| 1. |
- Piscitelli, Francesco, et al.
(författare)
-
Neutron reflectometry on highly absorbing films and its application to (B4C)-B-10-based neutron detectors
- 2016
-
Ingår i: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 472:2185
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the He-3-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular (B4C)-B-10. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a (B4C)-B-10 layer must fulfil in order to be employed as a converter in neutron detection.
|
|
| 2. |
- Persson, Jonas, et al.
(författare)
-
Responses in zooplankton populations to food quality and quantity changes after whole lake nutrient enrichment of an oligotrophic sub-alpine reservoir
- 2008
-
Ingår i: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1015-1621 .- 1420-9055. ; 70:2, s. 142-155
-
Tidskriftsartikel (refereegranskat)abstract
- To sustain production of higher trophic levels in oligotrophic systems it is important that the trophic transfer of energy and nutrients is efficient. The phytoplankton-zooplankton interface is of specific interest since nutritional constraints can decouple energy flow in this step. Increased nutrient loading to oligotrophic systems with initially low abundance of high quality phytoplankton could induce changes in seston composition that reduces the nutritional value for zooplankton. We carried out a whole lake enrichment experiment for five years in two ultraoligotrophic subalpine hydroelectric power reservoirs in Sweden. The first year was an untreated reference year. Phosphorus and nitrogen were added to Lake Stora Mjolkvattnet during the following four years, and upstream Lake Burvattnet was used as an untreated reference lake. The phosphorus content of seston in the experimental lake increased in the years of fertilization and seston phosphorus to carbon ratios (atomic) were non-limiting for zooplankton growth. Decreasing concentrations of phosphorus in the reference lake lead to low phosphorus to carbon ratios that probably affected zooplankton growth negatively. The seston fatty acid concentrations and phytoplankton composition indicated good food quality in both lakes. The phytoplankton increased in the experimental lake despite an increase in zooplankton biomass. Some changes in the relative contributions of plankton species occurred but the same species were present. The crustacean zooplankton community composition shifted towards smaller species during the latter years in the experimental lake, indicating increased predation pressure from fish. A major result of this whole-lake ecosystem fertilization experiment is that gentle fertilization can significantly boost phytoplankton production while food quality remains high, and plankton community composition is not substantially altered.
|
|
| 3. |
- Sunnerheim, Kerstin, et al.
(författare)
-
Quantitative structure-activity relationships of pine weevil antifeedants, a Multivariate approach
- 2007
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 55:23, s. 9365-9372
-
Tidskriftsartikel (refereegranskat)abstract
- Antifeedant activity of mainly phenylpropanoic, cinnamic, and benzoic acids esters was tested on the pine weevil, Hylobius abiefis (L.). Of 105 compounds screened for activity, 9 phenylpropanoates, 3 cinnamates, and 4 benzoates were found to be highly active antifeeclants. To understand the structure-activity relationships of these compounds, a multivariate analysis study was performed. A number of molecular and substituent descriptors were calculated and correlated to results from two-choice feeding tests with H. abietis. Three local models were developed that had good internal predictive ability. External test sets showed moderate predictivity. In general, low polarity, small size, and high lipophilicity were characteristics for compounds having good antifeeclant activity.
|
|
| 4. |
- Wiedorn, Max O., et al.
(författare)
-
Megahertz serial crystallography
- 2018
-
Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- The new European X-ray Free-Electron Laser is the first X-ray free-electron laser capable of delivering X-ray pulses with a megahertz inter-pulse spacing, more than four orders of magnitude higher than previously possible. However, to date, it has been unclear whether it would indeed be possible to measure high-quality diffraction data at megahertz pulse repetition rates. Here, we show that high-quality structures can indeed be obtained using currently available operating conditions at the European XFEL. We present two complete data sets, one from the well-known model system lysozyme and the other from a so far unknown complex of a beta-lactamase from K. pneumoniae involved in antibiotic resistance. This result opens up megahertz serial femtosecond crystallography (SFX) as a tool for reliable structure determination, substrate screening and the efficient measurement of the evolution and dynamics of molecular structures using megahertz repetition rate pulses available at this new class of X-ray laser source.
|
|
| 5. |
- Andersson, Erik, et al.
(författare)
-
Ambio fit for the 2020s
- 2022
-
Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 51:5, s. 1091-1093
-
Tidskriftsartikel (refereegranskat)
|
|
| 6. |
- Lönnell, Niklas, et al.
(författare)
-
The Fate of the Missing Spores - Patterns of Realized Dispersal beyond the Closest Vicinity of a Sporulating Moss
- 2012
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:7, s. e41987-
-
Tidskriftsartikel (refereegranskat)abstract
- It is well-known that many species with small diaspores can disperse far during extended temporal scales (many years). However, studies on short temporal scales usually only cover short distances (in, e.g., bryophytes up to 15 m). By using a novel experimental design, studying the realized dispersal, we extend this range by almost two orders of magnitude. We recorded establishment of the fast-growing moss Discelium nudum on introduced suitable substrates, placed around a translocated, sporulating mother colony. Around 2,000 pots with acidic clay were placed at different distances between 5 m and 600 m, in four directions, on a raised bog, with increased pot numbers with distance. The experiment was set up in April-May and the realized dispersal (number of colonized pots) was recorded in September. Close to the mother colony (up to 10 m), the mean colonization rates (ratio of colonized pots) exceeded 50%. At distances between 10 and 50 m colonization dropped sharply, but beyond 50 m the mean colonization rates stabilized and hardly changed (1-3%). The estimated density of spores causing establishments at the further distances (2-6 spores/m(2)) was realistic when compared to the estimated spore output from the central colonies. Our study supports calculations from earlier studies, limited to short distances, that a majority of the spores disperse beyond the nearest vicinity of a source. The even colonization pattern at further distances raises interesting questions about under what conditions spores are transported and deposited. However, it is clear that regular establishment is likely at the km-scale for this and many other species with similar spore output and dispersal mechanism.
|
|
| 7. |
- Reifarth, R., et al.
(författare)
-
Nuclear astrophysics with radioactive ions at FAIR
- 2016
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
-
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.
|
|
| 8. |
- Yuan, Ning, et al.
(författare)
-
Investigation of the Deactivation and Reactivation Mechanism of a Heterogeneous Palladium(II) Catalyst in the Cycloisomerization of Acetylenic Acids by In Situ XAS
- 2021
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435 .- 2155-5435. ; 11:5, s. 2999-3008
-
Tidskriftsartikel (refereegranskat)abstract
- A well-studied heterogeneous palladium(II) catalyst used for the cycloisomerization of acetylenic acids is known to be susceptible to deactivation through reduction. To gain a deeper understanding of this deactivation process and to enable the design of a reactivation strategy, in situ X-ray absorption spectroscopy (XAS) was used. With this technique, changes in the palladium oxidation state and coordination environment could be studied in close detail, which provided experimental evidence that the deactivation was primarily caused by triethylamine-promoted reduction of palladium(II) to metallic palladium nanoparticles. Furthermore, it was observed that the choice of the acetylenic acid substrate influenced the distribution between palladium(II) and palladium(0) species in the heterogeneous catalyst after the reaction. From the mechanistic insight gained through XAS, an improved catalytic protocol was developed that did not suffer from deactivation and allowed for more efficient recycling of the catalyst.
|
|
| 9. |
|
|
| 10. |
|
|
