Javier Vijande

Description of PVT behaviour of hydrofluoroethers using the PC-SAFT EOS

A description of the volumetric behaviour of segregated hydrofluoroethers has been carried out using PC-SAFT EOS. Characteristic parameters for several molecules were calculated where experimental data were available, and accurate results were obtained for compressed and saturated liquid density estimation, as well as for saturation curves. A functional group contribution scheme is proposed also for the calculation of the mentioned PC-SAFT EOS characteristic parameters, and this approach reproduces adequately the dependence on molecular structure of the parameters calculated in this work, and also gives good estimations when the parameters are extrapolated for other molecules of the same family.

Estimation of parameters of Nitta–Chao model for ester+1-alkanol mixtures

Abstract An updated database with experimental values on vapor–liquid equilibria, activity coefficient at infinite dilution, enthalpies of mixing and excess molar volumes of alkyl alkanoate+1-alkanol binary systems was used to redetermine structure and interaction parameters of the Nitta–Chao model. We have compared the theoretical results obtained with the Nitta–Chao model and our parameters with the experimental data. The percentual mean deviations with the parameters calculated in this work are quite good for all properties studied. We have used the same database to analyse the quality of the predictions of three versions of UNIFAC model for this type of mixtures.

Estimation of parameters of Nitta-Chao model for linear monoether + 1-alkanol mixtures

We have estimated the interaction parameters for ether and hydroxyl groups using an extensive experimental database of vapour-liquid equilibria, activity coefficients at infinite dilution, enthalpies of mixing and volumes of mixing of linear monoether + 1-alkanol binary systems. The theoretical results obtained with the parameters proposed are significantly closer to the experimental values than those determined with the parameters of Eckart et al. In addition, the values of thermodynamic properties obtained by the Nitta-Chao model with both set of parameters have been compared with the predictions resulting from other models, such as the DISQUAC model and the UNIFAC model, in its original version and those of Dang and Tassios, Larsen et al. (UNIFAC-Lingby) and Gmehling et al. (UNIFAC-Dortmund).

Estimation of the Nitta-Chao Parameters for the ether-group. Ether + n-alkane mixtures

Abstract In this work we have estimated the structural and interactional parameters of the ether- group for the group-contribution model of Nitta-Chao using a extensive experimental database of thermodynamic properties of ethers (monoethers, polyethers and acetals) and ether + n-alkane and ether + ether mixtures. The results obtained by Nitta-Chao model with this parameters get closer to the experimental values than those obtained with parameters of Eckart et al. (1986). The thermodynamic properties obtained by the Nitta-Chao model with old and new parameters were compared to predictions by other models such as Flory (1965) theory, DISQUAC (Kehiaian, 1977) model and UNIFAC model (versions of Dang and Tassios, 1986, and Larsen et al., 1987).

Estimation of carbonate–alcohol interaction parameters for Nitta–Chao group contribution model: application of a Genetic Algorithm

Abstract In this work, the characteristic parameters for the interaction of carbonate–hydroxyl pair for the Nitta–Chao model have been calculated using an updated data base of vapour–liquid equilibria, activity coefficients at infinite dilution, excess molar enthalpies and excess molar volumes of carbonate+1-alkanol binary mixtures. In the process of optimisation of the interaction parameters a Genetic Algorithm (GA) has been used.

Temperature dependence of the refractive index for the mixtures {CH3(CH2)xOH, x=1, 2}+ {(CH3)2CH(CH2)yOH, y=0, 1, 2} and estimation by means of cubic equations of state

The applicability of cubic equations of state for refractive index estimation for binary alcohol mixtures {CH3(CH2)xOH, x=1, 2}+{(CH3)2CH(CH2)yOH, y=0, 1, 2} at different temperatures was evaluated by using a derivation of the Heller equation. A qualitatively accurate response was obtained from the cubic equations and mixing rules applied, and the binary parameter obtained can be used for multicomponent refractive index prediction, or even for other thermodynamic properties.

