Prediction of Mechanical Properties of Polymers With Various Force Fields

The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide

Parametric studies in multiscale modeling of high-performance polymers

A computational parametric study has been performed to establish the effect of Representative Volume Element (RVE) size, force field type, and simulation temperature on the predicted mechanical properties of polyimide and polycarbonate materials modeled atomisticially. The results of the simulations indicate no clear effect of RVE size and force field type on the predicted mechanical response of the polyimide and polycarbonate polymer systems. A multiscale modeling technique was utilized to determine the equivalentcontinuum Young\u27s moduli, density, and stress-strain behavior for the set of mentioned modeling parameters. Parametric studies also indicate no clear effect of the simulation temperature on the predicted material densities of LaRC-CP2 when the AMBER force field is used. However, the MM3 force field predicts a steady decrease in the density of LaRC-CP2 as the temperature increases up to and beyond the glass transition temperature. These force fields vary slightly in form and with the associated parameters

Feline immunodeficiency virusinfection: a comparative study of different diagnostic techniques Infecção pelo vírus da imunodeficiência felina: estudo comparativo de diferentes técnicas de diagnóstico

This study evaluated an indirect immunofluorescence assay (IFA) to detect feline immunodeficiency virus infection (FIV) antibody in a comprehensive epidemiological survey of FIV in Argentina. IFA modified in our laboratory, was compared with two other immunoassays, western blot (WB) and a sandwich immunochromatographic commercial kit (SI), and also with a direct polymerase chain reaction (PCR) method that detects proviral DNA. IFA showed to be a test with high sensitivity and specificity, and could be useful as a diagnostic tool in epidemiological studies. The presence of a low percentage of results with non-specific reactivity in the IFA could be resolved with further testing or use of an alternative method.<br>Avaliou-se a técnica de imunofluorescência indireta (IFA) na detecção de anticorpos contra o vírus da imunodeficiência felina (FIV) numa pesquisa epidemiológica do FIV na Argentina. A IFA foi modificada e comparada com duas outras técnicas imunológicas: western blot (WB) e imunocromatografia em camadas (SI) com kit comercial e também com reação em cadeia de polimerase (PCR) para detecção do DNA proviral. A IFA mostrou ser um teste com alta sensibilidade e especificidade e poderá ser empregada como ferramenta útil em estudos epidemiológicos. A baixa porcentagem de reatividade não específica pode ser esclarecida com testes mais avançados ou usando métodos alternativos