Radiofrequency current

Figure 15.1—Inductively coupled plasma torch. A radiofrequency current (between 27 and 50 MHz) that induces circulation of the electrons in the inert gas drives the torch. The argon serves as an auxiliary gas, a cooling gas and the nebulisation gas. In the upper right is shown an optic device used to collect emitted light in the longitudinal axis of the plasma. Lower down, plasma generated by microwave.

Jackman WM, Wang Z, Eriday KJ, et al. Catheter ablation of accessory atrioventricular pathways (Wolff-Parkinson-White syndrome) by radiofrequency current. N Engl J Med 1991 324 1605-1611. 

Convection of heat via blood depends primarily on the local blood flow in the tissue and the vascular morphology of the tissue. Thermal diffusion is determined by thermal conductivity in the steady state, and thermal diffusivity in the unsteady state. In addition to these transport parameters, we need to know the volumes and geometry of normal tissues and tumor. In general, tumor volume changes as a function of time more rapidly than normal tissue volume. In special applications, such as hyperthermia induced by electromagnetic waves or radiofrequency currents, we need electromagnetic properties of tissues—the electrical conductivity and the relative dielectric constant. In the case of ultrasonic heating, we need to specify the acoustic properties of the tissue—velocity of sound and attenuation (or absorption) coefficient. 

During hyperthermia, terms representing the heat input to a specific tissue or whole body must be added to the proper system equation(s). For example, during whole-body or local hyperthermia induced by radiofrequency currents, microwaves, or ultrasound, a heat-generation term is added to the section of the body being heated. During hyperthermia with blood perfusion, the afferent blood temperature is set at a desired value, and the efferent blood is circulated to the central blood pool, or to the extracorporeal device used for heating the blood. Suitable numerical... 

Fig. 2.10. The quadrupole mass analyzer is an ion filtering device that creates an oscillating electric field between four rods, (a) Schematic of a quadrupole mass analyzer. -(L/+I/C0S (ot) and + U + 1/cos cot) are cumulative potential created by superimposed direct current potential U) and radiofrequency current potential (1/cos cot), (b) The encircled equation describes an area of stability for a particular m/z ion trajectory co = circular frequency to = field radius) depicted on the graph.

Dyke T R 1984 Microwave and radiofrequency spectra of hydrogen-bonded complexes in the vapor phase Topics in Current Chemistry 120 85-113... 

Electrical sources static electricity, electrical current, lightning, stray currents (radiofrequency electromagnetic radiation, overhead high voltage transmission lines, galvanic and cathodic protection stray currents)... 

The transverse magnetization and the applied radiofrequency field will therefore periodically come in phase with one another, and then go out of phase. This causes a continuous variation of the magnetic field, which induces an alternating current in the receiver. Furthermore, the intensity of the signals does not remain constant but diminishes due to T and T2 relaxation effects. The detector therefore records both the exponential decay of the signal with time and the interference effects as the magnetization vectors and the applied radiofrequency alternately dephase and re-... 

In addition to microwave plasma, direct current (dc) plasma [19], hot-filament [20], magnetron sputtering [21], and radiofrequency (rf) [22-24] plasmas were utilized for nanocrystalline diamond deposition. Amaratunga et al. [23, 24], using CH4/Ar rf plasma, reported that single-crystal diffraction patterns obtained from nanocrystalline diamond grains all show 111 twinning. 

Fig. 2.9.2 Radiofrequency, field gradient and current distributions requires a three-dimen-ionic current pulse sequences for two-dimen- sional imaging sequence [see Figure 2.9.1(a)] sional current density mapping. TE is the Hahn and multiple experiments with the orientation spin-echo time, Tc is the total application time of the sample relative to the magnetic field of ionic currents through the sample. The 180°- incremented until a full 360°-revolution is pulse combined with the z gradient is slice reached. The polarity of the current pulses...

FIGURE 6-2. Algorithm for the treatment of acute (top portion) paroxysmal supraventricular tachycardia and chronic prevention of recurrences (bottom portion). Note For empiric bridge therapy prior to radiofrequency ablation procedures, calcium channel blockers (or other atrioventricular [AV] nodal blockers) should not be used if the patient has AV reentry with an accessory pathway. (AAD, antiarrhythmic drugs AF, atrial fibrillation AP, accessory pathway AVN, atrioventricular nodal AVNRT, atrioventricular nodal reentrant tachycardia AVRT, atrioventricular reentrant tachycardia DCC, direct-current cardioversion ECG, electrocardiographic monitoring EPS, electrophysiologic studies PRN, as needed VT, ventricular tachycardia.)... 

A quadrupole mass analyzer is made of four hyperbolic or circular rods placed in parallel with identical diagonal distances from each other. The rods are electrically connected in diagonal. In addition to an alternating radiofrequency (RE) potential (V), a positive direct current (DC) potential (U) is applied on one pair of rods while a negative potential is applied to the other pair (Fig. 1.17). The ion trajectory is affected in x and y directions by the total electric field composed by a quadrupolar alternating field and a constant field. Because there is only a two-dimensional quadrupole field the ions, accelerated after ionization, maintain their velocity along the z axis. 

Quadrupoles are comprised of four metal rods, ideally of hyperbolic cross section, arranged as shown in Fig. 5.4. A combination of radiofrequency (RF) and direct current (DC) voltages are applied to each pair of rods, which creates an electric field within the region bounded by the rods. Depending on the RF/DC ratio, the electric field between the rods will allow ions in a narrow m/z range to pass, typically 0.8 m/z —just how narrow will depend on a number of factors which influence the resolution. Hence, by changing the RF/DC ratio in a controlled manner, the quadrupole can be... 

---