| 1. |
- Algesten, Grete, 1974-, et al.
(författare)
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Seasonal variation of CO2 saturation in the Gulf of Bothnia : Indications of marine net heterotrophy
- 2004
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Ingår i: Global Biogeochemical Cycles. - Washington, D.C : American Geophysical Union (AGU). - 0886-6236 .- 1944-9224. ; 18, s. 4021-4028
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Tidskriftsartikel (refereegranskat)abstract
- Seasonal variation of pCO2 and primary and bacterioplankton production were measured in the Gulf of Bothnia during an annual cycle. Surface water was supersaturated with CO2 on an annual basis, indicating net heterotrophy and a source of CO2 to the atmosphere. However, the Gulf of Bothnia oscillated between being a sink and a source of CO2 over the studied period, largely decided by temporal variation in bacterial respiration (BR) and primary production (PP) in the water column above the pycnocline. The calculated annual respiration-production balance (BR-PP) was very similar to the estimated CO2 emission from the Gulf of Bothnia, which indicates that these processes were major determinants of the exchange of CO2 between water and atmosphere. The southern basin (the Bothnian Sea) had a lower net release of CO2 to the atmosphere than the northern Bothnian Bay (7.1 and 9.7 mmol C m−2 d−1, respectively), due to higher primary production, which to a larger extent balanced respiration in this basin.
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| 2. |
- Boersma, Katja, 1973-, et al.
(författare)
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Lowering fear-avoidance and enhancing function through exposure in vivo : a multiple baseline study across six patients with back pain
- 2004
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Ingår i: Pain. - : Elsevier. - 0304-3959 .- 1872-6623. ; 108:1-2, s. 8-16
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the effects of an exposure in vivo treatment for chronic pain patients with high levels of fear and avoidance. The fear-avoidance model offers an enticing explanation of why some back pain patients develop persistent disability, stressing the role of catastrophic interpretations; largely fueled by beliefs and expectations that activity will cause injury and will worsen the pain problem. Recently, an exposure in vivo treatment was developed that aims to enhance function by directly addressing these fears and expectations. The purpose of this study was to describe the short-term, consequent effect of an exposure in vivo treatment. The study employed a multiple baseline design with six patients who were selected based on their high levels of fear and avoidance. The results demonstrated clear decreases in rated fear and avoidance beliefs while function increased substantially. These improvements were observed even though rated pain intensity actually decreased somewhat. Thus, the results replicate and extend the findings of previous studies to a new setting, with other therapists and a new research design. These results, together with the initial studies, provide a basis for pursuing and further developing the exposure technique and to test it in group designs with larger samples.
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| 3. |
- Falk, Johan, et al.
(författare)
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Direction Finding for Electronic Warfare Systems Using the Phase of the Cross Spectral Density
- 2002
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Ingår i: RadioVetenskap och Kommunikation (RVK). ; , s. 264-268
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Konferensbidrag (refereegranskat)abstract
- In modern electronic warfare systems there is a need for direction-finding of transmitters using waveforms for military stealth communication. In this paper, a correlation-based method is investigated utilizing the phase of the cross spectral density to estimate the time-difference-of-arrival from a two-channel digital receiver. A least squares method is reviewed, and its performance is investigated by theoretical analysisand by Monte-Carlo simulations. Proper Cramér-Raobounds are derived. It is shown that the method is statistically efficient for flat spectrum signals. The method is found to be a promising method for use against military communication in an electronic warfare direction-finding system.
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| 4. |
- Falk, Johan, et al.
