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- Lindeberg, Tony, 1964-
(författare)
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Scale-space for discrete signals
- 1990
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Ingår i: IEEE Transactions on Pattern Analysis and Machine Intelligence. - : IEEE Computer Society. - 0162-8828 .- 1939-3539. ; 12:3, s. 234-254
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses the formulation of a scale-space theory for discrete signals. In one dimension it is possible to characterize the smoothing transformations completely and an exhaustive treatment is given, answering the following two main questions:Which linear transformations remove structure in the sense that the number of local extrema (or zero-crossings) in the output signal does not exceed the number of local extrema (or zero-crossings) in the original signal?How should one create a multi-resolution family of representations with the property that a signal at a coarser level of scale never contains more structure than a signal at a finer level of scale?It is proposed that there is only one reasonable way to define a scale-space for 1D discrete signals comprising a continuous scale parameter, namely by (discrete) convolution with the family of kernels T(n; t) = e^{-t} I_n(t), where I_n are the modified Bessel functions of integer order. Similar arguments applied in the continuous case uniquely lead to the Gaussian kernel.Some obvious discretizations of the continuous scale-space theory are discussed in view of the results presented. It is shown that the kernel T(n; t) arises naturally in the solution of a discretized version of the diffusion equation. The commonly adapted technique with a sampled Gaussian can lead to undesirable effects since scale-space violations might occur in the corresponding representation. The result exemplifies the fact that properties derived in the continuous case might be violated after discretization.A two-dimensional theory, showing how the scale-space should be constructed for images, is given based on the requirement that local extrema must not be enhanced, when the scale parameter is increased continuously. In the separable case the resulting scale-space representation can be calculated by separated convolution with the kernel T(n; t).The presented discrete theory has computational advantages compared to a scale-space implementation based on the sampled Gaussian, for instance concerning the Laplacian of the Gaussian. The main reason is that the discrete nature of the implementation has been taken into account already in the theoretical formulation of the scale-space representation.
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| 3. |
- Brunnström, Kjell, et al.
(författare)
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Scale and Resolution in Active Analysis of Local Image Structure
- 1990
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Ingår i: Image and Vision Computing. - : Elsevier. ; 8:4, s. 289-296
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Tidskriftsartikel (refereegranskat)abstract
- Focus-of-attention is extremely important in human visual perception. If computer vision systems are to perform tasks in a complex, dynamic world they will have to be able to control processing in a way that is analogous to visual attention in humans. Problems connected to foveation (examination of selected regions of the world at high resolution) are examined. In particular, the problem of finding and classifying junctions from this aspect is considered. It is shown that foveation as simulated by controlled, active zooming in conjunction with scale-space techniques allows for robust detection and classification of junctions.
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| 4. |
- Larsson, Per, et al.
(författare)
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Atmospheric transport of persistent pollutants governs uptake by Holarctic biota
- 1990
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 24:10, s. 1599-1601
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric deposition of PCBs, DDT, and lindane,governed uptake in terrestrial biota in the Scandinavianpenninsula. Mammalian herbivores and predators as wellas predatory insects contained higher levels of pollutantsat locations where the fallout load was high than at stationswhere atmospheric deposition was lower, and the twovariables were significantly correlated.
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| 5. |
- Larsson, Per, et al.
(författare)
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Contaminated sediment as a source of PCBs in a river system
- 1990
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 47:4, s. 746-754
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Tidskriftsartikel (refereegranskat)abstract
- The transport of PCBs (Aroclor 1242) in a river system in southern Sweden was governed by outflow from sediment in a 26-ha contaminated lake. Experiments in the lake revealed that 14 g PCBs/d escaped from the sediment, while sedimentation was 3 g PCB/d. Volatilization of PCBs from the lake surface was 0.02 g/d, which was considerably higher than the atmospheric fallout . The majority of the sediment-desorbed compounds (80%) remained at the river mouth, 60 km downstream, and entered the Baltic Sea. Desorption increased the ratio of tetrachlorobiphenyls to pentachlorobiphenyls in the water. Transport across the water/air interface was higher for trichlorobiphenyls, while atmospheric deposition was dominated by penta- and hexachlorobiphenyls. Therefore, the sediment of the lake acted as a source of PCBs entering the river system as well as the atmosphere.
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| 8. |
- Eriksson, Ann-Kristin
(författare)
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Naturinventering Testboån : Gammelfäbodströmmen
- 1990
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna naturinventering av gammelfäbodströmmen i Testeboån är utförd på uppdrag av Ockelbo kraft AB.Inventeringen har haft som syfte att utreda konsekvenserna av en utbyggnad framför allt för flora och bottenfauna, men uppgifter om fisk och fiske har också samlats in. Fältarbetet utfördes under juli och augusti 1990. Bottenfauna och fisk är de som drabbas hårdast av en utbyggnad. Hur allvarliga konsekvenserna för dessa blir beror till stor del på vilken minimitappning det skulle bli. På de växtlokaler som skulle dränkas vid en dämning har inga rara växter påträffas. En utbyggnad av gammelfäbodströmmen skulle även vara negativ för fiske och friluftsliv samt de närboendes rekreationsmöjligheter.
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| 9. |
- Lindgren, Gunilla
(författare)
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Bottenfaunaundersökning i Skärjån 1990
- 1990
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Ljusnans- Voxnans Vattenvårdsförbund utförde 1987 en undersökning av bottenfaunan i Skärjån (LV- lab 1988) Syftet var att undersöka faunans kvalitativa sammansättning för att kartlägga eventuella försurningsskador. Undersökningen utgör också referensmaterial för den kalkning som inleddes 1988.Våren 1988 togs en kalknings doserar i drift i skärjån. Dosera en är placerad mellan station 1 och station 2. 1990 gjorde Länsstyrelsen miljövårdsenhet en ny bottenfaunan undersökning i syfte att följa upp de biologiska effekterna av kalkningen.
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| 10. |
- Koptioug, Andrei, 1956-, et al.
(författare)
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Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions
- 1990
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Ingår i: Physica. B, Condensed matter. - : Esevier. - 0921-4526 .- 1873-2135. ; 164:1-2, s. 200-204
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.
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