Computational studies of the purine-functionalized graphene sheets

We performed a computational work to investigate the properties of functionalized graphene sheets (S) by adenine (A) and guanine (G) purine nucleobases. To achieve the purpose of this work, we examined the functionalization of armchair and zigzag tips of the S model by each of the A and G purines. The results indicated that the optimized properties for the investigated hybrid structures are different depending on the tip of functionalization and the used purine nucleobase. Moreover, the atomic level properties of the investigated structures were investigated by evaluating quadrupole coupling constants (C_Q) for the atoms of the optimized structures. The remarkable trend of the C_Q parameters is that the changes of atomic properties are many more significant for the functionalization of the zigzag-tip by the G nucleobase, which is in agreement with the results of the optimized properties.     

Modification of Tao–Mason equation of state to ionic liquids

In our previous paper, we extended the Tao and Mason equation of state (TM EOS) to refrigerant fluids, using the speed of sound data. Here, we predict the equation of state for ionic liquids (ILs). The considered ILs are [Bmim][PF₆], [C₂mim][NtF₂], [C₃mim][NtF₂], [C₆mim][NtF₂], [C₇mim][NtF₂], [C₂mim][EtOSO₃], [Bmim][MeSO₄], [Bmim][OcSO₄], and [C₄mim][dca]. The equation of state consists of three temperature-dependent parameters: the second virial coefficient, a constant for scaling the softness of repulsive force, and an effective hard-sphere diameter equivalent to the van der Waals co-volume. The second virial coefficients of ILs are scare and there is no accurate potential energy function to allow their theoretical calculation. In this work, the second virial coefficient have been calculated using corresponding states correlation based on temperature and density at normal boiling point. The other two parameters of the equation of state can be calculated using a scaling rule. Analysis of our predicted results shows that the Tao?CMason equation of state is capable of accurately predicting the density of ILs at any temperature and pressure. The overall average absolute deviation densities for 1,633 data points are 2.05%. Also, the density of ILs obtained from the TM EOS has been compared with those calculated from vdW?CCS?C?? and Peng?CRobinson (PR) equation of state. Our results are in favor of the preference of the TM EOS over the two other equations of state. The overall average absolute deviation for 1,633 data points calculated by vdW?CCS?C?? and PR equation of state are 6.63% and 12.19%, respectively.     

Numerical solution of the nonlinear age-structured population models by using the operational matrices of Bernstein polynomials

In this paper a numerical method for solving the nonlinear age-structured population models is presented which is based on Bernstein polynomials approximation. Operational matrices of integration, differentiation, dual and product are introduced and are utilized to reduce the age-structured population problem to the solution of algebraic equations. The method in general is easy to implement, and yields good results. Illustrative examples are included to demonstrate the validity and applicability of the new technique.     

A numerical approach for analyzing quantum dot infrared photodetectors' parameters

Quantum dot infrared photodetectors (QDIPs) have many advantages over other types of semiconductor-based photodetectors. However some of its characteristics have been investigated theoretically, there are many unstudied points. In this paper a new approach is presented to evaluate quantum dot infrared photodetectors dark current and photocurrent. In this study, it is assumed that both thermionic emission and field-assisted tunneling mechanisms determine the dark current of quantum dot detectors. Based on these assumptions, new formula for average number of electron in a quantum dot for both, dark and illumination condition is calculated, which is more accurate than the previous reported formulas; because in deriving previous reported formulas, it was assumed only thermionic emission determines dark current but field-assisted tunneling mechanisms has not been considered. Then numerical method is used to calculate the average number of electron in a quantum dot and to determine dark current and photocurrent. The theoretical results are compared with experimental data. They have good agreement with available experimental data.     

Auger and photoluminescence analysis of ZnO nanowires grown on AlN thin film

ZnO nanowires were grown on AlN thin film deposited on the glass substrates using a physical vapor deposition method in a conventional tube furnace without introducing any catalysts. The temperature of the substrates was maintained between 500 and 600 °C during the growth process. The typical average diameters of the obtained nanowires on substrate at 600 and 500 °C were about 57 and 22 nm respectively with several micrometers in length. X-ray diffraction and Auger spectroscopy results showed Al diffused from AlN thin film into the ZnO nanowires for the sample grown at 600 °C. Photoluminescence of the nanowires exhibits appearance of two emission bands, one related to ultraviolet emission with a strong peak at 380-382 nm, and the other related to deep level emission with a weak peak at 503-505 nm. The ultraviolet peak of the nanowires grown at 500 °C was blue shifted by 2 nm compared to those grown at 600 °C. This shift could be attributed to surface effect.     

Improving piezoelectric and pyroelectric properties of electrospun PVDF nanofibers using nanofillers for energy harvesting application

In this study, it was aimed to increase the piezoelectric and pyroelectric properties of electrospun polyvinylidene fluoride (PVDF) nanofibers simultaneously by using specific nanofillers. Graphene oxide (GO), graphene, and halloysite nanotubes with different concentrations (0, 0.05, 0.4, and 1.6% wt/wt) were combined with PVDF solution and were fabricated in the form of nanofibers through electrospinning. Pyroelectric properties of samples were measured by submerging sealed samples in hot water (360°K) and ice (270°K). The piezoelectric properties of the samples were evaluated through bending tests. The microstructural, mechanical, and thermal properties of the electrospun PVDF nanocomposite were investigated using scanning electron microscope, Instron instrument, and thermogravimetric analysis, respectively. To further support the experimental observations for generating electric voltage in the bended nanogenerator, the PVDF nanogenerator (PNG) was also modeled by a finite element analysis based on the theory of linear piezoelectricity using COMSOL Multiphysics simulation software. Experimental results showed that adding nanofillers could improve the piezoelectric and pyroelectric properties of all samples, associated with the increment of β‐phase in the nanofibers. It was concluded that adding nanofillers could increase pyroelectricity about 50% more than piezoelectricity in pristine PVDF nanofiber web. The PNG containing 1.6 wt% GO showed the highest efficiency in terms of piezoelectricity and pyroelectricity. In addition, the results showed that the ratio of piezoelectric to pyroelectric coefficients was constant (~1.5) and it was independent of the nanofiller type and content. The effect of external force and vibration frequency on the output voltage was also investigated. Increasing the compressive force and vibration frequency caused a greater output voltage. Finally, the fabricated nanogenerator was integrated on insole and elbow to investigate its energy harvesting capabilities from body movement.     

Bilirubin Removal from Human Plasma with Albumin Immobilised Magnetic Poly(2‐hydroxyethyl methacrylate) Beads

Bioaffinity separation has a unique and powerful role as a support tool in the removal of toxic substances from human plasma. Magnetic beads have advantages as supports in comparison to conventional nonmagnetic beads because of low pressure drop, high mass transfer rates, and good fluid‐solid contact. In addition, they eliminate internal diffusion limitations. Human serum albumin (HSA) immobilised onto magnetic poly(2‐hydroxyethyl methacrylate) (mPHEMA) beads were investigated as an adsorbent for the selective bilirubin removal from human plasma. The mPHEMA beads were prepared by a modified suspension polymerisation. HSA was covalently coupled to the mPHEMA beads. Bilirubin adsorption was investigated from hyperbilirubinemic human plasma on the mPHEMA beads containing different amounts of immobilised HSA, (between 11–100 mg/g). The nonspecific bilirubin adsorption on the unmodified mPHEMA beads was 0.47 mg/g. Higher bilirubin adsorption capacities, up to 64.7 mg/g, were obtained with the HSA‐immobilised magnetic beads. Bilirubin adsorption increased with increasing temperature.

Effect of HSA loading on bilirubin adsorption.