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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: This review focuses on the use of solid-state NMR techniques for the characterization of pharmaceutical solids (drug substance and dosage form) through methods for studying structure and conformation, analyzing molecular motions, and measuring internuclear distances.
209 citations
TL;DR: The decay of the spin polarization within 1 ps is observed, which is associated with the hot carrier spin relaxation time in Au, and this is explained by a competition of ballistic and diffusive propagation considering energy-dependent hot carrier relaxation rates.
Abstract: Hot carrier-induced spin dynamics is analyzed in epitaxial Au=Fe=MgOð001Þ by a time domain approach. We excite a spin current pulse in Fe by 35 fs laser pulses. The transient spin polarization, which is probed at the Au surface by optical second harmonic generation, changes its sign after a few hundred femtoseconds. This is explained by a competition of ballistic and diffusive propagation considering energy-dependent hot carrier relaxation rates. In addition, we observe the decay of the spin polarization within 1 ps, which is associated with the hot carrier spin relaxation time in Au.
209 citations
TL;DR: In this paper, the authors investigated the relaxation problem for the hydrodynamic isentropic Euler-Poisson system when the momentum relaxation time tends to zero and obtained very sharp estimates on the solutions, independent of the relaxation time.
Abstract: We investigate the relaxation problem for the hydrodynamic isentropic Euler-Poisson system when the momentum relaxation time tends to zero. Very sharp estimates on the solutions, independent of the relaxation time, are obtained and used to establish compactness.
209 citations
TL;DR: In this article, the strongest resonances, those at 222 and 417 kv, were found to have a mean energy of 1.5 Mev or less, and it was concluded that these resonances probably belong to reaction (1).
Abstract: Curran and Strothers, found resonances in reaction (3) at 290, 314, 336, 388, 430, 451, and 494 kv, and resonances at 222, 310, 392, 417, 492, 508, and 525 kv accompanied by positron activity. Finding the y-radiation from the strongest of the latter resonances, those at 222 and 417 kv, to have a mean energy of 1.5 Mev or less, he concluded that these resonances probably belong to reaction (1). To solve this problem targets of separated Mg isotopes have been prepared in the isotope separator of the Nobel Institute in Stockholm, 4 and exposed to protons from the 500 kv van de GraafF machine of the University of Oslo. The thickness of the targets was about 35 pg/cd Mgs4, for Mg~s and Mge the isotopic quantities corresponded to twice the amount of Mg\". The targets were bombarded for 20 sec., giving saturation intensity of the positron activity, and the positrons escaping through a thin window in the target tube were counted for 15 sec. with a thinwalled G-M tube. As the proton current at present does not exceed 2 pA, only the strong resonances at 222 and 417 kv could be investigated. Positron activity corresponding to these resonances was found only on the Mg\" target, showing that the reaction Mgs4(p, y}AP' is that actually taking place. Of course, there may also be resonances yielding positrons from the Mg\" reaction, such as suggested by Curran and Strothers.
209 citations
TL;DR: The magnetic field dependence of the T1 and T2 relaxation times suggests that the spectral density contribution from fast internal motions is not negligible, and that the chemical shift anisotropy of peptide backbone amides, on average, is larger than the 160 ppm value commonly used in 15N relaxation studies of proteins.
Abstract: 15N NMR relaxation times in perdeuterated HIV-1 protease, complexed with the sub-nanomolar inhibitor DMP323, have been measured at 600 and 360 MHz 1H frequency. The relative magnitudes of the principal components of the inertia tensor, calculated from the X-ray coordinates of the protein-drug complex, are 1.0:0.85:0.44. The relation between the T1/T2 ratios observed for the individual backbone amides and their N-H orientation within the 3D structure of the protease dimer yields a rotational diffusion tensor oriented nearly collinear to the inertia tensor. The relative magnitudes of its principal components (1.00:1.11:1.42) are also in good agreement with hydrodynamic modeling results. The orientation and magnitude of the diffusion tensors derived from relaxation data obtained at 360 and 600 MHz are nearly identical. The anisotropic nature of the rotational diffusion has little influence on the order parameters derived from the 15N T1 and T2 relaxation times; however, if anisotropy is ignored, this can result in erroneous identification of either exchange broadening or internal motions on a nanosecond time scale. The average ratio of the T1 values measured at 360 and 600 MHz is 0.50 +/- 0.015, which is slightly larger than the value of 0.466 expected for an isotropic rigid rotor with tau c = 10.7 ns. The average ratio of the T2 values measured at 360 and 600 MHz is 1.14 +/- 0.04, which is also slightly larger than the expected ratio of 1.11. This magnetic field dependence of the T1 and T2 relaxation times suggests that the spectral density contribution from fast internal motions is not negligible, and that the chemical shift anisotropy of peptide backbone amides, on average, is larger than the 160 ppm value commonly used in 15N relaxation studies of proteins.
208 citations