Pr-0 system

The polyimide-base PR system [79,80] was designed on the premise that porphyrin-electron acceptor (quinones or imide moieties) systems are well-known model compounds for photosynthetic processes and exhibit very interesting charge transfer properties [81], A high quantum yield of charge separation can be achieved in these systems. Polyimides are found to be photoconductive and allow charge transport [82], Furthermore, polyimides possess high Tg and therefore, the electric field-induced dipole orientation can be fixed after imidization [83],... 

In summary, the steady state and transient performance of the poly(acrylamide) hydrogel with immobilized glucose oxidase and phenol red dye (pAAm/GO/PR) demonstrates phenomena common to all polymer-based sensors and drag delivery systems. The role of the polymer in these systems is to act as a barrier to control the transport of substrates/products and this in turn controls the ultimate signal and the response time. For systems which rely upon the reaction of a substrate for example via an immobilized enzyme, the polymer controls the relative importance of the rate of substrate/analyte delivery and the rate of the reaction. In membrane systems, the thicker the polymer membrane the longer the response time due to substrate diffusion limitations as demonstrated with our pAAm/GO/PR system. However a membrane must not be so thin as to allow convective removal of the substrates before undergoing reaction, or removal of the products before detection. The steady state as well as the transient response of the pAAm/GO/ PR system was used to demonstrate these considerations with the more complicated case in which two substrates are required for the reaction. 

The design of a polymer-based system requires understanding both the steady state and transient behavior in response to the substrate or analyte of interest. For sensor applications, this information is obtained during the operation of the sensor. However, for other applications of environmentally sensitive polymers, such as drag delivery systems, the polymer response to the substrate/analyte is not usually studied directly. Our work with the pAAm/GO/PR system illustrates the usefulness of an in situ probe to measure what governs the membrane s performance in response to the substrate/analyte and how to analyze it. We continue to use this valuable information in the further... 

Electronic Structure Calculations. We have used first-principles electronic structure calculations as manifest in the (spin) density functional linearized muffin-tin orbital method to examine whether the asymmetry in properties is reflected in a corresponding asymmetry in the one-electron band structure. While in a more complete analysis explicit electron correlation of the Hubbard U type would be intrinsic to the calculation,17 we have taken the view that one-electron bandwidths point to the possible role that correlation might play and that correlation could be a consequence of the one-electron band structure rather than an integral part of the electronic structure. We have chosen the Lai- Ca,Mn03 system for our calculations to avoid complications due to 4f electrons in the corresponding Pr system. 

Fig. 8.2 Comparison of the concentrationtime profiles in a batch (A) and a batch recirculation photoreactor (PR) system (B) (adopted from Levenspiel 972, p. 174/175). In...

Modem pRS systems are accompanied with powerful spectral acquisition and analysis software, which enables the creation of ID (cross section), 2D, and 3D maps of various features from the ID, 2D, or 3D array of spatially resolved Raman spectra. Various features that can be routinely mapped include intensity variations of specific peaks (by plotting the user-defined peak intensity or integrated area under the peak), intensity ratio of two different bands, peak position (by user-defined peak fitting routines such as Gaussian, Lorentzian), and peak widths. The obtained images can be further processed to highlight the spatial variations of the acquired spectra. For example. Boolean maps, which present a binary... 

Electronic noses and tongues are arrays of sensors used to characterize complex samples, with the former being arrays of gas sensors while the latter are composed of liquid sensors [1]. These devices are composed of a chemical sensing system and a pattern recognition (PR) system [usually an artificial neural network (ANN)]. The array sensing system allows different properties to be measured simultaneously [2], Each chemical, which reaches the sensor array, will produce a characteristic pattern and therefore a database of patterns will be built up for a series of chemicals [2],... 

The PR system allows the devices to be capable of recognizing simple or complex odors or tastes. PR techniques are used for data processing, and the data generated by each sensor are processed by a PR algorithm before the resnlts are analyzed. Advantages of this approach include the following ... 

A Pechini-type sol-gel process was used to synthesize YAG nanophosphors, YAG Ce,Pr system, with concentration of Pr " from 0.125 to 2 mol% while maintaining the content of Ce " constant at 2 mol%, for white light-emitting diode (LED) applications [278]. Yttrium and aluminum nitrates and acids were mixed... 

