Presence Of Electromagnetic Field Research Articles

The physical significance of gauge independence and gauge covariance in quantum mechanics

The distinction between gauge independence and gauge covariance in electrodynamics is considered for quantities of physical interest. The gauge independence of directly observable quantities, such as the spectra of operators and energy conserving transition rates, is discussed and contrasted with the gauge covariance of other quantities such as scalar products. The quasigauge-invariance of the classical Lagrangian and the invariance of the Euler-Lagrange equations under the addition of a total time derivative to the Lagrangian are discussed. The consequent inherent nonuniqueness of the Lagrangian and Hamiltonian formulations of classical mechanics is pointed out. A physical interpretation of the explicit gauge dependence of classical canonical momenta and of the expectation values of the corresponding quantum mechanical operators is presented. The gauge independence of energy conserving transition rates calculated in the conventional finite-order time dependent perturbation theory is discussed and illustrated. The gauge dependence of the conventional time dependent transition amplitudes in the presence of electromagnetic fields is then discussed, and gauge independent transition amplitudes are constructed. An alternative formulation of the quantum mechanics of charged particles is obtained in terms of a new gauge independent Hamiltonian, which is, as might be expected, unique only within an arbitrary canonical transformation.

Resonant scattering in the presence of an electromagnetic field

The theory of resonant reactions, in the projection-operator formulation of Feshbach, is generalized to account for the presence of an external electromagnetic field. The theory is used as the basis for the construction of low-frequency approximations for the transition amplitude. Results obtained here for scattering in a laser field confirm earlier versions of the low-frequency approximation when the resonances are isolated. However, if there are several closely spaced resonances additional terms must be included (their importance magnified by the appearance of near singularities) which account for the effect of radiative transitions between pairs of nearly degenerate resonant states. The weak-field limit of this result yields a low-frequency approximation for single-photon spontaneous bremsstrahlung which, through the inclusion of correction terms associated with closely spaced resonances, provides an improvement over the Feshbach-Yennie version derived some time ago. A separate treatment is required to deal with the limiting case of a static external field and this is worked out here in the context of a time-dependent formulation of the scattering problem. Linear and quadratic Stark splitting of the resonance positions, and resonance broadening due to the tunneling mechanism, are expected to play a significant role in the static limit and these effects are included in the approximation derived here for the transition amplitude.

A thermometer for measuring temperatures in the presence of electromagnetic fields.

A thermometer which uses the properties of the variation of vapour pressure of a liquid with temperature is described. By using a non-dispersive liquid in the thermometer, the true temperature of materials in the presence of electromagnetic fields may be measured.

Lagrangian formulation of a spinning test particle in a curved space-time with torsion

A consistent Lagrangian approach for the motion of a charged spinning test particle with anomalous magnetic moment in a curved space-time described by a Riemann-Cartan geometry and in the presence of electromagnetic field is proposed. A necessary and sufficient condition for solving the Cauchy problem for the mechanical momentum and spin tensor of the spinning particle is discussed. The constants of motion associated with existence of Killing vectors are considered. Some interesting consequences of equations of motion are discussed.

The singularity of homogeneous cosmological models with electromagnetic fields

The regime of approaching the singularity in the presence of electromagnetic fields has been found. The rotation angles of the Kasner axes are calculated.

Bioeffects of Extremely Low-Frequency Electromagnetic Fields: Variation with Intensity, Waveform, and Individual or Combined Electric and Magnetic Fields

Prolonged exposure of the myxomycete Physarum polycephalum to either continuous wave (75 Hz) or frequency modulated wave (76 Hz) electromagnetic fields (EMF) (0.1-2.0 G and 0.035-0.7 V/m) lengthens the mitotic cycle and depresses the respiration rate. Once induced, these effects persist indefinitely in the presence of EMF without increasing or decreasing in magnitude beyond that due to normal variability of the organism. Similar effects are observed when either individual electric fields (0.7 V/m) or magnetic fields (2.0 G) are applied; however, the magnitude of the response is less than that observed with simultaneous fields. The individual field effects appear to be additive for respiration but not for nuclear division rate. For fields applied simultaneously at levels below 0.14 V/m and 0.4 G the response was independent of field intensity. No threshold was observed for simultaneously applied electric and magnetic fields; however, indirect evidence is presented that suggests either the electric or magne...

