Electrode commutation sequence for honeycomb arrangement of electrodes in electrochemotherapy and corresponding electric field distribution

Electrochemotherapy is a treatment based on combination of chemotherapeutic drug and electroporation. It is used in clinics for treatment of solid tumours. For electrochemotherapy of larger tumours multiple needle electrodes were already suggested. We developed and tested electrode commutation circuit, which controls up to 19 electrodes independently. Each electrode can be in one of three possible states: on positive or negative potential or in the state of high impedance. In addition, we tested a pulse sequence using seven electrodes for which we also calculated electric field distribution in tumour tissue by means of finite-elements method. Electrochemotherapy, performed by multiple needle electrodes and tested pulse sequence on large subcutaneous murine tumour model resulted in tumour growth delay and 57% complete responses, thus demonstrating that the tested electrode commutation sequence is efficient.     

Wave-mechanical theory of field ionization and field-ion energy distributions

Although field-ion energy distributions have been measured for many years, no theoretical treatment has ever been published that is strictly compatible with the axioms of quantum mechanics. This article shows how a fully wave-mechanical theory of field ionization and field-ion energy distributions can be constructed, based on the idea that surface field ionization is the fermion analogy for Dirac's treatment of photon emission. The theory is formal and suggests, as expected, that existing quasiclassical treatments are essentially satisfactory in normal circumstances.The discussion comprises of three main steps. The first is to clarify the various definitions of energy and potential used in field-ion theory, and to codify the corresponding energy diagrams. The second is to derive and expression for the rate-constant for transfer from one vibrational state to another. The third is to sum over initial states to derive a formal expression for the ion energy distribution. The article concludes by discussing the possible development of this theory.     

Electrical field influence on molecular mass and electrical conductivity of polyaniline

We have described the primary studies on the conductivity and molecular weight of polyaniline in an electric field as it is used in a field effect experimental configuration. We report further studies on doped in-situ deposited polyaniline. First we have chemically synthesized polyaniline by ammonium peroxodisulfate in an acidic solution, with aqueous, organic and emulsion conditions at different times. Next, we measured mass and conductivity and obtained the best time of polymerizations. Then, we repeated these reactions under different electrical fields in constant time and measured mass and conductivity. The polyaniline is characterized by gel permeation chromatography (GPC), UV-visible spectroscopy and electrical conductivity. Polyanilines with high molecular weight are synthesized under electric field M _w = (5.2–6.8) × 10⁵, with M _w/M _n = 2.0–2.5. The UV-visible spectra of polyanilines oxidized by ammonium peroxodisulfate and protonated with dodecylbenzenesulfonic acid (PANi-DBSA), in N-methylpyrolidone (NMP) show a smeared polaron peak shifted into the visible. Electrical conductivity of polyaniline has been studied by four-probe method. The conductivity of the films of emeraldine protonated by DBSA cast from NMP is higher than 500 S/cm under (10 kV/cm² of potential) electric field and shows an enhanced resistance to ageing. Next, we carried chemical polymerization at the best electric field at different times. Finally, the best time and amount of electric field were determined. Polymers synthesized under an electric field probably have better physical properties regarding the existence of less branching and high electric conductivity.     

Simulation of non-equilibrium energy distributions of current carriers in proton-conducting oxides with perovskite structure

A simulation method based on the integral equation for the sticking probability of ion in well was discussed for its application to study energy distributions of protons carried in simple and complex perovskite-like structures. In the terms of the Wiener—Hopf computational technique, a numerical algorithm was developed to detect deviations of the energy distribution function from the Boltzmann distribution near the potential barrier peak due to random interaction of ion with the nearest environment. Being considered as non-equilibrium in this sense, the derived distributions essentially deviated from the equilibrium distribution for a wide energy loss range of protons carried from one lattice position to another. The developed simulation algorithm may be of methodological interest in general practice for numerical solution of the Wiener—Hopf equations, because the known solution techniques for integral equations of this type are inapplicable to the studied problems of electrochemical kinetics due to their essentially different boundary conditions.     

