Passive sources

Fig. 2.17 Pourbaix diagrams for selected metals showing regions of corrosion, immunity, and possible passivation. Source Ref 9...

In order to perform resource discovery and routing, both active and passive sources of information are important. Users provide active input when they reach safe areas and smartphones provide passive input by constantly storing GPS tracks. 

Four different methods used for integrated-path remote gas sensing are discussed here. One of these (tunable diode laser absorption spectroscopy, TOLAS) uses a narrow linewidth source of radiation (usually a laser diode) and the other three methods use broadband sources of radiation. These three analyze the spectrum of the radiation after it has traversed the atmospheric path in different ways both differential optical absorption spectroscopy (DOAS) and Fourier transform infrared (FTIR) spectroscopy analyze the entire spectrum over the spectral region of interest, whilst absorption correlation methods record the spectrum after it has been filtered optically with either an optical filter or a sample of the target gas itself. These four methods use an active source of radiation. It is also possible to carry out integrated-path remote gas sensing using a passive source. 

As long as the gas turbine serves as a passive cooling system, it can generate electricity for the NPP electric machinery and systems even after the reactor shutdown in other words, the gas turbine also provides the BN GT plant with a passive source of electricity. Electricity supply redundancy is achieved by placing an accumulator battery and an oil-fired emergency generator in the transportable module of the main equipment. 

Chen, B., A. K. Flatt, H. Jian, J. L. Hudson, and J. M. Tour. Molecular grafting to silicon surfaces in air using organic triazenes as stable diazonium sources and HF as a constant hydride-passivation source. Chem. Mater. 17, 2005 4832—4836. 

Seismic Tomography of Volcanoes ) with body or surface waves from active or passive sources, or using ambient seismic noise (see Noise-Based Seismic Imaging and Monitoring of Volcanoes and Seismic Noise ). 

For passive sources (local earthquakes), the depth of seismic model resolved from tomographic inversion cannot be larger than the maximum depths of sources. 

In order to be 100% safe from a hydrogen explosion (sources passivation air, CO2), a hydrogen removal system is installed before the CO2 passivation air enters the stripper. 

Dopant species can be codeposited with the Si02 by introducing small amounts of the dopants in hydride or haUde form. P-doped Si02, called P-glass, functions as an insulator between polysiUcon gates and the top metallisation layer of ICs. It is also used as a final passivation layer over devices, and as agettering source (17). 

Health and Safety. Remover formulas that are nonflammable may be used in any area that provides adequate ventilation. Most manufacturers recommend a use environment of 50—100 parts per million (ppm) time weighted average (TWA). The environment can be monitored with passive detection badges or by active air sampling and charcoal absorption tube analysis. The vapor of methylene chloride produces hydrogen chloride and phosgene gas when burned. Methylene chloride-type removers should not be used in the presence of an open flame or other heat sources such as kerosene heaters (8). 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

Acid Coolers. Cast Hon trombone coolers, once the industry standard (101), are considered obsolete. In 1970, anodically passivated stainless steel sheU and tube acid coolers became commercially available. Because these proved to have significant maintenance savings and other advantages, this type of cooler became widely used. Anodic passivation uses an impressed voltage from an external electrical power source to reduce metal corrosion. 

Use and Uimitations of Electrochemical Techniques A major caution must be noted as to the general, indiscriminate use of all electrochemical tests, especially the use of AC and EIS test techniques, for the study of corrosion systems. AC and EIS techniques are apphcable for the evaluation of very thin films or deposits that are uniform, constant, and stable—for example, thin-film protective coatings. Sometimes, researchers do not recognize the dynamic nature of some passive films, corrosion produc ts, or deposits from other sources nor do they even consider the possibility of a change in the surface conditions during the course of their experiment. As an example, it is note-... 

Today for this kind of object, the aluminum anodes are usually insulated and connected via cables outside the tank. By this means it is possible to purify and activate the anodes by applying anodic current pulses from an external voltage source. This is necessary during the course of operation since the anode surfaces can be easily passivated by oil films [7]. 

By identifying the potential sources of failures, it is possible to develop controls to address those hazards. These controls might be passive physical items (e.g., dikes, walls, vents), active physical systems (e.g., fire suppression, pressure limiters, temperature controls), or administrative procedures. 

Polarisation from an external source may also affect the range of passivity. Cathodic polarisation may depress the potential from the passive to the active region (see Fig. 3.14) and thus care should be taken to avoid contact with any other corroding metal. Anodic polarisation, on the other hand, can stabilise passivity provided that the potential is not increased into the range of transpassivity (see Fig. 3.14) and anodic protection is quite feasible. 

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