Modeling of CO2-brine interfacial tension: Application to enhanced oil recovery

Development of reliable and accurate models to estimate carbon dioxide–brine interfacial tension (IFT) is necessary, since its experimental measurement is time-consuming and requires expensive experimental apparatus as well as complicated interpretation procedure. In the current study, feed forward artificial neural network is used for estimation of CO₂–brine IFT based on data from published literature which consists of a number of carbon dioxide–brine interfacial tension data covering broad ranges of temperature, total salinity, mole fractions of impure components and pressure. Trial-and-error method is utilized to optimize the artificial neural network topology in order to enhance its capability of generalization. The results showed that there is good agreement between experimental values and modeling results. Comparison of the empirical correlations with the proposed model suggests that the current model can predict the CO₂–brine IFT more accurately and robustly.     

3D FEM analysis,dynamic modeling,and performance assessment of transverse flux PMSG for small‐scale gearless wind energy conversion systems

The transverse flux permanent magnet synchronous generator has a great potential for use in direct‐drive wind energy conversion systems due to its large pole numbers, high torque, and power density. This research work develops dynamic model of a single‐side transverse flux permanent magnet synchronous generator for use in a small‐scale gearless wind energy conversion system. For acquiring the parameters of the considered generator, required for dynamic modeling, 3D finite element model of the machine is developed and analyzed in both magneto‐static and transient modes. Field‐oriented control approach is employed for tracking maximum power point from the variable wind speed. The simulation results illustrate an accurate response of the system to the wind speed variation and proper performance of the developed dynamic model and control approach of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanical, rheological, and thermal behavior assessments in HDPE/PA-6/EVOH ternary blends with variable morphology

Visco-elastic and dielectric spectra of multiwalled carbon-nanotube reinforced silicon elastomer nanocomposites were used to study relaxation behavior. SEM photomicrographs shows well dispersion of MWCNT in elastomer matrix. In visco-elastic analysis primary relaxation was studied as a function of temperature (?100 to 100 °C) at frequency 1Hz and strain 1 %. The effect of MWCNT loadings on storage modulus, loss modulus, and loss tangent has been studied. The non-linearity in loss tangent, storage modulus and loss modulus was explained on the basis of MWCNT-elastomer interaction and the inter-aggregate attraction of MWCNT. The secondary β relaxation was studied using dielectric relaxation spectra in the frequency range of 0.1 Hz to 10⁶ Hz. The effect of MWCNT loadings on the complex and real parts of impedance was distinctly visible which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The dielectric formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The ‘percolation limit’ of the MWCNT in the silicon elastomer was found to be in the range of 4 phr loading.     

Preparation of porous PLLA/PCL blend by a combination of PEO phase and NaCl particulate leaching in PLLA/PCL/PEO/NaCl blend

In this study, the ternary blends containing microporosity based on poly(l-lactic acid) (PLLA), poly(ε-caprolactone) (PCL) and polyethylene oxide (PEO) were prepared using an internal mixer via a polymer leaching technique. The particulate leaching is the most widely used technique to create porosity. To introduce macroporosity besides micropores, NaCl particulates were incorporated into the ternary blends at 40–80 wt % and macropores were formed by particulate leaching. Samples porosity were evaluated by calculating the ratio of porous scaffold density (ρ*) to the non-porous material density (ρ _s). The results showed that with an increase in NaCl particulate content, the amount of porosity increased and the distribution of pore size was gradually transformed from monomodal into bimodal form. The porosity plays a key role in governing the compression properties. Mechanical properties are presented by Gibson–Ashby model. Compressive modulus decreased with an increase in NaCl particulate concentration due to the increase in porosity and thinning of pore wall that caused rupture at these weaker spots. Blending and forming of the bio-scaffold can be made using conventional polymer processing equipment. This process seems promising for a large-scale production of porous bio-scaffold of many sizes through an economic method.     

Synthesis of imidazo[2,1-b]thiazoles through the reaction of thiohydantoins and α-bromoketones

Imidazo-fused heterocycles are used as anticancer agents. In this study, some novel imidazo[2,1-b]thiazoles were synthesized from thiohydantoins and α-bromoketones in good yields. This method has the advantages of simple operation, high yields, and mild reaction conditions and uses less toxic and low-cost chemical reagents.     

