Oscillatory electric field

The effect of ac, rather than dc, fields on the steady shear viscosity has also been investigated. An ac field might be desirable as a means of periodically reversing, and thereby minimizing, electrically induced migration or chemical reactions. High-frequency ac fields are also required if one is to avoid a crossover to a conduction-dominated regime in which the effective polarizability is controlled by conductivities rather than polarizabilities of the particles and medium (see Section 8.2.1.1). Klass and Martinek (1967) found that at a fixed 

However, superimposed on this gradual decrease in t] they found a sharp, pronounced minimum in rj at an electric-field frequency of around 200 Hz (again see Fig. 8-9). A similar 

Although this mechanism is consistent with available data, a full test of the theory is still lacking. Also, some ER fluids don t seem to show a minimum in viscosity over the range of frequencies tested. Frequency dependencies can also occur because of a crossover to a conduction-dominated regime at low frequencies, and this was not included in the See-Doi calculations. 

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Figure 2.47 Micro mixer based on the excitation of an electro-osmotic flow around a cylinder by an oscillatory electric field (top). The bottom of the figure shows particle traces on both sides of the liquid/liquid interface with no electric field (above) and with the electric field switched on (below), as described in [145].

Szabo, I. (1986) New ion optical devices utilizing oscillatory electric fields principle of operation and analytical theory of multipole devices with two dimensional electric fields. Int. J. Mass Spectrom. Ion Process. 73, 197-235. 

It has be emphasised that no account has taken of any possible interaction between permanent dipoles, so that the equation will be valid only for polar gases and for dilute solutions of polar molecules in non-polar solvents. Moreover, the equation is not valid at high frequencies, because in that case the dipoles are not able to reorient sufficiently quickly in the oscillatory electric field, so that at optical frequencies a = oca-... 

Sonication This involves the generation of shear forces in a cell sample in the vicinity of a titanium probe (0.5 mm in diameter and 10 cm long) that vibrates at 20,000 Hz. The device contains a crystal of lead zirconate titanate that is piezoelectric, i.e., it expands and contracts when an oscillatory electric field is applied to it from an electronic oscillator. The ultrasonic pressure waves cause microcavitation in the sample, and this disrupts the cell membranes, usually in a few seconds. 

This Hamiltonian models a molecule composed of two atoms acted on by an oscillatory electric field. Thus, it is a prototype of diatomic molecules in laser fields. 

At optical frequencies a = 0 , because the molecules cannot reorient sufficiently quickly in the oscillatory electric field of the light wave for the orientational polarisability to contribute, as discussed further in section 9.2.4. Setting a = a in equation (9.9) gives in terms of the optical refractive index and, if this expression for is inserted, equation (9.16) can then be rearranged as follows ... 

The microwave ionization studies were extended to highly excited helium atoms, with the electron configuration ls(n 30)s It was found that the ionization rate does not increase monotonically as a function of the oscillatory electric field. The ionization curves of He exhibit one or more plateau regions and a bump near threshold. These structures are both absent in the respective curves of hydrogen. From this fact it can be concluded that these specific features are caused by the interaction between the highly excited He valence electron and the Is electron. The authors considered a quasistatic model that relates the structures to anticrossing effects of the He state under study with adjacent Stark states. 

In Eq. 30, eo and Soo denote the limiting low- and high-frequency dielectric constants, respectively, hi general, for the Ae co) of polar molecules embedded in non-polar solvents under an oscillatory electric field E = Eq exp(i6of) we have [27] ... 

Apply oscillatory electric field at that position. 

Fig. 6.3. Motions and crystalline arrangements of trapped charged particles. The left figure is a photo of a cluster of 32 charged micro-particles stored in a Paul trap. The two other figures are results from a numerical simulation of a 1000-ion Coulomb crystal confined in a linear quadrupole trap. In the left and the center panel the micro-motion of the particles in the oscillatory electric field can be seen. The amplitude increases proportionally to the distance from the center. The time-averaged positions plotted in the right part for a selected sample shows that the ions remain well-localized. This is the basis for defining an effective translational temperature of the ion cluster by subtracting the periodic oscillation from the overall motion.

In an oscillatory electric field, the field-induced polarization will lag behind the applied electric field in some angle 5e. The complex electric field E and the complex displacement D can be expressed as f 1]... 

T is the relaxation time, thus under an oscillatory electric field E=Eothe induced current density d due to the ion displacement polarization can be expressed as [43]... 

For X-rays, the interaction between radiation and matter is primarily via interaction between the electrons and the oscillatory electric field of the electromagnetic beam. E = EoCOs(a>t). An electron will, in the X-ray beam, be accelerated by the oscillating electric field an accelerated charged particle, on the other hand, will... 

Dielectric Spectroscopy - Surface Characterization ofLiquid-borne Colloids When an oscillatory electric field is applied to a colloidal suspension, the electric double layer around the particle will be polarized. The complex dielectric properties of the suspension, the loss factor, and the relative permittivity are determined by performing several isothermal scans as a function of frequency in the range of 100-10 ° Hz. The dielectric relaxation of particles can be determined through the dielectric spectroscopy and the... 

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