New measures of proximity for the assignment algorithms in the MDVRPTW

This paper proposes new proximity measures for assignment algorithms for the Multi-Depot Vehicle Routing Problem with Time Windows (MDVRPTW). Given the intrinsic difficulty of this problem class, two-step approximation methods of the type ‘cluster first, route second’ seem to be the most promising for practical size problems. The focus is on the clustering phase, the assignment of customers to depots. Our approach is to extend the existing metrics with time windows. New measures that include time windows and distances are added to two assignment heuristics, that previously only used distance to evaluate proximity between customers and depots. A computational study of their performance is presented, which shows that the inclusion of time windows in the measures of proximity gives better results, in terms of routing, than only using the distance.     

Phase composition, microstructure and electrical properties of alumina-zirconia eutectic composites

Oxide eutectic composites prepared by a directional solidification are noticeable for their good mechanical properties and high temperature stability in oxidizing environments. In this paper we study the influence of stabilizers (Y, Sc) on the phase composition, microstructure and electrical properties of Al₂O₃ - ZrO₂ eutectic composites. At a hypereutectic composition of the melt, we have prepared the composites with tetragonal ZrO₂, which possesses conductivities comparable to those of the composites containing cubic ZrO₂. An addition of Sc₂O₃ improves the ionic conductivity of the Al₂O₃ - (Y₂O₃)ZrO₂ eutectic composite at high temperatures. Both the microstructure and ionic conductivity do not change along the composite (grown at a constant growth rate). Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Strong short range magnetic order in ferromagnetic transition metals above Tc: A theoretical explanation

A theory for the existence of strong short range magnetic order in itinerant magnetism above T_c is presented. We derive a characteristic lengthscale for short range order, given by the square root of bandwidth over k_BT_c. This is of order 20 Å in the ferromagnetic transition metals.     

Solvent-free synthesis and properties of carboxymethyl starch fatty acid ester derivatives

Water-soluble, partially hydrophobized polysaccharides have become attractive due to their potential to act as polymeric surfactants. From carboxymethyl starch (CMS), water-soluble polymeric surfactants were prepared by esterification using two unconvential methods based on (A) a reaction with mixed anhydrides and (B) with methyl laureate (MELA) and methyl esters of the fatty acid complex of rape seed oil (MERO) under ‘solvent-free’ conditions. The obtained CMS derivatives were characterized by structural, surface-active and surfactant performance properties. Esterification using method B was successful in contrast to method A which yielded derivatives with a very low extent of esterification. Although the derivatives reduced the surface tension moderately, they exhibited remarkable emulsifying properties. The performance tests indicated good washing power and antiredeposition efficiency. The results suggest that suitable polymeric surfactants can be prepared by the unconventional esterification method B using both acylation agents. The preparations might substitute the expensive and invasive industrially applied conventional methods.     

Effect of the ionic radius on jump frequencies of alkaline earth cations in NaCl crystals

By comparing diffusion coefficientsD of bivalent cations Ba²⁺, Ca²⁺, Sr²⁺ in NaCl crystals it was shown that in the temperature range above 550 °CD (Ba²⁺)>D (Sr²⁺)>D (Ca²⁺) is valid. Temperature dependences of jump frequenciesw ₂ of these cations are described byw ₂ (Ba²⁺)=(2·15±0·55) × 10¹² × exp {?(0·817±0.007)/kT};w ₂ (Sr²⁺)=(2·9±1·1) × 10¹² × exp {?(0·84±0.02)/kT} andw ₂ (Ca²⁺)=(5·5±6·5) × 10¹⁰ × exp {?(0·51±0·07)/kT}. It was demonstrated that in NaCl crystals the activation enthalpy and the preexponential factor of the jump frequencyw ₂ increase with increasing ionic radius and mass of the bivalent alkaline earth cation.     

Ultrasound effect on Suzuki reactions. 1. Synthesis of unsymmetrical biaryls

Ultrasound effect on the Pd(0) catalysed reaction of arylboronic acid with halobenzenes was investigated. The effect of catalyst, base as well as solvent was tested. Heterogenous reaction of iodoarenes with different arylboronic acids, catalysed by Pd/C and KF as the base in methanol:water mixture resulted in good yields of cross-coupling products. Reaction time of sonochemical reaction was 1 h, while 4 h of reflux was necessary to achieve comparable results. Bromobenzenes gave best results using aqueous solution of PdCl2 as the catalyst, potassium carbonate as the base in toluene:water two phase system using TEBA (benzyltriethylammonium chloride) as PT catalyst. Chlorobenzenes gave just feeble yields of cross-coupling products.     

Intermediate frequency modes in Raman spectra of Ar+‐irradiated single‐wall carbon nanotubes

We study the effect of Ar⁺ irradiation on the intermediate frequency modes (IFM) in Raman spectra of single‐wall carbon nanotubes. We observe new features in the intermediate frequency region from 386 to 635 cm^–1 as the defect concentration increases, whereas at the same time there is a decrease of other IFM modes. After annealing in vacuum, the IFM modes recover and become similar to those of the nanotubes before irradiation. We interpret the new features in the Raman spectra as originating from the phonon density of states that becomes visible in the Raman process due to the presence of defects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Drift mobility and diffusion with an electric field of Ba2+ ions in NaCl crystals

Using a carrier-free tracer¹³³Ba the temperature dependences of the diffusion coefficientD and mobility of Ba²⁺ ions in an electric field have been measured on NaCl crystals in the temperature range from 500 to 750 °C. It is shown that the obtained values ofD are not affected by an electric field (30 V/cm) and that the temperature dependence of the mobility of Ba²⁺ ions is given by(T)=(12·3±1·9) exp [-(1·51±0·09) eV/kT]. Vacancy jump frequencies near a Ba²⁺ ion and the Gibbs free energy of association of this ion with a vacancy have been calculated in terms of a simple 5-frequency model for impurity diffusion by a vacancy mechanism.