Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Three-dimensional supernova explosion simulations of 9-, 10-, 11-, 12-, and 13-M⊙ stars

Abstract: Using the new state-of-the-art core-collapse supernova (CCSN) code F{\sc{ornax}}, we have simulated the three-dimensional dynamical evolution of the cores of 9-, 10-, 11-, 12-, and 13-M$_{\odot}$ stars from the onset of collapse. Stars from 8-M$_{\odot}$ to 13-M$_{\odot}$ constitute roughly 50% of all massive stars, so the explosive potential for this mass range is important to the overall theory of CCSNe. We find that the 9-, 10-, 11-, and 12-M$_{\odot}$ models explode in 3D easily, but that the 13-M$_{\odot}$ model does not. From these findings, and the fact that slightly more massive progenitors seem to explode \citep{vartanyan2019}, we suggest that there is a gap in explodability near 12-M$_{\odot}$ to 14-M$_{\odot}$ for non-rotating progenitor stars. Factors conducive to explosion are turbulence behind the stalled shock, energy transfer due to neutrino-matter absorption and neutrino-matter scattering, many-body corrections to the neutrino-nucleon scattering rate, and the presence of a sharp silicon-oxygen interface in the progenitor. Our 3D exploding models frequently have a dipolar structure, with the two asymmetrical exploding lobes separated by a pinched waist where matter temporarily continues to accrete. This process maintains the driving neutrino luminosty, while partially shunting matter out of the way of the expanding lobes, thereby modestly facilitating explosion. The morphology of all 3D explosions is characterized by multiple bubble structures with a range of low-order harmonic modes. Though much remains to be done in CCSN theory, these and other results in the literature suggest that, at least for these lower-mass progenitors, supernova theory is converging on a credible solution.

Pressure effects on the electronic and optical properties of A WO 4 wolframites ( A = Cd, Mg, Mn, and Zn): The distinctive behavior of multiferroic MnWO 4

Abstract: The electronic band-structure and band-gap dependence on the $d$ character of ${A}^{2+}$ cation in $A$WO${}_{4}$ wolframite-type oxides is investigated for different compounds ($A$ $=$ Mg, Zn, Cd, and Mn) by means of optical-absorption spectroscopy and first-principles density-functional calculations. High pressure is used to tune their properties up to 10 GPa by changing the bonding distances establishing electronic to structural correlations. The effect of unfilled $d$ levels is found to produce changes in the nature of the band gap as well as its pressure dependence without structural changes. Thus, whereas Mg, Zn, and Cd, with empty or filled $d$ electron shells, give rise to direct and wide band gaps, Mn, with a half-filled $d$ shell, is found to have an indirect band gap that is more than 1.6 eV smaller than for the other wolframites. In addition, the band gaps of MgWO${}_{4}$, ZnWO${}_{4}$, and CdWO${}_{4}$ blue-shift linearly with pressure, with a pressure coefficient of approximately 13 eV/GPa. However, the band gap of multiferroic MnWO${}_{4}$ red-shifts at \ensuremath{-}22 meV/GPa. Finally, in MnWO${}_{4}$, absorption bands are observed at lower energy than the band gap and followed with pressure based on the Tanabe-Sugano diagram. This study allows us to estimate the crystal-field variation with pressure for the MnO${}_{6}$ complexes and how it affects their band-gap closure.

Anomalous Collision-Free Multiple Ionization of Atoms with Intense Picosecond Ultraviolet Radiation

Abstract: Collisionless multiphoton absorption, resulting in multiple atomic ionization and exhibiting anomalously strong coupling, has been studied in the region spanning atomic number $Z=2$ (He) to $Z=92$ (U). The highest ion state identified is ${\mathrm{U}}^{10+}$, corresponding to absorption of 99 quanta (\ensuremath{\sim}633 eV). Models of stepwise ionization using standard theoretical techniques are incapable of describing these results. A mode of interaction involving radiative coupling to a collective motion of an atomic shell is proposed.

Excited-state absorption spectroscopy of Er 3 + -doped Y 3 Al 5 O 12 , YVO 4 , and phosphate glass

Abstract: The spectra of excited-state absorption (ESA) and stimulated-emission (SE) cross sections of ${\mathrm{Er}}^{3+}$ in ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12},$ ${\mathrm{YVO}}_{4},$ and phosphate glass have been registered between 0.4 and 3 \ensuremath{\mu}m with a pump and probe technique. The experimental setup, based on the use of cw light sources, is described in detail. The incidence of ESA on the laser properties of these ${\mathrm{Er}}^{3+}$-doped oxide hosts is evaluated particularly around 0.55, 1.6, and 2.8 \ensuremath{\mu}m, corresponding to the ${}^{4}{\mathrm{S}}_{3/2}{\ensuremath{\rightarrow}}^{4}{\mathrm{I}}_{15/2},$ ${}^{4}{\mathrm{I}}_{13/2}{\ensuremath{\rightarrow}}^{4}{\mathrm{I}}_{15/2},$ and ${}^{4}{\mathrm{I}}_{11/2}{\ensuremath{\rightarrow}}^{4}{\mathrm{I}}_{13/2}$ laser transitions, respectively. The migration $[{(}^{4}{\mathrm{I}}_{13/2}{,}^{4}{\mathrm{I}}_{15/2}{)\ensuremath{\rightarrow}(}^{4}{\mathrm{I}}_{15/2}{,}^{4}{\mathrm{I}}_{13/2})]$ and up-conversion $[{(}^{4}{\mathrm{I}}_{13/2}{,}^{4}{\mathrm{I}}_{13/2}{)\ensuremath{\rightarrow}(}^{4}{\mathrm{I}}_{9/2}{,}^{4}{\mathrm{I}}_{15/2})]$ energy transfers involved in some laser operations are analyzed by deducing the energy-transfer microparameters ${C}_{\mathrm{DD}}$ and ${C}_{\mathrm{DA}}$ from ESA and SE measurements. The Judd-Ofelt analysis, usually applied from the ground-state manifold, is then used to evaluate the ESA integrated cross sections and these calculated cross sections are found equal to the measured ones within about 20%.

Paramagnetic Resonance and Optical Spectra of Divalent Iron in Cubic Fields. II. Experimental Results

Abstract: The paramagnetic resonance absorption of ${\mathrm{Fe}}^{2+}$ in MgO is observed at $g=3.428 \mathrm{and} 6.86$. The optical absorption line is found at 10 000 ${\mathrm{cm}}^{\ensuremath{-}1}$. The paramagnetic resonance spectrum indicates considerable covalent bonding. The origin of the line at 6.86 is discussed.In tetrahedral ZnS a paramagnetic line is found at $g=2.25$ and optical absorption at 3 \ensuremath{\mu} and 0.7 \ensuremath{\mu}. Possible explanations of this spectrum are discussed.A short discussion of the optical absorption spectra of trivalent iron in MgO is presented.