Application of graphene oxide nanosheets as probe oligonucleotide immobilization platform for DNA sensing

In this work, a simple and novel electrochemical biosensor based on a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) was developed for detection of DNA sequences. The morphology of prepared nanoplatform was investigated by scanning electron microscopy, infrared (FTIR) and UV/Vis absorption spectra. The fabrication processes of electrochemical biosensor were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in an aqueous solution. The optimization of experimental conditions such as immobilization of the probe BRCA1 and its hybridization with the complementary DNA was performed. Due to unique properties of graphene oxide nanosheets such as large surface area and high conductivity, a wide liner range of 1.0 × 10^?17–1.0 × 10^?9 M and detection limit of 3.3 × 10^?18 M were obtained for detection of BRCA1 5382 mutation by EIS technique. Under the optimum conditions, the proposed biosensor (ssDNA/GO/GCE) revealed suitable selectivity for discriminating the complementary sequences from non-complementary sequences, so it can be applicable for detection of breast cancer.     

Determination of zinc in water samples by flame atomic absorption spectrometry after homogeneous liquid-liquid extraction

In this study, a new and simple homogeneous liquid-liquid extraction (HLLE) method based on a pH-independent phase-separation process was developed using a ternary solvent system [water-tetrabutylammonium ion (TBA ⁺)-chloroform] for the preconcentration of Zn²⁺ ions. A Schiff’s base ligand was used as the chelating agent prior to Zn²⁺ ions extraction. Flame atomic absorption spectrophotometry using acetylene-air flame was used for the quantification of analyte after preconcentration. The phase separation occurred due to ion-pair formation of TBA and perchlorate ion. The sedimented phase was then separated using a 100 μL micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH 9.0, [ligand] = 1.0 × 10⁻⁵ M, [TBA⁺] = 2.0 × 10⁻² M, 100.0 μL of [CHCl₃] and [CLO₄⁻] = 2.0 × 10⁻² M, a preconcentration factor of 100 was achieved for only 10 mL of the sample. The relative standard deviation was 2.3% (n = 10). The limit of detection was sufficiently low and at ppb level. The proposed method was applied to the extraction and determination of Zn²⁺ in natural water samples with satisfactory results.     

An efficient synthesis of dithiocarbamates under ultrasound irradiation in water

Abstract  

Multicomponent reactions with ultrasonic activation have been used as a simple, rapid, atom economic, and green method for the synthesis of dithiocarbamate derivatives in water. The one-pot, three-component condensation of primary and secondary amines with carbon disulfide and unsaturated carbonyl compounds or alkyl halides under ultrasonic irradiation was developed as a green and fast protocol for the rapid high-yielding preparation of dithiocarbamates in water.     

Perturbation Analysis of the Local Thermal Non-equilibrium Condition in a Fluid-Saturated Porous Medium Bounded by an Iso-thermal Channel

This study focuses analytically on the local thermal non-equilibrium (LTNE) effects in the developed region of forced convection in a saturated porous medium bounded by isothermal parallel-plates. The flow in the channel is described by the Brinkman–Forchheimer-extended Darcy equation and the LTNE effects are accounted by utilizing the two-equation model. Profiles describing the velocity field obtained by perturbation techniques are used to find the temperature distributions by the successive approximation method. A fundamental relation for the temperature difference between the fluid and solid phases (the LTNE intensity) is established based on a perturbation analysis. It is found that the LTNE intensity ( $\Delta \textit{NE}$ ) is proportional to the product of the normalized velocity and the dimensionless temperature at LTE condition. Also, it depends on the conductivity ratio, Da number, and the porosity of the medium. The intensity of LTNE condition ( $\Delta \textit{NE}$ ) is maximum at the middle of the channel and decreases smoothly to zero by moving to the wall. Finally, the established relation for the intensity of LTNE condition is simple and fundamental for estimating the importance of LTNE condition and validation of numerical simulation results.     

Four techniques based on the B‐spline expansion and the collocation approach for the numerical solution of the Lane–Emden equation

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

A Legendre spectral element method on a large spatial domain to solve the predator–prey system modeling interacting populations

A Legendre spectral element method is developed for solving a one-dimensional predator–prey system on a large spatial domain. The predator–prey system is numerically solved where the prey population growth is described by a cubic polynomial and the predator’s functional response is Holling type I. The discretization error generated from this method is compared with the error obtained from the Legendre pseudospectral and finite element methods. The Legendre spectral element method is also presented where the predator response is Holling type II and the initial data are discontinuous.     

A spectral element method for solving the Pennes bioheat transfer equation by using triangular and quadrilateral elements

A spectral element method is developed for the numerical solution of the Pennes bioheat transfer equation which models the thermal behavior of the living tissue. For the one and two dimensional cases, the implementation of this method is completely explained. In the two dimensional case, both triangular and quadrilateral elements are investigated. Through test problems, the discretization error generated from this method is reported. In the triangular elements, the error is obtained when quadrature points coincide and do not coincide with nodal points. This method is employed to solve the equation in order to obtain the temperature of the skin layers, healthy tissue, and tissue that contains the tumor.     

Determination of a control function in three‐dimensional parabolic equations by Legendre pseudospectral method

A Legendre pseudospectral method is proposed for solving approximately an inverse problem of determining an unknown control parameter p(t) which is the coefficient of the solution u(x, y, z, t) in a diffusion equation in a three‐dimensional region. The diffusion equation is to be solved subject to suitably prescribed initial‐boundary conditions. The presence of the unknown coefficient p(t) requires an extra condition. This extra condition considered as the integral overspecification over the spacial domain. For discretizing the problem, after homogenization of the boundary conditions, we apply the Legendre pseudospectral method in a matrix based manner. As a results a system of nonlinear differential algebraic equations is generated. Then by using suitable transformation, the problem will be converted to a homogeneous time varying system of linear ordinary differential equations. Also a pseudospectral method for efficient solving of the resulted system of ordinary differential equations is proposed. The solution of this system gives the approximation to values of u and p. The matrix based structure of the present method makes it easy to implement. Numerical experiments are presented to demonstrate the accuracy and the efficiency of the proposed computational procedure. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 28: 74‐93, 2012     

The general Jacobi matrix method for solving some nonlinear ordinary differential equations

In this paper, we obtain the approximate solutions for some nonlinear ordinary differential equations by using the general Jacobi matrix method. Explicit formulae which express the Jacobi expansion coefficients for the powers of derivatives and moments of any differentiable function in terms of the original expansion coefficients of the function itself are given in the matrix form. Three test problems are discussed to illustrate the efficiency of the proposed method.     

Numerical solution of Fokker‐Planck equation using the cubic B‐spline scaling functions

In this article a numerical technique is presented for the solution of Fokker‐Planck equation. This method uses the cubic B‐spline scaling functions. The method consists of expanding the required approximate solution as the elements of cubic B‐spline scaling function. Using the operational matrix of derivative, the problem will be reduced to a set of algebraic equations. Some numerical examples are included to demonstrate the validity and applicability of the technique. The method is easy to implement and produces very accurate results. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009