AC High Field Research Articles

Developing a new apparatus for inactivating Escherichia coli in saline water with high electric field AC

An electrical apparatus for inactivating microorganisms in saline water was designed. A continuous AC electric field (20 kHz, 14 kV/cm) was applied to 0.1% saline water containing Escherichia coli in order to examine the inactivation effect of the electrical apparatus. After the electric treatment, a reduction of 5 logarithmic orders was observed for E. coli when the final process temperature was controlled at 74 ° C . The temperature was maintained constant by alternating saline concentration with different electric field intensities. A higher electric field at the same process temperature produced a larger decrease of E. coli. Further, a higher process temperature at the same electric field also decreased the number of cells. It was concluded that high electric field combined with high temperature plays an important role in inactivation in a short time treatment.

Effect of High Electric Fields on the Oxidative Stability of Soybean Oil

The effect of AC high electric field on the oxidative stability of soybean oil was investigated. Four intensities of electric fields of alternating current with a frequency of 60Hz, ranging from 10 to 105kV/m, were applied to soybean oil at different times (10, 30, 60, 120, 480 min, and continuously), which were stored in the dark at 60°C. The increase of the oil weight was determined by weighting method (JOCS), and the conjugated diene and carbonyl value (COV) were determined by absorbance at 234nm and 440nm, respectively. When the soybean oils were treated with 10, 15 and 50kV/m for 60, 120 and 480 min by plate electrode, the oxidative stabilities increased on storage at 60°C, and a preventive effect of oxidation was also shown during storage at high temperature (120t). But by treatment with 15kV/m for continuity and 105kV/m for 120 min in plate electrode, or treatment with 15kV/m or 50kV/m for 120 and 480 min by wire electrode, the oxidative stability decreased. Consequently, the shelf life of soybean oil was considerably improved by treatment with moderate electric fields.

Evolution of the cluster glass system La0.5Sr0.5CoO3

The electrical and magnetic properties of thex=0.5 composition in the perovskite system La1–xSrxCoO3 , annealed in air at different temperatures, have been investigated. Results from powder XRD, ac magnetic susceptibility, high field and low field (FC and ZFC) dc magnetization, electrical resistivity and EDAX measurements revealed that differences in the properties between the samples annealed at different temperatures (1000–1300 °C) arise due to compositional inhomogeneity. A true compositionally homogeneous compound is formed when annealed in a narrow temperature region close to ca. 1150 °C. A pronounced resistivity anomaly at the Curie temperature with a maximum temperature coefficient of resistance and a well defined magnetic transition are observed for the samples annealed at 1150 °C. The results can explain most of the unusual and widely differing results reported in the literature on the electronic and magnetic properties of different compositions in the La1–xSrxCoO3 system which are synthesized and processed at different temperatures.

AC Field Induced Polarization Disordering in The Ferroelectric Phase Of Modified Pzt Ceramics

ABSTRACTPronounced nonlinear enhancements in dielectric responses and decreases in phase transformation temperatures were induced under moderate ac fields and high field cycling for La modified lead zirconate titanate (PZT) ceramics. Polarization disordering could be inhibited by introducing acceptor dopants into La modified PZT compositions and by DC bias field. Analysis of the frequency dispersion revealed that the field driven transformation in lower La content PZT is a field assisted activation process, while the transformation in higher La content PZT relaxors is intrinsically a thermal activated process.

Field-induced destabilisation of hard PZT ceramics

Abstract The effective internal bias field Ei within both poled and unpoled hard PZT ceramics was determined as a function of field amplitude, temperature, and frequency by high field AC cycling. It was shown that the apparent value of Ei increased with the amplitude of the applied field, reaching a maximum at a field level of around 2 kV/mm. A slight reduction in Ei was evident at higher field strengths, which was attributed to an increasingly pronounced transient de-ageing effect caused by the measuring field. Field-driven de-ageing studies revealed a gradual reduction in Ei with time, which appeared to follow a logarithmic time law for poled materials. The form of the de-ageing behaviour for unpoled materials followed more closely the exponential relationship reported by previous authors.

UNi 4B: ordered and disordered uranium moments

We demonstrate that the unusual magnetic properties of the hexagonal uranium compound UNi 4B can be understood by the formation of a partially antiferromagnetic ordered state below T N = 20 K. Two dissimilar uranium moments exist due to the existence of a crystallographic superlattice. New low-temperature, high-field AC susceptibility and resistivity data down to 30 mK and 16 T suggest that the nonordering moments are gradually compensated as the temperature is lowered from T N to zero. These moments do not undergo another phase transition.

