Electric Current System Research Articles

A comparison of high current and low voltage electrical stunning systems on broiler breast rigor development and meat quality

Experiments were conducted to compare the effects of a high current (HC) stunning system to a low voltage (LV) stunning system on broiler carcass and meat quality. A total of 360 broiler chickens were individually stunned using either 125 mA, 50 Hz, constant AC for 5 s (HC) or using 10.5 V, 500 Hz pulsed DC for 10 s (LV). Birds were individually weighted, killed by conventional neck cut, bled for 150 s, and reweighed to determine blood loss. Breast fillets (Pectoralis major) were removed from the carcass immediately after picking (0 h) or after aging for 24 h in a static ice-water slush. Breast muscle pH was determined at both 0 and 24 h. Raw breast meat color (CIELAB) and cooked breast meat Allo-Kramer shear values were determined on samples held at 2 C for 48 h. The LV stunning treatment significantly increased (P < 0.05) blood loss (4.0 vs 3.7%) and significantly reduced initial muscle pH (6.47 vs 6.67) when compared to the HC stunning treatment. There were no significant differences between the stunning systems for 24 h pH, raw breast color, and Allo-Kramer shear. High current stunning reduced initial blood loss and delayed early rigor development compared to the LV treatment, but appeared to have little effect on final meat quality.

Possible relations between the rotational axis of the Earth's inner core and the magnetic dipole axis

AbstractThe geomagnetic field is maintained by amagnetohydrodynamic dynamo process within the liquid outer core. The distribution of the associated electric currents is modified if the outer core is bounded by electrically conducting material. Then, eddy currents and the related magnetic fields are generated within these regions. In particular, the relative rigid rotation of the inner core produces a secondary magnetic field, which is superimposed on the dynamo field. The angle between the dipole axis of the total field and the rotational axis of the inner core is an important quantity needed for the theory of polar motion of the Earth. This angle is investigated for a broad spectrum of angular velocities of the inner core.To simplify the mathematical procedure, we model the dynamo field using an axisymmetric field generated by a system of electric currents within the outer core. The conductivity of the mantle is neglected. We find that the position of the dipole axis depends on the angular velocity of the inner core as well as on the distribution of the current system within the outer core. Coincidence of both axes can be reached if the angular velocity is high enough and if the current system is concentrated within a thin sheet near the outer core‐inner core boundary.

Accumulation of magnetic field energy in an active region due to the alpha-effect

The problem of accumulation of magnetic field energy in an active region (AR) as the energy of electric currents in the AR atmosphere is not yet completely clear. Along with the commonly accepted concept of generation of electric current systems in an AR due to large- scale shearing motions at the photospheric level [1,2], another possibility of magnetic field energy accumulation has recently been proposed theoretically [3]. Assuming that the AR magnetic field evolves via a sequence of force- free configurations, Seehafer shows that the energy of small- scale field and velocity fluctuations can be transformed into that of large-scale current systems of an AR (alpha-effect). The necessary condition for the alpha-effect to exist is the presence of the sign- dominant current helicity H c =B · (∇×B) in the volume is considered. The purpose of this paper is to clarify the fulfillment of this condition in various ARs. Based on the measurements of magnetic field vector in 40 active regions of the maximum of the 22nd cycle we calculated the current helicity of the field Bz · (∇×B) z in the photosphere and obtained the following results. In 36 ARs we found a significant imbalance of the current helicity of the field (5 to 75%) such that in 33 ARs the excess of the current helicity was positive in the southern hemisphere and negative in the northern hemisphere. Therefore, in ARs the necessary condition for transfer of the energy of small-scale fluctuations of the field and velocity into the energy of large- scale electric currents in ARs is fulfilled rather frequently.

Electric current injection NDE using a SQUID magnetometer

We built a portable low-cost superconducting quantum interference device (SQUID) magnetometer to be used as the sensing element of an electric current injection NDE system. Using this system, we measured the magnetic fields associated with aluminum plate with single flaws in the millimeter range (2 to 8 mm), at lift-off distances up to ten times the size of the flaw, with injection currents in the order of a few amps. Because the system is at a relatively large distance from the test plate, the signal generated by the flaw is masked by the sinal generated by the edges of the plate. This is independent of the amount of current injected. Due to this, visual inspection is difficult when the distance from the sensor to the flaw exceeds five times its size. To intensify the magnetic field disturbance due to the flaws, we used digital image-enhancement techniques. Applying the enhancement algorithm, magnetic field disturbances were visualized at distances up to ten times the size of the flaw.

