Simultaneous saccharification and extractive fermentation of lignocellulosic materials into lactic acid in a two-zone fermentor-extractor system

Simultaneous saccharification and extractive fermentation of lignocellulosic materials into lactic acid was investigated using a two-zone bioreactor. The system is composed of an immobilized cell reactor, a separate column reactor containing the lignocellulosic substrate and a hollow-fiber membrane. It is operated by recirculating the cell free enzyme (cellulase) solution from the immobilized cell reactor to the column reactor through the membrane. The enzyme and microbial reactions thus occur at separate locations, yet simultaneously. This design provides flexibility in reactor operation as it allows easy separation of the solid substrate from the microorganism, in situ removal of the product and, if desired, different temperatures in the two reactor sections. This reactor system was tested using pretreated switchgrass as the substrate. It was operated under a fed-batch mode with continuous removal of lactic acid by solvent extraction. The overall lactic acid yield obtainable from this bioreactor system is 77% of the theoretical.     

Hyaluronan-based glycoclusters as probes for chemical glycobiology

A strategy is described for the synthesis of β-(1,3)-GlcA-GlcNAc dimeric and tetrameric glycoclusters through the conjugation of disaccharide groups onto a diaminodiamide aromatic scaffold by reductive amination.     

Determination of rare earth elements in USGS rock standards by isotope dilution mass spectrometry and comparison with neutron activation and inductively coupled plasma atomic emission spectrometry

Rare earth element (REE) concentrations in United States Geological Survey (USGS) rock standards AGV-1, GSP-1, G-2 and PCC-1 were determined by isotope dilution mass spectrometry (IDMS), neutron activation and inductively coupled argon plasma atomic emission spectrometric techniques. The procedure involved acid digestion of samples in PTFE pressure bombs and group separation of REEs by an ion-exchange method. For IDMS an additional separation step using α-hydroxyisobutyric acid as an eluent was used in a cation-exchange column to split the REEs into subgroups. Comparison of the results with literature values showed that the IDMS values are the most precise and accurate. However, the precisions and the accuracies of the other techniques are acceptable.     

Complexities and algorithms for synchronized scheduling of parallel machine assembly and air transportation in consumer electronics supply chain

In this paper, we study the problem of synchronized scheduling of assembly and air transportation to achieve accurate delivery with minimized cost in consumer electronics supply chain. This problem was motivated by a major PC manufacturer in consumer electronics industry. The overall problem is decomposed into two sub-problems, which consist of an air transportation allocation problem and an assembly scheduling problem. The air transportation allocation problem is formulated as an integer linear programming problem with the objective of minimizing transportation cost and delivery earliness tardiness penalties. The assembly scheduling problem seeks to determine a schedule ensuring that the orders are completed on time and catch the flights such that the waiting penalties between assembly and transportation is minimized. The problem is formulated as a parallel machine scheduling problem with earliness penalties. The computational complexities of the two sub-problems are investigated. The air transportation allocation problem with split delivery is shown to be solvable. The parallel machine assembly scheduling problem is shown to be NP-complete. Simulated annealing based heuristic algorithms are presented to solve the parallel machine problem.     

ICP-AES determination of silver after chemical separation from uranium matrix

The separation of silver from a uranium matrix has been carried out using Cyanex-471X (triisobutylphosphine sulphide) in xylene. The effects of various parameters such as the Cyanex-471X concentration, the nitric acid molarity, the contact time and the nitrate ion concentration on the extraction of silver have been studied. The silver metal ion species extracted into the organic phase was found to be Ag(NO₃)·2S (where S is Cyanex-471X). The stripping of silver into an aqueous medium was carried out with 5% NaHSO₃, followed by its determination using ICP-AES.     

Photoinduced electron transfer between anionic fluorophores and methyl viologen in homogeneous and microheterogeneous media

The rate and extent of photoinduced electron transfer change significantly as a result of confinement in nanovolumes. Study of such processes is an active area of research in physical chemistry. The effect is most interesting when the molecules that participate in PET are charged. In the present article, the modulation of PET has been studied for two anionic fluorophores: Lucifer Yellow CH and chlorin p₆ with Methylviologen dication. PET, manifested in the quenching of fluorescence of the fluorophores, has been modulated by incorporating the molecules in organized assemblies like micelles, reverse micelles and supramolecular hosts. The dynamics of the process has been monitored in the femtosecond to nanosecond timescale. The modulation of the electron transfer has been found to be occurring mainly due to the disruption of contact ion pairs formed between the fluorophores and the quencher.     

A field theoretical approach to the quasi-continuum method

The quasi-continuum method has provided many insights into the behavior of lattice defects in the past decade. However, recent numerical analysis suggests that the approximations introduced in various formulations of the quasi-continuum method lead to inconsistencies—namely, appearance of ghost forces or residual forces, non-conservative nature of approximate forces, etc.—which affect the numerical accuracy and stability of the method. In this work, we identify the source of these errors to be the incompatibility of using quadrature rules, which is a local notion, on a non-local representation of energy. We eliminate these errors by first reformulating the extended interatomic interactions into a local variational problem that describes the energy of a system via potential fields. We subsequently introduce the quasi-continuum reduction of these potential fields using an adaptive finite-element discretization of the formulation. We demonstrate that the present formulation resolves the inconsistencies present in previous formulations of the quasi-continuum method, and show using numerical examples the remarkable improvement in the accuracy of solutions. Further, this field theoretic formulation of quasi-continuum method makes mathematical analysis of the method more amenable using functional analysis and homogenization theories.