Polyaniline-coated Fe(3) O(4) nanoparticles: An anion exchange magnetic sorbent for solid-phase extraction

In this study, the capability of the prepared polyaniline-coated Fe(3) O(4) nanoparticles for magnetic solid-phase extraction of three parabens from environmental wastewater, cream, and toothpaste samples is presented. Synthesized Fe(3) O(4) nanoparticles were coated with sulfate-doped polyaniline via polymerization of aniline in the presence of Fe(3) O(4) nanoparticles and sulfuric acid. Here, polyaniline-coated Fe(3) O(4) nanoparticles are presented as anion exchange sorbent, which extract anionic form of parabens via anion exchange with dopant of polyaniline. The experimental conditions affecting extraction efficiency were further studied and optimized. The experimental results showed that maximum extraction efficiency can be obtained at 70 mL sample solution of pH 8, extraction and desorption times of 2 and 1 min, respectively, 100 μL of 3% (v/v) acetic acid in acetonitrile as eluent, and 100 mg of the adsorbent. Under these conditions, the linear dynamic ranges were 0.5-100 μg/L with good correlation coefficients (0.998-0.999). The detection limits were in the range of 0.3-0.4 μg/L and the relative standard deviations were less than 2.4 (n = 5) for the three parabens. Finally, this fast and efficient method was further employed for determination of target analytes in cream, toothpaste, and environmental wastewater samples and satisfactory results were obtained.     

Nonlinear wave propagation analysis in Timoshenko nano-beams considering nonlocal and strain gradient effects

This article is aimed to investigate the geometrically nonlinear wave propagation of nano-beams on the basis of the most comprehensive size-dependent elasticity theory. To this end, the integral model of nonlocal elasticity theory in the most general form without any simplification in conjunction with the modified strain gradient theory is implemented in the analysis. Also, the Timoshenko beam model is utilized in the presented nonlocal strain gradient elasticity theory. By Hamilton’s principle, the governing integro-partial differential equations of motion are derived. Employing numerical integration and an efficient method called as periodic grid technique, a semi-analytical approach is presented for the solution procedure. To detect the impacts of nonlocality and small scale effects on the nonlinear wave propagation characteristics of beams at nanoscale, adequate numerical examples and comparison studies are presented.     

Molecular Dynamics Simulations of Adsorption of Polymer Chains on the Surface of B<Subscript>m</Subscript>N<Subscript>n</Subscript> Graphyne-Like Monolayers

Molecular dynamics simulations are used here to study the interactions between B_mN_n graphyne-like monolayers and four different polymer chains. BN, B₁N₉, and B₂N₈ graphyne-like monolayers are selected from the family of B_mN_n graphyne-like monolayers. It is observed that increasing the number of B atoms in the structure of B_mN_n graphyne-like monolayers results in larger interaction energies of nanosheet/polymer systems. It is also shown that the polymer chains with the linear adsorbed configurations on the nanosheets have larger interaction energies with the nanosheets. Investigating the effect of number of polymer repeat units on the polymer/nanosheet interaction energy, it is observed that increasing the number of repeat units of polymers leads to enhancing the polymer/nanosheet interaction energy.     

Mechanical properties of two-dimensional graphyne sheet under hydrogen adsorption

In the present work, the mechanical properties of graphyne, a class of graphene allotropes with carbon triple bonds, subjected to the hydrogen chemisorption are studied using a first-principles density functional approach. Two configurations for the maximum of hydrogen adsorption are considered: (I) adsorption of hydrogen atoms on carbon atoms at the two opposite sides of graphyne sheet and (II) adsorption of hydrogen atoms on carbon atoms at the same side of graphyne sheet. Formation energy for hydrogenated graphyne (H-graphyne) corresponding to these states of adsorption is calculated and it is indicated that state (I) is more stable than state (II). Density functional calculations within the generalized gradient approximation (GGA) in the harmonic elastic deformation range are performed to obtain the elastic constants of graphyne and H-graphyne in state (I). This study shows that H-graphyne has an in-plane stiffness of 125 N/m and a Poisson's ratio of 0.23. It is observed that the in-plane stiffness of H-graphyne is lower than that of graphyne. This clearly reveals the destructive effect of hydrogen adsorption on the mechanical properties of graphyne. The results of this paper are helpful for the design of future nanodevices in which H-graphyne acts as their basic element.     