Relationship between the dayside auroral electrojets and the DPY current

Three main electric current systems are known to flow in the high‐latitude ionosphere. These are the auroral electrojets, modulated by the interplanetary magnetic field (IMF) Bz; the DPY currents, modulated by the IMF By; and the Sq current system which is not modulated by the IMF. In the past several years, researchers have tried to establish whether or not there is a relationship between the DPY current and the auroral electrojets, with some researchers contending that the DPY is a separate current system while others believing that the DPY merely reflects a redistribution of the electrojet in a manner regulated by the IMF By. To further study this question, we inspect latitude profiles of the magnetic disturbance field recorded by the CANOPUS array in north central Canada and deal with subsets of these profiles during times of relative constant IMF Bz and positive and negative IMF By polarities. We find evidence for modulation of the auroral electrojets south of the cleft region by IMF By. Moreover, our results suggest that the DPY is part of a twin electrojet system consisting of two antiparallel Hall currents. Both these currents represent an extension across noon of the directly driven electrojets.

Analytic solution of the forward problem for induced current electrical impedance tomography systems

An analytic method of solving the forward problem for a single target in a two-dimensional induced-current electrical impedance tomography (EIT) system is presented. The solution, derived for a single circular target anywhere within a circular region, takes account of both conductivity and permittivity discontinuities between target and background, and yields quadrature components of peripheral potential differences. The solution is used to explore the effects that the position and size of the target and its conductivity and permittivity have on the peripheral potential differences and the required instrumentation sensitivity to detect the target. It is shown that the effects of a change in target conductivity and permittivity are almost indistinguishable from those of a change in target area. It is also shown how the induced-current analytic solution may be modified to simulate an injected-current EIT system.

Reduction, analysis, and properties of electric current systems in solar active regions

The specific attraction and, in large part, the significance of solar vector magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 degree ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 degree ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local preferred direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar beta gamma delta-regions studied. The largest current systems have j(sub z)'s which maximizes around 30 mA per square meter and have a linear decreasing distribution to a diameter of 30 Mm.

Evolution of vector magnetic fields and vertical currents and their relationship with solar flares in AR 5747

NOAA 5747 was a flare-productive active region during its transit across the solar disk in October 1989. After the resolution of the 180° ambiguity of the transverse field synthetically, and transformation of vector magnetograms from the image plane to the heliographic frame, we have determined the distribution of the photospheric vertical electric current density in the active region. By analyzing the evolution of vector magnetograms and vertical current over a 6-day period (October 17–22) in the active region, we get the following results: (1) Two magnetic fluxes of opposite polarities emerged synchronously with their separating motion, one of which converged with an old magnetic structure and caused a number of flares. (2) There appeared a new current system, with the emergence of the fluxes. (3) The initial Hβ bright kernels occurred in the vicinity of the neutral line of vertical current (Jz = 0) with a steep gradient, but not just on the sites of vertical current peaks. (4) The flares were probably triggered by the interaction between the new emerging electric current system and old current system.

Conductivity and permittivity images from an induced current electrical impedance tomography system

This paper describes a method for generating separate tomographic images of the conductivity and permittivity distributions within a region of interest. The method uses single frequency phase and amplitude measurements of peripheral voltage differences caused by electromagnetically induced internal current patterns. The basis of the separation technique is described and images constructed from simulated and measured data from a two-dimensional phantom are presented to demonstrate the separation process.

On possible magnetospheric dust interactions of comet Shoemaker‐Levy 9 at Jupiter

The plasma interaction of the dust coma of comet Shoemaker‐Levy 9 with the Jovian magnetosphere could result in the possible generation of a field‐aligned electric current system connecting the impinging dust cloud with the Jovian ionosphere. If the current flow is intense enough, transient auroral activity might be produced as a result. In this event, enhanced level of auroral and radio emissions would be expected an hour or so before the atmospheric impact.

Vertical current and a 3B/X12 flare in a highly sheared active region (NOAA 6659) on June 9, 1991

NOAA active region 6659, during its June 1991 transit across the solar disk, showed highly sheared vector magnetic field structures and produced numerous powerful flares, including five white-light flares. Photospheric vector magnetograms of this active region were obtained at the Huairou Solar Observing Station of the Beijing Astronomical Observatory. After the resolution of the 180° ambiguity of the transverse magnetic field and transformation of off-center vector magnetograms to the heliographic plane, we have determined the photospheric vertical current density and discussed the relationship with powerful flares. The following results were obtained: (a) The powerful 3B/X12 flare on June 9, 1991 was triggered by the interaction between the large-scale electric current system and magnetic flux of opposite polarity. (b) The kernels of the powerful Hβ flare (sites of the white-light flare) were close to the peaks of the vertical electric current density. (c) Some small-scale structures of the vertical current relative to the magnetic islands of opposite polarity have not been found. This probably implies that the electric current is not always parallel to the magnetic field in solar active regions.

