1,721,002 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
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Improving the Limit on the Electron EDM: Data Acquisition and Systematics Studies in the ACME Experiment
Full text linkThe ACME collaboration has completed a measurement setting a new upper limit on the size of the electron's permanent electric dipole moment (EDM). The existence of the EDM is well motivated by theories extending the standard model of particle physics, with predicted sizes very close to the current experimental limit. The new limit was set by measuring spin precession within the metastable H state of the polar molecule thorium monoxide (ThO). A particular focus here is on the automated data acquisition system developed to search for a precession phase odd under internal and external reversal of the electric field. Automated switching of many different experimental controls allowed a rapid diagnosis of major systematics, including the dominant systematic caused by non-reversing electric fields and laser polarization gradients. Polarimetry measurements made it possible to quantify and minimize the polarization gradients in our state preparation and probe lasers. Three separate measurements were used to determine the electric field that did not reverse when we tried to switch the field direction. The new bound of |de|-29 e cm is over an order of magnitude smaller than previous limits, and strongly limits T-violating physics at TeV energy scales.Physic
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First Single Particle Measurements of the Proton and Antiproton Magnetic Moments
Full text linkWe report a new comparison of the proton (p) and antiproton magnetic moments. In nuclear magnetons, = 2.792 846 (7) [2.5 ppm], while = 2.792 845 (12) [4.4 ppm]. The unprecedented accuracy of the antiproton measurement is 680 times more precise than previous work. These first single-particle measurements provide a stringent test of CPT invariance. Our comparison, = -1.000 000 (5) [5.0 ppm], is consistent with the prediction of the CPT theorem. We also report the observation of a single proton spin flip, opening a path to improved precision by an additional factor of or .Physic
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Trapped Positrons for High-Precision Magnetic Moment Measurements
Full text linkA single electron in a quantum cyclotron provides the most precise measurement of the electron magnetic moment, given in units of the Bohr magneton by g/2 = 1.001 159 652 180 73 (28) [0.28 ppt]. The most precise determination of the fine structure constant comes from combining this measurement with Standard Model theory, yielding [0.25 ppb], limited by the experimental uncertainty of the electron g-value. The most stringent test of CPT symmetry in leptons comes from comparing the electron and positron magnetic moments, limited by the positron uncertainty at 4.2 ppt. A new high-stability apparatus has been built and commissioned for improved measurements of the electron and positron magnetic moments, a greatly improved test of lepton CPT symmetry, and an improved determination of the fine structure constant. These new measurements require robust positron loading from a retractable radioactive source that is small enough to avoid compromising the high-precision environment of our experiment. The design and implementation of such a scheme is a central focus of this work. Robust positron loading at a rate of from a source has been demonstrated.Physic
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
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Towards antihydrogen spectroscopy and CW Lyman-alpha via four-wave mixing in mercury
No full textDuring 2018, the ATRAP collaboration demonstrated the production of trapped antihydrogen per trial. Improved positron accumulation increased reliability and reduced loading times, making 1.5 million positrons available for antihydrogen production every 15 seconds. This led to a better understanding the positron plasma within the ATRAP nested Penning-Ioffe trap. More recent progress on a CW Lyman-alpha laser at 121 nm is presented. The goal of the laser is to produce 1 W of continuous, coherent Lyman-alpha radiation by four-wave mixing in mercury. Simulations of a Zeeman slower with nested radial trap suggest that such a laser can slow hydrogen to increase atom flux at 40 m/s by a conservative factor of 5 to 10
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New Apparatus and Methods for the Measurement of the Proton and Antiproton Magnetic Moments
No full textThe first direct measurement of the antiproton magnetic moment was performed using a single particle in a Penning trap. The result, μˉp/μN = 2.792 845 (12) [4.4 ppm], is 680 times more precise than the previous best measurement. Together with a prior measurement of the proton magnetic moment in the same apparatus, this was the first direct comparison of the proton and antiproton magnetic moments. This stringent test of CPT invariance gave μˉp/μp = −1.000 000 (5) [5.0 ppm]. The observation of individual spin flips of a single proton, also reported here, opened the possibility of further improving measurement precision by orders of magnitude.
Improving this result by a factor of ~104 requires measuring μ outside the large magnetic field gradient needed to detect spin flips. Two methods are proposed to avoid the leading uncertainties in such a high-precision two-trap measurement. One of these is to measure single spin-flips of a single proton or antiproton. The other is to induce multiple spin flips in the presence of a spin-cyclotron coupling drive, and observe the resulting change in the cyclotron energy. The design, construction, and commissioning of an appropriate apparatus, with high-quality particle detection and newly designed Penning trap electrodes, is reported.Physic
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
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Advances in the Measurement of the Electron Electric Dipole Moment
No full textSearches for the electron electric dipole moment (eEDM) are powerful tests of physics beyond the standard model, as they probe for new evidence of time-reversal violating interactions. In 2018 our ACME collaboration reported a measurement of the eEDM which set a new limit of |d_e| 1.1 × 10^−29 e · cm, which improved on the sensitivity of the previous best measurement, also set by the ACME collaboration, by an order of magnitude. With the development of a new ACME III apparatus, we intend to perform a new measurement with an order of magnitude improved sensitivity over the ACME II result. The new experiment has should both upgrade the statistical uncertainty of the measurement and upgrade the suppression of the effects of known sources of systematic error. To upgrade our statistical sensitivity we have implemented upgrades to our molecular beam flux, increased our precession time, and increased to our detection efficiency. To suppress known sources of systematic error and noise below our projected new sensitivity we have developed new magnetic shields, improved our experiment timing controls, and developed new methods to sup- press laser polarization gradients in our system
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