Voltammetric cadmium(II) sensor based on a fluorine doped tin oxide electrode modified with polyamide 6/chitosan electrospun nanofibers and gold nanoparticles

The authors have developed an electrochemical sensor for cadmium(II) that is based on the use of a conventional fluorine doped tin oxide (FTO) electrode modified with polymeric electrospun nanofibers consisting of polyamide 6 (PA6) and chitosan which were further modified with gold nanoparticles (AuNPs). The materials were characterized by infrared spectroscopy, thermal analysis (DSC and TGA), and scanning electron microscopy. The modified electrode was applied to the detection of Cd(II) by square wave voltammetry. Response is linear in the 25 to 75 μg ? L^?1 Cd(II) concentration range, with a detection limit of 0.88 μg ? L^?1. The relative standard deviations are 4.6% and 8.2% for intra- and inter-electrode measurements, respectively. Mercury(II), lead(II), and copper(II) did not significantly interfere.

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Graphical abstract The sensing platform developed can detect cadmium(II) with a detection limit of 0.88 μg L^?1, with no significant interference by mercury(II) and lead(II).

     

Some considerations on leading edge vortices on wings in supersonic flow

The positions, the shapes and the intensities of leading edge vortices are obtained by interpretation of skin friction lines and by exploration of the theoretical and experimental pressure coefficients on the surface of three wing models in supersonic flow.     

Controlled Anisotropic Growth of Co‐Fe‐P from Co‐Fe‐O Nanoparticles

A facile approach to bimetallic phosphides, Co‐Fe‐P, by a high‐temperature (300 °C) reaction between Co‐Fe‐O nanoparticles and trioctylphosphine is presented. The growth of Co‐Fe‐P from the Co‐Fe‐O is anisotropic. As a result, Co‐Fe‐P nanorods (from the polyhedral Co‐Fe‐O nanoparticles) and sea‐urchin‐like Co‐Fe‐P (from the cubic Co‐Fe‐O nanoparticles) are synthesized with both the nanorod and the sea‐urchin‐arm dimensions controlled by Co/Fe ratios. The Co‐Fe‐P structure, especially the sea‐urchin‐like (Co_0.54Fe_0.46)₂P, shows enhanced catalysis for the oxygen evolution reaction in KOH with its catalytic efficiency surpassing the commercial Ir catalyst. Our synthesis is simple and may be readily extended to the preparation of other multimetallic phosphides for important catalysis and energy storage applications.     

A new approximation algorithm for the multilevel facility location problem

In this paper we propose a new integer programming formulation for the multilevel facility location problem and a novel 3-approximation algorithm based on LP-rounding. The linear program that we use has a polynomial number of variables and constraints, thus being more efficient than the one commonly used in the approximation algorithms for these types of problems.     

A capacitary method for the asymptotic analysis of dirichlet problems for monotone operators

Given a non-linear elliptic equation of monotone type in a bounded open set Ω ⊂ Rⁿ, we prove that the asymptotic behaviour, asj → ∞, of the solutions of the Dirichlet problems corresponding to a sequence (Ω_j) of open sets contained in Ω is uniquely determined by the asymptotic behaviour, asj → ∞, of suitable non-linear capacities of the setsKΩ _j, whereK runs in the family of all compact subsets of Ω.     

On k-domination and j-independence in graphs

Let $G$ be a graph and let $k$ and $j$ be positive integers. A subset $D$ of the vertex set of $G$ is a $k$-dominating set if every vertex not in $D$ has at least $k$ neighbors in $D$. The $k$-domination number ${\gamma }_k\left(G\right)$ is the cardinality of a smallest $k$-dominating set of $G$. A subset $I?V\left(G\right)$ is a $j$-independent set of $G$ if every vertex in $I$ has at most $j?1$ neighbors in $I$. The $j$-independence number ${\alpha }_j\left(G\right)$ is the cardinality of a largest $j$-independent set of $G$. In this work, we study the interaction between ${\gamma }_k\left(G\right)$ and ${\alpha }_j\left(G\right)$ in a graph $G$. Hereby, we generalize some known inequalities concerning these parameters and put into relation different known and new bounds on $k$-domination and $j$-independence. Finally, we will discuss several consequences that follow from the given relations, while always highlighting the symmetry that exists between these two graph invariants.     

A new proof of Frobenius theorem and applications

A proof of Frobenius theorem on local integrability of a given distribution on a finite or infinite dimensional manifold under weak differentiability conditions is given using holonomy methods and the curvature two form of the associated connection. The local curvature two form, which measures the non-integrability of a given distribution, is studied and a variety of applications are given. The Inverse Problem in the Calculus of Variations appears as a particular case.     

Structure and rheology of hyperbranched and dendritic polymers. I. Modification and characterization of poly(propyleneimine) dendrimers with acetyl groups

Commercially available fourth and fifth generation poly(propyleneimine) (PPI) dendrimers were functionalized with acetyl chloride and deuterated acetyl chloride. Their solution properties in water and D₂O were measured with dilution viscometry, densitometry, rheology, and small‐angle neutron scattering (SANS) and compared to molecular modeling. Both the acetylated and PPI dendrimers exhibited Newtonian rheology in solution at all concentrations, but the functionalized dendrimers were less viscous than the nonacetylated dendrimers at an equal weight fraction (50 wt %). The acetylated dendrimers exhibited a pronounced structure peak in SANS, however, that was not evident for PPI in solution and a greatly enhanced solubility. This structure peak, evident at concentrations as low as 0.2 wt %, was evidence for long‐range electrostatic interdendrimer forces, which were screened by added salt. A quantitative agreement was obtained between the dilute‐limiting absolute scattering spectra of both the nonacetylated and acetylated dendrimers in solution with model calculations via a homogeneous spherical model and input parameters independently obtained from dilution viscometry or direct calculation. The combined measurements verified significant solvent penetration for both dendrimer types. The form factors measured in this manner were also in good quantitative agreement with the results of molecular dynamics simulations, which pointed to significant backfolding of the terminal groups. SANS and rheology measurements at higher concentrations suggested dendrimer clustering and interpenetration with increasing concentration, leading to less structure and lower viscosity than would be predicted from the dilute‐limiting behavior. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 857–873, 2000     

In Vitro Bioaccessibility of Bioactive Compounds from Rosehip-Enriched Corn Extrudates

The rosehip (Rosa canina L.) fruit has gained researchers′ attention due to its rich chemical composition in vitamin C, phenols, carotenoids, and high antioxidant activity; meanwhile, polymers such as pea protein are generally recognized as exhibiting a protection role against the extrusion process. Corn snacks extrudates obtained by replacing corn flour with 10% R. canina powder (R) and 10% R. canina with pea protein (RPP) were evaluated for the physicochemical, textural, optical, and nutritional characteristics. A sample manufactured without R. canina powder was used as a control. Hardness, crispiness, chewiness, and solubility index (WSI) of the final extrudates were improved by addition of R. canina and pea protein powder (PP); meanwhile, b* (yellow/blue coordinate), C (chroma), and h* (tone) optical parameters were significantly different from the control sample (p < 0.05). Extrusion highlighted a negative impact on total phenols, carotenoids, vitamin C, and antioxidant activity extrudates, while PP exhibited a good protection against the extrusion process. In vitro digestion increased the bioaccessibility of vitamin C, folate, antioxidant activity, total phenols, and total carotenoids mainly on RPP extrudates.