Cosmological hydrogen recombination: The effect of extremely high-n states

Calculations of cosmological hydrogen recombination are vital for the extraction of cosmological parameters from cosmic microwave background (CMB) observations, and for imposing constraints to inflation and re-ionization. The Planck} mission and future experiments will make high precision measurements of CMB anisotropies at angular scales as small as l~2500, necessitating a calculation of recombination with fractional accuracy of ~10^{-3}. Recent work on recombination includes two-photon transitions from high excitation states and many radiative transfer effects. Modern recombination calculations separately follow angular momentum sublevels of the hydrogen atom to accurately treat non-equilibrium effects at late times (z<900). The inclusion of extremely high-n (n>100) states of hydrogen is then computationally challenging, preventing until now a determination of the maximum n needed to predict CMB anisotropy spectra with sufficient accuracy for Planck. Here, results from a new multi-level-atom code (RecSparse) are presented. For the first time, `forbidden' quadrupole transitions of hydrogen are included, but shown to be negligible. RecSparse is designed to quickly calculate recombination histories including extremely high-n states in hydrogen. Histories for a sequence of values as high as n_max=250 are computed, keeping track of all angular momentum sublevels and energy shells of the hydrogen atom separately. Use of an insufficiently high n_max value (e.g., n_max=64) leads to errors (e.g., 1.8 sigma for Planck) in the predicted CMB power spectrum. Extrapolating errors, the resulting CMB anisotropy spectra are converged to 0.5 sigma at Fisher-matrix level for n_max=128, in the purely radiative case.Comment: 19 pages, 12 figures, replaced with version published in Physical Review D (added discussion of collisions)

Molecular Density Functional Theory for water with liquid-gas coexistence and correct pressure

The solvation of hydrophobic solutes in water is special because liquid and gas are almost at coexistence. In the common hypernetted chain approximation to integral equations, or equivalently in the homogenous reference fluid of molecular density functional theory, coexistence is not taken into account. Hydration structures and energies of nanometer-scale hydrophobic solutes are thus incorrect. In this article, we propose a bridge functional that corrects this thermodynamic inconsistency by introducing a metastable gas phase for the homogeneous solvent. We show how this can be done by a third order expansion of the functional around the bulk liquid density that imposes the right pressure and the correct second order derivatives. Although this theory is not limited to water, we apply it to study hydrophobic solvation in water at room temperature and pressure and compare the results to all-atom simulations. With this correction, molecular density functional theory gives, at a modest computational cost, quantitative hydration free energies and structures of small molecular solutes like n-alkanes, and of hard sphere solutes whose radii range from angstroms to nanometers. The macroscopic liquid-gas surface tension predicted by the theory is comparable to experiments. This theory gives an alternative to the empirical hard sphere bridge correction used so far by several authors.Comment: 18 pages, 6 figure

Cidade e práticas urbanas: nas fronteiras incertas entre o ilegal, o informal e o ilícito

Neste artigo, pretende-se abordar o tráfico de drogas a partir de suas capilaridades no mundo social e nas tramas urbanas, tomando como "posto de observação" alguns de seus pontos de ancoramento na periferia da cidade de São Paulo. Essa é uma perspectiva descritiva (e analítica) que permite situar as práticas criminosas nas suas relações com o que poderíamos definir como a gestão das ilegalidades inscritas nos agenciamentos concretos da vida cotidiana. A rigor, esse é o foco da discussão a ser desenvolvida: as evidências de uma crescente e expansiva trama de ilegalidades (nova e velhas) entrelaçadas nas práticas urbanas, seus circuitos e redes sociais, e que são urdidas nas relações hoje redefinidas (e a serem bem compreendidas) entre o ilegal, o informal e o ilícito. Com base em resultados de pesquisa recente, o artigo pretende o exercício de "etnografia experimental" para tentar flagrar as mediações e conexões pelas quais esses deslocamentos das fronteiras do legal e do ilegal vêm se processando. São essas conexões e mediações que precisam ser bem compreendidas: é nelas que se tem uma chave para identificar e compreender a porosidade entre o legal e ilegal, e as fronteiras borradas entre o trabalho, expedientes de sobrevivência e práticas ilícitas; é nelas que se podem identificar e compreender as capilaridades do tráfico de drogas no mundo social, capilaridades urdidas nessas formas de junção e conjugação da trama urbana.This article intends to approach the drug trade from the perspective of its capillary network in the social world and in urban weaves, using one of its trafficking points in São Paulos periphery as an "observation station". This is a descriptive (and analytic) perspective that allows us to consider criminal practices in relation to what could be defined as the illegality management, which is present in concrete every-day life administration practices. This is, indeed, the focus of the discussion: evidences of a growing and expansive mesh of illegalities (both old and new ones), their circuits and social networks, which are woven in urban practices and warped in the redefined relations among the illegal, the informal and the illicit. Based on the results of a recent research, the article aims to put an "experimental ethnography" into practice, in an attempt to find out the mediations and connections through which the movements of the boundaries between the legal and the illegal have been taking place. These connections and mediations must be well understood for they contain the key to identifying and understanding the porosity existent between the legal and the illegal, and the blurry boundaries among work, survival expedients and illicit practices. In them, one may identify and comprehend the capillary network of the drug trade in the social world, which is warped in the junctions and conjunctions of the urban weave

What determines the shape of a Pine-Island-like ice shelf?

