Plasma frequency, definition

These are quantized vibrations of conduction electrons in a metal or semiconductor 4°). The quantized energy levels of the collective longitudinal vibrations of the electron gas are quasi-particles in the sense of the definition given above and are called plasmons. The frequency of this longitudinal vibration, the plasma frequency u>P, is given by 40>... 

Equation (8.1.24) implies that the dielectric constant e(co) becomes zero at co = cQp/ is real but negative for coelectromagnetic waves with frequencies smaller than the plasma frequency will be attenuated or absorbed by the solid), and is positive definite for co>cop... 

One can see that the definition of the ratio np-jmso as the plasma frequency becomes the dividing line where the metal goes from being transparent to an almost perfect reflector of... 

We have considered so far the case of free electrons. In a solid, however, there are not only the conduction electrons that can be considered as free, there are also the electrons in the core orbits. And they contribute to the dielectric constant. At frequencies the order of the plasma frequency, the contribution of the core electrons do not depend significantly on < this dependence occurs at much larger frequencies only. However, Eq. (13.50) implies that e( >optical spectra are measured at frequencies oo that, even significantly larger than ajp, stiU remain in the domain where the core contribution remains independent of m. Therefore, what the opticians call naturally e o, i-C., the value of e they measure at > > core electrons it is only at much larger frequencies that e will decreases to unity. We keep this definition of foo that is conventional, and it means that in Eq. (13.50), we have to replace 1 by Eoo-... 

This technique uses a argon plasma induced by high frequency radiation as an excitation source. A plasma is a volume of luminous gas with a portion of its atoms or molecules in an ionised state. This definition can also be applied to a flame however, in analytical spectroscopy the term plasma is normally reserved for an electrical discharge. 

The beneficial effects were related to these plasma concentrations, as were the time to the first bout of atrial fibrillation, the frequency of bouts of atrial fibrillation, and the time between episodes. However, when atrial fibrillation occurred there was no difference in the ventricular rate in the different groups. Adverse effects necessitated drug withdrawal in four patients one had heart failure and two had gastrointestinal symptoms. These effects were not dose-related, although there were too few occurrences for a definitive conclusion. The authors suggested that this stepwise approach, with increasing doses of propafenone and increasing doses of quinidine could be beneficial in the treatment of paroxysmal atrial fibrillation. 

By definition, sustained release formulations differ pharmaceutically and pharmacokinetically from the innovator drug. The excipients and particle sizes (usually larger) of the formulation are designed to dissolve more slowly and are almost always drugs for chronic diseases. The common advantages are reduction in dose frequency (and thus, hopefully, improved patient compliance see that chapter in this book) or reduction of Cmax for a standard AUC, which can improve tolerability when adverse events are plasma concentration related. Regulatory approval of these formulations... 

By definition, plasma is an ionized gas that is spacially neutral. That is, there are an approximately equal munber of positive and negative charges in a given volume. It should also be stressed that these are radio-frequency plasmas, not direct current plasmas. The terms anode and cathode have no meaning, on the time scale of diffusion, because the polarity of the electrodes is reversing every 37 nsec (at 13.56 MHz). Because there is only a few V/cm gradient in the plasma, and because of the enormous mass difference between electrons and ions, the motion of the ions is almost unaffected by the RF field. However, ions may be affected by the build-up of a DC self-bias on the electrodes if the electrodes are of different areas. 

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