A Note on Even Cycles and Quasirandom Tournaments

A cycle in a tournament T is said to be even, if when walking along C, an even number of edges point in the wrong direction, that is, they are directed from to . In this short article, we show that for every fixed even integer , if close to half of the k‐cycles in a tournament T are even, then T must be quasirandom.This resolves an open question raised in 1991 by Chung and Graham 1991.     

Cobalt Growth on the Tips of CdSe Nanorods

Best of both worlds : Reduction of an organometallic Co precursor on preformed CdSe nanorods yields two distinct semiconducting–magnetic heterostructures (see picture). The selective growth of Co on the tips of CdSe first gives nanosphere–nanorod dimers, which evolve into nanorod–nanorod structures. In the hybrid objects the magnetic properties of Co remain intact, while the luminescence properties of CdSe are affected but not completely quenched.

     

Size Dependence of Molar Absorption Coefficients of CdSe Semiconductor Quantum Rods

Fundamental properties: The molar absorption coefficients of CdSe quantum rods are determined experimentally as a function of their dimensions (see figure). Far above the band gap a simple dependence on volume is seen. The behavior at the band gap manifests a concentration of oscillator strength with decreased diameter in agreement with strong quantum confinement behavior.

     

Sur l'ensemble exceptionnel de Weyl

It is well known since H. Weyl's work that for any given real number $r>1$, the set $W_r$ consisting of positive real numbers λ for which the sequence ${(\lambda r^n)}_{n\in \mathbb{N}}$ is not uniformly distributed modulo 1, has Lebesgue measure zero. In this Note, without use the concept of Hausdorff dimension, one shows among other things that these sets $W_r$ are uncountable. To cite this article: B. Farhi, C. R. Acad. Sci. Paris, Ser. I 343 (2006).     

On a problem of chvatal

In this note we answer in the negative the following question posed by Chvátal [1].     

Electrical conductivity at high temperature and thermodynamic study of point defects in single crystalline cuprous oxide

In order to follow the variation of point defect interactions in relatively concentrated solutions we have studied the electrical conductivity of cuprous oxide in the range of temperature 650–1100°C and for oxygen partial pressures greater than 10^?6 atm. The P^{$\text{1}\text{π}$}_O2 dependence of the conductivity varied non linearly from about n = 8 for P_o2 close to 10^?6 atm. to lower values of n with increasing oxygen partial pressure. The activation enthalpy of conductivity determined in these ranges of temperature and oxygen partial pressure has been found to be also a function of temperature and varied between 12 and 17 kcal mol^?1.The interpretation of these results has permitted us to show that the departure from linearity of the plots of log or log $\text{σ = ?(}\text{l}\text{T}\text{)}$ excludes the existence of an ideal solution of ionized and non-ionized copper vacancies as was proposed previously in the literature. To explain these results it is possible to take into account a partially disordered distribution of these defects. It is shown that the increase of interactions and consequently the variation of the electrical conductivity as a function of the thermodynamic parameters, may be simulated by an ideal solution including new charged species of the type (V'_CuV^x_Cu).     

The density dependence of the quasi-free electron state in fluid xenon and krypton

Photoinjection measurements show that in liquid and gaseous krypton and xenon V₀ is negative. V₀ has a minimum (?0.77 eV for Xe and ?0.53 eV for Kr) near the density of the mobility maximum, becoming zero at densities of the order of 10²⁰ atoms/cm³.     

Thermodynamic study of point defects in single crystalline nickel oxide: Analysis of experimental results

Our preceding experimental results on electrical conductivity in nickel oxide at high temperature [1] have been interpreted assuming the simultaneous presence of singly and doubly ionized nickel vacancies. A thermodynamic model is proposed on this basis, which allows to determine, as functions of Po₂, and T, the laws of variations of n and of ΔH_σ, which are correlated with conductivity in the general expression:

$\text{d ln}\text{σ =}\text{1}\text{n}\text{d In Po}{}_2\text{?}\text{ΔH}{}_{\mathrm{\sigma }}\text{R}\text{d(}\text{1}\text{T}\text{)}$

.The ratios $\text{[V′}{}_{\mathrm{Ni}}\text{]}\text{{[V″}{}_{\mathrm{Ni}}\text{]}\text{+ [V′}{}_{\mathrm{Ni}}\text{]}}$ hae been determined for the whole range of existence of N values and experimental results of electrical conductivity are in good agreement.     

Superconductivity and magnetism in Y1−x Ca x Sr2GaCu2O7−δ

Samples of Y_1–x Ca _x Sr₂GaCu₂O_7– (x=0, 0.4) doped with⁵⁷Fe, prepared under various oxygen pressures, have been studied by magnetometry and Mössbauer spectroscopy. Most of the iron ions (Fe³⁺) enter the Ga(Cu(1)) site. For thex=0 sample, the Mössbauer spectra of the iron nuclei in the Cu(2) sublattice display magnetic order of Cu,T _N=370 K. The iron ions in the Ga site display magnetic order only at low temperatures. At temperatures above 90 K, these iron ions display a pure quadrupole doublet Mössbauer spectrum. The samplex=0.4 also displays magnetic order of the Cu(2) site,T _N370 K. A sharp drop in the hyperfine field is observed atT _N, probably associated with a first-order phase transition or two-dimensional ordering. The iron nuclei in the Ga site display paramagnetic long spin relaxation time phenomena at 4.2 K. Thex=0.4 sample prepared under 110 atm oxygen pressure, displays superconductivity,T _c50 K. The Mössbauer spectra give evidence of the presence of two phases. One displays magnetic order, the other is paramagnetic, the last is probably associated with the superconducting phase.