Effects of Electric and Magnetic Fields

A weak magnetic field B splits each spectral term into 27 + 1 components of energy separation  

Here juj is the Bohr magneton, Mj the component of total angular momentum in the field direction, and gj the Lande g factor given in the case of LS coupling by  

The consequent appearance of the spectrum is a splitting into several lines unless 5 = 0 for both terms involved, in which case a symmetric triplet results. The special case of singlet-singlet transitions split in a magnetic field is known, for historical reasons, as the normal Zeeman effect. Otherwise we are dealing with the anomalous Zeeman effect.  

In a magnetic field strong enough to make the split components of adjacent multiplets overlap, we have what is known as the Paschen-Back effect. 2 Once again L and S are uncoupled and the spectral splitting pattern tends toward series of triplets as for the normal Zeeman case with each triplet component itself showing the field-free multiplicity of the transition. 

Additional selection rules to those given in Section 2.1.2 arise for the Zeeman effect, namely  

At relatively high gas pressures ( 1 torr), an ECR plasma may not occur due to gas-phase collision. At relatively low gas pressures ( 0.1 torr), an ECR plasma occurs, and diamond has been grown at substrate temperatures as low as 500°C with a uniform dischai e area of 200 cm. l  

Deformations of nematic elastomers in electric fields have been described [44, 57, 58]. Reversible shape variations of a nematic sidechain LCE swollen with low molecular weight (LMW) materials in an electric field were reported, provided the elastomer is freely suspended [57]. If it is compressed between glass slides, no field effect is observed. Shape changes in mainchain LCEs swollen with a LMW material have been investigated in an electric field [44]. Similarly, reversible shape changes were observed for freely suspended LCEs on a time scale of one second and no shape changes were obtained for the unswollen elastomers [57]. More recently further experiments of the same type were done on swollen sidechain LCEs [58]. In addition it was checked that there was no response to an electric field if both, LMW material and LCE, were in their isotropic phase [58]. 

No reports on deformations and shape changes of nematic elastomers in external magnetic fields appear to exist yet. 

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The separation of ions according to their m/z ratios is achieved using electric and/or magnetic fields in a number of ways. The trajectories of ions moving in such fields are determined by their m/z values and these can be monitored to ascertain their mass. Double-focusing instruments use the combined effects of electric and magnetic fields to effect separation (Figure 3.19). In a typical instrument, after the ions have been accelerated away from the ion source... 

A distinction must be made between gravitational effects for which the presence of material in the field does not change the intensity of the field, and the electrostatic and magnetic effects for which the presence of material within the field does alter the intensity. A complete treatment of electrostatic and magnetic effects would require a discussion of electromagnetic theory and the use of Maxwell s equations. However, we wish only to illustrate the thermodynamic effects of electric and magnetic fields. We therefore accept the results of a complete treatment and apply the results to simple systems. 

Biological Effects of Electric and Magnetic Fields Associated with Proposed Project Seafarer" National Academy of Sciences-National Research Council Wash., DC, 1977. 

The effectiveness of electric and magnetic fields were compared for a value of the dielectric loss e" = 0.515. The ratio of E/H for a magnetic field of 500 gauss was 1.01 and for a field of 1000 gauss was 1.02. This is in agreement with Freedericksz and Zwetkoff, in that E/H appears to be independent of the magnetic field. The value they reported was 1.08, which is appreciably higher. It is felt that this difference is not caused by experimental error. 

R.B. Meyer, Effects of electric and magnetic fields on the structure of cholesteric liquid crystals, Appl. Phys. Lett. 12(9), 281-282, (1968). 

Dunmur, D.A., Palffy-Muhoray, P. Effect of electric and magnetic fields on orientational disorder in liquid crystals. J. Phys. Chem. 92, 1406-1419 (1988)... 

As before, the first term on the right of Eq. (47) represents the effect of electric and magnetic fields alone and the second term accounts for the effect of collisions. In the case of elastic collisions involving only an ion rrii in its own neutral gas as shown in the reaction... 

Since radiofrequency radiation is also associated with the effects of electric and magnetic fields, we also discuss the presence and hazards of these fields in this section. 

Thomson constructed a cathode-ray tube with a fluorescent screen, such as that shown in Figure 2.4 , so that he could quantitatively measure flie effects of electric and magnetic fields on the thin stream of electrons passing flirough a hole in the positively charged electrode. These measurements made it possible to calculate a value of 1.76 X 10 coulombs per gram for the ratio of the electron s electrical charge to its mass. ... 

D. Zhelev and D. Needham, in Biological Effects of Electric and Magnetic Fields, (ed.) D. O. Carpenter, Academic Press, Orlando, FL, 1994, pp. 105-142. 

Methods In this paper, the thermo-piezo-electro-m neto-elastic model of bone has been used and the effects of electric and magnetic fields with various magnitudes, types and frequencies on the existent models, have been evaluated through simulation. 

R. B. Meyer, Effects of Electric and Magnetic Fields on the Structures of Cholesteric Liquid Crystals, Appl. Rhys. Lett., 12, p. 281 (1968). 

In the overwhelming majority of studies of LC polymers with mesogenic side groups, most of the attention has been focused on synthesis and the study of the thermal properties and structure of this type of polymer. We have much less information on the physical properties of LC polymers, especially in comparison to the corresponding data on low-molecular-weight liquid crystals and LC polymers. It is important to note that many physical parameters of LC polymers are determined and calculated based on the study of their orientational behavior under the effect of electric and magnetic fields these data will be partially examined in Chapters 8 and 9. 

A specific property of liquid crystals is the ability to undergo structural transformadons under the effect of electric and magnetic fields. The appearance of lyo- and thermotropic mesomorphism in polymer systems also implies the possibility of controlling their structural-optical properties with external fields. This ability to alter the structure in electric and magnetic fields was one of the most convincing arguments in support of the validity of existence of polymers in the LC phase in general. 

The orientation of comb-shaped polymers under the effect of electric and magnetic fields, the types of observed electro- and magneto-optical effects, and the characteristic values of the orientation order parameter, dielectric, and diamagnetic anisotropy serve as the basis for drawing analogies in the orientational behavior of low-molecular-weight liquid crystals and comb-shaped LC polymers. 

Estimation of the anisotropic coefficients of the viscosity and the elasticity constants is necessary for und standing the essence of orientational phenomena in liquid crystals. The adequacy of the continuous models has been verified and the local situation on the molecular level has been described with them, which is important for describing the effects of orientation and reorientation (relaxation) of the system under the effect of electric and magnetic fields. The effect of anisotropy of the viscosity is so powerful that it affects almost all of the rheological characteristics of LC systems, including flow especially of an unoriented sample (the situation in die usual rheological experiments). 

In macroscopic media Maxwell s equations must be supplemented by the constitutive relations which enable the average effect of a large number of atoms to be taken into account without requiring detailed knowledge of the response of individual atoms to the effects of electric and magnetic fields. For an isotropic permeable conducting dielectric these relations are of the form ... 

One of the important topics not covered in this text is that concerning the effects of electric and magnetic fields on LCPs, and associated optical effects. To cover this vast subject would be difficult in one chapter, and the merest of introductions is given at the end of Chapter 7 readers are urged to read the recent texts texts given at the end of this preface for a thorough coverage of this subject. However, it is intended to cover this area in a future volume. 

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