1,721,032 research outputs found
Exploiting the wide dynamic range of silicon photomultipliers for quantum optics applications
Get PDFSilicon photomultipliers are photon-number-resolving detectors endowed with hundreds of cells enabling them to reveal high-populated quantum optical states. In this paper, we address such a goal by showing the possible acquisition strategies that can be adopted and discussing their advantages and limitations. In particular, we determine the best acquisition solution in order to properly reveal the nature, either classical or nonclassical, of mesoscopic quantum optical states
Modelling the behavior of the positron plasma temperature in antihydrogen experimentation
No full textAntihydrogen is now routinely produced at CERN by overlapping clouds of positrons and antiprotons. The mechanisms responsible for antihydrogen formation (radiative capture and the three-body reaction) are both dependent on the temperature of the positrons (T e ), though with a different weight. Here we present a simple model of the behavior of the positron temperature based on the main processes involved during antihydrogen synthesis, namely: antiproton–positron collisions, positron heating due to plasma expansion and cooling via the emission of synchrotron radiation. The time evolution of T e has been simulated by changing the relevant parameters of the mechanisms involved in order to highlight the importance of the different (competing) effects
Antiparticle cloud temperatures for antihydrogen experiments
Get PDFAn analysis of positron and antiproton cloud temperatures under condition similar to those found in antihydrogen experiments.Some simple general trends are brought out in the analysis, which includes the effects of cloud expansion for the first time
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Antiproton-nuclei annihilation cross section measurement at 125 keV
No full textThe experimental research with slow antiprotons and antineutrons to study hadron and nuclear physics has been widely performed in the 80’s and in the first half of the 90’s at LEAR (CERN). After the stop of LEAR in 1996, the activity in the nuclear physics field was continued and is currently carried out at at the Antiproton Decelerator (AD, CERN), the successor of LEAR, by the ASACUSA Collaboration who, alongside its main program devoted to the hyperfine spectroscopy of the ground state of antihydrogen and to the laser spectroscopy of antiprotonic helium, is also involved in performing measurements of the annihilation cross section of low energy antiprotons on nuclei. The motivations for these measurements include the possibility of gaining information on the strong interaction both for the quark model and for the potential model by fixing the parameters of the antinucleon-nucleon interaction. In addition, both quark and potential models predict the existence of a resonant or bound antinucleon-nucleon state which could be revealed studying the behaviour of at different energies and with different targets. Fundamental cosmology could benefit from a better knowledge of the antiproton as well. The models that assume the existence of 'islands' of antimatter to explain the antimatter-matter asymmetry, need to investigate the importance of the annihilation mechanism to describe the evolution of the process in the spatial region of overlap between matter and antimatter. The existing experimental data show behaviours that cannot be described in a simple way. For instance for low antiproton momenta p below 60 MeV/c, the annihilation cross sections measured at LEAR do not increase with the mass number but have similar values for H, D and He, while in the case of heavy nuclei at 100 MeV/c, the values measured by our group at AD seem to be larger than the one expected from a simple geometrical description. A 'modified black-disk model', which takes into account the focusing effect of the Coulomb attraction between the antiproton and the nuclei, seems to be in a quite good agreement with our experimental data. Also an extension of the high-energy Glauber model down to the MeV region, if the Coulomb and nuclear interaction and the change of the antiproton momentum inside a nucleus are introduced, reproduces quite well the experimental data for both high and low energy, although a mismatch between the model and some data needs more investigation. Recently, emphasis has been put also on a discrepancy between the results obtained at LEAR with antineutrons and those expected for antiprotons, since an optical potential that fits well all the available data on antiproton interactions with nuclei is not in agreement with the for antineutrons on nuclei. Our group in the ASACUSA Collaboration, after having measured the antiproton annihilation on Mylar, Sn, Ni and Pt at 5.3 MeV of kinetic energy, has addressed its experimental investigation to an energy below the MeV region where no data exist at all. This thesis work deals with the experimental apparatus, the technique to perform the measurements, the data analysis and the experiment results. Chapter 1 is devoted to the physical motivations of the experiment: after a brief historical introduction on the antiproton annihilation field, the open problems with the existing data will be presented. In Chapter 2 an introduction on the AD facility where the experiment has been performed will be given. The apparatus installed on the ASACUSA beam line will be described in all its parts, from the delivery of the antiprotons from the decelerator ring to the dump of the antiproton bunch on the end wall. The scintillators used for the detection of the antiproton annihilations in the target region, their acquisition system and the validation tests performed with cosmic rays and a dedicated beamtest, will be treated in Chapter 3. In Chapter 4 a description of the measurement technique which has been invented and developed for the experiment will be given. In the same Chapter, the data analysis and the needed Montecarlo simulations will be presented. Finally, the results of the antiproton measurements will be given together with a short discussion on the comparison with the existing data and a brief outlook on future possibilities
Enhancement of annihilation cross sections by electric interactions between the antineutron and the field of a large nucleus
No full textData relative to antineutron and antiproton annihilation on large nuclei in the range 75-200MeV/c present two unexpected features: a) antineutron and antiproton cross sections have a similar size, b) the rise of the antineutron cross section at decreasing energy is much steeper than predictable for an inelastic process of purely strong nature at that energy. The observed behavior of (Formula presented.)-nucleus annihilations is similar to what would be expected for (Formula presented.)-nucleus annihilations, where the Coulomb attraction focusses (Formula presented.) trajectories towards the nucleus, enhancing the inelastic cross section by a factor 1/p2with respect to (Formula presented.) on the same target. This results in a 1/p2behavior at small energies. The presence of a similar enhancement in the antineutron case may only be justified by an interaction with a longer range than strong interactions. Excluding a Coulomb force because of the (Formula presented.) neutrality, and taking into account that an intrinsic electric dipole is forbidden for the antineutron, the next choice is an electric dipole that is induced by the nuclear electric field. Recent theoretical works have shown that a nonnegligible electric polarization may be induced in a neutron by QED vacuum polarization. Assuming this as a possibility, we have used a simple model to calculate the polarization strengths that are needed to fit the available data in terms of this effect. These are within the magnitude predicted by the vacuum polarization model. We have also discussed alternative scenarios that could induce an electric polarization of the antineutron as a consequence of the interplay between strong and e.m. interactions
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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