| 1. |
- Woxenius, Johan, 1967, et al.
(författare)
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A combined approach to technology
- 1996
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Ingår i: European intermodal yearbook : directory of intermodal transport, equipment and services. - 1362-5438. ; , s. 18-20
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
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| 3. |
- Woxenius, Johan, 1967, et al.
(författare)
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Five Traffic Designs in Combined Transport Systems - A Theoretical Discussion
- 1993
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Ingår i: Logistyka Engineering Machines Problems. ; 2:2, s. 111-127
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Tidskriftsartikel (refereegranskat)abstract
- Transportation system design is influenced by geographical and infrastructural conditions as well as the demand of transport services, in terms of goods flow and transport quality. In this paper five significantly different theoretical layouts of traffic systems are described. These are direct connection, corridor, hub and spoke, fixed routes and finally allocated routes. The approach is rather universal, for example it can describe distribution networks of forwarding agents or, as in this application, systems for combined transport.The paper is divided into two sections. Part one is a theoretical discussion of the characteristics of the traffic designs, focusing on when they are suitable for general transportation. The system environment is described in terms of geographical and infrastructural factors and transport demand factors. Real world examples are given and one ideal transport situation is described for each of the five traffic patterns.Part two is an application to combined transport. Since the European railway network is dominated by national railway organisations, the size of the discussed traffic networks is comparable to the major European countries. Performance characteristics of different subsystems with special attention given to terminal performance, are described according to each solution. The discussion will include a survey of existing combined transport techniques and how these are related to the performance characteristics. The purpose of the paper is to discuss some alternate traffic solutions for combined transport systems.
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| 4. |
- Arlinger, Stig, 1939-, et al.
(författare)
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Clinical trial of a digital hearing aid
- 1998
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Ingår i: Scandinavian Audiology. - : Taylor & Francis. - 0105-0397 .- 1940-2872. ; 27:1, s. 51-61
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Tidskriftsartikel (refereegranskat)abstract
- A clinical trial of Oticon DigiFocus hearing aid was performed. The test aid was evaluated on 33 subjects with several years' experience as users of modern analog hearing aids. These aids were used as reference for the 1-month-long trial. The Abbreviated Profile of Hearing Aid Benefit (APHAB) showed a mean difference in benefit with superior ratings for the test aid concerning ease of communication, speech in reverberation and speech in background noise. The subjects' own aids were rated somewhat better concerning aversiveness of sounds, but this difference was not statistically significant. The Gothenburg Profile showed a statistically significant difference between the test aid and the reference aids in favour of the test aid. The difference was not most evident with regard to speech communication and the effects of hearing loss on social interactions. Sound quality ratings concerning clearness were significantly higher for the test aid. Speech recognition thresholds in noise were on average 0.7 dB better for the test aids when tested at speech levels 60 and 75 dB. The difference was statistically significant only at 75 dB. There was significant interaction between general preference and hearing aid type, indicating that overall sound quality was an important factor affecting the general preference for either the test aid or the reference aid. Twenty-three subjects generally preferred the test aid, six preferred their own aid and four stated no difference.
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| 5. |
- Hellgren, Johan, 1966-, et al.
(författare)
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Bias of feedback cancellation algorithms in hearing aids based on direct closed loop identification
- 2001
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Ingår i: IEEE transactions on speech and audio processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6676 .- 1558-2353. ; 9:8, s. 906-913
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Tidskriftsartikel (refereegranskat)abstract
- The undesired effects of acoustic feedback of hearing aids can be reduced with an internal feedback path that is an estimate of the external feedback path. This paper analyzes the limiting estimate of the feedback for feedback cancellation schemes that apply some recursive prediction error method with a quadratic norm, e.g., least mean square (LMS) and recursive least squares (RLS), to the output and input signals of the hearing aid to identify the feedback path. The data used for identification is then collected in closed loop and the estimate used in one recursion will affect the data used in succeeding recursions. These properties have to be considered in the analysis. The analysis shows that the limiting estimate may be biased if there is an error in the used model of the input signal to the hearing aid, and that the system is not identifiable unless a second input signal to the system is added to the output of the hearing aid or the signal processing of the hearing aid used to modify the signal to the impaired ear is nonlinear. The limiting estimate is presented as the solution to an optimization problem in the frequency domain. An analytical expression of the limiting estimate is presented for a special case. For other cases an algorithm is presented that can be used to find a numerical solution. The results can be useful when the model structure used with the recursive identification is chosen.
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| 6. |
- Hellgren, Johan, 1966-
(författare)
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Compensation for hearing loss and cancellation of acoustic feedback indigital hearing aids
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of integrated circuits during the last decades has made it possible to incorporate digital signal processing in hearing aids that fit into the ear canal and are powered by small zink-air batteries. The digital signal processing provides new possibilities for the hearing aid to modify the signal to fit the impaired ear. A linear phase filter bank that is intended as a basic building block of the signal processing in digital hearing aids is introduced in this dissertation. The filterbank is computationally very efficient and divides the input signal into a number of narrow band signals for further signal processing. The filter bank was combined with band specific gains and two compressors to form the signal processing of a hearing aid. The compressors allow leveldependent gain. Three alternative fitting strategies used to adjust the characteristics of this hearing aid to the individual hearing impaired listener were evaluated. The three fitting strategies differed mainly in the characteristics of the compressors. The strategies were evaluated by hearing impaired subjects in a field test and in laboratory tests. When the subjects were grouped according to their preference among the fitting strategies, the results showed significant differences in the hearing loss configuration between the groups.One of the main tasks of a hearing aid is to amplify the signal to make it audible for the hearing impaired user. The maximum gain that can be used in a hearing aid will be controlled by the feedback from the output to the microphone, as the hearing aid will be a part of a closed loop system. The feedback path depends on several factors such as the position of the microphone (differs between hearing aid categories), size of vent, and the acoustics around the hearing aid. The feedback, and thus the maximum gain that can be used in a hearing aid, has been identified with a number of different hearing aids in a number of conditions that can be expected when the hearing aid is used under real-life conditions.Feedback cancellation can be used to reduce the negative effects of feedback on the performance of the hearing aid. An internal feedback in the hearing aid that is an estimate of the external feedback is then used to cancel the feedback signal. The external feedback path will vary as the hearing aid is used ( e.g. when a telephone set is placed by the ear). It is thus desirable to continuously identify the feedback path. One approach to do this is to utilize closed loop identification with the direct method and some recursive identification method. The output and input signals of the hearing aid are then considered as input and output signal of the system to be identified, i.e. the feedback path. An advantage with this method is that the identification can be done without modifying the output signal. A drawback is that the estimate may be biased, depending on the characteristics of the input signal. A difference from many other closed loop identification problems is that the data used for identification will depend on previous estimates of the system. A feedback cancellation algorithm where Filtered-X LMS is used with the direct method has been analyzed. Filtered-XLMS is computationally efficient and gives a possibility to incorporate known characteristics of the feedback path in the model set used. Prefiltering was also used in the algorithm as it can provide an unbiased estimate if the spectrum of the input signal is known.
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| 9. |
- Hellgren, Johan, 1966-, et al.
(författare)
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Variations in the feedback of hearing aids.
- 1999
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Ingår i: Journal of the Acoustical Society of America. - 0001-4966 .- 1520-8524. ; 106, s. 2821-2833
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Tidskriftsartikel (refereegranskat)
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| 10. |
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