Electro-Catalytic Oxidation of Methanol on a Ni–Cu Alloy in Alkaline Medium

The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10⁻⁴ cm² s⁻¹ and 1979.01 cm³ mol⁻¹ s⁻¹, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω.     

Non-linear panel flutter for temperature-dependent functionally graded material panels

The non-linear flutter and thermal buckling of an FGM panel under the combined effect of elevated temperature conditions and aerodynamic loading is investigated using a finite element model based on the thin plate theory and von Karman strain-displacement relations to account for moderately large deflection. The aerodynamic pressure is modeled using the quasi-steady first order piston theory. The governing non-linear equations are obtained using the principal of virtual work adopting an approach based on the thermal strain being a cumulative physical quantity to account for temperature dependent material properties. This system of non-linear equations is solved by Newton–Raphson numerical technique. It is found that the temperature increase has an adverse effect on the FGM panel flutter characteristics through decreasing the critical dynamic pressure. Decreasing the volume fraction enhances flutter characteristics but this is limited by structural integrity aspect. The presence of aerodynamic flow results in postponing the buckling temperature and in suppressing the post buckling deflection while the temperature increase gives way for higher limit cycle amplitude.     

Electrochemical studies of the pitting corrosion of tin in citric acid solution containing Cl

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)₄ and/or SnO₂ film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (E_pit) and the repassivation potential (E_rp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second stages involve pit nucleation and growth and third stage involve repassivation. The impedance spectrum of pure Sn is found to consist of three intersecting capacitive semicircles at the high and medium frequencies with an inductive loop at low frequencies. The capacitive semicircles occurring at the high and medium frequency are due to the dielectric properties of surface oxide film and dissolution of underlying metal, respectively. The inductive loop at low frequencies results from Cl⁻ adsorption at the pitting region. By increasing the potential the pitting corrosion and the fractal dimension of surface due to pitting increase.     

Chemorheological characterization of thermosetting polyurethane formulations containing different chain extender contents

Chemorheological analyses of thermosetting polyurethane (PU) formulations containing various amounts of chain extender were carried out. In the first part of the present research, effect of chain extender content on the gel time and its dependency with temperature were investigated for PU formulations. Gelation temperature (T_gel) and gel time (t_gel) of reactive systems were determined using temperature sweep and time test measurements under dynamic linear viscoelastic deformations. The results of temperature sweep experiments for the samples containing various chain extender weight percents showed that the gelation temperature declined by increasing the chain extender content of PU formulations. The analysis made on gel times determined in a wide temperature range indicated that the activation energy for the gelation process declined and 1/t_gel, as a measure of the rate of gelation process, dramatically increased with increasing chain extender concentration. In the second part of this study, calculation of viscoelastic characteristics at the gel point was performed. The results showed that the relaxation exponent (n) declined with increasing chain extender, while the fractal dimension increased. These results confirmed that the gel structures became more elastic and with a tighter structure by increasing the chain extender concentration in PU formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Numerical simulation of two phase refrigerant flow through non-adiabatic capillary tubes using drift flux model

Journal of Mechanical Science and Technology - This research presents a drift flux model to simulate steady state refrigerant flow through horizontal lateral straight capillary tube-suction line...     

Leaf cuticle and wax ultrastructure of genus Alnus Mill. in Hyrcanian forests of Iran

The genus Alnus had three taxa in the old floral resources of Iran. Recently, five new taxa were added to the flora based on morphological studies. Individual samples were collected from 25 sites throughout three provinces covering Hyrcanian forests of Iran and classified into the eight mentioned taxa and then prepared for micro-morphological studies. Four groups of taxa including A. subcordata var. subcordata, A. subcordata var. villosa, A. orientalis, and A. glutinosa subsp. antitaurica had a specific structure. Similar structure was also found between two new species of A. djavanshirii and A. dolichocarpa, which were distinguished from the other groups. Simple trichomes with variation in size and density were observed among the taxa. Alnus subcordata var. villosa and A. glutinosa subsp. antitaurica had the densest trichomes on dorsal and ventral leaf surfaces. The results of this study show the suitability of ultrastructure features as a micro-morphological marker for solving the taxonomical ambiguities of the genus Alnus in Hyrcanian forests.     

