102 research outputs found
Exponential distribution of long heart beat intervals during atrial fibrillation and their relevance for white noise behaviour in power spectrum
The statistical properties of heart beat intervals of 130 long-term surface
electrocardiogram recordings during atrial fibrillation (AF) are investigated.
We find that the distribution of interbeat intervals exhibits a characteristic
exponential tail, which is absent during sinus rhythm, as tested in a
corresponding control study with 72 healthy persons. The rate of the
exponential decay lies in the range 3-12 Hz and shows diurnal variations. It
equals, up to statistical uncertainties, the level of the previously uncovered
white noise part in the power spectrum, which is also characteristic for AF.
The overall statistical features can be described by decomposing the intervals
into two statistically independent times, where the first one is associated
with a correlated process with 1/f noise characteristics, while the second one
belongs to an uncorrelated process and is responsible for the exponential tail.
It is suggested to use the rate of the exponential decay as a further parameter
for a better classification of AF and for the medical diagnosis. The relevance
of the findings with respect to a general understanding of AF is pointed out
Coulomb excitation of a 242Am isomeric target: E2 and e3 strengths, rotational alignment, and collective enhancement
A 98% pure242mAm (K = 5-, t1/2 = 141 years) isomeric target was Coulomb excited with a 170.5-MeV 40Ar beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18h{stroke} in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast KÏ = 6- rotational band, and 13 in a band tentatively identified as the predicted yrast KÏ = 5+ band. The rotational bands based on the KÏ = 5- isomer and the 6-bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The Îł -ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete ÎK = 1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5- and 6- bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the I ÏK= 6-6 state in the nominal 6-5 isomer band state is measured within the PRM as 45.6+0.3-1.1%. The E2 and M1 strengths coupling the 5- and 6- bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5+ band are reproduced by an E3 strength of â15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in 242Am are compared with the single-particle alignments in 241Am
- âŠ