EPR study of the high-TC superconductor YBa2Cu3O7−δ

EPR spectra of superconducting YBa₂Cu₃O_7-δ and insulating Y₂BaCuO₅ have been examined. The intensity of Cu²⁺ ions in YBa₂Cu₃O_7-δ is about 1/3000 of that in Y₂BaCuO₅ at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu²⁺ ions in YBa₂Cu₃O_7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa₂Cu₃O_7-δ specimen is shifted. An additional EPR line is found for YBa₂(Cu_2.94Cr_0.06)O_7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity.     

Cluster-Orbital Shell Model Approach with a Treatment of Partially Pauli-Forbidden States

We study the origin of a sudden change of the radius of oxygen isotopes at ²³O in terms of a coupled-channel model approach. We use the cluster-orbital shell model approach for describing the system. Qualitatively, the sudden change of the radius can be understood as the competition of occupation of the valence neutrons and the component of the core configuration. For the ²³O case, the effect of the partially Pauli-forbidden states of the 1s _1/2-orbit is small in the excited-core configuration.     

On convex decompositions of a planar point set

Let P be a planar point set in general position. Neumann-Lara et al. showed that there is a convex decomposition of P with at most elements. In this paper, we improve this upper bound to .     

Rao's conjecture on self-complementary graphs with K-factors

Rao posed the following conjecture, “Let G be a self-complementary graph of order p, π = (d₁ … dp) be its degree sequence. Then G has a k-factor if and only if π ? k, = (d1 ? k, … dP ? k) is graphical.” We construct a family of counterexamples for this conjecture for every k ? 3.     

A rodlike organogelator: fibrous aggregation of azobenzene derivatives with a syn-chiral carbonate moiety

A chiral azobenzene derivative containing a cyclic syn-carbonate moiety functions as a gelator for various organic solvents; the dipole-dipole interaction drives the fibrous self-assembly of the rodlike gelator.     

Radical addition of ethers to imines initiated by dimethylzinc

Ethers undergo addition to imines in the presence of dimethylzinc and air through a radical process. [reaction: see text]     

Novel antibacterial macrolides: synthesis of 15-membered diolides

Novel 15-membered macrolides possessing the dilactone skeleton, diolides 13a and 13b, have been synthesized in our research program aimed at finding new antibacterial macrolides. Key strategic elements of the approach include the ring-expanding reaction of 13-membered dilactones, prepared from erythromycin A (Ery-A), to 15-membered dilactones via intramolecular translactonization. The absolute configuration at the regenerated C-8 position of the new diolides was determined by chemical transformation, leading to the corresponding lactam analogues, whose stereochemistry is known in the literature. For further confirmation, X-ray analysis was performed. The X-ray structure determination of 13a revealed a backbone conformation similar to that of Ery-A. Novel 15-membered diolide 13a and the 11,12-diol 18 exhibited antibacterial activities comparable to that of Ery-A.     

Generalized Waiting Time Problems Associated with Pattern in Polya's Urn Scheme

Let X ₁, X ₂, ... be a sequence obtained by Polya's urn scheme. We consider a waiting time problem for the first occurrence of a pattern in the sequence X ₁, X ₂, ... , which is generalized by a notion score. The main part of our results is derived by the method of generalized probability generating functions. In Polya's urn scheme, the system of equations is composed of the infinite conditional probability generating functions, which can not be solved. Then, we present a new methodology to obtain the truncated probability generating function in a series up to an arbitrary order from the system of infinite equations. Numerical examples are also given in order to illustrate the feasibility of our results. Our results in this paper are not only new but also a first attempt to treat the system of infinite equations.