1,247 research outputs found
The Reduced Expression of 6ckine in the plt Mouse Results from the Deletion of One of Two 6ckine Genes
6Ckine is an unusual chemokine capable of attracting naive T lymphocytes in vitro. It has been recently reported that lack of 6Ckine expression in lymphoid organs is a prominent characteristic of mice homozygous for the paucity of lymph node T cell (plt) mutation. These mice show reduced numbers of T cells in lymph nodes, Peyer's patches, and the white pulp of the spleen. The genetic reason for the lack of 6Ckine expression in the plt mouse, however, has remained unknown. Here we demonstrate that mouse 6Ckine is encoded by two genes, one of which is expressed in lymphoid organs and is deleted in plt mice. A second 6Ckine gene is intact and expressed in the plt mouse
Fatigue crack paths and properties in A356-T6 aluminum alloy microstructurally modified by friction stir processing under different conditions
A356-T6 cast aluminum alloy is a light weight structural material, but fatigue crack initiates and propagates from a casting defect leading to final fracture. Thus it is important to eliminate casting defects. In this study, friction stir processing (FSP) was applied to A356-T6, in which rotating tool with probe and shoulder was plunged into the material and travels along the longitudinal direction to induce severe plastic deformation,resulting in the modification of microstructure. Two different processing conditions with low and high toolrotational speeds were tried and subsequently fully reversed fatigue tests were performed to investigate theeffect of processing conditions on the crack initiation and propagation behavior. The fatigue strengths weresuccessfully improved by both conditions due to the elimination of casting defects. But the lower tool rotationalspeed could further improve fatigue strength than the higher speed. EBSD analyses revealed that the higher tool rotational speed resulted in the severer texture having detrimental effects on fatigue crack initiation andpropagation resistances. 
Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
The spatial charge arrangement of a typical quasi-two-dimensional organic
conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis
using synchrotron radiation. The results show that the horizontal stripe type
structure, which was suggested by mean field theory, is established. We also
find the charge disproportion above the metal-insulator transition temperature
and a significant change in transfer integrals caused by the phase transition.
Our result elucidates the insulating phase of this material as a 2k_F charge
density localization.Comment: 8 pages, 5 figures, 1 tabl
Scope and Mechanistic Study of the Coupling Reaction of α,ÎČ-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways
The cationic ruthenium-hydride complex [(C6H6)(PCy3)(CO)RuH]+BF4â (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to α,ÎČ-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic CâH bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as follows: rate = k[1]1[propene]0[cinnamate]â1. A negligible deuterium kinetic isotope effect (kH/kD = 1.1 ± 0.1) was measured from both (E)-C6H5CHâC(CH3)CONHCH3 and (E)-C6H5CDâC(CH3)CONHCH3 with styrene. In contrast, a significant normal isotope effect (kH/kD = 1.7 ± 0.1) was observed from the reaction of (E)-C6H5CHâC(CH3)CONHCH3 with styrene and styrene-d8. A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C6H5CHâCHCO2Et with propene (13C(recovered)/13C(virgin) at CÎČ = 1.019(6)), while a negligible carbon isotope effect (13C(recovered)/13C(virgin) at CÎČ = 0.999(4)) was obtained from the reaction of (E)-C6H5CHâC(CH3)CONHCH3 with styrene. Hammett plots from the correlation of para-substituted p-X-C6H4CHâCHCO2Et (X = OCH3, CH3, H, F, Cl, CO2Me, CF3) with propene and from the treatment of (E)-C6H5CHâCHCO2Et with a series of para-substituted styrenes p-Y-C6H4CHâCH2 (Y = OCH3, CH3, H, F, Cl, CF3) gave the positive slopes for both cases (Ï = +1.1 ± 0.1 and +1.5 ± 0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, ÎH⧧ = 20 ± 2 kcal molâ1 and ÎS⧧ = â42 ± 5 eu. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies
An Experimental Study of Stable Operating Conditions for a High-Sensitivity Induction Gradiometer
