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Exposure of workers in the electric power industry to electric and magnetic fields.

A survey of 50 Hz electric and magnetic fields in the electric power industry has distinguished differences in exposure among the employees making it possible to compare health effects as a function of exposure. The workers that were most exposed to electric and magnetic fields were linemen and substation personnel who worked on facilities at operating voltages above 20 kV. On average, they were exposed to an electric field strength above 30 V/m for approximately 1.5 to 3 hours per day and to a magnetic flux density of around 1 to 2 microT. The least exposed group were linemen working in the 0.4 to 20 kV part of the network with exposure to a magnetic field of 0.10 microT. The electric field seldom exceeded 30 V/m.

Cohort Studies↗

Marginal cost pricing for coal fired electricity in coastal cities of China: the case of Mawan Electricity Plant in Shenzhen City, China.

By developing a GDMOD model to estimate the environmental externalities associated with electricity generation, this project provides a detailed analysis of the damages and costs caused by different pollutants at varying distances from the Mawan Electricity Plant in Shenzhen, China. The major findings of this study can be summarized that (1) environmental damages caused by electricity production are large and are mainly imposed on regions far away from the electricity plant; (2) air pollution is the most significant contributor to the total damages, and SO2, NO(x), and particulate matter are the three major pollutants with highest damages; (3) the damages caused per unit of particulate,NO(x), and SO2 emissions are much higher than pollution treatment and prevention costs. The research results of this project showed that China needs to have a more effective levy system on SO2, and a more manageable electricity tariff mechanism to internalize the environmental externalities. The results have also implications for pollution control strategies, compensation schemes as well an emission trading arrangements.

Air Pollutants↗

Adjunctive hyperbaric oxygen therapy contributes healing in electrical injury: a case report of high voltage electrical injury.

In electrical injuries, new treatment modalities and guidelines are needed for improving clinical outcome and the survival of damaged tissue. Although there is no published study about hyperbaric oxygen (HBO) therapy for electrical injury in the literature, it is indicated in conditions, which may contribute to the clinical presentation of electrical injury such as thermal burns, crush injuries, necrotizing soft tissue infections, problematic wounds and compromised skin grafts and flaps. An 11-year-old child with high voltage electrical injury treated with adjunctive hyperbaric oxygen for 90 minutes twice a day at 2,4 ATA for one week, then once a day for six days for a total of 20 sessions was presented to demonstrate the beneficial effects of hyperbaric oxygen therapy initiated before irreversible damage had taken place. Although hyperbaric oxygen therapy was initiated rather late, when the most effective window for intervention had already past, HBO was effective in fighting against necrosis, infection and tissue loss. Adjunctive HBO therapy is suggested for electrical injuries for its contribution to healing. In order to see the favourable effects of HBO, it is better to start the treatment within the first 24 hours following injury.

Child↗

Electrical stimulation of the thigh muscles after reconstruction of the anterior cruciate ligament. Effects of electrically elicited contraction of the quadriceps femoris and hamstring muscles on gait and on strength of the thigh muscles.

The effects of neuromuscular electrical stimulation on the strength of the thigh muscles and on gait were examined in ten patients after reconstruction of the anterior cruciate ligament. The patients were randomly assigned to one of two treatment groups: neuromuscular electrical stimulation and volitional exercise, or volitional exercise alone. A four-week course of electrically elicited co-contraction of the thigh muscles resulted in significant attenuation of the characteristic loss of strength of the quadriceps as compared with volitional exercise. There was no significant difference between groups in any measure of performance of the hamstring muscles. In the group that received neuromuscular electrical stimulation, the values for cadence, walking velocity, stance time of the involved limb, and flexion-excursion of the knee during stance were significantly different from those of the volitional exercise group. Flexion-excursion of the knee during stance was directly and significantly correlated with strength of the quadriceps femoris muscle. Flexion of the knee during stance was qualitatively different in the involved extremity as compared with the uninvolved extremity in all patients. There is a rapid flexion of the knee at weight acceptance that is maintained throughout stance and probably reflects stabilization of the joint by muscular coactivation to compensate for weakness of the quadriceps. The patients who received neuromuscular electrical stimulation had stronger quadriceps muscles and more normal gait patterns than those in the volitional exercise group.

