Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10(3)-10(6) V/cm exhibits exp beta U-1/2 behavior with beta = beta(Schottky) below the glass transition temperature (T-g congruent to 90 degrees C), and beta = beta(Poole-Frenkel) above T-g. Coordinated temperature measurements of de currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T-g is consistent with the so-called ''anomalous'' Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. (C) 1996 John Wiley & Sons, Inc.

Qualidade da água para a irrigação de plantas em viveiros: utilização de descargas elétricas sem efeito térmico e de campos de energia no controle de Meloidogyne incognita Raça 1

The effect of electrical discharges without thermic effect and of energy field on Meloidogyne incognita Rara 1 larvae elimination in weir water was tested. on an average, 63,22% of larvae were killed by electrical discharges, in comparison with 53,12% of dead larvae in the control (water that received only ammonium sulphate) as an electrolyte. Water exposed to energy fields presented higher percentages of dead larvae (50,01% for electromagnetic field, 43,78% for variable electric field and 40,48% for static electric field) in comparison with control, represented by water without exposition to any energy field and without ammonium sulphate (34,27%).

Unusual early morning development of the equatorial anomaly in the Brazilian sector during the Halloween magnetic storm

The solar events that occurred at the end of October 2003 gave rise to very strong geomagnetic disturbances that peaked twice with Dst values reaching -345 nT around 0000 UT on 30 October and -400 nT around 2300 UT, on the same day. Disturbances in several ionospheric parameters were observed over Brazil. This work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 October. The F layer peak height over the equator first decreased under the strong prompt penetration westward electric field, which was followed by significant height increase under eastward electric field. We have used Sheffield University Plasmasphere Ionosphere Model (SUPIM) with an intensified westward disturbed electric field in the presunrise hours, presumably due to prompt penetration from the magnetosphere, in order to study the effect of such a field in the ionosphere. The simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial F layer height decreases. The intensification of the equatorial ionization anomaly and the unusual enhancement on F layer peak density, which was not modeled by the SUPIM, are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional/transequatorial wind system as inferred from the F2 layer peak height variations. The highly dynamic wind pattern, with a short-term response (2-4 hours), is compatible with the predictions of some previous theoretical model calculations reported in the literature.

THERMAL-HISTORY-DEPENDENT TRANSITION IN PRESSED PELLETS OF CLO4(-)-DOPED POLY(3-METHYLTHIOPHENE)

Electron-spin-resonance and dc conductivity data show a thermal-history-dependent transition at 240 K in pressed pellets of ClO4--doped poly(3-methylthiophene) (P3MT). We discuss the possibility of this transition to be a Peierls transition from a room-temperature-metallic to a charge-density-wave state driven by anions ordering at this temperature. Below 100 K, dc conductivity shows a change from linear to exponential decay. Nonlinear conductivity has also been observed in this system for very low electric fields.

Electron field emission from boron doped microcrystalline diamond

Field emission properties of hot filament chemical vapor deposited boron doped polycrystalline diamond have been studied. Doping level (N-B) of different samples has been varied by the B/C concentration in the gas feed during the growth process and doping saturation has been observed for high B/C ratios. Threshold field (E-th) for electron emission as function of B/C concentration has been measured, and the influences of grain boundaries, doping level and surface morphology on field emission properties have been investigated. Carrier transport through conductive grains and local emission properties of surface sites have been figured out to be two independent limiting effects in respect of field emission. Emitter current densities of 500 nA cm(-2) were obtained using electric fields less than 8 V/mu m. (c) 2007 Elsevier B.V. All rights reserved.

Influence of simultaneous addition of MnO2 and CoO on properties of SnO2-based ceramics

This paper reports on a study of the: effect of replacing CoO by MnO2 on the sintering and electrical propel-ties of the 98.95% SnO2 + (1 - x)% CoO + x% MnO2 + 0.05% Ta2O5 system. All the samples were compacted into pellets and sintered at 1300 degrees C for 1 h, when they reached densities of about 98% of the theoretical density. An X-ray diffraction (XRD) analysis showed no other detectable phases other than SnO2. Current-voltage characterization indicated varistor behavior in the systems. The non-linear coefficient (alpha) and breakdown electric field (Eb) increased as the amount of MnO2 was increased. The results are explained in terms of an electric barrier modification, due to the presence of adsorbed negative oxygen species at the grain boundary inter face. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Non-Linear Dielectric Properties of PLMN-PT Relaxor Ferroelectrics

