Field excitation

Figure Bl.7.18. (a) Schematic diagram of the trapping cell in an ion cyclotron resonance mass spectrometer excitation plates (E) detector plates (D) trapping plates (T). (b) The magnetron motion due to tire crossing of the magnetic and electric trapping fields is superimposed on the circular cyclotron motion aj taken up by the ions in the magnetic field. Excitation of the cyclotron frequency results in an image current being detected by the detector electrodes which can be Fourier transfonned into a secular frequency related to the m/z ratio of the trapped ion(s).

Figure Cl.5.4. Comparison of near-field and far-field fluorescence images, spectra and lifetimes for the same set of isolated single molecules of a carbocyanine dye at a PMMA-air interface. Note the much higher resolution of the near-field image. The spectmm and lifetime of the molecule indicated with the arrow were recorded with near-field excitation and with far-field excitation at two different excitation powers. Reproduced with pennission from Trautman and Macklin [125].

Rotating armature These have a rotating armature and a static field excitation system. The output from the armature is taken through the sliprings. 

It is, however, recommended for better control and machine utilization that when the load s demand is for constant-speed operation, this must be met through separate synchronous motors at unity p.f. and the p.f. must be improved separately through synchronous condensers with variable field excitation. 

The above situation is, however, found when the machine is run singly. When it is operated in parallel with another source, the field excitation will not influence... 

If the field excitation is also lost, the generator will run as an induction motor again driving the primer mover as above. As an induction motor, it will now operate at less than the synchronous speed and cause slip frequency current and slip losses in the rotor circuit, which may overheat the rotor and damage it, see also Section. 1.3 and equation (1.9). A reverse power relay under such a condition will disconnect the generator from the mains and protect the machine. 

Figure 16.21 Variation in the load currents with a change In the field excitation on load...

This is a very good motor for direct connection to certain loads, particularly where constant speed is required. NEMA defines it as a synchronous machine which transforms electrical power from an alternating-current system into mechanical power. It usually has direct-current field excitation by a separately driven direct-current generator or one directly connected to the motor. This motor remains synchronous with the supply frequency and is not affected by the load. Proper application requires consideration of the following ... 

Pull-in torque For a synchronous motor, this is the maximum constant torque under which the motor will pull its connected inertia load into synchronism, at rated voltage and frequency, when its field excitation is applied. The speed to which a synchronous motor will bring its load depends on the power required to drive it, and whether the motor can pull the load into step from this speed depends on the inertia of the revolving parts. So, the pull-in torque cannot be determined without having the Wk as well as the torque of the load. 

Permanent Magnet Motor. A permanent magnet motor is a direct-current motor in which the field excitation is suppled by permanent magnets. 

Shunt-Wound Motors. These motors operate at approximately constant speed regardless of variations in load when connected to a constant supply voltage and with fixed field excitation. Maximum decrease in speed as load varies from no load to full load is about 10-12%. 

Figure 1. DC-biased, ten-well superlattice. A shaped laser field excites a wave packet localized initially in the injection well. The objective is to created the maximum density possible in the detection well, at a chosen target time.

Hayazawa, N Inouye, Y. and Kawata, S. (1999) Evanescent field excitation and measurement of dye fluorescence using a high N.A. objective lens in a metallic probe near-field scanning optical microscopy J. Microsc., 194, 472-476. 

We also tried measurements to demonstrate that hot spots make significant contributions to surface enhanced Raman scattering [34]. For this purpose, the sample of nanoparticie assembly was doped with Raman active molecules by a spincoating method, and near-field excited Raman scattering from the sample was recorded. We adopted Rhodamine 6G dye as a Raman active material, which is... 

Figure 3.10 (a) Topography of the sample, (b), (c) Near-field excited Raman spectra at dimers 1 and 2, respectively,taken attwodifferentincident polarizations. The peaks marked with are unassigned, (d) Near-field two-photon excitation images of dimers 1 and 2. (e) Near-field Raman excitation images of dimers 1 and 2 obtained for... 

While on the topic on electrical conduction and resistance offered by an electrically conducting medium it is usual to extend to a phenomenon called superconductivity this has now been recognized as having a profound impact on the electrical field. Exciting possibilities exist. The phenomenon is exhibited by certain types of matter and is characterized by two fundamental properties ... 

Figure 2. Regular reflectance Replication of Snellius law for reflected and refracted radiation at interface in dependence on the refractive indices of the media adjacent to this interface, demonstrating total internal reflectance and evanescent field, exciting fluorophores close to the waveguide or even surface plasmon resonance.

Finally, there is one other experiment that we know of that found a resonant signature in the strong field excitation of a molecule. In this experiment, the symmetric dissociation channel of 0 + was monitored in a high resolution coincidence ion spectrometer [41]. From the KER of the fragments, excitation to the B3iTg state was identified, among other states. However, this particular... 

The point is now to estimate the maximum number of photons that can be detected from a burst. The maximum rate at which a molecule can emit is roughly the reciprocal of the excited-state lifetime. Therefore, the maximum number of photons emitted in a burst is approximately equal to the transit time divided by the excited-state lifetime. For a transit time of 1 ms and a lifetime of 1 ns, the maximum number is 106. However, photobleaching limits this number to about 105 photons for the most stable fluorescent molecules. The detection efficiency of specially designed optical systems with high numerical aperture being about 1%, we cannot expect to detect more than 1000 photons per burst. The background can be minimized by careful dean-up of the solvent and by using small excitation volumes ( 1 pL in hydrodynamically focused sample streams, 1 fL in confocal exdtation and detection with one- and two-photon excitation, and even smaller volumes with near-field excitation). 

A. L. Stout and D. Axelrod, Evanescent field excitation of fluorescence by epi-illumination microscopy, Appl. Opt 28, 5237-5242 (1989). 

In most luminescence experiments, at least in the mineral luminescence field, excitation is due to absorption of a single photon. However, it is also possible for a luminescence center to absorb two or more long-wavelength photons to reach the excited state. Two-photon excitation occurs by the simultaneous absorption of two lower-energy photons. Such excitation requires special conditions including high local intensities, which can only be obtained from laser sources. 

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