Top ranking economics journals impact variability and a ranking update to the year 2002

In this paper I address four questions concerning the quality of scientific economic papers. First, I validate the ex-ante procedure of computing the average impact of economic papers by comparing its results with the expost values. Second, I calibrate an estimator of papers normalised impact. Third, I compute the ranking variability of journals using a bootstrap procedure. Fourth, I test the statistical hypothesis that journals’ ranking did not changed over the time interval between 1980 and 2000. I concluded that this hypothesis is rejected only for the ‘Quarterly Journal of Economics’ and ‘Econometrica’, which saw their citation impact improved.

One-loop conformal anomaly in an implicit momentum space regularization framework

In this paper we consider matter fields in a gravitational background in order to compute the breaking of the conformal current at one-loop order. Standard perturbative calculations of conformal symmetry breaking expressed by the non-zero trace of the energy-momentum tensor have shown that some violating terms are regularization dependent, which may suggest the existence of spurious breaking terms in the anomaly. Therefore, we perform the calculation in a momentum space regularization framework in which regularization dependent terms are judiciously parametrized. We compare our results with those obtained in the literature and conclude that there is an unavoidable arbitrariness in the anomalous term $\Box R$.Comment: in European Physical Journal C, 201

Robustness of the O(NN) universality class

We calculate the critical exponents for Lorentz-violating O($N$) $\lambda\phi^{4}$ scalar field theories by using two independent methods. In the first situation we renormalize a massless theory by utilizing normalization conditions. An identical task is fulfilled in the second case in a massive version of the same theory, previously renormalized in the BPHZ method in four dimensions. We show that although the renormalization constants, the $\beta$ and anomalous dimensions acquire Lorentz-violating quantum corrections, the outcome for the critical exponents in both methods are identical and furthermore they are equal to their Lorentz-invariant counterparts. Finally we generalize the last two results for all loop levels and we provide symmetry arguments for justifying the latter

Neuropilin 1 signaling guides neural crest cells to coordinate pathway choice with cell specification

Neural crest cells (NCCs) are highly motile embryonic stem cells that delaminate from the neuroectoderm early during vertebrate embryogenesis and differentiate at defined target sites into various essential cell types. To reach their targets, NCCs follow 1 of 3 sequential pathways that correlate with NCC fate. The firstborn NCCs travel ventrally alongside intersomitic blood vessels to form sympathetic neuronal progenitors near the dorsal aorta, while the lastborn NCCs migrate superficially beneath the epidermis to give rise to melanocytes. Yet, most NCCs enter the somites to form the intermediate wave that gives rise to sympathetic and sensory neurons. Here we show that the repulsive guidance cue SEMA3A and its receptor neuropilin 1 (NRP1) are essential to direct the intermediate wave NCC precursors of peripheral neurons from a default pathway alongside intersomitic blood vessels into the anterior sclerotome. Thus, loss of function for either gene caused excessive intersomitic NCC migration, and this led to ectopic neuronal differentiation along both the anteroposterior and dorsoventral axes of the trunk. The choice of migratory pathway did not affect the specification of NCCs, as they retained their commitment to differentiate into sympathetic or sensory neurons, even when they migrated on an ectopic dorsolateral path that is normally taken by melanocyte precursors. We conclude that NRP1 signaling coordinates pathway choice with NCC fate and therefore confines neuronal differentiation to appropriate locations

Spontaneous Combustion of South American Coal

Many causes can lead to mine fires and explosions in coal mines but one of the most relevant cause is the spontaneous combustion of coal. This event can cause serious environmental consequences such as release of huge quantities of greenhouse effect gases such as CO2 and CO, presents safety risks to the miners by igniting mine explosions, and also causes significant economic loss. Many countries in the world have faced these problems. In order to prevent and mitigate them, scientists develop methods to determine whether a coal deposit has propensity to spontaneous combustion or not.;Many methods have been developed around the world for the determination of the propensity of spontaneous combustion of coals such as the adiabatic method, the USBM empirical methods based on coal quality analysis. The methods, having their own advantages and limitations, are applicable to analyze every coal or just some specific ones. These methods were developed mainly in Australia, USA and China since these countries are the major victims of mine fires.;Despite the fact that mine fires have caused many problems around the world, South American coals and deposits have never been studied for their propensity to spontaneous combustion. So what are the chances that coal producers in Latin America like Colombia and Brazil can face this problem in a near future? What preventive measures the mine operators should take to ensure safe and smooth mining operation? What kinds of environmental issues the coal spontaneous combustion could bring the population living nearby the mines? To answer these questions, the author performed the following experimental analyses to determine the propensity of the South America\u27s coals. The results are presented in this thesis.;• The adiabatic analysis will be used to determine the intrinsic reactivity of coal samples obtained from Colombia at low temperatures. The reactivity will be calculated exposing the coal to dry and moist environment. • The thermogravimetry (TGA) will be used to determine the activation energy of the coal samples obtained and also to do the proximate analysis, which is important to the next step. • Use the proximate analysis to find parameters like self-heating temperature, quantified coal rank using US coal band which can be used to serve as a quick estimate of self-heating potential of South American coals

Influence of SiC reinforcement particles on the tribocorrosion behaviour of Al–SiCp FGMs in 0.05M NaCl solution

The main aim of this work was to study and understand the influence of SiC particles on the corrosion and tribocorrosion of Al-matrix composite materials. For that, Al–SiCp functionally graded composites were produced by centrifugal casting and different SiCp contents were achieved. Their mechanical properties were improved by age-hardening heat treatments. The tribocorrosion behaviour was studied in 0.05M NaCl solutions using a reciprocating motion tribometer involving an alumina ball sliding against the Al-based samples. Above critical SiC particles' content the matrix alloy surface was found to be protected against wear by SiC particles protruding from the surface. Below this threshold content, the SiC reinforcement was inefficient and the wear rate of the composite was the same as the non-reinforced alloy.The research team was financially supported by the Portuguese Foundation for Science and Technology (FCT-Portugal) under a PhD scholarship (SFRH/BD/27911/2006). The authors also thank Dr Edith Ariza (University of Minho) and Pierre Mettraux (EPFL) for SEM analysis