Excess molar volumes at 298.15 K of the ternary mixture: propyl propanoate + 2-hexanone + 1-chlorohexane

Abstract Excess molar volumes at 298.15 K of {x1 C2H5CO2(CH2)2CH3 + x2 CH3CO(CH2)3CH3 + x3 Cl(CH2)5CH3} and of the binary mixtures {x1 C2H5CO2(CH2)2CH3 + (1 − x1) CH3CO(CH2)3CH3}, {x1 C2H5CO2(CH2)2CH3 + (1 − x1) Cl(CH2)5CH3} and {x1 CH3CO(CH2)3CH3 + (1 − x1) Cl(CH2)5CH3} were determined using an Anton Paar DMA 60 602 densimeter. All the experimental values were compared with the results obtained by empirical expressions for estimating ternary properties from binary results. Variable-degree polynomials have been fitted to the results.

Analysis of the interaction between cycloalkanes and 1-alkanols by means of Nitta Chao group contribution model

Abstract The interaction between cyclic alkane (CH 2 r ) and hydroxyl (OH) structural groups was revised within the framework of Nitta Chao group contribution model. New interaction parameters were calculated using an updated database, and previous results were clearly improved. Comparison was established with other group contribution models (UNIFAC, DISQUAC).

SU-E-T-530: Comparison of Analytical and Monte Carlo Calculations for Heterogeneity Corrections in LDR Prostate Brachytherapy

PURPOSE It is well-known that tissue heterogeneities and calcifications have significant influence on low energy brachytherapy. The aim of this work is to study the application of a simplified analytic algorithm that could be compatible with commercial Treatment Planning System (TPS) based on TG-43. The algorithm, based on the classic equivalent path length method, has been compared with Monte Carlo (MC) computations using Penelope2009. METHODS The analytical model scales the distance from the seed to the calculation point according to the electronic density of the medium relative to water. Then, the dose is calculated from TG-43 consensus data (stored on a TPS) by scaling the radial dose function according to the equivalent path length, keeping the anisotropy function unaltered. A voxelized phantom obtained from clinical cases has been used. This benchmark was selected because the patient presented a significant proportion of calcifications inside the prostate. After this, a comparison between MC and the algorithm was performed. RESULTS The results given by the algorithm show a remarkable agreement with the complete Monte Carlo simulations taking into account the calcifications (real case). Several other realistic geometries and compositions of the calcification have been checked successfully. CONCLUSION The presented analytical dose calculation is applicable for any type of heterogeneity. Its high calculation speed makes it feasible for use in clinical real time-treatment planning and thus for improving treatment quality.

SU-E-T-316: New Design of the Valencia Applicators to Reduce Radiation Leakage

PURPOSE The Valencia applicators are designed to treat skin lesions with the microSelectron-HDR afterloader. Although the radiation is highly directed to the treatment area, radiation might leak through the backside of the applicator. Recently, the manufacturer has introduced a new applicator design to reduce such radiation leakage. This new design consists mainly in the addition of about 4 mm of tungsten in the backside of the applicator making it thicker. The purpose of this study is to evaluate by means of the Monte Carlo method the radiation leakage of this new design and to evaluate whether this modification affects the dose rate distributions in the treatment area. METHODS The complete geometry of the new applicators has been introduced in the Monte Carlo code GEANT4. The applicators have been located on the surface of a cylindrical water phantom following a methodology similar to the used in the original study of the Valencia applicators by Granero et al [Med.Phys 2008;35:495-503]. Kerma in the water phantom and kerma in air outside the phantom have been evaluated to estimate the radiation leakage of the new designed Valencia applicators. RESULTS The Monte Carlo simulations of the new applicators show that the radiation leakage has been reduced significantly from the previous design. The largest radiation leakage of this design is now about 30% of the dose at the prescription point and about 10% at 1 cm from the backside of the applicators. The dose rate distributions in the area of treatment have not changed. CONCLUSIONS In this study the radiation leakage of the new design of the Valencia applicators has been obtained. The radiation leakages have been largely reduced from the previous design without compromising dose rate distributions in the treatment area.