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Sökning: LAR1:uu > Chalmers tekniska högskola

  • Resultat 1-10 av 564
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1.
  • Abbasi, R., et al. (författare)
  • A Search for Coincident Neutrino Emission from Fast Radio Bursts with Seven Years of IceCube Cascade Events
  • 2023
  • Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 1538-4357 .- 0004-637X. ; 946:2
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents the results of a search for neutrinos that are spatially and temporally coincident with 22 unique, nonrepeating fast radio bursts (FRBs) and one repeating FRB (FRB 121102). FRBs are a rapidly growing class of Galactic and extragalactic astrophysical objects that are considered a potential source of high-energy neutrinos. The IceCube Neutrino Observatory's previous FRB analyses have solely used track events. This search utilizes seven years of IceCube cascade events which are statistically independent of track events. This event selection allows probing of a longer range of extended timescales due to the low background rate. No statistically significant clustering of neutrinos was observed. Upper limits are set on the time-integrated neutrino flux emitted by FRBs for a range of extended time windows.
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2.
  • Abbasi, Rosa, et al. (författare)
  • Combining rule- and SMT-based reasoning for verifying floating-point Java programs in KeY
  • 2023
  • Ingår i: International Journal on Software Tools for Technology Transfer. - : Springer Science and Business Media LLC. - 1433-2779 .- 1433-2787. ; 25:2, s. 185-204
  • Tidskriftsartikel (refereegranskat)abstract
    • Deductive verification has been successful in verifying interesting properties of real-world programs. One notable gap is the limited support for floating-point reasoning. This is unfortunate, as floating-point arithmetic is particularly unintuitive to reason about due to rounding as well as the presence of the special values infinity and ‘Not a Number’ (NaN). In this article, we present the first floating-point support in a deductive verification tool for the Java programming language. Our support in the KeY verifier handles floating-point arithmetics, transcendental functions, and potentially rounding-type casts. We achieve this with a combination of delegation to external SMT solvers on the one hand, and KeY-internal, rule-based reasoning on the other hand, exploiting the complementary strengths of both worlds. We evaluate this integration on new benchmarks and show that this approach is powerful enough to prove the absence of floating-point special values—often a prerequisite for correct programs—as well as functional properties, for realistic benchmarks.
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3.
  • Abdeldaim, Aly, 1993, et al. (författare)
  • Large easy-axis anisotropy in the one-dimensional magnet BaMo(PO4)(2)
  • 2019
  • Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9969 .- 2469-9950. ; 100:21
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)(2). The magnetic susceptibility reveals strong antiferromagnetic interactions theta(CW) = -167 K and long-range magnetic order at T-N = 22 K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the ac plane. Neutron spectroscopy reveals a large excitation gap Delta = 15 meV in the low-temperature ordered phase, suggesting a much larger easy-axis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Neel temperature, and collinear order observed experimentally and is furthermore reproduced in a first-principles calculations by using a new computational scheme. We therefore propose BaMo(PO4)(2) to host S = 1 antiferromagnetic chains with large easy-axis anisotropy, which has been theoretically predicted to realize novel excitation continua.
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4.
  • Aboulfadl, Hisham, et al. (författare)
  • Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se2 Thin Film Solar Cells
  • 2019
  • Ingår i: Microscopy and Microanalysis. - : CAMBRIDGE UNIV PRESS. - 1435-8115 .- 1431-9276. ; 25:2, s. 532-538
  • Tidskriftsartikel (refereegranskat)abstract
    • Surface sulfurization of Cu(In,Ga)Se 2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500°C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to ∼7 at% with traces of diffusion outwards into the grain interior.
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5.
