Application of photonic crystal ring resonator nonlinear response for full-optical tunable add–drop filtering

In this paper, we investigate the application of Kerr-like nonlinear photonic crystal (PhC) ring resonator (PCRR) for realizing a tunable full-optical add–drop filter. We used silicon (Si) nano-crystal as the nonlinear material in pillar-based square lattice of a 2DPhC. The nonlinear section of PCRR is studied under three different scenarios: (1) first only the inner rods of PCRR are made of nonlinear materials, (2) only outer rods of PCRR have nonlinear response, and (3) both of inner and outer rods are made of nonlinear material. The simulation results indicate that optical power required to switch the state of PCRR from turn-on to turn-off, for the nonlinearity applied to inner PCRR, is at least \(2000\, \hbox {mW}{/}\upmu \hbox {m}^{2}\) and, for the nonlinearity applied to outer PCRR, is at least \(3000\, \hbox {mW}{/}\upmu \hbox {m}^{2}\) which corresponds to refractive index change of \(\Delta n_\mathrm{NL }= 0.085\) and \(\Delta n_\mathrm{NL }= 0.15\), respectively. For nonlinear tuning of add–drop filter, the minimum power required to 1 nm redshift the center operating wavelength \((\lambda _{0} = 1550\, \hbox {nm})\) for the inner PCRR scenario is \(125\, \hbox {mW}{/}\upmu \hbox {m}^{2}\) (refractive index change of \(\Delta n_\mathrm{NL}= 0.005)\). Maximum allowed refractive index change for inner and outer scenarios before switch goes to saturation is \(\Delta n_\mathrm{NL }= 0.04\) (maximum tune-ability 8 nm) and \(\Delta n_\mathrm{NL }= 0.012\) (maximum tune-ability of 24 nm), respectively. Performance of add–drop filter is replicated by means of finite-difference time-domain method, and simulations displayed an ultra-compact size device with ultra-fast tune-ability speed.     

Evaluation of wax disappearance temperatures in hydrocarbon fluids using soft computing approaches

In this study, modeling wax disappearance temperatures (WDTs) in hydrocarbon fluids is presented using three different soft computing approaches, namely feed forward artificial neural network; multilayer perceptron (MLP), least squares support vector machines (LSSVM), and decision tree (DT). Results indicate that the models presented in this study provide acceptable results. Furthermore, a comparative study demonstrates the superiority of decision tree model in terms of accuracy compared to the other models investigated in this study.     

Application of reaction equilibrium thermodynamic model for correlation of H2S solubility in ionic liquids [emim][Ace] and [hmim][Ace] using CPA equation of state

Correlation of H₂S solubility in ionic liquids [emim][Ace] and [hmim][Ace] was performed using CPA EoS. For taking into account the effect of possible chemical reactions, the Reaction Equilibrium Thermodynamic Model (RETM) was used. This model assumes that an AB₂ type reaction mechanism between two IL molecules and one H₂S molecule is taken place. Both of H₂S and ILs was considered as association components following 4C and 2B association schemes, respectively. First, pure components parameters achieved using CPA EoS. Consequently, the binary systems were investigated applying RETM. The results show AAD% equal to 4.75 and 12.44 for [emim][Ace] and [hmim][Ace] respectively.     

The effect of a TEG additive on hydrate formation

In gas industry, gas hydrate formation has both advantages and disadvantages. The best advantage of gas hydrate is Persian Gulf water sweetening, carbon dioxide capture, and gas storage, and its drawbacks are pressure drop, plugging, and explosion in pipelines. In recent years, using the inhibitors to prevent hydrate formation is being considered among researchers. In this study, the new equilibrium data for hydrate formation of inlet natural gas to Gachsaran NGL-1200 refinery with addition of Tri ethylene glycol (TEG) with mass concentration of 5% and 15% in distilled and Persian Gulf waters were measured by constant-volume method. The experimental results show that the hydrate formation conditions will be hard with the increase of TEG concentration in distillated and Persian Gulf waters. In other words, TEG addition to Persian Gulf water had more inhibitory effect in hydrate formation than TEG addition to distilled water. The hydrate formation temperature, in pressure range of 28–29 bars, reduced 0.3°C and 2.7°C for distilled water and 2.8°C and 4.6°C for Persian Gulf water in presence of TEG with mass concentration of 5% and 15%, respectively.     

Nanoscale Optoregulation of Neural Stem Cell Differentiation by Intracellular Alteration of Redox Balance

Regulation of stem cell (SC) fate, a decision between self‐renewal and differentiation, is of immense importance in regenerative medicine and has been proven to be a powerful stimulus regulating many cell functions influencing the SC fate. This study uses triphenylphosphonium‐functionalized gold nanoparticles (TPP‐AuNPs) to explore the interplay of intracellular electromagnetic (EM) exposure and the SC fate. Localized EM waves are generated inside neural stem cells (NSCs) to stimulate TPP‐AuNPs (AuNPs), targeting the mitochondria through inducing reactive oxygen species and differentiating these cells into neurons. Following laser irradiation of TPP‐AuNPs‐transfected NSCs, their differentiation to neurons is monitored by tracing the relevant markers both at the genetic and protein levels. The electrophysiology technique is further used to examine the functionality of neurons. The results confirm that TPP‐AuNPs subjected to electromotive forces have the potential to regulate cellular fate, although further investigations are still required to shed light on the mechanisms underlying the interaction of EM‐stimulated TPP‐AuNPs on cellular fate to design highly adjustable cell differentiation and reprogramming methods.     