The morphology of flare phenomena, magnetic fields, and electric currents in active regions. I - Introduction and methods

Electric current systems in solar active regions and their spatial relationship to sites of electron precipitation and high-pressure in flares were studied with the purpose of providing observational evidence for or against the flare models commonly discussed in the literature. The paper describes the instrumentation, the data used, and the data analysis methods, as well as improvements made upon earlier studies. Several flare models are overviewed, and the predictions yielded by each model for the relationships of flares to the vertical current systems are discussed.

Three-dimensional structures of magnetostatic atmospheres. VI - Examples of coupled electric current systems

Exact solutions are presented which describe the static equilibrium of atmospheres stratified by a uniform gravity, in the presence of magnetic fields lying in parallel vertical planes. These equilibrium states are composed of different, highly varied structures in these planes stacked together in global equilibrium. They serve as simple models of three-dimensional, prominence-like condensations in the solar atmosphere, and, in the main theme of this series of papers, as illustrative examples of equilibrium states with coupled cross-field and field-aligned electric current systems. The preceding paper in this series has pointed out that such equilibrium states are a distinct class of their own

Three-dimensional structures of magnetostatic atmospheres. V - Coupled electric current systems

This paper completes the theoretical development in the third paper of this series. The task is to transform the magnetostatic equations describing equilibrium among the Lorentz, pressure, and gravitational forces, to a statement of Ampere's law incorporating the condition of equilibrium. Decomposing the electric current density into a system flowing along and another across the equilibrium magnetic field, the previous papers of this series have treated the restricted case in which these two current systems are separately conserved. A general derivation of the equilibrium Ampere's law is given to allow for the coupling between the two current systems

A global analytical representation of the magnetic field produced by the region 2 Birkeland currents and the partial ring current

A quantitative model is developed of the magnetic field produced by the electric current system of region 2 Birkeland currents, closed via the partial ring current. The distribution of j⊥ is computed from a given axially asymmetric spatial distribution of hot isotropic magnetospheric plasma over an infinitely thin L shell in an axisymmetric purely dipolar geomagnetic field, while the field‐aligned current density is found from the continuity of the net electric current. The magnetic field distribution is derived by a Biot‐Savart integral over the electric current system. An assumed cosine dependence of the plasma pressure on local time makes it possible to reduce the problem of analytical representation of the B field to two dimensions. The obtained numerical fits for the partial ring current/region 2 Birkeland current magnetic field are relatively simple, continuous, and valid throughout the whole extraterrestrial space from ionospheric heights up to tens of RE. To our knowledge, this is a first global analytical representation for the magnetic field of the partial ring current system which can be incorporated in future advanced models of the external geomagnetic field.

ULF magnetic fields generated by electrical storms and their significance to geomagnetic pulsation generation

The STAR Laboratory has been operating two independent electromagnetic noise monitoring systems in the vicinity of Stanford University for several years, one covering the ULF range (0.01–10 Hz) and the other the ELF/VLF range (10 Hz – 32 kHz). These two systems were operating during the relatively rare occurrence of a large local electrical storm on 23 September 1990 and their measurements (which cover 25 narrow frequency bands in the more than five‐decade range 0.01 Hz – 32 kHz) provide a detailed picture of the ULF and ELF/VLF magnetic field fluctuations that accompanied the storm. As would be expected, considering the important role played by lightning in its generation, ELF/VLF radio noise is enhanced. However, the ELF/VLF enhancements are smaller than those that occur at ULF: the amplitude of the magnetic field fluctuations in a 100 Hz band centered on 2 kHz was approximately doubled, whereas in the range 0.2–0.5 Hz the amplitude was increased roughly 20 times, and the increase was about 50 times for the range 0.01–0.02 Hz. Some years ago I proposed that repetitive lightning in electrical storms could trigger Pc 1 geomagnetic pulsation events, but these new results suggest that there may exist a broader link between electrical storms and geomagnetic pulsations. Considering that there are perhaps 2000 electrical storms in progress around the world at any time, and that large ULF electrical current systems below the ionosphere can stimulate ULF hydromagnetic waves in the ionosphere, the new measurements suggest that the electrical currents associated with thunderstorms, taken as a whole, may be a source of ULF energy in the magnetosphere and thus influence the generation and amplification of some classes of geomagnetic pulsations.

