Effect of vibration on behaviour of bifilms in A356 and A357 melts

The effect of applying vibration to a melt on the behaviour of bifilm defects in A356 and A357 melts was studied using a reduced pressure test technique. The results showed that vibrating a melt can have a dual effect on bifilms. This effect depends on the rate of phase transformations that occur in the oxide films. If the transformation occurs fast enough then the vibration would facilitate the formation of bonding between the layers of bifilm defects by causing the atmosphere of the defects to be consumed faster. Otherwise, the vibration might facilitate the diffusion of hydrogen into the atmosphere of the defects, and hence prevent or delay the formation of bonding between the oxide layers.     

Role of Double Oxide Film Defects in the Formal ion ol’ Gas Porosity in Commercial Purity and Sr-containing A1 Alloys

The role of double oxide film （bifilm） defects in the formation of gas porosity in commercial purity and Srcontaining AI alloys was investigated by means of a reduced pressure test （RPT） technique. The liquid metal was poured from a height into a crucible to introduce oxide defects into the melt. The melt was then subjected to different ＂hydrogen addition＂ and ＂holding in liquid state＂ regimes before RPT samples were taken. The RPT samples were then characterized by determining their porosity parameters and examining the internal surfaces of the pores formed in them by scanning electron microscopy. The results indicated oxide defects as the initiation sites for the growth of gas porosity, both in commercial purity and Sr-containing AI alloys. The results also rejected reduction of the surface tension of the melt, increase in the volumetric shrinkage and reduction in interdendritic feeding as the possible causes of an increase in the porosity content of the AI castings modified with strontium. The change in the composition of the oxide layers of double oxide film defects was suggested to be responsible for this behaviour.     

Mechanical properties and drug release rate of poly(vinyl alcohol)/poly(ethylene glycol)/clay nanocomposite hydrogels: Correlation with structure and physical properties

Poly(vinyl alcohol)/poly(ethylene glycol) hydrogels containing curcumin as a drug and the various amounts of a montmorillonite nanoclay are prepared using the freezing–thawing method. Nanoclay quantity influence on the physicomechanical properties and the drug release rate of the hydrogel as well as relationship between them is investigated. X-Ray diffraction and Atomic force microscopy analysis reveal the nanoclays have an intercalation structure in the hydrogel, and the hydrogel crystallization decreases with increasing the nanoclay inclusion. From the SEM micrographs observation, it was revealed that due to the presence of the nanoclay in the hydrogel, its porosity decreased. The naonoclay has an amount-depended dual effect on the hydrogel swelling. The swelling mechanism is a normal Fickian diffusion for all the hydrogel samples. Strong physical interactions between the nanoclays and the polymer chains in the nanocomposite hydrogels are evidenced by the rheological studies. These interactions lead to significant reinforcement of the hydrogel tensile strength, intensified by the nanoclay amount. Interestingly, the nanoclays show the capability of accelerating and, also, decelerating the drug release of the hydrogel. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47843.     

A cross coupled low phase noise oscillator using an output swing enhancement technique

A new voltage controlled oscillator (VCO) in a 0.18 μm CMOS process is offered in this paper. This paper?s argument is to provide an innovative approach to improve the phase noise which is one of the most controversial issues in VCOs. Contrary to most ideas that have been put forward to decrease phase noise which are based on higher current dissipation to increase output voltage swing, this new method offers better specifications with respect to traditional solutions. The presented circuit is capable of extra oscillation amplitude without increasing the current level, taking advantages of tail current elimination and topology optimization. Analysis of the presented peak voltage amplitude can verify the optimum performance of the proposed. Post-layout simulation results at 2.3 GHz with an offset frequency of 1 MHz and 3 MHz show a phase noise of about −125 dBc/Hz and −136.5 dBc/Hz, respectively, with the current of 1.3 mA from 1.8 V supply. Also, Monte Carlo simulation is used to ensure the sensitivity of the proposed circuit to process and frequency variations are very promising.     

Low power FGMOS-based four-quadrant current multiplier circuits

In this paper, low-power, high-speed four-quadrant analog multiplier circuits have been presented, based on simple current squarer circuits. The squarer circuits consist of a floating-gate MOS transistor, operating in saturation region plus a resistor. These multipliers have a unique property of greatly reduced power as they do not have any bias currents. For performance evaluation, the designs are simulated using HSPICE software in 0.18 µm (level-49 parameters) TSMC CMOS technology. Using ± 0.5 V DC supply voltages for the first design, the simulation resulted in a maximum linearity error of 0.8%, the ? 3 dB bandwidth of 635 MHz, the Total Harmonic Distortion of 0.57% (at 1 MHz), and maximum and static power consumption of 40.4 and 5.75 µW, respectively. Corresponding values for the second design with 1 V DC supply voltage are 0.4%, 394.8 MHz, 0.72%, 44 and 11.4 µW, respectively. Furthermore, in order to verify the robustness and reliability of the proposed works, Monte Carlo analysis are performed. For the mentioned analysis, 5% variations in channel width and length, gate oxide thickness and threshold voltage of all transistors and resistance values are considered.     

Role of Double Oxide Film Defects in the Formation of Gas Porosity in Commercial Purity and Sr-containing Al Alloys

The role of double oxide film(bifilm) defects in the formation of gas porosity in commercial purity and Srcontaining Al alloys was investigated by means of a reduced pressure test(RPT) technique.The liquid metal was poured from a height into a crucible to introduce oxide defects into the melt.The melt was then subjected to different "hydrogen addition" and "holding in liquid state" regimes before RPT samples were taken.The RPT samples were then characterized by determining their porosity parameters and examining the internal surfaces of the pores formed in them by scanning electron microscopy.The results indicated oxide defects as the initiation sites for the growth of gas porosity,both in commercial purity and Sr-containing Al alloys.The results also rejected reduction of the surface tension of the melt,increase in the volumetric shrinkage and reduction in interdendritic feeding as the possible causes of an increase in the porosity content of the Al castings modified with strontium.The change in the composition of the oxide layers of double oxide film defects was suggested to be responsible for this behaviour.     

The Application of Nanofluids for Enhanced Oil Recovery: Effects on Interfacial Tension and Coreflooding Process

Most oil reservoirs around the world are experiencing their second half of life. Hence, the necessity of appropriate enhanced oil recovery (EOR) method as a more efficient technology gets further importance. Nanotechnology is an advanced technology that has proved its potential to enhance oil recovery. In this study, some selected types of nanoparticles were used, which were aluminum oxide, iron oxide, and silicon oxide treated by silane, as EOR agents during different flooding scenarios and EOR experiments under surface conditions. For the first time, the application of propanol as a dispersing agent of nanoparticles and EOR agent in the formation was investigated by this research work. In order to examine the recovery mechanisms of nanofluids, interfacial tension (IFT), and contact angle measurements between different concentrations of nanofluids and crude oil were measured. Then, several coreflood experiments were conducted to investigate their impacts directly on recoveries. The experiment results show that the nanofluids can decrease the IFT between water and oil phases and make the solid surface more neutral wet. Results indicate that aluminum oxide and silicon oxide treated by silane are good agents for enhanced oil recovery, while silicon one changes rock wettability more in addition to reduction of interfacial tension between oil and water. According to the results the future expectation is that these nanoparticles with their dispersing agent could mobilize more oil in the pore network at field scale to improve oil recovery.