Relaxation time robustness

Bain A D and Duns G J 1994 Simultaneous determination of spin-lattioe (T1) and spin-spin (T2) relaxation times in NMR a robust and faoile method for measuring T2. Optimization and data analysis of the offset-saturation experiment J. Magn. Reson. A 109 56-64... 

The usefulness of NMR in such analysis is because the proton spin-relaxation time constants are different for different components, such as water, liquid fat and solid fat. For example, the signal from solid fat is found to decay rapidly while the liquid signals decay much slower. This phenomenon is the basis for an NMR technique to determine the solid fat content [20], However, as the relaxation time constant of water, for example, could depend on its local environment, such as protein concentration, it may overlap with that of oil and other components. As a result, it could be difficult to formulate a robust and universal relaxation analysis. It... 

Another general effect observed for a cycle is robustness of stationary rate and relaxation time. For multiscale systems with random constants, the standard deviation of constants that determine stationary rate (the smallest constant for a cycle) or relaxation time (the second in order constant) is approximately n times smaller than the standard deviation of the individual constants (where n is the cycle length). Here we deal with the so-called order statistics. This decrease of the deviation as n is much faster than for the standard error summation, where it decreases with increasing n as... 

Ensembles of cycles and robustness of stationary rate and relaxation time... 

Table 19.3 Examples of human in vivo 19F relaxation times. While T2 relaxation times are relatively consistent, in vivo T, values (e.g., for fluoxetine and FBAL) vary considerably, indicating the difficulty of implementing a robust T1 measurement method with low signal levels and broad spectral linewidths... 

One approximation that has proven to be surprisingly robust treats the solvent as a time-averaged continuum. On the time scale of interest, nanoseconds to microseconds, the discreteness of the bulk solvent, which has a relaxation time on the order of second, is lost in a blur of motion. To a... 

A typical 3-4 mM 0.50 ml sample on a modem 500 MHz spectrometer may require 6-12 hr for an informative TOCS Y or NOESY map. Measurement of steady-state NOEs generally require less than 1 hr of spectrometer time. Considering the range of relaxation times that are encountered and the need for optimizing parameters for each range of T values, between 6 and 10 2D maps are required to achieve a reasonably robust stmcture by 2D NMR, while the sequence-specific assignment of the cluster ligand could be achieved on the basis of as few as 3 or 4 2D maps. 

To optimize force fields for long time scale motions Aliev et al. propose a new robust approach to use NMR spin-lattice relaxation times Ti of both backbone and sidechain carbons. This allows a selective determination of both overall molecular and intramolecular motional time scales. In addition they use motionally averaged experimental/ coupling constants for torsional FF parameters. The force constants in the FFs and the correlation times are fitted in an Arrhenius-type of equation. 

Figure 3 The collapse of the peptide Ace-Nle30-Nme under deeply quenched poor solvent conditions monitored by both radius of gyration (Panel A) and energy relaxation (Panel B). MC simulations were performed in dihedral space 81% of moves attempted to change angles, 9% sampled the w angles, and 10% the side chains. For the randomized case (solid line), all angles were uniformly sampled from the interval —180° to 180° each time. For the stepwise case (dashed line), dihedral angles were perturbed uniformly by a maximum of 10° for 4>/ / moves, 2° for w moves, and 30° for side-chain moves. In the mixed case (dash-dotted line), the stepwise protocol was modified to include nonlocal moves with fractions of 20% for 4>/ J/ moves, 10% for to moves, and 30% for side-chain moves. For each of the three cases, data from 20 independent runs were combined to yield the traces shown. CPU times are approximate, since stochastic variations in runtime were observed for the independent runs. Each run comprised of 3 x 107 steps. Error estimates are not shown in the interest of clarity, but indicated the results to be robust.

Several other formal features of Huxley s trance condition are of interest with respect to the analogy we have drawn with REM sleep dreaming. We first consider the relaxed posture, indicating a step on the path to cataplexy. In full-blown cataplexy, the assumption of a flaccid posture is associated with the inability to move on command and is thus similar to the active motor paralysis of REM sleep dreams. Anesthesia and amnesia were both present in Huxley s trance, although they tended to be selective, and when Huxley attempted to make them global, his trance deepened. Time distortion, a distinctive component of the orientational instability of dreams, was a robust aspect of Huxley s altered state. 

The first optical laser, the ruby laser, was built in 1960 by Theodore Maiman. Since that time lasers have had a profound impact on many areas of science and indeed on our everyday lives. The monochromaticity, coherence, high-intensity, and widely variable pulse-duration properties of lasers have led to dramatic improvements in optical measurements of all kinds and have proven especially valuable in spectroscopic studies in chemistry and physics. Because of their robustness and high power outputs, solid-state lasers are the workhorse devices in most of these applications, either as primary sources or, via nonlinear crystals or dye media, as frequency-shifted sources. In this experiment the 1064-mn near-infrared output from a solid-state Nd YAG laser will be frequency doubled to 532 nm to serve as a fast optical pump of a raby crystal. Ruby consists of a dilute solution of chromium 3 ions in a sapphire (AI2O3) lattice and is representative of many metal ion-doped solids that are useful as solid-state lasers, phosphors, and other luminescing materials. The radiative and nonradiative relaxation processes in such systems are important in determining their emission efficiencies, and these decay paths for the electronically excited Cr ion will be examined in this experiment. 

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