Swelling instability of surface-attached gels as a model of soft tissue growth under geometric constraints

The purpose of this work is to provide a theoretical analysis of the mechanical behavior of the growth of soft materials under geometrical constraints. In particular, we focus on the swelling of a gel layer clamped to a substrate, which is still the subject of many experimental tests. Because the constrained swelling process induces compressive stresses, all these experiments exhibit surface instabilities, which ultimately lead to cusp formation. Our model is based on fixing a neo-Hookean constitutive energy together with the incompressibility requirement for a volumetric, homogeneous mass addition. Our approach is developed mostly, but not uniquely, in the plane strain configuration. We show how the standard equilibrium equations from continuum mechanics have a similarity with the two-dimensional Stokes flows, and we use a nonlinear stream function for the exact treatment of the incompressibility constraint. A free energy approach allows the extension both to arbitrary hyperelastic strain energies and to additional interactions, such as surface energies. We find that, at constant volumetric growth, the threshold for a wavy instability is completely governed by the amount of growth. Nevertheless, the determination of the wavelength at threshold, which scales with the initial thickness of the gel layer, requires the coupling with a surface effect. Our findings, which are valid in proximity of the threshold, are compared to experimental results. The proposed treatment can be extended to weakly nonlinearities within the aim of the theory of bifurcations.     

Bis(crown ether) and Azobenzocrown Derivatives of Calix[4]arene. A Review of Structural Information from Crystallographic and Modelling Studies

The association within one molecule ofcalix[4]arene and crown ether moieties leads toligands with new complexing properties. In particular,calix[4]arene bis(crown-6) and some of itsderivatives have been shown to be highly selectiveextractants for caesium ions. This review presents thebackground of the study and the results of crystalstructure determinations and molecular modellingcalculations performed during the investigation of twomolecular families, the bis(crown ether) and theazobenzocrown derivatives of calix[4]arene.     

A 1:1:1 chloro­form/tetra­hydro­furan solvate of p-tert-butyl­tetra­homo­dioxa­calix­[4]­arene

The title compound, 7,13,21,27-tetra-tert-butyl-3,17-di­oxa­penta­cyclo­[23.3.1.1^5,9.1^11,15.1^9,23]ditriaconta-1(29),­5,­7,­9(30),11(31),­12,­14,­19(32),­20,­22,­25,­27-do­deca­ene-29,­30,­31,­32-tetraol, crystallizes as a solvate with one mol­ecule of chloro­form and one mol­ecule of tetra­hydro­furan, C₄₆H₆₀O₆·CHCl₃·C₄H₈O. The calixarene assumes a cone-like conformation stabilized by intramolecular hydrogen bonds involving both phenolic and ether O atoms. The two solvent mol­ecules are located in each of the two half-cone cavities of the calixarene.     

TUNA FISH (T-30) – A new proficiency testing material for the determination of As and Hg in seafood

The quality of the aquatic and marine environment can be monitored by the determination of pollutants in organisms living in this environment. Certified reference materials and well-organised proficiency tests are powerful means of ensuring a constant level of quality and verifying the correct application of standardised methods. The preparation of a tuna fish proficiency testing material for the evaluation of quality of As and Hg monitoring in seafood is described. Preparation and characterisation of the material as well as studies on its homogeneity and stability are described. Concentrations of 3.4 ± 0.2 mg/kg total arsenic and 2.91 ± 0.09 mg/kg total mercury have been determined as target values. Moreover indicative values for some trace elements (Cd, Cu, Ni, Pb, Sr) and some major constituents (Al, Br, C, Ca, Cl, Fe, H, K, Mg, N, Na, P, S, Si, Zn) have also been measured. Received: 29 November 1996 / Revised: 17 February 1997 / Accepted: 22 February 1997     

Three-stage melting of an annelide-type copper complex. A new type of organized phase: Tegma crystals

The solid—solid phase transition of an annlide type copper complex are described. As the temperature is raised, three different constituents of the complex successively melt. In the temperature range 77–95°C, the polyethylene oxide chains and the paraffinic tail are both in a very mobile state while the copper complex sub-units still form a two-dimensional crystalline array.     

A branch-and-cut method for the obnoxious p-median problem

The obnoxious p-median (OpM) problem is the repulsive counterpart of the ore known attractive p-median problem. Given a set I of cities and a set J of possible locations for obnoxious plants, a p-cardinality subset Q of J is sought, such that the sum of the distances between each city of I and the nearest obnoxious site in Q is maximised. We formulate (OpM) as a {0,1} linear programming problem and propose three families of valid inequalities whose separation problem is polynomial. We describe a branch-and-cut approach based on these inequalities and apply it to a set of instances found in the location literature. The computational results presented show the effectiveness of these inequalities for (OpM). The work of the first author has been partially supported by the Coordinated Project C.A.M.P.O. and that of the third author by a short mobility grant, both of the Italian National Research Council.     

Direct access to 2-debenzoyl taxoids by electrochemistry, synthesis of 2-modified docetaxel analogs

A new route to semisynthetic 2-modified docetaxel analogs is described using electrochemical cleavage of the 2-benzoate as the key reaction. Subsequent reacylation at C-2 followed by sequential deprotections afforded the title analogs. Biological results of selected 2-docetaxel analogs are presented.     

Outcomes of voting and planning in single facility location problems

For a given set of users located at the vertices of a network N, we consider the location of a single facility. Two different decision making procedures, voting among the users and minimizing total distance travelled by the users, are compared.Provided that a voting solution exists, it is shown that the two solutions sets coincide if N is a so-called cactus. For general networks, the outcomes of the two procedures are compared in terms of the cyclic structure of N and the number of users.     

Identification of sulfur interferences during organotin determination in harbour sediment samples by sodium tetraethyl borate ethylation and gas chromatography-pulsed flame photometric detection

Because of the high toxicity of organotin compounds and the current regulation about their applications, analytical method usable in routine analysis is required. A speciation procedure based on NaBEt4 ethylation and GC-PFPD analysis has shown to be suitable for the organotin determination. Unfortunately, some matrix effects were observed during the analysis of harbour sediments from Chile. These effects were identified as the alkylation of elemental sulfur and the coelution between the organotin compounds and some dialkylsulfides. The re-optimization of GC parameters and application of solid phase microextraction (SPME) were proposed to solve these analytical problems. Certified reference materials and different harbour sediment samples were analysed in order to evaluate the suitability of the methods for organotin control in complex environment samples.