Hz AC Field Research Articles

Electroformation of liposomes and phytosomes using copper electrode

A novel method for electroformation of liposomes and phytosomes using copper electrode is described. Liposomes made at 2 V and 10 Hz AC field from L-α-egg-phosphatidylcholine (egg-PC), K. pneumoniae phosphatidylethanolamine, K. pneumoniae polar lipids and E. coli polar lipids on copper electrode were (777.9 ± 118.4), (370.2 ± 100.5), (825.3 ± 21.54), and (281.3 ± 42.3) nm in diameter, respectively. Giant vesicles were formed at 30 V and 10 Hz AC field from polar lipids of K. pneumoniae and E. coli were (106 ± 29.7) and (86 ± 24.3) µm in diameter, respectively. All liposomes were unilamellar as indicated by their unilamellar indices of 50 ± 2, had surface charge comparable to vesicles made from lipid(s) with similar composition and exhibited only 1–2 mol% of oxidized lipids. Cu concentration in the liposomal samples was <1.5 ppm for large unilamellar vesicles (LUVs) and ˂5 ppm for giant unilamellar vesicles (GUVs). The vesicles were stable for >15 d without loss of their size, charge, or unilamellarity. The method was successfully applied to prepare phytosomes from egg-PC and a phytochemical fraction of Dimorphocalyx glabellus, a medicinal plant with anti-diuretic properties. Phytosomes formed were 1000–1500 nm in diameter and exhibited altered fluorescence and absorbance properties compared to the unencapsulated phytochemical. Phytosomes with phytochemical: egg-PC ratio from 0.15 to 1.5 had encapsulation efficiency ranging 90–30%, respectively, and was stable for 1 month. Our method is easy, inexpensive and convenient that will prove to be useful for preparation of liposomes and phytosomes.

Space Charge Behavior in Ethylene Propylene Rubber Under a 50-Hz AC Electric Field

In this study, the space charge behavior in ethylene propylene rubber (EPR) under a 50-Hz AC field is studied based on the variation of space charge response, FTIR spectra and impurity contents inside EPR with thermal treatment. The space charge was detected with the pulsed electroacoustic (PEA) method and the phase shift of detecting pulse under 50 Hz AC field was realized according to the automatic equal phase shift (AEPS) principle. The results show three main types of impurities in untreated EPR. Three distinct regions of space charge distribution are seen in untreated EPR under a 50-Hz AC field. The mean phase density of space charge ρ θ is increased with the enhancement of the applied field from 15 to 61 kV/mm. The maximum electric field distortion rate of untreated EPR tends to rise first and then decrease, ranging from 6.65% to 31.87%. The impurity content and the ρ θ decreased significantly for EPR thermal treated at 150 °C for 18 h. Corresponding, the maximum electric field distortion rate is effectively reduced to 0.66%. Finally, the space charge source and migration process are speculated based on the diffusion trend of the space charge isodensity line and the migration direction of various charges under the electric field.

Optimal Anti-Noise Ability and High Sensitivity in Magnetic Nanothermometry

In this study, we present a novel noninvasive and real-time magnetic nanothermometry (MNTM) using both odd and even harmonics of magnetic nanoparticles (MNPs) under low frequency ( f = 117 Hz) ac and dc magnetic fields. Based on the first-order Langevin function, the mathematical models of weighted amplitude summation of odd and even harmonics of MNPs are proposed. Antinoise ability and sensitivity of MNTM determined by saturation magnetization, $M_{s}$ , and particle diameter, D , are discussed in detail to provide guidance for the synthesis of temperature-sensing MNPs applied in different temperature ranges. We have found that the method presented in this study has better antinoise ability, and MNPs ( $M_{s} = 477$ kA/m) with diameters of approximately 25 nm are more suitable for temperature probing in physiological temperature range. Experimental result shows that the maximum temperature measurement error of this novel method is below 0.28 K with a standard deviation of 0.09 K in 1 s measurement.