Charge Order with Structural Distortion in Organic Conductors: Comparison between \theta-(ET)2RbZn(SCN)4 and \alpha-(ET)2I3
Charge ordering with structural distortion in quasi-two-dimensional organic
conductors \theta-(ET)2RbZn(SCN)4 (ET=BEDT-TTF) and \alpha-(ET)2I3 is
investigated theoretically. By using the Hartree-Fock approximation for an
extended Hubbard model which includes both on-site and intersite Coulomb
interactions together with Peierls-type electron-lattice couplings, we examine
the role of lattice degrees of freedom on charge order. It is found that the
experimentally observed, horizontal charge order is stabilized by lattice
distortion in both compounds. In particular, the lattice effect is crucial to
the realization of the charge order in \theta-(ET)2RbZn(SCN)4, while the
peculiar band structure whose symmetry is lower than that of
\theta-(ET)2RbZn(SCN)4 in the metallic phase is also an important factor in
\alpha-(ET)2I3 together with the lattice distortion. For \alpha-(ET)2I3, we
obtain a phase transition from a charge-disproportionated metallic phase to the
horizontal charge order with lattice modulations, which is consistent with the
latest X-ray experimental result.Comment: 10 pages, 13 figures, to appear in J. Phys. Soc. Jpn. Vol. 77 (2008)
No.
Growth Dynamics of Photoinduced Domains in Two-Dimensional Charge-Ordered Conductors Depending on Stabilization Mechanisms
Photoinduced melting of horizontal-stripe charge orders in
quasi-two-dimensional organic conductors
\theta-(BEDT-TTF)2RbZn(SCN)4[BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene]
and
\alpha-(BEDT-TTF)2I3 is investigated theoretically. By numerically solving
the time-dependent Schr\"odinger equation, we study the photoinduced dynamics
in extended Peierls-Hubbard models on anisotropic triangular lattices within
the
Hartree-Fock approximation. The melting of the charge order needs more energy
for \theta-(BEDT-TTF)2RbZn(SCN)4 than for \alpha-(BEDT-TTF)2I3, which is a
consequence of the larger stabilization energy in \theta-(BEDT-TTF)2RbZn(SCN)4.
After local photoexcitation in the charge ordered states, the growth of a
photoinduced domain shows anisotropy. In \theta-(BEDT-TTF)2RbZn(SCN)4, the
domain hardly expands to the direction perpendicular to the horizontal-stripes.
This is because all the molecules on the hole-rich stripe are rotated in one
direction and those on the hole-poor stripe in the other direction. They
modulate horizontally connected transfer integrals homogeneously, stabilizing
the charge order stripe by stripe. In \alpha-(BEDT-TTF)2I3, lattice distortions
locally stabilize the charge order so that it is easily weakened by local
photoexcitation. The photoinduced domain indeed expands in the plane. These
results are consistent with recent observation by femtosecond reflection
spectroscopy.Comment: 9 pages, 8 figures, to appear in J. Phys. Soc. Jpn. Vol. 79 (2010)
No.
Finite-Temperature Properties across the Charge Ordering Transition -- Combined Bosonization, Renormalization Group, and Numerical Methods
We theoretically describe the charge ordering (CO) metal-insulator transition
based on a quasi-one-dimensional extended Hubbard model, and investigate the
finite temperature () properties across the transition temperature, . In order to calculate dependence of physical quantities such as the
spin susceptibility and the electrical resistivity, both above and below
, a theoretical scheme is developed which combines analytical
methods with numerical calculations. We take advantage of the renormalization
group equations derived from the effective bosonized Hamiltonian, where Lanczos
exact diagonalization data are chosen as initial parameters, while the CO order
parameter at finite- is determined by quantum Monte Carlo simulations. The
results show that the spin susceptibility does not show a steep singularity at
, and it slightly increases compared to the case without CO because
of the suppression of the spin velocity. In contrast, the resistivity exhibits
a sudden increase at , below which a characteristic dependence
is observed. We also compare our results with experiments on molecular
conductors as well as transition metal oxides showing CO.Comment: 9 pages, 8 figure
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