CuPc Adsorption on Au(110)-(1 × 2): From a Monomer to a Periodic Chain

Using scanning tunneling microscopy (STM), we study the adsorption of copper-phthalocyanine (CuPc) on the anisotropic Au(110)-(1 × 2) surface as a function of coverage. For the initial adsorption at room temperature, we observe CuPc monomers as well as a molecular chain that forms along the step edge. By STM manipulation, we reveal that the CuPc adsorption is accompanied by surface reconstruction from the initial adsorption stage; the periodicity beneath the monomer and the chain changes locally from (1 × 2) to (1 × 1) and (1 × 3), respectively. This finding highlights that the Au atom mobility of the surface plays an essential role in CuPc adsorption. At higher coverage, we observe the development of CuPc chains along the [110] direction on the terrace with periodicities of (7 × 5) and (5 × 5), and compare the obtained results with those from the previous studies by diffraction methods

Frustrated minority spins in GeNi2O4

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi$_2$O$_4$ at $T_{N1}=12.1$ K and $T_{N2}=11.4$ K, respectively \cite{matsuno, crawford}. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at $T_{N1}$ the spins on the \kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the triangular planes that separate the \kagome planes frustrated and disordered. At the lower $T_{N2}$, the triangular spins also order in the $$ plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions

An Expanding Shell of Neutral Hydrogen Associated with SN 1006: Hints for the Single-Degenerate Origin and Faint Hadronic Gamma-Rays

We report new HI observations of the Type Ia supernova remnant SN 1006 using the Australia Telescope Compact Array with an angular resolution of $4.5' \times 1.4'$ ($\sim$2 pc at the assumed SNR distance of 2.2 kpc). We find an expanding gas motion in position-velocity diagrams of HI with an expansion velocity of $\sim$4 km s$^{-1}$ and a mass of $\sim$1000 $M_\odot$. The spatial extent of the expanding shell is roughly the same as that of SN 1006. We here propose a hypothesis that SN 1006 exploded inside the wind-blown bubble formed by accretion winds from the progenitor system consisting of a white dwarf and a companion star, and then the forward shock has already reached the wind wall. This scenario is consistent with the single-degenerate model. We also derived the total energy of cosmic-ray protons $W_\mathrm{p}$ to be only $\sim$1.2-$2.0 \times 10^{47}$ erg by adopting the averaged interstellar proton density of $\sim$25 cm$^{-3}$. The small value is compatible with the relation between the age and $W_\mathrm{p}$ of other gamma-ray supernova remnants with ages below $\sim$6 kyr. The $W_\mathrm{p}$ value in SN 1006 will possibly increase up to several 10$^{49}$ erg in the next $\sim$5 kyr via the cosmic-ray diffusion into the HI wind-shell.Comment: 12 pages, 4 figures, 1 table, accepted for publication in The Astrophysical Journal (ApJ

Electronic and Magnetic Properties of Febr2

Electronic and magnetic (e-m) properties of FeBr2 have been surprisingly well described as originating from the Fe2+ ions and their fine electronic structure. The fine electronic structure have been evaluated taking into account the spin-orbit (s-o) coupling, crystal-field and inter-site spin-dependent interactions. The required magnetic doublet ground state with an excited singlet at D=2.8 meV results from the trigonal distortion. This effect of the trigonal distortion and a large magnetic moment of iron, of 4.4 mB, can be theoretically derived provided the s-o coupling is correctly taking into account. The obtained good agreement with experimental data indicates on extremaly strong correlations of the six 3d electrons in the Fe2+ ion yielding their full localization and the insulating state. These calculations show that for the meaningful analysis of e-m properties of FeBr2 the spin-orbit coupling is essentially important and that the orbital moment (0.74 mB) is largely unquenched (by the off-cubic trigonal distortion in the presence of the spin-orbit coupling).Comment: 11 pages in RevTex, 5 figure

Role of BMP, FGF, Calcium Signaling, and Zic Proteins in Vertebrate Neuroectodermal Differentiation

More than a decade has passed since Zic family zinc finger proteins were discovered to be transcription factors controlling neuroectodermal differentiation (neural induction) in Xenopus laevis embryos. Although BMP-signal blocking has been shown to be a major upregulator of Zic genes in neuroectodermal differentiation, recent studies have revealed that FGF signaling and intracellular calcium elevation are also involved in regulating the expression of Zic genes. Different regulatory mechanisms have been found for the Zic1 and Zic3 genes, raising the possibility that functional synergism between them partly accounts for the integration of BMP-signal blocking and FGF signaling in neuroectodermal differentiation. Furthermore, mammalian Zic1 and Zic3 have been found to be neural-cell-fate-inducing and pluripotency-maintaining factors, respectively, leading us to the intriguing question of whether the mechanism underlying amphibian neuroectodermal differentiation is applicable to mammals. Comprehensive understanding of the Zic family genes is therefore essential for the study of the neuroectodermal differentiation and stem cell biology

