Transient and steady state analysis of micro ring resonator array based photodetector in optical communication wavelength (linear and nonlinear operation)

Array of micro ring resonators based optical photodetectors is introduced and evaluated in this paper to operate in optical communication windows for broad band situation. In this work, we introduced an array of resonators to engineer the transfer function of the detector for broad band operation as well as very sharp edges. The electron and photon transport in the proposed structure is modeled based on rate equation and then transient and steady state behavior are extracted. Finally nonlinear operation added to the model and its effect on spectral behavior as well as transient operation is investigated.     

Collocation method for the numerical solutions of Lane–Emden type equations using cubic Hermite spline functions

Three numerical techniques based on cubic Hermite spline functions are presented for the solution of Lane–Emden equation. Some properties of Hermite splines are presented and are utilized to reduce the solution of Lane–Emden equation to the solution of algebraic equations. Illustrative examples are included to demonstrate the validity and applicability of these techniques. Copyright © 2013 John Wiley & Sons, Ltd.     

Modules satisfying the weak Nakayama property

Let R$R$ be a commutative ring with identity. We will say that an R$R$-module M$M$ satisfies the weak Nakayama property, if IM=M$IM=M$, where I$I$ is an ideal of R$R$, implies that for any x∈M$x\in M$ there exists a∈I$a\in I$ such that (a−1)x=0$(a-1)x=0$. In this paper, we will study modules satisfying the weak Nakayama property. It is proved that if R$R$ is a local ring, then R$R$ is a Max ring if and only if J(R)$J\left(R\right)$, the Jacobson radical of R$R$, is T$T$-nilpotent if and only if every R$R$-module satisfies the weak Nakayama property.     

Electrochemical determination of homocysteine using carbon nanotubes modified paste electrode and isoprenaline as a mediator

Homocysteine (HCy) is an important amino acid containing thiol group and is known as a risk factor in relation to ischemic heart disease and stroke. In this study the electrochemical determination of homocysteine (HCy) has been described using isoprenaline hydrochloride (ISP) as a mediator on multiwall carbon nanotubes modified paste electrode (MWCNTPE). Electrochemical behavior of homocysteine was investigated by cyclic voltarrtmetry and chronoamperometry. The cyclic voltammograms showed that the electrocatalytic oxidation of homocysteine occurs in the presence of ISP on the surface of MWCNTPE at a potential about 640 mV. Also, results showed that the oxidatation peak current of HCy at the modified carbon nanotubes electrode was more than unmodified electrode. The diffusion coefficient and the kinetic parameters including electron transfer coefficient and rate constant of electrocatalytic reaction were determined using electrochemical approaches. Linear sweep voltammetry results showed that electrocatalytic oxidation peak current of HCy had linear dynamic range in the range of 5.0 to 800 μmol L^?1 with a detection limit of 3.3 μmol L^?1 in pH 3.5 (universal buffer).     

Flexible polyurethane nanocomposite foam: Synthesis and properties

Flexible polyurethane (PU) nanocomposite foams were synthesized using organically modified montmorillonite clay (Cloisite 30B). The dispersion of organoclay was considered both in the isocyanate and polyol matrixes. Silicate layers of organoclay can be exfoliated in PU matrix by use of two steps mixing process. The presence of clay increased the cell density and reduced the cell size compared to the conventional PU foam. Clay dispersion was investigated by X-ray diffraction (XRD). The morphology and properties of PU nanocomposite foams were also studied. Generally, mechanical properties by addition of clay were improved. Foams in which clay was firstly dispersed in the isocyanate, showed better dispersion due to affinity of OH group on the clay surface to react with NCO groups. Better properties have been achieved with these nanofoams.     

Development of carbon‐nanotube‐assisted electromembrane extraction in the two‐phase mode combined with GC for the determination of basic drugs

In this work, carbon‐nanotube‐assisted electromembrane extraction in the two‐phase mode combined with GC was developed for the preconcentration and determination of basic drugs in body fluids. The multiwalled carbon nanotubes dispersed in organic solvent are held in the pores of the porous fiber wall by capillary forces and sonification. The membrane with immobilized carbon nanotubes acts as a sorbent and provides an additional pathway for analyte transport. This study demonstrates that the immobilization of carbon nanotubes in the supported liquid membrane is an excellent approach to enhance the performance of the extraction. Optimization of the variables affecting this method was carried out in order to achieve the best extraction efficiency. Optimal extractions were accomplished with octanol as the extraction solvent, 50 V as the driving force and pH 7.4 in the sample solution with the whole assembly agitated at 1000 rpm for 20 min. Under the optimized extraction conditions, the proposed technique provided good linearity (R² > 0.9990), repeatability (3.5–3.8%), low LODs (1.5 ng/mL), good preconcentration factors (292–316) and high recoveries (80–87%). Finally, this method was successfully used for the determination of tramadol and methadone in different body fluids including plasma and urine samples.     

Determination of residual monomers in latex by headspace hollow fiber protected liquid-phase microextraction combined with high-performance liquid chromatography

A simple and efficient method based on hollow fiber protected headspace liquid-phase in conjunction with high performance liquid chromatography has been introduced for extraction and determination of three residual monomers (2-ethylhexyl acrylate (EHA), vinyl acetate (VA), glycidyl methacrylate (GM)) in polymer latex. Using this methodology, the analytes of interest extracted from a sample are led into organic solvent located inside the porous hollow fiber membrane. Initially, several experimental parameters were controlled and optimized and the optimum conditions were reached with 8 cm neatly cut hollow fibers containing heptanol, which were exposed to the headspace of a 12 mL sample solution containing 20% (w/v) NaCl thermostated at 110 °C and stirred at 800 rpm for 20 min. Finally, 20 μL of the extraction solution was withdrawn into a syringe and injected into HPLC for analysis. The calibration curves were linear (r² ≥ 0.994) over the concentration range of 0.05-10 mg L⁻¹ for VA and 0.02-10 mg L⁻¹ for other analytes. The relative standard deviation (RSD%) for three-replicate extractions and measurements was below 8.6%. The limits of detection of this method for quantitative determination of the analytes were found within the range of 0.005 to 0.011 mg kg⁻¹ with the enrichment factors within the 5-164 range. The method was successfully applied for determination of residual monomers in polymer latex.     

Spin polarization and magnetoresistance through a ferromagnetic barrier in bilayer graphene

We study spin dependent transport through a magnetic bilayer graphene nanojunction configured as a two-dimensional normal/ferromagnetic/normal structure where the gate voltage is applied on the layers of ferromagnetic graphene. Based on the four-band Hamiltonian, conductance is calculated by using the Landauer-Buttiker formula at zero temperature. For a parallel configuration of the ferromagnetic layers of bilayer graphene, the energy band structure is metallic and spin polarization reaches its maximum value close to the resonant states, while for an antiparallel configuration the nanojunction behaves as a semiconductor and there is no spin filtering. As a result, a huge magnetoresistance is achievable by altering the configurations of ferromagnetic graphene around the band gap.