Influence of magnetic fields on the hydration process of amino acids: Vibrational spectroscopy study of L‐phenylalanine and L‐glutamine

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to investigate the effect of weak electromagnetic fields on the structure of L-glutamine (L-Gln) and L-phenylalnine (L-Phe) in aqueous solution. It has been found that the exposure to a DC field or a 50 Hz AC field, for a short time induces modifications in the spectra of exposed samples in agreement with our preceding observations on glutamic acid. Furthermore, the acid-base equilibrium has been investigated by using the ratio of the intensity of the deprotonated on protonated species. In the case of L-Phe, the exposure induces a measurable shift of acid dissociation constant pKa1 out of the experimental errors, while in case of L-Gln, the effect is under the limit detectable with this method. The phenomenon of the shift of the acid-base equilibrium has been connected elsewhere to modification of the water-water hydrogen bonds in the water around both the backbone and the residue (R). Here we suggest that the magnetic field modifies the water structure around the molecules and changes the hydrophobic interactions allowing the molecules of amino acids to aggregate. The differences observed in the behavior of L-Phe and L-Gln may be related to the differences in the polarity of their residues.

Equivalence of AC and DC electric field on retarding grain growth in yttria-stabilized zirconia

It is shown that the full-cycle mean value of a 60 Hz AC field is equivalent to a DC field in its effect on retarding grain growth in 3 mol.% yttria-stabilized zirconia. This equivalence is in keeping with the proposed physical mechanism for the retardation at E < ∼30 V cm−1. A second decrease in the grain size with field occurs at a mean AC field of ∼100 V cm−1, which may be the precursor for “flash” sintering.

Design, fabrication and application of an SOI-based resonant electric field microsensor with coplanar comb-shaped electrodes

This paper presents a highly sensitive resonant electric field microsensor based on silicon on insulator (SOI) technology. To improve the electric field coupling effect, the microsensor uses coplanar shutter electrodes and sense electrodes. To obtain higher conversion gain, both electrodes adopt novel comb-shaped structures. A finite element method (FEM) was used to simulate and optimize the structures of the comb-shaped electrodes. The sensitivity model of the microsensor was analyzed by the conversion gain of the vibration-amplitude-to-charge variation. The resolution of the microsensor is approximately 40 V m−1 with an uncertainty of 1% for the dc field, while the resolution is better than 10 V m−1 for the 50 Hz ac field. The microsensors were packaged and assembled to form an electric field probe to measure the atmospheric electric field. The test results showed that the probe precisely detected the occurrence of thunderstorms, and the plotted data agreed well with those of the conventional electric field mill.

Enhanced sintering rate of zirconia (3Y-TZP) by application of a small AC electric field

A small initial electric field E 0 = 13.9 V cm −1 enhanced the sintering rate of zirconia (3Y-TZP) powder, with a 60 Hz AC field having a greater effect than a DC field. The enhancement with both fields was in accord with the retardation of grain growth observed directly by scanning electron microscopy and with that which occurred during grain growth and plastic deformation. Some factors which could contribute to the observed behavior are given.

Effect of electropulsing on the tensile flow stress of ultrafine-grained 3Y-TZP at 1400°C

AbstractShort DC pulses (∼10– 4s duration with a maximum electric field strength of 2.0 – 9.3 kV cm– 1) applied continuously at a frequency of 10 Hz reduced the tensile flow stress of ultrafine-grained 3Y-TZP at 1400 °C. The decrease in flow stress was attributed to a retardation of dynamic grain growth by the average electric field. The degree of retardation decreased with strain, which correlated with the calculated reduction in electric field strength due to the change in dimensions of the specimen as it elongates. Considering the present electropulsing results along with those obtained previously employing DC and 60 Hz AC fields, it was found that the ratio of the decrease in grain size with field to the grain size without field, was proportional to the average effective electric field strength, relatively independent of test temperature in the range of 1400 – 1500 °C. The proportionality constant increased in the order DC, AC, EP, indicating that a varying field has a greater effect on retarding dynamic grain growth than a constant DC field.

In vitro modulation of endogenous rhythms by AC electric fields: Syncing with clinical brain stimulation

