Successive laser-induced breakdowns in atmospheric pressure air and premixed ethane–air mixtures

Two successive focused laser pulses are employed to experimentally simulate laser-induced breakdown plasmas at high repetition rates. We find that energy absorption of the second laser pulse by the plasma produced by the first laser pulse is enhanced slightly when the time interval between the pulses is shorter than several tens of nanoseconds but falls to almost zero when the time interval is between a few hundreds of nanoseconds and several tens of microseconds. This behavior is attributed to gas heating by the first breakdown event. In premixed ethane–air mixtures, we identify another strong reduction in the second laser pulse absorption when this pulse coincides with the heat released by combustion, typically milliseconds after the first laser pulse. The fuel–air equivalence ratio (?) and base flow speed are also varied in this study. The results show that the window of reduced absorption coinciding with heat release due to combustion is narrowed when the base flow speed is increased, and also under fuel lean and fuel rich conditions. These results suggest that the use of pulsed high frequency laser breakdowns for premixed combustion stabilization is optimized when laser pulse repetition rates below a certain frequency (e.g., 500 Hz at the conditions that ? is 1 and the base flow speed is 4.9 m/s) to maximize laser energy coupling and for improved anchoring of the flame base.     

Experimental investigation of highly pressurized hydrogen release through a small hole

The dispersion characteristics of hydrogen leaking through a small hole from a high-pressure source were investigated experimentally to develop guidelines for determining safety distances for hydrogen stations. Tests were carried out for leaking holes with diameters of 0.5, 0.7 and 1.0 mm and for release pressures of 100, 200, 300 and 400 bar. For these realistic hydrogen leaking conditions, the Froude numbers are so large that the buoyancy effect, manifested by the hydrogen jets bending upward, can be expected to be negligible. Flow visualization was performed using an Nd-YAG laser to confirm that the buoyancy effect was negligible. By letting a thin laser sheet penetrate the center line of a hydrogen jet conveying Al₂O₃ particles, the particles were illuminated and the hydrogen jet was visualized. The hydrogen concentration was measured by sampling hydrogen at five points along the jet centerline, based on the large Froude number. The measured data were always lower than the isentropic prediction.     

Parametric analysis of simultaneous humidification and cooling for PEMFCs using direct water injection method

The effects of different operating parameters on humidification and cooling for proton exchange membrane fuel cells (PEMFCs) using direct water injection method were experimentally investigated. Experiments with various injection water temperature, operating pressure and relative humidity of cathode side were carried out. In order to quantitatively analyze the performance of direct water injection method, polarization curves and dew point temperatures of cathode outlet gas were measured. Also, the possible mechanisms of the effect of each parameter were discussed. The experimental results showed that elevation of the injection water temperature and relative humidity of cathode side led to the improvement of stack performance. It resulted from humidification and cooling effect by the evaporation of injected water. Operating pressure also had an effect on the performance of direct water injection method. In pressurized operating condition, the evaporation of injected water was difficult to occur, and the effect of direct water injection method decreased. Based on the experimental results, it was demonstrated that the stack performance was remarkably improved because of humidification and cooling effect from direct water injection method.     

Buckling sensitivity of a connecting rod to the shank sectional area reduction

Yield, fatigue and buckling characteristics are often used as evaluation indexes for the performance of engine connecting rods in weight reduction design. There are, however, a limited number of studies on the buckling of connecting rods. Even the widely used field equations for the buckling have limitations in the application since they are derived from ideal support conditions. This study first presents an evaluation procedure for the buckling of a connecting rod via finite element analysis (FEA). The FEA approach allows us to treat the first and second modes of buckling collectively. The buckling stresses from the suggested FEA approach are closer to those measured in rig experiments than those from classical formula are. The stress sensitivities to the area reduction of rod shank are then examined in lights of yield, fatigue and buckling. The stress sensitivity in buckling indicates to be relatively higher than or comparable to those of yield and fatigue. Consequently, when weight reduction of connection rod shank is attempted, buckling should be considered as an essential factor along with the other criteria such as yield and fatigue.     

