Tunable radio-frequency photonic filter based on an actively mode-locked fiber laser

We propose the use of an actively mode-locked fiber laser as a multitap optical source for a microwave photonic filter. The fiber laser provides multiple optical taps with an optical frequency separation equal to the external driving radio-frequency signal of the laser that governs its repetition rate. All the optical taps show equal polarization and an overall Gaussian apodization, which reduces the sidelobes. We demonstrate continuous tunability of the filter by changing the external driving radio-frequency signal of the laser, which shows good fine tunability in the operating range of the laser from 5 to 10 GHz.     

Optimization of the assay of naphthodianthrones in dry St John’s wort extract by reversed-phase liquid chromatography

An optimization procedure for the reversed-phase liquid chromatography (RPLC) assay of naphthodianthrones in St John’s wort extract from the European Pharmacopoeia project is described. The results obtained from two screening designs showed that light exposure, recommended in the monograph as sample pretreatment, does not permit one to obtain a reproducible quantification of the main ingredients. Improvement of the method robustness implies the need to overcome the problem of light exposure, to subsequently quantify protonaphthodianthrones and to perform the separation on octadecyl (ODS)-bonded phase at optimized flow rate. The method robustness was checked by using a bifurcation sequential approach investigating the influence of 13 factors. The eluent recommended in the monograph is a ternary mixture of methanol, phosphate buffer and ethyl acetate. For the sake of simplicity, the phosphate buffer was substituted by an acetate buffer. The best composition of the ternary mixture was determined by a combined design including three mixture variables and the temperature as an independent variable. Chromatographic parameters were modelled in terms of analysis time, resolution and asymmetry. Desirability functions permit one to cope with these parameters and to determine the best compromise. The naphthodianthrones were separated on a conventional endcapped octadecyl silica gel column eluted by a ternary mobile phase at 40 °C in 10 min. Electronic Supplementary Material Supplementary material is available for this article at     

Heterogeneous Suzuki cross-coupling reactions over palladium/hydrotalcite catalysts

The efficiency of various heterogeneous solids consisting of palladium supported on hydrotalcite as catalysts in the Suzuki cross-coupling reaction between bromobenzene and phenylboronic acid was studied. Based on the catalytic activity results, the reaction develops to an acceptable extent with 100% selectivity at moderate temperatures in the presence of some of the catalysts. The best results were provided by a catalyst consisting of an acetate-pyridine complex of Pd supported on hydrotalcite that gave high conversion values even after three reuses. The reactions conditions were very mild (a temperature of 55 degrees C and atmospheric pressure). In fact, the catalyst provided conversion and selectivity results surpassing those of existing heterogeneous phase catalysts and most homogeneous phase catalysts for the same purpose.     

An iterative method for improving decimal calculations on computers

Since radix-10 arithmetic has been gaining renewed importance over the last few years, high performance decimal systems and techniques are highly demanded. In this paper, a modification of the CORDIC method for decimal arithmetic is proposed so as to improve calculations. The algorithm works with BCD operands and no conversion to binary is needed. A significant reduction in the number of iterations in comparison to the original decimal CORDIC method is achieved. The experiments showing the advantages of the new method are described. Also, the results with regard to delay obtained by means of an FPGA implementation of the method are shown.     

A gravity-independent single-phase electrode reservoir for capillary electrophoresis applications

Capillary electrophoresis (CE) holds great promise as an in situ analytical technique for a variety of applications. However, typical instrumentation operates with open reservoirs (e.g., vials) to accommodate reagents and samples, which is problematic for automated instruments designed for space or underwater applications that may be operated in various orientations. Microgravity conditions add an additional challenge due to the unpredictable position of the headspace (air layer above the liquid) in any two-phase reservoir. One potential solution for these applications is to use a headspace-free, flow-through reservoir design that is sealed and connected to the necessary reagents and samples. Here, we demonstrate a flow-through high-voltage (HV) reservoir for CE that is compatible with automated in situ exploration needs, and which can be electrically isolated from its source fluidics (in order to prevent unwanted leakage current). We also demonstrate how the overall system can be rationally designed based on the operational parameters for CE to prevent electrolysis products generated at the electrode from entering the capillary and interfering with the CE separation. A reservoir was demonstrated with a 19 mm long, 1.8 mm inner diameter channel connecting the separation capillary and the HV electrode. Tests of these reservoirs integrated into a CE system show reproducible CE system operation with a variety of background electrolytes at voltages up to 25 kV. Rotation of the reservoirs, and the system, showed that their performance was independent of the direction of the gravity vector.     

Rhenium Complexes with p-Fluorophenylisocyanide

p-Fluorophenylisocyanide (CNPh^pF) reacts with [Re(CO)₅Br] under stepwise exchange of the carbonyl ligands depending on the conditions applied. The reaction stops with the formation of fac-[Re(CO)₃Br(CNPh^pF)₂] in boiling THF. An ongoing carbonyl exchange is observed at higher temperatures, e. g. in refluxing toluene, with the final formation of the [Re(CNPh^pF)₆]⁺ cation. The progress of the reactions has been studied by ¹⁹F NMR spectroscopy and the structures of [Re(CO)Br(CNPh^pF)₄] and [Re(CNPh^pF)₆](BPh₄) have been elucidated by X-ray diffraction.