Observation of crystallization slowdown in supercooled para-hydrogen and ortho-deuterium quantum liquid mixtures

We report a quantitative experimental study of the crystallization kinetics of supercooled quantum liquid mixtures of para-hydrogen (pH$_2$) and ortho-deuterium (oD$_2$) by high spatial resolution Raman spectroscopy of liquid microjets. We show that in a wide range of compositions the crystallization rate of the isotopic mixtures is significantly reduced with respect to that of the pure substances. To clarify this behavior we have performed path-integral simulations of the non-equilibrium pH$_2$-oD$_2$ liquid mixtures, revealing that differences in quantum delocalization between the two isotopic species translate into different effective particle sizes. Our results provide first experimental evidence for crystallization slowdown of quantum origin, offering a benchmark for theoretical studies of quantum behavior in supercooled liquids.Comment: 6 pages, 3 figure

Multiple Sources toward the High-mass Young Star S140 IRS1

S140 IRS1 is a remarkable source where the radio source at the center of the main bipolar molecular outflow in the region is elongated perpendicular to the axis of the outflow, an orientation opposite to that expected if the radio source is a thermal jet exciting the outflow. We present results of 1.3 cm continuum and H2O maser emission observations made with the VLA in its A configuration toward this region. In addition, we also present results of continuum observations at 7 mm and re-analyse observations at 2, 3.5 and 6 cm (previously published). IRS 1A is detected at all wavelengths, showing an elongated structure. Three water maser spots are detected along the major axis of the radio source IRS 1A. We have also detected a new continuum source at 3.5 cm (IRS 1C) located ~0.6'' northeast of IRS 1A. The presence of these two YSOs (IRS 1A and 1C) could explain the existence of the two bipolar molecular outflows observed in the region. In addition, we have also detected three continuum clumps (IRS 1B, 1D and 1E) located along the major axis of IRS 1A. We discuss two possible models to explain the nature of IRS 1A: a thermal jet and an equatorial wind.Comment: 17 pages, 4 figures, to be published in A

Scale Radii and Aggregation Histories of Dark Haloes

Relaxed dark-matter haloes are found to exhibit the same universal density profiles regardless of whether they form in hierarchical cosmologies or via spherical collapse. Likewise, the shape parameters of haloes formed hierarchically do not seem to depend on the epoch in which the last major merger took place. Both findings suggest that the density profile of haloes does not depend on their aggregation history. Yet, this possibility is apparently at odds with some correlations involving the scale radius r_s found in numerical simulations. Here we prove that the scale radius of relaxed, non-rotating, spherically symmetric haloes endowed with the universal density profile is determined exclusively by the current values of four independent, though correlated, quantities: mass, energy and their respective instantaneous accretion rates. Under this premise and taking into account the inside-out growth of haloes during the accretion phase between major mergers, we build a simple physical model for the evolution of r_s along the main branch of halo merger trees that reproduces all the empirical trends shown by this parameter in N-body simulations. This confirms the conclusion that the empirical correlations involving r_s do not actually imply the dependence of this parameter on the halo aggregation history. The present results give strong support to the explanation put forward in a recent paper by Manrique et al. (2003) for the origin of the halo universal density profile.Comment: 13 pages, 8 figures, accepted for publication in MNRA

Reforço à flexão com compósitos de CFRP de vigas de madeira lamelada-colada

Neste trabalho apresenta-se uma campanha de ensaios em vigas de madeira lamelada-colada reforçadas à flexão com dois sistemas de compósitos unidireccionais de CFRP (polímeros reforçados com fibras de carbono), o curado “in situ” (manta) e o pré-fabricado (laminado). Para cada sistema de CFRP, o reforço foi aplicado externamente ou internamente na face inferior da penúltima lamela. No caso do reforço interno foi, também, avaliada a influência da colagem do CFRP numa pequena cavidade previamente executada na face da lamela a reforçar. Os resultados obtidos são analisados e interpretados, referindo-se as principais conclusões, tendo em vista avaliar a viabilidade do reforço à flexão de vigas de madeira lamelada-colada através da colagem de compósitos de CFRP.Flexilam. BeTTor MBT Portugal