Adolescent↗

[Motor-evoked potentials following electric and magneto-electric stimulation: the value and a comparison of both methods].

Motor evoked potentials (MEP) were recorded in a total of 145 patients with supratentorial (N = 29), infratentorial (N = 25) and spinal (N = 91) lesions affecting the descending pathways. In all cases potentials were evoked by electrical, in addition in 55 of them by electromagnetic stimulation of the motor cortex. The peripheral conduction time was determined in all patients by electrical stimulation of the cervical and lumbar nerve roots, respectively. This study was designed to compare both stimulation techniques (electrical vs. electromagnetic) regarding their significance in recording of potentials as well as in correlation of potentials with the motor status as established by clinical examination. Our results show that potentials were obtained in 87.6% following central (cortex) and in 100% following central electromagnetic stimulation. 87.9% of the recordings in infratentorial and spinal lesions show a correct and 12.2% a "false positive" correlation with the clinical motor status. On the other hand, the correlation was false negative in 13.8%, correct in 79.3% and "false positive" in 6.9% of the supratentorial cases. There was no difference between electrical and electromagnetic stimulation regarding diagnostic significance of potentials. Our results allow the following conclusions: both electrically and electromagnetically evoked potentials are sensitive for electrophysiological assessment of infratentorial and spinal lesions, but unreliable in evaluation of supratentorial lesions, especially in the acute stage. Due to its painlessness, electromagnetic stimulation is the method of choice for transcranial eliciting of MEP in the awake patient, who is capable of facilitation by voluntary background contraction of the target muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

Electric nerve stimulation (ENS): 70 clinical cases of bi-block aided by an electric bipolar signal.

INTRODUCTION: The practice of local anaesthesia aided by ENS, among other things, is based on the use of available electric signals searching peripheral nerves. Most electric generators produce a square monopolar signal that is potentially dangerous because it exists a risk of hyperpolarization damage with neural lesions by galvanic effect. AIM: To inform about the use of a bipolar signal, different than the usual square monophasic signal. In theory a bipolar signal prevents the risk of hyperpolarization by lessening average intensity of current crossing the tissues. METHODS: Our experience is based on 70 clinical cases of bi-block performed by searching the nerve by using an electric bipolar signal to locate a peripheral nerve. RESULTS: Local anaesthesia can be successfully performed by using bipolar electric signals not currently employed. In 2/70 patients it was needed to perform surgery under general anesthesia. The rate of successful blocks was similar to the results of current literature. DISCUSSION AND CONCLUSIONS: Most authors search peripheral nerves by square monophasic signals. It arrives because it's widely believed that a square signal is advantageous because of high ratio di/dt (intensity/time). Today, it's not assessed in clinical practice that an electric signal is deeply modified in its parameters and its form by capacitive and resistive properties of the human body.

Adolescent↗

Sex recognition and neuronal coding of electric organ discharge waveform in the pulse-type weakly electric fish, Hypopomus occidentalis.