Aging, rejuvenation and memory effects in Ising and Heisenberg spin glasses

We have compared aging phenomena in the Fe_{0.5}Mn_{0.5}TiO_3 Ising spin glass and in the CdCr_{1.7}In_{0.3}S_4 Heisenberg-like spin glass by means of low-frequency ac susceptibility measurements. At constant temperature, aging obeys the same `$\omega t$ scaling' in both samples as in other systems. Investigating the effect of temperature variations, we find that the Ising sample exhibits rejuvenation and memory effects which are qualitatively similar to those found in other spin glasses, indicating that the existence of these phenomena does not depend on the dimensionality of the spins. However, systematic temperature cycling experiments on both samples show important quantitative differences. In the Ising sample, the contribution of aging at low temperature to aging at a slightly higher temperature is much larger than expected from thermal slowing down. This is at variance with the behaviour observed until now in other spin glasses, which show the opposite trend of a free-energy barrier growth as the temperature is decreased. We discuss these results in terms of a strongly renormalized microscopic attempt time for thermal activation, and estimate the corresponding values of the barrier exponent $\psi$ introduced in the scaling theories.Comment: 8 pages, including 6 figure

The Nature of Ultra-Luminous Compact X-Ray Sources in Nearby Spiral Galaxies

Studies were made of ASCA spectra of seven ultra-luminous compact X-ray sources (ULXs) in nearby spiral galaxies; M33 X-8 (Takano et al. 1994), M81 X-6 (Fabbiano 1988b; Kohmura et al. 1994; Uno 1997), IC 342 Source 1 (Okada et al. 1998), Dwingeloo 1 X-1 (Reynolds et al. 1997), NGC 1313 Source B (Fabbiano & Trinchieri 1987; Petre et al. 1994), and two sources in NGC 4565 (Mizuno et al. 1999). With the 0.5--10 keV luminosities in the range 10^{39-40} ergs/s, they are thought to represent a class of enigmatic X-ray sources often found in spiral galaxies. For some of them, the ASCA data are newly processed, or the published spectra are reanalyzed. For others, the published results are quoted. The ASCA spectra of all these seven sources have been described successfully with so called multi-color disk blackbody (MCD) emission arising from optically-thick standard accretion disks around black holes. Except the case of M33 X-8, the spectra do not exhibit hard tails. For the source luminosities not to exceed the Eddington limits, the black holes are inferred to have rather high masses, up to ~100 solar masses. However, the observed innermost disk temperatures of these objects, Tin = 1.1--1.8 keV, are too high to be compatible with the required high black-hole masses, as long as the standard accretion disks around Schwarzschild black holes are assumed. Similarly high disk temperatures are also observed from two Galactic transients with superluminal motions, GRO 1655-40 and GRS 1915+105. The issue of unusually high disk temperature may be explained by the black hole rotation, which makes the disk get closer to the black hole, and hence hotter.Comment: submitted to ApJ, December 199

ENHANCED GROWTH OF THE RED ALGA PORPHYRA-YEZOENSIS UEDA IN HIGH CO2 CONCENTRATIONS

Leafy thalli of the red alga Porphyra yezoensis Ueda, initiated from conchospores released from free-living conchocelis, were cultured using aeration with high CO2. It was found that the higher the CO2 concentration, the faster the growth of the thalli. Aeration with elevated CO2 lowered pH in dark, but raised pH remarkably in light with the thalli, because the photosynthetic conversion of HCO3- to OH- and CO2 proceeded much faster than the dissociation of hydrated CO2 releasing H+. Photosynthesis of the alga was found to be enhanced in the seawater of elevated dissolved inorganic carbon (DIC, CO2 + HC O3- + CO3-). It is concluded that the increased pH in the light resulted in the increase of DIC in the culture media, thus enhancing photosynthesis and growth. The relevance of the results to removal of atmospheric CO2 by marine algae is discussed

CALCIFICATION IN THE ARTICULATED CORALLINE ALGA CORALLINA-PILULIFERA, WITH SPECIAL REFERENCE TO THE EFFECT OF ELEVATED CO2 CONCENTRATION

Calcification in Corallina pilulifera Postels et Ruprecht displayed diurnal variations in aerated (350 ppm CO2) culture media, with faster rates during the light than during the dark period. Addition of CO2 (air + 1250 ppm) inhibited calcification. This was attributable to the decreased pH resulting from CO2 addition. Both photosynthesis and calcification were enhanced in seawater, with elevated dissolved inorganic carbon concentrations at a constant pH of 8.2