(författare)
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Effects of frequency and phase error in electronic warfare TDOA direction-finding systems
- 2003
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Ingår i: Military Communications Conference. - : IEEE conference proceedings. - 0780381408 ; , s. 118-123
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Konferensbidrag (refereegranskat)abstract
- Electronic warfare systems for use against military communication sources include direction-finding. The considered direction-finding electronic-warfare system usestwo intercept receivers which is eavesdropping on thetransmitted signal with no knowledge of the waveformused, or its origin. Down-conversion to baseband is required in order to digitize the received signal. This canbe done using a superheterodyne receiver where an oscillator is used to mix the signal-of-interest to baseband.Errors in frequency and phase between the oscillatorsdegrade the performance. Because of this error, the per-formance derived in previous work by the authors willnot apply since the used model no longer is applicable.The extended model presented here considers the oscil-lator errors. The performance using the extended modelis determined numerically and the result is compared tothe Cramer-Rao lower bound for the ideal system usinga typical signal waveform.
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| 5. |
- Falk, Johan, et al.
(författare)
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Multisource time delay estimation subject to receiver frequency errors
- 2003
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Ingår i: CONFERENCE RECORD OF THE THIRTY-SEVENTH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, VOLS 1 AND 2. - 0780381041 ; , s. 1156-1160
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Konferensbidrag (refereegranskat)abstract
- An electronic warfare (EW) system with two spatially separated intercept receivers, targeting military communication systems is considered. The EW system estimates the direct ion-of-arrival via a correlation-based time-difference-of-arrival (TDOA) method without any prior knowledge of the signals-of-interest. An important practical consideration is the oscillator frequencies of the two intercept receivers where a difference, or error, degrades the TDOA estimator performance. A measure of this degradation, or loss in power due to the frequency error, is derived and used to describe the robustness against receiver frequency errors. In the multisource scenario, time and frequency overlapping sources can be separated using direction-filtering of the cross-correlation function between the receiver outputs with good result if one signal at a time can be selected by the direction-filter. However, the performance of the considered estimator is degraded in a multisource scenario compared to the single source case.
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| 6. |
- Fredin, Ola, 1972-
(författare)
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Mountain centered icefields in northern Scandinavia
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range.Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden.The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.
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| 7. |
- Förstberg, Johan, et al.
(författare)
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Simulatorer för spårburen trafik : kompletterande förstudie angående behov av och möjligheterna att realisera en körsimulator för spårburen trafik
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta notat motsvarar i princip dokumentationen från den kompletterade förstudie som skickades in till VINNOVA och Banverket september/oktober 2002, inför deras respektive beslut om finansiering av en körsimulator för spårburen trafik (SST). En viss redaktionell översyn av texten har gjorts, och budget och finansiering av simulatorn har tagits bort ur detta notat. Notatet bygger på Anders Janssons analys av behoven av forskning, utveckling av ny teknik och utbildning med hjälp av en simulator, på Johan Förstbergs förstudie, vilken är redovisad i VTI notat 5-2002 samt på möjligheterna för de deltagande organisationerna/företagen att deltaga i denna innovations- och utvecklingsprocess av en ny simulator. Antalet körsimulatorer, som är tillgängliga för forskning i järnvägs- och spårvägsmiljö, är få. De flesta simulatorer som finns är utvecklade och används för utbildning och träning av förare och ägs därför av olika järnvägsföretag/operatörer. Det är viktigt att kunna samverka i existerande och kommande europeiska forskningsprojekt, dvs. i kommande nätverk och projekt inom sjätte ramprogammet. Ett exempel på sådan samverkan är EU-projektet European Drivers Desk (EUDD) inom femte ramprogrammet. En simulator skulle kunna förbättra/vidga möjligheterna att utvärdera de förslag till förarbord för höghastighetståg och godståg som utvecklas inom EUDD. Ävenledes är en samverkan med existerande forskningsmiljöer, Lex. hos SNCF i Lille, viktig för att nå en god forskningsnivå på denna kommande simulator.
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| 8. |
- Gustafsson, Fredrik, et al.
