26,547 research outputs found
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 journalsâ ranking did not changed over the time interval between 1980 and 2000. I concluded that this hypothesis is rejected only for the âQuarterly Journal of Economicsâ and âEconometricaâ, which saw their citation impact improved.
Robustness of the O() universality class
We calculate the critical exponents for Lorentz-violating O()
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
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
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 .Comment: in European Physical Journal C, 201
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
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