Influence of the cyclic plastic zone size on the propagation of the fatigue crack in case of 12NC6 steel

Under cyclic loading, the plasticized zone becomes complicated; it contains in particular a second plasticized zone, resulting from the local compression which occurs at the time of the closing of the crack to each cycle. The two plastic zones, monotonous (r_m) and cyclic (r_c), are proportional to (K_max/R_e)² et (ΔK/R_e)², respectively. The objective of this work is to study the evolution of the fatigue crack grown rate (FCGR) and the influence of the plastic zone size (r_c), which represents the seat of the residual stresses, on this evolution in the case of 12NC6 steel. Generally, the plastic zone size increases with the crack advance. The FCGR can be correlated with the energy absorptive in these plastic zones.     

Optimizing substrate surface and catalyst conditions for high yield chemical vapor deposition grown epitaxially aligned single-walled carbon nanotubes

Single-crystal stable-temperature (ST)-cut quartz substrates, which have a (0 1 1 1) crystallographic plane with their surface normal lying close to 38° from the y axis ([0 1 0]), were annealed in air prior to use as a support for aligned carbon nanotube growth by chemical vapor deposition. Very smooth substrate surfaces were obtained with annealing times in the vicinity of 15 h at a temperature of 750 °C. These smooth surfaces are ideal for the growth of horizontally aligned SWCNTs with high spatial density, while less dense SWCNTs were obtained with less smooth surfaces. Under optimized growth conditions, only SWCNT are observed and they can grow to lengths in excess of 100 μm. Our findings suggest structural defects interfere with the growth process. A binary Fe/Co catalyst was employed to grow the nanotubes. No obvious dependence on the Fe:Co ratio is observed.     

Selection of Methodology for Neural Network Modeling of Constitutive Hystereses Behavior of Soils

Classic constitutive modeling of geomaterials based on the elasticity and plasticity theories suffers from limitations pertaining to formulation complexity, idealization of behavior, and excessive empirical parameters. This article capitalizes on the modeling capabilities of neural networks as substitutes for the classic approaches. The neural network–based modeling overcomes the difficulties encountered in understanding the underlying microscopic processes governing the material's behavior by redirecting the efforts into learning the cause-effect relations from behavioral examples. Several methodologies are presented and cross-compared for effectiveness in approximating a theoretical hysteresis model resembling stress-strain behavior. The most effective methodology was used in modeling the constitutive behavior of an experimentally tested soil and produced models that simulated the real behavior of the soil with high accuracy. Although these models are empirical, they are retrainable and thus, unlike classic constitutive modeling techniques, can be revised and generalized easily when new data become available.     

Determination of Sensory Thresholds of Selected Calcium Salts and Formulation of Calcium-fortified Pocket-type Flat Bread

Pita bread loaves were prepared from flours fortified with calcium carbonate, calcium sulfate, and tricalcium dicitrate at 8 ascending levels to provide ranges of 800 to 2500, 700 to 1500, and 400 to 2000 mg of added Ca/100 g flour, respectively. The detection thresholds of calcium salts in pita bread were determined by the 3‐alter‐native forced choice (3‐AFC) test and construction of dose‐response curves. Detection thresholds determined by calculating geometric mean of individual best estimate thresholds, using criterion of 50%‐above‐chance and probit analysis of 3‐AFC data, were in the middle region of calcium concentrations. Analysis of dose‐response curves yielded values for thresholds outside the range of surveyed calcium concentrations. The detection threshold of CaSO₄ (2724 mg/100 g) in pita bread was significantly higher (P < 0.01) than those of calcium carbonate (1984 mg/100 g) and tricalcium dicitrate (2132 mg/100 g). Calcium‐fortified pita bread was similar (P < 0.01) to its regular counterpart when formulated to contain 1254.6, 1772.5, or 1155 mg/100 g of CaCO₃, CaSO₄, or tricalcium dicitrate, respectively. At the indicated levels of fortification, calcium‐fortified pita bread is expected to provide between 61% and 126.5% of the recommended daily intake for calcium for Middle Eastern populations.     

The shift in US oil demand and its impact on OPEC's market share

Tremendous political pressure is being exerted on the US government by different political parties to diversify its sources of foreign oil supplies by switching from the reliance on OPEC's oil to that originating from non-OPEC nations. Without a doubt, such a shift would adversely impact the market share of some OPEC members, particularly Saudi Arabia, Venezuela and Nigeria. These countries should therefore consider seriously the negative impact of this scenario and consequently formulate individual or joint production policies aiming at protecting their oil market share. To help OPEC achieve this objective, there is a need to estimate the demand function of US oil imports. This paper proffers an estimate of such a function, taking into account, among other variables, the impact of US Strategic Petroleum Reserve (SPR).     

Analytical expressions for intermodulation distortion of a MESFET small-signal amplifier using the nonlinear Volterra series

Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (C_gd) explicitly as a nonlinear element. Previously developed analytical expressions treated C_gd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (C_gs and C_ds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit.     

Efficient multi‐hop wireless broadcast protocol in vehicular networks using automated threshold function design

Vehicular networking applications often use multi‐hop wireless broadcasting as a primary data dissemination mechanism. Therefore, protocols that efficiently and thoroughly propagate application data while adapting to a wide range of network density, vehicle distribution pattern, channel quality, and other conditions are critical for vehicular communications. Here, we design the Statistical Vehicular Broadcast (SVB) protocol to efficiently distribute data via multi‐hop broadcast in vehicular networks. First, we present an automated optimization technique for the design of threshold functions in statistical broadcasting methods. Next, we compare and analyze known statistical techniques, including different fundamental methods, assessment delay algorithms, and failsafe mechanisms. All combinations of these techniques are given threshold functions optimized using the proposed automated procedure then are evaluated in a wide range of simulations. High‐level statistical design principles and recommendations are established based on analysis of these results. Finally, we apply those principles to design SVB. It is evaluated in JiST/SWANS and is shown to achieve a high target reachability level while consuming less bandwidth than similar protocols across urban and highway vehicular networking scenarios.Copyright © 2014 John Wiley & Sons, Ltd.     

Heat transfer enhancement by metal screens and metal spheres in phase change energy storage systems

This study focuses on heat transfer enhancement in double pipe energy storage system. Enhancement is achieved by use of metal screens/spheres placed inside the phase change material (PCM), which is paraffin wax and results in increasing the effective thermal conductivity of the combined media of PCM and metal screens/spheres. The experiments are conducted as a function of the diameter and number of spheres inserted in the phase change material. Also, the experiments investigate the effect of increasing the temperature of the heat transfer fluid (HTF). Results are presented in terms of variations in the PCM Nusselt number and the melting Fourier number. Results indicate three-fold decrease in the Fourier number and similar increase in the Nusselt number. Replacing 2-volume percentage of the wax material by the metal spheres results in this large enhancement.     

Synthesis of S-dithiocarbonates with polymer-supported xanthates

Summary Polymer-supported ammonium salts of methyl and ethyl xanthates react with alkyl halides to yield S-dithiocarbonates.