are fully specified by the power
spectrum. The conventional method of characterizing non-Gaussian skies is to
evaluate higher order moments, the n-point functions and their Fourier
transforms. We argue that this method is inefficient, due to the redundancy of
information existing in the complete set of moments. In this paper we propose a
set of new statistics or non-Gaussian spectra to be extracted out of the
angular distribution of the Fourier transform of the temperature anisotropies
in the small field limit. These statistics complement the power spectrum and
act as localization, shape, and connectedness statistics. They quantify generic
non-Gaussian structure, and may be used in more general image processing tasks.
We concentrate on a subset of these statistics and argue that while they carry
no information in Gaussian theories they may be the best arena for making
predictions in some non-Gaussian theories. As examples of applications we
consider superposed Gaussian and non-Gaussian signals, such as point sources in
Gaussian theories or the realistic Kaiser-Stebbins effect. We show that in
these theories non-Gaussianity is only present in a ring in Fourier space,
which is best isolated in our formalism. Subtle but strongly non-Gaussian
theories are also written down for which only non-Gaussian spectra may accuse
non-Gaussianity.Comment: 23 pages (20 figures), uses RevTex and epsfig, submitted to PRD.
Figures available from ftp://euclid.tp.ph.ic.ac.uk/pub/magueijo/ng/ (in 4
files). Also, in same site, ng8.uu with it all (preferable
On the Nature of Income Inequality Across Nations
In this paper, we investigate the nature of income inequality across nations by first estimating, testing, and distinguishing between two types of aggregate production functions: the extended neoclassical model and a mincerian formulation of schooling-returns to skills. Next, given our panel-data estimates, we proceed in decomposing the variance of the (log) level of output per-worker in 1985 into that of three distinct factors: productivity, human capital, and the dynamic incentives to accumulate capital. Finally, we classify a group of 95 countries according to their relative position (above or below average) for each of these factors. The picture that emerges from these last two exercises is one where countries grew in the past for different reasons, which should be considered for policy design. Although there is not a single-factor explanation for the difference in output per-worker across nations, it seems that productivity differences can explain a considerable portion of income inequality, followed second by dynamic inefficiencies and third by human capital accumulation.
La cadena de valor de los productos forestales y los costes de su remodelaciĂłn: impacto multirregional de la reducciĂłn de las industrias de pulpa y papel en Portugal
Las evaluaciones macroeconĂłmicas de la industria forestal tienden a subestimar su impacto en las economĂas regionales. Este trabajo propone un concepto mĂĄs amplio â la "cadena de valor de los productos forestales"- que incluye la contribuciĂłn de las actividades que dependen (directa e indirectamente) de la silvicultura y los productos forestales. Con una metodologĂa basada en un modelo de input-output multirregional y centrado en la economĂa portuguesa. Los resultados elucidan el papel del eucalipto en las producciones de pulpa, papel y cartĂłn y artĂculos de papel y cartĂłn. Finalmente, se evalĂșan las consecuencias macroeconĂłmicas proyectadas para una reducciĂłn de estas producciones.Forestry industry macroeconomic assessments typically concentrate on the production, harvesting, and earliest processing of wood products, underestimating the full range of forests impacts in regional economies. This work proposes a broader concept â âforestry products value chainââ that ponders the contribution of the downstream activities relying (directly and indirectly) on Silviculture and Forestry products. The paper adopts a methodology based on a Multi-Regional Input-Output framework. We apply this approach to the Portuguese economy. Results clarify the role of eucalyptus in âPulpâ, âPaper and Cardboardâ and âPaper and Cardboard Articlesâ. Finally, the projected wider macroeconomic consequences from a reduction of these productions is evaluated
Causality, randomness, and the microwave background
Fluctuations in the cosmic microwave background (CMB) temperature are being
studied with ever increasing precision. Two competing types of theories might
describe the origins of these fluctuations: ``inflation'' and ``defects''. Here
we show how the differences between these two scenarios can give rise to
striking signatures in the microwave fluctuations on small scales, assuming a
standard recombination history. These should enable high resolution
measurements of CMB anisotropies to distinguish between these two broad classes
of theories, independent of the precise details of each.Comment: uuencoded tex file and 4 postscript figure files, 8 pages. Also
available at http://euclid.tp.ph/Papers/index.html; Changes: Minor changes
reflect final published versio
Avaliação do desempenho financeiro das empresas do setor eléctrico em Portugal
A avaliação do desempenho financeiro do sector elĂ©trico tem sido o foco de atenção de diversos estudos, mas existe uma escassez de literatura cientĂfica que aborde especificamente o desempenho financeiro das empresas deste sector. Assim, o presente trabalho tem como objetivo avaliar o desempenho financeiro das empresas reguladas que operam no mercado elĂ©trico PortuguĂȘs. Com este objetivo em mente, propĂ”e-se uma estrutura de modelagem que combina o uso do mĂ©todo de estimação Generalized Method of Moments (GMM) com a anĂĄlise Data Envelopment Analysis (DEA). Este estudo centra-se no perĂodo entre 2010 e 2014, altura em que o governo portuguĂȘs necessitou de ajuda financeira externa. O mĂ©todo de estimação GMM permitiu selecionar as variĂĄveis corporativas intrĂnsecas, que foram entĂŁo usadas para avaliar o desempenho financeiro das empresas do setor elĂ©trico atravĂ©s do modelo DEA Slack Based Measure (SBM). Neste contexto, o retorno sobre o patrimĂłnio lĂquido (ROE), a alavancagem (Leverage) e os fluxos de caixa sobre o total do ativo (CFTA) foram selecionados como outputs, enquanto o valor da soma das depreciaçÔes e das amortizaçÔes sobre o total de ativos (DATA) foram considerados como inputs. Os resultados sugerem que enquanto em 2010 a maioria das empresas nĂŁo eficientes deveriam investir em novos ativos fixos de modo a tornarem-se eficientes, em 2014, uma percentagem expressiva de empresas nĂŁo eficientes deve diminuir este tipo de investimento. Adicionalmente, em ambos os perĂodos, a maioria das empresas do sector elĂ©trico nĂŁo eficientes deveria aumentar o seu ROE para se tornar eficiente, destacando o papel do ROE na explicação da eficiĂȘncia financeira. Em 2014, as empresas nĂŁo eficientes sĂŁo capazes de gerar fluxos de caixa com eficiĂȘncia, uma vez que quase nĂŁo sĂŁo necessĂĄrios ajustes em relação aos valores de CFTA obtidos por estas empresas. Por fim, a necessidade de promover a alavancagem para aumentar o desempenho financeiro Ă© mais evidente em 2010 do que em 2014, reconhecendo que os novos investimentos feitos neste perĂodo utilizam capital alheio
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