The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s⁻¹. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s⁻¹. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.     

Radiosynthesis and biodistribution of [^18F]-tetracosactide using a semi-automated [^18F]SFB production module

In order to prepare a specific melanocortin type 2 receptor (MC2R) ligand, b1-24-corticotrophin was pre-pared in one-step reaction with [18F] SFB and b-1-24-corticotrophin pharmaceutical solution (1 mg/mL, pH=6.5). [18F]SFB was prepared in a semi-automated module in two steps with an overall radiochemical yield of 47% to EOB (not-decay corrected) in 90 min. The 18F-labeled intermediates and 18F-labeled peptide was checked by RTLC and HPLC. The results show that the radiochemical purity is >95% and the yield to EOB (not-decay corrected) is 29% for final 18F-labeled peptide at optimized conditions. Preliminary in vivo studies in normal mice were performed to deter-mine biodistribution of the 18F-labeled peptide for 150 min. The results show that the major tracer uptake is consistent with the natural distribution of MC2R receptors in mammals. Testes/blood and testes/muscle ratios for 18F-labeled peptide at 150 min were 184 and 1.56, respectively, and adipocyte/blood and adipocyte/muscle ratios at 120 min were 221 and 142, respectively. The data support the specific receptor binding of the radiolabeled peptide as reported for MC2R receptor accumulation in adipocytes and testes and demonstrates the retention of biological activity of the pep-tide. This tracer can be used in detection of MC2R distribution in malignancies and sex organ diseases.     

Energy efficiency optimization of one-way and two-way DF relaying considering circuit power

In this paper, the energy efficiency (EE) of a decode and forward (DF) relay system is studied, where two sources communicate through a half-duplex relay node in one-way and two-way relaying strategies. Both the circuitry power and the transmission power of all nodes are taken into consideration. In addition, three different coding schemes for two-way DF relaying strategy with two phases and two-way DF relaying with three phases are considered. The aim is to maximize the EE of the system for a constant spectral efficiency (SE). For this purpose, the transmission time and the transmission power of each node are optimized. Simulations are used to compare the EE–SE curve of different DF strategies with one-way and two-way amplify and forward (AF) strategies and direct transmission (DT), to find the best energy efficient strategy in different SE conditions. Analytical and simulation results demonstrate that in low SE conditions, DF relaying strategies are more energy efficient compared to that of AF strategies and DT. However, in high SE conditions, the EE of two-way AF relaying and DT strategy outperform some of the DF relaying strategies. In simulations, the impact of different circuitry power and different channel conditions on the EE–SE curves are also investigated.     

Creep response of glued-laminated beam reinforced with pre-stressed sub-laminated composite

In the past decades, the use of fibre-reinforced polymer (FRP) for enhancement of strength and stiffness of wood-based structural members has been established as an economical method. New developments have been ongoing to further improve the structural performance of glued-laminate beams. Recently, a novel integral sub-laminated composite, referred to as pre-stressed FRP–wood composite laminate (PWCL), was patented (KarisAllen and Tynes, 2000 [1]). This system is comprised of pre-stressed high performance fibres, sandwiched and glued within layers of pre-compressed wood strands. The resulting sub-laminated system may be attached to the tension zone of timber/glulam beams. A concern involved with the use of such pre-stressing scheme has been the issue of creep, which could affect the long-term performance of such composite beams. This paper presents the results of a study conducted to investigate the long-term performance of glulam beams reinforced with PWCL sub-laminate. Experimental investigations were conducted to determine the creep parameters of FRP composites and wood species employed in the fabrication of PWCL. The main objective was to develop a finite element model (FEM) to simulate the pre-stressing process and to predict the creep response of an entire reinforced glulam system, including the PWCL, under an externally applied load and constant environmental condition. The FEM was constructed in the Abaqus environment and the residual stress distribution was modeled in a step-wise scheme, corresponding to each step of PWCL and beam fabrication as well as the in situ response of the composite beam. The integrity of the creep model used in the simulation was verified by the experimental results obtained from tests performed on FRP reinforced small-size wood.     

Quenching and Partitioning (Q&P) Processing of Martensitic Stainless Steels

Austenite was stabilized in the martensitic stainless steel grade AISI 420 by means of quenching and partitioning (Q&P) processing. The effects of quenching temperature on the microstructure and mechanical properties were investigated. The specimens processed at low quench temperatures (regime I) had a microstructure consisting of tempered martensite and retained austenite. At high quench temperatures (regime II), fresh martensite was present too. The highest austenite fraction of about 0.35 was obtained at the quench temperature delineating regimes I and II. The amount of carbon in retained austenite increased as the quench temperature decreased. The carbon level of austenite was, however, much lower than the carbon concentrations expected from full partitioning assumption. This was mainly due to the extensive cementite formation in the partitioning step. Stabilization of austenite by Q&P processing was found not to be purely chemical. Austenite stabilization was also assisted by locking, because of local carbon enrichment, of potential martensite nucleation sites in the austenite/martensite boundaries and in austenite defects. The importance of the latter stabilization mechanism increased at higher martensite fractions. According to the tensile test results, the Q&P processed specimen with the highest austenite fraction was not associated with the best combination of strength and ductility. The mechanical stability of austenite was found to increase with its carbon concentration being the highest at the lowest quench temperature. The thermal stability, on the other hand, was almost inversely proportional to the retained austenite fraction, being low at intermediate quench temperatures where the retained austenite fraction was high.     