Use of electron charge and current distributions in the determination of atomic contributions to magnetic properties

It is shown how the electron charge and current distributions, which Professor McWeeny describes as fundamental property densities, may be used to determine the atomic and group contributions to magnetic response properties. © 1996 John Wiley & Sons, Inc.     

Electrical field induced phase-matched second harmonic generation in low Tg polymer waveguides

Second-harmonic generation in the guided waveguide configuration is very attractive because a high fundamental power density can be coupled over long propagation length therefore remarkably high conversion efficiencies can be expected compared to bulk materials.¹ Organic SHG devices in optical waveguides have not been developed extensively because of the difficulty encountered in phase-matching. To avoid this problem, the use of an artificial periodic structure, Cerenkov radiation, and non-colinear light path geometry have already been demonstrated. Recently, we reported an electric field-induced dynamic phase-matching in a guided wave configuration using a main-chain polymer in which the effective phase-matching thickness can be controlled by an applied electric field.² This technique is able to increase the waveguide dimension tolerances of phase-matching condition. In the case of a main-chain polymer, the thermal optic effects due to the heating prevent to satisfy the optimum phase-matching conditions, which causes a reduction in the conversion efficiency of devices. In order to overcome this problem, we have synthesized novel low glass transition temperature (Tg) nonlinear optical (NLO) polymers. In this presentation, we will discuss an electric field-induced dynamic phase-matching of a multilayer waveguide at room temperature using a low Tg NLO polymer which can increase both the waveguide dimension tolerances and overlap integral. Using this technique, efficient phase-matched SHG was generated from p-nitroaniline grafted NLO materials. The dimension tolerance of waveguides under an electric field will be described.     

Direct measurement of colloidal particle rotation and field dependence in alternating current electrohydrodynamic flows

We have measured the influence of both applied alternating current (AC) field strength and frequency on the electrohydrodynamic (EH) flows present in colloidal systems near an electrode surface. The effect of the flows is visualized by the rotation of the colloids, fluorescently labeled by a novel technique involving EH-driven aggregation of much smaller tracer colloids to the surface of the larger colloids. Our results show an E2 dependence of these flows, consistent with an induced charge mechanism for effective colloidal interactions. We have also observed a crossover in frequency that suggests a change in the origin of the induced charge, consistent with predictions from available theory. The EH flows appear to be hydrodynamically screened inside clusters, as evidenced by the lack of rotation of interior colloids and the cluster-size independent rotation rate of colloids on the boundary.     

Effectiveness of tumor electrochemotherapy as a function of electric pulse strength and duration

The aim of this study was to evaluate the effectiveness of electrochemotherapy (ECT) as a function of various combinations of pulse strength and duration. C57Bl mice bearing LLC tumors were injected i.p. with bleomycin (BLM) at doses 5 mg/kg in 0.2 ml of physiological saline. Thirty minutes later, tumors were positioned between plate electrodes and were pulsed with eight-square wave electric pulses with an individual pulse strength of 900, 1100, 1300 or 1500 V/cm and duration of 0.1, 0.25, 0.5 or 1 ms. Effectiveness of ECT was estimated by measuring inhibition of tumor growth and by estimating extent of necrosis in histological slices of the treated tumors. At pulse strength of 900 V/cm and duration of 0.1 ms, electrochemotherapy was ineffective. Noticeable inhibition of tumor growth (threshold of ECT) was obtained when pulse duration at this field strength was increased up to 0.25 ms. Further increase of pulse strength and/or duration resulted in progressive enhancement of antitumor effects. Using tumor doubling time (DT) as a criteria, we showed that the same efficacy of ECT could be achieved using various pairs of values for pulse strength and duration. Largest antitumor efficacy of ECT was obtained at pulse strength of 1500 V/cm and duration of 1 ms. These pulse conditions applied alone neither significantly suppressed tumor growth nor induced noticeable side effects of the surrounding tissues. The results of this study thus suggest that the effectiveness of electrochemotherapy can be enhanced (in comparison to widely accepted conditions of electrochemotherapy--8 pulses of 1300 V/cm, 0.1 ms) if 1500-V/cm, 1-ms electric pulses are used. Our study also implicates that other pulse conditions could be found for this enhanced ECT.     

