| 1. |
|
|
| 2. |
- Adolfsson, Göran, 1981, et al.
(author)
-
Realization of spectrally engineered semiconductor Fabry-Perot lasers with narrow geometrical tolerances
- 2011
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:9, s. 093112-
-
Journal article (peer-reviewed)abstract
- Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive index perturbations along the length of the resonator. However,the physical realization of these resonators is a challenge because of very narrow tolerances; in particular the need for precise positioning of the end facets of the resonator in relation to the perturbations, and the excess propagation loss associated with the perturbations, has been a majorconcern. We report on a method to achieve high-quality end facet mirrors enabling precise positioning relative to the perturbations, the latter which are realized as lateral corrugations of the waveguide. Measurements show that the mirror quality is comparable to that of cleaved mirrorsand that the additional loss introduced by the perturbations adds
|
|
| 3. |
- Adolfsson, Göran, 1981, et al.
(author)
-
Spectral engineering of semiconductor Fabry–Perot laser cavities in the weakly and strongly perturbed regimes
- 2010
-
In: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 27:1, s. 118-127
-
Journal article (peer-reviewed)abstract
- By inserting index perturbations at certain positions along a semiconductor Fabry–Perot laser cavity thethreshold gain for one or several of the longitudinal cavity modes can be selectively lowered to facilitate, e.g.,single-mode or two-color operation. Previous design methods were limited to a fairly small number of perturbations,leading to only weakly perturbed cavities and thus a limited freedom in tailoring the spectral propertiesof the laser. In our approach we fully account for all multiple-reflection events and use a search spacethat permits any distribution of the locations and lengths of the perturbations. We are therefore able to designcavities with almost arbitrary spectral properties with very low threshold gain values for, e.g., the lasingmodes of a two-color cavity. Constraining the design by reducing the geometrical freedom, which can be used toincrease the smallest feature size to simplify fabrication, we seamlessly approach the weakly perturbed regimewhile maintaining much of the freedom for spectral engineering.
|
|
| 4. |
- Bengtsson, Bengt Å., et al.
(author)
-
Fjärilar
- 2010. - 1
-
In: Rödlistade arter i Sverige 2010. - Uppsala : Artdatabanken i samarbete med Naturvårdsverket. - 9789188506351 ; , s. 361-392
-
Book chapter (other academic/artistic)
|
|
| 5. |
- Bengtsson, Göran, et al.
(author)
-
Microbial Diversity and PAH Catabolic Genes Tracking Spatial Heterogeneity of PAH Concentrations.
- 2012
-
In: Microbial Ecology. - : Springer Science and Business Media LLC. - 1432-184X .- 0095-3628.
-
Journal article (peer-reviewed)abstract
- We analyzed the within-site spatial heterogeneity of microbial community diversity, polyaromatic hydrocarbon (PAH) catabolic genotypes, and physiochemical soil properties at a creosote contaminated site. Genetic diversity and community structure were evaluated from an analysis of denaturant gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified sequences of 16S rRNA gene. The potential PAH degradation capability was determined from PCR amplification of a suit of aromatic dioxygenase genes. Microbial diversity, evenness, and PAH genotypes were patchily distributed, and hot and cold spots of their distribution coincided with hot and cold spots of the PAH distribution. The analyses revealed a positive covariation between microbial diversity, biomass, evenness, and PAH concentration, implying that the creosote contamination at this site promotes diversity and abundance. Three patchily distributed PAH-degrading genotypes, NAH, phnA, and pdo1, were identified, and their abundances were positively correlated with the PAH concentration and the fraction of soil organic carbon. The covariation of the PAH concentration with the number and spatial distribution of catabolic genotypes suggests that a field site capacity to degrade PAHs may vary with the extent of contamination.
|
|
| 6. |
- Bengtsson, Göran, et al.
(author)
-
Spatial uncoupling of biodegradation, soil respiration, and PAH concentration in a creosote contaminated soil.
