The effect of an electric field on the local stoichiometry of front waves in an ionic chemical system

A model based on an autocatalytic, two-step reaction mechanismincluding two ionic components (of the same charge) and twonon-ionic components, where both reactions are of second orderoverall, is considered when an electric field is applied tothe system. The model is motivated by experimental observationson the iodate-arsenous acid system. The travelling wave equationsare examined first and conditions obtained for the existenceand form of these waves. These conditions are then used to interpretthe results obtained from numerical simulations of the fullsystem. These results display all the main features observedexperimentally, the change in the local stoichiometry and thepossible wave annihilation for sufficiently strong fields. Themodel provides a clear explanation for these features as wellas predicting new features not reported from the experiments.The main one of which is the occurrence of an internal wavepropagating in the reacted part of the system in the directioninduced by the applied field.     

Rheology measurements of a biomass slurry: an inter-laboratory study

The conversion of biomass, specifically lignocellulosic biomass, into fuels and chemicals has recently gained national attention as an alternative to the use of fossil fuels. Increasing the concentration of the biomass solids during biochemical conversion has a large potential to reduce production costs. These concentrated biomass slurries have highly viscous, non-Newtonian behavior that poses several technical challenges to the conversion process. A collaborative effort to measure the rheology of a biomass slurry at four separate laboratories has been undertaken. A comprehensive set of rheological properties were measured using several different rheometers, flow geometries, and experimental methods. The tendency for settling, water evaporation, and wall slip required special care when performing the experiments. The rheological properties were measured at different concentrations up to 30% insoluble solids by mass. The slurry was found to be strongly shear-thinning, to be viscoelastic, and to have a significant concentration-dependent yield stress. The elastic modulus was found to be almost an order of magnitude larger than the loss modulus and weakly dependent on frequency. The techniques and results of this work will be useful to characterize other biomass slurries and in the design of biochemical conversion processing steps that operate at high solids concentrations.     

Solid-state 13C nuclear magnetic resonance characterization of MDI-based polyurethanes

¹³C solid-state nuclear magnetic resonance (NMR) experiments on linear polyurethanes and poly(ether-urethane) block copolymers demonstrate that ¹³C spin-lattice relaxation experiments in the laboratory [T₁(C)] and rotating [T_1p(C)] frames provide the most information about domain morphology in these microphase-separated polymer systems. T₁(H) TCH, and T_1p(H) data are less useful in a 4,4′-methylene bis(p-phenyl isocyanate)-1,4-butanediol (MDI/BD) hard-segment material, the MDI bridging methylene and the MDI urethane carbonyl T₁(C and T_1p(C) times fall in characteristic ranges for crystalline, amorphous, interfacial, and dissolved species. BD methylene carbons have short T_1p(C) for crystalline and long T_1p(C) for amorphous hard-segment aggregates. The distinct T_1p(C) and T₁(C) fractins observed are attributed to the presence of several crystalline polymorphs. Both T₁(C) results and DSC endotherms indicate that the crystalline polymorphs present in the poly(ether-urethane) are less ordered than the types seen in the pure hard-segment material. © 1993 John Wiley & Sons, Inc.     

Rheology of Dilute Acid Hydrolyzed Corn Stover at High Solids Concentration

The rheological properties of acid hydrolyzed corn stover at high solids concentration (20–35 wt.%) were investigated using torque rheometry. These materials are yield stress fluids whose rheological properties can be well represented by the Bingham model. Yield stresses increase with increasing solids concentration and decrease with increasing hydrolysis reaction temperature, acid concentration, and rheometer temperature. Plastic viscosities increase with increasing solids concentration and tend to decrease with increasing reaction temperature and acid concentration. The solids concentration dependence of the yield stress is consistent with that reported for other fibrous systems. The changes in yield stress with reaction conditions are consistent with observed changes in particle size. This study illustrates that torque rheometry can be used effectively to measure rheological properties of concentrated biomass.     

On the unusual fluorescence properties of xanthone in water

Photo-excited xanthone is known to undergo ultrafast intersystem crossing (ISC) in the 1 ps time domain. Correspondingly, its fluorescence quantum yield in most solvents is very small ( approximately 10(-4)). Surprisingly, the quantum yield in water is 100 times larger, while ISC is still rapid ( approximately 1 ps), as seen by ultrafast pump probe absorption spectroscopy. Temperature dependent steady state and time resolved fluorescence experiments point to a delayed fluorescence mechanism, where the triplet (3)npi* state primarily accessed by ISC is nearly isoenergetic with the photo-excited (1)pipi* state. The delayed fluorescence of xanthone in water decays with a time constant of 700 ps, apparently by internal conversion between the (3)npi* state and the lowest lying triplet state (3)pipi*.     

Octopamine increases the excitability of neurons in the snail feeding system by modulation of inward sodium current but not outward potassium currents

Background  

Although octopamine has long been known to have major roles as both transmitter and modulator in arthropods, it has only recently been shown to be functionally important in molluscs, playing a role as a neurotransmitter in the feeding network of the snail Lymnaea stagnalis. The synaptic potentials cannot explain all the effects of octopamine-containing neurons on the feeding network, and here we test the hypothesis that octopamine is also a neuromodulator.     

Identification of non-idealities in gel electrophoresis

The molecular weight separation, which is the second dimension of two-dimensional gel electrophoresis, is studied quantitatively with the goal of improving positional predictability and reproducibility. Mathematical modeling of carrier electrolyte dynamics is used to track the progress of a stacking front as a function of coulombs passed. In all test cases, the front moves more slowly than predicted and shows both curvature and tilt. These systematic deviations from the model are found to be influenced by a variety of factors, including both design and operating features. These factors are largely explained, and suggestions are made for improvements.     

New bonding modes of gas-phase deposited gamma-aminopropyltriethoxysilane on silica studied by 29Si CP/MAS NMR

Besides the well-known reaction between the ethoxy groups of the silane end of the gamma-aminopropyltriethoxysilane (APTS) molecule and the silanols of silica, the amino ends of APTS molecules were observed to react in the gas phase with ethoxy groups of other APTS molecules and silanols of silica at elevated temperatures on the silica surface, dehydroxylated at 600 degrees C, forming Si-N linkages, as established by 29Si CP/MAS NMR.     

Formation of a regular cellular structure on the surface of Zr<Subscript>67</Subscript>Ni<Subscript>30</Subscript>Si<Subscript>3</Subscript> alloy at electrochemical polishing in ionic liquids

The surfaces of the alloy based on Zr₂Ni doped by silicon (3 at.%) in the amorphous and crystalline states and of the Zr and Ni foils were electrochemically modified for the first time. The modification was carried out in the ionic liquid in the galvanostatic regime. The much more uniform distribution of the nanosized fragments can be obtained and stability of their geometric shapes can be retained in the absence of intergrain boundaries and texture in the amorphous materials.