Superconductivity in undoped T' cuprates with Tc over 30 K

Undoped cuprates have long been considered to be antiferromagnetic insulators. In this article, however, we report that superconductivity is achieved in undoped T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd). Our discovery was performed by using metal-organic decomposition (MOD), an inexpensive and easy-to-implement thin-film process. The keys to prepare the superconducting films are firing with low partial-pressure of oxygen and reduction at low temperatures. The highest Tc of undoped T'-RE2CuO4 is over 30 K, substantially higher than "electron-doped" analogs. Remarkably, Gd2CuO4, even the derivatives of which have not shown superconductivity so far, gets superconducting with Tconset as high as ~ 20 K. The implication of our discovery is briefly discussed.Comment: 22 pages, 5 figures, submitted to Physical Review Letter

Criterion for Generation of Winds from Magnetized Accretion Disks

An analytic model is proposed for non-radiating accretion flows accompanied by up or down winds in a global magnetic field. Physical quantities in this model solution are written in variable-separated forms, and their radial parts are simple power law functions including one parameter for wind strength. Several, mathematically equivalent but physically different expressions of the criterion for wind generation are obtained. It is suggested also that the generation of wind is a consequence of the intervention of some mechanism that redistributes the locally available gravitational energy, and that the Bernoulli sum can be a good indicator of the existence of such mechanisms.Comment: 24 pages, 0 figures, ApJ accepte

The Synthesis of Cyclic Enol Ethers via Molybdenum Alkylidene-Catalyzed Ring-Closing Metathesis

An efficient method for the construction of five- and six-membered cyclic vinyl ethers from unsaturated esters using stoichiometric titanium reagents to convert the esters to acyclic olefinic enol ethers which are then transformed to the desired products by catalytic ring-closing olefin metathesis with a molybdenum alkylidene complex is described

Radiation Spectra from Advection-Dominated Accretion Flows in a Global Magnetic Field

We calculate the radiation spectra from advection-dominated accretion flows (ADAFs), taking into account the effects of a global magnetic field. Calculation is based on the analytic model for magnetized ADAFs proposed by Kaburaki, where a large-scale magnetic field controls the accretion process. Adjusting a few parameters, we find that our model can well reproduce the observed spectrum of Sagittarius A$^{*}$. The result is discussed in comparison with those of well-known ADAF models, where the turbulent viscosity controls the accretion process.Comment: Accepted for publication in Ap

Lighting spectra for the maximum colorfulness

The advent of modern solid-state sources enabled almost any spectrum for lighting and a wide range of possibilities in color rendering. The quality of the lighting has been typically evaluated by the color rendering index which measures how much the colors of objects illuminated by the light under test look similar to those produced when the objects are illuminated by the daylight or a conventional incandescent light. On the other hand, how colorful or vivid the colors under the illumination are perceived is also an important quality to evaluate lighting. We investigated, computationally, the spectral profiles of the illumination that maximizes the theoretical limit of the perceivable object colors. A large number of metamers with various degree of smoothness were generated using the Schmitt’s elements method at chromaticity points on and around the Planckian locus ranging from 2,222 K to 20,000 K. The general color rendering index (CRI) and MacAdam volumes in CIELAB color space were calculated for each metamer. The metamers maximizing the CRI had smoother spectra than the metamers maximizing the MacAdam volume. These results show that maximum colorfulness in nature can only be obtained with spectrally non-smooth illuminatio

Realization of a collective decoding of codeword states

This was also extended from the previous article quant-ph/9705043, especially in a realization of the decoding process.Comment: 6 pages, RevTeX, 4 figures(EPS

Confirmation of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor and antiferromagnetic second-nearest-neighbor interactions in Rb2{}_{2}Cu2{}_{2}Mo3{}_{3}O12{}_{12}

We have investigated magnetic properties of Rb$_2$Cu$_2$Mo$_3$O$_{12}$ powder. Temperature dependence of magnetic susceptibility and magnetic-field dependence of magnetization have shown that this cuprate is a model compound of a one-dimensional spin-1/2 Heisenberg system with ferromagnetic first-nearest-neighbor (1NN) and antiferromagnetic second-nearest-neighbor (2NN) competing interactions (competing system). Values of the 1NN and 2NN interactions are estimated as $J_1 = -138$ K and $J_2 = 51$ K ($\alpha \equiv J_2 / J_1 = -0.37$). This value of $\alpha$ suggests that the ground state is a spin-singlet incommensurate state. In spite of relatively large $J_1$ and $J_2$, no magnetic phase transition appears down to 2 K, while an antiferromagnetic transition occurs in other model compounds of the competing system with ferromagnetic 1NN interaction. For that reason, Rb$_2$Cu$_2$Mo$_3$O$_{12}$ is an ideal model compound to study properties of the incommensurate ground state that are unconfirmed experimentally.Comment: 6 pages, 4 figure

Boundary S matrices for the open Hubbard chain with boundary fields

Using the method introduced by Grisaru et al., boundary S matrices for the physical excitations of the open Hubbard chain with boundary fields are studied. In contrast to the open supersymmetric t-J model, the boundary S matrix for the charge excitations depend on the boundary fields though the boundary fields do not break the spin-SU(2) symmetry.Comment: Latex,12 page

P-Process Nucleosynthesis inside Supernova-Driven Supercritical Accretion Disks

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M_solar, using the self-similar solution of an optically thick advection dominated flow. Supercritical accretion is expected to occur in a supernova with fallback material accreting onto a new-born compact object. It is found that appreciable amounts of p-nuclei are synthesized via the p-process in supernova-driven supercritical accretion disks (SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs have similar feature to those of the oxygen/neon layers in Type II supernovae when the abundance of the fallback gas far from the compact object is that of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in the SSADs as in Type II supernovae. If the fallback gas is mixed with a small fraction of proton through Rayleigh-Taylor instability during the explosion, significant amounts of Mo92 are produced inside the SSADs. Ru96 and La138 are also produced when the fallback gas contains abundant proton though the overall abundance profile of p-nuclei is rather different from that of the solar system. The p-process nucleosynthesis in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if several percents of fallback matter are ejected via jets and/or winds.Comment: 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty, accepted for publication by the Astronomical Journal (March, 2003