| 11. |
- Gahn, C, et al.
(författare)
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Generating positrons with femtosecond-laser pulses
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 77:17, s. 2662-2664
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing a femtosecond table-top laser system, we have succeeded in converting via electron acceleration in a plasma channel, low-energy photons into antiparticles, namely positrons. The average intensity of this source of positrons is estimated to be equivalent to 2x10(8) Bq and it exhibits a very favorable scaling for higher laser intensities. The advent of positron production utilizing femtosecond laser pulses may be the forerunner to a table-top positron source appropriate for applications in material science, and fundamental physics research like positronium spectroscopy. (C) 2000 American Institute of Physics. [S0003-6951(00)00143-1].
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| 12. |
- Gallardo González, I., et al.
(författare)
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Effects of the dopant concentration in laser wakefield and direct laser acceleration of electrons
- 2018
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 20:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we experimentally study the effects of the nitrogen concentration in laser wakefield acceleration of electrons in a gas mixture of hydrogen and nitrogen. A 15 TW peak power laser pulse is focused to ionize the gas, excite a plasma wave and accelerate electrons up to 230 MeV. We find that at dopant concentrations above 2% the total divergence of the electrons is increased and the high energy electrons are emitted preferentially with an angle of ±6 mrad, leading to a forked spatio-spectral distribution associated to direct laser acceleration (DLA). However, electrons can gain more energy and have a divergence lower than 4 mrad for concentrations below 0.5% and the same laser and plasma conditions. Particle-in-cell simulations show that for dopant concentrations above 2%, the amount of trapped charge is large enough to significantly perturb the plasma wave, reducing the amplitude of the longitudinal wakefield and suppressing other trapping mechanisms. At high concentrations the number of trapped electrons overlapping with the laser fields is increased, which rises the amount of charge affected by DLA. We conclude that the dopant concentration affects the quantity of electrons that experience significant DLA and the beam loading of the plasma wave driven by the laser pulse. These two mechanisms influence the electrons final energy, and thus the dopant concentration should be considered as a factor for the optimization of the electron beam parameters.
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| 13. |
- Hansson, M., et al.
(författare)
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Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp
- 2016
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 58:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.
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| 14. |
- Isasi, R., et al.
(författare)
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Disclosure and management of research findings in stem cell research and banking: policy statement
- 2012
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Ingår i: Regenerative Medicine. - : Future Medicine Ltd. - 1746-0751 .- 1746-076X. ; 7:3, s. 439-448
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Tidskriftsartikel (refereegranskat)abstract
- Prompted by an increased interest of both research participants and the patient advocacy community in obtaining information about research outcomes and on the use of their biological samples; the international community has begun to debate the emergence of an ethical 'duty' to return research results to participants. Furthermore, the use of new technologies (e.g., whole-genome and -exome sequencing) has revealed both genetic data and incidental findings with possible clinical significance. These technologies together with the proliferation of biorepositories, provide a compelling rationale for governments and scientific institutions to adopt prospective policies. Given the scarcity of policies in the context of stem cell research, a discussion on the scientific, ethical and legal implications of disclosing research results for research participants is needed. We present the International Stem Forum Ethics Working Party's Policy Statement and trust that it will stimulate debate and meet the concerns of researchers and research participants alike.
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| 15. |
- Johansson, S. G, et al.
(författare)
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Comparison of New Experimental and Astrophysical F-values For Some Ru-ii Lines, Observed In Hst Spectra of Chi-lupi
- 1994
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 421:2, s. 809-815
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Tidskriftsartikel (refereegranskat)abstract
- We report on experimental absolute oscillator strengths for 18 UV lines of Ru II, obtained by combining laser-induced fluorescence measurements of radiative lifetimes and branching fractions from line intensities in a calibrated Fourier-transform spectrum. HST/GHRS observations of the spectrum of the sharp-lined B star chi Lupi contain six of these lines, for which ''astrophysical'' relative f-values have been determined. The agreement is within 0.10 dex for a Ru abundance of log N(Ru)/N(H) = -7.90, which is 2.3 dex above the solar abundance.
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| 16. |
- Knoppers, B.M., et al.
(författare)
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Ethic's issues in stem cell research
- 2006
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 312:5772, s. 366-367
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
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| 17. |
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| 18. |
- MacLellan, D. A., et al.
(författare)
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Annular Fast Electron Transport in Silicon Arising from Low-Temperature Resistivity
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:9
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Tidskriftsartikel (refereegranskat)abstract
- Fast electron transport in Si, driven by ultraintense laser pulses, is investigated experimentally and via 3D hybrid particle-in-cell simulations. A transition from a Gaussian-like to an annular fast electron beam profile is demonstrated and explained by resistively generated magnetic fields. The results highlight the potential to completely transform the beam transport pattern by tailoring the resistivity-temperature profile at temperatures as low as a few eV.
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| 19. |
- MacLellan, D A, et al.
(författare)
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Tunable mega-ampere electron current propagation in solids by dynamic control of lattice melt.
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 113:18
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Tidskriftsartikel (refereegranskat)abstract
- The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.
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| 20. |
- Ovadia, C., et al.
(författare)
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Ursodeoxycholic acid enriches intestinal bile salt hydrolase-expressing Bacteroidetes in cholestatic pregnancy
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Ursodeoxycholic acid (UDCA) treatment can reduce itch and lower endogenous serum bile acids in intrahepatic cholestasis of pregnancy (ICP). We sought to determine how it could influence the gut environment in ICP to alter enterohepatic signalling. The gut microbiota and bile acid content were determined in faeces from 35 pregnant women (14 with uncomplicated pregnancies and 21 with ICP, 17 receiving UDCA). Faecal bile salt hydrolase activity was measured using a precipitation assay. Serum fibroblast growth factor 19 (FGF19) and 7α-hydroxy-4-cholesten-3-one (C4) concentrations were measured following a standardised diet for 21 hours. Women with a high ratio of Bacteroidetes to Firmicutes were more likely to be treated with UDCA (Fisher’s exact test p = 0.0178) than those with a lower ratio. Bile salt hydrolase activity was reduced in women with low Bacteroidetes:Firmicutes. Women taking UDCA had higher faecal lithocholic acid (p < 0.0001), with more unconjugated bile acids than women with untreated ICP or uncomplicated pregnancy. UDCA-treatment increased serum FGF19, and reduced C4 (reflecting lower bile acid synthesis). During ICP, UDCA treatment can be associated with enrichment of the gut microbiota with Bacteroidetes. These demonstrate high bile salt hydrolase activity, which deconjugates bile acids enabling secondary modification to FXR agonists, enhancing enterohepatic feedback via FGF19. © 2020, The Author(s).
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