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- Veith, Frank J., et al.
(författare)
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Collected world and single center experience with endovascular treatment of ruptured abdominal aortic aneurysms
- 2009
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Ingår i: Annals of Surgery. - 0003-4932 .- 1528-1140. ; 250:5, s. 818-824
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Case and single center reports have documented the feasibility and suggested the effectiveness of endovascular aneurysm repair (EVAR) of ruptured abdominal aortic aneurysms (RAAAs), but the role and value of such treatment remain controversial. OBJECTIVE: To clarify these we examined a collected experience with use of EVAR for RAAA treatment from 49 centers. METHODS: Data were obtained by questionnaires from these centers, updated from 13 centers committed to EVAR treatment whenever possible and included treatment details from a single center and information on 1037 patients treated by EVAR and 763 patients treated by open repair (OR). RESULTS: Overall 30-day mortality after EVAR in 1037 patients was 21.2%. Centers performing EVAR for RAAAs whenever possible did so in 28% to 79% (mean 49.1%) of their patients, had a 30-day mortality of 19.7% (range: 0%-32%) for 680 EVAR patients and 36.3% (range: 8%-53%) for 763 OR patients (P < 0.0001). Supraceliac aortic balloon control was obtained in 19.1% +/- 12.0% (+/-SD) of 680 EVAR patients. Abdominal compartment syndrome was treated by some form of decompression in 12.2% +/- 8.3% (+/-SD) of these EVAR patients. CONCLUSION: These results indicate that EVAR has a lower procedural mortality at 30 days than OR in at least some patients and that EVAR is better than OR for treating RAAA patients provided they have favorable anatomy; adequate skills, facilities, and protocols are available; and optimal strategies, techniques, and adjuncts are employed.
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- Holst, Ulla, et al.
(författare)
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Recursive estimation in switching autoregressions with Markov regime
- 1994
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Ingår i: Journal of Time Series Analysis. - : Wiley. - 0143-9782 .- 1467-9892. ; 15:5, s. 489-506
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Tidskriftsartikel (refereegranskat)abstract
- A hidden Markov regime is a Markov process that governs the time or space dependent distributions of an observed stochastic process. We propose a recursive algorithm for parameter estimation in a switching autoregressive process governed by a hidden Markov chain. A common approach to the recursive estimation problem is to base the estimation on suboptimal modifications of Kalman filtering techniques. The main idea in this paper is to use the maximum likelihood method and from this develop a recursive EM algorithm.
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- Lindström, Johan, et al.
(författare)
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Background and Foreground Modeling Using an Online EM Algorithm
- 2006
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Ingår i: IEEE International Workshop on Visual Surveillance. ; VS2006, s. 9-16
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Konferensbidrag (refereegranskat)abstract
- A novel approach to background/foreground segmentation using an online EM algorithm is presented. The method models each layer as a Gaussian mixture, with local, per pixel, parameters for the background layer and global parameters for the foreground layer, utilising information from the entire scene when estimating the foreground. Additionally, the online EM algorithm uses a progressive learning rate where the relative update speed of each Gaussian component depends on how often the component has been observed. It is shown that the progressive learning rate follows naturally from introduction of a forgetting factor in the log-likelihood. To reduce the number of mixture components similar foreground components are merged using a method based on the Kullback-Leibler distance. A bias is introduced in the variance estimates to avoid the known problem of singularities in the log-likelihood of Gaussian mixtures when the variance tends to zero. To allow a decoupling of the learning rate of the Gaussian components and the speed at which stationary objects are incorporated into the background a CUSUM detector is used instead of the prevailing method that uses the ratio of prior probability to standard deviation. The algorithm is scale invariant and its properties on gray-scale and RGB videos, as well as on output from an edge detector, is compared to that of another algorithm. Especially for the edge detector video performance increases dramatically.
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| 7. |
- Lindström, Johan, et al.
(författare)
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Influence of solar zenith angles on observed trends in the NOAA/NASA 8-km Pathfinder normalized difference vegetation index over the African Sahel
- 2006
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 27:9-10, s. 1973-1991
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Tidskriftsartikel (refereegranskat)abstract
- The strong systematic change in solar zenith angles (SZA) due to annual orbital drift of the NOAA satellites has raised the suspicion of the influence of residual illumination on the calibrated normalized difference vegetation index (NDVI) derived from the Pathfinder AVHRR Land (PAL) database. The aim of this work is to analyse if trends in AVHRR NDVI from 1982 to 2000 over the Sahel region in Africa depend on variations in SZA. The analysis uses both ordinary least squares regression and cointegration to analyse possible linear dependencies between NDVI and SZA on a per satellite basis. Tests for integration and cointegration fail to find any significant evidence for either. This, together with the ability of simple deterministic models to explain primarily SZA constitutes evidence against integration and cointegration, indicating that linear relationships can be examined using ordinary linear regression. Regression gives no consistent relationship between NDVI and SZA and the explanatory power (R 2) of the regression is low (on average 0.08). However there is some evidence for downward bias in NDVI due to nonlinear interactions between NDVI and SZA when SZA is large (>= 80 degrees) leading to the conclusion that PAL data from the year 2000 should not be used for analyses in these environments.
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| 9. |
- Malmberg, Anders, et al.
(författare)
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A real-time assimilation algorithm applied to near-surface ocean wind fields
- 2008
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Ingår i: Environmetrics. - : Wiley. - 1099-095X .- 1180-4009. ; 19:3, s. 319-330
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedMarine operations depend on the ability to forecast suddenly appearing storms, and failures often cause great damage. As part of a sea-state alarm study, meteorological forecasts overlaid with satellite observations sent to ships have been found to be a useful too]. In this paper we present a real-time assimilation algorithm that extends this tool using statistical methods. The algorithm is applied to near-surface ocean wind fields. A Kalman filter based on a spatio-temporal state-space model provides a basis for emulation of the atmospheric model. The main contribution of this paper is the algorithm that makes it possible to use the information in the satellite observations over the full spatial domain of interest at a real-time basis.
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| 10. |
- Malmberg, Anders, et al.
(författare)
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Forecasting near-surface ocean winds with Kalman filter techniques
- 2005
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Ingår i: Ocean Engineering. - : Elsevier BV. - 1873-5258 .- 0029-8018. ; 32:3-4, s. 273-291
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a statistical forecasting model designed for bounded areas of near-surface ocean wind speeds is implemented. Dimension reduction is achieved by decomposing the covariance structure into one large-scale and one small-scale component using empirical orthogonal functions. The large-scale component is modelled with an AR process and forecasts are calculated by applying a Kalman filter. The model is suited for stable weather situations as for unsteady situations it requires more frequent wind information. From the prediction variance fields it is possible to identify where unexpected weather usually enters the area.
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