New Magnesium Composite with Mg17Al12 Intermetallic Particles

Powder Metallurgy and Metal Ceramics - Although magnesium is one of the materials with the lowest density, its application is limited amongst other commercial materials due to insufficient...     

Thermo-physical performance of DGEBA/1,8-NDA/barium carbonate composite for coating applications

The toughening of epoxy resins by incorporating inorganic fillers is of great importance nowadays, due to their wide range of applications. The present work reports the results of the addition of barium carbonate into a polymeric matrix containing diglycidyl ether of bisphenol-A (DGEBA) epoxy resin using 1,8-naphthalene diamine (1,8-NDA) as hardener to produce a novel composite for industrial applications. Cure kinetics of the composite system was investigated by means of differential scanning calorimeter (DSC) in dynamic mode. Kinetics of the reaction was interpreted according to the two isoconversional methods of Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (OFW). Using non-isothermal conditions, average value of the cure reaction activation energy in the propagation step was determined to be 57 and 60.2 kJ/mol for the KAS and OFW models, respectively. DMTA and TGA measurements were used in order to assess the effectiveness of the filler amount (2 Phr) on the final mechanical and thermal properties of the produced composite. The results verified that the thermal stability of the composite could be improved with the incorporation of BaCO₃. Microstructural observations from images analysis of SEM micrographs revealed that the barium salt was dispersed into polymer matrix homogeneously.     

Effects of Silica Nanoparticles Content on the Properties and Corrosion Behavior of Electroless Ni-Ba-B Alloy Coatings

The beneficial role of silica nanoparticles addition as reinforcing agent on the various properties of the novel developed Ni-Ba-B coating was highlighted. Barium was considered as third element to act as an inhibiting alloying element for anodic passivation purposes. The ternary Ni-Ba-B coatings in three different concentrations of silica nanoparticles (0.5, 1.0 and 2.0 g/L) were coated on St 37 steel substrate in the presence of sodium dodecyl sulfate (SDS). The effect of nanoparticles on morphology and structure was investigated by FE-SEM, XRD and AFM tests. The nodularity and surface roughness of the coating increased by the presence of SiO2 nanoparticles in the electroless bath. The nanocomposite coating has amorphous and crystalline phases and its XRD peak at 44.50 is slightly sharper than the composite coating. DSC thermogram showed two exothermic peaks demonstrating its phase transformations. The WCA value of coating was confirmed its hydrophilicity property. Results also confirmed that the existence of silica nanoparticles results in an increase in the microhardness and corrosion resistance which may be attributed to the distribution of silica nanoparticles into Ni-Ba-B matrix.     

Highly sensitive amperometric sensor for micromolar detection of trichloroacetic acid based on multiwalled carbon nanotubes and Fe(II)–phtalocyanine modified glassy carbon electrode

A highly sensitive electrochemical sensor for the detection of trichloroacetic acid (TCA) is developed by subsequent immobilization of phthalocyanine (Pc) and Fe(II) onto multiwalled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrode. The GC/MWCNTs/Pc/Fe(II) electrode showed a pair of well-defined and nearly reversible redox couple correspondent to (Fe(III)Pc/Fe(II)Pc) with surface-confined characteristics. The surface coverage (Γ) and heterogeneous electron transfer rate constant (k_s) of immobilized Fe(II)–Pc were calculated as 1.26 × 10^? 10 mol cm^? 2 and 28.13 s^? 1, respectively. Excellent electrocatalytic activity of the proposed GC/MWCNTs/Pc/Fe(II) system toward TCA reduction has been indicated and the three consequent irreversible peaks for electroreduction of CCl₃COOH to CH₃COOH have been clearly seen. The observed chronoamperometric currents are linearly increased with the concentration of TCA at concentration range up to 20 mM. Detection limit and sensitivity of the modified electrode were 2.0 μM and 0.10 μA μM^? 1 cm^? 2, respectively. The applicability of the sensor for TCA detection in real samples was tested. The obtained results suggest that the proposed system can serve as a promising electrochemical platform for TCA detection.     

Electrochemical preparation and properties of polypyrrole and its blend with poly(vinyl sulfonate) doped with perchlorate anions

In this article, we report polypyrrole (PPy)/poly(vinyl sulfonate) (PVS) and PPy/perchlorate (ClO) composite films generated by the electrochemical oxidation of pyrrole on a glassy carbon electrode (GCE) in an aqueous solution. The response of the produced films to an applied potential at 0.7 V was obtained by a cyclic voltammetry study in acetonitrile media. The films were significantly similar in their electrochemical behavior when ClO ions doped during the redox process. We concluded that with an increasing number of cycles, the anodic current increased because the number of the electroactive participants transported in the copolymer matrix was increased. Theoretical studies based on the Nernst and Butler–Volmer equations indicated that the ClO ion was transported during the oxidation/reduction process of the PPY/PVS and PPY/ClO films. The produced films were characterized further by means of IR spectroscopy, electrochemical impedance spectroscopy, and scanning electron microscopy to verify that the anion of ClO was doped into the copolymer matrix as well. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Risk constrained self-scheduling of hydro/wind units for short term electricity markets considering intermittency and uncertainty

