Multiplexing fibre optic near infrared (NIR) spectroscopy as an emerging technology to monitor industrial bioprocesses

The application of near infrared spectroscopy in bioprocessing has been limited by its dependence on calibrations derived from single bioreactor at a given time. Here, we propose a multiplexed calibration technique which allows calibrations to be built from multiple bioreactors run in parallel. This gives the flexibility to monitor multiple vessels and facilitates calibration model transfer between bioreactors. Models have been developed for the two key analytes: glucose and lactate using Chinese hamster ovary (CHO) cell lines and using analyte specific information obtained from the feasibility studies. We observe slight model degradation for the multiplexed models in comparison to the conventional (single probe) models, decrease in r² values from 89.4% to 88% for glucose whereas for lactate from 92% to 91.8% and a simultaneous increase in the number of factors as the model incorporates the inter-probe variability, nevertheless the models were fit for purpose. The results of this particular application of implementing multiplexed-NIRS to monitor multiple bioreactor vessels are very encouraging, as successful models have been built on-line and validated externally, which proffers the prospect of reducing timelines in monitoring the vessels considerably, and in turn, providing improved control.     

An adaptive finite volume box scheme for solving a class of nonlinear parabolic equations

In this work we are interested in a fully nonconforming (Crouzeix–Raviart) finite element scheme for addressing a nonlinear parabolic equation. In addition to showing the equivalence with a finite volume box scheme we derive a posteriori error indicators in time and space, uncoupled as much as possible.     

Aziridination of 3-methyl-4-nitro-5-styrylisoxazoles

Herein we describe the preparation of a novel class of isoxazolyl aziridines. The products were obtained exclusively as cis diastereoisomers.     

Comparison of collision‐ versus electron‐induced dissociation of sodium chloride cluster cations

The collision‐induced dissociation (CID) and electron‐induced dissociation (EID) spectra of the [(NaCl)_m(Na)_n]ⁿ⁺ clusters of sodium chloride have been examined in a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. For singly charged cluster ions (n = 1), mass spectra for CID and EID of the precursor exhibit clear differences, which become more pronounced for the larger cluster ions. Whereas CID yields fewer product ions, EID produces all possible [(NaCl)_xNa]⁺ product ions. In the case of doubly charged cluster ions, EID again leads to a larger variety of product ions. In addition, doubly charged product ions have been observed due to loss of neutral NaCl unit(s). For example, EID of [(NaCl)₁₁(Na)₂]²⁺ leads to formation of [(NaCl)₁₀(Na)₂]²⁺, which appears to be the smallest doubly charged cluster of sodium chloride observed experimentally to date. The most abundant product ions in EID spectra are predominantly magic number cluster ions. Finally, [(NaCl)_m(Na)₂]^{+ .} radical cations, formed via capture of low‐energy electrons, fragment via the loss of [(NaCl)_n(Na)] ^. radical neutrals. Copyright © 2008 John Wiley & Sons, Ltd.     

An Eulerian exposition

An overview of Eulerian graphs is presented. In particular, characterizations of Eulerian graphs and digraphs as well as algorithms for constructing Eulerian circuits are discussed. A solution to the Chinese postman problem is followed by a study of subgraphs and supergraphs of Eulerian graphs. After an introduction to randomly Eulerian graphs and digraphs, we conclude with a summary of a variety of results involving enumeration.     

Reaction pathways to dimer in polystyrene pyrolysis: A mechanistic modeling study

A detailed mechanistic model for polystyrene pyrolysis was created that built on a modeling framework developed in our previous work and was used to probe three competing pathways to dimer formation: benzyl radical addition, 1,3-hydrogen shift, and 7,3-hydrogen shift, based on recent literature reports. To incorporate the chemistry involved in the 7,3-hydrogen shift pathway, the 1,7- and 7,3-hydrogen shift reaction families were added to the model. The updated version of the model tracks 75 species and over 3500 reactions. Rate parameters for all families were specified based on our previous work, more recent literature reports, and regression against limited experimental data. The model was able to accurately predict the experimental results for polystyrene pyrolysis for different reactor configurations for a temperature range of 100 °C and two orders of magnitude of initial molecular weight for experimental data collected in our own lab and from Bouster and coworkers and Bockhorn and coworkers. The results from our model were studied using net rate analysis to gain insight into the competitiveness of the various reaction pathways to dimer formation. The net rate analysis demonstrated that 7,3-hydrogen shift is the dominant reaction pathway to dimer formation at the temperatures studied. Benzyl radical addition becomes a more competitive reaction pathway as the temperature increases, which is caused predominantly by an increase in the benzyl radical concentration with increasing temperature. Overall, it is quantitatively shown that both 7,3-hydrogen shift and benzyl radical addition are important pathways for dimer formation, with their relative competitiveness influenced by temperature.