Humans are exposed to an increasing prevalence of weak and strong AC electric fields, as part of daily life in the modern world. Further, electric fields are being deployed to modulate brain function for research and clinical applications. A single electric field pulse, applied via transcranial electrical or magnetic stimulation, can transiently excite or disrupt activity in neural circuits. In contrast, extended exposure to steady electric fields or pulse trains can result in long-term effects on neural activity including potentiation or depression. In addition, it has been demonstrated that brain stimulation with electric fields can improve cognitive performance in normal subjects (Marshall et al. 2006). The impact of electric fields on brain function has motivated the development of therapies to treat a wide range of psychiatric and neurological diseases using transcranial electrical or magnetic stimulation (Wassermann & Lisanby, 2001), as well as deep brain stimulation with implanted electrodes. The mechanisms by which electric fields affect brain function have not been fully elaborated. A recent report in The Journal of Physiology by Deans et al. (2007) presents new data on the interaction of AC electric fields down to a cellular level as well as with neuronal population dynamics. The report reveals a frequency-specific ability of AC electric fields to rhythmically polarize pyramidal neurons of the CA3 region of the hippocampus and demonstrates the ability of AC fields to alter pharmacologically induced endogenous oscillations in the hippocampus. These data have important implications for understanding the effect of environmental AC fields and therapeutic stimulation on the activity of neuronal ensembles. A central finding of this study is that an AC electric field, applied in vitro to a brain slice set to oscillate in the gamma frequency range through bath application of kainate, shifts the ongoing oscillation to centre on the applied field frequency or a subharmonic of that frequency. This review of Deans et al. (2007) is intended to elucidate the connection between their work and other recent in vitro findings concerning electric fields in the brain with some recent clinical findings pertaining to cognitive function and electric fields.

Using nonlinear ac electrokinetics vortex flow to enhance catalytic activities of sol-gel encapsulated trypsin in microfluidic devices.

A novel microstirring strategy is applied to accelerate the digestion rate of the substrate N(alpha)-benzoyl-L-arginine-4-nitroanilide (L-BAPA) catalyzed by sol-gel encapsulated trypsin. We use an ac nonlinear electrokinetic vortex flow to stir the solution in a microfluidic reaction chamber to reduce the diffusion length between the immobilized enzyme and substrate in the solution. High-intensity nonlinear electroosmotic microvortices, with angular speeds in excess of 1 cms, are generated around a small ( approximately 1.2 mm) conductive ion exchange granule when ac electric fields (133 Vcm) are applied across a miniature chamber smaller than 10 mul. Coupling between these microvortices and the on-and-off electrophoretic motion of the granule in low frequency (0.1 Hz) ac fields produces chaotic stream lines to stir substrate molecules sufficiently. We demonstrate that, within a 5-min digestion period, the catalytic reaction rate of immobilized trypsin increases almost 30-fold with adequate reproducibility (15%) due to sufficient stirring action through the introduction of the nonlinear electrokinetic vortices. In contrast, low-frequency ac electroosmotic flow without the granule, provides limited stirring action and increases the reaction rate approximately ninefold with barely acceptable reproducibility (30%). Dye molecules are used to characterize the increases in solute diffusivity in the reaction reservoir in which sol-gel particles are placed, with and without the presence of granule, and compared with the static case. The solute diffusivity enhancement data show respective increases of approximately 30 and approximately 8 times, with and without the presence of granule. These numbers are consistent with the ratios of the enhanced reaction rate.

Nonlinear dielectric properties and temperature stabilization effect near the ferroelectricphase transition in sodium trihydrogen selenite

The ferroelectric phase transition of crystalline sodium trihydrogen selenite has beencharacterized by domain observations and measurements of electric permittivity,pyroeffect and spontaneous polarization. The first-order character of the phasetransition is clearly demonstrated by the phase coexistence and temperatureautostabilization. The considerable heating effect at 50 Hz ac field is described. Theelectric field effect on the temperature variation of the electric permittivity, inthe phase transition region, shows a considerable domain structure contributionto the permittivity value. It is demonstrated that the dielectric properties ofx- andy-samples can be described by classical dielectric state equations: theset of coefficients has been determined. It is concluded that thex-component of spontaneous polarization plays a predominant role in the phase transition.

AC Poling study of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites

It is experimentally known that a polymer matrix phase in a composite of ferroelectric particles dispersed in a ferroelectric polymer can be polarized by using a few cycles of an ac field, without causing much disturbance to the state of polarization of the inclusion particles. This paper attempts to investigate this special poling process for a typical ferroelectric composite system of lead zirconate titanate (PZT) ceramic particles in a vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) copolymer matrix, upon the application of 10 Hz ac fields of various amplitudes. Compared to a copolymer sample, the composite samples can be polarized at a lower field, and hence show a larger “remanent” polarization at the same poling field. Among the composites, the observed “remanent” polarization increases with increasing ceramic volume fraction. These experimental observations can be understood by a simple model, in which space charges are allowed to accumulate at the particle-matrix interfaces because of the electrical conductivity of the constituents. At a fast switching poling field of 10 Hz, the calculation shows that conductivity and charge accumulation effects in the composite are only minimal. Accordingly, although the PZT phase as well as the copolymer phase are both polarized under the ac field, the ceramic phase is only polarized to about 10% when the copolymer phase is almost fully polarized. Thus, one can still use an ac field to polarize only the copolymer phase of the composite without altering the polarization state of the ceramic phase significantly.