Ice shelf shape directly controls ocean heat intrusions, melting near the grounding line, and buttressing. Little is known about what determines ice-shelf shape because ice-ocean coupled simulations typically aim at projecting Antarctica's contribution to sea-level rise and they do not resolve small-scale ice-ocean interactive processes. We conduct ice-ocean coupled simulations for an idealized high-resolution, Pine-Island-like model configuration. We show that ocean melting and ice stretching caused by acceleration thin the ice shelf from the grounding line toward the ice shelf front, consistent with previous studies. In the across-flow direction, ocean melting and ice advection cancel each other out and flatten the ice shelf. More than one-third of the ice thinning from grounding line to ice front can be attributed to ocean melting at depths shallower than 500 m. Our results emphasize the importance of interactive processes between the entire ice shelf and the ocean for determining the ice shelf shape. Plain Language Summary Antarctic ice flows into the ocean and forms a floating extension of land ice called an ice shelf. The ice shelf shape directly controls the amount of ocean heat intrusions, melting near the grounding line, and buttressing. However, little is understood about ice-ocean interactive processes determining ice shelf shape because (a) ocean modelers apply a constant cavity geometry, (b) ice modelers mostly assume simplified melting parameterization, and (c) ice-ocean coupled simulations typically aim at projections of Antarctica's sea-level contributions and they require long model integration. We conduct ice-ocean coupled simulations for an idealized high-resolution Pine-Island-like model configuration. Basal melting and ice stretching create a typical ice shelf shape with steep thinning near the grounding line followed by gradual thinning toward the ice shelf front. In the across-flow direction, ice divergence from the center advects ice toward edges, compensating for melt-driven thinning and flattening ice shelf shape. We also show that ice melting at shallow depths contributes to about one-third of ice-shelf thinning. Although it is thought that ice shelf melting at the grounding line dominantly controls ice shelf behavior, our results suggest the importance of ice-ocean interactive processes for the entire ice shelf cavity for determining the ice shelf shape

Molecular Density Functional Theory of Water describing Hydrophobicity at Short and Long Length Scales

We present an extension of our recently introduced molecular density functional theory of water [G. Jeanmairet et al., J. Phys. Chem. Lett. 4, 619, 2013] to the solvation of hydrophobic solutes of various sizes, going from angstroms to nanometers. The theory is based on the quadratic expansion of the excess free energy in terms of two classical density fields, the particle density and the multipolar polarization density. Its implementation requires as input a molecular model of water and three measurable bulk properties, namely the structure factor and the k-dependent longitudinal and transverse dielectric susceptibilities. The fine three-dimensional water structure around small hydrophobic molecules is found to be well reproduced. In contrast the computed solvation free-energies appear overestimated and do not exhibit the correct qualitative behavior when the hydrophobic solute is grown in size. These shortcomings are corrected, in the spirit of the Lum-Chandler-Weeks theory, by complementing the functional with a truncated hard-sphere functional acting beyond quadratic order in density. It makes the resulting functional compatible with the Van-der-Waals theory of liquid-vapor coexistence at long range. Compared to available molecular simulations, the approach yields reasonable solvation structure and free energy of hard or soft spheres of increasing size, with a correct qualitative transition from a volume-driven to a surface-driven regime at the nanometer scale.Comment: 24 pages, 8 figure

Letalidade e ilegalismos de negócios em uma tríplice fronteira sul-americana: Primeira aproximação

The paper discusses the relationship between illegalisms and lethality through research conducted in the city of Tabatinga (AM), located in the border between Brazil, Colombia, and Peru. Firstly, it introduces three aspects often associated with the city and used to characterize it as a problematic place: homicides, cocaine markets, and institutional density. Secondly, an alternate hypothesis is formulated to re-situate the issue under different empirical-analytical parameters, seeking to highlight the political and economic networks that regulate the cocaine market and produce lethal effects through pistolagem and extermination groups.Este artigo versa sobre as relações entre ilegalismos e letalidade por meio de pesquisas realizadas na cidade de Tabatinga – AM, localizada na tríplice fronteira entre Brasil, Colômbia e Peru. Inicialmente, são apontados três aspectos que recorrentemente aparecem associados para caracterizar Tabatinga como um lugar problemático: homicídios, mercados da cocaína e densidade institucional. Uma hipótese alternativa é formulada para re-situar a questão sob outros parâmetros empíricos-analíticos, buscando iluminar as redes político-econômicas que regulam o mercado da cocaína e produzem efeitos letais através do fenômeno da pistolagem e dos grupos de extermínio

Reducing the weak lensing noise for the gravitational wave Hubble diagram using the non-Gaussianity of the magnification distribution

Gravitational wave sources are a promising cosmological standard candle because their intrinsic luminosities are determined by fundamental physics (and are insensitive to dust extinction). They are, however, affected by weak lensing magnification due to the gravitational lensing from structures along the line of sight. This lensing is a source of uncertainty in the distance determination, even in the limit of perfect standard candle measurements. It is commonly believed that the uncertainty in the distance to an ensemble of gravitational wave sources is limited by the standard deviation of the lensing magnification distribution divided by the square root of the number of sources. Here we show that by exploiting the non-Gaussian nature of the lensing magnification distribution, we can improve this distance determination, typically by a factor of 2--3; we provide a fitting formula for the effective distance accuracy as a function of redshift for sources where the lensing noise dominates.Comment: matches PRD accepted version (expanded description of the cosmological parameter space + minor changes