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Proton Accelerators
Published in Harald Paganetti, Proton Therapy Physics, 2018
The magnet pole consists of hills and valleys, and the Dees can be mounted in (some of) the valleys, so that the gap between the upper and lower hill can be minimized. A small gap needs less electric current in the magnet coils and also has a large effect on the exact shape of the magnetic field. The Dee is mounted on a copper pillar (stem), and the valley wall is covered with a grounded copper sheet (liner). At the bottom of the valley, a short plate connects the stem with the liner. The combination of Dee, stem, and liner acts as a resonant cavity. This means that an RF current can flow back and forth along the stem, with a frequency determined by the resonance frequency of this cavity. The Dee will get a negative potential when the electrons flow to the edge of the Dee, and when the electrons flow to the grounded liner, the Dee will get a positive potential. A quality factor Q of the cavity is defined in terms of the ratio of the energy stored in the cavity to the energy being dissipated in one RF cycle and can have a typical value in the order of 3,000–7,000.
Assembly of Microscopic Three-Dimensional Structures and Their Applications in Three-Dimensional Photonic Crystals
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
The successful outcome of the pilot study ensured that this approach would function in the fabrication of a 3D photonic crystal operating at shorter wavelengths. In addition to reduction of the working wavelength, active 3D photonic crystals with a resonant cavity structure and luminescent materials were targeted in the following study [4].
Electron Paramagnetic Resonance of Copper Proteins
Published in René Lontie, Copper Proteins and Copper Enzymes, 1984
In practice, the frequency of the alternating field is fixed, and the static or d.c. field is swept slowly through the resonance condition given by Equation (2). For reasons we will discuss later in this chapter, the energy levels are not sharply defined, so that the sample absorbs energy over a range of field values, giving an absorption line shape. The absorption of energy can be detected experimentally and its intensity depends on a number of factors, including the sample temperature, the number of electron spins in the sample, and the intensity of the applied alternating field. The source of the alternating radiation fields is usually a klystron, operating in the microwave frequency region between 1 and 100 GHz. The klystron is coupled by a waveguide to the resonant cavity in which the sample is placed and is locked electronically to the resonant frequency. A circulator is often incorporated between the klystron and the cavity to ensure optimum transfer of the microwave power from the klystron to the cavity and from the cavity to the detector. The cavity is coupled to the waveguide with a small iris, whose effective diameter can be controlled by the movement of a device such as a metal pin or a dielectric plunger. When the iris diameter is such that all the incident microwaves are absorbed by the cavity, the cavity is said to be critically coupled. The spectrometer is usually operated close to this condition. Inside the cavity the electromagnetic energy density is much higher than in the attached waveguide. The microwave energy absorbed by the sample at resonance depends on this energy density, expressed as a quality factor, Q, and on the size of the sample in relation to the cavity dimensions given by a filling factor, η.
The toxicity of respirable South African mine tailings dust in relation to their physicochemical properties
Published in Inhalation Toxicology, 2020
Charlene Andraos, Mary Gulumian
The surface activities of the samples were assessed using electron spin resonance (ESR) spectroscopy. The spin trap 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO, Sigma, St. Louis, MO), at a final concentration of 100 mM, was used to measure the short-lived •OH radicals generated by the particles (final concentration of 10 µg/mL). The production of •OH was measured in the presence of H2O2 at a final concentration of 10 mM. The addition of H2O2 facilitates ROS formation via the Fenton reaction. The reaction mixtures were directly transferred to an X band 9.8 GHz, Bruker EMX, Resonant cavity: TM 110; Sample cell holder: 4-bore AquaX ESR instrument (Bruker Instruments, Inc., Billerica, MA). The reaction was monitored at ambient temperature under the following settings: MW Power: 25 mW; Receiver Gain: 5.64 E 5; Time Constant: 40.96 msec; Conversion Time: 40.96 msec; Resolution X: 1024; Scans: 2; Sweep time: 41.94 sec; Sweep width: 100 G; Modulation Frequency: 100 kHz; Modulation amplitude: 3 G. The signal intensity from the splitting constants of the 1:2:2:1 spectrum in Supplementary Figure S2, which is characteristic of •OH (Halliwell and Gutteridge 2015), was used to measure the relative amount of radicals as arbitrary units (a.u.). More specifically, the intensities of the second and third peak in the 1:2:2:1 spectrum, as indicated by arrows in Supplementary Figure S2, correlated with the amount of •OH quantified and was therefore used to compare surface activities among tailings dusts.