Electric field sensor using electrostatic force deflection of a micro-spring supported membrane

An electric field sensor is shown which uses a micromachined micro-spring supported membrane as the sensing element. The sensing mechanism involves electrostatic force to deflect the membrane, and an optical position sensor to measure membrane movement. Measurement resolution was 5 kV/m for a dc field and 140 V/m for a 49 Hz ac field. It is shown that a bias voltage applied to the membrane can be used to increase measurement sensitivity. With a 17 kV/m dc bias field, a 0.3 V/m ac field at 97 Hz was detectable.

Eddy Current Effect of Magnets for J-PARC 3-GeV Synchrotron

The 3-GeV synchrotron proposed in the JAERI/KEK Joint Project (J-PARC) is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400-MeV to 3-GeV at a repetition rate of 25-Hz. The 3-GeV synchrotron is used to produce pulsed spallation neutrons and muons. It also works as an injector for a 50-GeV synchrotron. Since the magnets for the 3-GeV synchrotron are required to have a large aperture in order to realize the large beam power of 1 MW, there is a larger fringing field at a pole end than for a usual synchrotron magnet. In addition, the 25 Hz ac field induces eddy currents in magnet components: e.g., in the coil, magnet end plates, etc. The eddy current induced in the end plates is expected to be large. Therefore, it is important to investigate the effect of large leakage field and eddy current on the beam motion around the magnet end part. We have measured the eddy loss and the eddy current field at the edges of the dipole and quadrupole magnets. In this paper, we report the comparison between the results of the measurements and the two-dimensional eddy current model developed for this study.

Microfluidic Mixing by dc and ac Nonlinear Electrokinetic Vortex Flows

A novel micromixing strategy is proposed for microfluidic applications. High-intensity nonlinear electroosmotic microvortices, with angular speeds in excess of 1 cm/s, are generated around a small (∼1 mm) conductive ion-exchange granule when moderate dc and ac electric fields (30−125 V/cm) are applied across a miniature chamber smaller than 10 μL. Coupling between these microvortices and the fast electrophoretic motion (∼1 cm/s) of the granule in low frequency (between 0.3 and 1.0 Hz) ac fields and a slower backflow vortex (velocity ∼1 mm/s) in dc fields produces an intense chaotic micromixing action. Two segregated dye samples, normally requiring nearly 0.5 h to mix by diffusion, are observed to mix within 30 s in the mixing chamber. The effective diffusivity scales as E2 and is measured to be 2 orders of magnitude higher than molecular diffusivity at reasonable field strengths and optimal frequencies. The main vortices are generated by nonlinear versions of the Smoluchowski slip velocity on the granule ...

Stretching of megabase-sized deoxyribonucleic acid molecules by tuning electric-field frequency

Despite the technical difficulties of dealing with chromosome deoxyribonucleic acid (DNA) molecules, over a megabase pair (Mbp) in size, yeast chromosome DNA molecules, over hundreds of micrometers in length, were stretched from random coil conformation within a few minutes by careful tuning of the ac field frequency in a 1% agarose gel. This rapid and efficient stretching method was accomplished by a combination of optimal conditions for the stretching process and maintenance of stretched conformation. In the stretching process, Mbp DNA gets easily trapped in gel fibers. So achieving a stretched conformation without the trapping was accomplished by tuning the field frequency according to the conformation at the moment. Once stretched out, any sized DNA could be maintained in a stretched conformation under a 10 Hz ac field. As compared with shorter DNA, longer DNA existed in stretched conformation under a wide range of ac field frequencies.