- 2010
-
In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 158:9, s. 2865-2871
-
Journal article (peer-reviewed)abstract
- Hotspots and coldspots of concentration and biodegradation of polycyclic aromatic hydrocarbons (PAHs) marginally overlapped at the 0.5-100 m scale in a creosote contaminated soil in southern Sweden, suggesting that concentration and biodegradation had little spatial co-variation. Biodegradation was substantial and its spatial variability considerable and highly irregular, but it had no spatial autocorrelation. The soil concentration of PAHs explained only 20-30% of the variance of their biodegradation. Soil respiration was spatially autocorrelated. The spatial uncoupling between biodegradation and soil respiration seemed to be governed by the aging of PAHs in the soil, since biodegradation of added (13)C phenanthrene covaried with both soil respiration and microbial biomass. The latter two were also correlated with high concentrations of phospholipid fatty acids (PLFAs) that are common in gram-negative bacteria. However, several of the hotspots of biodegradation coincided with hotspots for the distribution of a PLFA indicative of fungal biomass.
|
|
| 7. |
|
|
| 8. |
- Bengtsson, Tommy, et al.
(author)
-
Famines and mortality crises in 18th to 19th century southern Sweden
- 2011
-
In: Genus: Journal of Population Sciences. - Rome : Università degli Studi di Roma La Sapienza. - 2035-5556. ; 67:2, s. 119-139
-
Journal article (peer-reviewed)abstract
- Causality is an important but complicated issue, not only within social sciences in general but also within economic and historical demography. Here we are dealing with two different, but related, problems of causality. The first is to what extent the impact of food prices on mortality is biased when selecting on years with mortality crises. The second concerns the problem of mixing factors that directly and indirectly have an impact on mortality. Dealing with the first problem, we compare the effects of food prices on child and adult mortality when selecting on mortality crises with a standard approach without selection. When dealing with the second problem we use the additive hazards model, in combination with dynamic path analysis, which allows for investigating the mediating effect of intermediate covariates in a causal framework. We use individual level data from the Scanian Economic Demographic Database for five rural parishes for the period 1766 to 1865. Data on food prices refers to the local area of these parishes. The statistical analyses are performed in the R statistical computing environment, especially with the aid of the package eha. The main findings are that selecting on mortality crises created a large bias in the direction of overestimating the impact of food prices and that that the direct effects of food prices are dominating.
|
|
| 9. |
- Berglund, Helena, et al.
(author)
-
Associations of invasive alien species and other threats to IUCN Red List species (Chordata: vertebrates)
- 2013
-
In: Biological Invasions. - : Springer Science and Business Media LLC. - 1387-3547 .- 1573-1464. ; 15:5, s. 1169-1180
-
Journal article (peer-reviewed)abstract
- Apart from acting synergistically or additively, threats to species may be associated or disassociated. Here we link global data on threatened Chordata species, mainly birds, mammals, and amphibians, with a probabilistic methodology to test whether the impact from invasive alien species co-occurs purely randomly, associated, or disassociated with impact from nine other major threats to biodiversity listed in the International Union for Conservation of Nature Red List database. Impacts from several of the other threats, in particular from natural disasters, are associated with the impact from invasive alien species. Three of the threats of anthropogenic origin, namely habitat loss, harvesting, and human disturbance, co-occur randomly with impact from invaders, and we suggest several explanations to this unexpected relationship, such as ambiguous evidence for associations between them and human-induced disturbances. Impact from invasive alien predators has a strong association with impact from native predators, indicating that similarity in autecology affects co-occurrences between threats. The threat from invasive predators is disassociated from intrinsic factors on islands, probably because species suffering from for instance inbreeding problems have low densities and rarely encounter invasive alien predators. The analysis of co-occurrence of impact from invasive alien species and other threats is a first step to understand and mitigate vulnerability of a community to the simultaneous exposure to invasive alien species and other threats. Association or disassociation between threats may depend on correlations between exposures and sensitivity to the threats or on the presence of one threat increasing or decreasing the sensitivity to another.
|
|
| 10. |
- Elofsson, Katarina, et al.
(author)
-
Optimal management of invasive species with different reproduction and survival strategies
- 2012
-
In: Natural Resource Modeling. - : Wiley. - 0890-8575 .- 1939-7445. ; 25:4, s. 599-628
-
Journal article (peer-reviewed)abstract
- In this paper, a numerical model is developed for analyzing the role of species life history and age structure for the optimal management of a commercial resident species that is exposed to an invasive species. It is shown that reproduction and mortality characteristics of both species ands age structure of the invader at the time of invasion are important for the costs of invasions when the invader and resident species compete for scarce resources. Commercially harvested species with low juvenile survival and high reproduction are found to be economically more robust against invasions. Species with these life-history traits are also the most damaging as invaders. Properties of the harvesting cost function and the discount rate are shown to be of importance for the development of the invader population over time. Hence, it is possible to identify specific combinations of life-history characteristics and economic conditions under which invasions cause particularly large economic damage.
|
|
