Dynamic Relaxation Time Research Articles

Magnetic Double Resonance Spectrometer for Dynamic Nuclear Polarization and Relaxation Time Measurements at 175 G

A magnetic nuclear-electron double resonance spectrometer operating in magnetic fields of about 175 G is described. It is suited for measurements of dynamic nuclear polarization and relaxation times in proton and fluorine containing solvents. The NMR spectrometer is a Q-meter device synchronized by a crystal oscillator. The uhf setup for the saturation of the ESR lines consists of a frequency multiplied driver stage and a 493 Mc power stage. The sample is placed inside a quarter wavelength coaxial cavity with the NMR coil around it. A rapid modulation technique allows u-mode detection and convenient comparison of NMR signals with and without ESR irradiation. The nuclear relaxation times (T2) are measured by observing the decay of the magnetization brought into the x,y plane by an adiabatic passage in the presence of a strong rf field. The performance is demonstrated with examples of proton polarization studies in organic solutions of free radicals.

Irreversibility in Small Stellar Dynamical Systems.

view Abstract Citations (157) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Irreversibility in Small Stellar Dynamical Systems. Miller, R. H. Abstract Irreversibility in stellar dynamical systems was studied by means of numerical experiments using n-body calculations carried out in a computer for n up to 32. In the experiments, two similar systems evolve simultaneously and the separation of their representative points in phase space was observed to grow exponentially with the time variable because of the effects of encounters. The time constant of this exponential growth defines a relaxation time different from the usual relaxation time of stellar dynamics. Certain properties of the calculation and comparisons of the observed values of this relaxation time with values expected on the basis of binary collisions led to the conclusion that n-body systems with inverse-square law forces behave as tightly coupled systems. The time constant is surprisingly short- about 4r/n, where r is the mean time between binary collisions of one particle. Hard spheres or potentials do not show the collective behavior of inverse-square law systems. Errors in calculations of n-body systems grow exponentially with the time through this mechauism, and may therefore invalidate the results of n-body calculations. Publication: The Astrophysical Journal Pub Date: July 1964 DOI: 10.1086/147911 Bibcode: 1964ApJ...140..250M full text sources ADS |