Lethal electric currents

Commercial-frequency currents of a few milliamperes flowing through the body will cause muscular contractions, resulting in the inability of the victim to release his grasp on a live conductor. Values of ``let-go' current are very important criteria in the establishment of safe-current requirements. Since ventricular fibrillation, a condition in which circulation is arrested, is probably the most common cause of death from electric shock, studies of minimum fibrillating currents under various conditions are also significant. This article discusses investigations of both let-go and fibrillating current and presents some of the experimental data that have been obtained to date.     

Stimulation of isolated ventricular myocytes within an open architecture microarray

This paper is concerned with the physiological responses of single heart cells within microfluidic chambers, in response to stimulation by integrated microelectrodes. To enable these investigations, which included the measurement of action potential duration, intracellular Ca2+ and cell shortening, a series of microfluidic chambers (50 microm wide, 180 microm long, 400 microm high, 500 microm pitch) and connecting channels (200 microm wide, 5000 microm long, 50 microm high, 500 microm pitch) were replica-moulded into the silicone elastomer, polydimethylsiloxane (PDMS). The structures were formed against a master of posts and lines, photolithograhically patterned into the high aspect ratio photoresist SU-8. The chambers within the slab of PDMS were aligned against pairs of stimulating gold microelectrodes (50 microm long, 20 microm wide, 0.1-10 microm thick, 180 microm apart) patterned on a microscope coverslip base, thus defining cavities of approximately 4 nL volume. The assembly was filled with physiological saline and single isolated rabbit ventricular myocytes were introduced by micropipetting, thus creating limited volumes of saline above individual myocytes that could be varied between 4 nL and > or = 4 microL. The application of transient current pulses to the cells via the electrodes caused transient contractions with constant amplitude (recorded as changes in sarcomere length), confirming that excitation contraction coupling (EC coupling) remained functional in these limited volumes. Continuous monitoring of the intracellular Ca2+ (using calcium sensitive dyes) showed, that in the absence of bath perfusion, the amplitude of the transients remained constant for approximately 3 min in the 4-nL volume and approximately 20 min for the 4 microL volume. Beyond this time, the cells became unexcitable until the bath was renewed. The action potential duration (APD) was recorded at stimulation frequencies of 1 Hz and 0.5 Hz using potential sensitive dyes and was prolonged at the higher pacing rate. These studies show the prolonged electrical stimulation of isolated adult cardiac myocytes in microchambers with unimpaired EC coupling as verified on optical records of the action potential, Ca2+ transients and cell shortening. The open architecture provided free (pipetting) access for drug dispensation without cross talk between neighboring microwells, and multiplexed optical detection can be realized to study EC coupling on arrays of cells under both control and experimental conditions.     

Model for the effect of electric fields on satellite-Earth microwave radio propagation

A model for crosspolarisation on satellite-Earth radio paths is proposed in which particles lying in the horizontal plane under aerodynamic-gravitational forces are aligned by electric fields. This model explains the abrupt crosspolarisation magnitude changes and abrupt 180° phase changes recently observed on satellite-Earth paths at microwave frequencies.     

Hall effect in quasi-two-dimensional superlattices in nonquantizing magnetic and strong electric fields

The transverse electric field E _y arising in quasi-two-dimensional superlattices (SLs) in a strong pulling electric field E _x and a weak magnetic field oriented in a direction perpendicular to the plane of the SL (H ∥ Z) is calculated. In the case where the electronic energy spectrum is nonadditive, the field E _y includes the Hall factor and the spontaneous transverse electric field that exists without H. The field E _y is a multivalued and sign-variable function of E _x . The asymptotically stable branches of the function E _y are determined. The (kinetic) “potential,” whose minimum corresponds to a stationary state of the nonequilibrium electron gas, is used. Fiz. Tekh. Poluprovodn. 31, 916–919 (August 1997)     

Some properties of electric current fields on a rectangle

A rectangle has two mirror-symmetry axes and a twofold rotational symmetry center. The symmetry leads us to some properties of electric current fields: the resistance R1between two electrodes attached to the special part of a rectangle and the reciprocal resistance R2of R1makes the relation R1R2= 2, etc.     

Metal-glass contacts in high electric fields

In the presence of high electric fields, the region adjacent to a metallic anode of an ionic conducting glass quickly becomes depleted of mobile ionic carriers. At the cathode, however, electrons are injected into the glass from the metal electrode and cause the effective conductivity of this region to increase.     

