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Träfflista för sökning "WFRF:(Agui A.) "

Sökning: WFRF:(Agui A.)

  • Resultat 1-26 av 26
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1.
  • Ho, Anna Y. Q., et al. (författare)
  • Cosmological Fast Optical Transients with the Zwicky Transient Facility : A Search for Dirty Fireballs
  • 2022
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 938:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Γinit below the Γinit ∼ 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g − r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day−1), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a γ-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three "orphan" events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in γ-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing γ-rays and the material producing early optical afterglow emission, finding that they must be comparable.
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2.
  • Eisebitt, S, et al. (författare)
  • Electronic structure of single-wall carbon nanotubes studied by resonant inelastic X-ray scattering
  • 1998
  • Ingår i: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING. - : SPRINGER VERLAG. - 0947-8396. ; 67:1, s. 89-93
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The electronic structure of single-wall nanotubes in "buckypaper" has been studied by using soft X-ray emission and resonant inelastic soft X-ray scattering. We observe electronic states derived from the K point and located close to E-F in the nanotubes,
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3.
  • Levan, Andrew J., et al. (författare)
  • A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy
  • 2023
  • Ingår i: Nature Astronomy. - 2397-3366. ; 7:8, s. 976-985
  • Tidskriftsartikel (refereegranskat)abstract
    • The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.
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4.
  • Magnuson, Martin, et al. (författare)
  • Electronic-structure investigation of CeB6 by means of soft-x-ray scattering
  • 2001
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:7, s. 075101-
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of the heavy fermion compound CeB6 is probed by resonant inelastic soft-x-ray scattering using photon energies across the Ce 3d and 4d absorption edges. The hybridization between the localized 4f orbitals and the delocalized valence-band states is studied by identifying the different spectral contributions from inelastic Raman scattering and normal fluorescence. Pronounced energy-loss structures are observed below the elastic peak at both the 3d and 4d thresholds. The origin and character of the inelastic scattering structures are discussed in terms of charge-transfer excitations in connection to the dipole allowed transitions with 4f character. Calculations within the single-impurity Anderson model with full multiplet effects are found to yield consistent spectral functions to the experimental data.
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5.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)
  • 1999
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 573-578
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.
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6.
  • Magnuson, Martin, 1965-, et al. (författare)
  • The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies
  • 1998
  • Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 237:3, s. 295-304
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and non-resonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the electron bands in line with symmetry selection and momentum conservation rules. The effect is most visual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of symmetry and are less frequency dependent.
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7.
  • Magnuson, Martin, 1965-, et al. (författare)
  • The electronic structure of polyaniline and doped phases studied by soft X-ray absorption and emission spectroscopies
  • 1999
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 111:10, s. 4756-4761
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant soft x-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant x-ray emission spectra show depletion of the π electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the x-ray emission spectra attributed to the π bands show unambiguous changes of the electronic structure upon protonation. By comparing to x-ray absorption measurements, the chemical bonding and electronic configuration is characterized.
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8.
  • Agui, A, et al. (författare)
  • Bulk and interface Al 2p core excitons in GaAs/AlAs/GaAs heterostructures
  • 1999
  • Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMERICAN PHYSICAL SOC. - 0163-1829. ; 59:16, s. 10792-10795
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Aluminum 2p soft-x-ray emission and absorption spectra (XES and XAS) of a GaAs/AIAs/GaAs heterostructure semiconductor have been measured with high-energy resolution. The Al 2p XES shows a similar feature to that of AlxGa1-xAs alloys. Strong Al 2p core ex
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9.
  • Agui, A, et al. (författare)
  • Direct observation of interface effects of thin AlAs(100) layers buried in GaAs
  • 2000
  • Ingår i: APPLIED SURFACE SCIENCE. - : ELSEVIER SCIENCE BV. - 0169-4332. ; 166:1-4, s. 309-312
  • Tidskriftsartikel (refereegranskat)abstract
    • A study of the electronic structure of ultrathin AlAs layers buried in GaAs(100) and their interfaces is presented. Al L-2,L-3 soft-X-ray-emission (SXE) spectra from the AlAs layers were measured. The spectra show distinct thickness-dependent features, wh
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10.
  • Agui, A., et al. (författare)
  • Direct observation of interface effects of thin AlAs(100) layers buried in GaAs
  • 2000
  • Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 166:1-4, s. 309-312
  • Tidskriftsartikel (refereegranskat)abstract
    • A study of the electronic structure of ultrathin AlAs layers buried in GaAs(100) and their interfaces is presented. Al L2,3 soft-X-ray-emission (SXE) spectra from the AlAs layers were measured. The spectra show distinct thickness-dependent features, which are reproduced using ab initio calculations.
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11.
  • Agui, A, et al. (författare)
  • Electronic structure of BP studied by resonant soft X-ray emission spectroscopy
  • 1999
  • Ingår i: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN. - : PHYSICAL SOCIETY JAPAN. - 0031-9015. ; 68:1, s. 166-169
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The B1s and P2p soft x-ray emission of BP has been measured using monochromatic synchrotron radiation as an excitation source. The band-gap, energy was estimated lu be about 2.1 eV which is in good agreement with other experiments. The emission bands whic
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12.
  • Agui, A, et al. (författare)
  • Resonant OK alpha emission spectra of CuGe0(3) single-crystal
  • 2001
  • Ingår i: SOLID STATE COMMUNICATIONS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-1098. ; 118:12, s. 619-622
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of CuGeO3 has been studied using soft X-ray absorption and emission spectroscopy. The unoccupied and occupied valence states are reflected by O 1s absorption and OK alpha emission spectra, respectively. An absorption pre-peak appe
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14.
