1,721,148 research outputs found
Development of diagnostic and manipulation systems for space-charge dominated electron beams and confined electron plasmas in ELTRAP
No full textModifications have been implemented in the Penning-Malmberg device ELTRAP aimed
at performing studies on the dynamics of space-charge dominated nanosecond electron bunches traveling along the magnetic field. In particular, a Thomson backscattering apparatus has been developed where an infrared (IR) laser pulse collides with the bunched electron beam. The frequency-shifted
backscattered radiation, acquired by means of a photomultiplier (PMT), can be exploited to evaluate information on energy, energy spread and density of the bunch. The achievable sensitivity
of the diagnostics has been estimated, and valuable information on the main parameters affecting the signal-to-noise (S/N) ratio has been obtained [B. Paroli, F. Cavaliere, M. Cavenago, F. De Luca, M. Ikram, G. Maero, C. Marini, R. Pozzoli, and M. Romé, JINST 7, P01008 (2012)]. A series of upgrades are under way, aimed at increasing the S/N ratio through the use of a new laser for the electron source, the insertion of a stray light shield, and the optimization of the detection electronics. Moreover, electromagnetic simulations relevant to the design and implementation of a microwave
heating system are presented. The generation of an electron plasma in ELTRAP by means of a low-power radio frequency (RF) drive in the MHz range applied on one of the trap electrodes and under ultra-high vacuum (UHV) conditions has previously been demonstrated [B. Paroli, F. De Luca,
G. Maero, F. Pozzoli, and M. Romé, Plasma Sources Sci. Technol. 19, 045013 (2010)]. The new heating system will allow the extension of the RF studies to the GHz range and in particular the
production of a more energetic electron plasma via cyclotron resonant excitation
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
Radio-frequency generation of an electron plasma in a Malmberg-Penning trap and its interaction with a stationary or pulsed electron beam.
Full text linkExperiments and numerical investigations on trapped electron plasmas and traveling electron bunches are discussed.
A Thomson backscattering diagnostics set up was installed in the ELTRAP (Electron TRAP) device, a Penning-Malmberg trap operating at the Department of Physics of the University of Milano since 2001. Here, an infrared (IR) laser pulse collides with nanosecond electron bunches with an energy of 1-20 keV traveling through a longitudinal magnetic field in a dynamical regime where space-charge effects play a significant role. The backscattered radiation is optically filtered and detected by means of a photomultiplier tube. The minimum sensitivity of the backscattering diagnostics has been estimated for the present set-up configuration. Constraints on the number of photons and thus on the information one can obtain with the Thomson backscattering technique are determined by the relatively low density of the electron beam as well as by noise issues. Solutions to increase the signal level and to reduce the noise are briefly discussed.
The generation of an electron plasma by stochastic heating was realized in ELTRAP under ultra-high vacuum conditions by means of the application of low power RF (1-20 MHz) drives on one of the azimuthally sectored electrodes of the trap. The relevant experimental results are reviewed. The electron heating mechanism has been studied by means of a two-dimensional (2D) particle-in-cell (PIC) code, starting with a very low electron density, and applying RF drives of various amplitudes in the range 1-15 MHz on different electrodes. The axial kinetic energy of the electrons is in general increasing for all considered cases. Of course, higher temperature increments are obtained by increasing the amplitude of the RF excitation. The simulation results indicate in particular that the heating is initially higher close to the cylindrical wall of the device. These results on the electron heating point in the same direction of the experimental findings, where the plasma formation due to the ionization of the residual gas is found to be localized close to the trap wall. The simulations indicate also major heating effects when the RF drive is applied close to one end of the trap. Similar results are obtained for an electron plasma at higher densities, simulating a situation in which the RF is applied to an already formed plasma.
With the aim to extend these RF studies to the microwave range, a bench test analysis has been performed of the transmission efficiency of a microwave injection system up to a few GHz. The test was based on the use of a prototype circular waveguide with the same diameter and length of the ELTRAP electrode stack and of a coupled rectangular waveguide with dimensions suitable for a future installation in the device.
Electromagnetic PIC simulations have also been performed of the electron heating effect, again both at very low and relatively high electron densities, applying a microwave drive with a frequency of approximately 3 GHz close to the center and close to one end of the trap.
Both the bench test of the injection system and the numerical simulations indicate that the new microwave heating system will allow the extension of the previous RF studies to the GHz range. In particular, the electron cyclotron resonance heating of the electrons will be aimed to increasing the electron temperature, and possibly its density as a consequence of a higher ionization rate of the residual gas. The installation of the new RF system will open up the possibility to study, e.g., the interaction between the confined plasma and traveling electron bunches
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
Axial heating and temperature of RF-excited non-neutral plasmas in Penning-Malmberg traps
No full textElectro-magnetostatic traps have been used for decades to provide long-term storage of charged particle samples or non-neutral plasmas. The dynamics and equilibrium states of these ideally simple systems can be strongly diverted from the usual working conditions (i.e. single-species, quiescent samples) in the presence of oppositely charged particles or external electric field perturbations. Both these conditions occur when the plasma is generated by means of a radiofrequency (RF) excitation continuously applied on a trap electrode. The application of RF drives of some volts over periods larger than typical collisional time scales leads to residual-gas ionization and to the accumulation of an electron plasma, a process that has previously been exploited as an alternative to thermionic or photoemission electron sources. The analysis of the axial energy distribution shows a deviation of the continuously excited final state from maxwellianity dependent on the radial position and the subsequent relaxation to equilibrium after the interruption of the drive. Systematic measurements also indicate the high sensitivity to the residual gas pressure of both the total confined charge and of the attainable densities and plasma profiles. The results are compared to the information obtained from a very simple one-dimensional electron heating model and show the validity of its most basic features together with its shortcomings
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
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