| 1. |
- Jelic, V., et al.
(författare)
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Initial LOFAR observations of epoch of reionization windows II. Diffuse polarized emission in the ELAIS-N1 field
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 568, s. A101-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications or extracting of the cosmological 21 cm signal from the LOw-Frequency ARray - Epoch of Reionization (LOFAR-EoR) data Methods. We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results. The brightness temperature of the detected Galactic emission is on average similar to 4 K in polarized intensity and covers the range from -10 to +13 rad m(-2) in Faraday depth, The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to approximate to 1.5%. There is no indication of diffuse emission in total intensity in the interferometric data. in line with results at higher frequencies Conclusions. The wide frequency range. high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of similar to 1-2 rad m(-2) in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.
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| 2. |
- Roccaforte, F., et al.
(författare)
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Towards vertical Schottky diodes on bulk cubic silicon carbide (3C-SiC)
- 2022
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Ingår i: Applied Surface Science. - : ELSEVIER. - 0169-4332 .- 1873-5584. ; 606
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we demonstrate the feasibility of fabricating vertical Schottky diodes on bulk cubic silicon carbide (3C-SiC) material obtained by combining sublimation epitaxy and chemical vapor deposition, starting from 4 degrees -off axis 4H-SiC. First, the good quality of the epilayers grown with this method was demonstrated by morphological and structural analyses. Then, fabricated vertical Pt/3C-SiC Schottky diodes exhibited an ideality factor of 1.21 and a barrier height of 0.6 eV, as determined by thermionic emission model. The temperature dependent forward current analysis indicated the formation of an inhomogeneous barrier, which has been related with the presence of conductive surface defects, detected by nanoscale local current measurements. On the other hand, the reverse leakage current could be described by thermionic field emission model, including image force lowering. These findings demonstrate the viability of the proposed approach for bulk 3C-SiC growth for device fabrication. The material quality and the feasibility of fabricating vertical diodes based on 3C-SiC with a low barrier pave the way for the application of this polytype for medium-voltage power devices.
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| 3. |
- Rolland, J., et al.
(författare)
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Conceptual and empirical bridges between micro- and macroevolution
- 2023
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Ingår i: Nature Ecology and Evolution. - 2397-334X. ; 7, s. 1181-1193
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Tidskriftsartikel (refereegranskat)abstract
- This Perspective discusses four questions of evolutionary biology that bridge macro and microevolution perspectives and proposes future research avenues to link evolutionary mechanisms and processes. Explaining broad molecular, phenotypic and species biodiversity patterns necessitates a unifying framework spanning multiple evolutionary scales. Here we argue that although substantial effort has been made to reconcile microevolution and macroevolution, much work remains to identify the links between biological processes at play. We highlight four major questions of evolutionary biology whose solutions require conceptual bridges between micro and macroevolution. We review potential avenues for future research to establish how mechanisms at one scale (drift, mutation, migration, selection) translate to processes at the other scale (speciation, extinction, biogeographic dispersal) and vice versa. We propose ways in which current comparative methods to infer molecular evolution, phenotypic evolution and species diversification could be improved to specifically address these questions. We conclude that researchers are in a better position than ever before to build a synthesis to understand how microevolutionary dynamics unfold over millions of years.
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| 4. |
- Titarenko, Yu E., et al.
(författare)
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Measurement and simulation of the cross sections for nuclide production in Fe-56 and Cr-nat targets irradiated with 0.04- to 2.6-GeV protons
- 2011
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Ingår i: Physics of Atomic Nuclei. - 1063-7788 .- 1562-692X. ; 74:4, s. 523-536
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Tidskriftsartikel (refereegranskat)abstract
- The cross sections for nuclide production in thin Fe-56 and Cr-nat targets irradiated by 0.04-2.6-GeV protons are measured by direct gamma spectrometry using two gamma spectrometers with the resolutions of 1.8 and 1.7 keV for the Co-60 1332-keV gamma line. As a result, 649 yields of radioactive residual product nuclei have been obtained. The Al-27(p, x)Na-22 reaction has been used as a monitor reaction. The experimental data are compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.
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| 5. |
- Titarenko, Yu E., et al.
