1,721,144 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
Beam-beam effects in future high energy circular lepton colliders
No full textHigh energy lepton colliders are factories of particles. By fine tuning these highly complex machines to resonances, these particles can be produced in large numbers. This allows to refine the precision on their measured physical properties, thereby perfecting the Standard Model (SM).
The Future Circular Collider (FCC) is currently the most favored next generation particle collider project at CERN. The first stage of the project is an electron-positron collider, called the FCC-ee, aimed to study the Z, W± and Higgs bosons, and the top quark with unprecedented high precision. To achieve the ambitious target in terms of the high number of particles generated in collisions, these will take place with high intensity and small beam size, which limit the choice of design parameters. As a result, the beam dynamics at the FCC-ee will be dominated by beam-beam effects at collisions, and the interplay of these with various other beam dynamical effects in the machine.
The focus of this thesis is to investigate these by developing appropriate simulation tools and using them to study the FCC-ee beam dynamics. Radiation mechanisms at collisions, such as beamstrahlung and Bhabha scattering, are also modeled. Using modern parallelization techniques, the developments enable fast and accurate multi-turn tracking simulations in a self-consistent way and pave the way for many other studies in the machine design. In one chapter, beamstrahlung and its effect on the beam equilibrium is investigated. The high number of emitted photons from beamstrahlung can potentially trigger a dynamical effect in which one beam blows up and the other shrinks. This, so-called, flip-flop effect is investigated by detailing the impact of perturbations in different machine and beam parameters and the tolerance to the parameter asymmetries is assessed.
A second chapter is dedicated to the study of beam lifetimes which are dominated by radiative Bhabha scattering. Until now, the best estimates for the FCC-ee lifetime contribution from this process are obtained with approximated analytical calculations. An event generator, optimized for multi-turn tracking, is used to study the FCC-ee beam lifetime and the impact of radiation on beam dynamics. While no significant effect on the dynamics is found, the ability to perform fast and accurate modeling of this effect is a first step towards using the radiation as diagnostics for tuning the machine, as well as to design the protection against beam losses using collimators.
In a third chapter, the scope of the thesis is extended to the SuperKEKB, an already operating electron-positron collider in Japan. A beam-beam induced incoherent synchro-betatron resonance is studied with qualitative discussions of the equilibrium beam parameters and their dependence on the amplitude and tune and the interplay with longitudinal wakefield.LPA
Transverse Noise, Decoherence, and Landau Damping in High-Energy Hadron Colliders
No full textHigh-energy hadron colliders are designed to generate particle collisions within specialized detectors. A higher number of collisions is achieved with high-quality beams of low transverse emittances, meaning a small transverse cross-section, and high intensity, meaning many particles per bunch. This thesis studies how noise negatively impacts the beam quality in high-energy hadron colliders, both in terms of beam instabilities and emittance growth. The impact is analyzed through the derivation of new theories, multi-particle tracking simulations, the numerical solving of partial differential equations, and dedicated experiments in CERN's Large Hadron Collider (LHC).
The impact of noise on beam stability cannot be treated with the first-order, linear Vlasov equation, which is commonly used to study the thresholds of collective instabilities. Therefore, the Vlasov equation has in this thesis been expanded to second order in the perturbation of the beam distribution, finding a diffusion mechanism driven by the interplay between noise, decoherence, and wakefields. The diffusion leads to a local flattening of the distribution, which can cause a loss of Landau damping after a time delay referred to as the latency. An analytical formula for the latency and a specialized numerical diffusion solver were successfully benchmarked against the latency measurements in a dedicated experiment conducted in the LHC. Precaution in the machine operation has to be taken to account for this new mechanism. In particular, it is found that the machine must be operated with a margin to the linear stability threshold. For the case of the LHC, it has previously been found empirically that the octupole current during operation must be increased by about a factor 2, and this thesis provides the explanation as to why that is. Alternative operational settings are suggested to reduce the required octupole current in the LHC. In addition, the new theory allows for extrapolations to future machines, such as the High-Luminosity LHC, as well as the estimation of the impact of new devices, such as crab cavities.