1. Hypopomus occidentalis, a weakly electric gymnotiform fish with a pulse-type discharge, has a sexually dimorphic electric organ discharge (Hagedorn 1983). The electric organ discharges (EODs) of males in the breeding season are longer in duration and have a lower peak-power frequency than the EODs of females. We tested reproductively mature fish in the field by presenting electronically generated stimuli in which the only cue for sex recognition was the waveshape of individual EOD-like pulses in a train. We found that gravid females could readily discriminate male-like from female-like EOD waveshapes, and we conclude that this feature of the electric signal is sufficient for sex recognition. 2. To understand the possible neural bases for discrimination of male and female EODs by H . occidentalis, we conducted a neurophysiological examination of both peripheral and central neurons. Our studies show that there are sets of neurons in this species which can discriminate male or female EODs by coding either temporal or spectral features of the EOD. 3. Temporal encoding of stimulus duration was observed in evoked field potential recordings from the magnocellular nucleus of the midbrain torus semicircularis. This nucleus indirectly receives pulse marker electroreceptor information. The field potentials suggest that comparison is possible between pulse marker activity on opposite sides of the body. 4. From standard frequency-threshold curves, spectral encoding of stimulus peak-power frequency was measured in burst duration coder electroreceptor afferents. In both male and female fish, the best frequencies of the narrow-band population of electroreceptors were lower than the peak-power frequency of the EOD. Based on this observation, and the presence of a population of wide-band receptors which can serve as a frequency-independent amplitude reference, a slope-detection model of frequency discrimination is advanced. 5. Spectral discrimination of EOD peak-power frequency was also shown to be possible in a more natural situation similar to that present during behavioral discrimination. As the fish's EOD mimic slowly scanned through and temporally coincided with the neighbor's EOD mimic, peak spike rate in burst duration coder afferents was measured. Spike rate at the moment of coincidence changed predictably as a function of the neighbor's EOD peak-power frequency. 6. Single-unit threshold measurements were made on afferents from peripheral burst duration coder receptors in the amplitude-coding pathway, and midbrain giant cells in the time-coding pathway.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

Simple circuit to improve electric field homogeneity in contour-clamped homogeneous electric field chambers.

We redesigned contour-clamped homogeneous electric field (CHEF) circuitry to eliminate crossover distortion, to set identical potentials at electrodes of each equipotential pair and to drive pairs with transistors in emitter follower stages. An equipotential pair comprised the two electrodes set at the same potential to provide electric field homogeneity inside of the hexagonal array. The new circuitry consisted of two identical circuits, each having a resistor ladder, diodes and transistors. Both circuits were interconnected by diodes that controlled the current flow to electrodes when the array was energized in the 'A' or 'B' direction of the electric field. The total number of transistors was two-thirds of the total number of electrodes. Average voltage deviation from potentials expected at electrodes to achieve a homogeneous electric field was 0.06 V, whereas 0.44 V was obtained with another circuit that used transistors in push-pull stages. The new voltage clamp unit is cheap, generated homogeneous electric field, and gave reproducible and undistorted DNA band patterns.

DNA, Mitochondrial↗

Comparative clinical evaluation of a prototype non-electric transport incubator and an electrical infant incubator in a neonatal unit.

A new non-electric transport incubator has been developed for transferring babies between health facilities in developing countries. The temperature performance of this prototype was compared with a commercial electric incubator. The warm-up time for the prototype was 51.8 min, compared with 48.1 min for the electric incubator. Forty-five non-distressed premature babies, aged 24-72 h, with a gestational age of less than 37 weeks, were continuously evaluated for a 2 h period. Twenty-five babies, with a mean weight of 2073 g (range 1500-2500 g), were studied in the prototype, and 20 babies, with a mean weight of 2076g (range 1550-2500 g), were studied in the electrical incubator. The rectal and abdominal skin temperature, heart rate, oxygen saturation and respiratory rate of the babies were recorded. The temperature, oxygen and humidity level of the canopy and the room temperature were also measured. The SaO2, heart rate and respiratory rate were within the normal range (in the prototype: 96.5%, 130.5 beats min(-1) and 43 breaths min(-1), respectively; and, in the electric incubator: 96.5%, 128.5 beats min(-1) and 40 breaths min(-1), respectively). No evidence of carbon dioxide narcosis, hypoxia, acidosis or adverse thermoregulatory behaviour were observed in the two groups. The mean rectal temperature for both groups was within the range 36.5 degrees C-37.5 degrees C. There was no significant difference between the measurements of the two groups. The level of oxygen inside the canopy was 21%, and no decrease was observed. The new nonelectric transport incubator confirmed its safety and efficiency in providing a warm environment for non-distressed premature babies over a 2 h period.

Body Temperature Regulation↗

Electric circuit model for electrical field flow fractionation.

