| 1. |
- Amin, Leila, et al.
(author)
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Swedish national population-based study shows an increased risk of depression among patients with Hirschsprung disease.
- 2019
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In: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 108:10, s. 1867-1870
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Journal article (peer-reviewed)abstract
- AIM: Hirschsprung disease is usually treated during infancy. The long-term impact on mental health has not been well studied. The aim of this study was to assess the risk for depressive disorders in individuals with Hirschsprung disease.METHODS: This was a nationwide, population-based cohort study. The study exposure was Hirschsprung disease and the study outcome was depression. The exposed cohort included all individuals with Hirschsprung disease, registered in the Swedish National Patient Register between 1964 and 2013 and the unexposed cohort included ten age- and sex-matched controls per patient. The diagnosis of depression was confirmed by diagnosis in the Swedish National Patient Register.RESULTS: The cohort included 739 (76.5% males) individuals with Hirschsprung disease and 7390 (76.5% males) controls. Among the patients with Hirschsprung disease, 35 (4.7%) of the patients had had a depressive disorder and 187 (2.5%) of controls, hazard ratio 1.98, 95% confidence interval 1.38-2.84. The mean age at diagnosis of first depression was 21.9 years (SD ± 7) in Hirschsprung disease patients and 23.4 years (SD ± 7), p = 0.236 in the unexposed group. There were no significant gender differences.CONCLUSION: We found an increased risk of having depressive disorders among individuals with Hirschsprung disease compared to controls.
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| 2. |
- Andersson, Tomas, et al.
(author)
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A COVQ-Based image coder for channels with bit errors and erasures
- 2008
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In: IEEE Transactions on Communications. - : IEEE Communications Society. - 0090-6778 .- 1558-0857. ; 56:2, s. 161-165
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Journal article (peer-reviewed)abstract
- We illustrate how channel optimized vector quantization (COVQ) can be used for channels with both bit-errors and bit-erasures. First, a memoryless channel model is presented, and the performance of COVQ's trained for this channel is evaluated for an i.i.d. Gaussian source. Then, the new method is applied in implementing an error-robust sub-band image coder, and we present image results that illustrate the resulting performance. Our experiments show that the new approach is able to outperform a traditional scheme based on separate source and channel coding.
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| 3. |
- Andersson, Tomas, et al.
(author)
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Design of n-channel multiple description vector quantizers
- 2005
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In: 2005 39th Asilomar Conference on Signals, Systems and Computers. - NEW YORK : IEEE. ; , s. 13-17
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Conference paper (peer-reviewed)abstract
- A new design approach for multiple description vector quantizers over more than two channels is presented. The design is inspired by the concept of channel optimized vector quantization. While most previous works have split the decoder into several independent entities, identifying the appropriate channel model makes it straightforward to implement the multiple description design problem using only one decoder. Our simulation results compare systems with 2, 4 and 8 channels. We demonstrate significant gains over previous designs, as well as over a benchmark scheme based on separate quantization and forward erasure-correcting error control.
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| 4. |
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| 5. |
- Andersson, Tomas, et al.
(author)
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Frequency estimation utilizing the Hadamard transform
- 2001
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In: 2001 IEEE WORKSHOP ON STATISTICAL SIGNAL PROCESSING PROCEEDINGS. - NEW YORK : IEEE. - 0780370112 ; , s. 409-412
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Conference paper (peer-reviewed)abstract
- Fast analog to digital conversion with only one bit per sample does not only make high sampling rates possible but also reduces the required hardware complexity. For short data buffers or block lengths, it has been shown that tone frequency estimators can be implemented by a simple table look-up. In this paper we present an analysis of such tables using the Hadamard transform. As an outcome of the analysis, we propose a class of nonlinear estimators of low complexity. Their performance is evaluated using numerical simulations. Comparisons are made with the proper Cramer-Rao bound and with the table look-up approach.
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| 6. |
- Andersson, Tomas, et al.
(author)
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Multiple description image coding based on multi-stage vector quantization
- 2007
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In: CONFERENCE RECORD OF THE FORTY-FIRST ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS. - NEW YORK : IEEE. ; , s. 243-246
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Conference paper (peer-reviewed)abstract
- A new design approach for multiple description coding, based on multi-stage vector quantizers, is presented. The design is not limited to systems with two descriptions, but is also well suited for the n-descriptions case. Inspired by the concept of channel optimized vector quantization, the design can easily be tailored to suit different erasure channels, e.g. packet erasure channels with memory (burst-losses). The optimization procedure used in the design takes a sample-iterative approach. All stage codebooks; are updated simultaneously for each vector in the training database. The resulting algorithm has the behaviour of a simulated annealing algorithm, with several good properties, e.g. it usually provides codebooks with good index assignments. Image results are presented for systems with 2 and 4 channels. The image coder is based on a subband transform followed by 64-dimensional vector quantization, to illustrate the capacity of the design to handle large problem sizes.
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| 7. |
- Andersson, Tomas, 1978-
(author)
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On error-robust source coding with image coding applications
- 2006
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Licentiate thesis (other academic/artistic)abstract
- This thesis treats the problem of source coding in situations where the encoded data is subject to errors. The typical scenario is a communication system, where source data such as speech or images should be transmitted from one point to another. A problem is that most communication systems introduce some sort of error in the transmission. A wireless communication link is prone to introduce individual bit errors, while in a packet based network, such as the Internet, packet losses are the main source of error. The traditional approach to this problem is to add error correcting codes on top of the encoded source data, or to employ some scheme for retransmission of lost or corrupted data. The source coding problem is then treated under the assumption that all data that is transmitted from the source encoder reaches the source decoder on the receiving end without any errors. This thesis takes another approach to the problem and treats source and channel coding jointly under the assumption that there is some knowledge about the channel that will be used for transmission. Such joint source--channel coding schemes have potential benefits over the traditional separated approach. More specifically, joint source--channel coding can typically achieve better performance using shorter codes than the separated approach. This is useful in scenarios with constraints on the delay of the system. Two different flavors of joint source--channel coding are treated in this thesis; multiple description coding and channel optimized vector quantization. Channel optimized vector quantization is a technique to directly incorporate knowledge about the channel into the source coder. This thesis contributes to the field by using channel optimized vector quantization in a couple of new scenarios. Multiple description coding is the concept of encoding a source using several different descriptions in order to provide robustness in systems with losses in the transmission. One contribution of this thesis is an improvement to an existing multiple description coding scheme and another contribution is to put multiple description coding in the context of channel optimized vector quantization. The thesis also presents a simple image coder which is used to evaluate some of the results on channel optimized vector quantization.
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| 8. |
- Appelgren, Patrik, et al.
(author)
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Disruption mechanisms in electrified solid copper jets
- 2011
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In: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
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Journal article (peer-reviewed)abstract
- Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.
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| 9. |
- Appelgren, Patrik, et al.
(author)
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Experimental Study of Electromagnetic Effects on Solid Copper Jets
- 2010
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In: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:1, s. 011010-
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Journal article (peer-reviewed)abstract
- In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]
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| 10. |
- Appelgren, Patrik, et al.
(author)
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Interaction between solid copper jets and powerful electrical current pulses
- 2011
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In: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
-
Journal article (peer-reviewed)abstract
- The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.
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