From a model based on a set of detailed-balance rate equations which expresses the two-reservoir coupling rate between F and Pr systems, we have confirmed that it is possible to establish an equilibrium net population of F spins in times much shorter than Tj, either at negative or positive temperature. This takes place when four simultaneous NMR saturation transitions couple into one of the two Pr transitions (Fig. 7). 

There are no available data about the phase diagram of the Sc-Pr system. Taking into consideration the data on the Sc-Ce system it is possible to predict a complete mutual miscibility of the components in each other in liquid and in bcc solid phases. aSc and aPr have different crystal structures (hep and dhep respectively), therefore, they probably form limited solid solutions. 

Attempts have been made to force praseodymium, which follows cerium in the lanthanide series, into an intermediate valent state. Since all intermetallic systems have a Pr ion with a valence close to three, pressure was applied to some of these systems, but all efforts have failed. Enhanced hybridization, however, was found in insulating Pr systems containing oxygen. Within the RBa2Cu307 a series, which usually exhibit high-temperature superconductivity, the suppression of superconductivity in PrBa2Cu07... 

Onsager, O. X, Wang, H., and Blindheim, U., Synthesis of Ce olefins by ethylene oligomerization in the presence of NifiT-LljXa-AljRe-xCk-PR system, Helv. Chimica Acta, 52, 107, 1969. 

Instead of using a passive molecule such as dioctylphthalate, active plasticizers that may contribute to either the charge-transport or EO effect can be utihzed. The molecule ECZ, widely used in PR polymers, is a plasticizer that contributes to charge transport as well. It has been reported that an inert plasticizer reduces the Tg more efficiently than a charge-transporting plasticizer, but reduces the charge-carrier mobility and the PR phase shift. The molecule 4-4 -n-pentylcyanobiphenyl (5CB) has been reported to lower the Tg of a PVK-based PR system from 230 to 25 °C... 

The role of push-pull molecules in PR systems is to provide refractive index modulation in response to an electric field. In polymers with a low glass transition temperature (Tg), where the molecules are relatively free to rotate due to a higher free volume, the chromophores can reorient in the applied/generated electric field. Because of the anisotropy in polarizability of the chromophores, such a reorientation will induce high refractive index anisotropy termed as orientational birefringence. The ability of a chromophore molecule to induce refractive index change is usually expressed as the figure of merit (FOM) defined by Equation 8.4 [44],... 

Another important PR polymer system based on PVK is the composite PVK PDCST BBP Cgo in the ratio 49.5 35 15 0.5 wt%. At an electric field of 120 V (xm this PR system exhibited a TBC gain coeffident of 200 cm and a response time of 50ms at lWcm writing intensity [54]. Later, the NLO molecules in this system were replaced by the dicyanostyrene derivatives AODCST and 4-(azepan-l-yl)benzyhdenemalononitrile (7-DCST) resulting in a very fast response time of 5 ms at 1W cm and at 100 V (x m while maintaining the... 

Figure 8.17 Charge-transporting polymer and the NLO molecule used in a stable PR system with a non-PVK backbone.

Figure 8.18 Dififraction efficiency as a function of electric field for the PR system PATPD/7-DCST/ECZ/C60, (54.5 25 20 0.5 w/w%).

Kotake, S., et al., 2005. Peasibihty study on commerciahzed fast reactor cycle systems current status of the PR system design. In Proceedings of GLOBAL 2005, Tsukuba, Japan, October 9-13, 2005. 

It should be mentioned also that the hypersensitive transition F2 -f— H4 has to be included in the fit of Pr " systems, because otherwise a negative value for the U2 parameter is found (just as is sometimes observed by inclusion of the transition in the fit). An intensity parameter with a negative value has no physical significance. Extraction of a reliable 2 parameter is often a problem for Pr " ", since the p2 <— H4 transition is situated in the infrared spectral region and caimot be observed in an aqueous solution (it is masked by vibrational transitions). In order to find more reliable intensity parameters for Pr +, Quimby and Miniscalco (1994) introduced a modified Judd-Ofelt theory in which the luminescence branching ratios are included in the fit (see sect. 7.7). 

Figure 5. Simplified Pourbaix diagram for the Pr system in aqueous solution.

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