Recent investigations on the non-linear (NL) dielectric properties of relaxor ferroelectrics systems, not only as ceramic bodies, but also, in thin films, have showed a significant technological and scientific interest. The most common practical applications of relaxors include multilayer capacitors and actuators. In this work, non-linear dielectric properties of hot-pressed (1-x)[Pb1 -(3/2) yLayMg1/3Nb2/3O3]-xPbTiO3 (PLMN-PT) ferroelectric ceramics were investigated. The NL properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the AC electric field with variable amplitude in the frequency and temperature range of 100 Hz-1 MHz and 50-450 K, respectively. An anomalous behavior of the non-linear dielectric response was observed when submitted to high electric fields levels. The obtained results were analyzed concerning one of the models for the dielectric response of relaxors ferroelectrics materials currently discussed in the literature.

Electrical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Metal-insulator transitions in pressed pellets of BF4 - doped poly(3-methylthiophene)

From Electron Spin Resonance (ESR) data in pressed pellets of BF4 - doped Poly(3-methylthiophene) (P3MT) we obtained simultaneously the paramagnetic susceptibility and. the microwave conductivity. We observed a transition from a high-temperature insulator state to a room-temperature metallic state. Around 240K. evidence of a Peierls transition is observed, but if the sample is slowly cooled, this transition is partially suppressed. DC conductivity data taken with the sample quenched to 79 K show a non-linear I-V response for very small electric fields, suggesting depinning of Charge-Density Wave (CDW). The data for heating and cooling the system above room temperature, indicate the formation of bipolarons.

Evaluation and identification of lightning models by artificial neural networks

This paper describes a novel approach for mapping lightning models using artificial neural networks. The networks acts as identifier of structural features of the lightning models so that output parameters can be estimated and generalized from an input parameter set. Simulation examples are presented to validate the proposed approach. More specifically, the neural networks are used to compute electrical field intensity and critical disruptive voltage taking into account several atmospheric and structural factors, such as pressure, temperature, humidity, distance between phases, height of bus bars, and wave forms. A comparative analysis with other approaches is also provided to illustrate this new methodology.

Influence of the processing conditions and corona poling on the morphology of β-PVDF

The α → β phase transformation of PVDF through the stretching process at different temperatures was investigated. The optimum stretching conditions were studied and characterised by infrared spectroscopy and differential scanning calorimetry. The maximum β-phase content was achieved at 80°C and a stretch ratio of 5. These samples were poled at several electric fields by the corona charge method. The effect of the electric field on the phase transformation was studied by infrared spectroscopy.

PHB/PZT composite

Flexible standing films of piezoelectric composite made of lead zirconate titanate (PZT) ceramic powder and Poly(3-hydroxybutyrate) (PHB) in powder form were obtained by mixing both polymers mechanically and pressed at 180°C. The piezoelectric coefficient d33 were investigated as function of PZT content, poling temperature and electric field. The highest value for d 33 coefficient was around 6pC/N for 50 vol% of PZT content in the composite. As PHB is a biodegradable polymer the composite has potential application as sensor minimizing the environmental problems.

Photocatalytic and photoelectrochemical treatment effects on the killing of escherichia coli cells

In this study, we report the efficiency of photocatalytic and photoelectrochemical treatment using titanium dioxide as semiconductor and its applications in water disinfection. It was compared the efficiency of the two methods on the killing of E.coli cells. The photoelectrochemical treatment with electric field enhancement showed a good result and could be a new technology to water treatment.

Developing new radiotherapy techniques using linac based gamma radiation sources

A major challenge in cancer radiotherapy is to deliver a lethal dose of radiation to the target volume while minimizing damage to the surrounding normal tissue. We have proposed a model on how treatment efficacy might be improved by interfering with biological responses to DNA damage using exogenous electric fields as a strategy to drastically reduce radiation doses in cancer therapy. This approach is demonstrated at this Laboratory through case studies with prokaryotes (bacteria) and eukaryotes (yeast) cells, in which cellkilling rates induced by both gamma radiation and exogenous electric fields were measured. It was found that when cells exposed to gamma radiation are immediately submitted to a weak electric field, cell death increases more than an order of magnitude compared to the effect of radiation alone. This finding suggests, although does not prove, that DNA damage sites are reached and recognized by means of long-range electric DNA-protein interaction, and that exogenous electric fields could destructively interfere with this process. As a consequence, DNA repair is avoided leading to massive cell death. Here we are proposing the use this new technique for the design and construction of novel radiotherapy facilities associated with linac generated gamma beams under controlled conditions of dose and beam intensity.