Principal component analysis and cluster analysis for the characterization of dental composites

Various experimental dental materials were characterized using chemometric methods. The main aim of the study was to ascertain which composite materials present the best properties for use in restorative dentistry. Bisphenol-alpha-glycidyl methacrylate-based composites containing hydroxyapatite as a filler and a coupling agent were prepared using a photocuring polymerization procedure. Several chemical and mechanical properties of experimental composites were measured and the corresponding data were further studied using principal component analysis and cluster analysis. Results from the characterization allowed the most appropriate materials to be selected. Various composites presented acceptable general properties suggesting their suitability as substitutes for commercial materials in dentistry.     

Modeling of (vapor + liquid) equilibrium and enthalpy of solution of carbon dioxide (CO2) in aqueous methyldiethanolamine (MDEA) solutions

A thermodynamic model was used to estimate enthalpy of solution of carbon dioxide (CO₂) in methyldiethanolamine (MDEA) aqueous solutions. The model was based on a set of equations for chemical equilibria, phase equilibria, charge, and mass balances. Non-ideality in the liquid phase was taken into account by interaction parameters fitted to (vapor + liquid) equilibrium data.The enthalpies of solution of CO₂ were derived from the model using classical thermodynamic relations and were compared to experimental values obtained in previous works.     

Enthalpy of solution of CO2 in aqueous solutions of methyldiethanolamine at T = 372.9 K and pressures up to 5 MPa

Experimental enthalpies of solution of CO₂ in aqueous solution of methyldiethanolamine (MDEA) of 15 wt% and 30 wt% are reported. The measurements were performed using a flow calorimetric technique at temperature of 372.9 K and pressures range from 0.5 MPa to 5 MPa. Gas solubilities data at same temperature and pressures were derived from the enthalpy data. Experimental enthalpies of solution are combined with available literature data in order to examine pressure and composition influences.     

Enthalpy of solution of CO2 in aqueous solutions of methyldiethanolamine at T = 322.5 K and pressure up to 5 MPa

Enthalpies of solution of CO₂ in aqueous solution of methyldiethanolamine (MDEA) are determined for two different concentrations, respectively, 15 wt% and 30 wt%, at the temperature of 322.5 K and at pressures up to 5 MPa using a flow calorimetric technique. Gas solubilities were consequently deduced from the calorimetric data and compared to available literature values. Experimental enthalpies of solution were compared to direct measurements and to values derived from VLE data available using a simple model based on ideal property considerations.     

Tied monoids

We construct certain monoids, called tied monoids. These monoids result to be semidirect products finitely presented and commonly built from braid groups and their relatives acting on monoids of set partitions. The nature of our monoids indicate that they should give origin to new knot algebras; indeed, our tied monoids include the tied braid monoid and the tied singular braid monoid, which were used, respectively, to construct new polynomial invariants for classical links and singular links. Consequently, we provide a mechanism to attach an algebra to each tied monoid; this mechanism not only captures known generalizations of the bt-algebra, but also produces possible new knot algebras. To build the tied monoids it is necessary to have presentations of set partition monoids of types A, B and D, among others. For type A we use a presentation due to FitzGerald and for the other type it was necessary to built them.