Critical Narrowing Research Articles

Mean-field calculation of the central peak due to the phonon-Ising dynamic crossover

A self-consistent numerical calculation of the onset of the central mode in a phonon phi/sup 4/ field theory, for T > T/sub c/, has been carried out. The central mode is attributed to crossover to Ising-like tunneling behavior, which is driven by indirect coupling to a collective excitation, corresponding to damped or overdamped second sound. Under the restrictive assumption that the central mode does not overlap the phonon sidebands, the self-consistency equation for the intensity parameter delta is found analogous to the BCS ''gap'' equation. Far from T/sub c/, delta is identically zero. After onset above T/sub c/, a 20--30% further change in coherence length is found sufficient for transfer of 80% of the phonon intensity into the central mode. The characteristic width of the (assumed Lorentzian) central mode is initially much broader than the phonon width, until about 80% intensity transfer occurs. Thereafter, critical narrowing is found to be anomalous. The formation of the central mode is characterized by a second short fluctuation length presumably controlling the surface energy between virtual domains. The (nonlocal) collective excitation presumably describes slow fluctuations into these virtual domains. The spectrum of the local two-phonon correlation function is found not to reflect the collectivemore » excitation but faster and more complicatedzero-point motion which is not analyzed here. An extension of the calculation to resolve this spectrum and other possible structure in the central mode is not out of the question, but this will be left for future calculation.« less

Electron paramagnetic resonance linewidth studies in AMnX 3 type compounds

Electron paramagnetic resonance (EPR) linewidth studies have been performed in TlMnCl 3 and TlMnF 3 which order in an antiferromagnetic structure at 118 and 85 K respectively. In both cases, a single exchange narrowed line is observed with linewidth ΔH exp much larger than that predicted by the simple theory of exchange narrowing developed by Van Vleck. Various line profiles—truncated Lorentzian, Gaussian-Lorentzian, truncated double Lorentzian, and Gaussian double Lorentzian—have been considered to account for this observation. The EPR linewidth has been measured as a function of temperature between 300 K and the ordering temperature T N. Critical narrowing of the EPR line is observed for temperatures T lying in the interval T N + 20> T > T N. This suggests that long-range order starts building up even above the ordering temperature T N.

Sudden death in patients awaiting coronary artery surgery.

<b>Lewis, B. S. and Gotsman, M. S. (1974).</b><i>Thorax</i>, <b>29</b>, 209-214. <b>Sudden death in patients awaiting coronary artery surgery.</b> Six patients with coronary artery disease are described who died suddenly while awaiting an operation to revascularize the myocardium. Each patient had recent onset of severe angina pectoris and this was caused by critical narrowing(s) of 90% or more of a major coronary artery(ies) supplying a large portion of the left ventricular myocardium. The syndrome can be diagnosed only by cardiac catheterization and high quality coronary arteriography. Patients in whom the myocardial blood supply is critically compromised must be recognized. These patients are liable to sudden death and require urgent myocardial revascularization.

Critical behaviour of the auto-correlation function in the XY model and NMR line narrowing

In the XY model for spin 1 2 , the autocorrelation function 〈 σ x o ( t) σ x o (0)〉 is calculated as a double series in t and the inverse temperature. The divergence as T → T c increases with increasing power of t, indicating critical narrowing of the NMR linewidth.

Clinical Correlation with Coronary Circulation

DOI: 10.3329/uhj.v6i2.7252University Heart Journal Vol. 6, No. 2, July 2010 pp.86-89