電子線照射架橋ポリエチレンフイルムの交流ランプ電圧印加時の高電界交流損失電流の過渡応答

電子線照射架橋ポリエチレンフイルムの交流ランプ電圧印加時の高電界交流損失電流の過渡応答

Co metamagnetism and magnetic phase diagram of Y1−xNdxCo3

AC susceptibility and high field magnetization were measured on oriented powder samples of Y1−xNdxCo3. The samples exhibit spontaneous and field-induced spin-reorientation transitions, together with two metamagnetic transitions of the Co sublattice. The experimental results suggest that the two metamagnetic transitions occur on different Co sites.

New type of magnetocaloric effect: Implications on low-temperature magnetic refrigeration using an Ericsson cycle

The low-temperature, high magnetic field heat capacity (1.5 to 70 K and 0 to 9.85 T), dc and ac magnetic behaviors of the compound (Gd0.54Er0.46)AlNi show that field-induced magnetic entropy change is significant and almost constant over the temperature region of ∼15 to ∼45 K. The resulting temperature dependence of the magnetocaloric effect, nearly constant over a 30+ K temperature range, is unprecedented (most magnetic materials have a caretlike shape temperature dependence). These data show that (Gd0.54Er0.46)AlNi can be used as an effective active magnetic regenerator material for an Ericsson-cycle magnetic refrigerator, and could substitute for complex composite layered materials suggested earlier.

Nonequilibrium phase transformation and magnetic properties of Ni3Sn2 during mechanical milling

A nonequilibrium phase transformation in stoichiometric Ni3Sn2 during mechanical impact in a high-energy ball mill was monitored by the measurements of high-field magnetization, ac susceptibility, and x-ray diffraction. X-ray diffraction showed that the material transformed from the low-temperature Ni3Sn2 phase with Ni3Sn2-type orthorhombic structure to the high-temperature Ni3Sn2 phase with partially filled-up B8-type structure after 40 h of milling. Quenching was used to confirm the phase transformation during ball milling. The magnetization of the ball-milled high-temperature phase (metastable) is much higher than that of the quenched high-temperature phase, where both ball-milled and quenched high-temperature phases have higher magnetization than the low-temperature phase. The Curie temperature of our metastable high-temperature phase is quite close to that of the equilibrium phases (high- and low-temperature phases). The result is discussed in terms of atomic disordering induced by mechanical milling.

High-field dielectric properties and AC dissipation current waveforms of polyethylene film

The authors have developed a new method for the detection of AC dissipation in dielectric materials under high AC field. Using this technique, high-field dielectric loss properties and their relation to AC dissipation current of low-density polyethylene (LDPE) films are measured. Near room temperature, tan delta of a LDPE film has small electric field dependence. In this temperature region, the dissipation current shows saturation around the voltage peaks in phase even with high-field application. At higher temperatures, however, the high-field tan delta tends to have a strong field dependence, and the AC dissipation current deforms and is nonlinear near the voltage peaks. The nonlinearity of the AC dissipation current decreases under the decrease of tan delta with the voltage application period. These results show that the large increase of tan delta in the high-field and high-temperature region is related to the loss due to DC-like carrier motion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of AC dissipation current in oil-film composite insulating system

The electric field dependence of tanδ in oil-film composite insulating system sometimes has a peak and then decreases. This is known as the Garton effect. It is caused by the fact that at high voltages, the contribution of carriers in oil to the conduction loss does not last through an entire alternating field cycle. Since the separation of the loss current from the extremely large capacitive current is usually very difficult, the nonlinear ac dissipation current waveform caused by the Garton effect has not been measured. The authors developed a new method for the measurement of high-field ac dissipation current in polymeric insulating materials. This technique was applied to the detection of nonlinear dissipation current and its waveform in oil-film composite insulating system associated with the Garton effect. We measured the variation of dissipation current with applied field and its frequency.

High-field dielectric properties of polyethylene in the high-temperature region

Nonpolar polymers such as polyethylene or polypropylene are widely used as insulation materials, often under conditions involving strong electric fields and high temperatures. Under these conditions, the conduction loss due to DC-like carrier transport may give rise to a high-field AC dissipation factor (tan δ). This paper describes the high-field dielectric properties of polyethylene films at frequencies from 50 to 400 Hz and temperatures from room temperature to 100°C, as measured with a new type electrode design developed by the authors. In the high-temperature region, the AC dissipation current waveform at 50 Hz was also measured. At room temperature, the electric-field dependence of tan δ is almost unaffected by the frequency of the applied field. But at high temperatures and strong electric fields, tan δ tends to have a large field dependence and to be almost inversely proportional to the frequency. Thus the AC conductivity becomes independent of the frequency of the applied field in the region of strong fields and high temperatures. A theoretical analysis shows that the high-field dielectric loss is governed by two processes, namely, the dielectric relaxation loss inherent to the AC field and the DC-like carrier transport loss that becomes prominent in the high-temperature region, where AC dissipation current waveform becomes significantly nonsinusoidal.

