Basic model for membrane electrode assembly design for direct methanol fuel cells

This research proposes a model that predicts the effect of the anode diffusion layer and membrane properties on the electrochemical performance and methanol crossover of a direct methanol fuel cell (DMFC) membrane electrode assembly (MEA). It is an easily extensible, lumped DMFC model. Parameters used in this design model are experimentally obtainable, and some of the parameters are indicative of material characteristics. The quantification of these material parameters builds up a material database. Model parameters for various membranes and diffusion layers are determined by using various techniques such as polarization, mass balance, electrochemical impedance spectroscopy (EIS), and interpretation of the response of the cell to step changes in current. Since the investigation techniques cover different response times of the DMFC, processes in the cell such as transport, reaction and charge processes can be investigated separately. Properties of single layers of the MEA are systematically varied, and subsequent analysis enables identification of the influence of the layer's properties on the electrochemical performance and methanol crossover. Finally, a case study indicates that the use of a membrane with lower methanol diffusivity and a thicker anode micro-porous layer (MPL) yields MEAs with lower methanol crossover but similar power density.     

Nanofibers from recycle waste expanded polystyrene using natural solvent

Summary A new recycling technique has been developed. In this method, EPS (expanded polystyrene), generally called Styrofoam, is dissolved with natural solvent, d-limonene and electrospun. This method can economically produce the nanofibers. The electrospinning process produces a nonwoven mat of long polymer fibers with diameters in the range of 10–500 nm and high surface areas per unit mass. PS (Polystyrene) polymer dissolved in different solvents such as THF (Tetrahydrofuran), DMF (Dimethylformaide), and DMAc (Dimethylacetamide) etc. may all be electrospun into nanofibers. These solvents cause environmental problem and difficulty of process handling. Natural solvent, d-limonene is used for dissolving PS. PS nanofibers are produced with PS solution using d-Limonene. This paper describes the use of polystyrene (PS) nanofibers electrospun from recycled EPS solution dissolved in d-limonene. The electrospun polystyrene nanofiber diameters vary from 300 to 900 nm, with an average diameter of about 700 nm.     

Dual wavelength OLEDs with blue and yellow emission peaks

New organic light emitting diodes (OLEDs) with dual peak emission spectra were fabricated and their electrical and optical characteristics were investigated. In the experiments, the blue emission materials GDI602 and GDI602 were doped with GDI691(2%)[GDI602∶GDI691(2%)] and the yellow emission material Alq3 was doped with Rubrene(10%)[Alq3∶Rubrene(10%)]. Under an applied voltage of 10 V, the OLED with the GDI602/Alq3∶Rubrene(10%) emission layer had a luminance of 325 Cd/m² and a power efficiency of 0.7 lm/W, whereas the OLED with the GDI602∶GDI691(2%)/Alq3∶Rubrene(10%) emission layer had a luminance of 500 Cd/m² and a power efficiency of 0.94 lm/W. The dual peak wavelengths of the OLEDs were fixed but the relative intensities of the peak wavelengths varied according to the applied voltage. The OLED with the GDI602/Alq3∶Rubrene(10%) emission layer showed a somewhat reddish-white emission with a Commission Internationale de L'Eclairage(CIE) coordinate of (0.33, 0.32) at 9 V. In contrast, the OLED with the GDI602: GDI691(2%)/Alq3∶Rubrene(10%) emission layer showed an almost pure white emission with a CIE coordinate of (0.32, 0.33) at 6 V; furthermore, the color changed to blue as the applied voltage was increased.     

The viscoelastic bending stiffness of fiber-reinforced composite Ilizarov C-rings

In order to optimize the design of unidirectional fiber-reinforced composite (Ilizarov) C-rings, the viscoelastic load relaxation behavior was analyzed under a point load. Initially, the deflection and bending stiffness were calculated from the Castigliano theorem and the Euler–Bernoulli bending theory for the elastic solution. The viscoelastic relaxation and creep behavior were then derived from the elastic solution by using the correspondence theorem. Besides the orthotropic mechanical properties of the composite, the asymmetric mechanical properties due to different tensile and compressive properties were also considered. With the exception of the deviation, which was affected by a relatively large thickness ratio to the radius of the C-ring, the calculated relaxation showed good agreement with the experimental result.     

