Dipole Loop Research Articles

The microwave structure of hot coronal loops

view Abstract Citations (18) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The microwave structure of hot coronal loops Holman, G. D. ; Kundu, M. R. Abstract The thermal cyclotron emission from model dipole magnetic loops is computed. It is shown that a simple, isothermal dipole loop can show a great deal of spatial and polarization structure at microwave frequencies. This structure is sensitive to the observation frequency and angle of observation. Two qualitatively distinct microwave loop structures can be distinguished: (1) 'thin loop,' observed as a string of independent microwave peaks, corresponding to different harmonics of the local electron gyrofrequency; and (2) 'thick loop,' the harmonics are merged, so that a more continuous microwave structure is observed. It is shown that the presence of an external plasma can result in a change in the observed mode of polarization along one leg of a loop, without a change in the sign of the line-of-sight magnetic field. Models such as these, along with high-resolution microwave and related observations, can provide an excellent diagnostic of the magnetic and plasma properties of coronal loops. Publication: The Astrophysical Journal Pub Date: May 1985 DOI: 10.1086/163159 Bibcode: 1985ApJ...292..291H Keywords: Coronal Loops; Cyclotron Radiation; Microwave Emission; Solar Radio Emission; Thermal Radiation; Brightness Temperature; Plasma Diagnostics; Polarization (Waves); Solar Magnetic Field; Solar Wind; Stellar Models; Solar Physics full text sources ADS |

Electrodynamics of moving media and the force on a current loop

The development of the Chu formulation of the electrodynamics of moving media is reviewed. The force on a current loop and/or magnetic dipole is developed for three different models and all three are shown to be identical, as already shown in previous publications. The electromagnetic momentum associated with the three different models is derived and the equality of the force expressions is confirmed on the basis of the momentum conservation theorem of electrodynamics. The paper is based on a lecture delivered at Technion at the occasion of Professor Franz Ollendorff's 80th birthday.

Simulation of dislocation motion through a dislocation forest

A computer simulation is carried out of the motion of a glide dislocation, under the action of an externally applied stress, through a dislocation forest creating a long-range stress field. The simulation is made to fit dislocation movement in (110) planes in NaC1-type crystals and (0001) planes in c.p.h. crystals. It is shown that the field irregularities in c.p.h. crystals are appreciably higher than in crystals with a structure of the NaCl type. The penetration stress of the glide dislocation through a dislocation forest τf is determined and it is shown that its dependence on the dislocation forest density ρ must obey the relation: τf = αGb √ρ. The obtained values of a are in good agreement with the experimental values α for NaC1-type crystals and found to be lower for Zn crystals. It is shown that the probable causes of the discrepancy between the values of α for Zn are the processes of intensive loop and dislocation dipole formation taking place in Zn as a consequence of strong irregularity of internal stress fields. [Russian Text Ignored].

On the magnetic dipole representation of small loop antenna

The use of a magnetic dipole to represent a small loop antenna is examined by comparing their field components. Particular attention is paid to the dipole approximation in the near field, and curves are presented which allow an accurate and rapid assessment to be made of the error as a function of angle and distance from the loop. The curves, which apply to any loop with a circumference between 0.0001 λ and 0.1 λ, enable the correction to the dipole field to be estimated. The difference between the loop and magnetic dipole fields is expressed algebraically for large distances from the loop, and for near-axial angles.

A glide induced mechanism of dipole loop annihilation

A glide induced mechanism of dipole loop annihilation

The Impedance of Dipoles in a Circular Tunnel with an Axial Conductor

The electromagnetic fields of dipole emitters located inside an empty tunnel or cylindrical cavity are first formulated. Both electric and magnetic types are considered. The results are used to deduce an expression for the change of self-impedance due to the presence of the tunnel walls. The input resistance R of the electric dipole is approximately a constant for frequencies less than about 25 MHz for a typical tunnel radius of 2 m. In contrast, for the same conditions, R for the magnetic dipole or small loop varies approximately as the square of the frequency. The theory is extended to allow for the presence of an axial conductor or cable within the tunnel. The presence of the cable increases R for both a transversely oriented electric dipole and a circumferentially oriented magnetic dipole but decreases R for an axial electric dipole. Not surprisingly, the axial magnetic dipole is only weakly influenced by the presence of the cable.

Source models to account for Lake Mungo palaeomagnetic excursion and their implications

INDICATIONS of large and rapid excursions in the direction of the ancient geomagnetic field continue to create considerable excitement and debate in palaeomagnetic circles. Barbetti and McElhinny1 have published detailed evidence of a remarkable excursion at Lake Mungo, Australia dated at about 30,000 yr ago, on which they had briefly reported previously2. I consider here various simple sources, all in the Earth's outer core, that could account for that excursion—an eccentric radial dipole or current loop, an eccentric horizontal dipole, and a pair of eccentric radial current loops of opposite sign—and discuss the merits of each in light of the modern geomagnetic field and with regard to the magnitude and spatial extent of the anomalous field produced.