Influences of feeding conditions and objective function on the optimal design of gas flow channel of a PEM fuel cell

Polymer electrolyte membrane fuel cell (PEMFC) is one of the promising electricity generating technologies with a wide range of applicability; however, it needs further improvements to be commercially viable. The design of a PEMFC plays a key role in its viability, and is often reduced to the design of gas flow channel (GFC) at the cathode side. In this study, it is attempted to figure out the optimal dimensions (i.e., width and height) of the rectangular cross sectional area of the cathode GFC of a PEMFC via numerical examination of various sets of dimensions. The optimization procedure is carried out for two different objective functions (the maximization of the maximum power and the maximization of the average power over a range of operating voltages) as well as for different sets of operating conditions (cell temperature, operating pressure, and stoichiometry and relative humidity of inlet gases). To the best of authors' knowledge, the following observations may be considered to be the contributions of the present work to the subject: First, the influence of cross sectional dimensions on the PEMFC performance is considerable, and this considerable influence is not limited to a specific set of operating conditions. Second, the performance of the PEMFC may both deteriorate and improve with the channel width or height, depending on its operating conditions as well as on its current dimensions. Third, there exists no single optimal cross section for different sets of operating conditions. Fourth, the polarization curves of two different cross sections may intersect, and as a result, one cross section may have a greater maximum power but at the same time lower average power in comparison to the other one. And fifth, among all the operating parameters, the relative humidity of inlet gases has the greatest effect on the optimal cross sectional dimensions.     

Effects of bed-load movement on flow resistance over bed forms

The effect of bed-load transport on flow resistance of alluvial channels with undulated bed was experimentally investigated. The experiments were carried out in a tilting flume 250mm wide and 12.5m long with glass-sides of rectangular cross-section and artificial dune shaped floor that was made from Plexi-glass. Steady flow of clear as against sediment-laden water with different flow depths and velocities were studied in the experiments with a fine sand (d ₅₀ = 0.5mm). The results indicate that the transport of fine particles (d ₅₀ = 0.5mm) can decrease the friction factor by 22% and 24% respectively for smooth and rough beds. Increasing the bed-load size (d ₅₀ = 2.84 mm) can decrease the friction factor by 32% and 39% respectively for smooth and rough beds. The decrease in flow resistance is due to filling up of the troughs of dunes. This separation zone is responsible for increasing the flow resistance. On the upstream side of dunes condition is similar to plane bed. Presence of bed-load causes to increase the shear velocity and hence increasing flow resistance. But decreasing in flow resistance is more and it causes to decrease the total flow resistance. Grains saturated the troughs in the bed topography, effectively helping in smoothening of bed irregularities.     

Preparation and characterization of P4MVPMnO4/SBA-15 as an efficient heterogeneous oxidant: An organic–inorganic hybrid polymer

This work is concerned about the preparation and characterization of MnO₄⁻ supported poly (4-methyl vinylpyridinium)/SBA-15 which was effectively employed as a heterogeneous oxidant for oxidation of aromatic alcohols. P4MVPMnO₄/SBA-15 exhibited excellent activity and selectivity under mild and solvent-less conditions.     

High temperature deformation and processing map of a NiTi intermetallic alloy

The deformation behavior of a 49.8 Ni-50.2 Ti (at pct) alloy was investigated using the hot compression test in the temperature range of 700 °C–1100 °C, and strain rate of 0.001 s^?1 to 1 s^?1. The hot tensile test of the alloy was also considered to assist explaining the related deformation mechanism within the same temperature range and the strain rate of 0.1 s^?1. The processing map of the alloy was developed to evaluate the efficiency of hot deformation and to identify the instability regions of the flow. The peak efficiency of 24–28% was achieved at temperature range of 900 °C–1000 °C, and strain rates higher than 0.01 s^?1 in the processing map. The hot ductility and the deformation efficiency of the alloy exhibit almost similar variation with temperature, showing maximum at temperature range of 900 °C–1000 °C and minimum at 700 °C and 1100 °C. Besides, the minimum hot ductility lies in the instability regions of the processing map. The peak efficiency of 28% and microstructural analysis suggests that dynamic recovery (DRV) can occur during hot working of the alloy. At strain rates higher than 0.1 s^?1, the peak efficiency domain shifts from the temperature range of 850 °C–1000 °C to lower temperature range of 800 °C–950 °C which is desirable for hot working of the NiTi alloy. The regions of flow instability have been observed at high Z values and at low temperature of 700 °C and low strain rate of 0.001 s^?1. Further instability region has been found at temperature of 1000 °C and strain rates higher than 1 s^?1 and at temperature of 1100 °C and all range of strain rates.     

Magnetic behavior of nickel–bismuth ferrite synthesized by a combined sol–gel/thermal method

The bulk NiFe_2?xBi_xO₄ ferrites with various Bi³⁺ concentration (x=0, 0.1, 0.15) were synthesized via sol–gel procedure, starting from nickel, bismuth and iron nitrate powders, followed by the conventional thermal treatment. The structural and magnetic properties of the as-prepared ferrites were studied by means of X-ray diffraction, alternating gradient force magnetometry and Faraday balance. The anisotropy constant was determined by the law of approach to saturation (LAS) model. An increasing Bi³⁺ concentration in NiFe_2?xBi_xO₄ leads to a decrease in the saturation magnetization, Néel temperature and the anisotropy constant of the material.