Effects of medium high pressure treatments on protease activity

The ability of Lactobacillus manihotivorans LMG 18010 to produce l(+)-lactic acid from a high concentration of starch by direct fermentation was investigated. To improve the production of lactic acid from a highly concentrated starch, fed-batch cultures were carried out with different feeding strategies to reduce substrate inhibition. The highest lactic acid production was 71.4 g/L, which was obtained by intermittent feeding of concentrated starch media containing nitrogen sources. After 5 days of fermentation, about 87% of the substrate was consumed with a volumetric productivity of 0.6 g/L·h which is 1.8 times higher than that obtained from batch fermentation. This result clearly shows that intermittant feeding of a highly concentrated substrate solution during fermentation is an efficient way of eliminating substrate inhibition.     

TV datacasting system: new opportunities in the audio subcarrier

This paper describes a new TV datacasting system for digital data broadcast, referred to as S-Channel, using digital modulation over the TV first audio subcarrier in Korea. The system is designed to achieve high capacity communication rates over the TV channel. I examine research and development results pertaining to a new method for on-carrier TV datacasting using the main audio subcarrier. I call it the “S-Channel” system. Interference with other stations is not an issue because it operates within the occupied bandwidth limitations of TV stations. It also does not impact video, the first audio, the second audio or VBI portions of the existing television signal. I conclude that the new TV datacasting method offers capabilities similar to those offered by proposed datacasting like Wavephore's TVT1/4 or Digiteck's D-channel while maintaining full compliance with current broadcast regulations     

Characterization of sulfonated poly(styrene-co-pyrrolidone) pore-filling membranes for fuel cell applications

Pore-filling membranes using three monomers, i.e., styrene, N-vinyl pyrrolidone (VP), and divinylbenzene (DVB), are prepared for polymer electrolyte fuel cell (PEFC) applications. A porous polyethylene (PE) film substrate is used to enhance the dimensional stability of the prepared membranes. The proton conductivity and the water uptake of the styrene/VP/DVB membranes are similar to those of the styrene/DVB membranes, even though their ion exchange capacity is slightly lesser than that of the styrene/DVB membranes. Furthermore, the thermal stability of the styrene/VP/DVB membranes is higher than that of the styrene/DVB membranes, and, for the same DVB content, the membranes containing VP exhibit better oxidative stability. VP increases the membrane’s water-absorbing ability due to its intrinsic hydrophilic property and decreases weak α-hydrogen derived from the sulfonated styrene. Finally, the membrane-electrode assembly (MEA) using the 80/10/10 (Styrene/VP/DVB in weight percentage) membrane shows better performance than that using the 90/0/10 membrane.     

Numerical analysis for electrokinetic soil processing enhanced by chemical conditioning of the electrode reservoirs

A numerical analysis was undertaken for enhanced electrokinetic soil processing. To perform chemical conditioning of the electrode reservoirs, the electrokinetic soil process employed a membrane as a barrier between the electrode reservoirs and the contaminated soil. An alkaline solution was purged in the anode reservoir that was bounded by the membrane. A mathematical model was used for demonstration of pH change and phenol removal from a kaolinite soil bed, the prediction of pH variations in both electrode reservoirs, and the determination of an optimized injection time of the anode-purging solution. The time-dependent dispersion coefficient was employed in consideration of the averaging effect of the velocity profile on a one-dimensional transport. The estimation of pH and phenol profiles in the soil bed reasonably agreed with the experimental data. The simulation revealed that the removal efficiency of phenol from the kaolinite soil could be improved by maintaining pH of the anode solution.     

Dynamic modeling of two cooperating flexible manipulators

In this paper, our aim is to develop a model for two cooperating flexible manipulators handling a rigid object by using lumped parameters. This model is in turn analyzed on MATLAB. In order to validate the model, a precise simulation model is developed using ADAMS^TM (Automatic Dynamic Analysis of Mechanical System). Moreover, to clarify the discussion, the motions of a dual-arm experimental flexible manipulator are considered. Using the developed model, we control a robotic system with a symmetric hybrid position/force control scheme. Finally, experiments and simulations are performed, and a comparison of simulation results with experimental results is given to a rerify the validity of our model.     

