Developmental effects of extremely low frequency electric and magnetic fields

Developmental effects of extremely low frequency (ELF) electric and magnetic fields are briefly reviewed in this paper. The results of animal studies on ELF electric fields are rather consistent, and do not suggest adverse effects on development. The results of studies on ELF magnetic fields suggest effects on bird embryo development, but not consistently in all studies. Results from experiments with other non-mammalian species have also suggested effects on developmental stability. In mammals, pre-natal exposure to ELF magnetic fields does not result in strong adverse effects on development. The only finding that shows some consistency is increase of minor skeleton alterations. Epidemiological studies do not establish an association between human adverse pregnancy outcomes and maternal exposure to ELF lields, although a few studies have reported increased risks associated with some characteristics of magnetic field exposure. Taken as a whole, the results do not show strong adverse effects on development. However, additional studies on the suggested subtle effects on developmental stability might increase our understanding of the sensitivity of organisms to weak ELF fields.     

Current–Voltage Measurements and Vortex Dynamics in a Bi2Sr2CaCu2O x Whisker: Observation of the Peak Effect and Calculation of the Critical Current in the Flux Flow Regime with and Without Applied Field

In this article, we report current–voltage measurements carried out on a Bi₂Sr₂CaCu₂O _x whisker in a large temperature range below the critical temperature with and without applied magnetic field. We examine the critical current peak effect and the vortex dynamics at low field. The critical current peak effect consists of the initial increase of the critical current that subsequently decreases as the applied field is increased. For current–voltage measurements, this effect is associated with a change in the current–voltage curves that are typical of the flux flow regime at low fields and resemble flux creep characteristics for higher fields. As a general rule, our observations are consistent with the models that link the peak effect to vortex phase transitions. We calculate the critical current in self-field in the flux flow regime taking into account intervortex forces. We suppose that most vortices are pinned by defects while mobile vortices move through plastic channels between the strongly pinned vortex regions. When an external field is applied, we suggest that the increase in the critical current that is observed is linked to oscillations of the pinned vortices.     

Low-frequency transient electric and magnetic fields coupling to child body

Much of the research related to residential electric and magnetic field exposure focuses on cancer risk for children. But until now only little knowledge about coupling of external transient electric and magnetic fields with the child's body at low frequency transients existed. In this study, current densities, in the frequency range from 50 Hz up to 100 kHz, induced by external electric and magnetic fields to child and adult human body, were investigated, as in residential areas, electric and magnetic fields become denser in this frequency band. For the calculations of induced fields and current density, the ellipsoidal body models are used. Current density induced by the external magnetic field (1 microT) and external electric field (1 V/m) is estimated. The results of this study show that the transient electric and magnetic fields would induce higher current density in the child body than power frequency fields with similar field strength.     

Cardiac electrophysiology: theoretical considerations of a potential target for weak electromagnetic field effects

With the widespread introduction of extra high voltage power transmission lines in the 1960s, and subsequent to early reports from Soviet Union scientists about health risks for transformer station personnel, public concern regarding the effects of electromagnetic fields (EMFs) on biological function has given rise to a large number of investigations and legislation to limit domestic and occupational exposure to EMFs. The underlying rationale for concern is related to the fact that living cells are electrically active, which makes them potentially vulnerable to electromagnetic interference. In the heart, electrical activity is crucial in coordinating the contraction of millions of cardiac cells, and disturbances in cardiac electrical activity, also known as arrhythmias, are often life threatening. Electrical fields induced in the heart by weak external EMFs (such as those encountered in a domestic setting) are understood to be at least 2 orders of magnitude smaller (< 1%) than those that occur naturally as an intrinsic consequence of cardiac activity. Using quantitative models of cardiac cellular electrophysiology, the effect of weak (1%) manipulation of key current mechanisms that give rise to the electrical activity of the heart is therefore assessed.     

Meissner Effect, Spin Meissner Effect and Charge Expulsion in Superconductors

The Meissner effect and the Spin Meissner effect are the spontaneous generation of charge and spin current respectively near the surface of a metal, making a transition to the superconducting state. The Meissner effect is well known but, I argue, not explained by the conventional theory; the Spin Meissner effect has yet to be detected. I propose that both effects take place in all superconductors, the first one in the presence of an applied magnetostatic field, the second one even in the absence of applied external fields. Both effects can be understood under the assumption that electrons expand their orbits and thereby lower their quantum kinetic energy in the transition to superconductivity. Associated with this process, the metal expels negative charge from the interior to the surface and an electric field is generated in the interior. The resulting charge current can be understood as arising from the magnetic Lorenz force on radially outgoing electrons, and the resulting spin current can be understood as arising from a spin Hall effect originating in the Rashba-like coupling of the electron magnetic moment to the internal electric field. The associated electrodynamics is qualitatively different from London electrodynamics, yet can be described by a small modification of the conventional London equations. The stability of the superconducting state and its macroscopic phase coherence hinge on the fact that the orbital angular momentum of the carriers of the spin current is found to be exactly ?/2, indicating a topological origin. The simplicity and universality of our theory argue for its validity, and the occurrence of superconductivity in many classes of materials can be understood within our theory.     