In electrical field flow fractionation (EFFF or ElFFF), an electric potential is applied across a narrow gap filled with a weak electrolyte fluid. Charge buildup at the two poles (electrodes) and the formation of an electric double layer shields the channel, making the effective field in the bulk fluid very weak. Recent computational research suggests that pulsed field protocols, however, should improve retention and may enhance separation in EFFF through systematic disruptions of the double layer resulting in a stronger effective field in the bulk fluid. Improved retention has already been demonstrated experimentally. Accurate modeling and subsequent device optimization and design, however, depends, in part, on formulating a suitable model for the capacitative response of the channel and double layer at the electrode surfaces. Early models do not correctly describe experimentally observed current-time response and are not physically meaningful even when accurate mathematical fits of the data are realized. A new model and conceptual framework based on electrical resistance and capacitance variations of the double layer is suggested here. Physical interpretations of the electrical response have been developed and compared to published experimental data sets.

Electrochemistry↗

Equilibrium orientation of an ellipsoidal particle inside a dielectric medium with a finite electric conductivity in the external electric field.

We study the stability of the orientation of an ellipsoidal dielectric particle immersed into a host dielectric medium under the action of the external electric field. It is assumed that the particle and the host medium have a finite electric conductivity. We demonstrate that an equilibrium orientation of the ellipsoidal particle changes with time in a stationary electric field with a constant direction. It was found that during time interval T1 an equilibrium orientation of the spheroidal particle with a finite electric conductivity remains the same as the equilibrium orientation of an ideal dielectric particle. During time interval T2 , where T= T1 + T2 is a period of the external electric field, the equilibrium orientation of the axis of symmetry of the particle is normal to the initial equilibrium direction.

Journal Article↗

Three-dimensional electric field visualization utilizing electric-field-induced second-harmonic generation in nematic liquid crystals.

An electric-field-induced second-harmonic-generation signal in a nematic liquid crystal is used to map the electric field in an integrated-circuit-like sample. Since the electric-field-induced second-harmonic-generation signal intensity exhibits a strong dependence on the polarization of the incident laser beam, both the amplitude and the orientation of the electric field vectors can be measured. Combined with scanning second-harmonic-generation microscopy, three-dimensional electric field distribution can be easily visualized with high spatial resolution of the order of 1 microm.

Journal Article↗

Task-based estimation of past exposures to 60-hertz magnetic and electric fields at an electrical utility.

OBJECTIVES: Past exposures of electric utility workers to extremely low-frequency (ELF) magnetic (B) and electric fields (E) in Quebec were estimated. METHODS: The current intensities were measured and durations of exposures determined for tasks or work locations in 14 job categories. Past task or location intensities were extrapolated from the present on the basis of interviews with long-term workers and utility personnel. Past task or location durations were estimated for the long-term workers. Time-weighted average (TWA) exposures for past periods were reconstructed for jobs from the intensity and duration estimates. RESULTS: Magnetic fields were estimated to have increased the most over time for substation and distribution-line jobs. Magnetic field exposures for jobs in the generation and transmission of electricity were estimated to have increased very little. For substation jobs, the ratios of magnetic fields in 1945 to those in 1990 ranged from 0.42 to 0.69; the corresponding figures for distribution-line jobs ranged from 0.36 to 0.94. For electric fields in substations, the estimated increase over time was less than for magnetic fields, the 1945:1990 ratios ranging from 0.59 to 0.88. For the distribution line jobs, the 1945:1990 ratios for electric fields were less than 1.0 in 4 cases (0.6 to 0.89), more than 1.0 in 3 others (1.13 to 2.01) and unchanged in 1. CONCLUSIONS: Reconstruction of TWA exposures allowed changes in the intensity and the duration of exposures to be considered separately. Documentation of the intensity and duration of exposures for different tasks allows exposure reconstruction for jobs that have ceased to exist. The method is applicable elsewhere if exposure-monitoring records allow the level and duration of exposures for tasks or locations to be calculated and if estimates of past durations and intensities of exposures can be reliably obtained.

Electromagnetic Fields↗

Effects of ouabain and electrical stimulation on the fine structure of nerve endings in the electric organ of Torpedo marmorata.

