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- Reifarth, R., et al.
(författare)
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Nuclear astrophysics with radioactive ions at FAIR
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
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Konferensbidrag (refereegranskat)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 2. |
- Nilsson, Christer, et al.
(författare)
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Ecological Forecasting and the Urbanization of Stream Ecosystems: Challenges for Economists, Hydrologists, Geomorphologists, and Ecologists
- 2003
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 6:7, s. 659-674
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Tidskriftsartikel (refereegranskat)abstract
- The quantity and quality of freshwater resources are now being seriously threatened, partly as a result of extensive worldwide changes in land use, and scientists are often called upon by policy makers and managers to predict the ecological consequences that these alterations will have for stream ecosystems. The effects of the urbanization of stream ecosystems in the United States over the next 20 years are of particular concern. To address this issue, we present a multidisciplinary research agenda designed to improve our forecasting of the effects of land-use change on stream ecosystems. Currently, there are gaps in both our knowledge and the data that make it difficult to link the disparate models used by economists, hydrologists, geomorphologists, and ecologists. We identify a number of points that practitioners in each discipline were not comfortable compromising on-for example, by assuming an average condition for a given variable. We provide five instructive examples of the limitations to our ability to forecast the fate of stream and riverine ecosystems one drawn from each modeling step: (a) Accurate economic methods to forecast land-use changes over long periods (such as 20 years) are not available, especially not at spatially explicit scales; (b) geographic data are not always available at the appropriate resolution and are not always organized in categories that are hydrologically, ecologically, or economically meaningful; (c) the relationship between low flows and land use is sometimes hard to establish in anthropogenically affected catchments; (d) bed mobility, suspended sediment load, and channel form-all of which are important for ecological communities in streams-are difficult to predict; and (e) species distributions in rivers are not well documented, and the data that do exist are not always publicly available or have not been sampled at accurate scales, making it difficult to model ecological responses to specified levels of environmental change. Meeting these challenges will require both interdisciplinary cooperation and a reviewed commitment to intradisciplinary research in the fields of economics, geography, quantitative spatial analysis, hydrology, geomorphology, and ecology.
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| 3. |
- Nyberg, A., et al.
(författare)
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Abdominal aortic aneurysm and the impact of infectious burden
- 2008
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1532-2165 .- 1078-5884. ; 36:3, s. 292-296
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Little is known about the biological processes causing aortic aneurysm rupture. Chronic Chlomydophila pneumoniae infection has been suggested as a possible contributing factor to the development and expansion of abdominal aortic aneurysm (AAA). The importance of infection in AAA may be related to the previous pathogen burden, that is, the number of significant titres of antibodies against infectious pathogens rather than to single infectious agents. The aim of this study was to examine the relationship between infectious burden and AAA rupture. Methods: In a case-control study, 119 patients with abdominal aortic aneurysm and 36 matched controls without aneurysm were prospectively investigated for specific. IgG class antibodies against C. pneumoniae, Helicobacter pylori, Cytomegalovirus, and Herpes simplex virus. Results: Patients with ruptured AAA have similar levels of pathogen burden as patients with nonruptured electively operated AAA, small AAA, and controls without aneurysm. Conclusion: The present study fails to demonstrate a connection between infectious burden and abdominal aortic aneurysm rupture. (C) 2008 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.
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| 4. |
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| 6. |
- Nilsson, Hans-Erik, et al.
(författare)
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Numerical modeling of hole interband tunneling in wurtzite GaN and SiC
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 90:6, s. 2847-2852
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Tidskriftsartikel (refereegranskat)abstract
- The time evolution of Bloch electrons (holes) moving in a constant electric field has been studied for GaN and 2H-SiC using a numerical model based on realistic band structures. The large band gap of GaN and the SiC polytypes provide much larger critical fields than in conventional semiconductors, which allows device operation at very high electric fields. At sufficiently high electric fields the carriers may change band during drift due to tunneling. GaN has a direct band gap, while the hexagonal SiC polytypes have indirect band gaps. In spite of this difference the valence band structure is very similar due to the wurtzite symmetry. In this work the GaN and the 2H-SiC polytype are considered as wurtzite prototype semiconductors in order to study valence band to band tunneling in wurtzite semiconductors for electric fields directed along the c axis. A large valence band to band tunneling probability was found for both materials at electric fields above 400 kV/cm. This shows the importance of considering band to band tunneling in studies of high field hole transport in wide band-gap hexagonal semiconductor materials. The proposed numerical approach can be used to enhance the interband tunneling models used in Monte Carlo simulation of carrier transport in hexagonal semiconductors.
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| 7. |
- Andersson, Elisabeth, et al.
(författare)
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Effects of river fragmentation on plant dispersal and riparian flora
- 2000
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Ingår i: Rivers Research and Applications. - 1535-1459 .- 1535-1467. ; 16:1, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated the effects of river fragmentation by dams on hydrochory (i.e. plant dispersal by water) and on plant distribution by comparing two adjacent rivers in northern Sweden, one free-flowing and the other regulated. We collected stranded drift material from both rivers in order to quantify the drift material and its species content. We also estimated the floristic continuity along the two rivers by comparing the drift flora with the riparian flora further upstream. The drift amount deposited on the riverbank, its species richness and its contribution to the species pool were higher in the free-flowing than in the regulated river. The floristic continuity was also higher in the free-flowing than in the regulated river.
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| 8. |
- Andersson, Elisabeth, et al.
