| 51. |
- Abrahamsson, Richard, et al.
(författare)
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Enhanced covariance matrix estimators in adaptive beamforming
- 2007
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Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, Vol II, Pts 1-3. ; , s. 969-972
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Konferensbidrag (refereegranskat)abstract
- In this paper a number of covariance matrix estimators suggested in the literature are compared in terms of their performance in the context of array signal processing. More specifically they are applied in adaptive beamforming which is known to be sensitive to errors in the covariance matrix estimate and where often only a limited amount of data is available for estimation. As many covariance matrix estimators have the form of diagonal loading or eigenvalue adjustments of the sample covariance matrix and as they sometimes offer robustness to array imperfections and finite sample error, they are compared to a recent robustified adaptive Capon beamforming (RCB) method which also has a diagonal loading interpretation. Some of the covariance estimators show a significant improvement over the sample covariance matrix and in some cases they match the performance of the RCB even when a priori knowledge, which is not available in practice, is used for choosing the user parameter of RCB.
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| 52. |
- Abrasonis, Gintautas, et al.
(författare)
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Nanoscale precipitation patterns in carbon-nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle
- 2010
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 108:4, s. 043503-
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Tidskriftsartikel (refereegranskat)abstract
- Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed filtered cathodic vacuum arc. We reveal the role of the film composition, ion energy and incidence angle on the film morphology using transmission electron microscopy and grazing incidence small angle x-ray scattering. Under these growth conditions, phase separation occurs in a thin surface layer which has a high atomic mobility due to energetic ion impacts. This layer is an advancing reaction front, which switches to an oscillatory mode, producing periodic precipitation patterns. Our results show that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion but conserves to a large extent the initial direction of the incoming ions. This results in a tilted pattern under oblique ion incidence. A dependence of the nanopattern periodicity and tilt on the growth parameters is established and pattern morphology control via ion velocity is demonstrated.
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| 53. |
- Abrikosov, Igor, et al.
(författare)
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Theoretical Modeling of Thermodynamic and Mechanical Properties of the Pure Components of Ti and Zr Based Alloys Using the Exact Muffin-Tin Orbitals Method
- 2014
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Ingår i: Russian Physics Journal. - : Springer Verlag (Germany). - 1064-8887 .- 1573-9228. ; 56:9, s. 1030-1038
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Tidskriftsartikel (refereegranskat)abstract
- The exact muffin-tin orbitals (EMTO) method belongs to the third and latest generation of first-principles methods of calculating the electronic structure of materials in the so-called approximation of muffin-tin (MT) orbitals within the framework of the density functional theory. A study has been performed of its applicability for modeling the thermodynamic and mechanical properties of the pure components of Ti and Zr based alloys. The total energies of Ti, Zr, Nb, V, Mo, and Al are calculated in three crystal structures - face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP). For all of these elements and crystal structures, we have calculated the theoretical values of the lattice constants, elastic constants, and equations of state. The stable crystal structures have been determined. In all cases, calculations by the EMTO method predict the correct structure of the ground state. For stable structures we compared the obtained results with experiment and with calculations using full potential methods. We have demonstrated the reliability of the EMTO method and conclude that its further application for effective modeling of the properties of disordered alloys based on Ti and Zr is possible.
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| 54. |
- Abugessaisa, Imad, et al.
(författare)
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A Systemic View on Swedish Traffic Accident Data Acquisition System
- 2007
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Ingår i: Proceedings of the 14th International Conference on Road Safety on Four Continents (RS4C), 14-16 November, Bangkok, Thailand. - Sweden : VTI. ; , s. 1-12
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Konferensbidrag (refereegranskat)abstract
- This paper presents work in progress to study information sharing among road safety organizations. The focus is to study accident data acquisition system. In 2002, Swedish Road Transport authority (SRT) has accepted STRADA as accident reporting system to be used by the police all over Sweden. Such system is vital for coordinating, maintaining and auditing road safety in the country. Normally road accidents are reported by the police or by Emergency unit at the hospital. However more than 50% of the hospitals in Sweden didn’t use the system which decrease the utilization of the system and reduce the quality of the information that demanded. By using system thinking approach in this study we try to see why such situation is occurred and how changes can be introduced and handle to overcome such problem. Interviews conducted with focus group and different users of the system. To investigate the issues related to the acceptance of the system we use Technology Acceptance Model (TAM). We recommend getting the user involved in the life cycle of the STRADA and also the developers could use enabling system to overcome problems in related to system usability and complexity. Also we suggest the use of iterative development to govern the life cycle.