The cycle of synaptic vesicles was studied in isolated nerve terminals and in the electric tissue of Torpedo marmorata. The synaptosomes, as used in this investigation, were a pure cholinergic subcellar fraction that captured dextran particles as an extracellular marker. This endocytotic phenomenon was enhanced by potassium depolarization. Field electrical stimulation (1 Hz and 10 Hz) of the electric organ induced the appearance of membrane foldings into presynaptic terminals. Morphometric studies showed that the number of synaptic vesicles did not decline until after at least 30 min. On the other hand, at 10 Hz these changes were accompanied by an increase in length of the membrane of the terminal. At 15 min of recovery after prolonged stimulation, there was a great increase in density of synaptic vesicles with a large number of vesicles of small diameter. This increase was accompanied by a decrease of membrane length, suggesting that reformation of vesicles is related to retrieval of membrane. Pharmacological stimulation with ouabain produced changes similar to those of long-term electrical stimulation. These changes in membrane were accompanied by a decrease of the population of synaptic vesicles and a wide variation in their diameters. It is concluded that structural changes reported here could not be correlated with kinetics of the transmitter release.

Animals↗

Small electric currents affecting farm animals and man: a review with special reference to stray voltage. I. Electric properties of the body and the problem of stray voltage.

The literature on the electrical properties of the body and sensitivity to steady electric current in humans and farm animals is reviewed and the problem of stray voltage is examined. Stray voltage poses a problem to animal health and protection in cattle and pigs and possibly also in other animals. Dairy cattle can perceive alternating currents exceeding 1 mA between the mouth and all four hooves. Behavioural effects in cows usually occur above 3 mA. In practice, the major influence on dairy cows appears to be behavioural. In experimental research on sensitivity to electric current, the effects studied should be related primarily to the actual current densities or electric fields in the affected tissues rather than to the total voltages applied. Under normal conditions, herdsmen are less likely to be affected by stray voltage than their animals.

Animals↗

Hormone-induced and maturational changes in electric organ discharges and electroreceptor tuning in the weakly electric fish Apteronotus.

Plasticity in the frequency of the electric organ discharge (EOD) and electroreceptor tuning of weakly electric fish was studied in the genus Apteronotus. Both hormone-induced and maturational changes in EOD frequency and electroreceptor tuning were examined. Apteronotus is different from all other steroid-responsive weakly electric fish in that estradiol-17 beta, rather than androgens, induces discharge frequency decreases. This result can account for the 'reversed' discharge frequency dimorphism found in Apteronotus in which, counter to all other known sexually dimorphic electric fish, females have lower discharge frequencies than males. Studies of electroreceptor tuning in Apteronotus indicate that electroreceptors are closely tuned to the frequency of the EOD. This finding was noted not only in adult animals, but also in juvenile animals shortly after the onset of their EODs. Tuning plasticity in Apteronotus, as in other species studied, is associated with altered EOD frequencies and was noted in both maturational EOD changes and in estrogen-induced changes. Thus, tuning plasticity appears to be a general phenomenon which occurs concurrent with a variety of EOD changes.

Androgens↗

Differential production of chirping behavior evoked by electrical stimulation of the weakly electric fish, Apteronotus leptorhynchus.

Aperonotus leptorhynchus (Gymnotiformes) produces wave-like electric organ discharges distinguished by a high degree of constancy. Transient frequency and amplitude modulations of these discharges occur both spontaneously and during social interactions, which can be mimicked by external electrical stimulation. The so-called chirps can be divided into four different types. Independent of the type of chirp produced under spontaneous conditions, the fish generate only significant numbers of type-2 chirps under evoked conditions. The rate of production of chirps of this type is largely determined by the frequency relative to the fish's frequency and signal intensity. Frequencies of + 10 Hz of the fish's own discharge frequency most effectively elicit chirps. Type-2 chirps can also be evoked through stimulation at or near the higher harmonic frequencies of the fish's frequency, but the chirp rate decreases with increasing number of the higher harmonic component. Over a certain range, the rate of production of type-2 chirps increases with increasing stimulus intensity. At very high intensities the generation of type-2 chirps is accompanied by the production of a novel type of electrical signal ("abrupt frequency rise") characterized by a frequency increase of approximately 20 Hz and high repetition rates of roughly 10 s(-1). We hypothesize that the different types of electric modulations subserve different behavioral functions.

Animals↗