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Absorption (logic)

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


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TL;DR: The Mossbauer effect in metallic iron has been studied from 4 to 1300\ifmmode^\circ\else\text degree\fi{}K, with particular emphasis on the region near the Curie temperature at 1043
Abstract: The M\"ossbauer effect in metallic iron has been studied from 4 to 1300\ifmmode^\circ\else\textdegree\fi{}K, with particular emphasis on the region near the Curie temperature at 1043\ifmmode^\circ\else\textdegree\fi{}K.Measurements of the internal field ${H}_{n}$ at the nucleus agree with nuclear magnetic resonance measurements and follow closely, but not exactly, the saturation magnetization curve of iron. No internal field is observed above the Curie temperature. At room temperature ${H}_{n}=330\ifmmode\pm\else\textpm\fi{}3$ kOe. The ratio of magnetic moments of the two lowest levels of ${\mathrm{Fe}}^{57}$ is $\frac{{\ensuremath{\mu}}_{1}}{{\ensuremath{\mu}}_{0}}=\ensuremath{-}1.715\ifmmode\pm\else\textpm\fi{}0.004$.The observed temperature shift in the energy of the resonant radiation may be attributed chiefly to relativistic time dilation. In the low-temperature region the variation is nonlinear and compatible with a Debye temperature $\ensuremath{\theta}=400\ifmmode\pm\else\textpm\fi{}30\ifmmode^\circ\else\textdegree\fi{}$ K, although the data indicate that $\ensuremath{\theta}$ is not strictly independent of temperature. At high temperatures, the classical limit $\frac{(\frac{1}{E})\ensuremath{\partial}E}{\ensuremath{\partial}T}=\ensuremath{-}\frac{3k}{2M{c}^{2}}$ for the relativistic shift is attained and perhaps exceeded. Disagreement with the classical limit would indicate a temperature variation in the isomer shift. At the Curie point and at the transition from $\ensuremath{\alpha}$ to $\ensuremath{\gamma}$ iron, the discontinuities observed in the temperature shift are too great to be attributed to the relativistic shift. If attributed to the isomer shift, these discontinuities indicate that the electron density at the nucleus increases at the transitions from the ferromagnetic to the paramagnetic state and from $\ensuremath{\alpha}$ to $\ensuremath{\gamma}$ iron.The strength of the resonant absorption was also determined as a function of temperature. These measurements are compatible with a Debye temperature that falls from about 400 to 300\ifmmode^\circ\else\textdegree\fi{}K in passing from low to high temperatures over the range studied.

412 citations

Journal ArticleDOI
TL;DR: In this article, a time-dependent analysis of four-wave mixing in an ultraslow-propagation regime was performed and the authors obtained the analytical expressions of pulsed probe laser, FWM-generated pulse, phase shifts and absorption coefficients, group velocities, and FWM efficiency.
Abstract: We perform a time-dependent analysis of four-wave mixing (FWM) in a double-$\ensuremath{\Lambda}$ system in an ultraslow-propagation regime and obtain the analytical expressions of pulsed probe laser, FWM-generated pulse, phase shifts and absorption coefficients, group velocities, and FWM efficiency. With these analytical expressions, we show that an efficiently generated FWM field can acquire the same ultraslow group velocity $({V}_{g}∕c\ensuremath{\sim}{10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}5})$ and pulse shape of a probe pump and that the maximum FWM efficiency is greater than 25%, which is orders of magnitude larger than previous FWM schemes in the ultraslow-propagation regime.

