The Steady-State Transport of Oxygen through Hemoglobin Solutions

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated

Diffusivity Measurements of Human Methemoglobin

Experimental measurements of the diffusion coefficient of human methemoglobin were made at 25°C with a modified Stokes diaphragm diffusion cell. A Millipore filter was used in place of the ordinary fritted disc to facilitate rapid achievement of steady state in the diaphragm. Methemoglobin concentrations varied from approximately 5 g/100 ml to 30 g/100 ml. The diffusion coefficient in this range decreased from 7.5 x 10^(-7) cm^2/sec to 1.6 x 10^(-7) cm^2/sec

Reconstruction of potential energy profiles from multiple rupture time distributions

We explore the mathematical and numerical aspects of reconstructing a potential energy profile of a molecular bond from its rupture time distribution. While reliable reconstruction of gross attributes, such as the height and the width of an energy barrier, can be easily extracted from a single first passage time (FPT) distribution, the reconstruction of finer structure is ill-conditioned. More careful analysis shows the existence of optimal bond potential amplitudes (represented by an effective Peclet number) and initial bond configurations that yield the most efficient numerical reconstruction of simple potentials. Furthermore, we show that reconstruction of more complex potentials containing multiple minima can be achieved by simultaneously using two or more measured FPT distributions, obtained under different physical conditions. For example, by changing the effective potential energy surface by known amounts, additional measured FPT distributions improve the reconstruction. We demonstrate the possibility of reconstructing potentials with multiple minima, motivate heuristic rules-of-thumb for optimizing the reconstruction, and discuss further applications and extensions.Comment: 20 pages, 9 figure

^25Mg NMR study of the MgB_2 superconductor

^25Mg NMR spectra and nuclear spin-lattice relaxation time, T_1, have been measured in polycrystalline ^25MgB_2 with a superconducting transition temperature T_c = 39.0 K in zero magnetic field. From the first order and second order quadrupole perturbed NMR spectrum a quadrupole coupling frequency nu_Q = 222(1.5) kHz is obtained. T_1T = 1090(50) sK and Knight shift K_c = 242(4) ppm are temperature independent in the normal conducting phase. The ^25Mg Korringa ratio equals to 0.95 which is very close to the ideal value of unity for s-electrons. The comparison of the experimental nu_Q, T_1T, and K_c with the corresponding values obtained by LDA calculations shows an excellent agreement for all three quantities.Comment: 4 pages including 4 eps-figures, revtex

Lattice and polarizability mediated spin activity in EuTiO_3

EuTiO_3 is shown to exhibit novel strong spin-charge-lattice coupling deep in the paramagnetic phase. Its existence is evidenced by an, until now, unknown response of the paramagnetic susceptibility at temperatures exceeding the structural phase transition temperature T_S = 282K. The "extra" features in the susceptibility follow the rotational soft zone boundary mode temperature dependence above and below T_S. The theoretical modeling consistently reproduces this behavior and provides reasoning for the stabilization of the soft optic mode other than quantum fluctuations.Comment: 8 pages, 4 figure

Evolution of two-gap behavior of the superconductor FeSe_1-x

The superfluid density, \rho_s, of the iron chalcogenide superconductor, FeSe_1-x, was studied as a function of pressure by means of muon-spin rotation. The zero-temperature value of \rho_s increases with increasing transition temperature T_c (increasing pressure) following the tendency observed for various Fe-based and cuprate superconductors. The analysis of \rho_s(T) within the two-gap scheme reveals that the effect on both, T_c and \rho_s(0), is entirely determined by the band(s) where the large superconducting gap develops, while the band(s) with the small gap become practically unaffected.Comment: 5 pages, 3 figure