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Sökning: hsv:(NATURVETENSKAP) hsv:(Fysik) hsv:(Astronomi astrofysik och kosmologi) > Konferensbidrag

  • Resultat 1-10 av 1376
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1.
  • Billnert, Robert, 1981, et al. (författare)
  • Novel Scintillation Detectors for Prompt Fission γ-Ray Measurements
  • 2012
  • Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 31, s. 29-34
  • Konferensbidrag (refereegranskat)abstract
    • In this work we present first results from measurements of prompt fission γ-rays from the spontaneous fission in 252Cf. New and accurate data on corresponding γ-rays from the reactions 235U(nth,f) and 239Pu(nth,f) are highly demanded for the modeling of new Generation-IV nuclear reactor systems. For these experiments we employed scintillation detectors made out of new materials (LaBr3, LaCl3 and CeBr3), whose properties were necessary to know in order to obtain reliable results. Hence, we have characterized these detectors. In all the important properties these detectors outshine sodium-iodine detectors that where used in the 1970s, when the existing data had been acquired. Our finding is that the new generation of scintillation detectors is indeed promising, as far as an improved precision of the demanded data is concerned.
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2.
  • Altstadt, S.G., et al. (författare)
  • B-13,B-14(n,gamma) via Coulomb Dissociation for Nucleosynthesis towards the r-Process
  • 2014
  • Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 1095-9904 .- 0090-3752. ; 120, s. 197-200
  • Konferensbidrag (refereegranskat)abstract
    • Radioactive beams of 14,15B produced by fragmentation of a primary 40Ar beam were directed onto a Pb target to investigate the neutron breakup within the Coulomb field. The experiment was performed at the LAND/R3B setup. Preliminary results for the Coulomb dissociation cross sections as well as for the astrophysically interesting inverse reactions, 13,14B(n,γ), are presented.
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3.
  • Gobel, K., et al. (författare)
  • Measurement of the Mo-92,Mo-93,Mo-94,Mo-100(gamma,n) reactions by Coulomb Dissociation
  • 2016
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1, s. art. no. 012034-
  • Konferensbidrag (refereegranskat)abstract
    • The Coulomb Dissociation (CD) cross sections of the stable isotopes Mo-92,Mo-94,Mo-100 and of the unstable isotope Mo-93 were measured at the LAND/(RB)-B-3 setup at GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of Mo-92,Mo-94 and Ru-96,Ru-98 in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction Mo-93(gamma,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the Mo-94(gamma,n) reaction is presented. Further analysis will complete the experimental database for the (gamma,n) production chain of the p-isotopes of molybdenum.
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4.
  • Marganiec, J., et al. (författare)
  • Experimental study of the O-15(2p, gamma) Ne-17 cross section by Coulomb Dissociation for the rp process
  • 2016
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
  • Konferensbidrag (refereegranskat)abstract
    • The time-reversed reaction O-15(2p, gamma) Ne-17 has been studied by the Coulomb dissociation technique. Secondary 17Ne ion beams at 500 AMeV have been produced by fragmentation reactions of Ne-20 in a beryllium production target and dissociated on a secondary Pb target. The incoming beam and the reaction products have been identified with the kinematically complete LAND-(RB)-B-3 experimental setup at GSI. The excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb Dissociation cross sections (sigma(Coul)) have been calculated, which provide a photoabsorption (sigma(photo)) and a radiative capture cross section (sigma(cap)). Additionally, important information about the nuclear structure of the Ne-17 nucleus will be obtained. The analysis is in progress.
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5.
  • 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.
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6.
  • Tanaka, Kei E. I., et al. (författare)
  • Multiple Feedback in Low-Metallicity Massive Star Formation
  • 2019
  • Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 14:S344, s. 190-194
  • Konferensbidrag (refereegranskat)abstract
    • We theoretically investigate the impact of feedback and its metallicity dependence in massive star formation from prestellar cores at all metallicity range. We include the feedback by MHD disk winds, radiation pressure, and photoevaporation solving the evolution of protostars and accretion flows self-consistently. Interestingly, we find that the feedback does not set the upper mass limit of stellar birth mass at any metallicity. At the solar metallicity, the MHD disk wind is the dominant feedback to set the star formation efficiencies (SFEs) from the prestellar cores similar to low-mass star formation. The SFE is found to be lower at lower surface density environment. The photoevaporation becomes significant at the low metallicity of Z < 10(-2) Z(circle dot). Considering this efficient photoevaporation, we conclude that the IMF slope is steeper, i.e., massive stars are rarer at the extremely metal-poor environment of 10(-5)-10(-3)Z(circle dot). Our study raises a question on the common assumption of the universal IMF with a truncated at 100M(circle dot). Since the total feedback strength in the cluster/galaxy scale is sensitive to the number fraction of massive stars, the re-evaluations of IMF at various environments are necessary.
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7.