Weak electric fields affect plant development

High-strength electric currents and fields can alter plant physiology by the production of heat within the plant tissue and by the ionization of air molecules at the plant tips. It has been suggested that weak low-frequency electric and magnetic filelds may alter germination and early plant development [4], [5], but the question has not been resolved. Our aim was to determine the possible existence of weak electric-field effects on sunflower germination and to calculate the electric-field threshold inside the seed for any such effects. We found that an applied electric field of 5 kV/m, 60 Hz, produced an internal electric field of 7.5 ×10-4 V/m in a seed in moist soil and resulted in a statistically significant decrease of about 5 percent in germination rate. No effect was found for an applied field of 1 kV/m (1.5 ×10-4 V/m inside the seed). These results established for the first time that electric fields can affect plants by a nonthermal mechanism other than air ionization.     

Effect of electric fields on long-wavelength response of infra-red detectors

The effect of electric fields on extrinsic semiconductor infrared-detector response at low temperatures is examined quantitatively at wavelengths beyond the zero-field cutoff. General formulas are presented along with numerical results for Si:P and Si:In. These results illustrate the possibility of narrow-bandwidth detection and electronically modulated response.     

Lethal effect of glucose load on tumor cells in hypoxia

The in vitro treatment of the Ehrlich ascites tumour (EAT) cells with glucose for 15 and 60 min under hypoxic conditions leads to a decrease in their survival by a factor of 10(2) and 10(4). Glucose load is ineffective under normal oxygenation. The mass destruction of EAT cells under the influence of glucose takes place within the first 24 hours in the interphase. The lethal effect of different pH values on EAT cells is independent of the way by which the given pH value was reached (glucose load or phosphate buffer). The same values of pH lead to the same effect on EAT cells. The lethal effect markedly increased when the value of pH was lower than 5.6. It is concluded that the lethal effect of the glucose load is due to self acidification of EAT cells.     

Frenkel’-Poole effect for boron impurity in silicon in strong warming electric fields

A method based on measurement of the thermally stimulated conductivity of a weakly compensated semiconductor, which is doped with a deep impurity and which contains an impurity component that is shallower than the main component, has been developed for investigating the Frenkel’-Poole effect. The results of an investigation of the thermally stimulated conductivity of Si:Ga samples with gallium density N _A =(2–3)×10¹⁸ cm⁻³ and low accompanying impurity content (⩽10¹³ cm⁻³) are reported. The conductivity was measured after extrinsic photoexcitation of samples heated at a rate β=0.6 K/s in the temperature range T=4.2–24 K in electric fields E=20–1000 V/cm. It is shown that the maximum on the curves of the thermally stimulated conductivity is due to the thermally stimulated emptying of the boron impurity and shifts to lower values of T as E increases. The decrease of the ionization energy of impurity B in an electric field, which turns out to be somewhat weaker than the field according to the Frenkel’-Poole model for singly charged Coulomb centers, is found from the shift of the maximum. Fiz. Tekh. Poluprovodn. 31, 777–780 (July 1997)     

Second-order model of membrane electric field induced by alternating external electric fields

With biological cells exposed to ac electric fields below 100 kHz, external field is amplified in the cell membrane by a factor of several thousands (low-frequency plateau), while above 100 kHz, this amplification gradually decreases with frequency. Below 10 MHz, this situation is well described by the established first-order theory which treats the cytoplasm and the external medium as pure conductors. At higher frequencies, capacitive properties of the cytoplasm and the external medium become increasingly important and thus must be accounted for. This leads to a broader, second-order model, which is treated in detail in this paper. Unlike the first-order model, this model shows that above 10 MHz, the membrane field amplification stops decreasing and levels off again in the range of tens (high-frequency plateau). Existence of the high-frequency plateau could have an important impact on present theories of high-frequency electric fields effects on cells and their membranes.     

Effects of high electric fields and temperature on conductivity of a-Si

At high electric fields the Poole-Frenkel effect and thermally-assisted tunneling give rise to an enhanced electric conductivity of amorphous silicon (a-Si). The occupancy of states in the gap, free, and trapped charge carrier concentrations and electric conductivity of a homogenous a-Si in steady-state conditions are calculated on the basis of space-charge neutrality and with time-unchangeable concentrations of charge carriers. Simplifying approximations are introduced, thus enabling easier calculations of carrier concentrations and conductivity. The theory of capture-emission dynamics in a-Si at high fields is further extended by expressing occupancy functions and nonequilibrium quasi-Fermi levels. Effects of the density of states distribution in a-Si and added impurities upon carrier concentrations and conductivity are revealed.     