Centrifuge study into the effect of liquefaction extent on permanent settlement and seismic response of shallow foundations

Centrifuge experiments were conducted to investigate how the liquefaction extent affects the seismic and post-seismic settlement of shallow foundations resting on saturated sand. Two rigid foundations with different bearing pressures were placed on the ground surface in a model container. Multiple input motions were applied to achieve different extents of soil liquefaction. The results indicate that foundation settlement can be divided into three distinct phases: (I) during shaking, (II) during the time period after shaking has ceased and before soil reconsolidation in the shallowest layers has taken place, and (III) during soil reconsolidation. Contrary to the free-field ground, most of the total settlement of the foundations occurred before soil reconsolidation, i.e., during Phases I and II. The volumetric strain during these phases was not significant as opposed to the shear strain produced by the foundation surcharge. It was demonstrated that foundation settlement is not necessarily proportional to the liquefied depth of the sand. The extent of the liquefaction in the sand medium mostly affected the post-seismic settlement of the foundations, while the co-seismic settlement was relatively the same for both foundations. The response of the foundations was significantly influenced by the liquefaction extent, whereas the foundations did not experience large accelerations when the soil profile was entirely liquefied. However, the foundations tolerated large settlement under severe liquefaction conditions. The results of this study highlight the role of the liquefaction extent on co-seismic and post-seismic settlement as well as the seismic response of shallow foundations.     

Temperature of a photovoltaic module under the influence of different environmental conditions – experimental investigation

The climate changes affect photovoltaic (PV) module temperature significantly. The module temperature is one of the most important factors that influence the PV module efficiency and a deep analysis of PV module temperature will aid in better understanding of the environmental influences on the PV module performance. The module temperature depends on many parameters such as solar radiation, ambient temperature, air humidity, speed and direction of the wind, PV module orientation, dust and sand deposition on PV module, and PV module materials. An experimental research was conducted to investigate the effect of these factors on the PV module temperature in the Renewable Energy Laboratory of the Graduate University of Advanced Technology in Iran. The results of this study highlighted that the deposited dust over the PV module surface increases the module temperature and this consequently decreases the PV module power. It was also revealed that a combination of the temperature increase and the incident solar radiation decrease due to the dust deposition over the PV module enhances significantly the module power reduction.     

Global impedance attenuation network for multistage OTAs driving a broad range of load capacitor

Advanced multistage amplifiers suffer from load-dependent stability issues, which limit the load capacitor range they can drive. In this work, the concept of global impedance attenuation (GIA) network is introduced to improve an amplifier's stability in the presence of significant load capacitor variations. Composed of multiple parallel resistor-capacitor (RC) branches, the equivalent high-frequency output impedance of gain stages is shaped by the GIA network such that a desired frequency spectrum is obtained over a wide range of load capacitor. The parasitic poles at the output of the gain stages are nullified by the proposed network, thereby simplifying the amplifier's transfer function and reducing the minimum load capacitor it can drive. The idea is applied to design a three-stage operational transconductance amplifier (OTA) with cascode global impedance attenuation (CGIA). Small-signal analysis shows that the OTA is stable regardless of the load capacitor, and it can drive very small to ultra-large load capacitors. This feature is verified by the post-layout simulations of a CGIA amplifier in 0.18-μm complementary metal-oxide semiconductor (CMOS) process. The core occupies a die area of 0.0053 mm² while consuming a static current of 10.97 μA from 1.8-V voltage supply. The unity-feedback configuration is unconditionally stable for any load capacitor higher than 10 pF. To the best of our knowledge, this corresponds to the widest range of load capacitance reported for prior-art three-stage amplifiers.