Tube cyclic expansion-extrusion (TCEE) as a novel severe plastic deformation method for cylindrical tubes

Tube cyclic expansion-extrusion (TCEE) is proposed as a novel severe plastic deformation method for processing cylindrical tubes. TCEE is capable of imposing large strains to cylindrical tubes without dimensional and geometrical changes. In TCEE process, peripheral small shallow grooves were devised on mandrel and inner surface of the chamber. The grooves allow tubular specimen to initially expand and then extrude to the initial thickness while it is deformed between mandrel and chamber. TCEE was first trialed on commercial AZ91 magnesium alloy and substantial grain refinement was recorded. Mean grain size of 1 μm was achieved after two cycles of TCEE. Microhardness assessment across tube thickness demonstrates good homogeneity of hardness distribution; microhardness of the initial tube increased from 65 to 90 Hv after two processing cycles of TCEE. After two processing cycles of TCEE, yield and ultimate strengths were increased by 2.9 and 2.6 times compared to those in as-cast condition. The elongation to failure was also increased from initial value of 1.6 % to about 8.1 %. The process was also numerically simulated by commercial FE code of ABAQUS/explicit to further investigate strain accumulation in TCEE process.     

Using a genetic algorithm for parameter identification of transformer R-L-C-M model

The R-L-C-M model of power transformer is obtained from geometrical structure and is extremely appropriate for studying transient phenomena in a transformer and detecting mechanical faults. The precision of this model depends strongly on the precision of its parameters. The accuracy of these parameters that are calculated by analytical formulas is limited due to different reasons. In this paper a genetic algorithm (GA) is introduced as a method to identify the parameters of R-L-C-M Model without employing any analytical formulas.     

Optimal placing and sizing of parking lots including different levels of charging stations in electric distribution networks

Background: Low emission, high efficiency, and convenience of using plug-in electric vehicles (PEVs) are considered as significant benefits of PEVs. However, installation of parking lots (PLs) in order to supply PEVs causes some financial and technical challenges for electric distribution networks. The changes in system reliability, power loss, voltage drop, and costs associated with the installation of PLs are considered as some of the aforementioned challenges. Therefore, optimal placing and sizing of PEV PLs including different levels of charging stations ((CS); slow, medium, and fast) are presented in this paper. Since PLs have the potential to exchange electricity by electric network, they can be taken into account as distributed generations (DGs) and their installation can be considered from the perspective of installation of DGs. An objective function including system reliability, power loss, voltage drop, and PL cost/revenue is proposed for the optimal planning. Results: Genetic algorithm is employed to solve the optimisation problem. Simulation is carried out on a 33-bus radial distribution network. For the planning purposes of PLs, three different levels of CSs (slow, medium, and fast) in PLs are considered. The effect of increasing the penetration of PEVs in PLs is also examined on planning the PLs. The effect of different dispatch times on the selection of different CS levels (slow, medium, and fast) is investigated as well. Furthermore, the effect of applying tariffs and incentives for the customers is analysed for the selection of CS levels. Finally, the effect and importance of combinations of the CSs with different levels are investigated.     

Omega-3 Polyunsaturated Fatty Acids Concentration Using Synthesized Poly-Vinylidene Fluoride (PVDF) Asymmetric Membranes

In this study, the performance of synthesized poly‐vinylidene fluoride (PVDF) membranes to concentrate ω3‐polyunsaturated fatty acids from lantern fish oil was evaluated. The PVDF membranes were prepared via the phase inversion method. The effect of coagulation bath temperatures (CBT: 0, 25 and 50 °C) on the morphology of the membranes and the ω3‐PUFA concentration process was examined and discussed. Scanning electron microscopy images showed that an increasing coagulation bath temperature (CBT) leads to a more porous structure in the membranes as well as a larger pore diameter. ω3‐PUFA concentration was evaluated at different pressures and temperatures, ranging from 3 to 5 bar and 20 to 40 °C, respectively. The PVDF membrane prepared at a CBT of 0 °C (M1) resulted in the best ω3‐PUFA concentration (40.4 %) at a pressure and temperature of 5 bar and 30 °C, respectively. Conversely, the PVDF membrane formed at CBT of 50 °C (M3) showed the highest oil flux. In addition, fouling analysis indicates that complete pore blocking was the predominant mechanism for the M1 membrane and intermediate pore blocking for the M2 and M3 membranes.     

Investigating the effect of PGA on physical and mechanical properties of electrospun PCL/PGA blend nanofibers

In the field of tissue engineering there is always a need for new engineered polymeric biomaterials which have ideal properties and functional customization. Unfortunately the demands for many biomedical applications need a set of properties that no polymers can fulfill. One method to satisfy these demands and providing desirable new biomaterials is by mixing two or more polymers. In this work, random nanofibrous blends of poly (ε‐caprolactone) (PCL) and polyglycolic acid (PGA) with various PCL/PGA compositions (100/0, 80/20, 65/35, 50/50, and 0/100) were fabricated by electrospinning method and characterized for soft‐tissue engineering applications. Physical, chemical, thermal, and mechanical properties of PCL/PGA blend nanofibers were measured by scanning electron microscopy (SEM), porosimetry, contact angle measurement, water uptake, attenuated total reflectance Fourier transform‐infrared spectroscopy (ATR‐FT‐IR), X‐ray diffraction (XRD), differential scanning calorimetric (DSC), dynamic mechanical thermal analysis (DMTA), and tensile measurements. Morphological characterization showed that the addition of PGA to PCL results in an increase in the average diameter of the nanofibers. According to these results, when the amount of PGA in the blend solution increased, the hydrophilicity and water uptake of the nanofibrous scaffolds increased concurrently, approaching those of PGA nanofibers. Differential scanning calorimetric studies showed that the PCL and PGA were miscible in the nanofibrous structure and the mechanical characterization under dry conditions showed that increasing PGA content results in a tremendous increase in the mechanical properties. In conclusion, the random nanofibrous PCL/PGA scaffold used in this study constitutes a promising material for soft‐tissue engineering. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An offset cancellation technique for comparators using body-voltage trimming

