Wavefront sensing with an axicon

The use of a large apex-angle axicon for common-path interferometric wavefront sensing is proposed. The approach is a variant of point-diffraction interferometry bearing similarities to pyramidal wavefront sensing. A theoretical basis for wavefront sensing with an axicon is developed, and the outcomes of numerical simulations are compared to experimental results obtained with spherical and cylindrical ophthalmic trial lenses. It is confirmed that the axicon can be used for wavefront sensing, although its refraction may ultimately complicate and limit its operational range.     

Solution of boundary and eigenvalue problems for second‐order elliptic operators in the plane using pseudoanalytic formal powers

We propose a method for solving boundary value and eigenvalue problems for the elliptic operator D = div p grad + qin the plane using pseudoanalytic function theory and in particular pseudoanalytic formal powers. Under certain conditions on the coefficients p and q with the aid of pseudoanalytic function theory a complete system of null solutions of the operator can be constructed following a simple algorithm consisting in recursive integration. This system of solutions is used for solving boundary value and spectral problems for the operator D in bounded simply connected domains. We study theoretical and numerical aspects of the method. Copyright © 2010 John Wiley & Sons, Ltd.     

An evaluation method for determination of non-polar pesticide residues in animal fat samples by using dispersive solid-phase extraction clean-up and GC-MS

A rapid and easy method has been proposed, optimized and evaluated for quantitative determination at trace level of a representative group of non-polar pesticides in fat samples. The method includes n-hexane-saturated acetonitrile extraction, fat precipitation by cooling pre clean-up followed by dispersive solid-phase extraction (d-SPE) based on QuEChERS procedure clean-up. Determination was performed by gas chromatography?Cmass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. Efficiency of the d-SPE clean-up step was evaluated by comparison with fat oxidation treatment and gel permeation chromatography. Different combinations of d-SPE extraction reagents and sample amounts were tested in order to minimize matrix co-extractives and interferences. Best recoveries were obtained with 1200?mg of MgSO₄, 400?mg of end-capped C₁₈, 400?mg of PSA and 1?g of sample amount. SIM method, matrix effect, precision, and accuracy were evaluated with spiked pork fat samples for 38 representative pesticides. Results of this study showed that this technique is applicable in routine analysis for its application into monitoring programs. It simplifies time-consuming clean-up steps and allows a satisfactory long-term chromatographic performance.     

Synthesis and characterization of covalent diphenylalanine nanotube-folic acid conjugates

Traditionally, organosilica nanoparticles have been prepared inside micelles with an external silica shell for mechanical support. Here, we compare these hybrid core–shell particles with organosilica particles that are robust enough to be produced both inside micelles and alone in a sol–gel process. These particles form from octadecyltrimethoxy silane as silica source either in microemulsions, resulting in water-dispersible particles with a hydrophobic core, or precipitate from an aqueous mixture to form particles with both hydrophobic core and surface. We examine size and morphology of the particles by dynamic light scattering and transmission electron microscopy and show that the particles consist of Si–O–Si networks pervaded by alkyl chains using nuclear magnetic resonance, infrared spectroscopy, and thermogravimetric analysis.     

Bloch,Besov and Dirichlet Spaces of Slice Hyperholomorphic Functions

In this paper we begin the study of some important Banach spaces of slice hyperholomorphic functions, namely the Bloch, Besov and weighted Bergman spaces, and we also consider the Dirichlet space, which is a Hilbert space. The importance of these spaces is well known, and thus their study in the framework of slice hyperholomorphic functions is relevant, especially in view of the fact that this class of functions has recently found several applications in operator theory and in Schur analysis. We also discuss the property of invariance of these function spaces with respect to Möbius maps by using a suitable notion of composition.     

Copper Versus Thioether‐Centered Oxidation: Mechanistic Insights into the Non‐Innocent Redox Behavior of Tripodal Benzimidazolylaminothioether Ligands

