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.     

Shape dependent properties of CdSe nanostructures

We investigate the impact of surface character, shape and size of CdSe particles on their electrostatic and structural properties and discuss consequences for their role as sensitizers. Other than previous theoretical studies which have focussed on a fixed particle shape and a small set of sizes we systematically investigate a large set of more than a thousand nanocrystals with different shapes, sizes, and aspect ratios. This novel approach allows us to draw conclusions on significant correlations of the relevant properties of these crystals with shape, surface character and size. In particular, we find significant differences between the properties of approximately spherically shaped particles, and particles with well defined surfaces along crystal planes but also between particles of the latter class. A surprisingly strong impact of the specific shape and surface configuration is found for the internal structure well inside the crystal as measured by bond lengths correlated with coordination numbers.     

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.

     

Electric field induced hyperfine level-crossings in (nD)Cs at two-step laser excitation: Experiment and theory

The pure electric field level-crossing of m_F Zeeman sublevels of hyperfine F levels at two-step laser excitation is described theoretically and studied experimentally for the nD_3/2 states in Cs with n = 7, 9 and 10, by applying a diode laser in the first 6S_1/2 → 6P_3/2 step and a diode or dye laser for the second 6P_3/2 → nD_3/2 step. Level-crossing resonance signals are observed in the nD_3/2 → 6P_1/2 fluorescence. A theoretical model is presented to describe quantitatively the resonance signals by correlation analysis of the optical Bloch equations in the case when an atom simultaneously interacts with two laser fields in the presence of an external dc electric field. The simulations describe well the experimental signals. The tensor polarizabilities α₂ (in ) are determined to be 7.45(20) × 10⁴ for the 7D_3/2 state and 1.183(35) × 10⁶ for the 9D_3/2 state; the electric field calibration is based on measurements of the 10D_3/2 state, for which α₂ is well established. The α₂ value for the 7D_3/2 state differs by ca. 15% from the existing experimentally measured value.     

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.     

Optode membrane for continuous measurement of silver ions

An optical sensor (optode) membrane for continuous monitoring of silver ion is presented. It is composed of plasticized poly(vinyl chloride) (PVC), a silver-sensitive chromo-ionophore, and a lipophilic borate salt acting as an anionic site. The membrane selectively responds to silver ion in the concentration range from 50 M to 10 mM, giving a reversible colour change from blue to pink, with response times of the order of 2 min. The acridinium dye acts as both the recognition element and the chromo—ionophore. Its long-wave absorption band is at around 680 nm, which makes it compatible with existing LED light sources and diode lasers. A lipophilic octadecyl side chain renders it highly lipophilic and this prevents its leakage out of the PVC membrane. Hence, the operational lifetime exceeds 1 week, without any changes in the work function.