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| 55. |
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| 56. |
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| 57. |
- Abugessaisa, Imad, et al.
(författare)
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ICT in regional networks in the field of culture and development cooperation in 15th Americas Conference on Information Systems 2009, AMCIS 2009, vol 4, issue , pp 2667-2674
- 2009
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Ingår i: AMCIS 2009 Proceedings, 15th Americas Conference on Information Systems 2009. ; , s. 2667-2674
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Konferensbidrag (refereegranskat)abstract
- This paper presents results from a mapping study commissioned by Swedish International Development Agency (Sida), which has supported regional and global networking within the field of culture. The mapping study was carried out in East Africa to find ways to collect and use experiences already made and to draw conclusions on the status and use of ICT in the culture networks supported by Sida. Another goal was to gain an understanding of the level to which ICT is used within the cultural sectors in East Africa. The study was focused on two main cultural sectors - museums and drama/theatre. A variety of research methods were used. It was found that there were well-established culture networks in both theatre and museum sectors. Through these networks, ICT has been used for sharing knowledge as well as being a tool for communication. Also it has supported dialogue among many different culture groups in the region. © (2009) by the AIS/ICIS Administrative Office All rights reserved.
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| 58. |
- Abugessaisa, Imad
(författare)
-
Knowledge Discovery in Road Accidents Database Integration of Visual and Automatic Data Mining Methods
- 2008
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Ingår i: International Journal of Public Information Systems. - 1653-4360. ; 1, s. 59-85
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Tidskriftsartikel (refereegranskat)abstract
- Road accident statistics are collected and used by a large number of users and this can result in a huge volume of data which requires to be explored in order to ascertain the hidden knowledge. Potential knowledge may be hidden because of the accumulation of data, which limits the exploration task for the road safety expert and, hence, reduces the utilization of the database. In order to assist in solving these problems, this paper explores Automatic and Visual Data Mining (VDM) methods. The main purpose is to study VDM methods and their applicability to knowledge discovery in a road accident databases. The basic feature of VDM is to involve the user in the exploration process. VDM uses direct interactive methods to allow the user to obtain an insight into and recognize different patterns in the dataset. In this paper, I apply a range of methods and techniques, including a paradigm for VDM, exploratory data analysis, and clustering methods, such as K-means algorithms, hierarchical agglomerative clustering (HAC), classification trees, and self-organized-maps (SOM). These methods assist in integrating VDM with automatic data mining algorithms. Open source VDM tools offering visualization techniques were used. The first contribution of this paper lies in the area of discovering clusters and different relationships (such as the relationship between socioeconomic indicators and fatalities, traffic risk and population, personal risk and car per capita, etc.) in the road safety database. The methods used were very useful and valuable for detecting clusters of countries that share similar traffic situations. The second contribution was the exploratory data analysis where the user can explore the contents and the structure of the data set at an early stage of the analysis. This is supported by the filtering components of VDM. This assists expert users with a strong background in traffic safety analysis to be able to intimate assumptions and hypotheses concerning future situations. The third contribution involved interactive explorations based on brushing and linking methods; this novel approach assists both the experienced and inexperienced users to detect and recognize interesting patterns in the available database. The results obtained showed that this approach offers a better understanding of the contents of road safety databases, with respect to current statistical techniques and approaches used for analyzing road safety situations.
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| 59. |
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| 60. |
- Abugessaisa, Imad, et al.
(författare)
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Ontological Approach to Modeling Information Systems
- 2004
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Ingår i: Proceedings of the Fourth International Conference on Computer and information Technology (Cit'04), 14–16 September, Wuhan, China: IEEE Computer Society, Washington, DC. ; , s. 1122-1127
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, the use of formal tools in information system modeling and development represents a potential area of research in computer science. In 1967, the term ontology appeared for the first time in computer science literature as S. H. Mealy introduced it as a basic foundation in data modeling. The main objective of this paper is to discuss the concept of ontology (from a philosophical perspective) as it was used to bridge the gap between philosophy and information systems science, and to investigate ontology types that can be found during ontological investigation and the methods used in the investigation process. The secondary objective of this paper is to study different design and engineering approaches of ontology as well as development environments that are used to create and edit ontologies.
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