Preparation and characterization of plasticized high molecular weight PVC-based polymer electrolytes

Poly(vinyl chloride) (PVC)-based polymer electrolytes films consisting of lithium trifluromethanesulfonate (LiCF₃SO₃)-ethylene carbonate (EC) were prepared by the solution-casting method. Ionic conductivities of the electrolytes have been determined by an impedance studies in the temperature range of 298–373 K. Complexation of the prepared electrolytes is studied by X-ray diffraction (XRD) analysis. Thermogravimetric analysis (TGA) was used to confirm the thermal stability of the polymer electrolytes. The conductivity-temperature plots were found to followan Arrhenius nature. All these films are found to be thermally stable until 132–167°C.     

Effects of n-type perylene derivative as an additive on the power conversion efficiencies of polymer solar cells

The synthesized n-type perylene derivative, N,N′-bis-(5-bromopyridine-2-yl)-1,6,7,12-tetrakis(4-n-butoxyphenoxy)-3,4,9,10-perylene tetracarboxydiimide (PPyB), was applied to polymer solar cells as an additive in P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl C₆₁-butyric acid methyl ester] blend films. The addition of 1 wt% PPyB into a P3HT:PCBM layer led to a considerable improvement of over 70% in power conversion efficiency due to the enhanced short circuit current when compared with that of reference cell without an additive. Photoluminescence, X-ray measurements and carrier mobility studies revealed that the perylene additives increased electron mobility and contributed to more effective exciton dissociation due to the presence of the additive, PPyB, in the interfaces between the P3HT and PCBM domains.     

Application of host‐specific source‐tracking tools for rapid identification of fecal contamination in fresh produce by humans and livestock

BACKGROUND: Fecal contamination in fresh produce is a public health concern because it may contain human pathogens. We introduced host‐specific quantitative real‐time polymerase chain reaction (qPCR) assays for the rapid detection and identification of fecal contamination sources from humans and farm animals (cow, pig, chicken) in fresh produce. Each composite fecal sample was spiked on lettuce at two contamination levels (0.2 mg or 2 mg feces g^?1), followed by qPCR assays for detecting each host‐specific genetic marker: BoBac (cow); PF163 (pig); CP3‐49 (chicken); and HF183 and gyrB (human). Two commercial DNA extraction kits were compared to evaluate DNA recovery yields and removal of PCR inhibition. Sketa2 assay was conducted to assess the presence of PCR inhibition in the contaminated lettuce. RESULTS: All the qPCR assays yielded reliable detection from contaminated lettuce (2 mg feces g^?1), where their target gene numbers were 1.5–5.0 × 10³ (HF183), 0.8–2.2 × 10³ (gyrB), 0.6–1.6 × 10³ (BoBac), 1.6–3.0 × 10³ (CP3‐49) and 1.1–2.2 × 10³ (PF163) copies g^?1 of lettuce. Among the two extraction kits, QIAamp DNA Stool Kit resulted in 2–3 times higher sensitivity and 20% less PCR inhibition than the PowerFood^? kit. CONCLUSION: This study provides information on the optimized host‐specific qPCR assay in identifying sources of fecal contamination in fresh produce and is useful for tracking the contamination source and improving agricultural practice. © 2012 Society of Chemical Industry     

Three dimensional stress analysis of a composite patch using stress functions

A stress function-based analysis is proposed to provide a simple and efficient approximation method of three-dimensional (3D) state of stress that exists near the free edge of bonded composite patches. In order to apply plane strain assumption in a composite patch, a linear superposition of sliced section from a bonded patch is used. In addition, to describe the load transfer mechanism from the substrate to the composite patch, a simple shear lag model is introduced. The 3D stress behavior at the free edge of the composite patch is modeled by Lekhnitskii stress functions, and the governing equations of the given composite patch are obtained by applying the principle of complementary virtual work. After a suitable expansion of the functions, the governing equations are transformed into two coupled ordinary differential equations, and they are solved by a general eigenvalue solution procedure. As the number of base functions increases, the interlaminar stresses converge. The interlaminar stresses reach maximum at the free edge and decrease sharply at the inner part of the patch. The interlaminar stresses are concentrated at the interface between the layers because of the mismatch of material properties and the geometric singularity. Since the proposed method accurately predicts the 3D stresses in a composite patch bonded on the metal substrate, it can be used as a simple and efficient analytical tool for designing such structural components.