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External Electromagnetic Field (external + electromagnetic_field)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Gauge-independent quantum dynamics on phase-space of charged scalar particles

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2-3 2003
S. Varró
On the basis of the Hamiltonian form of the Klein-Gordon equation of a charged scalar particle field introduced by Feshbach and Villars, the gauge-invariant 2×2 Wigner matrix has been constructed whose diagonal elements describe positive and negative charge densities and the off-diagonal elements correspond to cross-densities in phase-space. The system of coupled transport equations has been derived in case of interaction with an arbitrary external electromagnetic field. A gauge-independent generalization of the free particle representation due to Feshbach and Villars is given, and on the basis of it both the nonrelativistic and the classical limits of the general relativistic quantum Boltzmann-Vlasov equation(RQBVE) is discussed. In the non-relativistic limit (p/mc,0) the set of equations of motion decouple to two independent quantum transport equations describing the dynamics of oppositely charged positon and negaton densities separately. In the classical limit(,,0) two relativistic Boltzmann-Vlasov equations result for the diagonal positon and negaton densities. It is obtained that, though in the latter equations the Planck constant , is absent, the real part of the cross-density does not vanish. [source]

Electronic excitations and optical spectra of Pt2 and Pt4 on Cu(001) modeled by a cluster

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010
George Pal
Abstract The photoabsorption spectra of Pt2 and Pt4 clusters on the Cu(001) surface are computed using two different theoretical methods: the symmetry-adapted cluster expansion configuration interaction from quantum chemistry and a recently developed linear response approach to treat electron,hole correlations in the presence of an external electromagnetic field. Comparing the energetically low-lying optical excitations, we find very good agreement between the two methods. For different orientations of the adsorbed clusters with respect to the surface, we find that the most intense optical peaks occur when the polarization of the applied laser pulse is parallel to the surface. [source]

Modeling normal and altered human erythrocyte shapes by a new parametric equation: Application to the calculation of induced transmembrane potentials

BIOELECTROMAGNETICS, Issue 7 2006
S. Muñoz San Martín
Abstract We present simple parametric equations in terms of Jacobi elliptic functions that provide a realistic model of abnormal variations in size which maintain the biconcave shape of a normal erythrocyte (anisocytosis) and abnormal variations in shape which maintain the original volume of the erythrocyte (poikilocytosis), as well as continuous deformations from the normal to the altered shapes. We illustrate our results with parameterizations of microcytes, macrocytes, and stomatocytes, and we apply these parameterizations to the numerical calculation of the induced transmembrane voltage in microcytes, macrocytes, and stomatocytes exposed to an external electromagnetic field of 1800 MHz. Bioelectromagnetics 27:521,527, 2006. © 2006 Wiley-Liss, Inc. [source]

Calcite microcrystals in the pineal gland of the human brain: First physical and chemical studies

BIOELECTROMAGNETICS, Issue 7 2002
Simon Baconnier
Abstract A new form of biomineralization has been studied in the pineal gland of the human brain. It consists of small crystals that are less than 20 ,m in length and that are completely distinct from the often observed mulberry-type hydroxyapatite concretions. A special procedure was developed for isolation of the crystals from the organic matter in the pineal gland. Cubic, hexagonal, and cylindrical morphologies have been identified using scanning electron microscopy. The crystal edges were sharp whereas their surfaces were very rough. Energy dispersive spectroscopy showed that the crystals contained only the elements calcium, carbon, and oxygen. Selected area electron diffraction and near infrared Raman spectroscopy established that the crystals were calcite. With the exception of the otoconia structure of the inner ear, this is the only known nonpathological occurrence of calcite in the human body. The calcite microcrystals are probably responsible for the previously observed second harmonic generation in pineal tissue sections. The complex texture structure of the microcrystals may lead to crystallographic symmetry breaking and possible piezoelectricity, as is the case with otoconia. It is believed that the presence of two different crystalline compounds in the pineal gland is biologically significant, suggesting two entirely different mechanisms of formation and biological functions. Studies directed toward the elucidation of the formation and functions, and possible nonthermal interaction with external electromagnetic fields are currently in progress. Bioelectromagnetics 23:488,495, 2002. © 2002 Wiley-Liss, Inc. [source]