(författare)
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Plant dispersal in boreal rivers and its relation to the diversity of riparian flora
- 2000
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Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 27:5, s. 1095-1106
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Tidskriftsartikel (refereegranskat)abstract
- Aim The paper has four major objectives: (1) to determine whether diaspore mimics accurately represent dispersal dynamics of real diaspores in a free-flowing river; (2) to estimate distance travelled and reasons for stranding of floating diaspores along a free-flowing river; (3) to test if species composition and seedling recruitment vary with the ability of the riverbank to trap waterborne drift; and (4) to compare diaspore dispersal in a free-flowing river with that in a regulated river where current velocity has been reduced. Location The field work was conducted in two 7th-order boreal rivers in northern Sweden, the free-flowing Vindel River and the regulated Ume River. Methods We performed a series of dispersal experiments. We tested the usefulness wooden cubes of diaspore mimics for performing dispersal experiments by releasing cubes and achenes of Helianthus annuus and compare their dispersal patterns in the free-flowing Vindel River. We used the cubes to identify 50-m long sections along the river with different trapping capacity, i.e. the number of stranded diaspore mimics within a 50-m section. We then related the number of stranded diaspore mimics to the vascular plant flora, the proportions of species with long or short floating times (i.e. more than or less than 2 days, respectively), the number of seedlings, and to environmental variables within the sections. We also released wooden cubes in a run-of-river impoundment to determine the dispersal capacity of diaspores in a regulated river. Results The cubes were useful as diaspore mimics. They dispersed similarly to achenes of H. annuus. The stranding pattern of diaspore mimics was significantly associated with water current. Species richness of vascular plants per 50-m section increased with the number of stranded mimics. Seedling recruitment, and the proportions of species with short-floating and long-floating diaspores, did not vary with the number of stranded mimics. The ability of a river to transport diaspores downstream was strongly reduced by impoundment. Main conclusions We conclude that patterns of species richness of riparian vegetation is in part determined by the ability of the riverbank to trap waterborne diaspores, but differences in floating ability among species did not affect the species composition along free-flowing rivers.
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| 9. |
- Andersson, E., et al.
(författare)
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Temporal variation in the drift of plant litter and propagules in a small boreal river
- 2002
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 47:9, s. 1674-1684
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Tidskriftsartikel (refereegranskat)abstract
- 1. Rivers are linear ecosystems across landscapes with an effective transport of organisms, sediment and organic matter. Dispersal is studied mostly during single events and for single species, and there is little knowledge on how the drift of plant litter and propagules varies within and between years for entire communities. 2. We used floating traps for collecting waterborne plant litter and propagules in a small boreal river over 2 years. We installed the traps at four different locations along the river, and emptied them at least once a week during the ice-free season. We analysed propagule content by sorting and identifying species and through germination tests on bare soil. 3. In total, we recorded at least 54 taxa in the samples, and the highest density recorded in one sample was 5000 propagules per 100 g litter (dry weight). Large temporal variations in litter and propagule transport were revealed, both within and between years. 4. The longitudinal pattern was consistent between years, with an increasing mass of litter and number of propagule taxa downstream. The results highlight the importance of the temporal and longitudinal dimensions in river management.
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| 10. |
- Asem, H., et al.
(författare)
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Functional Nanocarriers for Drug Delivery by Surface Engineering of Polymeric Nanoparticle Post-Polymerization-Induced Self-Assembly
- 2021
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Ingår i: ACS Applied Bio Materials. - : American Chemical Society. - 2576-6422. ; 4:1, s. 1045-1056
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Tidskriftsartikel (refereegranskat)abstract
- Engineered polymeric nanoparticles (NPs) have been comprehensively explored as potential platforms for diagnosis and targeted therapy for several diseases including cancer. Herein, we designed functional poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) NPs using reversible addition-fragmentation chain-transfer (RAFT)-mediated emulsion polymerization via polymerization-induced self-assembly (PISA). The hydrophilic PAA-macroRAFT, forming a stabilizing shell (i.e., corona), was chain-extended using the hydrophobic monomer n-butyl acrylate (n-BA), resulting in stable, monodisperse, and reproducible PAA-b-PBA NPs, typically having a diameter of 130 nm. The surface engineering of the PAA-b-PBA NP post-PISA were explored using a two-step approach. The hydrophilic NP-shell corona was modified with allyl groups under mild conditions, using allylamine in water, which resulted in stable allyl-functional NPs (allyl-NPs) suitable for further bioconjugation. The allyl-NPs were subsequently conjugated with a thiol-functional fluorescent dye (BODIPY-SH) to the allyl groups using "thiol-ene"-click chemistry, to mimic the attachment of a thiol-functional target ligand. The successful attachment of BODIPY-SH to the allyl-NPs was corroborated by UV-vis spectroscopy, showing the characteristic absorbance of the BODIPY-fluorophore at 500 nm. Despite modification of NPs with allyl groups and attachment of BODIPY-SH, the NPs retained their colloidal stability and monodispersity as indicated by DLS. This demonstrates that post-PISA functionalization is a robust method for synthesizing functional NPs. Neither the NPs nor allyl-NPs showed significant cytotoxicity toward RAW264.7 or MCF-7 cell lines, which indicates their desirable safety profile. The cellular uptake of the NPs using J774A cells in vitro was found to be time and concentration dependent. The anti-cancer drug doxorubicin was efficiently (90%) encapsulated into the PAA-b-PBA NPs during NP formation. After a small initial burst release during the first 2 h, a controlled release pattern over 7 days was observed. The present investigation demonstrates a potential method for functionalizing polymeric NP post-PISA to produce carriers designed for targeted drug delivery.
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