Synchronisation mechanisms of circadian rhythms in the suprachiasmatic nucleus

In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus is considered as the master circadian pacemaker. Each cell in the SCN contains an autonomous molecular clock, and the SCN is composed of multiple single-cell circadian oscillators. The fundamental question is how the individual cellular oscillators, expressing a wide range of periods, interact and assemble to create an integrated pacemaker that can govern behavioural and physiological rhythmicity and be reset by environmental light. The key is that the heterogeneous network formed by the cellular clocks within the SCN must synchronise to maintain timekeeping activity. To study the synchronisation mechanisms and the circadian rhythm generation, we propose a model based on the structural and functional heterogeneity of the SCN. The model is a heterogeneous network of circadian oscillators in which individual oscillators are self-sustained. The authors show that the dorsomedial region can smooth the periodic light?dark (LD) signal curve and affect its wave form. The authors also study the rhythmic process of the circadian oscillators under the effect of the daily LD cycle, including three courses: information afferent inputs, oscillation and information efferent outputs. The numerical simulations are also given to demonstrate the theoretical results.     

Effects of chronotype and time of day on the vigilance decrement during simulated driving

The current study tested for the first time the effect of individual differences in circadian rhythmicity (chronotype) on both driving performance and its evolution along time on task. Morning-type and evening-type female participants were tested in morning (8 am) and evening (8 pm) sessions, in which we controlled for prior sleep duration and prior wake. Measures of body temperature, subjective activation and affect, reaction times (RT) in the Psychomotor Vigilance Task (PVT), behavioral performance (error position) and EEG alpha power during simulated driving were collected. The main result showed strong linear increments of mean and standard deviation of error position along time on task (vigilance decrement) when evening-type participants drove at their non-optimal time of day, that is, during the morning session. In contrast, driving performance in the morning-type group remained stable over time on task and was not affected by time of day. This finding can be due to differences in personality traits (e.g., conscientiousness, sensation seeking) and task appraisal associated to extreme chronotypes. The consideration of chronotype in vigilance and driving tasks can enhance safety and human performance by promoting work schedules and countermeasures to prevent failures in the accomplishment of tasks under non-optimal circadian conditions.     

Exposure to magnetic fields of railway engine drivers: a case study in Italy

A case study of exposure assessment of railway workers to static and extremely low frequency (ELF) magnetic fields is presented. A measurement campaign was conducted in aboard Italian main line trains. All measurements were performed on board during regular service (two engine drivers were simultaneously present), in all places potentially accessible to personnel, considering routes ranging from a few tens of kilometres to hundreds of kilometres. The measurement protocol was mostly based on broadband metres and personal metres were employed to assess individual exposure. Surveys on static and ELF magnetic fields were performed for seven different models of engine or electrified train. Traction motors were fed by alternating current (AC) current, except for two engines, where AC current fed only auxiliary services. The final result is that the average exposure to static magnetic field was a little higher than the background geomagnetic field; occasionally in few areas it could reach levels of the order of millitesla. The average exposure to ELF magnetic fields was in the order of 1-2 μT, with higher levels (few microtesla) only for one engine; occasionally in hot spots, close to wiring or specific equipment, the field values could reach several tens of microtesla.     

Evaluation and measurement of magnetic field exposure at a typical high-voltage substation and its power lines

This study presents a survey of magnetic field measurements including those resulting from 380/154 kV power substations, which play a vital role in human body biological studies. The survey was carried out in the main power substation of Antalya, Turkey, located at the suburban region of the city, under actual loads. The paper also presents the actual magnetic field strength measured near the 380/154 kV substation and power transmission lines (380 and 154 kV) connecting to the substation. Since most part of these lines pass through a residential area, they have been included in the study, and the actual magnetic field variation around them has been investigated by comparative analysis of measured data. For the occupants working at substations, occupational exposure has been analysed with actual magnetic fields at operating locations. Induced internal electric fields and current densities in the occupants' body due to exposure to external magnetic fields produced by a conventional 380/154 kV power substation have been investigated.     

