1,720,958 research outputs found
Feasibility Study on Longitudinal Phase-Space Measurements at GSI UNILAC using Charged-Particle Detectors
No full textAccelerator facilities require access to many beam parameters during operation. The field
of beam instrumentation serves this crucial role in commissioning, setup and optimisation
of the facility. An important information is contained in the phase-space distribution of the
accelerated particles. In case of GSI (Helmholtzzentrum für Schwerionenforschung) those
are ions from protons to uranium.
If established methods to access certain beam parameters do not exist, new approaches have
to emerge. This is the case for the presented measurement setup which has been designed
and realised by Forck et al. to support commissioning of the GSI high-current injector. It
is aiming at an experimental method to access the longitudinal phase-space distribution
at low energies of 1.4 AMeV. Established methods for higher energies and based on the
measurement of the electric field distribution are not feasible at non-relativistic velocities.
The presented method is based on a time-of-flight (TOF) measurement between two particle
detectors. A modification allows, alternatively, the direct measurement of the kinetic energy
using a mono-crystalline (MC) diamond detector.
Currently, besides others, the focus of the optimisation of the injector is put on the longitudinal
phase-space distribution. It allows for a systematic optimisation of the matching
into the accelerator cavities and, thus, an improved transmission as well as lower emittance
values. The new accelerator facility FAIR (Facility for Antiproton and Ion Research), a
large-scale upgrade at GSI, requires an improved beam quality at the existing injector.
In this work the experimental setup is investigated for its feasibility to measure the longitudinal
phase-space distribution. To this end, the phase and momentum of the single ions
along the beam axis have to be determined with high precision. Finally, the longitudinal
phase-space distribution is identified with the measured ensemble.
The setup is presented in detail, introducing necessary concepts such as the phase space
and emittance and is followed by a discussion of the data acquisition and data analysis.
An important part of the latter is the introduction of a robust estimator for the covariance
matrix of the measured distribution which is directly connected to the RMS emittance.
However, the classical estimator is very sensitive to outliers in the measured data. The
usual approach of subjective selection of cut regions is thereby avoided.
The TOF setup has been tested with low and high current beams where a general sensitivity
to the longitudinal phase-space distribution was confirmed. Furthermore, the gas pressure at
the stripper section and the setup of the high-current slits, required for beam attenuation,
have an impact on the measured distributions. Scattering of ions at the slits leads to a
larger energy spread, larger bunch length and, consequently, emittance. Independent of the
configuration, deviations from the expected values of the energy spread ∆E/⟨E⟩ ≈ 1 % and
the Twiss parameter α ≈ 4 have been measured. The energy spreads were larger than the theory values by a factor of 1.5-1.6. However, a direct measurement of the bunch structure,
while using sensible high-current slit settings, proved valuable.
Low-current measurements with the MC diamond detector featured a gain loss of 5 % pulse
height and 2 % pulse integral after irradiation with ≈ 3×10^4 argon ions. Although this effect
is corrected in the data analysis, the energy spread is significantly larger than expected,
like in the TOF measurements. Similarly, the values for α were below 0.5. Prominent trails
in the measured distribution showed a broad energy spectrum and could be quantitatively
attributed to interaction with the collimator apertures.
As the measurements hint an insufficient energy resolution, this effect has been investigated
in a Gaussian model space. The discrepancies between expected and measured values
∆E/⟨E⟩, α and emittance could be resolved by assuming a system response of 1.3 %. In the
scope of this model space and knowledge of the TOF resolution an approximation to the
real longitudinal phase-space parameter by back transformation of the covariance matrix
was suggested.
Furthermore, the Gaussian model space allowed to deduce an analytic formula for the
required energy resolution. This showed a high dependency of the resolution on the Twiss
parameter α which scales with 1/α. For instance, to target a precision of the emittance
within 10 % requires a TOF resolution of better than 30 ps.
This motivated a survey on the possible systematic contributions. The dominating contribution
was found to be the inhomogeneity of the foils. The tantalum foil alone contributes
an energy broadening of σE/⟨E⟩ ≈ 1 % and is of the same size of the expected energy spread
of beam. Including all systematic sources quantitatively supports the considerations made
in the Gaussian model space.
While the experimental setup is not yet able to measure the full longitudinal phase-space
distribution, it is capable of providing valuable information about the bunch structure.
Several campaigns have been successfully supported with bunch-structure measurements
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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