An adaptive current tomography using voltage sources.

This paper describes the development of an adaptive electric current tomography system which contains a novel front-end analog architecture. Programmable voltage sources have been used to deliver currents into the study object and to avoid the difficulties of obtaining high quality current sources. Through inverting an admittance matrix, the system is capable of achieving a desired current drive pattern by applying a computed voltage pattern. The tomograph, operating at 9.6 kHz, comprises 32 driving electrodes and 32 voltage measurement electrodes. The study of system noise performance shows high SNR in the data acquisition which is enhanced by a digital demodulation scheme. In vitro reconstruction images have been obtained with the data collected by the tomograph.

Computer simulations of field‐aligned currents generated by fast magnetic reconnection in three dimensions

MHD simulations have studied the evolution of an electric current system associated with fast reconnection development in three dimensions. The initial equilibrium is a one‐dimensional antiparallel magnetic field with a current sheet (or plasma sheet) in the middle. Fast reconnection is initiated by a localized resistivity and spontaneously develops in a finite region of the current sheet, leading to an Alfvénic plasma jet. Ahead of the plasma jet the plasma sheet is notably compressed, forming a plasmoid which swells and propagates. In the fast reconnection region, notable plasma rarefaction occurs so that the plasma flow converges, whereas in the plasmoid, plasma is compressed so that the plasma flow diverges. The resulting velocity shear gives rise to a magnetic shear along the plasmoid boundary, which is directly related to a (positive) field‐aligned current along the zero‐order magnetic field. The field‐aligned current is thus formed like a tube extending along the plasmoid boundary, and it becomes larger as the plasma compression in the plasmoid becomes larger. The fast reconnection development in three dimensions causes a drastic change in the overall current system to generate a redistribution of current.

The substorm current wedge and field‐aligned currents in MHD simulations of magnetotail reconnection

We present results of a three‐dimensional MHD simulation of magnetotail reconnection, which, in contrast to earlier ones, starts from an equilibrium configuration that contains a region 1 type field‐aligned current system at the plasma sheet/lobe boundary. This current system is found from equilibrium theory as the consequence of boundary conditions, which require that field lines at large distances from the Earth become aligned with the tail axis, consistent with observations and the expected consequences of the interaction with the solar wind. As in earlier simulations, the dynamic evolution develops from a slow diffusion to the fast growth of a three‐dimensional tearing mode, initiated by the sudden occurrence or increase of resistivity, leading again to the formation and subsequent tailward ejection of a plasmoid, associated with fast plasma flows. In addition, we find changes of the electric current system which are consistent with the substorm current wedge picture inferred from observations, i.e., a deviation of cross‐tail current from a near‐Earth tail region toward the Earth on the dawn side and away on the dusk side, associated with field‐aligned currents of the same signature. While the total cross‐tail current is reduced at the location of the near‐Earth reconnection site, the local current density at the near‐Earth X line actually increases, consistent with the strong plasma sheet thinning in that region. The source regions of the field‐aligned currents, indicated by strong peaks of ▽·j∥, are identified as regions of strong plasma flow vorticity near the boundaries of the fast earthward flow earthward of the reconnection site. This flow shear increases preexisting magnetic shear resulting in an increased twist of magnetic flux tubes connected with these regions and thus a generation or increase of the field‐aligned currents. We note that the current diversion in our simulation is not caused by a locally enhanced resistivity (although in reality this might be the case) but by the localization of reconnection in a three‐dimensional tail configuration.

Models of Magnetospheric Magnetic Field

Configuration of the magnetic field in the near-Earth space is known to be the most important factor determining links between the magnetosphere and ionosphere such as thermal plasma flows, electric field mapping, solar particle trajectories, low-frequency electromagnetic wave and heat propagation. One of methods for constructing the magnetospheric magnetic field models implies using large amounts of spacecraft data which are sorted out in intervals of geomagnetic disturbance indices and/or solar wind characteristics. The obtained datasets are then used for least squares fitting parameters of functions which approximate contributions to the total field coming from the main magnetospheric B sources. This opens a possibility for studying the average dependence of geometry and intensity of the magnetospheric electric current systems on the ground activity level as well as on the solar wind state. Recent progress and future prospects in this area is reviewed and discussed.