A novel offset cancellation technique based on body-voltage trimming is presented to be used in the comparators employed in high-speed analog-to-digital converters (ADCs) such as Flash ADCs. The proposed offset cancellation is achieved by body-voltage adjustment using a low-power simple analog control feedback circuit without any additional capacitive loading at the comparator output or complicated digital calibration scheme. The accuracy of the proposed technique is higher than its digital calibration counterparts due to its analog nature. Simulation results in a 1.8?V 0.18???m CMOS technology show that using the proposed technique the standard deviation of the comparator offset is significantly reduced from 36.2 to 7.1?mV operating at 1?GHz with only 32???W of power dissipation in the offset cancellation circuit.     

A dynamic joint scheduling and call admission control scheme for IEEE 802.16 networks

We propose a dynamic joint scheduling and call admission control (CAC) scheme for service classes defined in IEEE 802.16 standard. Using priority functions, equipped with service weights and service arrival rates, the proposed scheduling scheme differentiates service classes from each other. Based on obtained priority values, we first allocate the achievable bandwidth proportionally. Within individual service classes, we then use appropriate local schedulers to transmit packets accordingly. Moreover, instead of immediate admitting or blocking a new connection request, the proposed CAC scheme computes the average transmission rate that can be allocated to that connection during a time interval. The connection is admitted if its required rate is satisfied while at the same time QoS requirements of ongoing connections are not violated. Our numerical results demonstrate the effectiveness of the proposed schemes compared to the other schemes in the literature.     

Influence of Alumina Particles on Thermal Behavior of High Density Polyethylene (HDPE)

This study evaluated the effects of alumina (Al₂O₃) particles on thermal properties of High Density Polyethylene (HDPE). HDPE and HDPE/5, 10 & 15 wt% Al₂O₃ composites were prepared by compression molding. Differential scanning calorimetery (DSC) was used to analyze the thermal and crystallization behavior of the samples. The results indicated that the alumina particles affected the crystallization behavior of HDPE matrix, significantly. However, the DSC results showed that alumina content did not influence the melting temperature of HDPE in this composite. The results also showed that the incorporation of alumina particles caused the decrease of specific heat capacity coefficient and entropy.     

STUDIES OF IRANIAN HEAVY OILS PERTINENT TO RESERVOIR CONDITIONS FOR THEIR AUTO-IGNITION TO INITIATE FIRE FLOODING

In this work, the potential for the auto-ignition of Iranian heavy oil during in situ combustion (ISC) process conditions was studied. Kinetic studies were carried out using thermal analysis techniques. Effects of oxygen partial pressure, reservoir pressure, and clay on the auto-ignition condition were investigated. Based on the experimental results obtained, a kinetic equation was derived for each of the different oil samples in the presence of different sands. The effect of partial pressure of oxygen in the injected air showed that at atmospheric pressure, low temperature combustion (LTC) was initiated at 275°C. Also, enriching the injected air by oxygen lowers the initial LTC temperature by up to 50°C. ARC experiments were undertaken to extend the studies to reservoir pressure conditions (1300 psi). It was found that activation energy in the LTC region was lowered as a consequence. As a result, initiation of LTC commenced at 115°C when air was injected. The effect of clay as a catalyst was also studied, and it was found that the activation energy decreases considerably when clay is present in the system. Experiments in a high-pressure combustion tube showed that LTC was initiated in the temperature range 120°–150°C, which is in line with the results obtained in the ARC. Fire flooding was sustained during the combustion tube test.     

Activated carbon nanofibers as an alternative cathode catalyst to platinum in a two-chamber microbial fuel cell

This paper evaluated the oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) system by using chemically and physically activated electrospun carbon nanofibers (ACNFs) in an MFC and comparing their performance with that of plain carbon paper. The chemical and physical activation was carried out by KOH reagents and CO₂ gas to increase the electrode surface area and the catalytic activity. As a result, it was found that the MFC with the chemically activated carbon nanofibers (ACNFs) exhibited better catalytic activity than that of the physically activated ACNFs. Chemically ACNFs with 8 M KOH were found to be one of the most promising candidates for the ORR and could generate up to 3.17 times more power than that of the carbon paper. The ACNFs with 8 M KOH exhibited 78% more power generation than that of the physically activated ACNFs and exhibited 16% more power generation than the chemically activated ACNFs with 4 M KOH. The power per cost of ACNFs with 8 M KOH is 2.65 times greater than that of the traditionally used platinum cathode. Thus, ACNFs are a good alternative catalyst to Pt for MFCs.