1,720,958 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Modélisation magnétohydrodynamique résistive des propulseurs magnétoplasmadynamiques
No full textSelf-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J⁴), voltage drop (∼J³), and thrust (∼J²). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions.Self-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J4), voltage drop (∼J3), and thrust (∼J2). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions
Modélisation magnétohydrodynamique résistive des propulseurs magnétoplasmadynamiques
No full textSelf-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J⁴), voltage drop (∼J³), and thrust (∼J²). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions.Self-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J4), voltage drop (∼J3), and thrust (∼J2). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions
Modélisation magnétohydrodynamique résistive des propulseurs magnétoplasmadynamiques
No full textSelf-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J⁴), voltage drop (∼J³), and thrust (∼J²). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions.Self-Field MagnetoPlasmaDynamic Thrusters (MPDTs) are a class of electric space propulsion (EP) devices where quasineutral plasma is mainly accelerated by the volumetric Lorentz force (~j × ~B). The latter is produced by the discharge current density, ~j, and the induced (self) magnetic field, ~B, in the de- vice’s coaxial electrode system. MPDTs have relatively simple designs and can efficiently convert very high powers into thrust. However, the deployment of MPDTs is limited by the lack of sufficient available power onboard space missions and their unstable behaviour at currents above a critical value. Existing MPDT simulations normally adopt simplified ”hot” injection conditions - the inlet is considered to be already fully ionised and hot, ∼1.3 eV (15000 K). These injection conditions are needed to overcome existing difficulties in reproducing full ionisation of the propellant close to the inlet, as it is observed ex- perimentally. However, such injection implies large velocities (∼3 km/s), cold thrust (∼20 N) and power to ionise the propellant (∼230 kW). It may also have implications on the in-domain power balance. The primary aim of this work is to study MPDTs under realistic conditions by building upon and extend a multi-physics computational platform. Here we focus on understanding the effects of different propellant injection boundary conditions on the plasma dynamics, energy budget and efficiencies. In particular, we focus on the case of a ”cold” propellant injection when electron-neutral collisions cannot be neglected. We carry out simulations of argon-fed self-field MPDTs in 2D cylindrical axisymmetric geometry. We use the single-fluid, two-temperature magnetohydrodynamic (MHD) code FLASH with tabulated equation of state calculated with the IONMIX code. A weakly ionised, ”cold propellant” (T ∼0.13 eV) injection boundary condition is implemented and the effects of electron-neutral collisions on the resis- tivity is also taken into account. We demonstrate that an appropriate choice of the boundary conditions for the injected propellant is essential for recovering experimental measurements of propulsion-relevant parameters. The simulations are also able to capture the experimentally well-known MPDT working regimes at both low and high cur- rents. We also reproduce the MPDT scaling laws known experimentally for high currents (J & 15 kA) for power (∼J4), voltage drop (∼J3), and thrust (∼J2). We note that the calculated values of electric power and thrust efficiency are consistent with experimental data. We also show that the Lorentz efficiency differs drastically from that found with the commonly used ”hot” injection model. We observer that electron and ion components are generally not in thermal equilibrium with each other. At high currents, J ≥ 15 kA, the cold injection model allows the propellant to become fully ionised ( ¯Z ≥ 1) at almost all radii, which is qualitatively consistent with available experimental data. We provide a new, robust and consistent way of modeling MPDTs with argon propellant. We em- phasize that the modeling of realistic injection boundary conditions, magnetic diffusivity transport model and real gas effects are crucial to correctly evaluate the parameters that are important to MPDT propul- sion. At the same time, we largely extend the state-of-the-art modeling of MPDTs, previously limited to electrical currents /10-20 kA, to both lower and larger values, J ∈ [5, 40] kA. We note that the FLASH simulations show stable plasma behaviour at super-critical currents, &20 kA, which are unstable exper- imentally. The results indicate that to trigger the ”onset”, simulations will need to incorporate more physical processes and be extended to three dimensions
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