| 51. |
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| 52. |
- Andersson, A, et al.
(författare)
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Effect of nutrient enrichment on the distribution and sedimentation of polychlorinated biphenyls (PCBs) in seawater
- 1998
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. ; 377, s. 45-56
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Tidskriftsartikel (refereegranskat)abstract
- The effect of nutrient enrichment on the distribution of polychlorinated biphenyl's (PCBs) in the microbial food web and the residence time of PCBs in seawater was studied in an experimental mesocosm system. Two 5 m high temperature and light controlled mesocosm tubes (empty set = 0.5 m) were filled with seawater from the northern Baltic Sea. Inorganic phosphorus and nitrogen were added daily to one mesocosm, while the other served as a control. Experiments were conducted at 5, 10 and 20 degrees C. Three C-14-labelled PCBs of different degree of chlorination were added to subsamples of the mesocosms: 4-chlorobiphenyl (MCB), IUPAC # 3, 2,2',5,5'-tetrachlorobiphenyl (TCB), IUPAC # 52 and 2,2',4,4',5,5'-hexachlorobiphenyl (HCB) IUPAC # 153. The biomasses and growth rates of the microorganisms as well as the sedimentation rate of particulate organic material increased with nutrient enrichment. The size distribution of the microorganisms changed with nutrient status, from dominance of picoplankton (< 2 mu m) in the control towards increased importance of micro (> 10 mu m) and nanoplankton (2-10 mu m) in nutrient enrichment. The specific growth rate of the bacterial community was found to be more temperature dependent than that of the phytoplankton community. The relative proportion of PCBs in the > 2 mu m fraction was observed to be in the order MCB < TCB < HCB, while the opposite distribution prevailed in the < 2 mu m fraction. We hypothesize that this is due to the combined effect of the different K-ow values of the PCBs and a different composition of the particulate organic carbon in the > 2 mu m and < 2 mu m fractions (e.g. different lipid composition). The residence time of the PCBs in the mesocosm generally decreased with nutrient enrichment, but was dependent on the degree of chlorination of the PCB. Our results indicate that the transport of organic pollutants up through the food web is more important in nutrient poor than in nutrient rich waters and that the importance of sedimentation is higher in eutrophic ecosystems.
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| 53. |
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| 54. |
- Appelblad, Patrik, et al.
(författare)
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Determination of C-21 ketosteroids in serum using trifluoromethanesulfonic acid catalyzed precolumn dansylation and 1,1’-oxalyldiimidazole postcolumn peroxyoxalate chemiluminescence detection
- 1998
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Ingår i: Analytical Chemistry. - Washington : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 70:23, s. 5002-5009
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Tidskriftsartikel (refereegranskat)abstract
- A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-catalyzed precolumn dansylation and coupled column liquid chromatographic separation, followed by postcolumn 1,1‘-oxalyldiimidazole peroxyoxalate chemiluminescence detection is presented. In the simultaneous optimization of chromatographic resolution and chemiluminescence intensity, a coupled column chromatographic system and a stopped-flow system were used. An eluent containing 20 mM phosphate buffer at pH 6.7 accomplished an efficient separation of 3α-hydroxy-5β-pregnan-20-one from a mixture containing 10 C-21 ketosteroids. Phosphate buffer also proved to be the most advantageous, among the six buffers tested, for sensitive detection. Experimental design and multivariate data analysis were used to characterize and optimize the postcolumn reaction chemistry in the chromatographic system. A valid full factorial design with excellent predictability showed that the flow rates for both 1,1‘-oxalyldiimidazole and hydrogen peroxide were the factors most strongly affecting the sensitivity of the system. The theoretical plate numbers were above 11 000 for all 10 dansylated ketosteroids. The 3σ detection limit estimated from 3α-hydroxy-5β-pregnan-20-one calibration curve data was 1.6 pmol (n = 4, 125 μL injected) and spiked serum containing 0−74 pmol of this compound showed overall recoveries of 73 ± 9% (n = 12). Quantitation of 3α-hydroxy-5β-pregnan-20-one was finally carried out on 45 serum samples and the results compared to those from a radioimmunoassay (RIA) method. The data acquired with the procedure described in this work compare well with the results from RIA, which confirms the reliability of the new analytical procedure.