50-60 Hz electric and magnetic field effects on cognitive function in humans: a review

This paper reviews the effect of 50-60 Hz weak electric, magnetic and combined electric and magnetic field exposure on cognitive functions such as memory, attention, information processing and time perception, as determined by electroencephalographic methods and performance measures. Overall, laboratory studies that have investigated the acute effects of power frequency fields on cognitive functioning in humans are heterogeneous, in terms of both electric and magnetic field (EMF) exposure and the experimental design and measures used. Results are inconsistent and difficult to interpret with regard to functional relevance for possible health risks. Statistically significant differences between field and control exposure, when they are found, are small, subtle, transitory, without any clear dose-response relationship and difficult to reproduce. The human performance or event related potentials (ERPs) measures that might specifically be affected by EMF exposure, as well as a possible cerebral structure or function that could be more sensitive to EMF, cannot be better determined.     

Effective magnetization and forces due to eddy currents

A simple method for evaluating the effective magnetization due to eddy currents excited by AC magnetic fields in finite conductive objects is presented. The values of magnetization enable the estimation of the forces exerted on the object by the effect of eddy currents. The method relies on assuming a similarity between eddy current magnetization and the magnetization due to diamagnetic effects, which is easier to evaluate. Its validity is checked by comparing results from the eddy current forces with data obtained from conventional but much more complicated methods or from experimental data. The approach may be useful for evaluating the eddy current losses in finite conductive objects excited by AC magnetic fields or the influence of small conductive objects on AC excitation coils. The method combines techniques related to the conventional evaluation of eddy currents in certain 1-D geometries with techniques that approximate behavior of the AC magnetic field in finite objects in a way similar to that followed when the magnetic forces acting on a diamagnetic object are calculated     

WHO's health risk assessment of ELF fields

The World Health Organization (WHO), the International Commission on Non-Ionizing Radiation Protection (ICNIRP), WHO's scientific collaborating centres (including the UK's National Radiological Protection Board (NRPB)) and over 50 participating Member States are participants of WHO's International EMF Project. As part of WHO's health risk assessment process for extremely low frequency fields (ELF), this workshop was convened by NRPB to assist WHO in evaluating the potential health impacts of electrical currents and fields induced by ELF in molecules, cells, tissues and organs of the body. This paper describes the process by which WHO will conduct its health risk assessment. WHO is also trying to provide information on why exposure to ELF magnetic fields seems to be associated with an increased incidence of childhood leukaemia. Are there mechanisms that could lead to this health outcome or does the epidemiological evidence incorporate biases or other factors that need to be further explored?     

多裂纹导电薄板电热温度场和应力场的计算

讨论了对带有n个共线裂纹的薄板,在无穷远处加载电流实施止裂时板内的温度场和应力场。文中利用了复变函数的方法计算得到了电流场、温度场和应力场的分布状态。计算中考虑了材料热传导系数、线胀系数、弹性模量随温度的变化。作为算例,以带有两个共线裂纹、牌号为GH2132GH的高温合金制成的薄板进行了计算,给出了应力、温度与加载的电流密度及裂纹尺寸的关系;分析了导热系数随温度的变化对温度场数值的影响。     

Arc dynamics in the rail gun

A one-dimenslonal model is discussed which is suitable for analyzing the properties of the plasma in an arc-driven rail gun. It is pointed out that a set of twelve coupled equations can be derived, the solution of which yields the electromagnetic fields associated with the arc as well as its fluid-dynamical characteristics. The calculations are then applied to analyze the arc in a recent experiment by Rashleigh and Marshall. From a limiting-case analytic solution of the governing equations, some approximate scaling laws can be derived which determine how the arc characteristics vary with gun dimensions, projectile mass, arc mass, and accelerating current. The accuracy of the scaling relations is discussed by comparing results predicted by them for various arcs with results predicted by the more general, numerical solutions of the governing equations.     