In view of the intermittency and uncertainty associated with both the electricity production sector of restructured power system and their competitive markets, it is necessary to develop an appropriate risk managing scheme. So that it is desirable to trade-off between optimum utilization of intermittent generation resources (i.e. renewable energy resources), uncertain market prices and related risks in order to maximize participants' benefits and minimize the corresponding risks in the multi-product market environment. The main goal of this paper is to investigate risk management by introducing a novel multi-risk index to quantify expected downside risk (EDR) which is caused by both the wind power and market price uncertainties. Value-at-Risk (VaR) method is used to assess the mentioned risk issue by the proposed weighted EDR, so that an optimal trade-off between the profit and risk is made for the system operations. Also, the roulette wheel mechanism is employed for random market price scenario generation wherein the stochastic procedure is converted into its respective deterministic equivalents. Moreover, the autoregressive integrated moving average (ARIMA) model is employed to characterize the stochastic wind farm (WF) generation by predetermined mean level and standard deviation of wind behavior as well as temporal correlation. The problem is formulated as a mixed-integer stochastic framework for a hydro-wind power system scheduling and tested on a generation company (GENCO).     

Recognition of electrocardiographic left arm/left leg lead reversal

The electrocardiographic error of left arm/left leg lead reversal is difficult to identify. PI amplitude greater than PII as a terminal positive component to PIII may diagnose 90% of such errors.     

Verification of numerical study of scour around spur dikes using experimental data

Scour phenomenon around a series of impermeable, nonsubmerged spur dikes has been investigated with both experimental and numerical methods. The experiments were conducted under different states of flow intensity (U/U_cr). The scour geometry was measured with a high‐resolution laser bed‐profiler (LBP). For the numerical simulation phase, a three‐dimensional computational fluid dynamics (CFD) model, namely SSIIM 2.0, was used to compute the sediment transport around the spur dikes. The numerical model was based on the finite‐volume method. Two turbulence models, namely k‐ε standard and k‐ε with re‐normalization group (RNG) extensions, were used to predict turbulence, and the k‐ε model with some RNG extensions was selected because of its best agreement with the measurements. Furthermore, a variety of grids and empirical sediment transport equations were used to find the best state for simulation of scour around a series of spur dikes. Finally, a comparison between experimental and numerical results was carried out to verify the CFD model.     

Reanalyzing the basic bandgap reference voltage circuit considering thermal dependence of bandgap energy

The basic bandgap reference voltage generator, BGR, is thoroughly analyzed and relations are reconstructed considering dependency of bandgap energy, E_g, to absolute temperature. The previous works all consider E_g as a constant, independent of temperature variations. However, E_g varies around 25 meV when the temperature is increased from 2 to 92 °C. In this paper the dependence of E_g to absolute temperature, based on HSPICE mosfet models in HSPICE MOSFET Models Manual (Version X-2005.09, 2005), is approximated by a third-order polynomial using Lagrangian interpolating method within the temperature range of 2–92 °C. Accurate analysis on the simplified polynomial reveals that the TC of V_BE must be corrected to ?1.72 mV/°K at 27 °C which has been formerly reported about ?1.5 mV/°K in Razavi (Design of analog CMOS integrated circuits, 2001) and Colombo et al. (Impact of noise on trim circuits for bandgap voltage references, 2007), ?2 mV/°K in Gray et al. (Analysis and design of analog integrated circuits, 2001), Leung and Mok (A sub-1-V 15-ppm/°C CMOS bandgap voltage reference without requiring low threshold voltage device, 2002), Banba et al. (A CMOS bandgap reference circuit with sub-1-V operation, 1999), and ?2.2 mV/°K in Jones and Martin (Analog integrated circuit design, 1997), Tham and Nagaraj (A low supply voltage high PSRR voltage reference in CMOS process, 1995). Another important conclusion is that the typical weighting coefficient of TC+ and TC? terms is modified to about 19.84 at 27 °C temperature from otherwise 16.76, when E_g is considered constant, and also 17.2, in widely read literatures, (Razavi in Design of analog CMOS integrated circuits, 2001). Neglecting the temperature dependence of E_g might introduce a relative error of about 20.5 % in TC of V_BE. Also, resistance and transistor size ratios, which denote the weighting coefficient of TC+ term, might be encountered to utmost 20.3 % error when the temperature dependence of E_g is ignored.     

Life-cycle prediction of steel bridges using reliability-based fatigue deterioration profile: Case study of neka bridge

Fatigue deterioration profiles of critical elements in a railway truss bridge are determined using a probabilistic approach. A performance function including fatigue strength, R, and fatigue action, D, is used, where R is a material property with lognormal distribution. The random variable D depends on AASHTO category, stress spectrum and traffic features. By applying Monte-Carlo simulations on the performance function of each year, reliability index profile is calculated. The reliability profile decreases with life, and whenever reaches to a critical value, an MR&R action should be implemented. A numerical approach is presented to specify the effects of MR&R actions on the deterioration profile. These actions include re-welding, attaching CFRP and combination of them. The structural model is calibrated by results of a loading test. In addition, the uncertainties arisen from future traffic volume and the relevant S-N curve are considered by a statistical analysis. For a target reliability of 2.0, the retrofit time for deck and truss are estimated. Finally, the outputs of the research are used to recommend a plan for maintenance of Neka Bridge.