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| 55. |
- Axelsson, Roger, et al.
(författare)
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A panel study of migration, self-selection and household real income
- 1998
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Ingår i: Journal of Population Economics. ; 11:1, s. 113-26
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Tidskriftsartikel (refereegranskat)abstract
- "The impact of migration on income for Swedish multi-adult households is examined using panel data pertaining to a sample of stable household constellations during the period 1980-1990. In contrast to previous studies, data on household disposable income is employed in estimating the income function. The empirical results indicate no significant effect on real disposable income from migration. In addition, the hypothesis of no self-selection, or zero correlation between the errors in the decision function and the income function, cannot be rejected."
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| 56. |
- Barrlund, A.
(författare)
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Efficient solution of constrained least squares problems with Kronecker product structure
- 1998
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Ingår i: Siam Journal on Matrix Analysis and Applications. ; 19:1, s. 154-160
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Tidskriftsartikel (refereegranskat)abstract
- A computational method for efficient solution of linear constrained least squares problems with Kronecker product structure is presented. The equality constraints are assumed to be linearly independent. The computational efficiency of the method is analyzed. Conditions for uniqueness of solutions are given.
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| 57. |
- Barrlund, A.
(författare)
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On a conjecture on the closest normal matrix
- 1998
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Ingår i: Mathematical Inequalities & Applications. ; 1:3, s. 305-318
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Tidskriftsartikel (refereegranskat)abstract
- Let A be a complex n x n matrix and let N-n be the set of normal n x n matrices. A conjecture is that parallel to A - N(n)parallel to(F)(2) less than or equal to n - 1/ndep(2)(A), where dep(2)(A) = parallel to A parallel to(F)(2) - Sigma(i=1)(n) lambda(i)(2)(A) and lambda(i)(A), i = 1,...,n are the eigenvalues of A. We prove that the conjecture is correct for all even n and for n = 3, 5, 7. However, for the dimensions, n = 3, 5, 6, 7, and presumably also other problem dimensions it is possible to derive sharper bounds. We also prove a bound for odd n which converges to the bound in the conjecture when n tends to infinity. The main idea in the proofs is to use LP problems with constraints based on different ways to approximate A with normal matrices.
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| 58. |
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| 59. |
- Behndig, Anders, et al.
(författare)
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Aqueous humor lidocaine concentrations in topical and intracameral anesthesia
- 1998
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Ingår i: Journal of cataract and refractive surgery. - 0886-3350 .- 1873-4502. ; 24:12, s. 1546-1647
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To assess aqueous humor lidocaine concentrations in 2 common regimens of topical anesthesia and after intracameral injection of the anesthetic agent. SETTING: University hospital eye clinic. METHODS: Twenty patients having routine cataract surgery were randomized into 3 groups: 1 given 3 drops of lidocaine 4% before surgery; 1 given 6 drops; 1 given 3 drops plus an intracameral injection of 0.1 mL lidocaine 1%. Lidocaine concentration was measured in aqueous humor samples taken before surgery. RESULTS: With 3 drops, aqueous lidocaine concentration was 1.4 micrograms/mL +/- 0.5 (SD) and with 6 drops, 4.3 +/- 1.5 micrograms/mL (P = .0015). With an intracameral injection, it was 341.8 +/- 152.6 micrograms/mL. CONCLUSION: Measurable amounts of lidocaine entered the anterior chamber in topical anesthesia, and more entered when more drops were given. It is likely that concentrations in this range could anesthetize the iris, but they are far lower than concentrations after an intracameral injection.
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| 60. |
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