402 citations

Journal ArticleDOI
TL;DR: It is suggested that the enhancement of the scattering cross section, which scales with the observed optical-absorption coefficient and diffuse elastic light scattering, is due to enhanced coupling of the electromagnetic field of the incident light to the charge-density fluctuations at the grain boundaries of the quasi-isolated crystallites.
Abstract: The intensity of the Raman-active ${\ensuremath{\Gamma}}_{25\mathcal{'}}$ mode of nanometer-sized crystalline silicon, nc-Si, normalized to that of calcium fluoride, ${\mathrm{CaF}}_{2}$, at 322 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was measured for samples deposited under controllably varied conditions. Changes of the intensity by a factor of up to approximately 6.7 were found. These are correlated with the lattice expansion and with the compressive stress in thin films of the material. It is suggested that the enhancement of the scattering cross section, which scales with the observed optical-absorption coefficient and diffuse elastic light scattering, is due to enhanced coupling of the electromagnetic field of the incident light to the charge-density fluctuations at the grain boundaries of the quasi-isolated crystallites.

397 citations

Journal ArticleDOI
TL;DR: In this article, a least squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression for the P-T dependence of Ti-in-quartz solubility, where R is the gas constant 8.3145 J/K, T is temperature in Kelvin, and M is the mole fraction of TiO2 in quartz.
Abstract: Quartz and rutile were synthesized from silica-saturated aqueous fluids between 5 and 20 kbar and from 700 to 940°C in a piston-cylinder apparatus to explore the potential pressure effect on Ti solubility in quartz. A systematic decrease in Ti-in-quartz solubility occurs between 5 and 20 kbar. Titanium K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that Ti4+ substitutes for Si4+ on fourfold tetrahedral sites in quartz at all conditions studied. Molecular dynamic simulations support XANES measurements and demonstrate that Ti incorporation onto fourfold sites is favored over interstitial solubility mechanisms. To account for the P–T dependence of Ti-in-quartz solubility, a least-squares method was used to fit Ti concentrations in quartz from all experiments to the simple expression $$ RT\ln X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} = - 60952 + 1.520 \cdot T(K) - 1741 \cdot P(kbar) + RT\ln a_{{{\text{TiO}}_{ 2} }} $$ where R is the gas constant 8.3145 J/K, T is temperature in Kelvin, $$ X_{{{\text{TiO}}_{ 2} }}^{\text{quartz}} $$ is the mole fraction of TiO2 in quartz and $$ a_{{{\text{TiO}}_{ 2} }} $$ is the activity of TiO2 in the system. The P–T dependencies of Ti-in-quartz solubility can be used as a thermobarometer when used in combination with another thermobarometer in a coexisting mineral, an independent P or T estimate of quartz crystallization, or well-constrained phase equilibria. If temperature can be constrained within ±25°C, pressure can be constrained to approximately ±1.2 kbar. Alternatively, if pressure can be constrained to within ±1 kbar, then temperature can be constrained to approximately ±20°C.

395 citations

Journal ArticleDOI
TL;DR: The absorption spectrum of NiO has been measured in the 0.1 to 6 ev range and its reflectivity spectrum from 0.025 to 10 ev as mentioned in this paper, showing a series of lines from 1 to 3.5 ev arising from internal transitions of the Ni ion.
Abstract: The absorption spectrum of single crystal NiO has been measured in the 0.1 to 6 ev range and its reflectivity spectrum from 0.025 to 10 ev. The absorption spectrum shows a series of lines from 1 to 3.5 ev arising from internal transitions of the Ni ion. A continuous background absorption occurs in the range from 0.1 to 3.5 ev whose magnitude increases with impurity concentration. The absorption coefficient rises steeply above 3.5 ev and reaches a value of ${10}^{6}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at and above 4 ev. An absorption line at 0.24 ev is found to be temperature sensitive in both intensity and frequency in the range above 300\ifmmode^\circ\else\textdegree\fi{}K. Its behavior suggests that it is connected with the antiferromagnetic ordering. The reststrahlen spectrum was observed with the following parameters: high- and low-frequency dielectric constants 5.4 and 12, respectively; energies of longitudinal and transverse optical mode vibrations are 0.076 and 0.044 ev, respectively.

393 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2021290
2020249
2019220
2018230
2017162
2016163