Liquidus surfaces in a part of the systems ZnO-PbO-SiO_2 and ZnO-"FeO"-SiO_2

Liquidus surfaces in a part of the systems ZnO-PbO-SiO_2 and ZnO-"FeO"-SiO_2 were constructed by quenching method. The experiments were carried out in air in the system ZnO-PbO-SiO_2. In the part investigated the primary phases were three ternary compounds (PbO・ZnO・SiO_2, 2PbO・ZnO・2SiO_2 and barysilite) , three lead silicates, Zn_2SiO_4 and SiO_2. Isotherms on the liquidus surface of each primary phase field were determined from 750 to 1300℃. In the system ZnO-"FeO"-SiO_2 the experiments were carried out in an atmosphere of purified nitrogen. In the part investigated the primary phases were Fe_2SiO_4, Zn_2SiO_4 and SiO_2. Isotherms on the liquidus surface of each primary phase field from 1150 to 1300℃ and the ternary eutectic (1130℃, 15.9% ZnO, 48.2% "FeO" and 35.9% SiO_2) were determined

A possible route to spontaneous reduction of the heat conductivity by a temperature gradient driven instability in electron-ion plasmas

We have shown that there exists low-frequency growing modes driven by a global temperature gradient in electron and ion plasmas, by linear perturbation analysis within the frame work of plasma Kinetic theory. The driving force of the instability is the local deviation of the distribution function from the Maxwell-Boltzmann due to global temperature gradient. Application to the intracluster medium shows that scattering of the particles due to waves excited by the instability is possible to reduce mean free paths of electron and ion down to five to seven order of magnitude than the mean free paths due to Coulomb collisions. This may provide a hint to explain why hot and cool gas can co-exist in the intracluster medium in spite of the very short evaporation time scale due to thermal conduction if the conductivity is the classical Spitzer value. Our results suggest that the realization of the global thermal equilibrium is postponed by the local instability which is induced for quicker realization of local thermal equilibrium state in plasmas. The instability provides a new possibility to create and grow cosmic magnetic fields without any seed magnetic field.Comment: Accepted for publication in ApJ: 16 pages, 1figur

Weak Lensing Mass Measurements of Substructures in COMA Cluster with Subaru/Suprime-Cam

We obtain the projected mass distributions for two Subaru/Suprime-Cam fields in the southwest region (r\simlt 60') of the Coma cluster (z=0.0236) by weak lensing analysis and detect eight subclump candidates. We quantify the contribution of background large-scale structure (LSS) on the projected mass distributions using SDSS multi-bands and photometric data, under the assumption of mass-to-light ratio for field galaxies. We find that one of eight subclump candidates, which is not associated with any member galaxies, is significantly affected by LSS lensing. The mean projected mass for seven subclumps extracted from the main cluster potential is = (5.06\pm1.30)10^12h^-1 M_sun after a LSS correction. A tangential distortion profile over an ensemble of subclumps is well described by a truncated singular-isothermal sphere model and a truncated NFW model. A typical truncated radius of subclumps, r_t\simeq 35 h^-1 kpc, is derived without assuming any relations between mass and light for member galaxies. The radius coincides well with the tidal radius, \sim42 h^-1 kpc, of the gravitational force of the main cluster. Taking into account the incompleteness of data area, a projection effect and spurious lensing peaks, it is expected that mass of cluster substructures account for 19 percent of the virial mass, with 13 percent statistical error. The mass fraction of cluster substructures is in rough agreement with numerical simulations.Comment: ApJ, accepted, 16 pages, 10 figures and 4 tables. High-resolution pictures available at http://www.asiaa.sinica.edu.tw/~okabe/files/comaWL.pd

Experimental conversion of a defensin into a neurotoxin: Implications for origin of toxic function

Scorpion K+ channel toxins and insect defensins share a conserved three-dimensional structure and related biological activities (defense against competitors or invasive microbes by disrupting their membrane functions), which provides an ideal system to study how functional evolution occurs in a conserved structural scaffold. Using an experimental approach, we show that the deletion of a small loop of a parasitoid venom defensin possessing the “scorpion toxin signature” (STS) can remove steric hindrance of peptide-channel interactions and result in a neurotoxin selectively inhibiting K+ channels with high affinities. This insect defensin-derived toxin adopts a hallmark scorpion toxin fold with a common cysteine-stabilized α-helical and β-sheet motif, as determined by nuclear magnetic resonance analysis. Mutations of two key residues located in STS completely diminish or significantly decrease the affinity of the toxin on the channels, demonstrating that this toxin binds to K+ channels in the same manner as scorpion toxins. Taken together, these results provide new structural and functional evidence supporting the predictability of toxin evolution. The experimental strategy is the first employed to establish an evolutionary relationship of two distantly related protein families