Reflectivity modulation

A schematic of a PL system layout is shown in Figure 5. This optical system is very similar to that required for absorption, reflectance, modulated reflectance, and Raman scattering measurements. Many custom systems are designed to perform several of these techniques, simultaneously or with only small modifications. 

A more recent example of this technique has been the study on human absorption characteristics of fexofenadine [109], Fexofenadine has been shown to be a substrate for P-gp in the in vitro cell lines its disposition is altered in knockout mice lacking the gene for MDRla, and co-administration of P-gp inhibitors (e.g. ketoconazole and verapamil) was shown to increase the oral bioavailability of fexofenadine [110-113], Hence, it is suggested that the pharmacokinetics of fexofenadine appears to be determined by P-gp activity. In the human model, the intestinal permeability estimated on the basis of disappearance kinetics from the jejunal segment is low, and the fraction absorbed is estimated to be 2% [114], Co-administration of verapamil/ketoconazole did not affect the intestinal permeability estimates however, an increased extent of absorption (determined by de-convolution) was demonstrated. The increased absorption of fexofenadine was not directly related to inhibition of P-gp-mediated efflux at the apical membrane of intestinal cells as intestinal Peff was unchanged. Furthermore, the effect cannot be explained by inhibition of intestinal based metabolism, as fexofenadine is not metabolised to any major extent. It was suggested that this may reflect modulation of efflux transporters in hepatocyte cells, thereby reducing hepatobiliary extraction of fexofenadine. 

Section III deals with the surface excitations of the anthracene crystal, confined in the first (SJ, second (S2) and third (S3) (001) lattice planes. The experimental observations are briefly summarized. A simple model shows how the fast radiative decay arises and how the underlying bulk reflection modulates this superradiant emission, as well as why gas condensation on the crystal surface strongly narrows this emission, thus accounting for the observed structures. An intrinsic process is proposed to explain the surface-to-bulk relaxation at low temperatures, observed in spite of the very weak surface-to-bulk coupling for k 0 states. 

Parietal cell, thyroid, and antinuclear antibodies have been reported to be increased in lithium-treated patients (145-147). Autoantibodies directed at pituitary functions have also been demonstrated in lithium-treated patients and this may reflect modulation by lithium of pituitary and hypothalamic centers (148, 149). Tissue-specific autoantibodies such as these may or may not be related to autoimmune disease lithium may, in any case, modulate preexisting autoimmune processes rather than induce them (150). 

As already mentioned, the reflection modulation technique is relatively simple but for thicker or absorbing thin films it becomes much more complicated due to the multiple reflection effects in the used multilayer structure (Fig. 1) which may lead to erroneous results, if not correctly taken into account [10,20]. In that case, the measurement of the incidence angle dependence of the modulation intensity is required. Through a correct analysis of experimental data one can get both real and imaginary parts of r, as well as its anisotropy and ri3 tensor components). 

Otto suggested that, as in electroreflectance, where changes in the structure of the interface cause changes in the reflectance, modulations of the interface by the molecular vibrations can change it as well. Thus, the reflectivity R is given by... 

Saul, J. P. (1990). Beat-to-beat variations of heart rate reflect modulation of cardiac autonomic outflow. News in Physiological Science, 3,32-37. 

Polyaniline films have not only been shown to exhibit electrochromism in the visible region, but also in the microwave and far-IR regions of the electromagnetic spectrum. A polyaniline film doped with camphorsulfonic add and incorporated into a sohd state microwave shutter demonstrated that the transmittance and reflectance of X-band microwave energy could be modulated [6]. At a wavelength of 10 GHz, the shutter could be switched between 4.8% transmission when the polymer is oxidized and 42% transmission when the polymer is neutral. When utilized in a reflective device configuration in combination with poly(diphenylamine), polyamline yields a high reflective modulation in the far-IR [119,120]. This device shows a reflectance contrast of 53% at 10.5 p,m, 28% at 16.5 p,m, and 46% at 620 nm. 

The discussion above illustrates how the application of hydrostatic or uniaxial stress can shift the exciton energy and features such as peaks A and A in the reflection spectrum. If such pertu2d>ations aire applied periodically and the reflected light analysed using a phase sensitive detector than various spectral features %diich are not obvious in the direct reflection spectrum can be enhanced (30). The reflectance modulation is given by... 

The rear glass wall can be replaced by a silicon VLSI die to make a silicon backplane SLM as in Fig. 5 b. The SLM is now a reflective modulator with the aluminum from the second metal layer of the VLSI process acting as a mirror [8]. Circuitry on the backplane can be used to address the FLC pixels as either dynamic random access memory (DRAM) [9] or static RAM (SRAM) [10]. The silicon backplane SLM is very important to the development of nondisplay applications as it allows large arrays of small pixels to be built on a silicon wafer capable of high addressing speeds. Compared with line-at-a-time multiplexed SLMs, these sil-... 

The relative humidity of the ambience plays a large role for devices operated in air, and designs incorporating MgFj, SiO, and LiF become nonfunctional if the water is desorbed, as under vacuum. Such a strong dependence on the ambient conditions is not a necessary limitation for Deb devices, though, but designs with CrjOj are able to maintain their incorporated water at least to a pressure <10 Torr, as found by Inoue et al. Such devices have been operated for >5 x 10 c/b cycles at a reflectance modulation of 50%. 

Modem instruments cover the range 400-2S00nm and include a reflectance module. Samples can be measured non destructively with no pretreatment. Samples can be even scanned in their containers. 

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