Background: Understanding environmental correlates of physical activity can inform

The purpose of this study was to determine whether the initial rate of hemoglobin and myoglobin deoxygenation during immediate postexercise ischemia, a reflection of muscle O2 consumption (VO2mus), can be a quantitative measure of muscle oxidative metabolism. The finger flexor muscles of five healthy men (aged 25-31 yr) were monitored by 31P-magnetic resonance spectroscopy for changes in phosphocreatine (PCr), Pi, and pH. Tests were conducted during 15 min of cuff ischemia and during 5 min of submaximal isotonic grip exercise at 10, 20, 30, and 40% of maximal voluntary contraction, one contraction every 4 s. The VO2mus changes were also monitored by near-infrared spectroscopy with continuous wave. The VO2mus during exercise was expressed relative to the resting value. The resting metabolic rate, calculated from the PCr breakdown rate after complete O2 depletion, was 0.0010 (SD) mM ATP/s. During submaximal exercise (pH > 6.9), the VO2mus increased with a rise in intensity (0.036 +/- 0.011, 0.054 +/- 0.016, 0.062 +/- 0.012, and 0.067 +/- 0.020 mM ATP/s during 10, 20, 30, and 40% maximal voluntary contraction, respectively) and showed significant correlation with changes in both calculated ADP and PCr values (r2 = 0.98 and r2 = 0.99, respectively). In conclusion, because of the significant correlation with regulatory metabolites (ADP and PCr) of oxidative phosphorylation, O2 decline rate in immediate postexercise ischemia determined by near-infrared spectroscopy with continuous wave can be utilized for the quantitative evaluation of localized muscle oxidative metabolism.

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Cuprous oxide quantum particles as small as 2 nm (comparable to the Bohr exciton radius) were synthesized using an electrochemical route. Quantum confinement effects are evident from a blueshift in the optical absorption. The optical absorption spectra of Cu2O nanoparticles of different sizes are discussed. Structural analysis by x-ray diffraction as well as electron diffraction shows the nanoparticles to be cubic and single phased Cu2O. X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface of Cu2O core nanoparticles.

Fluorescence properties have been studied for Mn:ZnS crystallites with average diameter of 4 nm prepared by an aqueous colloidal method under 266 nm light excitation. The intensity ratio of the blue band at ∼430 nm to the orange band at ∼590 nm has decreased after the preparation on a time scale of hours in aqueous solution. On the other hand, hyperfine structures of Mn 2+ in the electron paramagnetic resonance spectrum have increased markedly on the same time scale in solution samples. These phenomena are attributed to the redistribution of defect centers in nanocrystals. Such phenomena have not been observed in samples incorporated into poly(vinyl alcohol). The orange emission is mainly due to the 6 A 1 r 4 T 1 transition of Mn 2+ , while the blue emission is tentatively assigned to the donor-acceptor pair transition in which the acceptor is related to the Zn 2+ vacancy. Fluorescence decay times of the blue and orange bands have been found to be ∼10 ns and ∼1 ms, respectively, the latter being the same as in the bulk samples. A weak fluorescent component with fast kinetics observed in the orange region has been identified as a tail of the blue band. No lifetime shortening of the Mn 2+ emission due to quantum confinement has been observed, contrary to reports in the literature.