Three-Class Association Schemes

We study (symmetric) three-class association schemes. The graphs with four distinct eigenvalues which are one of the relations of such a scheme are characterized. We also give an overview of most known constructions, and obtain necessary conditions for existence. A list of feasible parameter sets on at most 100 vertices is generated.     

Synthesis,structure, and magnetic properties of the fullerene-based ferromagnets Eu3C70 and Eu9C70

Intercalation of C(70) with europium affords two kinds of magnetic compounds, a canted antiferromagnet Eu(x)C(70) (x approximately 3) and a ferromagnet Eu(x)C(70) (x approximately 9) with transition temperatures (T(C)) of 5 and 38 K, respectively. The Curie constants in the paramagnetic phase and the saturation moment in the ferromagnetic phase are both understood by the full moment of Eu(2+) for both systems. The structure of Eu(3)(-)(delta)C(70) (delta approximately 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu(9)(-)(delta)C(70) (delta approximately 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu(2+) ions is observed in the enhanced size octahedral holes. The observed T(C) of the Eu(9)(-)(delta)C(70) ferromagnet is comparable to or larger than those of simple binary Eu-based ferromagnets, such as Eu chalcogenides or carbides, despite the low atomic ratio of Eu in the chemical formulas. This can be understood by the short Eu(2+)-Eu(2+) distances and high coordination numbers permitted by the multiple occupation by Eu(2+) ions of the expanded octahedral interstitial sites in higher fullerene-based solids.     

A non-uniformly travelling shock-wave in an LMS-gas

In this paper an LMS-gas is considered. This is an ideal gas with constant specific heats but with a special entropy distribution, so that generalized Riemann invariants r* and s* exist. A flow with r* and s* constant has the property that the gas moves as a rigid body with a constant acceleration or deceleration. It is shown that a flow composed of two domains, in each of which r* and s* are constant, separated by a plane normal shock-wave is admitted by the Rankine-Hugoniot equations. The path of the shock-wave is calculated exactly and a reasonably realistic situation is suggested to generate this composite flow.     

Structural and optical properties of MgxAl1-xHy gradient thin films: a combinatorial approach

The structural, optical and dc electrical properties of Mg_xAl_1-x (0.2≤x≤0.9) gradient thin films covered with Pd/Mg are investigated before and after exposure to hydrogen. We use hydrogenography, a novel high-throughput optical technique, to map simultaneously all the hydride forming compositions and the kinetics thereof in the gradient thin film. Metallic Mg in the Mg_xAl_1-x layer undergoes a metal-to-semiconductor transition and MgH₂ is formed for all Mg fractions x investigated. The presence of an amorphous Mg-Al phase in the thin film phase diagram enhances strongly the kinetics of hydrogenation. In the Al-rich part of the film, a complex H-induced segregation of MgH₂ and Al occurs. This uncommon large-scale segregation is evidenced by metal and hydrogen profiling using Rutherford backscattering spectrometry and resonant nuclear analysis based on the reaction ¹H(¹⁵N,αγ)¹²C. Besides MgH₂, an additional semiconducting phase is found by electrical conductivity measurements around an atomic [Al]/[Mg] ratio of 2 (x=0.33). This suggests that the film is partially transformed into Mg(AlH₄)₂ at around this composition. PACS 78.20.-e; 68.55.-a; 64.75.+g     

Nano-Fe3O4@silica sulfuric acid as a reusable and magnetically separable potent solid acid catalyst in Biginelli-type reaction for the one-pot multicomponent synthesis of fused dihydropyrimidine derivatives: A greener NOSE and SFRC approach

An efficient, highly product selective, eco-friendly, one-pot multicomponent synthesis of dihydropyrimidine derivatives via Biginelli reaction has been described. The reaction was developed by greener nanoparticle-catalyzed organic synthesis enhancement (NOSE) chemistry and solvent free reaction condition (SFRC) approaches, which helped us in making the procedure greener. The reaction went smoothly with a diverse range of aromatic, aliphatic, hetero-aromatic aldehydes, different amine sources, as well as various β-dicarbonyl compounds, showing the flexibility of this methodology. Magnetically separable nano-Fe₃O₄@SiO₂@SO₃H, which acts as a potent solid acid catalyst, was characterized by FT-IR, SEM, EDX and TEM, VSM, and TGA analyses. The catalyst was recycled from the reaction mixture easily by an external magnet and reused in five more consecutive runs without much decrease in catalytic activity. Its catalytic efficiency was compared to other nano and bulk solid acid catalyst in order to ascertain the best combination for the conversion.     

Modeling the drying of ink-jet-printed structures and experimental verification

This article presents a numerical model that was developed for the drying of ink-jet-printed polymer solutions after filling the pixels in a polymer LED display. The model extends earlier work presented in the literature while still maintaining a practical approach in limiting the number of input parameters needed. Despite some rigorous assumptions, the model is in fair agreement with experimental data from a pre-pilot ink-jet printing line. Comparison inside a single pixel is shown, as well as a general trend in which the amount of polymer that is transported out of the central part of the pixel decreases with the rate of viscosity increase as a function of polymer concentration. Moreover, the effect of a varying solute diffusion coefficient is studied.