External noise and noise from the transverse beam feedback system cause an emittance growth rate due to decoherence of the noise kicks. Analytical theories for the suppression of the emittance growth rate with a bunch-by-bunch feedback have here been extended to a multi-bunch feedback. The numerical study of suppression during collision was conducted by means of a newly developed parallel multi-beam multi-bunch algorithm. For the typical case of low-frequency external noise and non-negligible feedback noise, a multi-bunch feedback has both analytically and numerically been found superior to a bunch-by-bunch feedback, as it can suppress the impact of the external noise equally well, while simultaneously reducing the noise generated by the feedback itself. Suggestions for a more optimal operation of the LHC are discussed, including a reduction of the upper cutoff frequency of the feedback system.LPHE
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Head-On Beam-Beam Interactions in High-Energy Hadron Colliders - GPU-Powered Modelling of Nonlinear Effects
Full text linkThe performance of high-energy circular hadron colliders, as the Large Hadron Collider, is limited by beam-beam interactions. The strength of the beam-beam interactions will be higher after the upgrade to the High-Luminosity Large Hadron Collider, and also in the next generation of machines, as the Future Circular Hadron Collider. The strongly nonlinear force between the two opposing beams causes diverging Hamiltonians and drives resonances, which can lead to a reduction of the lifetime of the beams. The nonlinearity makes the effect of the force difficult to study analytically, even at first order. Numerical models are therefore needed to evaluate the overall effect of different configurations of the machines.
For this thesis, a new code named CABIN (Cuda-Accelerated Beam-beam Interaction) has been developed to study the limitations caused by the impact of strong beam-beam interactions. In particular, the evolution of the beam emittance and beam intensity has been monitored to study the impact quantitatively, while frequency map analysis has been performed to understand the impact qualitatively. The bunches in the beams have been modelled based on a three-dimensional Gaussian distribution. The bunches in the Large Hadron Collider are well approximated by cylindrically symmetric Gaussian bunches, which allows for certain consequences to be derived analytically. The mapping of both round and flat beams have been implemented with the weak-strong model, considering one beam to stay fixed throughout the simulation, while the other beam is changing. The simulations have been run on graphic cards, well adapted for studying this highly parallelisable problem, to reduce the computation time.
The beam-beam driven resonances have been shown both analytically and numerically to be stronger at lower order and further from the design orbit of the beam. Stronger beam-beam interactions cause a wider spread of the betatron frequencies/tunes within a single bunch, making it increasingly difficult to avoid resonances that cause detrimental effects on the beam quality. This has been seen in both simulations and experiments. In such scenarios, the common working point in the Large Hadron Collider, (Q_x , Q_y ) = (0.31, 0.32), is found to be suboptimal. Two alternative working points, (0.315, 0.325) and (0.475, 0.485), have been found to give better performance. Without long-range interactions, the beam quality is best preserved for zero crossing angle. Increasing the crossing angle activates odd resonances that can reduce the performance further, but it also reduces the tune spread within the bunch, making the bunch exposed to fewer strong resonances. Mixing between the longitudinal and transverse planes, caused by either a crossing angle, the hourglass effect or chromaticity, drives synchro-betatron resonances that also reduce the performance. However, a nonzero chromaticity is usually necessary to avoid coherent instabilities. A significant hourglass effect, σ_s /β_q^∗ = 2/3, has been found to reduce the detrimental effects caused by the chromaticity, and vice versa. A scheme designed to cancel beam-beam driven resonances, by applying a specific intermediate phase advance, has been found to have an extremely positive impact on the beam quality for zero crossing angle, but only a marginal impact for a nonzero crossing angle. A dedicated experiment with strong head-on beam-beam interactions has been performed in the Large Hadron Collider. Simulations run in CABIN for the same configurations show good quantitative agreement. A realistic maximum beam-beam tune shift from the LHC working point has been found to be ∆Q_Tot = 0.043 with zero crossing angle. With a Piwinski angle of φ_PIW = 1, this limit is reduced to ∆Q_Tot = 0.028, smaller than the largest beam-beam tune shift expected in the Future Circular Hadron Collider. These limits are slightly larger for the alternative working point, (0.315, 0.325), raised to ∆Q_Tot = 0.067 and 0.036 for zero and nonzero crossing angle respectively
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