Indirect probes

Indirect Probes Some types of probes do not measure corrosion directly, but yield measurements that also are useful in detecting corrosion. Examples include ... 

No investigation of a solid, such as the electrode in its interface with the electrolyte, can be considered complete without information on the physical structure of that solid, i.e. the arrangement of the atoms in the material with respect to each other. STM provides some information of this kind, with respect to the 2-dimensional array of the surface atoms, but what of the 3-dimensional structure of the electrode surface or the structure of a thick layer on an electrode, such as an under-potential deposited (upd) metal At the beginning of this chapter, electrocapillarity was employed to test and prove the theories of the double layer, a role it fulfilled admirably within its limitations as a somewhat indirect probe. The question arises, is it possible to see the double layer, to determine the location of the ions in solution with respect to the electrode, and to probe the double layer as the techniques above have probed adsorption Can the crystal structure of a upd metal layer be determined In essence, a technique is required that is able to investigate long- and short-range order in matter. 

Although use of the second harmonic signal from metal surfaces as an indirect probe of chemisorption lacks structural specificity, the utility of the technique is clearly demonstrated by the experiments reported here. The next step in our studies will be to demonstrate how one can directly monitor chemisorption with some degree of molecular specificity via the resonant second harmonic signal from the nonlinear susceptibility of adsorbed species. 

An indirect probe of the A s for a series of compounds is obtained from a consideration of the half wave potentials. The reduction potential is related to the electron affinity by the following equation 243 ... 

Until a recent x-ray diffraction study (17) provided direct evidence of the arrangement of the pigment species in the reaction center of the photosynthetic bacterium Rhodopseudomonas Viridis, a considerable amount of all evidence pertaining to the internal molecular architecture of plant or bacterial reaction centers was inferred from the results of in vitro spectroscopic experiments and from work on model systems (5, 18, 19). Aside from their use as indirect probes of the structure and function of plant and bacterial reaction centers, model studies have also provided insights into the development of potential biomimetic solar energy conversion systems. In this regard, the work of Netzel and co-workers (20-22) is particularly noteworthy, and in addition, is quite relevant to the material discussed at this conference. 

This reaction was chosen for study because it can indirectly probe the geometry and charge changes. If the bending idea is correct, the H+ of HC1 should interact with the bent NO- and the Cl should interact with the Co+. On the other hand, if photolysis merely activates the linear species, then Cl-could interact with N0+ to produce N0C1. The experimental results are shown in eq. 12. The system is photoactive (with negligible thermal reactivity on the time... 

Metal loading studies of this type serve to enlighten the factors which control the impregnation of organometallics into zeolites, as well as providing an indirect probe of internal versus external location of the metal guests. In the following, a direct spectroscopic probe of this kind of process is presented. 

Similar to indirect absorbance detection, indirect fluorescence has been employed to detect MPA, EMPA, IMPA, and PMPA, using tetrakis(4-sul fopheny 1 iporphine (TSPP) as the indirect probe (19). A violet diode laser operating at 415nm was used for excitation. Using an electrolyte composed of 50 tM TSPP and 5mM [Bios(2-hydroxyethyl)-amino]tris-(hydroxymethyl)methane (Bistris) at pH 7.2 under normal polarity, baseline separation was achieved in less than 2 min. A limit of detection of 0.1 xM (9ppb) for MPA was achieved. 

The mantle is the Earth s largest chemical reservoir comprising 82% of its total volume and 65% of its mass. The mantle constitutes almost all of the silicate Earth, extending from the base of the crust (which comprises only 0.6% of the silicate mass) to the top of the metallic core at 2,900 km depth. The chemical compositions of direct mantle samples such as abyssal perido-tites (Chapter 2.04) and peridotite xenoliths (Chapter 2.05), and of indirect probes of the mantle such as basalts from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) (Chapter 2.03), and some types of primitive... 

Interviewing patients to detect nonadherence is most effective when indirect probes are used. For instance, the probe Most people have trouble remembering to take their medications. Do you have any trouble remembering to take yours will solicit more reliable information than asking Are you taking your medications as prescribed Table 2 gives examples of specific probes that the pharmacist can use to assess whether a patient has been or is likely to be adherent. 

Given the low ratio of cross-linked to uncross-linked chain segments, direct spectroscopic detection of cross-link densities is difficult [142-144], but the relaxation times T2 [101-103] and Tip [104, 105] are good indirect probes for cross-link densities. Quantitative results can be obtained by NMR imaging from parameterizations of relaxation curves for each voxel (cf. Fig. 5.8) [101, 145-147]. 

Although PGC/MS is an extremely important analytical tool, it provides only an indirect probe of the chemistry of the pyrolysis. By x-ray powder diffrac-... 

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