1,721,131 research outputs found
Charging the conformal window
Full text linkWe investigate the properties of near-conformal dynamics in a sector of large charge when
approaching the lower boundary of the conformal window from the chirally broken phase. To elucidate our approach we use the time-honored example of the phenomenologically relevant SU (2) color theory featuring Nf Dirac fermions transforming in the fundamental representation of the gauge group. In the chirally broken phase we employ the effective pion Lagrangian featuring also a pseudodilaton to capture a possible smooth conformal-to-nonconformal phase transition. We charge the baryon symmetry of the Lagrangian and study its impact on the ground state and spectrum of the theory as well as the would-be
conformal dimensions of the lowest large-charge operator. We moreover study the effects of and dependence on the fermion mass term
Near-conformal dynamics at large charge
Full text linkWe investigate four-dimensional near-conformal dynamics by means of the large-charge limit. We first introduce and justify the formalism in which near-conformal invariance is insured by adding a dilaton and then determine the large-charge spectrum of the theory. The dilaton can also be viewed as the radial mode of the effective field theory. We calculate the two-point functions of charged operators. We discover that the mass of the dilaton, parametrizing the near-breaking of conformal invariance, induces a novel term that is logarithmic in the charge. One can therefore employ the large-charge limit to explore near-conformal dynamics and determine dilaton-related properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Cluster analysis of signals from spectral activity indicators to search for shared periods
No full textContext. A multitude of spectral activity indicators are routinely computed nowadays from the spectra generated as part of planet-hunting radial velocity surveys. Searching for shared periods among them can help to robustly identify astrophysical quantities of interest, such as the stellar rotation period. However, this identification can be complicated due to the fact that many different peaks occur in the periodograms. This is especially true in the presence of aliasing and spurious signals caused by environmental influences affecting the instrument. Aims. Our goal is to test a clustering algorithm to find signals with the same periodicity, (i.e. with the stellar rotation period) in the periodograms of a large number of activity indicators. On this basis, we have looked to evaluate the correlations between activity indicators and fundamental stellar parameters. Methods. We used generalised Lomb–Scargle periodograms to find periodic signals in 24 activity indicators, spanning the VIS and NIR channels of the CARMENES spectrograph. Common periods were subsequently determined by a machine learning algorithm for density-based spatial clustering of applications with noise ( DBSCAN ). Results. The clustering analysis of the signals apparent in the spectral activity indicators is a powerful tool for the detection of stellar rotation periods. It is straightforward to implement and can be easily automated, so that large data sets can be analysed. For a sample of 136 stars, we were able to recover the stellar rotation period in a total of 59 cases, including 3 with a previously unknown rotation period. In addition, we analysed spurious signals frequently occurring at the period of one year and its integer fractions, concluding that they are likely aliases of one underlying signal. Furthermore, we reproduced the results of several previous studies on the relationships between activity indicators and the stellar characteristics
RV-detected planets around M dwarfs: Challenges for core accretion models
Full text linkPlanet formation is sensitive to the conditions in protoplanetary disks, for
which scaling laws as a function of stellar mass are known. We aim to test
whether the observed population of planets around low-mass stars can be
explained by these trends, or if separate formation channels are needed.
We address this question by confronting a state-of-the-art planet population
synthesis model with a sample of planets around M dwarfs observed by the HARPS
and CARMENES radial velocity (RV) surveys. To account for detection biases, we
performed injection and retrieval experiments on the actual RV data to produce
synthetic observations of planets that we simulated following the core
accretion paradigm.
These simulations robustly yield the previously reported high occurrence of
rocky planets around M dwarfs and generally agree with their planetary mass
function. In contrast, our simulations cannot reproduce a population of giant
planets around stars less massive than 0.5 solar masses. This potentially
indicates an alternative formation channel for giant planets around the least
massive stars that cannot be explained with current core accretion theories. We
further find a stellar mass dependency in the detection rate of short-period
planets. A lack of close-in planets around the earlier-type stars () in our sample remains unexplained by our model and
indicates dissimilar planet migration barriers in disks of different spectral
subtypes.
Both discrepancies can be attributed to gaps in our understanding of planet
migration in nascent M dwarf systems. They underline the different conditions
around young stars of different spectral subtypes, and the importance of taking
these differences into account when studying planet formation.Comment: Accepted for publication in A&A. 19 pages, 9 figure
- …