Effects of electric fields on annealing of radiation damage in MOSFET's

Radiation damage inp-channel MOS devices by 1.5 MeV electrons has been studied by thermal annealing in conjunction with electric fields between the metallic gate and the substrate. Both positive and negative gate biases retard the process of annealing. Annealing with negative gate bias reveals 1) that during thermal annealing the majority of the electrons that recombine with the positive charge in the oxide originate from the conduction band of the silicon, and 2) that during irradiation a great number of ionized electrons that remain in the oxide do not recombine with the holes, but are trapped in weakly bound states. The effect of positive bias on annealing of radiation damage is obscured by the positive charge induced due to positive bias-temperature treatment alone. No effect of drain-to-source potential on annealing has been observed.     

Negative electron diffusivity in high electric fields

The prediction that the electron diffusivity may be negative in high electric fields under some conditions has been examined starting from the Boltzmann equation and assuming a Maxwellian distribution function. It is found that the diffusion constant is positive for predominant acoustic phonon, polar optical phonon or impurity atom scattering. But the constant may be negative when effects of nonparabolicity are important and energy relaxation is limited by non-polar optical phonon scattering but the momentum relaxation is dominated by impurity atom scattering. Calculations with the parameter values of InSb, silicon and germanium show that only in materials like germanium at low temperatures of about 27 K the diffusion constant may be negative for impurity concentrations of 10¹⁷–10¹⁸ cm^?3.     

Photoconductivity in ZnSe under high electric fields

High voltage photoconductive switches utilizing polycrystalline ZnSe mere investigated. Experiments have been performed on polycrystalline ZnSe switches in a longitudinal geometry. Electrodes of perforated metal films, a transparent liquid electrolyte, plasma, and ultraviolet-light-generated carriers were used. High-bias fields of up to 100 kV/cm and current densities over 100 kA/cm² can be applied to the polycrystalline ZnSe switches. Nonlinear effects were observed at high fields with near band edge illumination. Applications of these effects are discussed     

Electronic properties of BN nanocones under electric fields

The electronic properties of BN nanocones with 240° disclination under electric fields are investigated using first-principles calculations based on the density-functional theory. The cones are studied under the influence of electric fields, up to 1.13 V/Å, applied along the cone axis. The densities of states (DOS) of these BN nanocones show different patterns depending on the termination two atoms (BN, BB or NN) and the electric field strength. A decreasing of the gap is observed with increasing field. The field emission properties are very sensitive to the DOS and we show that the termination atoms, as well as the electric field, contribute to enhance the electron field emission.     

Visualization of electric fields around a biological body

A system was developed that can visualize the spatial distribution of the ELF (extremely low frequency) electric field around an object with a complex shape such as a biological body. A mechanical X- Y scanner controlled by a microcomputer moves an optical sensor, automatically scanning the space around the object. The measured data are processed and the field distribution is represented in a color distribution pattern. Using an object with a simple shape such as a cylinder, the accuracy of the measurement was confirmed by comparison to a numerical calculation. The field distributions around experimental animals (a rat and a cat) were measured and it was shown that a conductor model can be used instead of a living body in the ELF range. The field distribution around a human model was measured in various postures, showing reasonable agreement with measurements for a real human body standing under transmission lines     

Prediction of magnetically induced electric fields in biologicaltissue

There are many potential medical applications in which it is desirable to noninvasively induce electric fields. One such application that serves as the backdrop of this work is that of stimulating neurons in the brain. The magnetic fields necessary must be quite high in magnitude, and fluctuate rapidly in time to induce the internal electric fields necessary for stimulation. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential (analogous to A in classical magnetic field theory where DEL x A = B) and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using Biot Savart (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners.     

Three-dimensional computer model of electric fields in internaldefibrillation

The automatic internal defibrillator delivers a low-energy shock directly to the heart. Optimal strategies for these shock deliveries are determined by studying a three-dimensional computer model of the electric fields produced by initial defibillation electrodes. A finite-element analysis technique is used to calculate energy and current density distributions in three commonly used electrode configurations: (1) patch-patch (PP), (2) catheter-patch (CP), and (3) catheter-catheter (CC). analysis of these simulations indicates that : (1) the PP and CP configurations are more effective at channeling energy to the myocardium than the CC configuration; (2) small electrodes and the edges of the electrodes give rise to high local current densities which might cause damage to the myocardium: (3) energy delivered to the myocardium is not significantly altered for different electrode placements tested; (4) electrode size influences current density distribution, especially near the electrodes; and (5) energy distribution is sensitive to the relative conductances of the myocardial tissue and blood