Synthesis of a key intermediate of novel galbonolide analogues via efficient construction of a conjugated diene system

The development of an efficient synthetic method enabled multi-gram synthesis of a key intermediate, which is useful for the modification at the C6-functional group of galbonolide analogues. The structure of a key intermediate including a conjugated diene was afforded by Horner-Emmons reaction, alkylation of Weinreb amide with alkyl lithium and a subsequent Wittig reaction.     

A planning model for crisis management in the tourism sector

The article proposes an analytical planning framework for managing crisis situations in the tourism industry. It applies the principle of acting in successive phases by which each stage aims to reduce the residual negative effects remaining after implementing the preceding one. The first phase relates to pre-crisis policy measures designed to reduce the overall sensitivity of the industry to crisis situations, the second phase deals with response policies to be implemented when conditions of crisis-certainty exist, and the third phase considers various specific short-term supplementary measures.The optimization process employs portfolio theory and linear programming models. It can be used by governmental agencies in charge of long-range countrywide or regional planning as an auxiliary tool for policy decesions.     

New relaxation phenomena in the outer atomic layers of Fe{211}

A low-energy electron diffraction analysis of a {211} surface of body-centered cubic iron reveals relaxations in the directions perpendicular and parallel to the surface plane. Both relaxations alternate in successive layers. The perpendicular relaxation goes from contraction of 10.5% to expansion of 5% to contraction of 1%. The parallel relaxation goes from a shift of the first layer of 0.24Å (10% of the nearest neighbor distance) toward more symmetrical registration with the second layer, to an opposite shift of 0.035 Å of the second layer with respect to the third.     

The negative activity limit of stability and the coagulation values of silver halides

Summary The negative stability limit of AgI shifts with increasing concentrations of the solvents ethanol, acetone and glycine in water asymptotically to a lower limiting pAg value. The main shift occurs in 10 mol% of acetone and ethanol and 1.8 mol% of glycine from pAg 6.2 in water to 3.0, 4.2 and 3.0 resp. In solutions of the same solvent content the coagulation values remain practically equal to the coagulation values in pure water, the change being less than 0.2. In the negative stability region from pI 1 to the negative stability limit in the water solvent mixture the coagulation values of cations of valency 1,2 and 3 are practically constant and independent of the activity of the potential determining ion in excess. The negative limit in 10 to 15 mol% acetone and ethanol in the AgBr system is 4.7 and 5.4 resp. The present results were shown to confirm well the ion exchange theory of coagulation.

---

Zusammenfassung Die negative Stabilit?tsgrenze von AgI verlagert sich mit steigenden Konzentrationen der L?sungsmittel ?thylalkohol, Aceton und Glycin in Wasser asymptotisch zu niedrigeren pAg-Grenzwerten. Die Hauptverschiebung findet in 10 Mol%igem Aceton und ?thylalkohol und 1,8 Mol%igem Glycin von pAg 6,2 in Wasser zu 3,0, 4,2 und 3,0 resp. statt. In L?sungen vom selben Gehalt bleiben die Koagulationswerte praktisch gleich denen im reinen Wasser; die ?nderung ist kleiner als 0,2. Im negativen Stabilit?tsbereich von pI 1 zur negativen Stabilit?tsgrenze in Wasser-L?sungsmittel-Gemischen sind die Koagulationswerte von Kationen der Valenz 1–3 praktisch konstant und unabh?ngig von der Aktivit?t des potentialbestimmenden Ions. Die negative Grenze ist in 10–15 Mol% Aceton und ?thyl?ther im AgBr-System 4,7 und 5,4 resp. Diese Resultate best?tigen gut die Ionenaustauschtheorie der Koagulation.

---

---

Contribution No. 102 from the Department of Physical Chemistry, Faculty of Science, University of Zagreb, Zagreb, Yugoslavia.     

Rowers coupled hydrodynamically. Modeling possible mechanisms for the cooperation of cilia

We introduce a model system of stochastic entities, called rowers which include some essentials of the behavior of real cilia. We introduce and discuss the problem of symmetry breaking for these objects and its connection with the onset of macroscopic, directed flow in the fluid. We perform a mean field-like calculation showing that hydrodynamic interaction may provide for the symmetry breaking mechanism and the onset of fluid flow. Finally, we discuss the problem of the metachronal wave in a stochastic context through an analytical calculation based on a path integral representation of our model equation. Received 12 June 2001 and Received in final form 9 January 2002