Mechanical properties of graphene under molecular hydrogen physisorption: An ab initio study

This paper investigates the mechanical properties of graphene subjected to adsorption of molecular hydrogen through an ab initio approach. First, using density functional theory (DFT) with both generalized gradient and local density approximation functionals, the most stable configuration for physisorption of molecular hydrogen on the graphene is determined. All possible adsorption sites are considered, and it is revealed that the most stable state happens above the center of a hexagon with the equilibrium distance of 2.7 Å when the axis of the hydrogen molecule is parallel to the graphene surface. Thereafter, DFT calculations are performed to obtain the in-plane stiffness and Poisson’s ratio of graphene under the above-mentioned adsorption position. It is found that the effect of hydrogen physisorption on the mechanical properties of graphene is not very significant.     

Two bit all-optical analog-to-digital converter based on nonlinear Kerr effect in 2D photonic crystals

We have demonstrated the performance of a novel design for a single wavelength 2-bit all-optical analog-to-digital converter (ADC). This converter consists of two high efficient channel drop filters with a coupled cavity-based wavelength selective reflector in a 2D photonic crystal with total length of 15.87 μm. The A/D conversion is achieved by using nonlinear Kerr effect in the cavities. The output ports switch to state ‘1’ at different input power levels to generate unique states preferred for an ADC. This conversion is simulated by the finite difference time domain (FDTD) method for 5 different power levels. The proposed structure can function as a two-bit ADC with a 60 mW/μm input pulse and its maximum sampling rate is found to be ~ 45 GS/s.     

A fast and sensitive nanosensor based on MgO nanoparticle room-temperature ionic liquid carbon paste electrode for determination of methyldopa in pharmaceutical and patient human urine samples

In this study, we describe an ionic liquid–MgO nanoparticle modified carbon paste electrode (MgO/NPs/IL/CPE) was used as a simple, fast, and sensitive tool for the investigation of the electrochemical oxidation of methyldopa (MDOP) using voltammetric methods. The MgO/NPs was characterized with different methods such as TEM, SEM, and XRD. The oxidation peak potential of the MDOP at a surface of MgO/NPs/IL/CPE appeared at 450 mV that was about 100 mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode (CPE) under similar conditions. The electro-oxidation of MDOP occurred in a pH-dependent 2e^? and 2H⁺ process, and the electrode reaction followed a diffusion-controlled pathway. Under optimal conditions at pH 7.0, the anodic peak currents increased linearly with the concentration of MDOP in the range of 0.08–380 μmol L^?1 with a detection limit of 0.03 μmol L^?1 (3σ). The proposed sensor was successfully applied to the determination of MDOP in real samples such as drug and urine.     

STABILITY CHARACTERISTICS OF SINGLE-LAYERED ZINC OXIDE NANOSHEETS UNDER UNIAXIAL LOADING

This paper is aimed to propose a three-dimensional model which would be used for investigation on the mechanical behavior of single-layered zinc oxide nanosheets. To develop this model, molecular mechanics is coupled with the density functional theory. Simulating the hexagonal lattices of nanosheets as a hexagonal mechanical structure composed of structural beam elements, the buckling behavior of zinc oxide nanosheets is studied. Effects of different parameters on the stability of armchair and zigzag nanosheets are examined. It is shown that the buckling forces of zigzag nanosheets are slightly greater than those of armchair ones. However, with increasing size of nanosheets the effect of atomic structure on the stability of nanosheets diminishes.By studying the effect of end conditions on the buckling behavior of nanosheets, it is shown the stability of nanosheets is affected significantly by boundary conditions.     

Inegalite relative des genres

Let (K, v₀) be an algebrically closed valued field. Let M/L be an extension of function fields of one variable over K and {v_i}_1≤i≤s be distinct valuations on L which prolong v₀ and have transcendental residue extensions (Lv_i/Kv₀). If {w_j}_1≤j≤t are prolongations of the {v_i}_1≤i≤s to M, we show the following inequality between the genera of the functions fields: $$g(M/K) - \sum\limits_{1 \leqslant j \leqslant t} {g(Mw_j /Kv_0 ) \geqslant g(L/K)} - \sum\limits_{1 \leqslant i \leqslant s} {g(Lv_i /Kv_0 ) \geqslant 0.} $$ . As an application we show that if M/K has good reduction, L/K also has good reduction. This result generalizes a result of H. Lange [L]. In the appendix we give other “known” results related to Lange's theorem.