Measurement of axial stress using mode-converted ultrasound

A new ultrasonic technique for stress measurement using mode conversion is proposed and applied to the estimation of axial stresses in high-tension bolts. The effect of axial stresses on acoustic wave velocities in axisymmetric cylindrical solids is analyzed, and a linear acousto-elastic equation is formulated. Theoretical ray analysis is performed to compute time of flight (TOF) of mode-converted waves in cylindrical solids. To evaluate the validity of the proposed method, mode-converted longitudinal and shear waves in carbon-steel bolts are generated and captured to measure the TOF of the waves. Simultaneous velocity measurement of two differently polarized acoustic waves are made with enough resolution to estimate axial stresses with values less than 10% of the yield stress of the bolt material. It is observed from experimental results that the TOF ratio of longitudinal and shear waves is linearly proportional to the axial stress in bolts within 5% error, as expected from theory.     

Fabrication and characterization of functionalized wet-chemical silver coated films on glass for optical systems

A method for fabricating an Ag coated beam splitter is reported. This shows a specific patterned transmittance by immersing glass substrates in a mixture of H₂SO₄ and H₂O₂ to make negatively charged oxygen sites at the silica surface and then in ethanolic solutions of AgNO₃ and butylamine. We controlled the soaking time and molar ratios of the mixture of AgNO₃ and butylamine to a pattern % transmittance of electroless coated glass surface. Finally, we made a functionalized beam splitter showing step function like transmittance and applied this to make multiple laser beams for display and laser machinings.     

Vertical handoff in integrated CDMA and WLAN systems

Future wireless networks are expected to consist of different types of wireless networks such as code division multiple access (CDMA) networks and public wireless local area networks (WLANs). The integrated network will require vertical handoffs between different networks. In this letter, we propose vertical hard- and soft-handoff algorithms and evaluate their performance in commercial wireless networks.     

Thermal modelling of the multi-stage heating system with variable boundary conditions in the wafer based precision glass moulding process

In the precision glass moulding process, the heat transfer and the resulting transient temperature distributions of the molten glass are of great importance because they significantly affect the productivity as well as the thermally induced residual stresses in the final product. Thermal modelling of the heating system in the glass moulding process considering detailed heating mechanisms therefore plays an important part in optimizing the heating system and the subsequent pressing stage in the lens manufacturing process.The current paper deals with three-dimensional transient thermal modelling of the multi-stage heating system in a wafer based glass moulding process. In order to investigate the importance of the radiation from the interior and surface of the glass, a simple finite volume code is developed to model one dimensional radiation–conduction heat transfer in the glass wafer for an extreme case with very high temperature difference considering temperature dependant thermal conductivity and heat capacity. Afterwards, by using three-dimensional FEM modelling along with a predefined experimental test, the equivalent glass–mould interface contact resistance is determined for two different pressures. Finally, the three-dimensional modelling of the multi-stage heating system in the wafer based glass moulding process is simulated with the FEM software ABAQUS for a particular industrial application for mobile phone camera lenses to obtain the temperature distribution in the glass wafer. In the numerical modelling, the interface boundary conditions for each heating stage are changed according to the determining heat transfer mechanism(s). Numerical results are compared with experimental data to show the validity of the numerical modelling. The obtained results show that the right thermal modelling is highly dependent on the proper choice of thermal boundary conditions in different stages according to the real physical phenomena behind the process.     

ESD sensitivity of a GaAs MMIC microwave power amplifier

The EOS/ESD sensitivity of the main circuit blocks of a complete GaAs multi-stage power amplifier for microwave applications was investigated under HBM, MM and TLP regimes. Hard breakdown failure modes were identified due to passive components failure. The high current injection state of active components was also analyzed.     

Electrochemical and thermal properties of graphite electrodes with imidazolium- and piperidinium-based ionic liquids

The electrochemical and thermal properties of graphite electrodes with electrolytes containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) and N-methyl,N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (MPPpTFSI) ionic liquids are investigated. The ionic liquids undergo extensive reductive decomposition on a graphite electrode during the first charge. The effect of a fluoroethylene carbonate (FEC) additive on the reductive decomposition of the ionic liquids is examined by electrochemical, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. Thermal reactions between a lithiated graphite electrode and an ionic liquid-containing electrolyte are investigated with differential scanning calorimetry (DSC). The introduction of an ionic liquid can effectively reduce the exothermic heat evolution from the thermal reactions between a lithiated graphite electrode and an electrolyte.