1,721,271 research outputs found
Measuring the hydrogen ground state hyperfine splitting through the pi1 and sigma1 transitions
No full textDie ASACUSA Kollaboration arbeitet an einer Messung der
Hyperfeinstruktur von Antiwasserstoff im Grundzustand (GSHS) mittels Rabi Spektroskopie, um die CPT Symmetrie zu testen. Die
Hyperfeinstruktur von Wasserstoff wurde mit hoher Präzision bestimmt, weshalb der Vergleich mit diesem Wert für Antiwasserstoff auf einer absoluten Energieskala potenziell einer der genauesten Tests der CPT Symmetrie werden kann. Eine gute Charakterisierung des Spektrometers für dieses Experiment ist eine Voraussetzung, um die angestrebte Präzision zu erreichen. Der hohe Aufwand, der für die Produktion selbst von geringen
Mengen von Antiwasserstoff erforderlich ist, verlangt nach alternativen Ansätzen für die Charakterisierung und rechtfertigt vorbereitende Messungen mit Materie. Aus diesem Grund hat das Stefan-Meyer-Institut (SMI) als Teil der ASACUSA Kollaboration ein Wassserstoffstrahlexperiment aufgebaut. Dieses wird dazu beitragen, dass der Zeitbedarf der Antiwasserstoffexperimente reduziert werden kann.
Die Hauptkomponenten des Wasserstoffstrahlexperiments sind: Eine Quelle von gekühlten und modulierten atomaren Wasserstoff; ein Set von Permanentsextupolmagneten für die Polarisation des Strahls; ein Hohlraumresonator um die Hyperfeinübergänge zu treiben; McKeehan-artige Spulen um ein konstantes externes Magnetfeld zu generieren; ein weiteres Set von Permanentsextupolmagneten zwecks Analyse der Zustände; und ein Quadrupolmassenspectrometer als Wasserstoffdetektor.
Im Rahmen der vorliegenden Arbeit wurde der Hohlraumresonator und Spulen-Aufbau verbessert, um die Untersuchung von zwei Hyperfeinübergängen zu ermöglichen. Während bereits im vorangegangen Aufbau der sigma1-Übergang zugänglich war, verlangt die Untersuchung des pi1-Übergangs eine verbesserte Homogenität des externen Magnetfeldes auf (sigmaB/|B|) < 1000 ppm. Deshalb wurden eine neue Magnetfeldabschirmung und McKeehan-artige Spulen konstruiert. Die Charakterisierung dieser neuen Bauteile ist ein wesentlicher Bestandteil dieser Arbeit und ein erreichter Wert von (sigmaB/|B|) ~ 590 ppm konnte verifiziert werden.
Sowohl der sigma1- als auch der pi1-Übergang wurden zum ersten Mal unter Verwendung der neuen Abschirmung und Spulen vermessen. Von diesen Ergebnissen lässt sich die Hyperfeinstrukturaufspaltung von Wasserstoff im Grundzustand im feldfreien Fall ableiten. Die beiden Übergange erlauben unabhängig von einander die Extrapolation zum Nullfeld und alternativ können auch die Ergebnisse beider Übergänge beim gleichen Magnetfeldwert für eine Bestimmung benutzt werden. Die Extrapolationsmethode basierend auf dem pi1-Übergang wurde im Rahmen dieser Arbeit zum ersten Mal angewandt. Die Ergebnisse dieser Messungen sind alle innerhalb einer Standardabweichung in Übereinstimmung mit dem Literaturwert: nu0 = (1420405753 +- 8) Hz für die Methode mit beiden Übergängen beim gleichen externen Magnetfeld; nu0 = (1420405760 +- 34) Hz für die Extrapolation der Ergebnisse mittels pi1-Übergängen; und nu0 = (1420405767 +- 15) Hz für die Extrapolation der Ergebnisse mittels sigma1-Übergängen.The ASACUSA collaboration is aiming to measure the ground state hyperfine structure (GSHS) of antihydrogen to test the CPT symmetry in a Rabi like experiment. The GSHS of hydrogen is a very precisely known value. In addition the hyperfine splitting frequency is a small quantity, therefore a comparison with antihydrogen has the potential to yield one of the most precise tests of the CPT symmetry on an absolute energy scale. A good characterization of the experiment's spectrometry is a premise to achieve a high precision. The high cost and the low production rates of antihydrogen require alternative methods for this characterization and justify the use of matter for such preparations. For this reason the Stefan Meyer Institute (SMI) as part of the ASACUSA collaboration constructed a hydrogen beam experiment. This will help to shorten the time frame needed for the antihydrogen measurements.
The main components of the hydrogen-beam setup are: a source of cold, modulated atomic hydrogen, a set of permanent sextupoles for polarization, a cavity to induce the spin flips, McKeehan-like coils to produce a homogeneous external magnetic field, another set of permanent sextupoles for state analysis and a quadropole mass spectrometer as detector. The same cavity is going to be used on the antihydrogen experiment and hence its characterization is highly relevant.
Within the scope of this work, the cavity and coils assembly was modified to enable measurements of two transitions. While the sigma1-transition has been accessible by the previous setup as well, the pi1-transition requires an improved external magnetic field homogeneity of (sigmaB/|B|) < 1000 ppm. Therefore a new shielding as well as new McKeehan-like coils have been constructed. The characterization of these two new pieces of equipment is also part of the present work and a homogeneity of (sigmaB/|B|) ~ 590 ppm has been verified.
Both pi1 and sigma1 transitions in hydrogen were measured for the first time using an upgraded setup. From these results the GSHS at zero magnetic field are calculated by extrapolation using the pi1 or sigma1 transitions separately and it will also be calculated using both transitions at the same static magnetic field. The results presented in this work of the GSHS using the pi1 extrapolation are the first results ever made using this method.
The obtained GSHS result has the value of nu0 = (1420405753 +- 8) Hz using both transitions at the same static magnetic field. For the pi1 extrapolation, nu0 = (1420405760 +- 34) Hz. For the sigma1 extrapolation, nu0 = (1420405767 +- 15) Hz
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
