Molecular interactions in the poly(vinyl chloride)-di-n-butylphthalate system determined by infrared spectroscopy

Infrared studies of the poly(vinyl chloride) (PVC)/di-n-butylphthalate (DBP) system are reported. Spectra of DBP in different solvents seem to be indicative of the ability of DBP to interact with PVC chains in the same way as with polyesters and of competitive interactions between DBP molecules and DBP with PVC. Plots of the width at half-height of the carbonyl stretching vibration, measured at 25 and at ?180°C, as a function of composition, show a sudden change of slope at about 60% PVC concentration by weight, indicating that above this polymer composition interaction between DBP and PVC dominates that between DBP molecules. This change corresponds to a “singularity” observed in the dependence of the glass transition temperature on composition.     

Contribution to the Study of the Solid-state Reaction of Mercury With Pure Rhodium

Thermogravimetry (TG) and other analysis techniques (EDX, SEM, Mapping surface, X-ray diffraction, inductively coupled argon plasma emission spectroscopy and atomic spectrometry with cold vapor generation) were used to study the reaction of Hg with Rh. The results permitted the suggestion that, when subjected to heat, an electrodeposited Hg film reacts with Rh to form intermetallic products with different stabilities, as indicated by at least three mass loss steps. In the first step, between room temperature and 160°C, only the bulk Hg is removed. From this temperature up to about 175°C, the mass loss can be attributed to the desorption of a film of metallic Hg. The last step, from 175 to 240°C, can be ascribed to the removal of Hg from a thin dark film of RhHg₂ . This revised version was published online in July 2006 with corrections to the Cover Date.     

Coordination behaviour of 2-halo-1,3,4-thiadiazoles towards cobalt(ii) and nickel(ii)

Summary A series of cobalt(II) and nickel(II) 2-X-1,3,4-thiadiazole complexes (X=Cl or Br) were investigated by electronic, n.m.r., Raman and i.r. spectroscopy, and by thermogravimetric analyses, magnetic moments and conductivity measurements.The complexes havepseudo-tetrahedral or pseudo-octa-hedral stereochemistries with MN₂X₂ (X=Cl or Br), MN₄X₂ (X=Cl, Br or O) or MN₃O₃ chromophores.The ligands are mono- or bi-dentate without involving the sulphur atom. Surprisingly, the chloro-derivative ligand seems to be more nucleophilic than the bromo-analogue.The computed (CNDO/2) molecular orbital indices for the uncomplexed ligands indicate that the coordination sites are the nitrogen atoms.In connection with our previous work⁽¹⁾ on the coordination ability of heterocyclic ligands with interesting biological^(2,3) and pharmaceutical⁽⁴⁾ properties and containing endocyclic nitrogen and sulphur donor atoms, we have considered the 1,3,4-thiadiazole ring, which is the main framework of a very important class of diuretic drugs, the sulphonamide inhibitors⁽⁵⁾ of the zinc m tallo-enzyme carbonic anhydrase.In this study we have investigated the coordination behaviour of the 2-chloro-1,3,4-thiadiazole(ctz) and the 2-bromo-1,3,4-thiadiazole (btz).     

Semisynthesis of dimeric proteins by expressed protein ligation

A one-pot synthesis of homodimeric proteins is described. The synthetic strategy is based on a double expressed protein ligation reaction between thioester peptides and a new bis-cysteinyl linker. The protocol was also applied to the synthesis of heterodimers.     

On the quantum Teichmüller invariants of fibred cusped 3-manifolds

This paper defines the pressure metric on the Moduli space of Margulis spacetimes without cusps and shows that it is positive definite on the constant entropy sections. It also demonstrates an identity regarding the variation of the cross-ratios.     

A fast 3D dual boundary element method based on hierarchical matrices

In this paper a fast solver for three-dimensional BEM and DBEM is developed. The technique is based on the use of hierarchical matrices for the representation of the collocation matrix and uses a preconditioned GMRES for the solution of the algebraic system of equations. The preconditioner is built exploiting the hierarchical arithmetic and taking full advantage of the hierarchical format. Special algorithms are developed to deal with crack problems within the context of DBEM. The structure of DBEM matrices has been efficiently exploited and it has been demonstrated that, since the cracks form only small parts of the whole structure, the use of hierarchical matrices can be particularly advantageous. Test examples presented show that, with the proposed technique, substantial increase in number of elements over the crack surfaces leads only to moderate increases in memory storage and solution time.     

Relative topological degree and variational inequalities

We give a new definition of the relative topological degree for multimaps compositions of approximable multimaps and continuous map. We apply this notion to prove an existence result for variational inequalities of Stampacchia’s type in finite dimensional vector spaces. Finally we obtain the same results also for multimaps compositions of selectionable multimaps and continuous map.     

Sulla caratterizzazione dei grafi domistabili

Riassunto Viene presentato un algoritmo atto a verificare se un grafo è domistabile, tale essendo ogni grafo in cui qualsiasi insieme dominante minimale di nodi è indipendente. L’algoritmo, che implica un numero di confronti polinomiale, rispetto al numero dei nodi, si basa sulla ricerca di insiemi di nodi dotati di particolari proprietà.

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Summary In the present paper an algorithm is proposed which verifies ?domistability? in graphs. A graph is called domistable when each minimal dominating set of nodes is also an independent one. The algorithm, polynomial in the number of nodes, is based on the systematic search for node subsets with particular properties.

     

Supercharacters,symmetric functions in noncommuting variables,and related Hopf algebras

We identify two seemingly disparate structures: supercharacters, a useful way of doing Fourier analysis on the group of unipotent uppertriangular matrices with coefficients in a finite field, and the ring of symmetric functions in noncommuting variables. Each is a Hopf algebra and the two are isomorphic as such. This allows developments in each to be transferred. The identification suggests a rich class of examples for the emerging field of combinatorial Hopf algebras.