  • Guo, JH, et al. (författare)
  • Spectroscopic study of CNx films grown by magnetron sputter deposition
  • 1999
  • Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 551-554
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The electronic structure of carbon nitride films has been studied using soft X-ray absorption and emission spectroscopy. Resonant N K-emission spectra show a strong dependence on excitation photon energies and the substrate temperatures, while C K-emissio
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15.
  • Hellgren, N., et al. (författare)
  • Nitrogen bonding structure in carbon nitride thin films studied by soft x-ray spectroscopy
  • 2001
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:26, s. 4348-4350
  • Tidskriftsartikel (refereegranskat)abstract
    • Soft x-ray absorption (SXAS) and emission (SXES) spectroscopies were applied to study the nitrogen bonding structure in magnetron sputtered CNx thin films. By comparing with calculated spectra of N in different model systems, N in three main bonding environments can be identified: (i) C equivalent toN bonds, with a sharp SXAS peak at 399.5 eV, (ii) pyridine-like N (i.e., N bonded to two C atoms), with an x-ray absorption resonance at similar to 398.5 eV, and (iii) N substituted in graphite, possibly with one sp(3) carbon as a neighbor (SXAS energy similar to 401 eV). These bondings are present in all CNx films analyzed; however, as shown earlier, the relative intensities between the peaks may vary with the growth conditions. Differences in the coordination of the nearest or second nearest C neighbors only cause slight changes in the peak positions and spectrum shape.
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16.
  • Hjorvarsson, B, et al. (författare)
  • Probing the local electronic structure in the H induced metal-insulator transition of Y
  • 1999
  • Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. ; 11, s. L119-
  • Tidskriftsartikel (refereegranskat)abstract
    • The occupied acid unoccupied valence band states of yttrium (Y) metal, Y dihydride and Y trihydride were measured by soft x-ray emission and absorption spectroscopy. The experiments were complemented by first principles calculations. Both experiments and
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17.
  • Inoue, K, et al. (författare)
  • Angular dependence of Al-2p X-ray yield spectra of GaAs/AlAs/GaAs heterostructures
  • 1999
  • Ingår i: JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS. - : JAPAN J APPLIED PHYSICS. - 0021-4922. ; 38, s. 572-575
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The X-ray emission yield by the Al-2p core-exciton excitation in GaAs/AlAs/GaAs heterostructures is studied theoretically: especially the angular correlation between absorbed and emitted X-rays are discussed. It becomes clear that the angular dependence o
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18.
  • Ma, YJ, et al. (författare)
  • Structural and electronic properties of low dielectric constant fluorinated amorphous carbon films
  • 1998
  • Ingår i: APPLIED PHYSICS LETTERS. - : AMER INST PHYSICS. - 0003-6951. ; 72:25, s. 3353-3355
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Fluorinated amorphous carbon (a-CFx) films were studied by high-resolution x-ray absorption, emission, and photoelectron spectroscopy. The composition and local bonding information were obtained and correlated with substrate temperature during deposition.
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21.
  • Mankefors, S., et al. (författare)
  • Theoretical investigation of the thickness dependence of soft-x-ray emission from thin AlAs(100) layers buried in GaAs
  • 2000
  • Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 61:8, s. 5540-5545
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrathin AlAs(100) layers of 1-, 2-, and 5-ML thickness buried in GaAs are investigated by ab initio calculations. Unique experimental soft-x-ray emission spectra are explained in terms of interface effects and changes with layer thickness are found in the density of states. Only the central layer in the 5-ML geometry is bulklike. A valence-band offset of 0.53 eV is also found for this structure, while no offset exists in the 1- and 2-ML cases. Very good agreement is achieved between theory and experiment.
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22.
  • Qian, L, et al. (författare)
  • Formation of titanium fulleride studied by x-ray spectroscopies
  • 1999
  • Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - 0163-1829. ; 59:19, s. 12667-12671
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The chemical interaction between titanium and C-60 in coevaporated titanium-fulleride films has been investigated by x-ray photoelectron spectroscopy, (XPS), x-ray absorption spectroscopy (XAS), and x-ray emission spectroscopy. Two titanium-fulleride film
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24.
  • Såthe, C., et al. (författare)
  • Resonant LII;III x-ray raman scattering from HCl
  • 2006
  • Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 74:6, s. 062512-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the spectral features of Cl LII,III resonant x-ray Raman scattering of HCl molecules in gas phase both experimentally and theoretically. The theory, formulated in the intermediate-coupling scheme, takes into account the spin-orbital and molecular-field splittings in the Cl 2p shells, as well as the Coulomb interaction of the core hole with unoccupied molecular orbitals. Experiment and theory display nondispersive dissociative peaks formed by decay transitions in both molecular and dissociative regions. The molecular and atomic peaks collapse in a single narrow resonance because the dissociative potentials of core-excited and final states are parallel to each other along the whole pathway of the nuclear wave packet.
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26.
  • Takata, Y., et al. (författare)
  • Valence excitations observed in resonant soft X-ray emission spectra of K2Ni(CN)4.H2O at the Ni 2p edge
  • 2001
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 114-116, s. 909-913
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant soft X-ray emission spectra have been measured at the Ni 2p edge of a planar nickel complex K2Ni(CN)4·H2O and interpreted by performing ab initio configuration interaction calculations. This cyano complex shows characteristic metal-to-ligand charge transfer (MLCT) bands in the Ni 2p photoabsorption spectra. Resonant soft X-ray emission via the MLCT intermediate states can be interpreted as valence MLCT excitations within a one-electron picture. On the other hand, resonant soft X-ray emission via the intra-atomic Ni 2p–3d intermediate state corresponding to the white line excitation shows significant electron correlation effects.
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