On the construction of models of continuous media interacting with an electromagnetic field: PMM vol. 43, no. 3, 1979, pp. 387–400

A general theory of constructing models of continuous media in the presence of interaction between material bodies and electromagnetic field is proposed which takes into account electric currents, polarization, and magnetization, and is based on the use of the fundamental variational equation. A closed system of equations, including the Maxwell equation, the equation of state, which define polarization, magnetization, and internal mechanical stresses, is established for continuous motions under specified external effects. (As shown in [1,2], it is possible to obtain from the fundamental variational equation, also, conditions at strong discontinuities). It is shown that for actual phenomena the fundamental variational equation locally reduces to the first and second laws of thermodynamics also in the presence of electromagnetic fields. A number of important aspects (such as the meaning of used partial time derivatives and of tensor component variations; fee concept of the electric field energy as a four-dimensional scalar; selection of scalar function for the Lagrangian, fixing of a nonzero functional δW∗; expressions for the uncompensated heat, for variational and real processes, etc.) that occur in the details of analysis related to the conversion of the first and second laws of thermodynamics to the universal variational equation. Typical specific examples of models of solid and fluid material media reacting with an electromagnetic field are considered.

Nonmetallic electrode system for recording EEG and ECG in electromagnetic fields

The construction of a nonmetallic electrode/lead system for recording biopotentials in the presence of electromagnetic fields is described. The system is simple to prefabricate and about as versatile and easy to use as metallic electrodes and connecting wires. It has been used for acute and chronic EEG and ECG recordings from chelonians (turtles and tortoises) with consistently satisfactory results.

Coherent pairing of excitons in insulators and semiconductors

A microscopic theory is developed concerning the coherent pairing of Wannier-Mott type excitons in insulators and semiconductors. The coherent pairing of excitons occurs in the presence of a resonant electromagnetic field and the resulting energy gap is in competition with that induced by the electromagnetic field. Due to the electrical neutrality of the electron-hole pairs, the excitation spectrum is of the excitonic insulator type and the presence of the electromagnetic field results in the splitting of the energies of excitation. The expression for the coherent gap function depends on the exciton density, the effective exciton mass, the exciton-exciton interaction, and the effective energy band gap, which is equal to the difference between the transition frequency and the frequency of the field and the binding energy of the exciton. Under resonance conditions and at temperatures below some valueT c , the biexciton state can exist provided that the dielectric gap is less than that for the biexciton state. The ground-state energy resulting from the coherent pairing of excitons is calculated and is found to be lower in energy than the normal exciton state. This indicates the existence of a bound biexciton state as long as there is a net attractive exciton-exciton interaction.

Gravitation field theory in flat space (in the presence of an electomagnetic field) with the most general stress tensor: equivalence with einstein's theory

Gravitational field equations and equations of motion for charged particles are obtained by an iterative method, starting from a Lagrangian density in the ''unrenormalized'' flat space-time. Assuming (a) that the proper masses and charges of the particles are constant and (b) that the gravitational potential is a tensor (no scalar component) in the linearized version (first order in the coupling constant f) we obtain, by imposing consistency to all orders in f, Einstein's theory which is therefore sounder in the field-theoretic approach than in the usual Riemannian one where there is some arbitrariness (cosmological term, etc.). The convergence of our procedure is based on Deser's method but also includes the presence of electromagnetic fields and considers in addition to the energy-momentum tensor T/sub alpha//sub beta/, the most general divergenceless tensor t/sub alpha//sub beta/ depending on four arbitrary parameters which prove to be no longer observable in the ''renormalized'' space. (AIP)

Charge-particle scattering in the presence of electromagnetic field: eikonal approximation

It is shown that the approximation which gives the equivalence of the results obtained by Zont (1975) and by the present authors is the low-frequency approximation.