  • Abrahamsson, Maria, 1975, et al. (författare)
  • High Extinction Coefficient Ru-Sensitizers that Promote Hole Transfer on Nanocrystalline TiO2
  • 2014
  • Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 15:6, s. 1154-1163
  • Tidskriftsartikel (refereegranskat)abstract
    • Two series of Ru-II polypyridyl compounds with formulas [(bpy)(2)RuL](PF6)(2) and [(deeb)(2)RuL](PF6)(2), where bpy is 2,2-bipyridine, deeb is 4,4-diethylester-2,2-bpy, and L is one of several substituted 9-(1,3-dithiole-2-ylidene)-4,5-diazafluorene ligands, were studied as potential photosensitizers for TiO2. These compounds possess notably high extinction coefficients (40000M(-1)cm(-1) @470 nm) which are shown by time-dependent density functional theory (TD-DFT) calculations to result from overlapping metal-to-ligand charge transfer (MLCT) and ligand-localized transitions. Low-temperature absorption and photoluminescence measurements were suggestive of a short-lived MLCT excited state. When adsorbed onto TiO2 thin films, both the free ligands (L) and their corresponding [(deeb)(2)RuL](2+) complexes exhibited rapid excited-state electron injection into TiO2; in the case of the complexes, this was followed by rapid (k>10(8) s(-1)) hole transfer from Ru-III to the 1,3-dithiole ring of the L ligand. Observation of diffusion-limited reductive quenching of the [Ru(bpz)(3)](2+)* (bpz is 2,2-bipyrazine) excited state by the L ligands in solution supported the occurrence of intramolecular hole transfer following electron injection by the TiO2-anchored complexes.
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6.
  • Abrahamsson, Maria, et al. (författare)
  • Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands.
  • 2008
  • Ingår i: Inorganic Chemistry. - : ACS. - 0020-1669 .- 1520-510X. ; 47:9, s. 3540-3548
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)-polypyridyl complexes based on the terpyridine-like ligands [6-(2,2'-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2'-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)(2)](2+)) and a heteroleptic complex ([Ru(ttpy)(2)](2+)) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)(2)](2+). The excited-state lifetime of the homoleptic Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic Ru-II complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central Ru-II ion less octahedral in [Ru(2)(2)](2+) than in [Ru(1)(2))(2+). Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (MLCT)-M-3 states to short-lived (MC)-M-3 states.
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7.
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8.
  • Addazi, A., et al. (författare)
  • New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the HIBEAM/NNBAR experiment at the European Spallation Source
  • 2021
  • Ingår i: Journal of Physics G. - : Institute of Physics Publishing (IOPP). - 0954-3899 .- 1361-6471. ; 48:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The violation of baryon number, , is an essential ingredient for the preferential creation of matter over antimatter needed to account for the observed baryon asymmetry in the Universe. However, such a process has yet to be experimentally observed. The HIBEAM/NNBAR program is a proposed two-stage experiment at the European Spallation Source to search for baryon number violation. The program will include high-sensitivity searches for processes that violate baryon number by one or two units: free neutron–antineutron oscillation () via mixing, neutron–antineutron oscillation via regeneration from a sterile neutron state (), and neutron disappearance (n → n'); the effective process of neutron regeneration () is also possible. The program can be used to discover and characterize mixing in the neutron, antineutron and sterile neutron sectors. The experiment addresses topical open questions such as the origins of baryogenesis and the nature of dark matter, and is sensitive to scales of new physics substantially in excess of those available at colliders. A goal of the program is to open a discovery window to neutron conversion probabilities (sensitivities) by up to three orders of magnitude compared with previous searches. The opportunity to make such a leap in sensitivity tests should not be squandered. The experiment pulls together a diverse international team of physicists from the particle (collider and low energy) and nuclear physics communities, while also including specialists in neutronics and magnetics.
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10.
  • af Hällström, Anna, 1987, et al. (författare)
  • The role of social ties in collaborative project networks: A tale of two construction cases
  • 2021
  • Ingår i: Construction Management and Economics. - : Informa UK Limited. - 1466-433X .- 0144-6193. ; 39:9, s. 723-738
  • Tidskriftsartikel (refereegranskat)abstract
    • Collaborative project delivery models (CPDMs) are increasing in popularity as infrastructure con-struction projects become more complex and grow in scale and scope. CPDMs build on highlevels of trust, information exchange and formal contractual relations, creating complex relation-ships between actors in the project network. The literature emphasizes the procurement phaseand contractual aspects of CPDMs; however, few studies explicitly focus on the role of socialrelationships in CPDM projects. Social network theory has recently been introduced in the archi-tecture, engineering and construction industry industry to study relationships between networkactors, but the role of social ties within CPDM project networks is still unclear. Through twoqualitative case studies, we have analyzed the role of social ties in projects applying a CPDMcontract. The empirical evidence of 41 semi-structured interviews and observations points toaspects that affect the development of social ties in CPDMs, such as initial project setup, projectidentification, perception of actors, resource sharing and shared space, as well as the importanceof formal and informal ties for supporting collaborative project practices. The evidence showshow social ties develop into negative or positive bonds affecting the level of collaboration. Thisstudy contributes by emphasizing the interplay between project networks using CPDMs andsocial ties.
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