Applications thermography

Gautherie M 1969 Application des cristaux liquides cholesteriques a la thermographie cutanee J. 

See Dths, application and evaduation Electrophotography Printing processes Thermography. 

By far the most important commercial applications of nematic liquid crystals are in the a multi-billion dollar display industry. Cholesteric, or chiral nematic liquid crystals have been used in coloured guest-host displays and in thermography/ther-mochromic applications. 

However, it was not until 1967 that the technology was woken from its slumber by Americans James Fergason and George Heilmeier. These two developed the first technical applications of liquid crystals in thermography and the first liquid crystal displays Merck resumed its interest in liquid crystals, and the business began. 

Nonetheless, they became a mere laboratory curiosity for decades until technical applications in thermography and displays were suggested in the USA and Merck resumed its interest in them. 

The general applicability of IR-thermography renders it a good tool for monitoring catalytic activity. The method is, however, limited by the lack of information on the structure of the reaction products formed. 

The demand for enzyme assays that not only monitor overall activity but also en-antioselectivity stimulated the development of further assay systems that are still, however, in a rather experimental state with respect to high-throughput enzyme screening applications. These methods include assays based on electron spin resonance spectroscopy (ESR) [91], nuclear magnetic resonance (NMR) [92,93], IR-thermography [94] or electrospray ionization spectrometry (ESI-MS) [95]. 

For reasons of cost, image quality", and process speed, none of the above processes is competitive with xerography. For these reasons, there has been little commercial emphasis on alternative electrophotographic processes during the past two decades. For office and desktop nonimpact printing applications, the principal alternatives to xerography are thermography and inkjet. 

Another technique utilizing radiation from an object as a means of measuring its temperature is that of thermography, that is, the mapping of surface temperature distributions over extended areas. This is fairly widely used in the medical field for the detection of tumors near the surface of the skin and in industrial applications for detection of hot spots, such as defective insulators on power lines, defects in furnace walls, and areas of heat leaks in buildings. Usually, comparison measurements, rather than the actual determinations of temperature values, are made in thermography. Resolutions of 0.05°C to 0.1 °C are attainable under the best conditions. 

Finally, we mention several current applications somewhat outside of biochemistry in the usual sense. Thermography has slowly been coming to the fore. Many of the problems associated with the analysis of thermograms were treated at the Fifth International Symposium on Temperature (Plumb, 1972) in 1972 and new applications were discussed at the Sixth Symposium (Schooley, 1982) in 1982. Of perhaps more current interest is the greatly expanded interest in temperature measurement in hyperthermia and hypothermia. A recent New York Academy of Sciences conference has done an excellent job of reviewing this (Ann. N.Y. Acad., 1980). Cetas also wrote a general review of thermometry in this field (Cetas, 1968). Perhaps the most exciting new method in thermometry is that of optical fluorescence, which we described earlier. Catheters, whole-body scanners, etc., have been made for use with this method. At this point, 0.01°C is probably the least imprecision that can be obtained with the commercial instrument (Luxtron), with data obtained every 0.1 sec. Improvements are likely, however, as needs are made known to the company. 

The reflective wavelength of cholesteric liquid crystals varies according to temperature. Such an effect has been made useful in thermography. It has been applied in the diagnosis of cancers by displaying the skin temperature distribution. It has also been applied to test faults in integrated circuits. The applications also include thermometers and temperature warning indicators and non-destructive detection. 

In the fifth part of this article (Section VI), heat transfer in tumors is discussed with application in thermography and hyperthermia. Similar to mass transfer, two theoretical approaches—lumped and distributed parameter—to describing heat transfer in normal and neoplastic tissues are described and used to predict temperature distributions during normo-and hyperthermia. Various techniques to induce localized and whole-body hyperthermia are also summarized. 

Gautherie M 1969 Application des cristaux liquides cholesteriques a la thermographie cutanea J. Physique. Coll. C 4 122-6... 

Therefore, the condition D/d = 2 is a critical value, above which the thermography is applicable to detect the delamination or air voids in the C/SiC composite panel. More importantly, the errors in diameter measurement decrease with the increase of D/d and within the detectable range of D/d >2, the errors in depth measurement seem to decrease with depth increase. 

Dependence of pitch on temperature applications to thermography In most pure cholesteric materials, the pitch is a decreasing function of the temperature. An elementary picture of the temperature dependence of the pitch can be given in analogy with the theory of thermal expansion in crystals. " Assuming anharmonic angular oscillations of the molecules about the helical axis, the mean angle between successive layers... 

The strong temperature dependence of the pitch has practical applications in thermography, as was first demonstrated by Fergason. " " The material has to be so chosen that the pitch is of the order of the wavelength of visible light in the temperature range of interest. This is achieved by preparing suitable mixtures. Small variations of temperature... 

The subject of liquid crystals has now grown to become an exciting interdisciplinary field of research with important practical applications. This book presents a systematic and self-contained treatment of the physics of the different types of thermotropic liquid crystals - the three classical types, nematic, cholesteric and smectic, composed of rod-shaped molecules, and the newly discovered discotic type composed of disc-shaped molecules. The coverage includes a description of the structures of these four main types and their polymorphic modifications, their thermodynamical, optical and mechanical properties and their behaviour under external fields. The basic principles underlying the major applications of liquid crystals in display technology (for example, the twisted and supertwisted nematic devices, the surface stabilized ferroelectric device, etc.) and in thermography are also discussed. 

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