Some aspects of linear irreversible thermodynamics and continuum mechanics in the presence of electromagnetic fields

Irreversible thermodynamics, conservation principles, andMaxwell relations are used to obtain the constitutive equations for a homogeneous fluid and aKelvin-Voigt viscoelastic solid in a electromagnetic field. Heat conduction equations for aVan der Waals gas and the viscoelastic media are obtained in a natural way and the effects of the electromagnetic fields are investigated.

Structure of Hydromagnetic Ionizing Shock Waves

A physical model is formulated to describe the changes taking place within a strong ionizing shock wave in the presence of electromagnetic fields. The model assumed is composed of a strong adiabatic shock to translational equilibrium followed by initiation of ionization and interaction between the flow and the electromagnetic fields. Eventually, recombination causes the flow to relax to a downstream state of thermodynamic equilibrium and zero current flow. Mathematical equations are derived to describe the changes in flow parameters and electromagnetic fields within the nonequilibrium current-carrying region for an arbitrary gas and arbitrary upstream magnetic field configuration. The analysis removes the indeterminacy in the solution of the shock jump conditions arising from the inability to fix the upstream electric field for ionizing shock waves. The particular case of switch-on shock waves in argon is then considered in detail. Solutions were only found when the downstream transverse magnetic field component was much less than the axial component.

Some aspects of linear irreversible thermodynamics in the presence of electromagnetic fields

Skew symmetricOnsager coefficients, which arise in the presence of magnetic fields, are included in the linear theory of irreversible thermodynamics. The motion of the thermodynamic coordinates is affected by a) decrease of the damping terms; b) an oscillatory motion is imparted; and c) the motion cannot be expanded in orthogonal components. Irreversible thermodynamics, conservation principles, andMaxwell relations are then applied to a charged particle moving in an electromagnetic field.

Energy of Infinitely Long, Cylindrically Symmetric Systems in General Relativity

A definition of is proposed for systems invariant under rotations about, and translations along, a symmetry axis. This (which is called energy or energy) takes the form of a covariant vector Pi, which obeys the conservation law Pi; i=0. C is localizable and locally measurable: The component of Pi along the world line of an observer is the C-energy density he measures. Near the symmetry axis of a static system, where strong gravitational fields are absent, C-energy density reduces to proper mass density T00. C is propagated by Einstein-Rosen gravitational waves and by cylindrical electromagnetic waves. In vacuo and in the presence of electromagnetic fields the C on a space-like hyper-surface is minimized when the system is static; and the difference between the potential part and the kinetic part is a Lagrangian for the Einstein-Maxwell field equations. C can be a powerful tool in the analysis of finite as well as infinite cylindrically symmetric systems. Here it is used to elucidate the nature of Einstein-Rosen gravitational radiation, and to suggest and support the conjecture of flux resistance to gravitational collapse: In any configuration of electromagnetic fields collapsing toward a singularity, each electric and magnetic-field line is either entirely ejected from the collapsing region or entirely swallowed by it as collapse proceeds; there can be no flux threading a collapsed region.

Der Drehimpulssatz in der Thermodynamik der irreversiblen Prozesse

The conservation law of the angular momentum has not been given sufficient attention in thermodynamics of irreversible processes. It plays an important part, however, when irreversible processes in the presence of electromagnetic fields are examined and the intrinsic angular momentum, due to spins of electrons and nuclei and electron orbits in atoms and molecules, is taken account of. Then the thermodynamic properties of matter with the macroscopic intrinsic angular momentum as an additional extensive parameter can be developed. Thermodynamics of irreversible processes is completed by the fact that a characteristic irreversible process is now associated also with the conservation law of angular momentum and Bloch's equation of nuclear induction is thus obtained in a straightforward way as one of the phenomenological equations.

Some Questions in Relativistic Hydromagnetics

The basic equations describing the motion of an ideal relativistic fluid in the presence of electromagnetic fields are formulated both in their differential and in their integral form. From the integral equations shock conditions are derived. In the limit of weak shocks the velocities of propagation of the various kinds of shocks and the discontinuities of the various physical quantities are calculated.