(författare)
-
Particle Filters for Positioning, Navigation and Tracking
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A framework for positioning, navigation and tracking problems using particle filters (sequential Monte Carlo methods) is developed. It consists of a class of motion models and a general non-linear measurement equation in position. A general algorithm is presented, which is parsimonious with the particle dimension. It is based on marginalization, enabling a Kalman filter to estimate all position derivatives, and the particle filter becomes low-dimensional. This is of utmost importance for high-performance real-time applications. Automotive and airborne applications illustrate numerically the advantage over classical Kalman filter based algorithms. Here the use of non-linear models and non-Gaussian noise is the main explanation for the improvement in accuracy. More specifically, we describe how the technique of map matching is used to match an aircraft's elevation profile to a digital elevation map, and a car's horizontal driven path to a street map. In both cases, real-time implementations are available, and tests have shown that the accuracy in both cases is comparable to satellite navigation (as GPS), but with higher integrity. Based on simulations, we also argue how the particle filter can be used for positioning based on cellular phone measurements, for integrated navigation in aircraft, and for target tracking in aircraft and cars. Finally, the particle filter enables a promising solution to the combined task of navigation and tracking, with possible application to airborne hunting and collision avoidance systems in cars.
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| 9. |
- Gustafsson, Fredrik, et al.
(författare)
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Particle Filters for Positioning, Navigation and Tracking
- 2002
-
Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 50:2, s. 425-437
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Tidskriftsartikel (refereegranskat)abstract
- A framework for positioning, navigation and tracking problems using particle filters (sequential Monte Carlo methods) is developed. It consists of a class of motion models and a general non-linear measurement equation in position. A general algorithm is presented, which is parsimonious with the particle dimension. It is based on marginalization, enabling a Kalman filter to estimate all position derivatives, and the particle filter becomes low-dimensional. This is of utmost importance for high-performance real-time applications. Automotive and airborne applications illustrate numerically the advantage over classical Kalman filter based algorithms. Here the use of non-linear models and non-Gaussian noise is the main explanation for the improvement in accuracy. More specifically, we describe how the technique of map matching is used to match an aircraft's elevation profile to a digital elevation map, and a car's horizontal driven path to a street map. In both cases, real-time implementations are available, and tests have shown that the accuracy in both cases is comparable to satellite navigation (as GPS), but with higher integrity. Based on simulations, we also argue how the particle filter can be used for positioning based on cellular phone measurements, for integrated navigation in aircraft, and for target tracking in aircraft and cars. Finally, the particle filter enables a promising solution to the combined task of navigation and tracking, with possible application to airborne hunting and collision avoidance systems in cars.
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| 10. |
- Hultdin, Johan, et al.
(författare)
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Elevated plasma homocysteine : cause or consequence of myocardial infarction?
- 2004
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Ingår i: Journal of Internal Medicine. - : Wiley. - 0954-6820 .- 1365-2796. ; 256:6, s. 491-498
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To determine whether a first myocardial infarction leads to increased plasma homocysteine concentrations and whether the association between homocysteine and myocardial infarction was greater at follow-up compared with baseline. DESIGN: A population-based, prospective, nested case-referent study. SETTING: Screening took place at the nearest health survey centre in northern Sweden. SUBJECTS: Of more than 36,000 persons screened, 78 developed a first myocardial infarction (average 18 months after sampling). Fifty of these had participated in a follow-up health survey (average 8(1/2) years between surveys) and were sex- and age-matched with 56 referents. MAIN OUTCOME MEASURES: Comparison of plasma homocysteine levels in case and referent subjects before and after development of a first myocardial infarction. RESULTS: No statistically significant difference was found between cases and referents regarding homocysteine at baseline or follow-up. Plasma homocysteine and plasma creatinine increased significantly, and plasma albumin decreased significantly over time. Conditional univariate logistic regression indicated that high homocysteine at follow-up but not baseline was associated with first myocardial infarction (OR 2.49; 95% CI: 1.03-6.02), but the relation disappeared in multivariate analyses including plasma creatinine and plasma albumin. High plasma creatinine remained associated with first myocardial infarction at both baseline (OR 2.94; 95% CI: 1.05-8.21) and follow-up (OR 3.38; 95% CI: 1.21-9.48). CONCLUSION: In this study, first myocardial infarction did not cause increased plasma homocysteine concentration.
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