Solid phase extraction of gold by sorption on octadecyl silica membrane disks modified with pentathia-15-crown-5 and determination by AAS

A simple and selective method for rapid and efficient concentration and determination of μg l⁻¹ levels of Au(III) ions in aqueous solution using octadecyl silica membrane disks modified by pentathia-15-crown-5 and flame atomic absorption spectrometry is presented. The influence of flow rates of eluent and sample solution, amount of ligand, types and least amount of eluent for elution of Au from disks were investigated. Break through volume and limit of detection of the membrane disks modified by 5 mg of the thiacrown ether was found to be 2.0 l and 1.0 μg l⁻¹, respectively. The effects of various cationic interferences on percent recovery of gold were studied. The method was successfully applied for the determinations of gold in some pharmaceutical samples and for the recovery of trace Au³⁺ ions from synthetic and water samples.     

Synthesis of novel fluorene-functionalised nanoporous silica and its luminescence behaviour in acidic media

Fluorene-functionalised nanoporous silica (FL-NH₂-SBA-15) was prepared using the post-synthesis grafting method of SBA-15. The material thus obtained was characterised by means of small- and wide-angle X-ray diffraction, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and elemental analysis. The results showed that the organised structure is preserved after the post-grafting procedure. Surface area and pore-size decreased by attaching functional groups to the pore surface. In addition, the pore volume was reduced with functionalisation. The amount of fluorene grafted onto the surface of SBA-15 was 0.55 mmol with a yield of approximately 46 %. The emission spectra of FL-NH₂-SBA-15 in acidic media were studied and are discussed in detail. The structural change between FL-NH₂-SBA-15 and the protonated form might be an effective candidate for acid-dependent molecular-sensor models for advanced application in molecular sensors in the future.     

Gabor Frames in $${\ell }^2({\mathbb {Z}})$$ ℓ 2 ( Z ) and Linear Dependence

We prove that an overcomplete Gabor frame in \({\ell }^2({\mathbb {Z}})\) generated by a finitely supported sequence is always linearly dependent. This is a particular case of a general result about linear dependence versus independence for Gabor systems in \({\ell }^2({\mathbb {Z}})\) with modulation parameter 1 / M and translation parameter N for some \(M,N\in {\mathbb {N}},\) and generated by a finite sequence g in \({\ell }^2({\mathbb {Z}})\) with K nonzero entries.

     

Frame properties of systems arising via iterated actions of operators

Motivated by recent progress in dynamical sampling we prove that every frame which is norm-bounded below can be represented as a finite union of sequences ${\{{(T_j)}^n{\phi }_j\}}_{n=0}^{\infty },j=1,\dots ,J$ for some bounded operators $T_j$ and elements ${\phi }_j$ in the underlying Hilbert space. The result is optimal, in the sense that it turns out to be problematic to replace the collection of generators ${\phi }_1,\dots ,{\phi }_J$ by a singleton: indeed, for linearly independent frames we prove that we can represent the frame in terms of just one system ${\{T^n\phi \}}_{n=0}^{\infty }$, but unfortunately this representation often forces the operator T to be unbounded. Several examples illustrate the connection of the results to typical frames like Gabor frames and wavelet frames, as well as generic constructions in arbitrary separable Hilbert spaces.     

Influence of non-metallic atoms on the absorption of amphetamines on B12N12 nano-cages

Structural Chemistry - Density functional theory (DFT) calculations at B3LYP/6-31+G(d) level were employed to investigate the influence of the non-metal encapsulation of the second row of the...     

An aptasensor for tetracycline using a glassy carbon modified with nanosheets of graphene oxide

Microchimica Acta - The authors describe an aptasensor for tetracycline (TET) based on the use of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets. The latter were placed on...     

Evaluating nonlinear variability of mental fatigue behavioral indices during long‐term attentive task

This study investigates the behavioral indices of attention. A simple repetitive attentive task that resulted in mental fatigue was used consecutively in four trials. In the first step, reaction time and error responses were recorded to evaluate differences among trials. During the task, subjects showed different responses to stimulations. In the second part, to recognize the strategies, multiple clustering methods such as k‐means and fuzzy c‐means were performed in which behavioral indices and nonlinear features were used. In the last section, mental behavior was identified as a result of the chaotic properties of variations in reaction time. Therefore, the Lyapunov exponent of reaction times was evaluated. Results revealed that behavioral indices could distinguish attention from the occurrence of mental fatigue in trials. In addition, the three strategies used by subjects during the test protocol were assessed. Finally, variation of indices extracted from nonlinear analysis, that is, decrease in degree of chaotic behavior determined the transition from attention to mental fatigue. © 2012 Wiley Periodicals, Inc. Complexity, 2012     

Experimental and numerical investigation of tendons and tendon cells

Tendon injuries are a common problem in medicine. While healthy tendons do not rupture, tendon injuries are mostly accompanied by pathological changes and microruptures. Unfortunately, still less is known about the underlying processes. Thus, in the present study, we introduce artificial damages into native tendon tissue and investigate its mechanical behaviour experimentally. In the second part of this study, we propose a theoretical model for predicting the mechanical behaviour of the damaged tendon and present its validity. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)