Modelling fatigue and the use of fatigue models in work settings

In recent years, theoretical models of the sleep and circadian system developed in laboratory settings have been adapted to predict fatigue and, by inference, performance. This is typically done using the timing of prior sleep and waking or working hours as the primary input and the time course of the predicted variables as the primary output. The aim of these models is to provide employers, unions and regulators with quantitative information on the likely average level of fatigue, or risk, associated with a given pattern of work and sleep with the goal of better managing the risk of fatigue-related errors and accidents/incidents. The first part of this review summarises the variables known to influence workplace fatigue and draws attention to the considerable variability attributable to individual and task variables not included in current models. The second part reviews the current fatigue models described in the scientific and technical literature and classifies them according to whether they predict fatigue directly by using the timing of prior sleep and wake (one-step models) or indirectly by using work schedules to infer an average sleep-wake pattern that is then used to predict fatigue (two-step models). The third part of the review looks at the current use of fatigue models in field settings by organizations and regulators. Given their limitations it is suggested that the current generation of models may be appropriate for use as one element in a fatigue risk management system. The final section of the review looks at the future of these models and recommends a standardised approach for their use as an element of the ‘defenses-in-depth’ approach to fatigue risk management.     

Dosimetry considerations in the head and retina for extremely low frequency electric fields

Magnetophosphenes are investigated from the viewpoint of electromagnetic dosimetry. Induced current density and internal electric fields at the threshold of perception are estimated by analytical and numerical calculations, assuming different models. Dosimetry for electrophosphenes is also discussed and compared with that for magnetophosphenes. The distribution of current density and internal electric fields is consistent with the experimental observation that flashing sensations reach their greatest intensity at the periphery of the visual field, for both electro and magnetophosphenes. The estimated thresholds in internal electric fields are consistent for magnetophosphenes and for electrophosphenes, respectively. The magnitudes of the thresholds, however, differ by about 10-fold. The thresholds in induced current density are critically dependent on the conductivity of the eye assumed for the calculations. The effect of thin membrane structure is also discussed with regard to the difference between electric field and magnetic field exposures.     

Current–Voltage Measurements on a Bi2Sr2CaCu2O x Whisker and Investigation of Its Vortex Dynamics in Self Field

We report current–voltage measurements carried out on a high quality Bi₂Sr₂CaCu₂O _x whisker in a large temperature range below the critical temperature. When a perpendicular field is applied, the current–voltage curves are typical of the flux flow regime at low fields and resemble flux creep characteristics at high fields. This change, related to what is described as the critical current peak effect is associated to a transition between different vortex phases. In this contribution, we focus on the dynamics of the vortices in self field. We show that the critical current in the flux flow regime can be calculated straightforwardly taking into account inter-vortex forces only, supposing that free vortices run between pinned vortices.     

The assessment of human exposure to low frequency and high frequency electromagnetic fields using the boundary element analysis

Analysis of the human body exposed to low frequency and high frequency electromagnetic fields is presented in this work. The formulation of the problem is based on a simplified thick wire model of the human body. The current distribution induced in the body is determined by solving the Pocklington integral equation for a straight thick wire via the Galerkin–Bubnov boundary element method. Once the axial current along the equivalent antenna of the body is obtained, one may calculate the induced current density, electric field, specific absorption rate, and the total absorbed power in the human body. Several realistic exposure examples are given.     

Performance improvement and optimization of a high-temperature superconducting coil having different transport current portions by employing persistent current mode

To improve the performance of a high-temperature superconducting (HTS) coil, it is important to improve its transport current performance. In general, the critical current and n-value of an HTS (Bi-2223/Ag) tape depend on the applied magnetic fields and the angle between the magnetic field and the tape under a constant temperature. The critical currents in the coil edge of the tapes are particularly low because of the distribution of the magnetic fields. However, the critical currents in the central portion remain high. A large amount of current can be supplied to the central portion and the coil performance will improve by supplying different currents between these areas. In this study, I propose an HTS coil in which the coil edge and central portion are isolated for each excitation. Namely, I employ the characteristics of the persistent current mode. The analysis of varying regions of current separation confirmed an optimum current separation. This optimized coil improves the central magnetic field by 21% and the stored energy by 50% compared to those of a normal rectangular coil with an HTS tape of the same length.     

Transient Electromagnetic and Heat Transfer Characteristics of the MgB2 Superconductor in Liquid Helium

A transient current density analysis is carried out for the type II superconductor (SC) material MgB₂ in liquid Helium. Variable magnetic fields are used as the unknown in solving the curl-curl relations of the electromagnetic fields applying the finite element method (FEM) for 2D axis symmetric cylindrical wires. Assuming an exponential current rise, the magnetic flux, current density and temperature distribution in the SC and He are calculated. This study gives the limiting current values to avoid the normal state, the temperature distribution profile with time as well as the changes in the magnitude of the current and time constant. Oscillations and non-uniform temperature distributions are observed in He and in the SC respectively if one varies the parameters which are related to the different heat transfer mechanisms. A slight instability in the current distribution is also observed which might transfer to a thermal instability, i.e. could signal He boiling.