1,721,001 research outputs found
Calibration and Validation of a Swedish Space-time Analytical Model
No full textAbstractThe present capacity models for freeways descended from the early 70th, and were partly using the HCM 1965 Highway Research Board (1965) as background. Not especially valid for the todays freeway network. During the last decade one large project, Traffic Performance on Major Arterials (TPMA) Carlsson et al. (2000a), Carlsson et al. (2000b) and Carlsson et al. (2002) has been implemented. New models for basic freeway segment, merging and weaving segment was developed. A new model for weaving were developed 2010 with new empirical data Strömgren (2011). In addition to the manual calculation method for not oversaturated condition a time-space model that also handled oversaturated conditions has been included.The development of the model started with analysis of video and aerial photo to be able to calculate the jam density, the last point in the oversaturated regime curve. The oversaturated flow-density curve has been developed using the density at capacity for a certain cross section and speed limit based on empirical data of flow and density in oversaturated conditions including jam density.The development of the Swedish space-time model used FREEVAL Transport research Board (2010). The resulting computer model, called CALMAR, CALculation of performance for Motorway ARterial facilities, was built in VB.NET and VBA. Calibration of the model was done by using the Swedish capacity models for link, merging, diverging and weaving but also flow-density estimations. All other country specific parameters as speed limits etc. was set to Swedish conditions. A traffic environmental factor was implemented describing the environment where the freeway is situated, and divided into rural or urban. Urban conditions has an interchange density higher or equal to 0.5 (interchanges/km), rural conditions has a density lower than 0.5 (interchanges/km).The model was calibrated for four and six lane freeways with merging or weaving lanes. The speed limit range from 70 kph to 120 kph in step of 10 kph. The model has its limitations. Lane width, shoulder width, distance to obstacles, gradients for ramps and length of merging was not taken into account, since no relationship could be found in the empirical data.The validation of the model was carried out for three different cases on the A4 freeway south of Stockholm, one accident, one vehicle break down and one at oversaturated condition due to high demand flow. Recorded flows from the motorway control system (MCS) as well as the automatic incident detection (AID) data from this system were used to identify queue increases and decreases. Reports from the roadside assistance team were also used to identify the degree and duration of bottleneck blockade.A careful collection of flows including bottleneck throughput and upstream demand were collected in the cases of accidents. The throughput and the upstream flow (demand) on the upstream not affected link before the end of the queue were registered for each time step (60minutes). The throughput flow was used as the capacity value in CALMAR, and the demand flow upstream as the segment demand. This was repeated for each time step of 60minutes. In the case with oversaturated condition no explicit change of the capacity in the bottleneck was done. The capacity was indirectly changed by the related interchange, where the number of lanes was changed from 3 to 2 lanes and the speed limit decreased from 100 kph to 80 kph. The demand flow was captured as in the two first cases.To estimate the queue length AID data was collected from the MCS database and converted from binary to decimal format. Data from 12 MCS gantries for each accident in the southbound direction, and 18 gantries in the northbound direction were collected. The average gantry spacing was 200-300 m.For each time step the end of the queue was registered as a length from the bottleneck where the AID alarm was registered. The AID gives a sign of 30 kph without flashing lamps and has a threshold of 22 kph. This means that the speed is in the range of 0 to 22 kph. A check is also done in the speed flow data from the MCS, if speed less than approximately 10 kph the density is too high for the radar detectors and no data will be recorded.The result from the validation showed a good fit. The CALMAR model gives in case 1, southbound accident, a maximum queue length of 2472 m and the maximum empirical queue length was 2635 m. Case 2, northbound vehicle breakdown gave a CALMAR queue length result of 3608 m compared to a maximum empirical queue length of 3530 m. Case 3, northbound oversaturated condition, gave a CALMAR result of 4149 m queue length and an maximum empirical queue length of 4310 m
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
Analysis of the Weaknesses in the Present Freeway Capacity Models for Sweden
No full textAbstractThe aim of the work is to scrutinize the present Swedish capacity manual and new models from a project in the early 2000's. It only covers freeway facilities. By using new and extended empirical data the models that have to be improved can be further developed. The result shall be the freeway models in the new Swedish Capacity Manual. The manual for freeway facilities include a time-space model for bottleneck analysis of urban and rural freeways. The work has been based on the documentation for the present models. The models have also been compared to other international models to check the reasonableness. The project includes three parts, freeway mainline section, freeway weaving and freeway merging.The review of the models revealed several deficiencies.- The Swedish capacity model for main line section doesn’t take into account the gradient, which is an important factor and is one of the most significant parameters according to German experiences.- Another large knowledge gap is the fact that the capacity model doesn’t take into account lane width and distance to obstacle.- The model for weaving has one large weakness, it is based on empirical data where the on-ramp flow is almost equal with the off-ramp flow. The model has then been design with a total weaving flow, which means that the model is insensitive to flow cases where e.g. the on-ramp flow is much larger than the off-ramp flow.- The model for on-ramp merging does only take into account the on-ramp flow, other international models also have ramp length.The work with the new capacity models during 1998-2001 had a lack of empirical data, which gave the result that relation between different parameters where difficult to find. E.g. the weaving model has only 6hours empirical data. The models should preferable add the following parameters:- Gradient for main line- Lane width- Distance to obstacle- Separate on- and off-ramp flow in the weaving model- On-ramp lengthWith the data collection system STRESS new data have been analyzed and a new model for oversaturated conditions has been developed. Also a new model for capacity in weaving segments has been developed. The new model takes into account both on-ramp and off-ramp flow. The TPMA model for link capacity has been further developed with a parameter that takes into account the gradient.A time-space model for calculation and identification of bottlenecks should also be developed. The time-space model should be answering the following questions:• How to calculate the emergence of bottlenecks in a system of adjacent interchanges?• Which bottlenecks arise because of geometric design?• How to conduct an analysis of the geometric configuration's impact on the occurrence of the bottleneck?• How to model the changes in the geometric design to eliminate or reduce the bottleneck in time and/or place?The state of art shows that only one model is adequate and gives a relatively fully cover of different on-and off ramp configurations, the model is Freeval and is a part of HCM 2010. The Swedish model will use the method for time and space calculation in HCM 2010
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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