A time-domain noise-coupling technique for continuous-time sigma-delta modulators

In this paper, a time-domain noise-coupling technique based on the pulse width modulation is proposed. The time-domain quantization error is digitally extracted and shaped by an asynchronous digital filter. This digitally filtered quantization error is applied to the quantizer input to increase the modulator’s noise-shaping order. By using this technique in continuous-time sigma-delta modulators, the modulator’s shaping property is significantly enhanced. Comparative analytical calculations and simulation results are presented to estimate the performance of modulators employing the proposed quantizer. System-level simulation results reveal a (L + 2)th order noise-shaping capability of the proposed modulator while it employs only L analog integrators. The effects of main circuit non-idealities in the modulator’s performance are analytically investigated and confirmed by the simulation results.     

Design of CMOS three-stage amplifiers for fast-settling switched-capacitor circuits

In this paper, a time-domain design procedure for fast-settling three-stage amplifiers is presented. In the proposed design approach, the amplifier is designed to settle within a specific time with a given settling accuracy and circuit noise budget by optimizing both the power consumption and silicon die area. Both linear and nonlinear settling regions of three-stage amplifiers are considered and optimal values of the amplifier stages transconductance and compensation capacitors are obtained using the genetic algorithm optimization. Detailed design equations are provided and circuit level simulation results using a 90 nm CMOS technology are presented to evaluate the usefulness of the proposed design scheme respected to the previously reported design approaches.     

Energy Detector in Ultra Wideband Systems Using Phase Compensation Technique

Energy detectors have the advantage of simple structure and inexpensive price. Due to the low signal to noise ratio (SNR) of the received signal in ultra-wideBand (UWB) system, these desirable advantages can be achieved at the expense of non-trivial performance degradation. This paper presents a phase compensation (PC) technique to improve the performance of energy detector in UWB systems. In PC-UWB, the frequency dependent phase of the system response at the transmitter is extracted and its opposite spectral phase is used as prefilter. Because of Low complexity, cost and energy consumption of energy detectors, PC techniques has extensive potential for future of UWB communication systems. Measurement results show that the use of PC-UWB leads to signal power concentration at the receiver, which reduces the number of RAKE fingers required in coherent detection as well as achieves a higher data rate with less intersymbol interference. However time reversal UWB can achieve secure data transmission, but its performance is worse than PC-UWB. Simulation results show that phase compensation reduces the inter symbol interference impacts. Therefore it is possible to use a simple receiver with insignificant performance degradation. It is also shown that PC-UWB considerably outperforms TR-UWB and has satisfying performance in SNR greater than 13 dB.     

Low-Power Symmetrical Rectifier for Passive UHF RFID Transponder

Rectifier design is one of the challenging issues in passive radio-frequency identification (RFID) systems. Differential structures are good candidates as rectifiers to their high conversion efficiencies. In this paper, a novel structure is proposed to produce symmetrical power-supply utilizing differential circuit configuration simulated in 130nm CMOS technology. The proposed rectifier can provide 1.34 V DC power with 382% voltage conversion efficiency, thus demonstrated its higher performance over existing designs.     

A Novel Evolutionary-Based Cooperative Spectrum Sensing Mechanism for Cognitive Radio Networks

Cognitive radio (CR) is considered as a feasible intelligent technology for 4G wireless networks or self-organization networks and envisioned as a promising paradigm of exploiting intelligence for enhancing efficiency of underutilized spectrum bands. In CR, one of the main concerns is to reliably sense the presence of primary users, to attain protection against harmful interference caused by the potential spectrum access of secondary users (SUs). In this paper, evolutionary algorithms, namely, genetic algorithm (GA) and particle swarm optimization (PSO) are investigated. An imperialistic competitive algorithm (ICA) is proposed to minimize error detection at the common soft data fusion (SDF) center for structurally centralized cognitive radio network (CRN). By using these techniques, evolutionary operations are invoked to optimize the weighting coefficients applied on the sensing measurement components received from multiple cooperative SUs. The proposed method is compared with other evolutionary algorithms, as well as other conventional deterministic, such as maximal ratio combining- (MRC-), modified deflection coefficient- (MDC-), normal deflection coefficient- (NDC-) based SDF schemes and OR-rule HDF based. MATLAB simulations confirm the superiority of the ICA-based scheme over the PSO-, GA-based and other conventional schemes in terms of detection performance. In addition, the ICA-based scheme also shows promising convergence and time running performance as compared to other iterative-based schemes. This makes ICA an adequate solution to meet real-time requirements.