(författare)
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Measurement and simulation of the cross sections for nuclide production in Nb-93 and Ni-nat targets irradiated with 0.04- to 2.6-GeV protons
- 2011
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Ingår i: Physics of Atomic Nuclei. - 1063-7788 .- 1562-692X. ; 74:4, s. 537-550
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Tidskriftsartikel (refereegranskat)abstract
- The cross sections for nuclide production in thin Nb-93 and Ni-nat targets irradiated by 0.04- to 2.6-GeV protons have been measured by direct gamma spectrometry using two gamma spectrometers with the resolutions of 1.8 and 1.7 keV in the Co-60 1332-keV gamma line. As a result, 1112 yields of radioactive residual nuclei have been obtained. The Al-27(p, x)Na-22 reaction has been used as a monitor reaction. The experimental data have been compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.
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| 6. |
- Titarenko, Yu E., et al.
(författare)
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Measurement and simulation of the cross sections for nuclide production in W-nat and Ta-181 targets irradiated with 0.04- to 2.6-GeV protons
- 2011
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Ingår i: Physics of Atomic Nuclei. - 1063-7788 .- 1562-692X. ; 74:4, s. 551-572
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Tidskriftsartikel (refereegranskat)abstract
- The cross sections for nuclide production in thin (nat)Wand Ta-181 targets irradiated by 0.04-2.6-GeV protons have been measured by direct gamma spectrometry using two gamma spectrometers with the resolutions of 1.8 and 1.7 keV in the Co-60 1332-keV gamma line. As a result, 1895 yields of radioactive residual product nuclei have been obtained. The Al-27(p, x)Na-22 reaction has been used as a monitor reaction. The experimental data have been compared with the MCNPX (BERTINI, ISABEL), CEM03.02, INCL4.2, INCL4.5, PHITS, and CASCADE07 calculations.
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| 7. |
- Titarenko, Yu E., et al.
(författare)
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Measurement and simulation of the cross sections for the production of Gd-148 in thin W-nat and Ta-181 targets irradiated with 0.4- to 2.6-GeV protons
- 2011
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Ingår i: Physics of Atomic Nuclei. - 1063-7788 .- 1562-692X. ; 74:4, s. 573-579
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Tidskriftsartikel (refereegranskat)abstract
- The cross sections for the production of Gd-148 in W-nat and Ta-181 targets irradiated by 0.4-, 0.6-, 0.8-, 1.2-, 1.6-, and 2.6-GeV protons at the ITEP accelerator complex have been measured by direct alpha spectrometry without chemical separation. The experimental data have been compared with the data obtained at other laboratories and with the theoretical simulations of the yields on the basis of the BERTINI, ISABEL, CEM03.02, INCL4.2, INCL4.5, CASCADE07, and PHITS codes.
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| 8. |
- Titarenko, Yu. E., et al.
(författare)
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Verification of high-energy transport codes on the basis of activation data
- 2011
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:6, s. 064612-
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Tidskriftsartikel (refereegranskat)abstract
- Nuclide production cross sections measured at the Institute for Theoretical and Experimental Physics (ITEP) for the targets of (nat)Cr, (56)Fe, (nat)Ni, (93)Nb, (181)Ta, (nat)W, (nat)Pb, and (209)Bi irradiated by protons with energies from 40 to 2600 MeV were used to estimate the predictive accuracy of several popular high-energy transport codes. A general agreement of the ITEP data with the data obtained by other groups, including the numerous GSI data measured by the inverse kinematics method was found. Simulations of the measured data were performed with the MCNPX (BERTINI and ISABEL options), CEM03.02, INCL4.2 + ABLA, INCL4.5 + ABLA07, PHITS, and CASCADE.07 codes. Deviation factors between the calculated and experimental cross sections have been estimated for each target and for the whole energy range covered by our measurements. Two-dimensional diagrams of deviation factor values were produced for estimating the predictive power of every code for intermediate, not measured masses of nuclei targets and bombarding energies of protons. Further improvements of all tested here codes are recommended. In addition, new measurements at ITEP of nuclide yields from the (208)Pb target irradiated by 500-MeV protons are presented. A good agreement between these new data and the GSI measurements obtained by the inverse kinematics method was found.
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