1,720,960 research outputs found
Radiation effects for the next generation of synchrotron radiation facilities
Full text linkHigh energy radiation is an important tool for many fields of research as it allows for the measurement of smaller structures and atomic interactions. The current best method of generating coherent and narrow bandwidth synchrotron radiation is with a free electron laser. It requires very high charge density, to start the amplification process and concurrently leads to its high level of coherency, and high energies (GeV to obtain keV photons). The
stringent parameters on the electron bunch are met by linear accelerators. These are typically kilometre long straight structures that operate from tens to 100 Hz repetition rate. A novel design was proposed by the INFN Milan research group called MariX [1]. Here a LINAC is used in combination with a com- pression arc. This reduces the size of the facility, because the electron bunch can be accelerated twice by the same LINAC. As the electrons pass through dipoles in the compression arc the fields emanating from the particles in the bunch can cause deterioration to it. These fields, consisting out of the relativistic Coulomb-and radiation field, travel with the speeds of light, and thus originate from a point in the past. For this reason the behaviour of these retarded fields is investigated from first principles and developed into a 3D algorithm for calculating the forces within a bunch. An in depth overview is given on how the constituent fields behave over a large range of electron energies. Proportionality relations are given that determine which one is dominant. To reach unprecedented high energy photons is through the scattering of intense lasers with electron bunches; (inverse) Thomson or Compton scattering. Photon energies of keV can be reached with tens of MeV electrons, and MeV photons with GeV electrons. High repetition rate collisions are possible with cavity based laser systems. Currently the power in-side the cavity is several hundreds of kW with an intensity at the focus up to 1014−15 [W/cm2]. With these high powers the cavities can become degenerate, i.e. higher order transverse modes are excited, either by imperfections of the mirrors or deformations caused by heat dissipation. A short study provides insights to the observability of these modes in the Thomson spectrum. The general method for Thomson scattering is to have a (quasi) monochromatic laser pulse collide with an electron bunch with a very small energy spread. The latter usually leads to a reduction of the number of charges, and therefore the flux of scattered photons. The frequency of the scattered radiation is linearly dependent on that of the laser’s, and therefore the energy spread of the electrons could be compensated by including a frequency modulation. The highest intensity lasers obtained are by chirped pulse amplification and thus readily available. Two schemes have been investigated: longitudinal and transverse chirp. Both can reach the limit in bandwidth and number of photons scattered of the mono-energetic and mono-chromatic case. For ultra shorted pulses the carrier envelope phase becomes an important variable. Thomson scattering can be used to measure For intensities where non-linear effects dominate, because the scattered radiation contains the information of the laser pulse.. A model of its signature in the Thomson spectrum has been developed: it shifts the peaks of higher harmonics that overlap. This shift is also correlated to the emission direction of harmonics. A detailed analysis is given how to measure it experimentally
Decreasing the bandwidth of linear and nonlinear Thomson scattering radiation for electron bunches with a finite energy spread
Full text linkRelative narrow bandwidth-high energy radiation can be produced through Thomson scattering, where highly relativistic electrons collide with a laser pulse. The bandwidth of such a source is determined, among others factors, by the bandwidth of the laser pulse and the energy spread of the electrons. Here we investigate how the bandwidth of such a source can be minimized, with a particular emphasis on electron bunches with a correlated energy spread of several percent, that are typical for plasma based accelerator schemes. We show that by introducing a chirp on the laser pulse it is possible to compensate the broadening effect due to the energy spread of the electrons, and obtain the same bandwidth as a quasi-monochromatic plane wave laser pulse colliding with a monoenergetic electron bunch. Ultimately, the bandwidth of a Thomson source is limited by the acceptance angle and the initial transverse momentum of electrons (emittance)
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
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