Spatially-Resolved Measurements

Spatially resolved measurements, based on the confocal laser microscope and related techniques, have recently enabled direct detection of individual molecules, single nanoparticles, and molecular assemblies, leading to elucidation of the heterogeneous nature of these systems and its dependence on the individual environments. 

To date, in-bed filtration was more or less a black box as any measurement within the bed was virtually impossible. The design of such filters was based on models that could be validated only by integral measurements. However, with the MRI method even the (slow) dynamics of the filtration process can be determined. The binary gated data obtained by standard MRI methods are sufficient for the quantitative description of the system. With spatially resolved measurements the applicability of basic mass balances based on improved models can be shown in detail. 

Viscometric flow theories describe how to extract material properties from macroscopic measurements, which are integrated quantities such as the torque or volume flow rate. For example, in pipe flow, the standard measurements are the volume flow rate and the pressure drop. The fundamental difference with spatially resolved measurements is that the local characteristics of the flows are exploited. Here we focus on one such example, steady, pressure driven flow through a tube of circular cross section. The standard assumptions are made, namely, that the flow is uni-directional and axisymmetric, with the axial component of velocity depending on the radius only. The conservation of mass is satisfied exactly and the z component of the conservation of linear momentum reduces to... 

The discussion above that led to Eqs. (4.2.6 and 4.2.7) assumes that the no-slip condition at the wall of the pipe holds. There is no such assumption in the theory for the spatially resolved measurements. We have recently used a different technique for spatially resolved measurements, ultrasonic pulsed Doppler velocimetry, to determine both the viscosity and wall slip velocity in a food suspension [2]. From a rheological standpoint, the theoretical underpinnings of the ultrasonic technique are the same as for the MRI technique. Flence, there is no reason in principle why MRI can not be used for similar measurements. 

Spatially-resolved measurement of the droplet size distribution can be accomplished by the implementation of velocity compensated pulse sequences, such as the double PGSTE [81] in a spatially resolved imaging sequence. Accurate measurements of spatially resolved droplet size distributions during flow and mixing of emulsions would provide truly unique information regarding flow effects on the spatial distribution of droplets. 

Moudrakovski, I.L. McLaurin, G.E. Ratcliffe, C.I. Ripmeester, J.A. (2004). Methane and Carbon Dioxide Hydrate Formation in Water Droplets Spatially Resolved Measurements from Magnetic Resonance Microimaging. J. Phys. Chem. B, 108, 17591-17595. 

In theory, spatially resolved measurements of concentrations of atmospheric trace substances could be made by remote sensing from either surface-based or satellite platforms, but remote sensing capabilities have not yet been developed for many species. Furthermore, both surface- and satellite-based remote sensing methods have distinct limitations in resolving... 

In this section, we describe time-resolved, local in-situ measurements of chemical potentials /, ( , f) with solid galvanic cells. It seems as if the possibilities of this method have not yet been fully exploited. We note that the spatial resolution of the determination of composition is by far better than that of the chemical potential. The high spatial resolution is achieved by electron microbeam analysis, analytical transmission electron microscopy, and tunneling electron microscopy. Little progress, however, has been made in improving the spatial resolution of the determination of chemical potentials. The conventional application of solid galvanic cells in kinetics is completely analogous to the time-dependent (partial) pressure determination as explained in Section 16.2.2. Spatially resolved measurements are not possible in this way. 

To elucidate the contribution of the different histological structures to the average Raman spectral signatures from intact pollen grains, we conducted spatially resolved measurements on sections of rye pollen grains. Such mapping experiments can help separation of predominant spectral contributions from different substructures. 

Figure 6.45. Test fuel cell with straight channel design [40], (Reprinted from Journal of Power Sources, 145(2), Hakenjos A, Hebling C. Spatially resolved measurement of PEM fuel cells, 307-11, 2005, with permission from Elsevier and the authors.)...

Hakenjos A, Hebling C (2005) Spatially resolved measurement of PEM fuel cells. J Power Sources 145(2) 307-11... 

The critical need to achieve high signal-to-noise ratios for spatially resolved measurement of several free radicals has spawned a number of research efforts aimed at improving our ability to observe such radicals as OH, HO2, NO, NO2, etc., with orders of magnitude better sensitivity than was previously available. A major impetus behind this research has been the realization that atmospheric variability on the spatial scale of a hundred meters in the vertical drives fluctuations in several of the key reactiye species, which provide ample concentration variation to carry out covariance studies to establish cause and effect within subsets of free radical reaction sets. 

Horn, R., Williams, K. A., Degenstein, N.J., and Schmidt, L.D. Syngas by catalytic partial oxidation of methane on rhodium Mechanistic conclusions from spatially resolved measurements and numerical simulations. Journal of Catalysis, 2006, 242, 92. 

C. (1998) Spatially resolved measurements and plasma tomography with respect to the rotational temperatures for a microwave plasma torch, J Anal At Spectrom 13 955-961. 

The time-resolved microwave reflectivity (TRMR) techiuque is well established for contactless characterisation of minority-carrier lifetimes in semiconductors. It can be applied to map surface recombination in this case the sample is moved by an X-Y stage to allow spatially resolved measurement of the minority-carrier lifetime. 

---