On the computational complexity of partial covers of Theta graphs

By use of elementary geometric arguments we prove the existence of a special integral solution of a certain system of linear equations. The existence of such a solution then yields the NP-hardness of the decision problem on the existence of locally injective homomorphisms to Theta graphs with three distinct odd path lengths.     

On-Line Multielement Preconcentration and Inductively Coupled Plasma Atomic Emission Spectrometric Determination of Transition Metals Using a Flow Injection Hydraulic High-Pressure Nebulization–Desolvation Sample Introduction System

A method was developed for simultaneous preconcentration and on-line determination of 15 transition metals (Ag, Au, Cd, Cr, Cu, Fe, In, Ni, Pb, Pd, Pt, Ti, Tl, V, Zn). A polyether–ether–ketone (PEEK) loop as preconcentration unit introduced by us earlier was used for the multielement flow injection (FI) preconcentration of transition metal–pyrrolidinedithiocarbamate complexes. The preconcentrated complexes were eluted with isobutylmethyl ketone and introduced into the inductively coupled plasma with a hydraulic high-pressure nebulizer (HHPN) and desolvation unit. The desolvation system, the use of which was necessary for aerosol of isobutylmethyl ketone eluant, was optimized. The enrichment factors of the 15 transition metals were 14–67 due to 2 min of preconcentration time.     

Evaluation of the inelastic mean free path (IMFP) of electrons in polyaniline and polyacetylene samples obtained from elastic peak electron spectroscopy (EPES)

The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters ( _ach ) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.      

A lower estimate for the achromatic number of irreducible graphs

The achromatic number of a graph is the largest number of independent sets its vertex set can be split into in such a way that the union of any two of these sets is not independent. A graph is irreducible if no two vertices have the same neighborhood. The achromatic number of an irreducible graph with n vertices is shown to be $\text{≥(}\text{1}\text{2}\text{?0(1))log}\text{n?}\text{log log}\text{n,}$ while an example of Erdös shows that it need not be log n/log 2+2 for any n. The proof uses an indiscernibility argument.     

High-temperature determination of the rate coefficient for the reaction H2 + CN → H + HCN

The rate coefficient of the reaction has been determined in the temperature range of 2700–3500 K using a shock tube technique. C₂N₂? H₂? Ar mixtures were heated behind incident shock waves and the early-time CN history was monitored using broad-band absorption spectroscopy. The rate coefficient providing the best fit to the data was in good agreement with extrapolations of previously published low-temperature results.     

Complexation of nitrostyrenes with soluble β-cyclodextrin polymer studied by reversed-phase thin-layer chromatography

Cyclodextrin complexation decreases the apparent lipophilicity of hydrophobic guest molecules. A higher complex stability results in a larger decrease of lipophilicity as determined by reversed-phase thin-layer chromatography. The method was applied to study the complex formation of 33 nitrostyrene derivatives with a water soluble cross linked -cyclodextrin polymer (weight average molecular weight: 4300). The substituents in thepara position of the benzene ring had a higher impact on the complex stability than those in themeta andortho positions. The substituents on the alkyl side chain influenced the complex stability to the same extent as those on the benzen ring.     

The reaction of alkoxides with dicobalt octacarbonyl: Trapping of the Co(I) intermediate in the disproportionation (“base reaction”) with a hardLewis base

Dicobalt octacarbonyl reacts with alcoholates (RO^–) yielding alkoxycarbonylcobalt tetracarbonyls,ROC(O)Co(CO)₄.

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Reaktion von Alkoxiden mit Dicobaltoctacarbonyl: Abfangen des Co(I) Zwischenproduktes in der Disproportionierung (Basen-Reaktion) mit einer hartenLewis Base (Kurze Mitteilung)

Zusammenfassung Dicobaltoctacarbonyl reagiert mit Alkoxiden (RO^–) zu Alkoxycarbonylcobalt tetracarbonylen,ROC(O)Co(CO)₄.

     

Organic layered crystals with adjustable interlayer distances of 1-naphthylmethylammonium n-alkanoates and isomerism of hydrogen-bond networks by steric dimension

A series of 1-naphthylmethylammonium n-alkanoates from acetate to triacontanoate produce isomorphic layered structures in the crystalline state. The interlayer distances, d-spacings, are proportional to the lengths of the alkyl chains. This is attributed to synergic intermolecular interactions; pi-pi and CH-pi interactions of the naphthalene rings between the cations, hydrophobic interactions of the alkyl chains, and two-dimensional hydrogen-bond networks between the primary ammonium cations and the carboxylate anions. Salts made from carboxylic acids wider than 5.5 A in the cross sections produce another columnar structure with a one-dimensional ladder-type hydrogen-bond network. Steric parameters of the acid components provide an explanation for the isomerism of the hydrogen-bond network.     

Synthesis of Racemic and Enantiomerically Enriched a-Oxyfunctionalized Benzocyclanones and Chromanones by Dimethyldioxirane and Dimethyldioxirane/Mn(III) salen System

Enolacetates of benzocyclanones and chromanones were synthesized and treated with dimethyldioxirane and the asymmetric oxidizing system dimethyldioxirane/chiral, non-racemic Mn(III) salen complex/axial ligand. The latter reagent resulted in the corresponding enantiomerically enriched cyclic -hydroxy ketones and their acetates in moderate-to-good yields and modest enantioselectivity under mild and neutral conditions from tetralone and chromanone. On the contrary, flavanone provided poor yields due to the competitive C–H insertion at position 2. The use of R,R-Mn(III)salen catalyst induced an S absolute configuration at the position in the whole series.