1,721,075 research outputs found
Correction of atmospheric stray light in restored slit spectra
No full textContext. A long-standing issue in solar ground-based observations has been the contamination of data due to stray light, which is particularly relevant in inversions of spectropolarimetric data.
Aims. We aim to build on a statistical method of correcting stray-light contamination due to residual high-order aberrations and apply it to ground-based slit spectra.
Methods. The observations were obtained at the Swedish Solar Telescope, and restored using the multi-frame blind deconvolution restoration procedure. Using the statistical properties of seeing, we created artificially degraded synthetic images generated from magneto-hydrodynamic simulations. We then compared the synthetic data with the observations to derive estimates of the amount of the residual stray light in the observations. In the final step, the slit spectra were deconvolved with a stray-light point spread function to remove the residual stray light from the observations.
Results. The RMS granulation contrasts of the deconvolved spectra were found to increase to approximately 12.5%, from 9%. Spectral lines, on average, were found to become deeper in the granules and shallower in the inter-granular lanes, indicating systematic changes to gradients in temperature. The deconvolution was also found to increase the redshifts and blueshifts of spectral lines, suggesting that the velocities of granulation in the solar photosphere are higher than had previously been observed
Staande golven geinduceerd door inhomogene beluchting van een twee dimensionaal bad
No full textIn beluchte vloeistof reservoirs zijn staande golven mogelijk onder invloed van de bellenstroom. Dit onderzoek aan een twee dimensionaal bad heeft zich bij de beschrijving van dergelijke oscillaties geconcentreerd op de dynamica van de wervels aan weerszijden van de bellenstroom. Initiatie en versterking van de staande golven kunnen volgens het dynamische gedrag van deze wervels worden beschreven. Er zijn twee modellen ontwikkeld na observatie van vertraagde opnamen van het stromingsveld. Op basis van deze beelden is de modellering van de wervels in het stromingsveld tot stand gekomen en is getracht de aannamen in de modellen aan te tonen met behulp van vloeistof snelheidsmetingen. In het initiatiemodel is de geopperde precessie van de wervel slechts ten dele aangetoond, maar de metingen hebben wel tot nieuwe inzichten geleid wat betreft de interactie tussen de wervels en de bellenstroom. In het oscillatiemodel vormt een verhoogde vloeistofaanstroom over de bodemplaat een beslissende grootheid voor de mate waarmee versterking van de staande golf plaatsvindt. Deze verhoogde vloeistofaanstroom is aantoonbaar aanwezig in het stromingsveld van de staande golf. De overgangen tussen de staande golven kunnen inzichtelijker worden gemaakt door het optreden van vierkantstructuren, waarin ronde wervels circuleren. Vanuit deze stabiele situatie kunnen zich weer nieuwe staande golven instellen. Het oscillatiemodel biedt voor de lagere watervulhoogten (vulhoogte/badbreedte verhouding 1/2) zijn de bestaande modellen beter toepasbaar ter beschrijving van het optreden van de staande golven in een inhomogeen belucht vloeistofreservoir.Kramers Laboratorium voor Fysische TechnologieApplied Science
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
A Scaling-upMethod for Assessing the Impacts of ITS on Traffic Efficiency
No full textHuman beings today have to face a series of problems brought by transport development — severe urban congestion, increasing number of injuries and fatalities as well as global warming caused by excessive emissions. Intelligent Transport Systems (ITS), as effective tools to solve these problems, thus have drawn much attention. In the future, it is expected that more and more ITS would be developed and applied in real practice. Before adopting ITS measures, it is necessary for policy makers to know the impacts of the ITS measure on on a large scale (e.g. national/European level). In many cases, the impacts of ITS are evaluated on a much smaller scale, for example from a microscopic traf- fic simulation or a field experiment. These effects need to be scaled up to the larger scale. There are two known scaling-up methods. The modelling method can accurately represent the large scale scenario, but requires considerable effort and a large amount of data which may not be available. Furthermore, it requires a macroscopic model of the ITS, which may be a challenge to derive. The statistical method describes the local scenarios via situational variables (like road types, vehicle types and traffic situations), classifies the local scenar- ios into categories and calculates the impacts on large scale as the weighted average of the local impacts. This method is easier and faster than the modelling method. However, the statistical method is only applicable for cases which only consider categorical situational variables, because the classification of the local scenarios into categories is not feasible when numerical situational variables are used. As a result, the statistical method is only suitable for ITS whose impacts are on the microscopic mechanisms (e.g speed and headway) and thus mainly affected by categorical situational variables (e.g road type and vehicle type). A scaling-up method to assess the impacts of ITS on traffic efficiency which is generally suitable for all ITS is still missing. To start filling this gap, this study develops a new scaling-up method for ITS that have direct network-wide influences to assess their large-scale impacts on traffic efficiency. The framework of the new scaling-up method is shown in Figure 2.2 and the graphical and mathematical