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Introduction
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
Shoogo Ueno, Tsukasa Shigemitsu
The properties of electromagnetic waves necessary for understanding the various effects of electromagnetic fields on biological systems will be briefly presented. They describe the fundamental aspects of electric and magnetic fields as well as the electromagnetic wave. To begin, consider the case where a direct current (DC) power supply is connected to a single wire stretched in the air. The wire is being charged by the electric charge from the power source, and electric lines of force are generated from the wire to the ground. Although the electric lines of force are invisible to the eye, their existence can be confirmed by the fact that when another charged particle is placed between the wire and the ground, it can receive either an attractive or repulsive force in the direction of the electric lines of force. The space where these electric lines of force exist, that is the field where the electric force act, is called electric field. Its strength is defined by the force that acts when a unit charge is placed there. Now, if an alternating current (AC) power source is connected to the same cable instead of a DC power supply, the polarity of the cable charge reverses direction with its frequency. Therefore, the direction of the electric lines of force is also reversing with its frequency, but the pattern of distribution remains the same. In short, an electric field is a region of space over which an electric charge exerts a force on charged objects in its vicinity. The unit of the electric field strength is Newton/Coulomb (N/C), and in practical use, the unit is expressed in Volt/Meter (V/m).
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Electrical energy is a form of energy arising from the existence of charged bodies. A body is said to be electrically charged if, on rubbing with another body, it acquires the ability to attract light objects, like pieces of paper, fur, etc. The charge produced on a glass rod rubbed with silk is called positive charge, whereas that created on an ebonite rod rubbed with flannel is known as negative charge. Unlike charges attract each other and like charges repel. Electric field is the region of space in which force is exerted by the charge. Electric field strength or intensity (E) at a point in an electric field is defined as the force per unit charge experienced by a small charge placed at that point. Electric current (I) is the flow of electric charge and its magnitude is given by the rate of flow of charge, that is, the amount of charge per unit time. Circuit is the closed path around which electric current flows. Electrical potential (V) at a point in an electric field is the work done in transferring a unit positive charge from infinity to that point, whereas potential difference between two points (ΔV) is the work done in transferring a unit positive charge from one point to the other.
Electrical Basics
Published in Albert Thumann, Harry Franz, Efficient Electrical Systems Design Handbook, 2020
“Electric Field Strength”—Around a charge, a region of influence exists called an “electric field.” The electric field strength is defined by the magnitude and direction of the force on a unit positive charge in the field (i.e., force/unit charge).
A spectral deferred correction strategy for low Mach number reacting flows subject to electric fields
Published in Combustion Theory and Modelling, 2020
Lucas Esclapez, Valentina Ricchiuti, John B. Bell, Marcus S. Day
Under the electrostatic assumption, the local electric field is obtained from Gauss' law: where is the local total charge number density of the mixture and and are the vacuum permittivity and the relative permittivity of the gaseous medium, respectively. The electric field is the negative gradient of the electrostatic potential φ, i.e: Inserting Equation (13) in Equation (14) we obtain the electrostatic potential equation: The drift velocity can also be written as , where is the mobility of species m in the mixture. Thus, consistent with the Einstein relation [37], the mobility is defined as:
A review of demulsification technique and mechanism for emulsion liquid membrane applications
Published in Journal of Dispersion Science and Technology, 2022
Meor Muhammad Hafiz Shah Buddin, Abdul Latif Ahmad, Afiqah Tasneem Abd Khalil, Siti Wahidah Puasa
Electrical field treatment of emulsion is normally conducted in a device that consists of 2 electrodes. The electrodes are subjected to voltage supply, either AC,[119] DC[120] or pulsed.[65] Phase separation of emulsion using electric field is possible due to the effect of polarization and elongation of water droplets. Yang et al.[81] constructed a demulsifier unit using acrylic resin tube and Pt electrodes where the electric field could be altered by varying the height of the upper electrode in the emulsion phase. Although better demulsification rate was achieved at higher electric field strength but complete demulsification was not attained (voltage applied between 0.5 to 10 kV), even for a long period over than 3 hours. Meanwhile, Correia and Carvalho[82] achieved complete demulsification by applying a 4 kV and 2.7 kHz electric field through a high voltage unit prototype. Comparison of these two studies leads to the apparent effect of surfactant concentration on the demulsification efficiency. The presence of surfactant causes the emulsion to become too stable hence, requires an extremely high electric field intensity to destabilize the emulsion droplets. The electric field strength was defined as the applied voltage divided by the distance between the two electrodes. A simple way to manipulate the voltage supplied is to reduce the distance between two electrodes, apart from the voltage value itself.[68] Three zones in the emulsion during demulsification process were introduced; (i) oil phase, (ii) emulsion phase (sponge-like layer) and (iii) aqueous phase to quantify the occurrence of phase separation in the emulsion.[81]
Plasma Sheath Modelling for Computational Aerothermodynamics and Magnetohydrodynamics
Published in International Journal of Computational Fluid Dynamics, 2021
Bernard Parent, Kyle M. Hanquist
Recently, it has been shown that the excessively slow convergence of the sheath model was not due, as previously believed, to the discrepancy of the wave speeds but rather due to error amplification of the terms on the right-hand side of the potential equation based on Gauss's law (see Parent, Shneider, and Macheret 2013 for details). A new approach at solving non-neutral plasmas was then proposed in Parent, Shneider, and Macheret (2013) and Parent, Macheret, and Shneider (2014) which gets rid of this error amplification by obtaining the electric field potential equation from a form of Ohm's law rather than Gauss's law. To ensure that Gauss's law is conserved, some source terms are added to the right-hand side of the ion transport equations. Further, it was shown that a further recast of the electron and negative ion transport equations in the so-called ambipolar form (Parent, Macheret, and Shneider 2011) lead to a further improvement in computational efficiency by increasing the resolution. The resulting mass conservation equation for the charged species (either electrons, positive ions, or negative ions) was then shown to become (Parent, Macheret, and Shneider 2015) where and the ambipolar tensor α is defined as with σ the conductivity of the plasma and the Kronecker delta. The velocity component due to magnetic field effects corresponds to The electric field is obtained from the potential equation based on Ohm's law which can be derived from the physical model outlined in the previous section following the approach shown in Parent, Shneider, and Macheret (2011): from which the electric field can be found from the negative of the gradient of the potential.