Dedicated coils

An electron gun produces and accelerates the electron beam, which is reduced in diameter (demagnified) by one or more electromagnetic electron lenses. Electromagnetic scanning coils move this small electron probe (i.e., the beam) across the specimen in a raster. Electron detectors beyond the specimen collect a signal that is used to modulate the intensity on a cathode-ray tube that is scanned in synchronism with the beam on the specimen. A schematic of the essential components in a dedicated STEM system is shown in Figure 2. 

For a manufacturer the difficulty is to estimate future developments or trends in NMR microscopy. Based on dedicated laboratory-made hardware developed by the NMR microscopy users and on their requests for new commercial hardware and software, the following topics could become more important micro-coil applications, multiple receiver systems and multi-coil arrangements, NMR microscopy at very high magnetic fields, MAS imaging and localized 1H MAS spectroscopy and localized single-shot 2D spectroscopy. There are no clear-cut distinctions between most of the individual topics, as will be discussed in the following sections. 

Fig. 5. Pulse sequence for MR detection of vibration using a radiofrequency field gradient. A binomial 1331 radiofrequency pulse (pulse length D, interpulse delay r) is applied in-phase with the mechanical wave. Thus the vibration period 7V is equal to 4(D + r). The number of cycles can be increased to ensure a better frequency selectivity. The constant RF field gradient generated by a dedicated RF coil allows space encoding without using conventional static field gradients (from Ref. 16 with permission from Elsevier).

Fig. 7. MR detection of ultrasonic waves oscillating at 515 kHz. (a) Phase image of a phantom without insonation. (b) Phase image with 40 W peak power insonation. In the NMR sequence 50,000 cycles of synchronized sine-shaped motion-sensitizing gradient were applied. Arrows indicate the null-gradient positions of the dedicated gradient coil system. Wavelength is around 2.9 mm and peak matter displacement is around 120 nm. From Ref. 30, reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley Sons, Inc.

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

The wire which would normally go to the spark plug is replaced by a wire which is taken to a box containing one pre-war mechanical twin-coil relay or vibrator per cylinder. Each of these wires drives its own dedicated relay , the current energises the relay coil but the other side of the relay coil is left unconnected. The wiring arrangement is shown in the diagrams below. 

Phosphorus-31 MRS continues to be a powerful tool to study cancer models in rodent xenografts. Because such studies are conducted at high magnetic fields with dedicated surface or volume coils, SNR and... 

Os) special probes with dedicated low-frequency coils are available. ... 

Fig.4.4 Animal MR image with 100 urn resolutio obtained on a clinical 3 Tesla MR scanner usin dedicated MR receive coil (Philips Research, Ha burg, Germany).

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