Practical distinction between optically

Figure 4. A practical distinction between optically uniaxial and optically biaxial drawn (or extruded) material. For optically uniaxial material, the area fraction exhibiting extinction between crossed circular polars is greatest when the normal to the plane of the thin section is parallel to the draw axis. For optically biaxial material, the greatest area fraction is observed in a section cut so that the angle between its normal and the draw axis is equal to half the optic axial angle of a monodomain.

BRET [31, 32]), lock-in detection techniques exploiting optical switches [33], and schemes for alternating D/A excitation (ALEX [34]). The increased attention to quantitative FRET imaging encompasses the use of polarization [35-39], the perennial issue of calibration and standards [40-44], and practical guides to operational principles and protocols ([45, 46] and other references above). The fundamental distinctions between the requirements for live and fixed cell imaging cannot be overemphasized, as is exemplified in a report of erroneous FRET determinations with visible fluorescent proteins (VFPs) in fixed cells [47],... 

This expression highlights an important distinction between EELS and optical experiment, namely that the virtual photon field associated with the fast electron is longitudinal ( 11 ) whereas the real photon field is transverse (E q) [3.23]. This difference does not affect the main point of the photon analogy namely that electron energy loss and optical experiments measure the same quantity e(a>) in most (and practically all the) cases. It does mean that the polarisation of the electric field acting on the atomic system is defined differently in both cases, a fact of obvious importance for anisotropic materials. 

The im< e mode produces an image of the illuminated sample area, as in Figure 2. The imj e can contain contrast brought about by several mechanisms mass contrast, due to spatial separations between distinct atomic constituents thickness contrast, due to nonuniformity in sample thickness diffraction contrast, which in the case of crystalline materials results from scattering of the incident electron wave by structural defects and phase contrast (see discussion later in this article). Alternating between imj e and diffraction mode on a TEM involves nothing more than the flick of a switch. The reasons for this simplicity are buried in the intricate electron optics technology that makes the practice of TEM possible. 

An optical flame sensor installed at the beginning of the pipeline is the most suitable device for such an isolation system, since the propagating flame from the explosion has to be detected and extinguished. Pressure detectors alone are, in principle, not suited to the case on hand because there is no distinct separation between the pressure and flame fronts for explosion in pipelines. Optical ir sensors that have a relatively low sensitivity to daylight are normally chosen and have proved themselves amply in industrial practice. Therefore, daylight into the pipe in the vicinity of the sensor must be avoided. It is necessary to flush the optical lens with gas (e.g., nitrogen, air) to keep it dust-free. 

Evidently, such an idealization need not be found in practice. Entropically driven fluctuations of the bilayers can bend them beyond planarity, and punctures and channels between bilayers may occur. Conventionally, one calls a mesophase lamellar when it is (i) optically anisotropic, and (ii) exhibits a smectic diffraction pattern. In some systems, more than one distinct lamellar mesophase is found. 

---