We demonstrate that micrometre and sub-micrometre particles can be trapped, aggregated and concentrated in planar quadrupole electrode configurations by positive and negative dielectrophoresis. For particles less than in diameter, concentration is driven by thermal gradients, hydrodynamic effects and sedimentation forces. Liquid streaming is induced by the AC field itself via local heating and results, under special conditions, in vortices which improve the trapping efficiency. Microstructures were fabricated by electron-beam lithography and modified by UV laser ablation. They had typical gap dimensions between 500 nm and several micrometres. The theoretical and experimental results illustrate the basic principles of particle behaviour in ultra-miniaturized field traps filled with aqueous solutions. The smallest single particle that we could stably trap was a Latex bead of 650 nm. The smallest particles which were concentrated in the central part of the field trap were 14 nm in diameter. At high frequencies (in the megahertz range), field strengths up to 56 MV can be applied in the narrow gaps of 500 nm. Further perspectives for microparticle and macromolecular trapping are discussed.

Electrorotation (ROT) has been applied widely for determining the dielectric properties of cells (and bio-particles) with single-cell resolution. However a serious limitation of ROT has been the tedious manual measurements required. A new real-time PC-based machine vision algorithm and hardware implementation are presented that achieve measurements of cell rotational motion and analysis of ROT spectra. The system is equipped with a computer-controlled quadrature digital synthesizer and is capable of measuring a ROT spectrum of a single cell with the frequency range 1 kHz-200 MHz in less than 5 min, taking four measurement points per frequency decade. Laser tweezers are used to facilitate cell selection and positioning in order to maximize the flexibility and accuracy of the system. The performance of this system is characterized in terms of robustness, accuracy and linearity with respect to manual measurements of real spinning cells under the influence of a rotating electric field. The system is quite generally applicable to a wide variety of mammalian cell morphologies and optical appearances. Membrane capacitance values derived from automated ROT measurements averaged within 10% of those obtained from manual measurements.

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In this paper, we extend and improve the formal, executable framework for automated multi-issue negotiation between two autonomous competitive software agents proposed by Cadoli. This model is based on the view of negotiation spaces (or “areas”), representing the admissible values of the goods involved in the process as convex regions. However, in order to speed up the negotiation process and guarantee convergence, there was the restriction of potential agreements to vertices included in the intersection of the two areas. We present and assess experimentally an extension to Cadoli's approach where, for both participating agents, interaction is no longer vertex based, or at least not necessarily so. This eliminates the asymmetry among parties and the limitation to polyhedral negotiation areas. The extension can be usefully integrated to Cadoli's framework, thus obtaining an enhanced algorithm that can be effective in many practical cases. We present and discuss a number of experiments, aimed at assessing how parameters influence the performance of the algorithm and how they relate to each other. We discuss the usefulness of the approach in relevant application fields, such as, for instance, supply chain management in the fashion industry, which is a field of growing importance in economy and e-commerce.

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