Switching of banana liquid crystal mesophases under field

Taking advantage of the great number of bent-core or "banana" compounds synthesized and studied in the laboratory, we describe their behaviour under the application of an external electric field. If the field were a static one, we would work within the frame of an equilibrium phase diagram in a (field E, temperature T) space where some phases would be simple dielectrics and others ferroelectric ones with a macroscopic polarization, either spontaneous or induced by the field. In this paper, we deal with the basic responses of "banana" liquid crystals under the application of a low frequency (1 to 100 Hz) AC field. Firstly square-wave voltages allow us to locate the phase boundary between dielectric (at lower field) and ferroelectric phases (higher field) at a given temperature and field threshold. Then we apply slowly varying AC voltages with shapes like triangle or "triple-plateau" to check out the stability of the induced ferroelectric phase versus field removal. Three behaviours are encountered, the unstable one (short lifetime of the high-field ferroelectric phase) where the macroscopic polarization is destroyed and then rebuilt in the opposite direction during each half period and usually called "antiferroelectric"; the stable one (long lifetime) with a polarization that rotates at constant modulus which is labeled as "ferroelectric" and a new one where the macroscopic polarization is proportional to the applied field, we named this behaviour as "superparaelectric". Let us stress that these observations apply to the ferroelectric phases of the (E, T) phase diagram not to the zero field (0,T) phases observed in the usual phase characterization experiments except for an eventual spontaneous ferroelectric phase.

The magnetic properties of Tb(Mn 1− xFe x) 2 solid solutions with 0.35⩽ x⩽0.65

The temperature (4.5–700 K) and magnetic field (0–50 kOe) dependencies of the DC magnetization, and AC magnetic susceptibility (5 Oe, 125 Hz AC field) of the polycrystalline C15 Laves phase Tb(Mn 1− x Fe x ) 2 alloys with x=0.35, 0.5, and 0.65 have been measured. The substitution of Fe for Mn decreases the lattice parameter. At 5 K, the Tb(Mn 1− x Fe x ) 2 alloys exhibit a ferrimagnetic state because of the antiparallel alignment of the magnetic moments of Tb and the Fe+Mn atoms. The Curie temperature increases with increasing x, while remanence and coercivity decrease with x at low temperatures, and increase in the high temperature region. A slope change of the inverse DC magnetic susceptibility, χ DC −1, was observed for all alloys and the corresponding temperature increases with increasing x. The temperature dependencies of the inverse AC magnetic susceptibility, ( χ′ AC) −1, exhibit a peak at temperature close to the Curie temperature of each alloy and follow the Curie–Weiss law above this temperature.

Ac and dc electroluminescence in insulating polymers and implicationfor electrical ageing

Electroluminescence detected in many different polymers underuniform 50 Hz ac and dc fields exhibits a threshold-like character,i.e. the light emission increases supralinearly with the applied voltageabove a critical value called the emission threshold. The significance ofthis threshold is not straightforward. It could be a true physicalthreshold corresponding to the onset of the luminescence excitation asopposed to a sensitivity-limited threshold without specific significance.This paper discusses this issue on the basis of electroluminescenceanalysis in several polymers used in electrical engineering, such aspolyethylenes, polyesters and polyimides. The analysis relies on theconsideration of the field dependence of the electroluminescence and itsimaging in the sample plane. It is shown that the threshold-like characterunder a dc field reveals the onset of the electroluminescence excitationwhereas it has no specific meaning under ac stress where the detection issensitivity-limited. The significance of the luminescence-voltagecharacteristic, as regards the electrical ageing and its possible use fordiagnostic purposes, is further considered.

Power consumption measurements for ac and pulsed dc for electrostatic coalescence of water-in-oil emulsions

True root mean square power consumption measurements for coalescence of well-defined water-in-oil (W/O) emulsions [reverse osmosis water dispersed in Isopar M and stabilized with Paranox 100 surfactant] are presented for a 2-l Teflon insulated electrostatic coalescer. Estimated electricity costs for processing 1000 barrels (42 gal basis) of the emulsion were as low as $0.37 and $0.39 under 60 Hz ac and pulsed dc (i.e., half-wave rectified ac) fields, respectively. These data compare favorably with actual operating costs for an equivalent volume of crude oil for NATCO designed full-scale electrostatic coalescer systems with non-insulated electrodes. Contrary to observations by other investigators including past tests in our own laboratory, ac fields were more effective in increasing coalescence rate than pulsed dc fields. Normalized power consumption data show that the optimized frequency for coalescence with electricity costs as the important factor was at 60 Hz (i.e., the lowest frequency tested) in spite of dramatic increases in throughputs at higher frequencies of 120, 400 and 600 Hz. Comparative tests using identically prepared W/O emulsions showed that the coalescence rate with the present system was up to 11-fold higher as compared to a geometrically similar coalescer using a patented plastic-sealed electrode under identical 600 Hz ac fields.