Let us consider some of the above plots qualitatively for the simplest possible cases a resistor R in parallel or in series with a capacitor C. Let the single time constant t = RC and define the Debye function D((ot) = D -jD = [1 + ymr], which leads to a semicircle in the complex plane. The D = ((ut)/[1 + (oxf]. A plot of this functions vs. co yields a peak at co = r and an eventual dropoff proportional to tu at m cOm and to m at co (0. Thus the final slopes of log(D ) vs. log( T) are -Hi and -1. It is easy to show that for the parallel connection Z = RD (ot), -Z = RD Xcox), M = (CJQ ijcox) D(o)x), and M = (CJQ D (ox). For the series connection, one finds F = (jcoQ D(o)x), Y = GD Xcox), e = (C/O D (ox), and e = (CICc)D ((ox). These results demonstrate that under different conditions -Z , M , Y , and e all exhibit D (cox) response. Further, in some sense, the pairs Z and M = ijcoCc)Z, and e and F = (j(oCc)s are closely related. Real materials often do not lead to IS results of the simple D (ox) semicircle form, however, but frequently involve a distorted or depressed semicircle in the complex plane which may arise from not one but several relaxation times or from a continuous distribution of relaxation times. Under such conditions, curves of-Z vs. v, for example, are often appreciably broader than that following from D (OX). [Pg.188]

It has been customary in much past work to plot -Z or M vs. v and either not give estimates of parameters, such as R and C, leading to the response or to estimate them roughly by graphical means. It is often found that the frequency at the peak, is at least approximately thermally activated. But this frequency involves both R and C, quantities which may be separately and differently thermally activated. Thus instead of using the composite quantity (0, which may be hard to interpret properly, we believe it to be far preferable to find estimates of all the parameters entering into an equivalent circuit for the situation. As we shall see, such estimates can best be obtained from CNLS fitting. [Pg.188]

One other type of plotting has been very common in the dielectric field in earlier [Pg.188]

Thus, a critical departure from previous approaches, common to all our learning methodologies, is the adoption of a solution format that consists of hyperrectangles (not points) defined in the decision space. [Pg.107]

For a detailed description of spectral map analysis (SMA), the reader is referred to Section 31.3.5. The method has been designed specifically for the study of drug-receptor interactions [37,44]. The interpretation of the resulting spectral map is different from that of the usual principal components biplot. The former is symmetric with respect to rows and columns, while the latter is not. In particular, the spectral map displays interactions between compounds and receptors. It shows which compounds are most specific for which receptors (or tests) and vice versa. This property will be illustrated by means of an analysis of data reporting on the binding affinities of various opioid analgesics to various opioid receptors [45,46]. In contrast with the previous approach, this application is not based on extra-thermodynamic properties, but is derived entirely from biological activity spectra. [Pg.402]

The previous approach is valid as long as the molecular reorientation can be described by a single correlation time. This excludes molecules involving internal motions and/or molecular shapes which cannot, to a first approximation, be assimilated to a sphere. Due to its shape, the molecule shown in Figure 15 cannot evidently fulfil the latter approximation and is illustrative of the potentiality of HOESY experiments as far as carbon-proton distances and the anisotropy of molecular reorientation are concerned.45 58... [Pg.118]

A second general approach is to use an alkali metal in conjunction with an electron carrier such as naphthalene. The electron carrier is normally used in less than stoichiometric proportions, generally 5 to 10 mole percent based on the metal salt being reduced. This procedure allows reductions to be carried out at ambient temperatures or lower in contrast to the previous approach which requires refluxing. A convenient reducing metal is lithium. [Pg.228]

During the same year as Hauser s reported synthesis of calphostin D, the Coleman laboratories published an alternative approach to this family of natural products [32]. This report included the enantioselective syntheses of both phleichrome and calphostin A and, like the previous approaches, started from an enantioenriched naphthalene. [Pg.163]

The common denominator for all the previous approaches to the perylenequinones is a diastereoselective oxidative coupling of homochiral 2-naphthols. Our group proposed an alternative enantioselective convergent synthesis that would greatly... [Pg.167]

The previous approach for solving the reconciliation problem allows the calculation, in a systematic recursive way, of the residual covariance matrix after a measurement is added or deleted from the original adjustment. A combined procedure can be devised by using the sequential treatment of measurements together with the sequential processing of the constraints. [Pg.137]

The higher surface area of CNTs can support a much higher density of enzymes than previous approaches such as thin films. Their high aspect ratio aids in the retention of enzyme-CNT conjugates in the matrix. CNTs also enhance the stability of adsorbed proteins relative to micro- or macro-scale supports, thereby helping to preserve or enhance enzyme bioactivity in the nanocomposites (Wang,... [Pg.187]

The ort/zo-quinone cyclization to the carbazole-3,4-quinones carbazoquinocin C 51 and ( )-carquinostatin A ( )-55a is more convergent than the previous approaches to these natural products, which required transformation to the ort/zo-quinone and/or introduction of substituents (prenyl or heptyl) following the carbazole ring formation (cf. Schemes 20,21, and 37). [Pg.143]

Few of the Venetian nobility go back to work after their noon break and a meat inspector would find little to do by that time of day anyway. Confident that one or other of the Mchiel brothers should be home, I copied out the Bernardo letter in an honest Roman hand and then created one to Domenico, giving myself the same glowing introduction without mentioning Bernardo s previous approach to the Maestro. [Pg.47]

The coupling of electronic and vibrational motions is studied by two canonical transformations, namely, normal coordinate transformation and momentum transformation on molecular Hamiltonian. It is shown that by these transformations we can pass from crude approximation to adiabatic approximation and then to non-adiahatic (diabatic) Hamiltonian. This leads to renormalized fermions and renotmahzed diabatic phonons. Simple calculations on H2, HD, and D2 systems are performed and compared with previous approaches. Finally, the problem of reducing diabatic Hamiltonian to adiabatic and crude adiabatic is discussed in the broader context of electronic quasi-degeneracy. [Pg.383]

© 2024 chempedia.info