A simple Monte Carlo method for modeling arborescent polymer production in continuous stirred tank reactor

A dynamic mathematical model was developed to predict the molecular weight distribution (MWD) and branching distribution for arborescent polyisobutylene (arbPIB) in a continuous stirred tank reactor (CSTR). ArbPIB a promising biomaterial for human implantation [1] made by copolymerization of isobutylene and an inimer [2]. An inimer is a special molecule that contains an initiating group (initiator) and a vinyl group (monomer), which can form a T-shaped branch on a polymer chain. The model builds on a previous kinetic Monte Carlo (MC) algorithm developed for arbPIB production in a batch reactor [3]. A key innovation of our proposed MC approach is that inflow and outflow events are treated separately from reaction events, so that simulations are faster than would be obtained using existing approaches where inflow and outflow are treated as if they were reactions [4]. As such, we anticipate that the proposed methodology will be useful for other polymerization systems. To our knowledge, this is the first dynamic MC model for branched polymer production in a CSTR and the first model to predict the MWD of arbPIB in a CSTR, which tends to be much broader than the MWD of the corresponding batch copolymer. Model predictions are verified using a multi-dimensional method-of-moments model that predicts number and weight-average molecular weights, but not the MWD [5]. CSTR start-up was simulated beginning with fresh monomer and inimer in the reactor (no polymer at time zero). The model shows how the MWD continuously shifts to the high molecular weight region as time passes. For some operating conditions with relatively high inimer concentration or long residence times, the MWD does not reach steady state because larger and larger molecules that would eventually clog the reactor tend to form over time. Please click Additional Files below to see the full abstract

Multivariate GR&R through factor analysis

Several measurement tasks present multivariate nature. In the cases with quality characteristics highly correlated within groups, but with a relatively small correlation between groups, the available multivariate GR&R methods are not suitable to provide a correct interpretation of the results. The present work presents a new multivariate GR&R approach through factor analysis. Factor analysis is a multivariate statistical method which focuses on the explanation of the covariance structure of the data. Through orthogonal rotation of the factors a suitable structure can be achieved with loadings easy to relate the variables to the factors. The proposed multivariate GR&R method through factor analysis is described and applied in the quality evaluation of holes obtained through helical milling process of AISI H13 hardened steel. The method succeeded in achieving a simple structure, with one factor related to the roughness outcomes and other related to the roundness ones, simplifying the gage capability evaluation.publishe

Differences in the Diets of Female and Male Red Deer: The Meaning for Sexual Segregation

Sexual segregation is a common phenomenon among animals, particularly dimorphic ones. Although widely addressed, the reasons and consequences of sexual segregation are still an important topic in need of better understanding. In this study, we mainly evaluate the diet composition and feeding behaviour of animals, which are related to the use of different habitats by the sexes, a special case of sexual segregation also termed habitat segregation. Sexually size dimorphic males and females often have different energetic and nutritional needs and, thus, different diets. We collected fresh faecal samples from wild Iberian red deer (Cervus elaphus L.) in Portugal. Samples were analysed in terms of diet composition and quality. As expected, both sexes differed in their diet composition, with males eating more arboreous species than females, but this difference was affected by sampling periods. Diet composition of both sexes had the biggest differences (and the lowest overlap) in spring, which corresponds to the end of gestation and beginning of birth. These differences might be a consequence of the sexual body size dimorphism characteristic of this species, as well as of different needs due to different reproductive costs. No differences regarding the quality of the excreted diet were observed. Our results may help to understand some patterns of sexual segregation observed in this red deer population. However, besides foraging ecology, other factors may also be contributing to sexual segregation in this Mediterranean population of red deer, and further studies focusing on sexual differences regarding feeding behaviour and digestibility are needed