A series of Cu⁺ complexes with ligands that feature varying numbers of benzimidazole/thioether donors and methylene or ethylene linkers between the central nitrogen atom and the thioether sulfur atoms have been spectroscopically and electrochemically characterized. Cyclic voltammetry measurements indicated that the highest Cu²⁺/Cu⁺ redox potentials correspond to sulfur‐rich coordination environments, with values decreasing as the thioether donors are replaced by nitrogen‐donating benzimidazoles. Both Cu²⁺ and Cu⁺ complexes were studied by DFT. Their electronic properties were determined by analyzing their frontier orbitals, relative energies, and the contributions to the orbitals involved in redox processes, which revealed that the HOMOs of the more sulfur‐rich copper complexes, particularly those with methylene linkers (? N? CH₂? S? ), show significant aromatic thioether character. Thus, the theoretically predicted initial oxidation at the sulfur atom of the methylene‐bridged ligands agrees with the experimentally determined oxidation waves in the voltammograms of the NS₃‐ and N₂S₂‐type ligands as being ligand‐based, as opposed to the copper‐based processes of the ethylene‐bridged Cu⁺ complexes. The electrochemical and theoretical results are consistent with our previously reported mechanistic proposal for Cu²⁺‐promoted oxidative C? S bond cleavage, which in this work resulted in the isolation and complete characterization (including by X‐ray crystallography) of the decomposition products of two ligands employed, further supporting the novel reactivity pathway invoked. The combined results raise the possibility that the reactions of copper–thioether complexes in chemical and biochemical systems occur with redox participation of the sulfur atom.     

Assessment of metals bound to marine plankton proteins and to dissolved proteins in seawater

Studies based on laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP-MS) have been performed to assess metal bound to dissolved proteins and proteins from marine plankton after two-dimensional polyacrylamide gel electrophoresis (2D PAGE). Dissolved proteins were pre-concentrated from surface seawater (60 L) by tangential ultrafiltration with 10 kDa molecular weight cut-off (MWCO) membranes and further centrifugal ultrafiltration (10 kDa) before proteins isolation by methanol/chloroform/water precipitation. Proteins isolation from plankton was assessed after different trichloroacetic acid (TCA)/acetone and methanol washing stages, and further proteins extraction with a phenol solution. LA–ICP-MS analysis of the electrophoretic profiles obtained for dissolved proteins shows the presence of Cd, Cr, Cu, and Zn in five spots analyzed. These proteins exhibit quite similar molecular weights (within the 10–14 kDa range) and pIs (from 5.8 to 7.3). Cd, Cr, Cu, and Zn have also been found to be associated to proteins isolated from plankton samples. In this case, Cd has been found to be bound to proteins of quite different molecular weight (9, 13 and 22 kDa) and pIs (4.5, 5.2, 5.5, and 10). However, trace elements such as Cr, Cu and Zn appear to be mainly bound to plankton proteins of low molecular weight and variable pI.     

A new approach based on off‐line coupling of high‐performance liquid chromatography with gas chromatography‐mass spectrometry to determine acrylamide in coffee brew

A new method based on off‐line coupling of LC with GC in replacement of conventional sample preparation techniques is proposed to analyze acrylamide in coffee brews. The method involves the preseparation of the sample by LC, the collection of the selected fraction, its concentration under nitrogen, and subsequent analysis by GC coupled with MS. The composition of the LC mobile phase and the flow rate were studied to select those conditions that allowed separation of acrylamide without coeluting compounds. Under the conditions selected recoveries close to 100% were achieved while LODs and LOQs equal to 5 and 10 μg/L for acrylamide in brewed coffee were obtained. The method developed enabled the reliable detection of acrylamide in spiked coffee beverage samples without further clean‐up steps or sample manipulation.     

Structural and luminescent study in lanthanide doped sol–gel glass–ceramics comprising CeF<Subscript>3</Subscript> nanocrystals

Sol–gel derived glass–ceramics containing CeF₃ nanocrystals have been developed for the first time, to the best of our knowledge, by adequate heat treatments of precursor bulk glasses with composition 95SiO₂–5CeF₃ doped with 0.1 Eu³⁺ or 0.1 Sm³⁺ and co-doped with 0.3 Yb³⁺ and 0.1 Er³⁺ ions (in mol%). X-Ray Diffraction and High Resolution Transmission Electron Microscopy confirm the precipitation of CeF₃ nanocrystals. Moreover, this structural analysis is completed using Eu³⁺ and Sm³⁺ as probe ions of the different local environments for rare-earth ions in the nano-structured glass–ceramics. Luminescence measurements led us to discern the final environments for the ions, revealing the partition of a large fraction of these ions into like-crystalline environment of the precipitated CeF₃ nanocrystals. Near infrared emission at 1.5 μm was observed after excitation at 980 nm in Yb³⁺–Er³⁺ co-doped samples for potential applications in telecommunications.