Spider-web-like chitosan/MIL-68(Al) composite nanofibers for high-efficient solid phase extraction of Pb(II) and Cd(II)

Microchimica Acta - The authors describe the synthesis of spider-web-like chitosan/MIL-68(Al) composite nanofibers, their application to fast solid phase extraction (SPE) of trace levels...     

Dependence structure and test of independence for some well-known bivariate distributions

In this paper, we study the dependence structure of some bivariate distribution functions based on dependence measures of Kochar and Gupta (Biometrika 74(3):664–666, 1987) and Shetty and Pandit (Stat Methods Appl 12:5–17, 2003) and then compare these measures with Spearman’s rho and Kendall’s tau. Moreover, the empirical power of the class of distribution-free tests introduced by Kochar and Gupta (1987) and Shetty and Pandit (2003) is computed based on exact and asymptotic distribution of U-statistics. Our results are obtained from simulation work in some continuous bivariate distributions for the sample of sizes \(n=6,8,15,20\) and 50. Also, we apply some examples to illustrate the results. Finally, we compare the common estimators of dependence parameter based on empirical MSE.     

Dispersive solid‐phase extraction adsorbent of methamphetamine using in‐situ synthesized carbon‐based conductive polypyrrole nanocomposite: focus on clinical applications in human urine

Determination of methamphetamine is of great importance in clinical and forensic laboratories because there are low dosages of drugs in the biological media and social problems created due to the methamphetamine consumption. Polymeric carbon based‐nano composites are reasonable candidates for dispersive solid phase extraction method due to facial and affordable synthesis process and high selectivity and sensitivity. Nano graphene oxide polypyrolle composite was synthesized and employed as dispersive solid‐phase extraction adsorbent for methamphetamine extraction from complex urine matrix. Full characterization of the prepared nano graphene oxide polypyrolle composite was completed and the influential extraction parameters were investigated through one‐parameter‐at‐a‐time method. High‐performance liquid chromatography detectors were applied as detection and quantification instrument. The optimized extraction parameters included 300 µL of methanol, 10 min of extraction and desorption time, 6000 stirring rate, urine pH value of 10, 60 mg of adsorbent, and 6 mL of urine volume. After outlining the calibration curve, the linear range of the method was considered as 30–800 ng/mL. The detection limit for the suggested method was 9 ng/mL. The analysis of addicted subjects with the proposed method confirmed the utility of the method in different analytical and clinical laboratories.     

An electrochemical study of safranin O binding to DNA at the surface

The interaction of safranin O (SO) with double-stranded calf thymus DNA was investigated electrochemically, using a DNA-modified glassy carbon (GC-DNA) electrode. The results were compared with those obtained using a bare GC electrode. The formal potential of SO was more negative when using the GC-DNA electrode, although the rate of heterogeneous electron transfer was not altered. The GC-DNA electrode enabled preconcentration of the SO on the electrode surface, despite the fact that the mass transfer effects in the thin DNA layer adsorbed on the surface were still observed. The diffusion coefficient of SO and the binding ratio for the oxidized and reduced forms of the bound species were obtained. A binding isotherm for SO at the GC-DNA electrode was plotted from coulometric titrations, giving a binding constant of 5.8×10⁴ L mol⁻¹.     

Electrochemical oxidation and determination of ceftriaxone on a glassy carbon and carbon-nanotube-modified glassy carbon electrodes

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10⁻⁶ cm² s⁻¹. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10⁻⁶ M with the proposed method.     

Robust trajectory tracking control of cable-driven parallel robots

Nonlinear Dynamics - In this paper, a robust tracking controller is designed for fully constrained cable-driven parallel robots (CDPRs). One of the main challenges of controller design for this...     

A revised key agreement protocol based on chaotic maps

Very recently, Chen et al. proposed a security-enhanced key agreement protocol based on Chebyshev chaotic map. They claimed that the proposed protocol can achieve session key agreement shared among the server and user with security and users anonymity. Although, in this paper, we will prove that Chen et al.’s protocol cannot guarantee security and user anonymity against internal adversary who is a legal user. Furthermore, we give some improvements to dominate the mentioned shortcomings. The analysis shows that our proposed improvements are secure and efficient.     

Combined effect of osteopontin and BMP-2 derived peptides grafted to an adhesive hydrogel on osteogenic and vasculogenic differentiation of marrow stromal cells

The objective of this work was to investigate the combined effect of grafting the peptide corresponding to amino acid residues 162-168 of osteopontin (OPD peptide) and the peptide corresponding to amino acid residues 73-92 of bone morphogenetic protein-2 (BMP peptide) to an RGD-conjugated inert hydrogel on osteogenic and vasculogenic differentiation of bone marrow stromal (BMS) cells. RGD-conjugated three-dimensional (3D) porous hydrogel scaffolds with well-defined cylindrical pore geometry were produced from sacrificial wax molds fabricated by fused deposition modeling rapid prototyping system. Propargyl acrylate and 4-pentenal were conjugated to the hydrogel for orthogonal grafting of BMP and OPD peptides by click reaction and oxime ligation, respectively. The OPD peptide was grafted by the reaction between aminooxy moiety of aminooxy-mPEG-OPD (mPEG = mini-poly(ethylene glycol)) and the aldehyde moiety in the hydrogel. The BMP peptide was grafted by the reaction between the azide moiety of Az-mPEG-BMP and the propargyl moiety in the hydrogel. The hydrogels seeded with BMS cells were characterized by biochemical, immunocytochemical, and mRNA analyses. Groups included RGD control hydrogel (RGD), RGD and BMP peptides without OPD (RGD+BMP), RGD and BMP peptides with mutant OPD (RGD+BMP+mOPD), and RGD and BMP peptides with OPD (RGD+BMP+OPD) grafted hydrogels. The extent of mineralization of RGD, RGD+BMP, RGD+BMP+mOPD, and RGD+BMP+OPD groups after 28 days was 650 ± 70, 990 ± 30, 850 ± 30, and 1150 ± 40 mg/(mg of DNA), respectively, indicating that the BMP and OPD peptides enhanced osteogenic differentiation of the BMS cells. The BMS cells seeded on RGD+BMP+OPD grafted hydrogels stained positive for vasculogenic markers α-SMA, PECAM-1, and VE-cadherin while the groups without OPD peptide (RGD+BMP and RGD+BMP+mOPD) stained only for α-SMA but not PECAM-1 or VE-cadherin. These results were consistent with the significantly higher PECAM-1 mRNA expression for RGD+BMP+OPD group after 21 and 28 days, compared to the groups without OPD. These findings suggest that the RGD+BMP+OPD peptides provide a favorable microenvironment for concurrent osteogenic and vasculogenic differentiation of progenitor marrow-derived cells.     

On a Banach Algebra Generated in its Multiplier Space and Applications to Locally Compact Groups

In this paper, we present a general version of the algebra A_M(G) which was introduced by B. Forrest. Indeed, for a faithful commutative Banach algebra A, we embed it in ?(A), the multiplier algebra of A, and obtain Banach algebra A_M. Then, we study the spaceability of A_M? A and A_M (G) ? ?A(G). These results give some characterizations of compactness and discreteness of locally compact groups. Also, we show that A_M(G) is an ideal in its second dual if and only if G is discrete. Finally, we study the BSE-property of A_M(G).