Droplet fusion by alternating current (AC) field electrocoalescence in microchannels

We present a system for the electrocoalescence of microfluidic droplets immersed in an immiscible solvent, where the undeformed droplet diameters are comparable to the channel diameter. The electrodes are not in direct contact with the carrier liquid or the droplets, thereby minimizing the risk of cross-contamination between different coalescence events. Results are presented for the coalescence of buffered aqueous droplets in both quiescent and flowing fluorocarbon streams, and on-flight coalescence is demonstrated. The capillary-based system presented here is readily amenable to further miniaturization to any lab-on-a-chip application where the conductivity of the droplets is much greater than the conductivity of the stream containing them, and should aid in the further application of droplet microreactors to biological analyses.     

Determination of radical re-encounter probability distributions from magnetic field effects on reaction yields

Measurements are reported of the effects of 0-23 mT applied magnetic fields on the spin-selective recombination of Py*- and DMA*+ radicals formed in the photochemical reaction of pyrene and N,N-dimethylaniline. Singlet <--> triplet interconversion in [Py*- DMA*+] radical pairs is probed by investigating combinations of fully protonated and fully deuterated reaction partners. Qualitatively, the experimental B1/2 values for the four isotopomeric radical pairs agree with predictions based on the Weller equation using known hyperfine coupling constants. The amplitude of the "low field effect" (LFE) correlates well with the ratio of effective hyperfine couplings, aDMA/aPy. An efficient method is introduced for calculating the spin evolution of [Py*- DMA*+] radical pairs containing a total of 18 spin-1/2 and spin-1 magnetic nuclei. Quantitative analysis of the magnetic field effects to obtain the radical re-encounter probability distribution f (t )-a highly ill-posed and underdetermined problem-is achieved by means of Tikhonov and maximum entropy regularization methods. The resulting f (t ) functions are very similar for the four isotopomeric radical pairs and have significant amplitude between 2 and 10 ns after the creation of the geminate radical pair. This interval reflects the time scale of re-encounters that are crucial for generating the magnetic field effect. Computer simulations of generalized radical pairs containing six spin-1/2 nuclei show that Weller's equation holds approximately only when the radical pair recombination rate is comparable to the two effective hyperfine couplings and that a substantial LFE requires, but is not guaranteed by, the condition that the two effective hyperfine couplings differ by more than a factor of 5. In contrast, for very slow recombination, essentially any radical pair should show a significant LFE.     

Magnetic field effects on emission and current in Alq3-based electroluminescent diodes

The light output and the current driving tris-(8-hydroxyquinolinato) aluminum (III) (Alq₃)-based light-emitting-diodes were found to increase by up to 5% and 3%, respectively, as an external magnetic field increased to 300 mT. The positive magnetic-field effects were sensitive to the applied voltage. These observations made clear that the emissive singlet exciton formation proceeds via a correlated electron–hole pair state and the excitonic injection of electrons contributes to the driving current, the concentration of singlet excitons being modulated by the hyperfine scale magnetic-field-dependent mixing of singlet and triplet pair states constituting precursors of molecular excitons.     

On the correlation between emitter heating current and emitter temperature in field desorption mass spectrometry

Calibration curves have been established that give an estimate of the temperature in the emission region of high temperature activated field desorption emitters. Two characteristic types of field anodes have been investigated: (1) emitter wires carrying microneedles of 25 to 30 μm length, preferentially used for field desorption of organic compounds; (2) emitters with microneedles of 50 to 60 μm length, which are used for the investigations of polymers by pyrolysis field desorption mass spectrometry.     

