We introduce several variations of the Turan and Ramsey numbers, including zero-sum and bounded-average Ramsey numbers. Some interesting relations between these concepts are presented. In particular, a generalization of the k-local Ramsey numbers is established. 相似文献
Yttria-stabilized zirconias Zr1?xYxO2?0.5x (tetragonal, cubic fluorite, and cubic CLn2O3-type forms) are investigated by spectroscopic methods. Optically active europium ions that partially substitute yttrium ions act as a structural microprobe. Both conventional ultraviolet and dye laser (site-selective) excitation are used. The yttria-stabilized zirconias may be well described by a cationic sublattice in which tetravalent and trivalent cations are statistically distributed. The anionic sublattice accommodates vacancies at random on oxygen positions. These vacancies in turn cause complex oxygen displacements giving rise to what may be described as a “glass of anions.” 相似文献
Abstract Dipole molecules become arranged in a highly ordered manner within zeolite pores. They are oriented nearly parallel to the straight channels and aligned collectively into one specific direction. They form arrangements different from the crystallization in the free bulk as well as different from arrangements in amorphous hosts. This polar arrangement results in (i) a lowering of the symmetry of the guest-host system compared to the host, (ii) nonlinear optical effects of second order such as second harmonic generation, (iii) a macroscopic polarization giving rise to pyroelectric effects and (iv) special phase transition phenomena in these one-dimensional systems. 相似文献
Oxygen scrambling is observed when a 1:1 mixture of 16O2 and 18O2 in nitrogen/helium buffer (total O2: 5–20%) is treated at atmospheric pressure in a surface discharge plasma reactor. The statistical isotope distribution (16O2/18O2/16O18O = 1:1:2) is achieved with a very low SIE (i.e., the energy per unit volume). This process, implemented by kinetic simulations, is proposed as a chemical probe for the determination of the average O‐atom density in atmospheric plasmas. It was found that, within the explored composition range (5–20% O2 in N2/He buffer), the average O‐atom density increases with SIE, while it decreases with increasing content of O2 in the gas being treated. In contrast, an opposite trend is observed for ozone production, which increases with the concentration of O2 in the treated gas. These observations are consistent with the known reaction of O‐atoms with O2 to form ozone, which, at constant total pressure, is expected to favor ozone production as the concentration of O2 is increased.
