Endurance training facilitates myoglobin desaturation during muscle contraction in rat skeletal muscle.

At onset of muscle contraction, myoglobin (Mb) immediately releases its bound O2 to the mitochondria. Accordingly, intracellular O2 tension (PmbO2) markedly declines in order to increase muscle O2 uptake (mVO2). However, whether the change in PmbO2 during muscle contraction modulates mVO2 and whether the O2 release rate from Mb increases in endurance-trained muscles remain unclear. The purpose of this study was, therefore, to determine the effect of endurance training on O2 saturation of Mb (SmbO2) and PmbO2 kinetics during muscle contraction. Male Wistar rats were subjected to a 4-week swimming training (Tr group; 6 days per week, 30 min × 4 sets per day) with a weight load of 2% body mass. After the training period, deoxygenated Mb kinetics during muscle contraction were measured using near-infrared spectroscopy under hemoglobin-free medium perfusion. In the Tr group, the VmO2peak significantly increased by 32%. Although the PmbO2 during muscle contraction did not affect the increased mVO2 in endurance-trained muscle, the O2 release rate from Mb increased because of the increased Mb concentration and faster decremental rate in SmbO2 at the maximal twitch tension. These results suggest that the Mb dynamics during muscle contraction are contributing factors to faster VO2 kinetics in endurance-trained muscle

Stability of the Accretion Flows with Stalled Shocks in Core-Collapse Supernovae

Bearing in mind the application to the theory of core-collapse supernovae, we performed a global linear analysis on the stability of spherically symmetric accretion flows through a standing shock wave onto a proto neutron star. As unperturbed flows, we adopted the spherically symmetric steady solutions to the Euler equations obtained with realistic equation of state and formulae for neutrino reaction rates taken into account. Then we solved the equations for linear perturbations numerically, and obtained the eigen frequencies and eigen functions. We found (1) the flows are stable for all modes if the neutrino luminosity is lower than $\sim 1\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$. (2) For larger luminosities, the non-radial instabilities are induced, probably via the advection-acoustic cycles. Interestingly, the modes with $\ell=2$ and 3 become unstable at first for relatively low neutrino luminosities, e.g. $\gtrsim 2-3\times 10^{52}$ ergs/s for the same accretion rate, whereas the $\ell=1$ mode is the most unstable for higher luminosities, $\sim 3-7\times 10^{52}$ ergs/s. These are all oscillatory modes. (3) For still larger luminosities, $\sim 7\times 10^{52}$ ergs/s for $\dot{M}=1.0M_{\odot}/{\rm s}$, non-oscillatory modes, both radial and non-radial, become unstable. These non-radial modes were identified as convection. We confirmed the results obtained by numerical simulations that the instabilities induced by the advection-acoustic cycles are more important than the convection for lower neutrino luminosities.Comment: 46 pages, 19 figures, Accepted by Ap

Standing Accretion Shocks in the Supernova Core: Effects of Convection and Realistic EOS

We investigated the structure of the spherically symmetric accretion flows through the standing shock wave onto the proto-neutron star in the post-bounce phase of the collapse-driven supernova. We assume that the accretion flow is in a steady state controlled by the neutrino luminosity and mass accretion rate that are kept constant. We obtain solutions of the steady Euler equations for a wide range of neutrino luminosity and mass accretion rate. We employ a realistic EOS and neutrino-heating rates. More importantly, we take into account the effect of convection phenomenologically. For each mass accretion rate, we find the critical neutrino luminosity, above which there exists no steady solution. These critical points are supposed to mark the onset of the shock revival. As the neutrino luminosity increases for a given mass accretion rate, there appears a convectively unstable region at some point before the critical value is reached. We introduce a phenomenological energy flux by convection so that the negative entropy gradient should be canceled out. We find that the convection lowers the critical neutrino luminosity substantially. We also consider the effect of the self-gravity. It is found that the self-gravity is important only when the neutrino luminosity is high. The critical luminosity, however, is little affected if the energy transport by convection is taken into account.Comment: accepted by ApJ, 20 pages, 8 figure

Effects of rotation on the revival of a stalled shock in supernova explosions

In order to infer the effects of rotation on the revival of a stalled shock in supernova explosions, we investigated steady accretion flows with a standing shock. We first obtained a series of solutions for equations describing non-rotating spherically symmetric flows and confirmed the results of preceding papers that, for a given mass accretion rate, there is a critical luminosity of irradiating neutrinos, above which there exists no steady solution. Below the critical value, we found two branches of solutions; one is stable and the other is unstable against radial perturbations. With a simple argument based on the Riemann problem, we can identify the critical luminosity as the one, at which the stalled shock revives. We also obtained the condition satisfied by the flow velocity for the critical luminosity, which can be easily applied to the rotational case. If a collapsing star rotates, the accretion flow is non-spherical due to centrifugal forces. Flows are accelerated near the rotation axis whereas they are decelerated near the equatorial plane. As a result, the critical luminosity is lowered, that is, rotation assists the revival of a stalled shock. According to our calculations, the critical luminosity is $\sim25$% lower for the mass accretion rate of 1M$_{\odot}$/sec and the rotation frequency of 0.1 Hz at a radius of 1000 km than that of the spherically symmetric flow with the same mass accretion rate. We found that the condition of the flow velocity at the critical luminosity is first satisfied at the rotation axis. This suggests that the shock revival is triggered on the rotation axis and a jet-like explosion ensues.Comment: 26 pages, 10 figures, submitted to Ap

Intracellular oxygen tension limits muscle contraction-induced change in muscle oxygen consumption under hypoxic conditions during Hb-free perfusion.

