1,720,972 research outputs found
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
Evaluation of Interdependencies between the Hydrogen Supply System and the Electrical Supply System for Aircraft Conceptual Design
No full textDuring the development of the hydrogen storage and supply system for a hydrogen-powered concept aircraft, it is essential to account for interactions with other onboard systems due to hydrogens unique properties. Hydrogen is a relatively volatile gas and reaches its lower flammability limit at a concentration of 4 vol.-% in air. Concentration levels above 4 vol.-%, which may, for instance, be caused by leakage, can lead to potentially catastrophic events. This paper discusses potential interdependencies between the hydrogen supply system and other on-board systems by performing sensitivity studies focused on the pipe routing of the hydrogen supply system and the cable routing of the electric power supply system in smaller installation spaces, such as inside the wing. Additionally, design rules for on-board systems are derived based on the results of these sensitivity studies. Thus, it is recommended to route hydrogen pipes in the highest possible position within the installation space to maintain a minimum distance from the electrical cables. In case the minimum distance condition cannot be met, housing should be applied to the cable or the pipe. However, in the case of the electrical system, the study shows that adding cable housing in these areas does not significantly impact the total on-board systems mass, as the mass increase is approximately 1% for the considered concept aircraft. Nevertheless, these interdependencies must be considered during the conceptual design phase to evaluate criteria like safety, segregation, and the required installation space
Assessment of an auto-routing method for topology generation of aircraft power supply systems
No full textBundesministerium für Wirtschaft und Klimaschutz (BMWK
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
Overall parametric design and integration of on-board systems for a hydrogen-powered concept aircraft
No full textTo reach climate neutrality in aviation, new technologies and concepts for aircraft power supply have to be considered. For regional and short-range aircraft, hybrid fuel cell systems (fuel cells and batteries) are proposed as a promising solution for aircraft power supply. However, the integration of hybrid fuel cell systems and the electrification of the powertrain also affects the power supply for aircraft on-board systems, i.e. normal and emergency secondary power supply. In this context, concept studies need to be performed during the aircraft conceptual design phase to assess systems architectures and power supply strategies for hydrogen-powered concept aircraft.
In this paper, such concept studies are performed during the conceptual design phase of the aircraft, proposing a systems architecture for a hydrogen-powered concept aircraft with an estimated entry into service in 2040. The in-house GeneSys software framework is being developed for overall systems design during the conceptual design phase to support system engineers by conducting such studies and evaluating the results.
To this end, relevant system sizing laws need to be adjusted and verified to perform and assess concept studies for secondary power supply for hydrogen-powered concept aircraft. In this context, the considered aircraft is the ESBEF-Concept Plane 1 (CP1) which is derived from an ATR 72-like aircraft model. The following steps are performed to adapt and verify the system sizing laws of GeneSys accordingly. First, the systems architecture of the existing ATR 72 aircraft is evaluated. The implemented system sizing laws are adjusted based on known system parameters (e.g. mass and power consumption). Second, the systems architecture of the ATR 72 is updated to a state-of-the-art systems architecture. Last, this systems architecture is fully electrified for the integration in the ESBEF-CP1 and projected to an entry into service in 2040, adding technology factors to estimate improvements of relevant technologies.
To identify and select a suitable systems architecture for the ESBEF-CP1, architecture variants are generated and evaluated. The evaluation is performed based on safety and reliability, system masses, and power requirements. The selected systems architecture presented in this paper is the baseline for more detailed analyses, conducting, for example, time-dependent studies for energy management of the aircraft
Fuel Cell Cooling System Design for Hydrogen-Powered Concept Aircraft
No full textThe integration of hydrogen as an energy source and fuel cell systems as power sources in disruptive aircraft concepts introduces new challenges for on-board systems design. One such challenge is the heat management of low-temperature proton-exchange membrane fuel cells, which have an average efficiency of around 50 %. Although this efficiency is higher than conventional propulsion technologies like gas turbines, these fuel cells operate at a relatively low temperature, between 60°C and 90°C, requiring an active cooling system. This paper presents the design of a cooling system for this fuel cell technology integrated into a hydrogen-powered regional concept aircraft with ten propulsion units based on a potential analysis. Different baseline cooling system layouts are evaluated, analyzing both one-phase and two-phase cooling fluids, along with potential synergy effects with other systems. For example, hydrogen can be used as a heat sink in addition to the air from ram air channels. These architectures are assessed based on systems mass and their influence at the aircraft level, taking into account additional drag from the ram air and the electric power requirements of the cooling system. The results show that for cooling system with ram air as single heat sink, the system mass can be decreased by 43% when using a two-phase cooling fluid instead of a one-phase cooling fluid. Additionally, on system level, the mass of a cooling system with ram air as single heat sink is significantly lower than a cooling system that uses hydrogen as an additional heat sink. However, on aircraft level, the electric power required for hydrogen conditioning needs to be taken into account as well because the hydrogen needs to be conditioned fully electrically for the single-sink architecture
- …