Electrical field distribution on the cross-linked polyethylene insulation surface under partial discharge testing

Cross-linked polyethylene (XLPE) insulated power cables are widely used in transmission and distribution networks. The enhanced localised electrical field/stress can result in surface discharges (SD), i.e. partial discharges on the surface of the dielectric. To measure discharges, very low frequency (VLF-0.1 Hz or lower) excitation has emerged as an attractive alternative to the conventional power frequency (PF- 50/60 Hz) testing as it significantly reduces the required reactive power from the test supply. As the discharge process mainly resulted from the enhanced electric stress; it is necessary to understand how the electric field distributes on the XLPE dielectric surface when it is exposed to a high voltage AC excitation. In this study, the distribution of surface electric field before, during and after a PD event at VLF and PF test voltage is investigated. Finite element analysis (FEA) based numerical simulation shows that the space charge dynamics cause the differences in the field distribution and supports the experimental results.     

Classical motion of a charged particle in the magnetic field of a rectilinear current

We investigate the classical dynamics of charged particles with spin 0 or spin 1/2 in the magnetic field of a rectilinear current filament. It is shown that the motion is confined in the direction perpendicular to the wire. For initial velocities not too great compared to a scaling velocity _scal , an analytic solution of the equations of motion is possible.     

The influence of polymer molecular-weight distributions on pulsed field gradient nuclear magnetic resonance self-diffusion experiments

 The influence of polymer molecular-weight distributions on the outcome of pulsed field gradient (PFG) NMR self-diffusion experiments has been considered. The self-diffusion coefficient, D, of monodisperse poly(ethylene oxide) (PEO) polymers has been determined in order to accurately determine the scaling behavior of D both with molecular weight and concentration. In order to investigate the influence of polydispersity on the PFG NMR signal, a model system consisting of ten reasonably monodisperse PEO polymers was made, and the PFG NMR signal intensities were recorded at a low total concentration. The data were analyzed using both inverse Laplace transformation and nonlinear least-squares fitting to a prescribed distribution function of D. Finally, the molecular-weight distribution was obtained by use of the values of the scaling parameters. We also present some model calculations used to investigate the sensitivity of the degree of polydispersity on the NMR signal decays. Received: 27 May 1999 Accepted in revised form: 19 October 1999     

Non-catalytic and template-free growth of aligned CdS nanowires exhibiting high field emission current densities

Various CdS nanostructures, including nanoparticle film, bundles of quasi-aligned and well-aligned nanowires, were fabricated with a non-catalytic and template-free MOCVD process. The well-aligned CdS nanowires exhibit unusually high field emission current densities of 225 mA cm(-2) at the applied electric field of 20 V microm(-1).     

Polarization of a diffuse soft particle subjected to an alternating current field

The polarization of a diffuse soft particle submerged in an aqueous electrolyte and subjected to a uniform alternating electric field is theoretically analyzed with the standard electrokinetic model (the Poisson-Nernst-Planck equations). The particle consists of a rigid uncharged core and a charged diffuse polyelectrolytic shell (soft layer) permeable to ions and solvent. Our focus is on the impact of the characteristics of the soft layer including the Donnan potential, the soft layer thickness, and the friction coefficient of the soft layer on the dipole coefficient, characterizing the strength of the polarization. Under the limits of thin double layers and thin polyelectrolytic shells, approximate analytical expressions to evaluate the dipole moment coefficients are derived for high-frequency and low-frequency ranges, respectively. The analytical results are compared and agree favorably with those numerically computed by the standard model. Interestingly, we discover that when the double layer is comparable to the soft layer the dipole moment behaves qualitatively differently at different Donnan potentials. When the Donnan potential is small, the dipole moment decreases as the double layer increases. In contrast, at large Donnan potentials, the dipole moment increases with the increase in the double layer. The distinct responses to Donnan potentials are attributed to the impact of the associated double layer on the charge distribution of mobile ions inside the soft layer. The theoretical model provides a fundamental basis for interpreting the polarization of heterogeneous systems, including environmental or biological colloids or microgel particles.     

Bubble-size distributions in foams

Bubble-size distributions in foams can be used to study foam properties and to distinguish between the physical processes that contribute to the breakdown of the foam. These processes are drainage, coalescence and disproportionation. A new Foam Analyzer was developed to measure various foam characteristics like the rate of drainage, the rate of foam collapse, the gas fraction in the foam and the bubble-size distribution.