| 1. |
- Börjesson, Per Ola, et al.
(författare)
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Free-riding in Group Work - Mechanisms and Countermeasures
- 2006
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Ingår i: [Host publication title missing].
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Konferensbidrag (refereegranskat)abstract
- Studies have shown that group work offers great possibilities for deeper learning compared to some more traditional teaching formats [1], but it can also lead to some new problems such as free-riding. Different aspects of group psychology and behaviour as well as impropriate group sizes can be used to explain why and how free-riding develops in groups. With careful course planning teachers can seriously discourage students from free-riding. Especially the grading system should be carefully chosen not to promote free-riding but to stimulate deeper learning
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| 2. |
- Richter, Ulrike, et al.
(författare)
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Right atrial organization and wavefront analysis in atrial fibrillation.
- 2009
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Ingår i: Medical & Biological Engineering & Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 47, s. 1237-1246, s. 271-278
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to develop techniques to quantify the propagation pattern of the electrical activation during atrial fibrillation (AF) along a one-dimensional catheter. Taking intra-atrial signal organization aspects into account, the atrial activations are detected and combined into wavefronts. Parameters describing wavefront consistency and activation order along the catheter are defined, and the relationship of wavefront consistency to body surface parameters, namely AF frequency and exponential decay, is investigated. The database consisted of 26 10-s recordings from patients during drug-refractory AF, in which five adjacent bipolar electrograms from a catheter in the right atrium were recorded. The 12-lead ECG was recorded simultaneously. The degree of wavefront consistency provided insights into the temporal variability of the activation order, an aspect which was not reflected by the body surface parameters. However, AF frequency was able to distinguish between recordings with different degrees of intra-atrial signal organization (p = 0.008).
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| 3. |
- Richter, Ulrike, et al.
(författare)
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Spatial characteristics of atrial fibrillation electrocardiograms
- 2008
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Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 41:2, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The present study investigates spatial properties of atrial fibrillation (AF) by analyzing vectorcardiogram loops synthesized from 12-lead electrocardiograms (ECGs). METHODS: After atrial signal extraction, spatial properties are characterized through analysis of successive, fixed-length signal segments and expressed in loop orientation, that is, azimuth and elevation, as well as in loop morphology, that is, planarity and planar geometry. It is hypothesized that more organized AF, expressed by a lower AF frequency, is associated with decreased variability in loop morphology. Atrial fibrillation frequency is determined using spectral analysis. RESULTS: Twenty-six patients with chronic AF were analyzed using 60-second ECG recordings. Loop orientation was similar when determined from either entire 60- or 1-second segments. For 1-second segments, the correlation between AF frequency and the parameters planarity and planar geometry were 0.608 (P < .001) and 0.543 (P < .005), respectively. CONCLUSIONS: Quantification of AF organization based on AF frequency and spatial characteristics from the ECG is possible. The results suggested a relatively weak coupling between loop morphology and AF frequency when determined from the surface ECG.
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| 4. |
- Richter, Ulrike
(författare)
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Spatial characteristics of atrial fibrillation using body surface and intra-atrial signals
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis is in the field of biomedical signal processing with main focus on processing of cardiac signals measured on the body surface or invasively from patients with atrial fibrillation (AF). The first part addresses spatial analysis of AF using VCG data synthesized from the 12-lead ECG. Two parameters each are extracted to characterize the spatial orientation as well as the spatial extent of the VCG data during AF. In addition, the relation of the parameters to AF organization, which is expressed in AF frequency, is evaluated. It is concluded that the quantification of AF organization based on AF frequency and spatial characteristics from the surface ECG is possible. The results suggest a relatively weak coupling between loop morphology and AF frequency when determined from the surface ECG. In the second part, a novel technique to quantify the propagation pattern of the electrical activation during AF along a one-dimensional catheter in the right atrium is presented. Taking intra-atrial signal organization aspects into account, the atrial activations are detected from the electrograms and combined into wavefronts. Parameters related to the consistency of the detected wavefronts over time and the activation order along the catheter are developed and their relationship to body surface measures such as AF frequency is investigated. While the degree of wavefront consistency is not reflected by the body surface measures, AF frequency is able to distinguish between recordings with different degrees of intra-atrial signal organization, supporting the role of AF frequency as an organization measure of AF.
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| 5. |
- Richter, Ulrike, et al.
(författare)
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Spatial characteristics of atrial fibrillation using the surface ECG
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 273-276
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Konferensbidrag (refereegranskat)abstract
- The present study investigates spatial properties of atrial fibrillation (AF) by analyzing VCG loops synthesized from 12-lead ECGs. During intervals with ventricular activity, the atrial signal is extracted using spatiotemporal QRST cancellation, thus making continuous f-wave analysis possible. Spatial properties are characterized through joint analysis of successive fixed-length signal segments, either of 1-s length or related to the typical length of an f-wave. The spatial properties are expressed in terms of loop orientation, i.e., angles of azimuth and elevation, as well as in morphologic terms such as planarity and planar geometry of the loops and related temporal variability. Several parameters have been suggested to characterize the degree of AF organization from electrogram analysis, but only a few parameters for noninvasive, ECG-based characterization of which AF frequency is the most studied. This parameter is related to atrial refractoriness and reflects AF organization. In the present study, the significance of spatial (loop morphology) parameters is studied in relation to AF frequency, hypothesizing that more organized AF, being expressed by a lower frequency, is associated with decreased variability in loop morphology. A total of 26 patients with chronic AF were analyzed with respect to spatial properties, using 60-s ECG recordings. For the database AF frequency ranged from 3.9 to 7.7 Hz, with a mean of 6.4±1.0 Hz (mean±std). The results showed that loop orientation can be determined from global analysis (i.e., the entire 60-s segment was used for determining the two angles) or the mean of segment-based analysis, both types of analysis leading to similar results. The hypothesis that more organized AF is associated with decreased variability in loop morphology was to some extent confirmed for the parameters planarity and planar geometry; for 1-s segments, the correlation to AF frequency was 0.608 (p<0.001) and 0.543 (p<0.005). This finding also applied to segment lengths related to f-wave duration. In conclusion, the simpler analysis based on 1-s segments may be preferred since it does not require f-wave delineation. Global analysis and the mean of segment-based analysis (1-s segments) showed increased planarity and decreased planar geometry for lower AF frequencies, possibly related to higher similarity of successive loops in more organized AF.
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| 6. |
- Richter, Ulrike, et al.
(författare)
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Wavefront detection from intra-atrial recordings
- 2007
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Ingår i: Computers in Cardiology. - 0276-6574. - 9781424425334 ; 34, s. 97-100
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Konferensbidrag (refereegranskat)abstract
- The present study deals with detection of intra-atrial wavefronts from atrial activation times in adjacent bipolar electrograms. A statistic of the delays within each wave-front was calculated and served as a basis for quantifying the wavefront consistency as well as the propagation of the electrical activity along the catheter. The database consisted of 19 patients for which five electrograms were recorded simultaneously during 10 s. The analysis resulted in 38plusmn2 complete wavefronts per patient, i.e., wavefronts consisting of one activation from each recording site. Two parameters were evaluated for quantifying wavefront consistency, which together with the propagation profile well reflect the overall wavefront timing. In most cases, electrical activity was observed first in the high septal right atrium, and then spread along the catheter.
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