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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, a forward reconvolution fit procedure based on a microscopic incoherent transport model, including diagonal disorder, dipolar intersite coupling, and a density-of-states (DOS) of molecular site excitations, is presented.
Abstract: Exciton relaxation in poly(phenylenevinylene), PPV, has been probed by femtosecond luminescence-up-conversion. We report on excitonic luminescence profiles that depend on the spectral position of the detection window (e=2.7,2.6,2.5, and 2.4 eV, respectively). In an attempt to reveal the transient steps implied in fs relaxation, we present a quantitative forward reconvolution fit procedure that is based on a microscopic incoherent transport model, including diagonal disorder, dipolar intersite coupling, and a density-of-states (DOS) of molecular site excitations. Special emphasis has been placed (i) on the analysis of luminescence lifetime distributions 〈φ(τ;e,τ0)〉 which directly map out the spectra of hopping modes of energy-cascading neutral excitations, and (ii) on the rigorous evaluation of (radiationless) transfer population from high-energy subensembles to low-energy tail states of the DOS. We quantitatively show that the absence of significant rise terms in the S0ν=0←S1ν=0 luminescence transition ...

129 citations

Journal ArticleDOI
TL;DR: In this paper, a theory for finding a certain average width of each composite hyperfine line in terms of the inner products of the tensors was given, where the anisotropy of the g tensor and the nuclear hyperfine tensors is the dominant cause of relaxation.
Abstract: The hyperfine lines in the electron resonance spectra of radicals in solution can show marked variations in width, and each line may itself be a sum of Lorentzian components with different relaxation times. In radicals of spin ½, where the anisotropy of the g tensor and the nuclear hyperfine tensors is the dominant cause of relaxation, a theory is given for finding a certain average width of each composite hyperfine line in terms of the inner products of the tensors. The width varies both linearly and quadratically with nuclear spin quantum numbers in a way which agrees qualitatively with previous work by Kivelson. Spectra of several aromatic radicals agree with the theory. The calculations use operator methods based on Bloch’s master equation for the spins. In the simpler problem of relaxation by dipolar electron spin-spin coupling in triplet, quartet, or higher spin states the operator method gives a complete description of the composite line shapes.

129 citations

Journal ArticleDOI
TL;DR: In the absence of paramagnetic impurities, surface relaxivities of quartz sand and silica gel samples of known porosity and surface area at any pH were lower than any previously reported values.

129 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the longest relaxation times of polymer solutions of semi-flexible T4 DNA and flexible 18 M molar mass polyacrylamide (PAAm) in dilute and semi-dilute concentration range.
Abstract: The longest relaxation times of polymer solutions of semi-flexible T4 DNA and flexible 18 M molar mass polyacrylamide (PAAm) in dilute and semi-dilute concentration range are studied by the polymer extension relaxation of stretched single DNA molecules and by the stress relaxation of PAAm solutions measurements. For both polymer solutions, the longest relaxation time normalized by the value at infinite dilution with the same solvent viscosity τ/τ0 increases with increasing concentration. In the dilute regime, the longest relaxation time increases just slightly with increasing concentration as τ/τ0=[1+cA−2(cA)1.5+2(cA)2] as well as the empirical relation of τ/τ0=exp(cA) up to c∼3c∗ with A≈0.5[η], where c∗ is the overlap concentration, in accord with the theory and previous experiments. For the semi-dilute solutions, the scaling of τ/τ0 with concentration shows two different exponents in two concentration regions, corresponding to the unentangled and entangled regimes. The exponents are consistent with thos...

129 citations

Journal ArticleDOI
TL;DR: The steady state of a finite XX chain coupled at its boundaries to quantum reservoirs made of free spins that interact one after the other with the chain is studied and it is shown that the steady state can be described by a generalized Gibbs state.
Abstract: We study the steady state of a finite XX chain coupled at its boundaries to quantum reservoirs made of free spins that interact one after the other with the chain. The two-point correlations are calculated exactly, and it is shown that the steady state is completely characterized by the magnetization profile and the associated current. Except at the boundary sites, the magnetization is given by the average of the reservoirs' magnetizations. The steady-state current, proportional to the difference in the reservoirs' magnetizations, shows a nonmonotonic behavior with respect to the system-reservoir coupling strength, with an optimal current state for a finite value of the coupling. Moreover, we show that the steady state can be described by a generalized Gibbs state.

129 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202227
2021652
2020582
2019614
2018638
2017645