Topic
Relaxation (NMR)
About: Relaxation (NMR) is a research topic. Over the lifetime, 29342 publications have been published within this topic receiving 689851 citations.
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TL;DR: In this article, the authors studied the vibrational energy exchange relative to the rate of energy transfer from translational to vibrational degrees of freedom in a shock-heated mixture of 1% CO and 99% N2.
Abstract: The vibrational energy exchange N2(v=1)+CO(v=0)=N2(v=0)+CO(v=1) should be fast, due to near resonance of the energy levels. We have studied the rate of this exchange relative to the rate of energy transfer from translational to vibrational degrees of freedom in a shock‐heated mixture of 1% CO—99% N2. Vibrational relaxation of the CO is observed by its infrared emission near 2000 cm—1. The density change behind the incident shock is simultaneously observed with an interferometer and gives a measurement of the N2 relaxation time. In the 3200°—4200°K range both methods are applicable; they yield identical relaxation times within the data scatter of ±20%. In contrast, at 3600°K, the vibrational relaxation time of pure N2 is four times that of pure CO. The exchange reaction thus appears fast enough to make the vibrational temperatures of the N2 and CO equal during the vibrational relaxation of the mixture. In the 1900° to 5400°K range, our study gives vibrational relaxation times in seconds for pure N2 (p=1 at...
144 citations
TL;DR: In this paper, the bilinear calibration method was used to correct the permittivity spectra and the corrected spectra could be fitted with a single relaxation time with a small amount of Cole-Davidson behaviour.
Abstract: Dielectric relaxation measurements in the frequency range 10 MHz–10 GHz have been carried out in tert-butyl alcohol–water mixtures with various concentrations over the temperature range 273–313 K using a time-domain reflectometry (TDR) method. The bilinear calibration method as suggested by Cole has been used to correct the permittivity spectra. The corrected spectra could be fitted with a single relaxation time with a small amount of Cole–Davidson behaviour. Deviations from ideal mixing behaviour in the permittivity parameter (Iµo–Iµ∞) and relaxation time (τ) suggested the formation of a polymeric structure in tert-butyl alcohol–water mixtures. The dielectric relaxation behaviour showed the same structural changes as observed in ultrasonic relaxation. However, the maxima in excess permittivity and excess relaxation time occurred at different positions. This could not be explained by a simple model of the polymeric structure.
143 citations
TL;DR: In this article, the superparamagnetic relaxation was analyzed on the basis of the Neel-Brown expression for the relaxation time, τ = τ 0 exp[KV/kT], and the value of τ0 increases with increasing particle volume, whereas the magnetic anisotropy energy constant, K, decreases.
Abstract: Samples of nanoparticles of hematite (α-Fe2O3) with average size between 6 and 27 nm have been studied by use of Mossbauer spectroscopy. The superparamagnetic relaxation was analysed on the basis of the Neel-Brown expression for the relaxation time, τ = τ0 exp[KV/kT]. It was found that the value of τ0 increases with increasing particle volume, V, whereas the magnetic anisotropy energy constant, K, decreases. The electric quadrupole interaction, the isomer shift and the magnetic hyperfine field extrapolated to 0 K were found to be essentially independent of particle size.
143 citations
TL;DR: In this paper, the authors derived closed-form solutions to the relaxation oscillation (resonance) frequency and damping term, as well as the low-frequency damping terms, and discussed design rules for maximizing resonance frequency and broadband performance.
Abstract: The modulation response of injection-locked lasers has been carefully analyzed, theoretically and experimentally, with a focus on the strong optical injection regime. We derive closed-form solutions to the relaxation oscillation (resonance) frequency and damping term, as well as the low-frequency damping term, and discuss design rules for maximizing resonance frequency and broadband performance. A phasor model is described in order to better explain the enhancement of the resonance frequency. Experimental curves match closely to theory. Record resonance frequency of 72 GHz and broadband results are shown.
143 citations
TL;DR: It is found in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T1ρ dispersion, in the context of the model used to interpret the relaxation data.
Abstract: Magnetic relaxation has been used extensively to study and characterize biological tissues. In particular, spin-lattice relaxation in the rotating frame (T1ρ) of water in protein solutions has been demonstrated to be sensitive to macromolecular weight and composition. However, the nature of the contribution from low frequency processes to water relaxation remains unclear. We have examined this problem by studying the water T1ρ dispersion in peptide solutions (14N- and 15N-labeled), glycosaminoglycan solutions, and samples of bovine articular cartilage before and after proteoglycan degradation. We find in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T1ρ dispersion, in the context of the model used to interpret the relaxation data. Further, low frequency dispersion changes are correlated with loss of proteoglycan from the extra-cellular matrix of articular cartilage. This finding has significance for the noninvasive detection of matrix degradation.
143 citations