We developed a theory of excitation energy transfer (EET) which is applicable to all the values of the coupling strength U in the presence of homogeneous and inhomogeneous broadening. In constructing the theory, we adopted a decoupling procedure corresponding to the factorization by a two-time correlation function of the excitation transfer interaction in the integro-differential equation of a renormalized propagator. We also assumed that the two-time correlation function decreases exponentially with time. Under these assumptions, we could handle our theory nonperturbatively and analytically. We derived formulas of criteria among exciton, intermediate coupling, and Förster mechanisms. We exploited a novel method for determining the EET rate applicable to all the mechanisms from Förster to exciton. Then, we obtained compact formulas for the EET rate and the degree of coherency involved in the EET. We demonstrated how the exciton state is destabilized by the presence of inhomogeneity in the excitation energy of the constituents. The theory was applied to a light-harvesting system LH2 of photosynthetic bacteria.

We developed a portable needle-probe videomicroscope with a charge-coupled device (CCD) camera to visualize the subendocardial microcirculation. In 12 open-chest anesthetized pigs, the sheathed needle probe with a doughnut-shaped balloon and a microtube for flushing away the intervening blood was introduced into the left ventricle through an incision in the left atrial appendage via the mitral valve. Images of the subendocardial microcirculation of the beating heart magnified by 200 or 400 on a 15-in. monitor were obtained. The phasic diameter change in subendocardial arterioles during cardiac cycle was from 114±46 ,um (mean+SD) in end diastole to 84±26 ,um in end systole (p<0.001, n=13, ratio of change=24%) and that in venules from 134±60 ,m to 109±45 ,um (p<0.001, n=15, ratio of change=17%). In contrast, the diameter of subepicardial arterioles was almost unchanged (2% decrease, n=5, p<0.01), and the venular diameter increased by 19%1 (n=8, p<0.001) from end diastole to end systole. Partial kinking and/or pinching of vessels was observed in some segments of subendocardial arterioles and venules. The percentage of systolic decrease in the diameter from diastole in the larger (>100 ,um) subendocardial arterioles and venules was greater than smaller (50-100 ,m) vessels (both p<0.05). In conclusion, using a newly developed microscope system, we were able to observe the subendocardial vessels in diastole and systole. The vascular compression by cardiac contraction decreased the diameters of subendocardial arterioles and venules by about 20o, whereas subepicardial arterial diameter changed very little during the cardiac cycle and subepicardial venules increased in diameter during systole. (Circulation Research 1993;72:939-946) KEY WORDS * subendocardial microcirculation heart * needle-probe videomicroscope he phasic flows in the left coronary artery and T vein are unlike those of other organs; the arterial inflow is greatest during diastole, whereas the venous outflow is greatest during systole.1-6 This unique pattern of coronary arterial and venous flow was inferred in 1695 by Scaramucci,7 who is considered the founder of coronary physiology. He hypothesized that the myocardial vessels are squeezed by the contraction of the muscle fibers around them, which

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We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ^{7}Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ^{7}Li(p,n)^{7}Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the p+^{7}Li reaction is also discussed.

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