interpretations are presented in Figure 2.3 and Figure 2.4. In brief, the new scaling-up method firstly chooses the suitable indicator of the impacts and situational vari- ables, then collects needed data and builds deterministic relationships between the indi- cator and the numerical situational variables, at last uses scaling sideways to calculate all local impacts and aggregates the local impacts to large scale. From the theoretical perspec- tive, the designed method is considered to be able to evaluate the impacts of ITS measures with direct network-wide influence on traffic efficiency in a large-scale scenario. To provide an evidence of the quality of the new scaling-up method, this study applies it to a specific ITS measure, that is the on-trip dynamic navigation system. Although the final large-scale impacts of the on-trip dynamic navigation system is not calculated due to the limitation of data source, it is proved that the new method is able to accurately assessthe large-scale impacts of the on-trip dynamic navigation system with enough available data. Other findings from the case study are also valuable. For example, the choice of the indicator and the situational variables, and the built deterministic relationship can be directly adopted in other projects that study the impacts of the on-trip dynamic navigation system, which indicates the practical contribution of this study. From a methodological perspective, the new scaling-up method is a great improvement of the current scaling-up approaches. The new scaling-up method expands the applica- tion area of scaling-up methods to ITS that have network-wide influences. Compared to the current methods, the new scaling-up method also improves the accuracy of scaling up and leads to more reliable assessments. Apart from the merits, there are also some dis- advantages of the new scaling-up method, such as the possibility of more time cost and data needed, as well as the possible difficulty to explain the deterministic relationships in a sensible way. The new scaling-up method is regarded to be with significant political value. The out- puts can provide useful information to support policy making. On one hand, according to the political economy model designed by Beuthe, the impacts of ITS play an important role in making policy decisions. The impacts of ITS can directly reflect the perceived effectiveness and the perceived distribution of benefits and costs. On the other hand, based on the outputs of the new scaling-up method, there are also other policy advices that could be made. For instance, the built deterministic relationship(s) can suggest the to-be-set value of the related parameters when adopting a certain ITS measure. For future researches, the attention could be focusing on applying the new method to more ITS measures and investigating the applicability of the new method on assessing the impacts on safety and environment. Specifically regarding the study of the on-trip dynamic navigation system, if the needed data is available, it would be beneficial to conduct a com- plete assessment of the large-scale impacts in a specific scenario in the future. In addition, the influences of other situational variables besides the considered situational variables could also be taken into account. Furthermore, a more specific classification of network structure is expected in future researches.Transport, Infrastructure and LogisticsTransport & PlanningCivil Engineering and Geoscience
Speed advice for cyclists; design task to reduce the stops at traffic lights
No full textStops en route are a main concern for cyclists as they want to travel in the most comfortable fashion possible. The braking and acceleration at traffic lights cause losses of kinetic energy and make the trips of cyclists more strenuous than they would have been without stops. By reducing the number of stops for cyclists, the attraction of the bicycle as transport mode could be increased. This research will focus on the reduction of stops by implementing a speed advice for cyclists that will help the cyclist to arrive at intersections when the traffic light is green. The design of a system that can reduce the number of stops is presented for the situation with a fixed time controller and an vehicle actuated controller. The design for the fixed time controller consists of a speed advice that is given once to the cyclist approaching the traffic light. The cyclist can approach the traffic light with this speed to arrive at the intersection with a green light. The advice is given by a road side sign that can be read by the cyclist. Reductions in the fraction of stopped cyclists are in the order of 10-20%. The actuated controller asks for a more flexible structure of the speed advice in which the cyclist should adjust its speed dependent on the state of the traffic light controller. The speed advice system must be implemented in a way that the consequence of the state of the controller for the advice of the cyclist can be distributed to the cyclist at the moment this change of state occurs. The flexible appearance of the system allows it to adjust its speed advice to the preferences of the user. This is done by a score function that takes into account the probability to catch the green light and the sacrifice the cyclist has to make in his desired speed to end up at the green traffic light. The reductions in fraction of stopped cyclists are largely dependent on the chosen values for the attributes in the speed advice system. The tested scenarios indicate a maximum reduction of stopped cyclists of 45%.Transport and PlanningTransport & PlanningCivil Engineering and Geoscience
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
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