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New series of ethynyl-terminated sulfonated-fluorinated poly(arylene ether)s (ESF-6Fs) were synthesized via nucleophilic aromatic substitution reaction (SNAr) from potassium 2,5-dihydroxybenzenesulfonate (SHQ), 4,4′-(hexafluoroisopropylidene)diphenol (6FBPA), and decafluorobiphenyl (DFBP), followed by the reaction with 3-ethynylphenol. The cross-linked ESF-6F membranes exhibited high glass-transition temperatures in the range of 258−276 °C and good thermal degradation temperatures in the range of 308−328 °C. To optimize the proton conductivity and water uptake of the cross-linked ESF-6F membranes, various volume-related parameters (length-scaled parameters) were introduced. Using those parameters, the proton conductivity and water uptake of the cross-linked ESF-6F membranes were compared with sulfonated poly(arylene ether sulfone) random copolymer (BPSH), Nafion membrane, and another cross-linked membrane. In addition, the proton conductivity of optimized ESF-6F membrane was observed as a function of relative humidity (RH) at 80 °C and compared with other membranes. Excellent proton conductivity was observed at the percent conducting volume (PCV) (0.39, ESF90-6F) corresponding to the maximum volume-based ion exchange capacity in the hydrate state (IECv(wet)) and the atomic force microscopy (AFM) image showed good ionic channels at that point. Also, for the direct methanol fuel cell (DMFC) application, the cross-linked ESF-6F membranes exhibited lower methanol crossover (11 × 10−8−103 × 10−8cm2/s) and higher selectivities (130 × 103−492 × 103s Ω−1cm−3) than those of Nafion 117 (167 × 10−8cm2/s and 55 × 103s Ω−1cm−3). [ABSTRACT FROM AUTHOR]

End-group cross-linkable sulfonated poly(arylene ether) polymer (E-SFQK) was synthesized via direct polymerization of potassium 2,5-dihydroxybenzenesulfonate (SHQ) and decafluorobiphenyl (DFBP), followed by a reaction with ethynylphenol (EP). The cross-linking reaction of the ethynyl end group of E-SFQK was performed at 250 °C. After cross-linking, proton conductivity, water uptake, and swelling ratio of cross-linked membrane decreased from 0.16 (noncross-linked membrane) to 0.13 S/cm, from 86% to 42%, and from 31% to 13%, respectively. The effect of cross-linking time on proton conductivity, water uptake, and swelling ratio were also investigated. Methanol permeability of cross-linked membrane was compared with Nafion 117 due to solubility of noncross-linked membranes in methanol. The cross-linked membrane performed better, with a methanol permeability of 88 × 10−8cm2/s, as compared with 154 × 10−8cm2/s for Nafion 117. The cross-linked membrane also exhibited improved chemical resistance and oxidative stability from solubility and Fenton‘s tests. In order to study morphological changes of cross-linked and noncross-linked membranes, hydrophilic domain sizes from an AFM phase image were evaluated. These results showed that the sizes of hydrophilic domains of the cross-linked membrane (5−20 nm) are much smaller than those of noncross-linked membrane (20−50 nm). [ABSTRACT FROM AUTHOR]

A new nonlinear finite element formulation is presented to predict the thermal buckling and flutter boundaries of shape memory alloy hybrid composite cylindrical panels at elevated temperatures. The governing equations are obtained using Marguerre curved-plate theory and the principle of virtual work. The effect of large deflection is included in the formulation through the von Kármán nonlinear strain-displacement relations. To account for the temperature dependence of material properties, the thermal strain is stated as an integral quantity of the thermal expansion coefficient with respect to temperature. The aerodynamic pressure is modeled using the quasi-steady first-order piston theory. The Newton-Raphson iteration method is employed to obtain the nonlinear thermal postbuckling deflections, and a frequency-domain solution is presented to predict the critical dynamic pressure at elevated temperatures. Numerical results are presented to illustrate the effect of shape memory alloy fiber embeddings, temperature rise, height-to-thickness ratios, and boundary conditions on the panel response. [ABSTRACT FROM AUTHOR]

Switching controller design for a class of Markovian jump nonlinear systems with unmodeled dynamics is considered in this paper. Based on the differential equation and infinitesimal generator of jump systems, the concept of Jump Input-to-State practical Stability (JISpS) in probability and stochastic Lyapunov stability criterion are put forward. By using backsetpping technology and stochastic small-gain theorem, a switching controller is proposed which ensures JISpS in probability for the jump nonlinear system. A simulation example illustrates the validity of this design. [ABSTRACT FROM AUTHOR]

Reduction of outgassing in a high temperature superconducting (HTS) power cable cryostat is very important to achieve a lung interval vacuum pumping and to drop the minimum vacuum condition in the cryostat. So, in order to reduce outgassing from the cryostat surface, cleaning and baking are needed processes in manufacturing the cryostat. The outgassing surface of the cable cryostat is larger than the vacuum space of the cable cryostat, therefore the vacuum condition of the cable cryostat degrades quickly at a small outgassing rate. In this paper, to analyze the thermal insulation performance of cable cryostat, we have measured the outgassing rate of the sample HTS power cable cryostat in various structures of thermal insulation (with or without multilayer insulation and filled with liquid nitrogen or without liquid nitrogen) and predicting the trend of the vacuum condition changes by the measured outgassing rate data. A long term outgassing test is performed for three months. [ABSTRACT FROM AUTHOR]

The article investigates the effects of the pore density of aluminum foam heat sinks, the jet velocity, the jet-to-jet spacing and the nozzle plate-to-heated surface separation distance in a 3 x 3 square multi-Jet impinging array on the averaged Nusselt number. The current trend for dense packaging and high-performance of state-of-the-art electronics has been accompanied with a serious requirement for effective cooling schemes. Jet impingement provides a higher cooling performance compared to a duct flow type convective cooling. It is attributed to thin boundary layer formed on a heated surface by a jet impingement, which results in a higher convective heat transfer coefficient.

A nonlinear finite element model is provided for the supersonic flutter behavior of functionally graded material panels subject to combined aerodynamic, thermal, and random acoustic loads. Material properties are assumed to be temperature dependent and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations are derived using the classical plate theory with von Kármán geometric nonlinearity and the principle of virtual work. The first-order piston theory is adopted to model aerodynamic pressures induced by supersonic airflows. The thermal load is assumed to be steady-state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. The Newton—Raphson iteration method is employed to obtain the dynamic response at each time step of the Newmark scheme for numerical integration. Finally, numerical results are provided to study the effects of the volume fraction exponent, aerodynamic pressure, temperature rise, and the random acoustic load on the panel response. [ABSTRACT FROM AUTHOR]

A nonlinear finite element model is provided for the nonlinear random response of functionally graded material panels subject to combined thermal and random acoustic loads. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations are derived using the first-order shear-deformable plate theory with von Karman geometric nonlinearity and the principle of virtual work. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. Newton–Raphson iteration method is employed to obtain the dynamic response at each time step of the Newmark implicit scheme for numerical integration. Finally, numerical results are provided to study the effects of volume fraction exponent, temperature rise, and the sound pressure level on the panel response. [ABSTRACT FROM AUTHOR]