A study on fabrication of sulfonated poly(ether ether ketone)-based membrane-electrode assemblies for polymer electrolyte membrane fuel cells

The porosity effect of catalyst electrodes in membrane-electrode assemblies (MEAs) using a hydrocarbon-based polymer as electrolyte and ionomer was investigated on physical and electrochemical properties by varying the content of ionomer binder (dry condition) in the catalyst electrodes. The MEAs were compared with the Nafion^®-based MEA using Nafion^® 112 and 5 wt.% ionomer solution (EW = 1100) in terms of porosity values, scanning electron microscopic images, Nyquist plots, dielectric spectra and I–V polarization curves. In this study, sulfonated poly(ether ether ketone) (SPEEK) membranes with 25 ± 5 μm of thickness and 5 wt.% ionomer solutions have been prepared. The prepared membranes were characterized in terms of FT-IR, DSC and proton conductivity. Proton conductivity of the SPEEK membranes was compared with one of the Nafion^® membranes with relative humidity. The porosity of the catalyst electrodes was calculated using the properties of catalyst, ionomer solution and solvent. As a result, the performance of the new type polymer (i.e., SPEEK in this study)-based MEA with the similar membrane conductivity and porosity of the catalyst electrode in the Nafion^® MEA was similar to that of the Nafion^® MEA.     

Preparation of organic/inorganic composite membranes using two types of polymer matrix via a sol–gel process

Organic/inorganic composite membranes were prepared using two different polymers. BPO₄ particles were introduced into polymers via an in situ sol–gel process. Pre-/post-sulfonated polymers were used to prepare composite membranes as matrix. Pre-sulfonated poly(aryl ether ketone) (SPAEK-6F) copolymer was synthesized via nucleophilic aromatic substitution. Degree of sulfonation was adjusted by the percentage of sulfonated monomer. Post-sulfonated poly(ether ether ketone) (SPEEK) was prepared using concentrated sulfuric acid as sulfonation agent. The membranes were characterized in terms of the ion-exchange capacity (IEC), proton conductivity, water uptake, AFM, SEM and their thermal properties. The SPAEK-6F plain membranes showed higher proton conductivity than that of the SPEEK plain membranes at similar water uptake or IEC due to their structural difference. SEM images of the composite membranes showed that the BPO₄ particles were homogenously dispersed in the polymer matrices and BPO₄ particle size was greatly influenced by polymer matrix. The SPAEK-6F/BPO₄ composite membranes had much smaller BPO₄ particle size than the SPEEK/BPO₄ composite membranes due to well dispersion of BPO₄ sol-like particulates in SPAEK-6F polymer solutions forming more hydrophobic/hydrophilic nanophase than SPEEK polymer solutions. The latter containing a few micrometer-scale BPO₄ particles showed higher proton conductivity than the former containing hundreds nanometer-scale BPO₄ particles at similar water uptake due to the increase in freezable water and effect of particle size.     

Facile characterization of ripple domains on exfoliated graphene

Ripples in graphene monolayers deposited on SiO(2)∕Si wafer substrates were recently shown to give rise to friction anisotropy. High friction appears when the AFM tip slides in a direction perpendicular to the ripple crests and low friction when parallel. The direction of the ripple crest is, however, hard to determine as it is not visible in topographic images and requires elaborate measurements of friction as a function of angle. Here we report a simple method to characterize ripple crests by measuring the cantilever torsion signal while scanning in the non-conventional longitudinal direction (i.e., along the cantilever axis, as opposed to the usual friction measurement). The longitudinal torsion signal provides a much clearer ripple domain contrast than the conventional friction signal, while both signals show respective rotation angle dependences that can be explained using the torsion component of the normal reaction force exerted by the graphene ripples. We can also determine the ripple direction by comparing the contrast in torsion images obtained in longitudinal and lateral scans without sample rotation or complicated normalization.     

Role of Liquid Phase in Achieving a Fine Microstructure and Diffusive Phase Transition of MgO-Doped BaTiO3

Two types of glass compositions, with MgO and CaO modifiers, respectively, were used to promote l`iquid-phase sintering of 2 mol% MgO–BaTiO₃ at 1280°C in reducing atmosphere ( p O₂=10⁻⁹ atm). By combining the observations of the grain size of about 1 μm for both specimens and the diffusive phase transition only when MgO modifier was used, it has been interpreted that an appropriate solubility of BaTiO₃ is necessary to yield the fine and composite microstructures via a dissolution–reprecipitation process. Further, a reasonable dopant provision to BaTiO₃ has been shown to be required to achieve the diffusive phase transitions.