Heat and mass transport in bundles that move and give off gas

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 6, pp. 96–103, November–December, 1992.     

Controlled ventilation during NMR spectroscopic studies: hemodynamic and biochemical consequences

The effects of different ventilation methods on cardiac output measured by the indicator-dilution method, liver blood flow measured by a deuterium washout technique using 2H nuclear magnetic resonance (NMR) and liver concentrations of ATP and intracellular pH determined with 31P NMR were compared in anesthetized rats. No differences in mean arterial blood pressure were demonstrable with the different modes of ventilation. However, significant drops in cardiac output were observed between freely breathing and animals ventilated with positive pressure but not the high frequency oscillatory method (407 +/- 46 and 520 +/- 88 vs. 633 +/- 86 ml/min/kg, p less than 0.05 and p = NS, respectively). Moreover, liver blood flow was significantly reduced during positive pressure but not high frequency oscillatory ventilation compared with free breathing rats (32 +/- 4 and 43 +/- 10 vs. 46 +/- 8 ml/100 g, p less than 0.05 and p = NS, respectively). 31P NMR spectroscopy revealed no effects of either ventilation method on tissue ATP or intracellular pH as estimated by the chemical shift of inorganic phosphate. These data suggest that controlled ventilation in normal rats accomplished with standard positive pressure methods is associated with major decreases in cardiac output and liver blood flow despite maintenance of normal blood pressure. High frequency oscillatory ventilation appears to effect less compromise of cardiac output and hepatic perfusion than positive pressure ventilation and may, therefore, be preferable for some biological studies.     

Dynamics of fluorescence of solid solutions of quantum dots and the organic dye DODCI: Experiment and numerical simulation

The fluorescence of solid solutions of CdSe/ZnS quantum dots and the organic dye DODCI is investigated. It is shown that nonradiative transfer of electronic excitation energy to dye molecules, which with some probability lose their acceptor properties as a result of photoisomerization or photodegradation, is responsible for a significant increase in the fluorescence intensity of a donor. The degree of polarization of the donor fluorescence attains values exceeding 0.5, which is due to the difference in the fluorescence quantum yields of donors with different orientations of the oscillator with respect to the electric vector of an excitation light wave. A numerical simulation of the experimentally observed dependences is performed.     

Failure of an infinitely compressible composite containing a finite cylindrical crack in axial compression

S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of the Ukraine. Translated from Prikladnaya Mekhanika, Vol. 31, No. 9, pp. 15–23, September, 1995.     

Average and local magnetic moments on Fe atoms in microcrystalline and amorphous Fe100−xPx alloys

We have measured the concentration dependence of the average magnetic moment per Fe atom _Fe(x) in microcrystalline and amorphous Fe-P alloys obtained over a wide concentration range using electrochemical deposition. The model of local magnetic moments has been used to described _Fe(x). On the basis of this model the effects of phosphorus on the value _Fe are explained in terms of the parameters of the local environment of the Fe atom.     

Sticking of carbon nanotube Y junction branches

The coalescence of branches in the Y junctions of single-wall carbon nanotubes (10 nm long) is predicted to occur when the branches approach each other under the action of a load (～10 nN) applied to their ends. A transition to the new state with parallel branches bound by molecular interactions was simulated and the energy characteristics were calculated by the molecular dynamics method. The Y junctions with parallel branches are stable at temperatures up to 2000 K. It is established that there is a threshold distance between the branch ends, below which the branches exhibit spontaneous sticking under the action of molecular attraction forces. If the branches are unloaded before this threshold distance is reached, they oscillate (acting as a nanodimensional “tuning fork”) at a frequency of ～100 GHz.