Under acute hypoxic conditions, the muscle oxygen uptake (mV˙O2) during exercise is reduced by the restriction in oxygen-supplied volume to the mitochondria within the peripheral tissue. This suggests the existence of a factor restricting the mV˙O2 under hypoxic conditions at the peripheral tissue level. Therefore, this study set out to test the hypothesis that the restriction in mV˙O2 is regulated by the net decrease in intracellular oxygen tension equilibrated with myoglobin oxygen saturation (∆PmbO2) during muscle contraction under hypoxic conditions. The hindlimb of male Wistar rats (8 weeks old, n = 5) was perfused with hemoglobin-free Krebs-Henseleit buffer equilibrated with three different fractions of O2 gas: 95.0%O2, 71.3%O2, and 47.5%O2 The deoxygenated myoglobin (Mb) kinetics during muscle contraction were measured under each oxygen condition with a near-infrared spectroscopy. The ∆[deoxy-Mb] kinetics were converted to oxygen saturation of myoglobin (SmbO2), and the PmbO2 was then calculated based on the SmbO2 and the O2 dissociation curve of the Mb. The SmbO2 and PmbO2 at rest decreased with the decrease in O2 supply, and the muscle contraction caused a further decrease in SmbO2 and PmbO2 under all O2 conditions. The net increase in mV˙O2 from the muscle contraction (∆mV˙O2) gradually decreased as the ∆PmbO2 decreased during muscle contraction. The results of this study suggest that ΔPmbO2 is a key determinant of the ΔmV˙O2

Hydrogen Production from Methane in Atmospheric Non-Equilibrium Plasma

The instability of supplied power is a serious problem for chemical plants in developing countries. An easy start-up/shut-down system is important in this situation. The present report describes a hydrocarbon decomposition system using nonequilibrium plasma for hydrogen production. A microwave oven was used as a preliminary microwave reactor, which contained a quartz glass tube that passed through the top panel to the bottom panel of the microwave oven. Argon and methane flow were directed into the reactor, where the argon gas became plasma in the tube. A carbon stick was set in the tube as the excitation material of argon to plasma. Initially, the reaction was conducted under a methane partial pressure of 200 hPa. The main products were hydrogen and acetylene, with a small amount of ethylene also produced. Conversion and yields decreased with increasing methane partial pressure. Hydrogen production rate initially increased with methane partial pressure, but then decreased. The optimum methane partial pressure was determined. Gas flow rate had no effect on conversion or yield. The reactant and products reached an equilibrium state as soon as the reactant was introduced to the plasma. Pure hydrogen, 95%, was obtained by adjusting the experimental conditions

One-loop analyses of lattice QCD with the overlap Dirac operator

We discuss the weak coupling expansion of lattice QCD with the overlap Dirac operator. The Feynman rules for lattice QCD with the overlap Dirac operator are derived and the quark self-energy and vacuum polarization are studied at the one-loop level. We confirm that their divergent parts agree with those in the continuum theory.Comment: 19pages, 7figures, latex; added references :final version for publicatio

Clustering under the line graph transformation: application to reaction network

BACKGROUND: Many real networks can be understood as two complementary networks with two kind of nodes. This is the case of metabolic networks where the first network has chemical compounds as nodes and the second one has nodes as reactions. In general, the second network may be related to the first one by a technique called line graph transformation (i.e., edges in an initial network are transformed into nodes). Recently, the main topological properties of the metabolic networks have been properly described by means of a hierarchical model. While the chemical compound network has been classified as hierarchical network, a detailed study of the chemical reaction network had not been carried out. RESULTS: We have applied the line graph transformation to a hierarchical network and the degree-dependent clustering coefficient C(k) is calculated for the transformed network. C(k) indicates the probability that two nearest neighbours of a vertex of degree k are connected to each other. While C(k) follows the scaling law C(k) ~ k(-1.1 )for the initial hierarchical network, C(k) scales weakly as k(0.08 )for the transformed network. This theoretical prediction was compared with the experimental data of chemical reactions from the KEGG database finding a good agreement. CONCLUSIONS: The weak scaling found for the transformed network indicates that the reaction network can be identified as a degree-independent clustering network. By using this result, the hierarchical classification of the reaction network is discussed