1,721,160 research outputs found
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
Measurement of the Partial Branching Fraction for Inclusive Semileptonic B Meson Decays to Light Hadrons B->Xu l nu and an Improved Determination of the Quark-Mixing Matrix Element |V_ub|
Full text linkThis thesis presents an analysis of inclusive semileptonic decays using approximately 454 million decays collected during the years 1999 to 2008 with the BABAR detector.
The electron energy, , and the invariant mass squared of the electron-neutrino pair,, are reconstructed, where the neutrino kinematics is deduced from the decay products of both B mesons.
The final hadronic state,, consists of a sum of many hadronic channels, each of which contains at least one quark.
The variables and are then combined to compute the maximum kinematically allowed invariant mass squared of the hadronic system, .
Using these kinematic quantities, the partial branching fraction, , unfolded for detector effects, is measured to be
\Delta BR(E_e>2.0 GeV, s_h^{max}<3.52 GeV^2) = (3.33 \pm 0.18 \pm 0.21) \times 10^{-4}
in the \Upsilon(4S) and
\Delta \tilde{\BR}(\tilde E_e>1.9 GeV, \tilde {s}^{max}_{h} < 3.5 GeV^2) = (4.57 \pm 0.24 \pm 0.32) \times 10^{-4}
in the B|V_{ub}|\Delta \tilde{\BR}|V_{ub}| = (4.19 \pm 0.18{}^{+0.26}_{-0.20} {}^{+0.26}_{-0.25}) \times 10^{-3}, where the errors represent experimental uncertainties, uncertainties from HQE parameters and theoretical uncertainties, respectively
Studien zur Rekonstruktion der invarianten Masse von Top-Antitop-Paaren im dileptonischen Kanal mit Hilfe eines neuronalen Netzwerkes am ATLAS Detektor.
No full textThe studies in this thesis are motivated by the measurement of the top quark Yukawa coupling Ytrelative to the SM value in the dileptonic decay channel of top-antitop (t¯t) pairs at the ATLAS experiment. The used (simulated) data correspond to the proton-proton collision data recorded between 2015 and 2018 at √s=13 TeV with an integrated luminosity of 140 fb−1. In the dileptonic channel, the t¯t pair decays into two b quarks and two W bosons, which then decay into one lepton and neutrino each. Virtual corrections through the exchange of a Higgs boson between the produced top quarks modify the spectrum of the invariant mass of the top-antitop pair mt¯t in the region of the production threshold (≈2mt). A precise analysis of this distribution provides insights into the strength of the top-Yukawa coupling. Due to the two neutrinos in the final state, the reconstruction of mt¯t is only possible through approximation methods that incorporate kinematic constraints on the W mass and top quark mass as well as the reconstructed missing transverse momentum. Therefore, a neural network using techniques from the field of deep learning is motivated and presented in this thesis, which reconstructs mt¯t through regression using high-level observables as input. As inputs, the invariant masses meμ, meb1, meb2, mμb1, mμb2, and mb1b2 of the electrons, muons, and b-jets in the final state, together with the magnitude of the missing transverse momentum EmissT, are used. The output distribution of the neural network is analyzed for datasets generated by pythia8 and Herwig7 to investigate the influence of different t¯t modeling. Additionally, the agreement between simulation and experimental data is examined. A maximum-likelihood fit for a future measurement of Yt is presented. Here, the experimental data and the expected t¯t signal for different values of Yt are compared, and the best agreement is given as an estimate for Yt, considering systematic uncertainties. Since the systematic uncertainties were not implemented due to time constraints, an initial fit based on Asimov data is performed to estimate the measurement precision. Compared to the easily reconstructed invariant mass mrecobbll of the leptons and b-jets, the distribution from the neural network shows an approximately 3.5% lower uncertainty in the estimation of Yt (excluding systematics). The systematic uncertainty of the t¯t modeling differences by Pythia8 and Herwig7 is also examined
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
Simulation and measurement of charge transport in the guard region of planar silicon sensors
Full text linkSiliziumsensoren werden aufgrund ihrer hohen Strahlenhärte und mechanischen Stabilität in der Hochenergiephysik breit eingesetzt. Während des Herstellungsprozesses werden jedoch einige Defekte auf der Sensoroberfläche erzeugt, was zu komplexen Oberflächeneigenschaften führt. Die großflächigen Siliziumsensoren für das ATLAS Inner Tracker (ITK) Upgrade zeigen eine Sensitivität auf Luftfeuchtigkeit, was dazu führt, dass die Sensoren einen hohen Leckstrom aufweisen und dadurch mitunter nicht mehr als Teilchendetektoren unter einer hohen Spannung in einer Umgebung mit hoher Luftfeuchtigkeit betrieben werden können. Zur Erforschung der Oberflächeneigenschaften und um den Breakdown-Mechanismus zu verstehen, wird die Top Transient Current Technique (Top TCT) eingesetzt, um den Ladungstransportprozess in Siliziumsensoren zu analysieren. Diese Methode verwendet schnelle Laserpulse, die auf einen mikrometergroßen Bereich fokussiert sind, um die Vorderseite des Sensors zu beleuchten und Elektron-Loch-Paare innerhalb der ersten Mikrometer unter der Oberfläche zu erzeugen. Diese Ladungsträger bewegen sich unter dem Einfluss des angelegten elektrischen Feldes, wodurch transiente Ströme an der