  • Gurvits, L. I., et al. (författare)
  • The science case and challenges of spaceborne sub-millimeter interferometry: the study case of TeraHertz Exploration and Zooming-in for Astrophysics (THEZA)
  • 2021
  • Ingår i: Proceedings of the International Astronautical Congress, IAC. - 0074-1795. ; A7
  • Konferensbidrag (refereegranskat)abstract
    • Ultra-high angular resolution in astronomy has always been an important vehicle for making fundamental discoveries. Recent results in direct imaging of the vicinity of the super-massive black hole in the nucleus of the radio galaxy M87 by the millimeter VLBI system Event Horizon Telescope (EHT) and various pioneering results of the Space VLBI mission RadioAstron provided new momentum in high angular resolution astrophysics. In both mentioned cases, the angular resolution reached the values of about 10−20 microrcseconds (0.05−0.1 nanoradian). Angular resolution is proportional to the observing wavelength and inversely proportional to the interferometer baseline length. In the case of Earth-based EHT, the highest angular resolution was achieved by combining the shortest possible wavelength of 1.3 mm with the longest possible baselines, comparable to the Earth’s diameter. For RadioAstron, operational wavelengths were in the range from 92 cm down to 1.3 cm, but the baselines were as long as ∼350,000 km. However, these two highlights of radio astronomy, EHT and RadioAstron do not”saturate” the interest to further increase in angular resolution. Quite opposite: the science case for further increase in angular resolution of astrophysical studies becomes even stronger. A natural and, in fact, the only possible way of moving forward is to enhance mm/sub-mm VLBI by extending baselines to extraterrestrial dimensions, i.e. creating a mm/sub-mm Space VLBI system. The inevitable move toward space-borne mm/sub-mm VLBI is a subject of several concept studies. In this presentation we will focus on one of them called TeraHertz Exploration and Zooming-in for Astrophysics (THEZA), prepared in response to the ESA’s call for its next major science program Voyage 2050 (Gurvits et al. 2021). The THEZA rationale is focused at the physics of spacetime in the vicinity of super-massive black holes as the leading science drive. However, it will also open up a sizable new range of hitherto unreachable parameters of observational radio astrophysics and create a multi-disciplinary scientific facility and offer a high degree of synergy with prospective “single dish” space-borne sub-mm astronomy (e.g., Wiedner et al. 2021) and infrared interferometry (e.g., Linz et al. 2021). As an amalgam of several major trends of modern observational astrophysics, THEZA aims at facilitating a breakthrough in high-resolution high image quality astronomical studies.
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8.
  • Kantzas, D., et al. (författare)
  • Black-hole X-ray binaries in the new era of multi-messenger Astronomy
  • 2022
  • Ingår i: Proceedings of Science. - 1824-8039. ; 395
  • Konferensbidrag (refereegranskat)abstract
    • Since their discovery, cosmic rays (CRs) remain among the most mysterious phenomena of modern physics. The dominant sources, as well as the exact acceleration mechanisms, remain unknown. The CRs up to the “knee”, are considered to originate in the shock waves of Galactic supernova remnants, however, due to the lack of a “smoking-gun” TeV counterpart in many cases, this scenario has been recently questioned. In this work, we motivate how the small-scale analogues of active galactic nuclei, namely black-hole X-ray binaries (BHXBs), can potentially contribute to the Galactic CR spectrum. To investigate this idea, we developed a new, multi-zone, lepto-hadronic jet model to take advantage of the entire broadband multiwavelength spectra observed by BHXBs. We statistically apply this model to the first-ever simultaneous radio-to-X-ray spectrum of Galactic BHXB Cygnus X–1 obtained in 2016 (via the CHOCBOX program), and to a quasi-simultaneous dataset of another Galactic BHXB, GX 339–4, during a bright outburst in 2010. In this work, we discuss how the different assumptions on proton acceleration affect both the jet properties and the observed spectrum. In particular, we focus on the GeV-to-TeV regime and discuss its strong dependence on the rest of the multiwavelength spectrum. Finally, we discuss the implication of the results for the next-generation gamma-ray facilities, such as the Cherenkov Telescope Array (CTA), as well as next-generation neutrino detectors, such as KM3NeT, concluding how they can help to constrain the potential BHXB contribution to the Galactic CR spectrum.
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9.
  • Kluck, H., et al. (författare)
  • Latest results of CRESST-III's search for sub-GeV/c(2) dark matter
  • 2020
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 1468:1
  • Konferensbidrag (refereegranskat)abstract
    • The CRESST-III experiment searches for direct interactions of dark matter with ordinary matter. The main event signature would be a nuclear recoil inside one of the scintillating CaWO4 crystals. Operating the crystals as cryogenic calorimeters provides a phonon signal as measure of the deposited energy. The simultaneous readout of both signals is used to actively discriminate backgrounds. CRESST-III focuses on the sub-GeV/c(2) mass region where the sensitivity is driven by the threshold. In the first data taking campaign of CRESST-III from 2016-2018 an unprecedented low threshold of 30.1 eV for nuclear recoils was obtained. In this contribution, we will report the status of the experiment and the latest results. [GRAPHICS]
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10.
  • Surcis, G., et al. (författare)
  • 6.7 GHz CH 3 OH masers polarization in massive star-forming regions: The Flux-Limited Sample
  • 2023
  • Ingår i: Proceedings of Science. - 1824-8039. ; 428
  • Konferensbidrag (refereegranskat)abstract
    • The formation process of high-mass stars (M > 8Msun) is still unclear; this is mainly due to their fast evolution and large distances that make difficult to observe them in details. The observational and theoretical efforts made in the last decades have shown that a common and essential component in the formation of high-mass stars is the presence of molecular outflows during the protostellar phase, similarly to what is observed during the formation of low-mass stars. Theoretically, it has been convincingly demonstrated that the magnetic field plays an important role in launching and shaping molecular outflows in massive young stellar objects (YSOs). Therefore, providing new observational measurements of magnetic fields close (10s-100s au) to massive YSOs is of great importance. More than 10 years ago we started a large EVN campaign to measure the magnetic field orientation and strength toward a sample of 30 massive star-forming regions, called the "Flux-Limited sample", by observing the polarized emission of 6.7 GHz CH3OH masers. Here, we present a summary of the final statistics of the Flux-Limited sample, extensively reported in [1], which are focused on the relative orientation of the outflows with the magnetic fields and on the polarized characteristics of 6.7 GHz CH3OH masers.
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