Focused heat source

Materials having a higher vapor pressure at low temperatures ate typically vaporized from resistively heated sources such as those shown in Figure 5a. Refractory materials requite a high temperature to be vaporized. A focused high energy electron-beam heating is necessary for vaporization (Fig. 5b). 

Fig. 5. Thermal vaporization sources (a) hairpin (b) spiral (c) basket (d) boat and (e) canoe, which ate all resistively heated sources and (f) focused...

Pyrolytic-laser-assisted CVD is analogous to thermally driven CVD, but instead of a diffuse heating source, a focused laser beam is used to define deposition areas spatially (32, 38, 39) or to heat the gas phase selectively (228). The use of laser has the added advantages of increased energy flux and rapid heating. To avoid photochemistry, the gas phase must be transparent to the radiation. 

The temperature profile evolves according to the heat equation (5) with the heat source supplied by absorption of the focused laser beam. An additional advection term accounts for the influence of convection ... 

Because of their intimate link with energy production in nuclear reactors, fission products and their nuclear data have long occupied an important position in reactor technology. In recent years, interest in short-lived fission-product decay data has increased markedly, as their relevance to different areas of research and technology has become recognized. In addition to their importance for estimation of the fission-product decay-heat source term in nuclear reactors, the increasing attention being focused on the assessment of the hazards associated with the release, transport and... 

Discussions on how to increase the hydrogen generation efficiency therefore often focus on how to maximise the temperature that can be used by the process, whether by maximising the HTR outlet helium temperature or by reducing pinches in heat exchangers. On the lower end of the secondary helium temperature spectrum, the importance of the helium return temperature is often overlooked. However, as a component of the average heat source temperature, it must, according to the Carnot principle, have an influence on the efficiency. 

Laser pyrolyzers are practically the only type of radiative heating pyrolyzer with certain applicability. Attempts were made in the past to use a strong light/heat source and focus the beam with lenses [20] to achieve the desired power output. However, the laser as a radiative energy source is much more convenient. The laser beam can be focused onto a small spot of a sample to deliver the radiative energy. This provides a special way to pyrolyze only a small portion of a sample. A variety of laser types were used for pyrolysis purposes normal pulsed, Q-switched, or continuous wave (cw) [21], at different energy levels. More common are the normal pulsed high-power lasers. 

Decomposition involves the liberation of the analyte (metal) of interest from an interfering matrix by using a reagent (mineral/oxidizing acids or fusion flux) and/or heat. The utilization of reagents (acids) and external heat sources can in itself cause problems. In elemental analysis, these problems are particularly focused on the risk of contamination and loss of analytes. It should be borne in mind that complete digestion may not always be required as atomic spectroscopy frequently uses a hot source, e.g. flame or inductively coupled plasma, which provides a secondary method of sample destruction. Therefore, methods that allow sample dissolution may equally be as useful. 

Noncontact heating utilizing a focused microwave source was demonstrated by Fermer et al. [141]. In their work, a single-mode microwave cavity was used to heat 100 pL of PCR mixture in a 0.5-mL polypropylene tube for 25 cycles. Most recently, microwave-induced milliliter-scale PCR (see Fig. 8) was reported [142] for real-time PCR analysis. Although the amount of amplified nucleic acid product... 

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