ELECTRONICS

Electronics



Electronics

Task 1

lectric fields of 1-2 V/cm have been shown to orient the movements of a wide variety of cells in vitro. Because similar electrical potentials occur across wounds in mammalian skin and cornea, and even larger electric fields (up to 5 V/cm) have been measured in developing limb buds, it has been proposed that endogenous, trans-tissue electric fields play a significant role in directing cell movements during vertebrate development and wound repair. Application of an external voltage to counter these endogenous fields can inhibit normal cell migration in amphibian limb buds, while supplementing the endogenous field accelerates it.

In the magnetospheric environment, a variety of accelerated particle populations is observed. Many spacecraft have detected energetic particles and even beams in the geomagnetic tail, with energies in the range of tens of keV and sometimes up to 100200 keV. Sometimes these particles are observed as beamlets at the lobeward edge of the plasma sheet boundary layer (PSBL), and are assumed to be accelerated in the distant tail due to the fulfillment of the ion resonance conditions. The resonant effect in the ion nonlinear dynamics in the magnetotail was discovered in the pioneering work of Chen and Palmadesso and it was studied in detail by Burkhart and Chen.

In addition, a current variation at a circuit position (e.g., at L^sub 1^) can induce a voltage into another (e.g., at L^sub 2^), and vice versa. In this example, the circuit parameter is the mutual inductance (M), being equal to each other in both cases, i.e., the mutual inductance from L^sub 1^ to L^sub 2^ is equal to that from L^sub 2^ to L^sub 1^. Moreover, the value of mutual inductance is proportional to the geometric mean of the self-inductances involved. For instance, the mutual inductance between L^sub 1^ and L^sub 2^ is proportional to ... The maximum value of M, in this example, can be demonstrated to be ... (tightly coupled self-inductances), while the minimum is zero (completely uncoupled self-inductances). Thus, a coefficient of coupling (k) ranging between zero and one (0 = k = 1) can be defined, so that ... In fact k, and consequently M, incorporates factors such as the relative distance and orientation between the involved parts.

In 1820, H.C. Oersted, from Copenhagen, discovered that the flow of electric current in a conductor would cause a magnetic field, thereby producing a deflection of a compass needle. This discovery led to research in the field of electromagnetics, the interaction between electricity and magnetism, an early pioneer of which was the Frenchman A.M. Ampère. Ampère gave clear definitions of electric current, the flow of electric charge in a conductor, and electric voltage, the tension of 'pressure' of electricity which would cause the flow of current in a closed circuit (McConaghy, 2007, 52).

Ampère, however, saw no relationship between the current and voltage, and it was G.S. Ohm in 1827 who finally postulated that voltage was proportional to the current by a constant known as the resistance of the ...