Magnetic properties of Fe-rich amorphous Fe-La alloys

A magnetic phase diagram of Fe-rich amorphous Fe100-xLax alloys has been determined from high-field magnetisation and AC susceptibility measurements. The alloys with x>10 are ferromagnetic, but show a reentrant spin glass behaviour at low temperature. The ferromagnetic state becomes unstable when x approaches 10. For x<or=10, the ferromagnetic state disappears and a direct transition from a paramagnetic to a spin glass state is observed. Extrapolation of the phase diagram to x=0 suggests that pure amorphous Fe is no longer a ferromagnet but a spin glass with a freezing temperature of about 110K. The irreversible process of magnetisation characterising the theoretically proposed spin glass picture has been observed in the low-temperature phases of the alloys.

Characteristics of Multilayer Eddy-Current Type Coil with Core

This paper describes a new multilayer coil with core for AC high magnetic field. This new device is constructed by eddy-current type multilayer coil in which the core is set to decrease the exciting current. The core always works in the unsaturated condition. The device has a good efficiency for concentrating the AC magnetic flux and makes it easier to obtain a high magnetic field. The structure and characteristics of the device are also discussed in this paper.

Analysis of a novel laminated coil using eddy currents for AC high magnetic field

The analysis and performance of an eddy current type laminated coil for a high AC magnetic fields are described. It is usually difficult to obtain a high AC magnetic field using an air-gap coil because of eddy currents. The present coil circumvents this limitation by making use of the magnetic shielding effect of eddy currents. Two different realizations of the coil are proposed to provide design flexibility. The field distributions are analyzed by the two-dimensional finite-element method. The coils can also be applied to an induction electromagnetic pump.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Heavy ion beam‐ionosphere interactions: Charging and neutralizing the payload

The argon release controlled studies (ARCS 1‐3) rocket flights carried ion generators to altitudes of 400‐500 km in the nighttime auroral ionosphere. Three distinct electrical charging and neutralization processes were seen on the payloads during gun operation: steady or dc vehicle charging, brief charging at gun turn‐on, and extended oscillatory sequences. Many of the unexpected consequences of gun firings are attributed to these payload charging and neutralization processes. Electrical charging is regulated by the rate at which low‐energy electrons escape from the generator, which in turn is dependent on magnetic field geometry. Each ion generator produced a dipolar magnetic field which merged with the Earth's field near the rocket. The resulting local magnetic field guided electrons back to the rocket for certain gun orientations, thereby inhibiting neutralization. Transient charging was attributed to the formation of an electron cloud around at least some vehicles, while dc charging altered the rocket's surroundings until the electron escape rate balanced the ion beam flux. We concluded that during oscillatory events the entire environment of a payload could alternate between hot electron and cold electron configurations at very high rates, possibly exceeding 10 kHz. These changes in the plasma environment did not produce substantial electric field perturbations at the dc or ac high impedance electric field sensors, so were not seen in data from typical wave detectors. However, changes in plasma density and temperature produced dramatic effects on low impedance electric current sensors such as Langmuir probes. These observations illustrate the importance of carrying both low and high impedance detectors on vehicles involved in active experiments. A number of possible future experiments are suggested to test and extend our understanding of the proposed charging and neutralization mechanisms.

Characteristics of a multilayer eddy-current-type ac magnetic coil with a cooling system

This paper deals with the performance characteristics of a new ac high magnetic field generator based on the effect of eddy currents. We have proposed a new ac high magnetic field generator and have obtained magnetic fields up to 15 T at 60 Hz. The proposed structure consists of layers of exciting coils and conductors built in concentric circles. The eddy currents in the conductor flow close to the hole in the conductor. The magnetic flux induced by the eddy currents is concentrated within the hole, and an ac high magnetic field is produced. A procedure for estimating the optimum shape and number of layers required to increase the concentration effect, together with a design of the colling system necessary for continuous operation, is presented.

Quenching of ferrimagneticlike ordering in SrCr8Fe4O19 hexagonal ferrite

We report here measurements of high field (H≤150 kOe) isothermal magnetization, dc and ac susceptibility, and Mössbauer spectroscopy of the exchange frustrated insulator SrCr8Fe4O19. The isothermal magnetization and Mössbauer spectroscopy results are consistent with a ferrimagneticlike transition at TC≊250 K. Low field dc and ac susceptibility measurements reveal a reentrant spin-glass transition at low temperature but they fail to show any anomaly at the nominal Curie temperature TC. This unusual feature is interpreted as indicative of a transition where long range ferrimagnetic ordering has been replaced by a correlated spin-glass phase with finite spin correlation length.

Analysis of Flux Concentration Phenomena in Eddy-Current Type A.C. High Magnetic Field Generator

The magnetic field in an eddy-current type ac high magnetic field generator was numerically analyzed employing boundary element and finite element methods in order to improve the flux concentration. The effect of the construction and size of the copper plate on the magnetic field intensity due to eddy currents was investigated. Through this analysis, the optimal construction was determined for the model used.