Systematic Approach for Design of Broadband,High Efficiency,High Power RF Amplifiers

This paper demonstrates a systematic approach for the design of broadband, high efficiency, high power, Class‐AB RF amplifiers with high gain flatness. It is usually difficult to simultaneously achieve a high gain flatness and high efficiency in a broadband RF power amplifier, especially in a high power design. As a result, the use of a computer‐aided simulation is most often the best way to achieve these goals; however, an appropriate initial value and a systematic approach are necessary for the simulation results to rapidly converge. These objectives can be accomplished with a minimum of trial and error through the following techniques. First, signal gain variations are reduced over a wide bandwidth using a proper pre‐matching network. Then, the source and load impedances are satisfactorily obtained from small‐signal and load‐pull simulations, respectively. Finally, two high‐order Chebyshev low‐pass filters are employed to provide optimum input and output impedance matching networks over a bandwidth of 100 MHz–500 MHz. By using an EM simulation for the substrate, the simulation results were observed to be in close agreement with the measured results.     

Regulation of the Stem Cell–Host Immune System Interplay Using Hydrogel Coencapsulation System with an Anti‐Inflammatory Drug

The host immune system is known to influence mesenchymal stem cell (MSC)‐mediated bone tissue regeneration. However, the therapeutic capacity of hydrogel biomaterial to modulate the interplay between MSCs and T‐lymphocytes is unknown. Here it is shown that encapsulating hydrogel affects this interplay when used to encapsulate MSCs for implantation by hindering the penetration of pro‐inflammatory cells and/or cytokines, leading to improved viability of the encapsulated MSCs. This combats the effects of the host pro‐inflammatory T‐lymphocyte‐induced nuclear factor kappaB pathway, which can reduce MSC viability through the CASPASE‐3 and CASPASE‐8 associated proapoptotic cascade, resulting in the apoptosis of MSCs. To corroborate rescue of engrafted MSCs from the insult of the host immune system, the incorporation of the anti‐inflammatory drug indomethacin into the encapsulating alginate hydrogel further regulates the local microenvironment and prevents pro‐inflammatory cytokine‐induced apoptosis. These findings suggest that the encapsulating hydrogel can regulate the MSC‐host immune cell interplay and direct the fate of the implanted MSCs, leading to enhanced tissue regeneration.     

Mechanistic Analysis of Drug Release from Theophylline Pellets Coated by Films Containing Pectin,Chitosan and Eudragit® RS

The objective of this study was to obtain detailed information on the mechanism of drug release from mixed-film of pectin-chitosan/Eudragit® RS. Pellets (710–840 μm in diameter) containing 60% theophylline and 40% microcrystalline cellulose were prepared by extrusion-spheronization method. Eudragit® L100-55 enteric coating capsules included film-coated pellets of theophylline in theoretical coating weight gains of 10, 15, and 20%, with pectin-chitosan complex contents of 5, 10, 15, and 20% for each level of weight gain were prepared and subjected to in vitro drug release. Drug release from this system showed a bimodal release profile characteristic with the drug release enhancement, being triggered (burst release) in the colonic medium. The reason for burst drug release may be due to the enzymatic degradation of pectin via pectinolytic enzymes in the simulated colonic medium. The mechanism of drug release from each formulation was evaluated in the terms of zero-order, first-order, Higuchi and Korsmeyer-Peppas models. It was observed that none of the enteric coating capsules showed any drug release in the simulated gastric medium (phase I). The analysis of release profiles showed that zero-order kinetics was found as the better fitting model for all formulations in the simulated small intestine (phase II) and it could be due to the pectin-chitosan swelling and subsequent formation of aqueous channels. In the colonic medium (phase III), due to degradation of pectin and its leaching from the mixed-film, there was a modification in drug release kinetics from swelling-controlled at phase II to anomalous at phase III. It also was found that both zero-order and Higuchi models contributed in colonic drug release from most of the formulations.     

Variational approach development in analysis of matrix cracking and induced delamination of cross-ply composite laminates subjected to in-plane shear loading

Matrix microcracking and induced delamination propagating from the edge of microcracks in cross-ply composite laminates with [0_n/90_m]_s and [90_m/0_n]_s layups under in-plane static shear loading are investigated. An admissible stress field, which satisfies all of equilibrium equations, boundary conditions, and continuity of interfaces, is approximated. Then using the principle of the minimum complementary energy, the stress state is obtained from calculations of variation. The calculated stress state gives the stiffness reduction and the total strain energy of the laminated composite structure. Finally, the strain energy release rate of a general cross-ply laminate due to initiation and propagation of matrix cracking and induced delamination can be deduced. Results of the developed approach are in good agreement with experimental observations and finite element analyses, which confirms its accuracy.     

Fractional anisotropy‐weighted front evolution algorithm for white matter tractography based on diffusion tensor imaging data

Tractography is one of the most important applications of diffusion tensor imaging (DTI) which noninvasively reconstructs 3D trajectories of the white matter tracts. Because of the intravoxel orientation heterogeneity of DTI data, some of tractography algorithms are unable to follow the correct pathways after the crossing and branching regions. Front propagation techniques are efficient methods in tracking the crossing fibers. A key parameter influencing the performance of these algorithms is the cost function which is mainly based on the colinearity of tensors' eigenvectors. The effect of the eigenvalues on the anisotropy strength of tensor has not been previously addressed in the definition of the speed function. In this article, a new speed function, based on the effect of diffusion anisotropy and the colinearity of eigenvectors is proposed. The performance of the suggested method on fiber tracking and crossing fiber detection has been evaluated using synthetic datasets, and the feasibility of the proposed method was shown by fiber tracking implemented on real DTI data. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 307–314, 2011