Compósitos de CFRP unidireccionais no reforço de vigas de madeira lamelada-colada

Neste trabalho apresenta-se a campanha de ensaios realizada para avaliar a eficiência da aplicação de dois sistemas compósitos de CFRP no reforço à flexão de vigas de madeira lamelada-colada: o curado “in situ” (manta) e o pré-fabricado (laminado). Cada um dos sistemas de CFRP foi aplicado quer em reforço externo (colagem na face traccionada da viga) quer em reforço interno (colagem na face inferior da penúltima lamela). No caso do reforço interno foi, ainda, avaliada a influência da colagem do CFRP numa cavidade previamente executada na face da lamela a reforçar. Numa fase precedente, avaliou-se a aderência madeira- CFRP por intermédio de ensaios de “pull-off”, tendo-se analisado as seguintes variáveis: o tipo de cola, a utilização de primário e o tratamento da superfície.Flexilam.BeTTor MBT Portugal

The impact of biogenic VOC emissions on photochemical ozone formation during a high ozone pollution episode in the Iberian Peninsula in the 2003 summer season

Throughout Europe the summer of 2003 was exceptionally warm, especially July and August. The European Environment Agency (EEA) reported several ozone episodes, mainly in the first half of August. These episodes were exceptionally long-lasting, spatially extensive, and associated to high temperatures. In this paper, the 10$ndash;15 August 2003 ozone pollution event has been analyzed using meteorological and regional air quality modelling. During this period the threshold values of the European Directive 2002/3/EC were exceeded in various areas of the Iberian Peninsula. <br><br> The aim of this paper is to computationally understand and quantify the influence of biogenic volatile organic compound (BVOC) emissions in the formation of tropospheric ozone during this high ozone episode. Being able to differentiate how much ozone comes from biogenic emissions alone and how much comes from the interaction between anthropogenic and biogenic emissions would be helpful to develop a feasible and effective ozone control strategy. The impact on ozone formation was also studied in combination with various anthropogenic emission reduction strategies, i.e., when anthropogenic VOC emissions and/or NO<sub>x</sub> emissions are reduced. The results show a great dependency of the BVOC contribution to ozone formation on the antropoghenic reduction scenario. In rural areas, the impact due to a NO<sub>x</sub> and/or VOC reduction does not change the BVOC impact. Nevertheless, within big cities or industrial zones, a NO<sub>x</sub> reduction results in a decrease of the biogenic impact in ozone levels that can reach 85 μg/m<sup>3</sup>, whereas an Anthropogenic Volatile Organic Compound (AVOC) reduction results in a decrease of the BVOC contribution on ozone formation that varies from 0 to 30 μg/m<sup>3</sup> with respect to the contribution at the same points in the 2003 base scenario. On the other hand, downwind of the big cities, a decrease in NO<sub>x</sub> produces a minor contribution of biogenic emissions and a decrease in AVOCs results in greater contributions of BVOCs to the formation of ozone

Sensitivity analysis of surface ozone to modified initial and boundary conditions in both rural and industrial zones

International audienceA three-dimensional air quality model based on a set of chemical species mass conservation equations describes the time evolution of chemical species in the atmosphere. In order to solve this set of equations, proper choices of initial and boundary conditions are needed. Ideally, initial and boundary conditions should be determined on the basis of observations. However, since such high-resolution observations are generally not available, it becomes necessary to use other information sources to specify the initial and boundary values. The fact that both the initial and the boundary conditions are specified with some degree of presumption makes it important to evaluate their influence in the model results. In this paper we present a study of the impact of initial and boundary concentrations on the modelled surface ozone concentration over two environments: Huelva and Badajoz, an industrial and a rural zone, respectively. The impacts are analysed for the same meteorological period (10?15 August 2003)