Elektrode induziert werden. Durch die Analyse dieser transienten Signale, in Abhängigkeit von der Position des laserinjizierten Bereiches und der angelegten Spannung, kann das elektrische Feld in der Nähe der Oberfläche qualitativ abgeschätzt werden. In dieser Arbeit werden sowohl Simulation als auch Messung unter Verwendung der Top TCT-Methode an einer planaren Diode durchgeführt. Die Simulation erfolgt mithilfe der Software Allpix Squared, einem Monte-Carlo-Simulationsframework, das speziell für Halbleiterdetektoren entwickelt wurde. Die effektive Dotierstoffkonzentration, die Vollverarmungsspannung und die aktive Dicke einer planaren Silizium n-in-p Diode werden mit der Top TCT-Methode gemessen. Die Übertragungsfunktion des externen Stromkreises wird durch Fourier-Transformationsanalyse sowohl der simulierten als auch der gemessenen Daten extrahiert. Ein neuer Parameter „Oberflächenreflektivität" wird in Allpix Squared implementiert und modifiziert, um den Ladungstransport an der Silizium-Siliziumdioxid-Grenzfläche zu simulieren, an welcher ein Feld existiert, das die Elektronen zur Grenzfläche drängt. Laser-Scans zwischen dem Edge-Ring und dem Guard-Ring der Diode werden für verschiedene angelegte Spannungen simuliert und gemessen. Durch den Vergleich der Simulationsergebnisse mit den Messungen hinsichtlich der transienten Pulse, Geschwindigkeitsprofile und Ladungsprofile kann ein besseres Verständnis der Oberflächeneigenschaften einer Siliziumdiode gewonnen werden, auf dessen Basis sich die Feuchtigkeitsabhängigkeit der Oberflächendegradation untersuchen lässt.Silicon sensors are widely used in high-energy physics due to their high radiation hardness and mechanical stability. However, during the fabrication process, several defects are introduced to the sensor surface, resulting in complex surface properties. The large-area silicon sensors for the ATLAS Inner Tracker (ITK) Upgrade show signs of early surface breakdown at high humidity. This results in the sensors experiencing a high leakage current and are not inoperable as particle detectors when biased in a high-humidity environment. To investigate the surface properties and understand the breakdown mechanism, the Top Transient Current Technique (Top TCT) is used to study the charge transport process in silicon sensors. This method utilizes fast laser pulses, focused to a micrometer-sized spot, to illuminate the front side of the sensor, generating electron-hole pairs within the first several micrometers from the surface. These charge carriers then drift under the influence of the applied electric field, inducing transient currents on the electrode. By analyzing these transient signals as a function of the laser-injected position and the applied bias voltage, the distribution of the surface electric field can be qualitatively estimated. In this work, both simulation and measurement using the Top TCT method on a planar diode are performed. The simulation is conducted using the Allpix Squared software, a Monte Carlo simulation framework specially developed for semiconductor detectors. The effective doping concentration, full-depletion voltage, and active thickness of a planar silicon n-in-p diode are measured using the Top TCT method. The transfer function of the read-out electric circuit is extracted through Fourier transform analysis of both the simulated and measured data. A new parameter ”surface reflectivity” is implemented and modified in Allpix Squared to simulate the charge transport at the silicon-silicon dioxide interface, where a field pushing the electrons toward the interface exists. Laser scans between the edge ring and guard ring of the diode for different bias voltages are simulated and measured. By comparing the simulation results to the measurement in aspects of the transient pulses, velocity profile and charge profile, a better understanding of the surface properties of a silicon diode can be obtained, from which the humidity dependence on the surface breakdown may be explored
Studien zur Bestimmung der Di-Higgs-Masse mitHilfe neuronaler Netze
No full text(di-Higgs) events using simulated data from the ATLAS detector at the Large Hadron Collider ata center-of-mass energy of √s = 13TeV and an integrated luminosity of 140 fb−1. In the studiedchannel, one Higgs boson decays into a bottom quark-antiquark pair (b¯b), the other into two photons(γγ). Direct measurement of Higgs self-coupling through di-Higgs processes serves as a consistencytest for the Higgs potential in the Standard Model and may indicate physics beyond it. Sensitivityto the coupling modifier for Higgs self-coupling depends on the di-Higgs mass spectrum resolution,which is limited by the energy resolution of bottom-quark jets and missing energy from undetectableneutrinos in the decays. The first method uses missing transverse energy to correct the energiesof bottom-quark jets. The second employs a neural network to regress the di-Higgs mass fromreconstructed observables. For events where the correction is applicable, the jet energy correctionimproves the b¯b mass distribution’s median value by about 9.6 GeV compared to the calibration inthe current ATLAS analysis. The neural network reduces the standard deviation of the relativedeviation from the true di-Higgs mass by approximately 23% and the interquartile range by about3% compared to the kinematic fit used in the current ATLAS analysis.I
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