Magnetic field distortions

No distortion, neither geometrical neither due to magnetic fields, thanks to proximity focusing. The non sensitivity of the tube to magnetic fields enables software enhancement of the images such as flat field corrections. 

With a standard image intensifier, characterized by a gain of more than x10,000, the quantum well effect is clearly avoided. Nevertheless this very high gain reduces the image dynamics unless strong attenuation is introduced at the tube output (iris or neutral filter). Also a standard intensifier is bulky, affected by pincushion distortion and magnetic fields which can be a serious limitation in some applications. 

Note Wherever a cable lead connecting the above devices (such as for RTDs) has to pass through a magnetic field, it may be screened with tinned copper-braided wires to nullify the effect of stray fields. The field may distort the readings. 

A brief review is given on electronic properties of carbon nanotubes, in particular those in magnetic fields, mainly from a theoretical point of view. The topics include a giant Aharonov-Bohm effect on the band gap and optical absorption spectra, a magnetic-field induced lattice distortion and a magnetisation and susceptibility of ensembles, calculated based on a k p scheme. 

The situation changes drastically in the presence of a high magnetic field perpendicular to the axis. As has been discussed in Sec. 2, Landau levels without dispersion appear at the Fermi level considerably, leading to a magnetic-field induced distortion [13,14]. 

Table 2. Calculated energy gap due to an in-plane Kekul distortion for CNTs having chiral vector L/a = (m, 2m). The critical magnetic flux (p. and the corresponding magnetic field are also shown. The coupling constant is A, = 1.62.

Fig. 9. An example of calculated in-plane lattice distortions induced by a high magnetic field (left) and the dependence of the maximum gap due to in-plane lattice distortions on a magnetic field (right).

Electronic properties of CNTs, in particular, electronic states, optical spectra, lattice instabilities, and magnetic properties, have been discussed theoretically based on a k p scheme. The motion of electrons in CNTs is described by Weyl s equation for a massless neutrino, which turns into the Dirac equation for a massive electron in the presence of lattice distortions. This leads to interesting properties of CNTs in the presence of a magnetic field including various kinds of Aharonov-Bohm effects and field-induced lattice distortions. 

Various theories have been postulated to explain the phenomenom that magnetic fields can change the way in which calcium carbonate precipitates and crystallizes, the most probable one being that the applied field distorts the electrical charge carried by small particles of calcium carbonate that have already formed in the water, thus affecting the way in which they adhere to form large particles. 

The significant improvements in sensitivity achieved during the last 5 years have been because of improved probe design and radiofrequency circuits. Since the probe needs to be located very close to the sample, it must be made of a material with a low magnetic susceptibility, for otherwise it would cause distortions of the static magnetic field thereby adversely affecting line shape and resolution. Much research has therefore been undertaken by NMR spectrometer manufacturers to develop materials that... 

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