Optical phase-based beamformer using MZM SSB modulation combined with crystal polarization optics and a spatial light modulator

The performance of a widely tunable phase-based beamformer for phased array antennas using a new technique to cross-polarized the carrier and the sideband, in order to allow the phase control by means of a spatial light modulator, is experimentally demonstrated. The technique relies on the combination of single sideband amplitude modulation (SSB) using a Mach-Zehnder modulator (MZM) and birefringence (to cross-polarized the carrier and the sideband). The architecture has the potential of controlling multiple independent beams simultaneously. The beamformer feeds an eight elements array showing an insertion loss and a reset speed of around 12 dB and 70 ms, respectively. Far-field antenna patterns between 7.5 GHz and 8.5 GHz for nine elevation angles within a range of ±20° have been measured showing beam steering capability, amplitude distribution weighting as well as multibeam operation.     

On-line reversed-phase liquid chromatography-gas chromatography coupled to mass spectrometry for enantiomeric analysis of chiral compounds in fruit beverages

A method based on the on-line coupling of reversed phase liquid chromatography with gas chromatography/mass spectrometry (RPLC-GC-MS) for the chiral evaluation of characteristic constituents of fruit beverage aroma was investigated. The consideration of a variety of parameters involved in the transfer step allowed to achieve relative standard deviations ranging from 0.4 to 10% in most cases and detection limits from 0.2 to 2.5 mg/l. By applying the developed method to fruit beverages, racemic mixtures of ethyl 2-methylbutanoate and gamma-nonalactone were found. This fact suggests the eventual addition of artificial aromas. The method proposed in the present work can be useful to assess reliably the authenticity of aqueous samples, such as fruit beverages.     

Polydimethylsiloxane as a packing material in a programmed temperature vaporizer to introduce large-volume samples in capillary gas chromatography

The viability of using polydimethylsiloxane (PDMS) as a retaining material inside a programmed temperature vaporizer injector for the introduction of large-volume samples in gas chromatography is assessed. To that end, materials made up of Volaspher A-2 and coated with different percentages of PDMS (5%, 15%, and 50%) are considered. In addition, adsorbent (Tenax TA) and absorbent (PDMS) materials are comparatively studied in terms of their retention capacity. A relative standard deviation lower than 5.0% is obtained from the injection of PDMS, whereas values up to 49% are provided by Tenax TA. Significantly higher amounts of different volatile compounds are retained by PDMS in comparison with Tenax TA. In conclusion, the use of PDMS as a packing material seems to be viable for large-volume sampling and particularly recommendable for minor compounds occurring in complex matrices.     

Multiobjective evolutionary optimisation for surface-enhanced Raman scattering

In most optimisation experiments, a single parameter is first optimised before a second and then third one are subsequently modified to give the best result. By contrast, we believe that simultaneous multiobjective optimisation is more powerful; therefore, an optimisation of the experimental conditions for the colloidal SERS detection of l-cysteine was carried out. Six aggregating agents and three different colloids (citrate, borohydride and hydroxylamine reduced silver) were tested over a wide range of concentrations for the enhancement and the reproducibility of the spectra produced. The optimisation was carried out using two methods, a full factorial design (FF, a standard method from the experimental design literature) and, for the first time, a multiobjective evolutionary algorithm (MOEA), a method more usually applied to optimisation problems in computer science. Simulation results suggest that the evolutionary approach significantly out-performs random sampling. Real experiments applying the evolutionary method to the SERS optimisation problem led to a 32% improvement in enhancement and reproducibility compared with the FF method, using far fewer evaluations.     

Pore-size distributions of cationic polyacrylamide hydrogels of different compositions maintained at the same swelling capacity

Pore-size distributions have been measured for cationic acrylamide-based hydrogels of different compositions maintained at the same swelling capacity (27.8 ± 0.7 g swollen gel/g dry gel) by varying the ionic strength of the surrounding solution. Swelling equilibria were measured at about 6°C in pure water and aqueous sodium azide solutions ranging in concentration from to 10^?3 to 10^?1 M. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve, which represents the amount of imbibed liquid inside the gel inaccessible to a solute of radius r. The pore-size distribution was obtained by using Casassa's Brownian-motion model and numerically solving the Fredholm integral equation. The modes of the pore radii range from 20.4 to 47.1 Å for acrylamide-based hydrogels containing varying amounts of cationic comonomer (1.5 and 4.0 %M), crosslinker (0.3 and 1.0 %C), and initial concentration of total monomer (15 and 35 % T).     

Numerical aspects of Mathieu eigenvalues

Rendiconti del Circolo Matematico di Palermo Series 2 -     

A multi‐component optimisation of experimental parameters for maximising SERS enhancements

We present a multi‐component optimisation strategy for a range of commonly used Ag colloids as surface‐enhanced Raman scattering (SERS) spectroscopy substrates. The concentration‐dependent interactions of a wide range of parameters, including colloid and aggregating agent species, were considered in order to achieve optimal SERS enhancements. Few papers in the literature discuss the optimisation of these parameters, never mind multi‐component optimisation, and suboptimal responses result in SERS not being utilised to its true capabilities. Significant differences in enhancement factor were observed as a consequence of colloid–aggregating agent interactions and these are shown to be analyte specific. Both the cation and anion of the aggregating agent were found to play an important role in the optimisation process. We show that through the optimisation of experimental conditions, the reliability and applicability of SERS can be significantly improved. Copyright © 2009 John Wiley & Sons, Ltd.